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Paper No1Publication ID : 751   &   Year : 2019  
TitleBasin-wide sea level coherency in the tropical Indian Ocean driven by Madden-Julian Oscillation.
Authors Rohit, B and Paul, A and Durand, F and Testut, L and Prerna, S and Afroosa, M and Ramakrishnaa, SSVS and Shenoi, SSC.
Source Nature Communications, 10. p. 125
AbstractChanges in sea level may be attributed either to barotropic (involving the entire water column) or baroclinic processes (governed by stratification). It has been widely accepted that barotropic sea level changes in the tropics are insignificant at intraseasonal time scales (periods of 30⿿80 days). Based on bottom pressure records, we present evidence for significant basin-wide barotropic sea level variability in the tropical Indian Ocean during December⿿April with standard deviations amounting to ⿼30⿿60% of the standard deviation in total intraseasonal sea level variability. The origin of this variability is linked to a small patch of wind over the Eastern Indian Ocean, associated with boreal winter Madden⿿Julian Oscillations (MJO). These large fluctuations are likely to play a prominent role in the intraseasonal sea level and mass budgets. Because of their much faster propagation than baroclinic processes, they allow the basin to adjust to climatic perturbations much more rapidly than was previously thought.

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Paper No2Publication ID : 750   &   Year : 2019  
TitleWyrtki Jets: Role of intraseasonal forcing
Authors Prerna, S., Chatterjee, A., Mukherjee, A., Ravichandran, M., Shenoi, S.S.C.
Source Journal of Earth System Science, 128 (1), art. no. 21,.
AbstractDirect current measurements observed from the acoustic Doppler current profilers in the equatorial Indian Ocean (EIO) and solutions from an ocean general circulation model are investigated to understand the dynamics of the Wyrtki jet. These jets are usually described as semiannual direct wind forced zonal currents along the central and eastern EIO. We show that both, spring and fall, Wyrtki jets show predominant semiannual spectral peaks, but significant intraseasonal energy is evident during spring in the central and eastern EIO. We find that for the semiannual band, there is a strong spectral coherence between the overlying winds and the currents in the central EIO, but no coherency is observed in the eastern part of the EIO. Moreover, for the intraseasonal band, strong coherency between the winds and currents is evident. During spring, intraseasonal currents induced by the Madden⿿Julian oscillation (MJO) superimpose constructively with semiannual currents and thus intensify the strength of the spring Wyrtki jet. Also, the atmospheric intraseasonal variability accounts for the interannual variabilities observed in spring Wyrtki jets. © 2019, Indian Academy of Sciences.

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Paper No3Publication ID : 749   &   Year : 2019  
TitleOn the relationship between the Indian summer monsoon rainfall and the EQUINOO in the CFSv2 (2019)
Authors Vishnu, S., Francis, P.A., Ramakrishna, S.S.V.S., Shenoi, S.S.C.
Source Climate Dynamics, 52 (1-2), pp. 1263-1281.
AbstractSeveral recent studies have shown that positive (negative) phase of Equatorial Indian Ocean Oscillation (EQUINOO) is favourable (unfavourable) to the Indian summer monsoon. However, many ocean⿿atmosphere global coupled models, including the state-of-the-art Climate Forecast System (CFS) version 2 have difficulty in reproducing this link realistically. In this study, we analyze the retrospective forecasts by the CFS model for the period 1982⿿2010 with an objective to identify the reasons behind the failure of the model to simulate the observed links between Indian summer monsoon and EQUINOO. It is found that, in the model hindcasts, the rainfall in the core monsoon region was mainly due to westward propagating synoptic scale systems, that originated from the vicinity of the tropical convergence zone (TCZ). Our analysis shows that unlike in observations, in the CFS, majority of positive (negative) EQUINOO events are associated with El Niño (La Niña) events in the Pacific. In addition to this, there is a strong link between EQUINOO and Indian Ocean Dipole (IOD) in the model. We show that, during the negative phase of EQUINOO/IOD, northward propagating TCZs remained stationary over the Bay of Bengal for longer period compared to the positive phase of EQUINOO/IOD. As a result, compared to the positive phase of EQUINOO/IOD, during a negative phase of EQUINOO/IOD, more westward propagating synoptic scale systems originated from the vicinity of TCZ and moved on to the core monsoon region, which resulted in higher rainfall over this region in the CFS. We further show that frequent, though short-lived, westward propagating systems, generated near the vicinity of TCZ over the Bay moved onto the mainland were responsible for less number of break monsoon spells during the negative phase of EQUINOO/IOD in the model hindcasts. This study underlines the necessity for improving the skill of the coupled models, particularly CFS model, to simulate the links between EQUINOO/IOD and the Indian summer monsoon for reliable predictions of seasonal and intraseasonal variation of Indian summer monsoon rainfall. © 2018, Springer-Verlag GmbH Germany, part of Springer Nature.

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Paper No4Publication ID : 708   &   Year : 2018  
TitleAn operational wave forecasting system for the east coast of India.
Authors Sandhya, K.G., Murty, P.L.N., Deshmukh, A.N., Balakrishnan Nair, T.M., Shenoi, S.S.C.
Source Estuarine, Coastal and Shelf Science, 202, pp. 114-124.
AbstractDemand for operational ocean state forecasting is increasing, owing to the ever-increasing marine activities in the context of blue economy. In the present study, an operational wave forecasting system for the east coast of India is proposed using unstructured Simulating WAves Nearshore model (UNSWAN). This modelling system uses very high resolution mesh near the Indian east coast and coarse resolution offshore, and thus avoids the necessity of nesting with a global wave model. The model is forced with European Centre for Medium-Range Weather Forecasts (ECMWF) winds and simulates wave parameters and wave spectra for the next 3 days. The spatial pictures of satellite data overlaid on simulated wave height show that the model is capable of simulating the significant wave heights and their gradients realistically. Spectral validation has been done using the available data to prove the reliability of the model. To further evaluate the model performance, the wave forecast for the entire year 2014 is evaluated against buoy measurements over the region at 4 waverider buoy locations. Seasonal analysis of significant wave height (Hs) at the four locations showed that the correlation between the modelled and observed was the highest (in the range 0.78⿿0.96) during the post-monsoon season. The variability of Hs was also the highest during this season at all locations. The error statistics showed clear seasonal and geographical location dependence. The root mean square error at Visakhapatnam was the same (0.25) for all seasons, but it was the smallest for pre-monsoon season (0.12 m and 0.17 m) for Puducherry and Gopalpur. The wind sea component showed higher variability compared to the corresponding swell component in all locations and for all seasons. The variability was picked by the model to a reasonable level in most of the cases. The results of statistical analysis show that the modelling system is suitable for use in the operational scenario.

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Paper No5Publication ID : 711   &   Year : 2018  
TitleAn assessment on oil spill trajectory prediction: Case study on oil spill off Ennore Port.
Authors S J Prasad, T M Balakrishnan Nair, Hasibur Rahaman, S S C Shenoi and T Vijayalakshmi
Source Journal of Earth System Science (2018) 127:111
AbstractA Liquefied Petroleum Gas (LPG) tanker and a chemical tanker collided two nautical miles off Ennore port on 28 January, 2017. Around 196.4 metric tons (MT) of Heavy Furnace Oil (HFO) was spilled and drifted towards the shore. Oil spill drift advisory and prediction was made by Indian National Centre for Ocean Information Services (INCOIS) using General National Oceanic and Atmospheric Administration (NOAA) Operational Modeling Environment (GNOME), an oil spill trajectory model. The trajectory model was forced with analysed and forecasted ocean currents from Global Ocean Data Assimilation System (GODAS) based on Modular Ocean Model 4p1 (GM4p1). It was found that spread of HFO obtained from oil spill trajectory model GNOME, has matched well with the observed spread from Sentinel-1A satellite dataset. However, the spread of the HFO was underestimated by the trajectory model, when forced with forecasted GM4p1 currents. Additional ground truth observation from Indian Coast Guard also corroborates this finding.

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Paper No6Publication ID : 710   &   Year : 2018  
TitleOn the relationship between the Pacific Decadal Oscillation and monsoon depressions over the Bay of Bengal
Authors Sasidharannair Vishnu, Pavanathara Augustine Francis, Satheesh Chandra Shenoi, Surireddi Satya Venkata Siva Ramakrishna
Source Atmospheric Science Letters.
AbstractThis study investigates the relationship between inter-decadal variation in the number of monsoon depressions (MDs) over the Bay of Bengal (BoB) and the Pacific Decadal Oscillation (PDO). It is shown that there is an out-of-phase variation in the number of MDs over the BoB and the PDO, except during 1927?1945. Quantitative estimates of the relative contributions of individual environmental parameters show that the variation in the mid-tropospheric relative humidity over the BoB is the primary reason for the observed variation in the number of MDs. It is further postulated that the variation in the sea surface temperature in the western equatorial Indian Ocean associated with the PDO could be one of the reasons for the changes in the moisture advection over to the BoB and hence the variation in the number of MDs in inter-decadal timescale.

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Paper No7Publication ID : 709   &   Year : 2018  
TitleOn the relationship between the Indian summer monsoon rainfall and the EQUINOO in the CFSv2.
Authors Vishnu, S., Francis, P.A., Ramakrishna, S.S.V.S., Shenoi, S.S.C.
Source Climate Dynamics, pp. 1-19.
AbstractSeveral recent studies have shown that positive (negative) phase of Equatorial Indian Ocean Oscillation (EQUINOO) is favourable (unfavourable) to the Indian summer monsoon. However, many ocean⿿atmosphere global coupled models, including the state-of-the-art Climate Forecast System (CFS) version 2 have difficulty in reproducing this link realistically. In this study, we analyze the retrospective forecasts by the CFS model for the period 1982⿿2010 with an objective to identify the reasons behind the failure of the model to simulate the observed links between Indian summer monsoon and EQUINOO. It is found that, in the model hindcasts, the rainfall in the core monsoon region was mainly due to westward propagating synoptic scale systems, that originated from the vicinity of the tropical convergence zone (TCZ). Our analysis shows that unlike in observations, in the CFS, majority of positive (negative) EQUINOO events are associated with El Niño (La Niña) events in the Pacific. In addition to this, there is a strong link between EQUINOO and Indian Ocean Dipole (IOD) in the model. We show that, during the negative phase of EQUINOO/IOD, northward propagating TCZs remained stationary over the Bay of Bengal for longer period compared to the positive phase of EQUINOO/IOD. As a result, compared to the positive phase of EQUINOO/IOD, during a negative phase of EQUINOO/IOD, more westward propagating synoptic scale systems originated from the vicinity of TCZ and moved on to the core monsoon region, which resulted in higher rainfall over this region in the CFS. We further show that frequent, though short-lived, westward propagating systems, generated near the vicinity of TCZ over the Bay moved onto the mainland were responsible for less number of break monsoon spells during the negative phase of EQUINOO/IOD in the model hindcasts. This study underlines the necessity for improving the skill of the coupled models, particularly CFS model, to simulate the links between EQUINOO/IOD and the Indian summer monsoon for reliable predictions of seasonal and intraseasonal variation of Indian summer monsoon rainfall.

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Paper No8Publication ID : 706   &   Year : 2017  
TitleCoral Bleaching Along Andaman Coast Due to Thermal Stress During Summer Months of 2016: A Geospatial Assessment.
Authors Mohanty, P.C., Venkateshwaran, P., Mahendra, R.S., Shiva Kumar, Srinivasa Kumar, T., Vinithkumar, N.V., Ramalingam K, Sethuraman R., Raju R., Dharmaraj, S., Prakash, V.D., Ramadasss, G.A., Shenoi, S.S.C.
Source American Journal of Environmental Protection, 6(1), pp. 1-6.
AbstractCoral bleaching reported in the North Bay, Andaman Islands during the April last week of 2016 due to thermal stress. The Coral Bleaching Alert System (CBAS) a service providing by Indian National Centre for Ocean Information Services (INCOIS) has reported the warning and the bleaching has been confirmed from the field survey conducted on April 26, 2016. As coral reef is important fragile eco-system of the shallow marine environment suffers due to human and natural impacts. Bleaching has been initiated as weather predictions of the various agencies have suggested the elevated temperatures in the Indian subcontinent this year. We have put forward our remote sensing analysis of coral bleaching warning as Alert Level-1 followed by the initiation of the coral bleaching in the in-situ observation at Andaman Islands enhances the credibility of satellite observation and the service of INCOIS. These results were useful for the coastal management authority for taking suitable measure and policy on important coral eco-system.

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Paper No9Publication ID : 705   &   Year : 2017  
TitlePerformance of WRF-ARW winds on computed storm surge using hydodynamic model for Phailin and Hudhud cyclones.
Authors Lakshmi, D.D., Murty, P.L.N., Bhaskaran, P.K., Sahoo, B., Kumar, T.S., Shenoi, S.S.C., Srikanth, A.S.
Source Ocean Engineering, 131, pp. 135-148.
AbstractExtreme weather events such as tropical cyclones can lead to storm surge during the time of landfall inundating low lying coastal areas. Storm surge computations are sensitive to input wind forcing and local bathymetric gradients especially during the landfall time of cyclones. Therefore, it is an essential pre-requisite to specify accurate wind field and mean sea level pressure as a primary input to hydrodynamic models in order to compute precisely the peak storm surge and its envelope including the extent of coastal flooding. The present study performs a comprehensive analysis on storm surge computation utilizing WRF-ARW (version 3.7.1) winds run with three different grid resolutions for the recent very severe cyclonic storms Phailin and Hudhud that had landfall along the east coast of India. The study considers two different sets of WRF-ARW winds constructed using GFS and FNL initial conditions under three varied horizontal grid resolutions. In addition the study explores the efficacy of the best possible combination considering the initial conditions together with different grid resolutions for Phailin and Hudhud cyclones. Further, numerical experiments conducted with these different wind combinations provided an opportunity to ascertain the characteristics of storm surge development and its spatial variability along the coast. The study highlights that the 3 km grid resolution performed the best during both these cyclonic events having implications on storm surge prediction.

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Paper No10Publication ID : 704   &   Year : 2017  
TitleReal-time storm surge and inundation forecast for very severe cyclonic storm 'Hudhud'.
Authors Murty, P.L.N., Padmanabham, J., Srinivasa Kumar, T., Kiran Kumar, N., Ravi Chandra, V., Shenoi, S.S.C., Mohapatra, M.
Source Ocean Engineering, 131, pp. 25-35.
AbstractThe high population density along the coastal stretch of India necessitates a real-time storm surge warning system. Keeping this in view, the Earth System Science Organization (ESSO) - Indian National Centre for Ocean Information Services (INCOIS) initiated the Storm Surge Early Warning System (SSEWS) for Indian coasts using the ADCIRC (Advanced Circulation) model. ADCIRC is a finite-element based, depth-integrated shallow water model that can be used to model storm surges and for other coastal applications. This warning system utilizes the automated Decision Support System (DSS) based on Geographic Information System (GIS) and database technology. Wind and pressure fields are generated using the Jelesnianski and Taylor dynamic wind model which make use of track forecasts from IMD. While DSS was initially tested for the very severe cyclonic storm ⿿Phailin⿿ (October, 2013) in experimental mode, it was used for the first time to provide real-time storm surge and inundation forecasts during cyclone ⿿Hudhud⿿ (October, 2014). In this paper, we highlight the performance of SSEWS during this event while comparing with observations. Forecasts from SSEWS were found to be quite promising and proving its capability.

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Paper No11Publication ID : 707   &   Year : 2017  
TitleAn optical remote sensing approach for ecological monitoring of red and green Noctiluca scintillans.
Authors Baliarsingh, S.K., Dwivedi, R.M., Lotliker, A.A., Sahu, K.C., Kumar, T.S., Shenoi, S.S.C.
Source Environmental Monitoring and Assessment, 189 (7), art. no. 330.
AbstractAn ecosystem disruptive bloom of red Noctiluca scintillans (hereafter Noctiluca) was observed in coastal waters of the north-western Bay of Bengal during April 2014. Based on the principle of phytoplankton group/species specific remote sensing reflectance (Rrs), a technique of detecting green Noctiluca and diatom was developed earlier using Rrs at 443, 488, and 531 nm of Moderate Imaging Spectroradiometer-Aqua (MODIS). This was appropriately modified to detect bloom of red Noctiluca in coastal waters of the Bay of Bengal. Additional Rrs data at longer wavelengths viz. 667 and 678 nm were included in the existing algorithm, and the spectral shapes were accounted to detect the bloom of red Noctiluca. The classification scheme discriminates red Noctiluca from the green form of the same species and diatom. Phytoplankton group/species products were generated using the modified approach and validated with the reported events of red and green Noctiluca blooms in the Indian coastal waters. The present study also highlights two specific results based on MODIS retrieved time-series phytoplankton group/species image analysis: first, the observation of coexistence of diatom, red, and green Noctiluca in coastal waters of the north-western Bay of Bengal, and the second, phytoplankton community shift resulting in red/green Noctiluca proliferation following diatom.

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Paper No12Publication ID : 703   &   Year : 2016  
TitleRecent advances in the Indian Tsunami Early Warning System.
Authors Manneela, S., Devi, U.E., Saikia, D., Kumar, T.S., Shenoi, S.S.C.
Source Proceedings of the Indian National Science Academy, 82 (3), pp. 1005-1012
AbstractThe Government of India established the Indian Tsunami Early Warning System (ITEWS) at Earth System Science Organization-Indian National Centre for Ocean Information Services (INCOIS), Hyderabad, as an autonomous institution of Ministry of Earth Sciences (MoES). ITEWC continuously monitors the seismic waves recorded by a network of seismic stations, well spread across the globe to determine the magnitudes, depths and locations of earthquake's. Then it combines the parameters with pre-computed hazard estimates based on tsunami models based on from similar events to decide, the potential of the earthquake for generating a tsunami, and if so, then it estimates the anticipated height of the tsunami wave at different locations on the coast. The ITEWC uses data from national and international observational network of seismic stations, sea level gauge stations and tsunami buoys around the Indian and Pacific Oceans. Data from approximately 400 seismometers. As soon as the earthquake is detected, warning centre transmits the first bulletin based on seismic data describing the location of earthquake, its magnitude, depth and other characters of the event. After the first bulletin, seismic data are further analysed for improved accuracy of earthquake parameters. The pre-computed scenario database which is used for issuing the tsunami warnings is created based on the risk estimated from historical earthquakes in the tsunamigenic sources in the Indian Ocean reported by Rastogi and Jaiswal. Water level inversion, realtime inundation modeling, real-time estimation of focal mechanism of earthquake to show the style of faulting and incorporation of GNSS data into the warning chain are the few key issues that ITEWC has taken up on priority.

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Paper No13Publication ID : 702   &   Year : 2016  
TitleOn the decreasing trend of the number of monsoon depressions in the Bay of Bengal.
Authors Vishnu, S., Francis, P.A., Shenoi, S.S.C., Ramakrishna, S.S.V.S.
Source Environmental Research Letters, 11 (1), art. no. 014011
AbstractThis study unravels the physical link between the weakening of the monsoon circulation and the decreasing trend in the frequency of monsoon depressions over the Bay of Bengal. Based on the analysis of the terms of Genesis Potential Index, an empirical index to quantify the relative contribution of large scale environmental variables responsible for the modulation of storms, it is shown here that the reduction in the mid-tropospheric relative humidity is the most important reason for the decrease in the number of monsoon depressions. The net reduction of relative humidity over the Bay of Bengal is primarily due to the decrease in the moisture flux convergence, which is attributed to the weakening of the low level jet, a characteristic feature of monsoon circulation. Further, the anomalous moisture convergence over the western equatorial Indian Ocean associated with the rapid warming of the sea surface, reduces the moisture advection into the Bay of Bengal and hence adversely affect the genesis/intensification of monsoon depressions. Hence, the reduction in the number of monsoon depression over the Bay of Bengal could be one of the manifestations of the differential rates in the observed warming trend of the Indian Ocean basin.

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Paper No14Publication ID : 701   &   Year : 2016  
TitleGround-zero met-ocean observations and attenuation of wind energy during cyclonic storm Hudhud.
Authors Harikumar, R., Balakrishnan Nair, T.M., Rao, B.M., Prasad, R., Ramakrishna Phani, P., Nagaraju, C., Ramesh Kumar, M., Jeyakumar, C., Shenoi, S.S.C., Nayak, S.
Source Current Science, 110 (12), pp. 2245-2252.
AbstractOcean-met observations from INCOIS real-time automatic weather station on-board a ship RV Kaustubh served as strong ground truth for satellite- and modelderived forecasts during the very severe cyclonic storm Hudhud, which made a landfall at Visakhapatnam, India. The ship recorded maximum wind speed of 204 km/h (with a minimum central pressure of 945 hPa), which is the highest (lowest) ever instrumentally recorded value at a location on the Indian coastline during any cyclone. Though the global model forecasts of wind fields have shown good agreement inland, they failed in representing the reality along the coasts. Variation in wind energy from ocean towards inland suggests that it is attenuated exponentially inland (the maximum wind power density had reduced by 93,406 W/m2 at Anakapalle (~25 km) compared to the ocean, and by 7022 W/m2 at Chintapalle (~100 km inland) compared to Anakapalle). The present study reinforces the significance of having realtime near-shore ocean-met observations, and their operational usage for evaluation (assimilation) of (into) ocean-met forecast models in realtime.

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Paper No15Publication ID : 700   &   Year : 2015  
TitleOcean state forecast along ship routes: Evaluation using ESSO-INCOIS real-time ship-mounted wave height meter and satellite observations.
Authors Harikumar, R., Hithin, N.K., Balakrishnan Nair, T.M., Sirisha, P., Krishna Prasad, B., Jeyakumar, C., Nayak, S., Shenoi, S.S.C.
Source Journal of Atmospheric and Oceanic Technology, 32 (11), pp. 2211-2222.
AbstractOcean state forecast (OSF) along ship routes (OAS) is an advisory service of the Indian National Centre for Ocean Information Services (INCOIS) of the Earth System Science Organization (ESSO) that helps mariners to ensure safe navigation in the Indian Ocean in all seasons as well as in extreme conditions. As there are many users who solely depend on this service for their decision making, it is very important to ensure the reliability and accuracy of the service using the available in situ and satellite observations. This study evaluates the significant wave height (Hs) along the ship track in the Indian Ocean using the ship-mounted wave height meter (SWHM) on board the Oceanographic Research Vessel Sagar Nidhi, and the Cryosat-2 and Jason altimeters. Reliability of the SWHM is confirmed by comparing with collocated buoy and altimeter observations. The comparison along the ship routes using the SWHM shows very good agreement (correlation coefficient > 0.80) in all three oceanic regimes, [the tropical northern Indian Ocean (TNIO), the tropical southern Indian Ocean (TSIO), and extratropical southern Indian Ocean (ETSI)] with respect to the forecasts with a lead time of 48 h. However, the analysis shows ~10% overestimation of forecasted significant wave height in the low wave heights, especially in the TNIO. The forecast is found very reliable and accurate for the three regions during June-September with a higher correlation coefficient (average = 0.88) and a lower scatter index (average = 15%). During other months, overestimation (bias) of lower Hs is visible in the TNIO.

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Paper No16Publication ID : 699   &   Year : 2014  
TitleWave forecasting and monitoring during very severe cyclone Phailin in the Bay of Bengal
Authors Balakrishnan Nair, T.M., Remya, P.G., Harikumar, R., Sandhya, K.G., Sirisha, P., Srinivas, K., Nagaraju, C., Nherakkol, A., Krishna Prasad, B., Jeyakumar, C., Kaviyazhahu, K., Hithin, N.K., Kumari, R., Sanil Kumar, V., Ramesh Kumar, M., Shenoi, S.S.C., Nayak S.
Source Current Science, 106 (8), pp. 1121-1125
AbstractWave fields, both measured and forecast during the very severe cyclone Phailin, are discussed in this communication. Waves having maximum height of 13.54 m were recorded at Gopalpur, the landfall point of the cyclone. The forecast and observed significant wave heights matched well at Gopalpur with correlation coefficient of 0.98, RMS error of 0.35 m and scatter index of 14%. Forecasts were also validated in the open ocean and found to be reliable (scatter index < 15%). The study also revealed the presence of Southern Ocean swells with a peak period of 20-22 sec hitting Gopalpur coast along with the cyclone-generated waves.

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Paper No17Publication ID : 495   &   Year : 2013  
TitleThe Indian ocean forecast system
Authors Francis,P.A.,Vinayachandran,P.N,Shenoi,S.S.C.
Source Current Science,104(10),1354-1368pp.
AbstractIn order to meet the ever growing demand for the prediction of oceanographic parametres in the Indian Ocean for a variety of applications, the Indian National Centre for Ocean Information Services (INCOIS) has recently set-up an operational ocean forecast system, viz. the Indian Ocean Forecast System (INDOFOS). This fully automated system, based on a state-of-the-art ocean general circulation model issues six-hourly forecasts of the sea-surface temperature, surface currents and depths of the mixed layer and the thermocline up to five-days of lead time. A brief account of INDOFOS and a statistical validation of the forecasts of these parametres using in situ and remote sensing data are presented in this article. The accuracy of the sea-surface temperature forecasts by the system is high in the Bay of Bengal and the Arabian Sea, whereas it is moderate in the equatorial Indian Ocean. On the other hand, the accuracy of the depth of the thermocline and the isothermal layers and surface current forecasts are higher near the equatorial region, while it is relatively lower in the Bay of Bengal.

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Paper No18Publication ID : 497   &   Year : 2013  
TitlePerformance of the Ocean State Forecast system at Indian National Centre for Ocean Information Services
Authors T. M. Balakrishnan Nair, P. Sirisha, K. G. Sandhya, K. Srinivas, L. Sabique, Arun Nherakkol, B. Krishna Prasad, Rakhi Kumari, C. Jeyakumar,K. Kaviyazhahu, M. Ramesh Kumar, R. Harikumar and S.S.C. Shenoi
Source Current Science,105(2),pp.175-181.
AbstractThe reliability of the operational Ocean State Forecast system at the Indian National Centre for Ocean Information Services (INCOIS) during tropical cyclones that affect the coastline of India is described in this article. The performance of this system during cyclone Thane that severely affected the southeast coast of India during the last week of December 2011 is reported here. Spectral wave model is used for forecasting the wave fields generated by the tropical cyclone and validation of the same is done using real-time automated observation systems. The validation results indicate that the forecasted wave parameters agree well with the measurements. The feedback from the user community indicates that the forecast was reliable and highly useful. Alerts based on this operational ocean state forecast system are thus useful for protecting the property and lives of the coastal communities along the coastline of India. INCOIS is extending this service for the benefit of the other countries along the Indian Ocean rim

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Paper No19Publication ID : 496   &   Year : 2013  
TitleShip-mounted real-time surface observational system on board Indian vessels for validation and refinement of model forcing fields
Authors Harikumar, R., T. M. Balakrishnan Nair, G.S. Bhat, Shailesh Nayak, Venkat Shesu Reddem, S.S.C. Shenoi,
Source Journal Atmospheric and Oceanic Technology, 30(3), 626-637pp.
AbstractA network of ship-mounted real-time Automatic Weather Stations integrated with Indian geosynchronous satellites [Indian National Satellites (INSATs)] 3A and 3C, named Indian National Centre for Ocean Information Services Real-Time Automatic Weather Stations (I-RAWS), is established. The purpose of I-RAWS is to measure the surface meteorological-ocean parameters and transmit the data in real time in order to validate and refine the forcing parameters (obtained from different meteorological agencies) of the Indian Ocean Forecasting System (INDOFOS). Preliminary validation and intercomparison of analyzed products obtained from the National Centre for Medium Range Weather Forecasting and the European Centre for Medium-Range Weather Forecasts using the data collected from I-RAWS were carried out. This I-RAWS was mounted on board oceanographic research vessel Sagar Nidhi during a cruise across three oceanic regimes, namely, the tropical Indian Ocean, the extratropical Indian Ocean, and the Southern Ocean. The results obtained from such a validation and intercomparison, and its implications with special reference to the usage of atmospheric model data for forcing ocean model, are discussed in detail. It is noticed that the performance of analysis products from both atmospheric models is similar and good; however, European Centre for Medium-Range Weather Forecasts air temperature over the extratropical Indian Ocean and wind speed in the Southern Ocean are marginally better

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Paper No20Publication ID : 503   &   Year : 2013  
TitleObserved tidal currents on the continental shelf off the west coast of India
Authors Subeesh, M.P., Unnikrishnan, A.S., Fernando, V., Agarwadekar, Y., Khalap, S.T., Satelkar, N.P., Shenoi, S.S.C.
Source Continental Shelf Research, 69, pp. 123-140
AbstractObserved currents from ADCPs, deployed at 100m and 150m depths, on the continental shelf at five different locations along the west coast of India, were used to study the characteristics of both barotropic and baroclinic tidal currents. The observations extended over a 6-month period (March-August), which includes two seasons, pre-monsoon (March-April) and southwest (SW) monsoon (May-August) during 2008, 2009 and 2011. Tidal ellipses, constructed for M2 and K1 constituents, show that barotropic tidal currents propagate in along-isobath direction at the southern shelf (off Kollam at about 9�N) and they are oriented more or less in a cross-isobath direction at the northern shelf locations (off Jaigarh and Mumbai at about 17�N and 20�N, respectively). Maximum cross-isobath tidal current is found at northern shelf locations (for instance, about 32cms-1 off Mumbai) than those in south (about 10cms-1 off Bhatkal, at 13�N). This could be due to the amplification of semidiurnal tidal currents from south to north of the shelf due to an increase in shelf widths towards north. The rotary spectra of baroclinic currents showed large peaks at semidiurnal and diurnal bands with a dominant clockwise rotation showing the presence of strong internal tidal currents. Semidiurnal variability occurs mainly in M2 and S2 and diurnal variability occurs mainly in K1 and O1. An increase in the amplitude of semidiurnal and diurnal internal tide is apparent when the stratification on the shelf increases from pre-monsoon to SW monsoon period. The presence of strong internal tide during May to August is attributed to increased seasonal stratification on the shelf. EOF analysis showed that the first three modes are sufficient to describe most of the variability in both semidiurnal and diurnal internal tides on the shelf, as they represent about 70-90% of total variance. The small scale vertical shear in the velocity field, induced by diurnal internal tide, is found to be larger than that induced by semidiurnal internal tide

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Paper No21Publication ID : 444   &   Year : 2012  
TitleA new atlas of temperature and salinity for the North Indian Ocean
Authors Chatterjee,A.,Shankar,D.,Shenoi,S.S.C.,Reddy,G.V.,Michael,G.S., Ravichandran,M.,Gopalkrishna,V.V.,Rama Rao,E.P.,Udaya Bhaskar, T.V.S.,Sanjeevan, V.N.
Source Journal of Earth System Science,121(3),pp.559-595.
AbstractThe most used temperature and salinity climatology for the world ocean, including the Indian Ocean, is the World Ocean Atlas (WOA) (Antonov et al 2006, 2010; Locarnini et al 2006, 2010) because of the vast amount of data used in its preparation. The WOA climatology does not, however, include all the available hydrographic data from the Indian Exclusive Economic Zone (EEZ), leading to the potential for improvement if the data from this region are included to prepare a new climatology. We use all the data that went into the preparation of the WOA (Antonov et al 2010; Locarnini et al 2010), but add considerable data from Indian sources, to prepare new annual, seasonal, and monthly climatologies of temperature and salinity for the Indian Ocean. The addition of data improves the climatology considerably in the Indian EEZ, the differences between the new North Indian Ocean Atlas (NIOA) and WOA being most significant in the Bay of Bengal, where the patchiness seen in WOA, an artifact of the sparsity of data, was eliminated in NIOA. The significance of the new climatology is that it presents a more stable climatological value for the temperature and salinity fields in the Indian EEZ.

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Paper No22Publication ID : 504   &   Year : 2012  
TitleSuccessful monitoring of the 11 April 2012 tsunami off the coast of Sumatra by Indian Tsunami Early Warning Centre
Authors Kumar, T.S., Nayak, S., Kumar, C.P., Yadav, R.B.S., Kumar, B.A., Sunanda, M.V., Devi, E.U., Kumar, N.K., Kishore, S.A., Shenoi, S.S.C.
Source Current Science, 102 (11), p. 1519
AbstractThe Indian Tsunami Early Warning Centre (ITEWC) in Hyderabad monitored the 11 April 2012 tsunami off the coast of Sumatra, which was generated by a shallow strike-slip earthquake and it largest aftershock of magnitude Mw (mB) 8.5 and 8.2 respectively, that occurred inside the subducting slab of the Indian plate. The earthquake generated a small ocean-wide tsunami that has been recorded by various tide gauges and tsunami buoys located in the Indian Ocean region. ITEWC detected the earthquake within 3 min 52 s and issued six advisories (bulletins) according to its Standard Operating Procedure. The ITEWC performed well during the event, and avoided false alarms and unnecessary public evacuations, especially in the mainland part of India region

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Paper No23Publication ID : 443   &   Year : 2012  
TitlePerformance of the tsunami forecast system for the Indian Ocean
Authors Srinivasa Kumar, T., Nayak, S., Kumar, P., Yadav, R.B.S., Kumar, A., Sunanda, M.V., Uma Devi, E., Shenoi, S.S.C.
Source Current Science, 102 (1), pp. 110-114.
AbstractThe Indian Tsunami Early Warning System (ITEWS) at the Indian National Centre for Ocean Information Services, Hyderabad, is responsible for issuing tsunami bulletins in India. The tsunami centre operates on a 24 7 basis and monitors seismological stations, bottom pressure recorders and tidal stations throughout the Indian Ocean to evaluate potentially tsunamigenic earthquakes and disseminating tsunami bulletins. The end-to-end capabilities of this warning system have been well proven during all the tsunamigenic earthquakes that occurred since September 2007. Comparison of the earthquake parameters estimated by ITEWS with other international seismological agencies suggests that the system is performing well and has achieved the target set up by the Inter- governmental Oceanographic Commission.

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Paper No24Publication ID : 442   &   Year : 2012  
TitleWeakening of spring Wyrtki jets in the Indian Ocean during 2006-2011
Authors Joseph, S., Wallcraft, A.J., Jensen, T.G., Ravichandran, M., Shenoi, S.S.C., Nayak, S.
Source Journal of Geophysical Research C: Oceans, 117 (4), art. no. C04012
AbstractBeginning in 2006, the Indian Ocean experienced climatologically anomalous conditions due to large-scale coupled air-sea interactions that influenced the surface circulation of the equatorial Indian Ocean. Here we present evidence from observations as well as a general circulation model to demonstrate that spring Wyrtki jets (WJ) were weak during the past 6years and were even reversed to westward flow during 2008. We note that this weakening coincided with uniformly high sea level as well as positive east to west gradient anomalies along the equatorial Indian Ocean during the month of May each year, starting in 2006. The weakened jets occur in conjunction with the latitude of zero zonal wind (LUZ) being close to the equator during these years, resulting in weaker than normal zonal winds along the equator from 2006 and onward. We find that starting in 2006, the normal tendency of westward propagation of the annual harmonic mode switches to eastward propagation, coherent with the wind forcing. In comparison to the annual harmonic component of the zonal current, the weak WJs are mainly associated with the semiannual harmonic WJs, as evident from an amplitude reduction of that mode by at least 0.3m s -1 during the post-2005 period. Our analysis demonstrates that the variance explained by the semiannual harmonic is reduced to half (30-40%) at the core of the WJ in 2006 and later years in comparison with earlier years when it was 70-80%.

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Paper No25Publication ID : 441   &   Year : 2012  
TitleAn anomalous cooling event observed in the Bay of Bengal during June 2009
Authors Chacko, N., Ravichandran, M., Rao, R.R., Shenoi, S.S.C.
Source Ocean Dynamics, 62 (5), pp. 671-681.
AbstractSea surface temperature (SST) variability over the Bay of Bengal (BoB) has the potential to trigger deep moist convection thereby affecting the active-break cycle of the monsoons. Normally, during the summer monsoon season, SST over the BoB is observed to be greater than 28C which is a pre-requisite for convection. During June 2009, satellite observations revealed an anomalous basin-wide cooling and the month is noted for reduced rainfall over the Indian subcontinent. In this study, we analyze the likely mechanisms of this cooling event using both satellite and moored buoy observations. Observations showed deepened mixed layer, stronger surface currents, and enhanced heat loss at the surface in the BoB. Mixed layer heat balance analysis is carried out to resolve the relative importance of various processes involved. We show that the cooling event is primarily induced by the heat losses at the surface resulting from the strong wind anomalies, and advection and vertical entrainment playing secondary roles. 2011 Springer Science+Business Media, LLC.

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Paper No26Publication ID : 475   &   Year : 2012  
TitleTsunami and the effects on coastal morphology and ecosystems: A report
Authors Devi, E.U., Shenoi, S.S.C.
Source Proceedings of the Indian National Science Academy 78(3),pp.513-521
AbstractTsunamis are one of the most destructive natural hazards that affect the coastal areas. Tsunami waves that impact the coast with enormous energy are capable of destroying the objects on the coast and re-shaping the coastal geography, geomorphology and ecosystem. These waves can also cause extensive damage and disruption to human lives, their livelihood, infrastructure and economic activities. The 26 December 2004 Sumatra-Andaman earthquake, one of the largest recorded and deadliest tremor, created an unparalleled catastrophic tsunami wiping out thousands of human lives and throwing millions homeless. This event attracted the interest of several geoscientists in India and stimulated extensive scientific research. This article summarizes the tsunami related research work carried out in India during the past four years.

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Paper No27Publication ID : 440   &   Year : 2012  
TitleObservational evidence from direct current measurements for propagation of remotely forced waves on the shelf off the west coast of India
Authors Amol, P., Shankar, D., Aparna, S.G., Shenoi, S.S.C., Fernando, V., Shetye, S.R., Mukherjee, A., Agarvadekar, Y., Khalap, S., Satelkar, N.P.
Source Journal of Geophysical Research C: Oceans, 117 (5), art. no. C05017
AbstractWe use data from six Acoustic Doppler Current Profiler (ADCP) moorings deployed during March-September 2008 on the continental shelf and slope off Bhatkal, Goa, and Jaigarh on the central west coast of India to present evidence for poleward propagation of shelf or coastal-trapped waves (CTWs). Wave propagation is seen on the shelf in the 20-40-day, 10-14-day, and 3-5-day-period bands. The lag from south to north indicates that remote forcing is important even at periods as short as 4days. Using QuikSCAT wind data, we show that the contribution of remote forcing to the shelf West Indian Coastal Current (WICC) is significant even when the local alongshore wind is strong, as during the summer-monsoon onset during May-June, and forces a strong local response that masks the effect of remote forcing. Forced wave calculations using CTW theory show that remote forcing of the WICC is present at all times, but is most striking when the local winds are weak, as during March-April. The CTW calculations show that the source region for the remote forcing may extend beyond the west coast into the Gulf of Mannar between India and Sri Lanka. On the slope, propagation is seen only at the 4-day period. At higher periods, the slope WICC decorrelates rapidly along the coast, but upward phase propagation, implying downward propagation of energy associated with poleward propagation, is evident even at these higher periods. Copyright 2012 by the American Geophysical Union.

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Paper No28Publication ID : 99   &   Year : 2011  
TitleFactors controlling January-April rainfall over southern India and Srilanka.
Authors Vialard J.;Terray P.;Duvel J.P.;Nanjundiah R.S.; Shenoi S.S.C.; Shankar D.
Source Climate Dynamics;37(3); 2011; pp.493-507.
AbstractMost of the annual rainfall over India occurs during the Southwest (JuneSeptember) and Northeast (OctoberDecember) monsoon periods. In March 2008, however, Southern peninsular India and Sri Lanka received the largest rainfall anomaly on record since 1979, with amplitude comparable to summer-monsoon interannual anomalies. This anomalous rainfall appeared to be modulated at intraseasonal timescale by the Madden Julian Oscillation, and was synchronous with a decaying La Nina event in the Pacific Ocean. Was this a coincidence or indicative of a teleconnection pattern? In this paper, we explore factors controlling rainfall over southern India and Sri Lanka between January and April, i.e. outside of the southwest and northeast monsoons. This period accounts for 20% of annual precipitation over Sri Lanka and 10% over the southern Indian states of Kerala and Tamil Nadu. Interannual variability is strong (about 40% of the January April climatology). Intraseasonal rainfall anomalies over southern India and Sri Lanka are significantly associated with equatorial eastward propagation, characteristic of the Madden Julian Oscillation. At the interannual timescale, we find a clear connection with El Nino-Southern Oscillation (ENSO); with El Ninos being associated with decreased rainfall (correlation of -0.46 significant at the 98% level). There is also a significant link with local SST anomalies over the Indian Ocean, and in particular with the inter-hemispheric sea surface temperature (SST) gradient over the Indian Ocean (with colder SST south of the equator being conducive to more rainfall, correlation of 0.55 significant at the 99% level). La Ninas/cold SSTs south of the equator tend to have a larger impact than El Ninos. We discuss two possible mechanisms that could explain these statistical relationships: (1) subsidence over southern India remotely forced by Pacific SST anomalies; (2) impact of ENSO-forced regional Indian Ocean SST anomalies on convection. However, the length of the observational record does not allow distinguishing between these two mechanisms in a statistically significant manner.

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Paper No29Publication ID : 362   &   Year : 2011  
TitleTrapped waves of the 27 November 1945 Makran tsunami: observations and numerical modeling
Authors Neetu, S.;Suresh, I.;Shankar, R.;Nagarajan, B.; Sharma, R.; Shenoi, S.S.C.;Unnikrishnan, A.S.; Sundar, D.
Source Natural Hazards; 2011; pp.1-10 (Article in Press)
AbstractThe 27 November 1945 earthquake in the Makran Subduction Zone triggered a destructive tsunami that has left important problems unresolved. According to the available reports, high waves persisted along the Makran coast and at Karachi for several hours after the arrival of the first wave. Long-duration sea-level oscillations were also reported from Port Victoria, Seychelles. On the other hand, only one high wave was reported from Mumbai. Tide-gauge records of the tsunami from Karachi and Mumbai confirm these reports. While the data from Mumbai shows a single high wave, Karachi data shows that high waves persisted for more than 7 h, with maximum wave height occurring 2.8 h after the arrival of the first wave. In this paper, we analyze the cause of these persistent high waves using a numerical model. The simulation reproduces the observed features reasonably well, particularly the persistent high waves at Karachi and the single high wave at Mumbai. It further reveals that the persistent high waves along the Makran coast and at Karachi were the result of trapping of the tsunami-wave energy on the continental shelf off the Makran coast and that these coastally-trapped edge waves were trapped in the along-shore direction within a ∼300-km stretch of the continental shelf. Sensitivity experiments establish that this along-shore trapping of the tsunami energy is due to variations in the shelf width. In addition, the model simulation indicates that the reported long duration of sea-level oscillations at Port Victoria were mainly due to trapping of the tsunami energy over the large shallow region surrounding the Seychelles archipelago.

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Paper No30Publication ID : 439   &   Year : 2011  
TitleCoastal Multi-hazard vulnerability mapping: A case study along the coast of Nellore District, East Coast of India
Authors Mahendra, R.S., Mohanty, P.C., Srinivasa Kumar, T., Shenoi, S.S.C., Nayak, S.R.
Source Italian Journal of Remote Sensing / Rivista Italiana di Telerilevamento, 42 (3), pp. 67-76.
AbstractThe study area coastal zone of Nellore district is experiencing frequent inundation by natural disasters. The current study is focused on generating Multi-hazard vulnerability map using the parameters historical storm surge heights, future sea level, future shoreline and high resolution coastal topography. The area is experiencing the severe coastal erosion up to 7 m/y along some stretches poses a threat. An area totaling 1708.36 sq. km. is found to fall under the multi-hazard zone and the coastal population are under threat due to future storms, erosion, accelerated sea level rise, etc. The image enhancement, interpretation and GIS overlay techniques along with data used here are effective to produce Multi-hazard vulnerability maps. These Maps are become vital tools for the coastal disaster management during an event and to take suitable decision on the future developments.

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Paper No31Publication ID : 361   &   Year : 2010  
TitleIntra-seasonal variability of the coastal currents around India: A review of the evidences from new observations
Authors Shenoi, S.S.C.
Source International journal of Geo Marine Science;39(4); 2010; pp.489-496.
AbstractThe seasonal cycle of the coastal currents along the Indian coast and their dynamics is well known. Till recently, it was believed that the seasonal signal dominates the coastal currents due the seasonal reversals of monsoonal winds. But the recent studies using satellite based altimeter and in situ measurements using moored instruments provided evidences on the importance of intra and interannual variabilities embedded in them. This article reviews the evidences available from these observations.

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Paper No32Publication ID : 363   &   Year : 2010  
TitleMinima of interannual sea-level variability in the Indian Ocean
Authors Shankar, D.;Aparna, S.G.;McCreary, J.P.;Suresh, I.; Neetu, S.; Durand, F.; Shenoi, S.S.C.; Al Saafani, M.A.
Source Progress in Oceanography,84(3-4); 2010; pp.225-241.
AbstractWavelet analysis of altimeter sea level in the Indian Ocean shows regions of high variability (maxima) and low variability (minima) at all time scales. At interannual time scales, i.e., at periods of 17 months or more, minima are seen at several places: in the central equatorial Indian Ocean; in the Arabian Sea along the south and west coasts of India and Sri Lanka, along the northern boundary, in the Gulf of Aden, and in patches along the coast of Oman; and in the Bay of Bengal along the east coasts of Sri Lanka and India south of ∼10N, and in the southern bay east of the Sri Lanka thermal dome. We investigate the cause of these interannual minima using a linear, continuously stratified numerical model, which is able to simulate the observed minima. We separate the forcing into a set of processes: direct forcing by winds in the interior ocean, forcing by winds blowing along continental boundaries, and forcing by Rossby waves generated by the reflection of equatorial Kelvin waves at the eastern boundary. At interannual periods, minima (maxima) of interannual variability occur where the direct wind forcing and reflected Rossby waves interfere destructively (constructively). At interannual periods within the tropics, the adjustment time scale of the system is less than that of the forcing, leading to a quasi-steady balance, a property that distinguishes the interannual minima from those at annual and semiannual time scales. Idealized solutions show that the presence of India causes the minimum along the Indian west coast, and that it extends around the perimeter of the Arabian Sea into the Gulf of Aden.

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Paper No33Publication ID : 79   &   Year : 2009  
TitleSpatiotemporal structure of the East India Coastal Current from satellite altimetry
Authors Durand, F.; Shankar, D.; Birol, F.; Shenoi, S.S.C.
Source Journal of Geophysical Research C: Oceans 114(2);C02013; 2009; doi:10.1029/2008JC004807,18 pp
AbstractA newly processed altimeter data set to present a hitherto unprecedented description of the spatiotemporal structure of the East India Coastal Current (EICC) is used: the data set resolves timescales ranging from a few months to a few years, and the high along-track resolution yields the first description of the cross-shore structure of the current. The seasonal cycle dominates the variability, but the nonannual timescales have similar energy levels all along the EICC path. There are short-lived, intense intraseasonal bursts. In contrast to the seasonal cycle, the interannual and intraseasonal components are decorrelated along the coast, and possible mechanisms for the decorrelation (discontinuity in the flow) are discussed. In the cross-shore direction, the current is highly correlated at all timescales: the EICC is trapped against the shelf with the current offshore flowing in the opposite direction at most locations. The EICC appears as an inherently discontinuous flow, taking the form of a few recirculating loops along the EICC path, with a typical cross-shore spatial scale of 150-200 km. The loops are highly variable in direction at all timescales from intraseasonal to interannual. This discontinuity of the EICC in space and time implies that the basic pathways and advective timescales for the interbasin exchange of water masses between the Bay of Bengal and the Arabian Sea are not robust when the full spatiotemporal variability of the EICC is considered.

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Paper No34Publication ID : 78   &   Year : 2009  
TitleOn the diurnal ranges of sea surface temperature (SST) in the north Indian Ocean
Authors Shenoi, S.S.C.; Nasnodkar, N.; Rajesh, G.; Joseph, K.J.; Suresh, I.; Almeida, A.M.
Source Journal of Earth System Science; 118(5);2009; pp.483-496
AbstractThis paper describes the variability in the diurnal range of SST in the north Indian Ocean using in situ measurements and tests the suitability of simple regression models in estimating the diurnal range. SST measurements obtained from 1556 drifting and 25 moored buoys were used to determine the diurnal range of SSTs. The magnitude of diurnal range of SST was highest in spring and lowest in summer monsoon. Except in spring, nearly 75-80 % of the observations reported diurnal range below 0.5 degrees C. The distributions of the magnitudes of diurnal warming across the three basins of north Indian Ocean (Arabian Sea, Bay of Bengal and Equatorial Indian Ocean) were similar except for the differences between the Arabian Sea and the other two basins during November-February (winter monsoon) and May. The magnitude of diurnal warming that depended on the location of temperature sensor below the water level varied with seasons. In spring, the magnitude of diurnal warming diminished drastically with the increase in the depth of temperature sensor. The diurnal range estimated using the drifting buoy data was higher than the diurnal range estimated using moored buoys fitted with temperature sensors at greater depths. A simple regression model based on the peak solar radiation and average wind speed was good enough to estimate the diurnal range of SST at approx. 1.0 m in the north Indian Ocean during most of the seasons except under low wind-high solar radiation conditions that occur mostly during spring. The additional information on the rate of precipitation is found to be redundant for the estimation of the magnitude of diurnal warming at those depths.

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Paper No35Publication ID : 28   &   Year : 2009  
TitleIntraseasonal response of the northern Indian Ocean coastal waveguide to the Madden-Julian Oscillation
Authors Vialard, J.; Shenoi, S.S.C.; McCreary, J.P.; Shankar, D.; Durand, F.; Fernando, V.; Shetye, S.R.
Source Geophys. Res. Lett.: 36(14); 2009; doi:10.1029/2009GL038450; 5 pp.
AbstractA new observational record of upper-ocean currents at 15 degrees N on the western coast of India is dominated by intraseasonal (55-110 day) variations of alongshore currents, whereas sea level at the same location has a clear seasonal signal. These observations can be interpreted within the framework of linear wave theory. At 15 degrees N, the minimum period for planetary waves is approx. 90 day, meaning that intraseasonal energy is largely trapped at the coast in the form of poleward-propagating Kelvin waves, while lower-frequency signals associated with the annual cycle can radiate offshore as planetary waves. This dynamical difference results in a steeper offshore slope of sea level at intraseasonal timescale, and thus stronger geostrophic alongshore currents. A consequence is that the alongshore currents are in-phase with intraseasonally-filtered sea level near the coast, and a gridded satellite product is shown to reproduce the current variations reasonably well. The intraseasonal current variations along the west coast of India are part of basin-scale sea-level fluctuations of the Northern Indian Ocean equatorial and coastal waveguides. The wind forcing associated with this basin scale circulation closely matches surface wind signals associated with the Madden-Julian Oscillation.

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Paper No36Publication ID : 240   &   Year : 2009  
TitleForecasting the Oceans: The oceanographic services from the Indian National Centre for ocean information services
Authors S S C Shenoi,T.Srinivasa Kumar,T.M.Bala krishnan Nair, E.Pattabhi Rama Rao, M.Nagaraja Kumar, Ch.Patanjali Kumar, E.Uma devi, K. G.Sandhya and K.Annapurnaiah
Source Indian Journal of Marine Sciences, 34;2009; pp.440-448; International Journal of Remote Sensing, 26. 2029-2034;
AbstractThis article describes the various services, including the tsunami early warnings, provided by INCOIS for the benefit of society, decision makers, researchers and industry on a day-to-day basis.

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Paper No37Publication ID : 30   &   Year : 2008  
TitleEstimating boundary currents from satellite altimetry: A case study for the east coast of India
Authors Durand, F.; Shankar, D.; Birol, F.; Shenoi, S.S.C.
Source Journal of Oceanography; 64(6), 2008; pp.831-845.
AbstractA methodology to derive surface geostrophic current from a newly released altimetric sea-level data set is presented. TOPEX/Poseidon data were first completely reprocessed from Geophysical Data Records using new algorithms accommodating marginal seas and coastal conditions. The methodology applied to the reprocessed data essentially consists of a smoothing of the raw along-track coastal altimetric data at scales at which the geostrophic equilibrium holds. This was reduced to a computational procedure using a set of objective criteria. The method to the East India Coastal Current (EICC) at the western boundary of the Bay of Bengal is applied. This paper first examines the quality of the new data set, which compares well with tide-gauge data; the current we derived is consistent with independent estimates. The methodology reveals the full spectrum of the along-shore current, ranging from intra-seasonal to inter-annual time scales, from the deep ocean to the shelf-break area where the EICC exists. The algorithm can be applied to any coastal region where an order of the Rossby radius can be defined, and it therefore opens up bright prospects for mapping the variability of other boundary-current systems in the world ocean from altimetry.

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Paper No38Publication ID : 32   &   Year : 2007  
TitleWestward movement of eddies into the Gulf of Aden from the Arabian Sea
Authors AlSaafani, M.A.; Shenoi, S.S.C.; Shankar, D.; Aparna, M.; Kurian, J.; Durand, F.; Vinayachandran, P.N.
Source Journal of Geophysical Research C: Oceans;112(11);Article number C110041004
AbstractSea level anomalies (SLA) from satellite altimetry (1993-2003) reveal the westward movement of mesoscale eddies in the Gulf of Aden. Inside the gulf the eddies move at a speed of ∼6.0-8.5 cm s-1, comparable to the first-mode baroclinic Rossby wave speed of 7.2 cm s-1. We show that the eddies, which enter the gulf from the Arabian Sea, owe their existence to more than one mechanism. Local Ekman pumping in the western Arabian Sea is important during the summer monsoon (June-September). In May and during the latter half of the summer monsoon (late July to September) and the fall intermonsoon (October), the dominant mechanism is the generation of eddies by the instabilities in the Somali Current and the large eddies associated with it (Great Whirl and Socotra eddy). During the winter monsoon (November-April) the dominant mechanism involves the westward propagating Rossby waves generated either in the Arabian Sea by Ekman pumping or along the west coast of India by poleward propagating Kelvin waves. These Rossby waves from the Arabian Sea propagate slower on entering the gulf because of a shallower thermocline in the gulf. Analysis shows that the SLA signal consists of low (annual and subannual) and high (∼100-180 d) frequencies. The low-frequency signal (mainly annual) shows a discontinuity between 52E and 60E. Though the high-frequency signal is seen at all longitudes, a wavelet analysis shows that it was significant only west of 60E. An energy analysis, based on model simulations, suggests that barotropic instabilities are important during the entire year and that baroclinic instabilities are also important during the summer monsoon. Copyright 2007 by the American Geophysical Union.

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Paper No39Publication ID : 31   &   Year : 2007  
TitleBasin-wide seasonal evolution of the Indian Oceans phytoplankton blooms
Authors Levy, M.; Shankar, D.; Andre, J.M.; Shenoi, S.S.C.; Durand, F.; DeBoyer Montegut, C.
Source Journal of Geophysical Research C: Oceans 112 (12); art. no. C12014; doi:10.1029/2007JC004090; 14pp.
AbstractA climatology of Sea-viewing Wide Field-of-View Sensor (SeaWiFS) chlorophyll data over the Indian Ocean is used to examine the bloom variability patterns, identifying spatio-temporal contrasts in bloom appearance and intensity and relating them to the variability of the physical environment. The near-surface ocean dynamics is assessed using an ocean general circulation model (OGCM). It is found that over a large part of the basin, the seasonal cycle of phytoplankton is characterized by two consecutive blooms, one during the summer monsoon, and the other during the winter monsoon. Each bloom is described by means of two parameters, the timing of the bloom onset and the cumulated increase in chlorophyll during the bloom. This yields a regional image of the influence of the two monsoons on phytoplankton, with distinct regions emerging in summer and in winter. By comparing the bloom patterns with dynamical features derived from the OGCM (horizontal and vertical velocities and mixed-layer depth), it is shown that the regional structure of the blooms is intimately linked with the horizontal and vertical circulations forced by the monsoons. Moreover, this comparison permits the assessment of some of the physical mechanisms that drive the bloom patterns, and points out the regions where these mechanisms need to be further investigated. A new outcome of this study is that in many distinct areas, time shifts of 1-2 months are witnessed in the timing of the bloom onsets in adjoining regions. These time shifts are rationalized in terms of horizontal advection and Rossby wave propagation.

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Paper No40Publication ID : 33   &   Year : 2007  
TitleArabian Sea mini warm pool and the monsoon onset vortex
Authors Vinayachandran, P.N.; Shankar, D.; Kurian, J.; Durand, F.; Shenoi, S.S.C.
Source Current Science 93(2); 2007; pp. 203-214.
AbstractWarm pools ? regions with sea surface temperature (SST) in excess of 28 degrees C ? in the ocean occupy a special place in tropical climate owing to their impact on tropical convection. The southeastern Arabian Sea presents SST in excess of 30 degrees C for two to three months preceding the onset of the summer (southwest) monsoon over India. Recently, several attempts have been made to understand the processes that cause such high SSTs in the region. The literature is also strewn with observations and modelling of a ?monsoon onset vortex? forming over the warm pool. This paper is a review of our current understanding of the Arabian Sea mini warm pool and its possible role in the formation of the monsoon onset vortex.

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Paper No41Publication ID : 80   &   Year : 2007  
TitleSimulated seasonal and interannual variability of the mixed layer heat budget in the northern Indian Ocean
Authors DeBoyer Montegut, C.; Vialard, J.; Shenoi, S.S.C.; Shankar, D.; Durand, F.; Ethe, C.; Madec, G.
Source Journal of Climate 20 (13); 2007; pp. 3249-3268.
AbstractA global ocean general circulation model (OGCM) is used to investigate the mixed layer heat budget of the Northern Indian Ocean (NIO). The model is validated against observations and shows fairly good agreement with mixed layer depth data in the NIO. The NIO has been separated into three sub basins: the western Arabian Sea (AS), the eastern AS, and the Bay of Bengal (BoB). This study reveals strong differences between the western and eastern AS heat budget, while the latter basin has similarities with the BoB. Interesting new results on seasonal time scales are shown. The penetration of solar heat flux needs to be taken into account for two reasons. First, an average of 28 W m sup(-2) is lost beneath the mixed layer over the year. Second, the penetration of solar heat flux tends to reduce the effect of solar heat flux on the SST seasonal cycle in the AS because the seasons of strongest flux are also seasons with a thin mixed layer. This enhances the control of SST seasonal variability by latent heat flux. The impact of salinity on SST variability is demonstrated. Salinity stratification plays a clear role in maintaining a high winter SST in the BoB and eastern AS while not in the western AS. The presence of freshwater near the surface allows heat storage below the surface layer that can later be recovered by entrainment warming during winter cooling (with a winter contribution of + 2.1 degrees C in the BoB). On an interannual time scale, the eastern AS and BoB are strongly controlled by the winds through the latent heat flux anomalies. In the western AS, vertical processes, as well as horizontal advection, contribute significantly to SST interannual variability, and the wind is not the only factor controlling the heat flux forcing.

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Paper No42Publication ID : 81   &   Year : 2007  
TitleModeling the barrier-layer formation in the southeastern Arabian Sea
Authors Durand, F.; Shankar, D.; DeBoyer Montegut, C.; Shenoi, S.S.C.; Blanke, B.; Madec, G
Source Journal of Climate,20(10); 2007; pp. 2109-2120.
AbstractThe effect of salinity on the formation of the barrier layer (BL) in the southeastern Arabian Sea (SEAS) is investigated using an ocean general circulation model. In accordance with previous studies, the runoff distribution and the India Sri Lanka passage have a strong impact on the realism of the salinity simulated in the area at seasonal time scales. The model simulates a BL pattern in fairly good agreement with available observations. Eulerian and Lagrangian approaches show that the BL is formed by two complementary processes, the arrival of low-salinity surface waters that are cooled en route to the SEAS and downwelling of waters mostly local to the SEAS in the subsurface layers. The surface waters are partly of Bay of Bengal origin and are partly from the SEAS, but are cooled east and south of Sri Lanka in the model. That the downwelled subsurface waters are warm and are not cooled leads to temperature inversions in the BL. The main forcing for this appears to be remotely forced planetary waves

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Paper No43Publication ID : 82   &   Year : 2007  
TitleWater masses in the Gulf of Aden
Authors AlSaafani, M.A.; Shenoi, S.S.C.
Source Journal of Oceanography 63(1); 2007; pp. 1-14.
AbstractHydrographic data collected from Gulf of Aden since 1920 have been compiled to identify and refine the definitions of water masses in the Gulf of Aden (GA) and to describe their spatio-temporal variability. Four water masses have been identified based on their theta-S characteristics. The Red Sea Water (RSW) that flows from the Red Sea is the most prominent water in the GA; this occupies about 37 % of the total volume of Gulf of Aden. The Gulf of Aden Surface Water (approx. 3 %) forms as a mixture of local water and the water from western Arabian Sea during winter and Red Sea surface water during summer. The intermediate water, identified as Gulf of Aden Intermediate Water (GAIW), occupies about 9 % of the total volume of GA; a characteristic salinity minimum is associated with it at Sigma sub (theta) = 26.50 kg m sup(-3). The northward spread of sub-tropical subsurface water from the south appears to be the major source of GAIW. The bottom water, named Gulf of Aden Bottom Water, showed the least variability. It was formed due to the mixing of Red Sea Water and water of southern origin. Mixing triangles have been used to analyze the composition of water in the GA.

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Paper No44Publication ID : 85   &   Year : 2006  
TitleThe great tsunami of 26 December 2004: A description based on tide gauge data from Indian subcontinent and surrounding areas
Authors Nagarajan, B.; Suresh, I.; Sundar, D.; Sharma, Rakesh; Lal, A.K.; Neetu, S.; Shenoi, S.S.C.; Shetye, S.R.; Shankar, D.
Source Earth, Planets and Space 58 (2); pp. 211-215.
AbstractThe Great Tsunami of 26 December 2004 is described using data from seven tide gauges in India and others from surrounding areas in the Indian Ocean. The tsunami struck the Indian east coast around 0330 UTC. The amplitude was 2 m above the tide at Chennai (Tamil Nadu), Paradip (Orissa), and Colombo. The east coast of India (and of Sri Lanka) was hit shortly after high tide, Tuticorin (Tamil Nadu) and Colombo, however, were hit shortly after low tide. The tsunami wave propagated northward along the Indian west coast. All these gauges are to the west of the earthquake zone and the detided sea levels show first a rise in sea level with the arrival of the tsunami, and then a sharp decrease. Spectral and wavelet analysis of the detided series show that the maximum amplitude was at a period of 35�45 minutes, with another maximum around 20 minutes. Along the Indian east coast, however, there is another broad peak between 1�2 hours within the first few hours after the first tsunami wave.

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Paper No45Publication ID : 83   &   Year : 2006  
TitleSurface freshwater from Bay of Bengal runoff and Indonesian throughflow in the tropical Indian Ocean
Authors Sengupta, D.; Raj, G.N.B.; Shenoi, S.S.C.
Source Geophysical Research Letters, 33(22); 2006; art. no. L22609 doi:10.1029/2006GL027573, 5 pp.
AbstractAccording to recent estimates, the annual total continental runoff into the Bay of Bengal (BoB) is about 2950 km sup(3), which is more than half that into the entire tropical Indian Ocean (IO). Climatological observations are used to trace the seasonal pathways of near surface freshwater from BoB runoff and Indonesian Throughflow (ITF) by removing the net contribution from precipitation minus evaporation. North of 20 degrees S, the amount of freshwater from BoB runoff and ITF changes with season in a manner consistent with surface currents from drifters. BoB runoff reaches remote regions of the Arabian Sea; it also crosses the equator in the east to join the ITF. This freshwater subsequently flows west across the southern tropical in the South Equatorial Current.

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Paper No46Publication ID : 84   &   Year : 2006  
TitleThe 2004 Indian Ocean tsunami: Description of the event and estimation of length of the tsunami source region based on data from Indian tide gauge
Authors Suresh, I.; Neetu, S.; Shankar, D.; Shenoi, S.S.C.; Shetye, S.R.; Sundar, D.; Shankar, R.; Nagarajan, B.
Source The Eleventh Asian Congress of Fluid Mechanics (11ACFM), 22-25 May 2006, Kuala Lumpur, Malaysia. eds. by: Tso, C.P.; Viswanath, P.R.; Fukunishi, Y.; Cui, E.(11. Asian Congress of Fluid Mechanics; Kuala Lumpur; Malaysia; 22-25 May 2006). The Institution of Engineers; Malaysia; 2006; 1-6.
AbstractThe Great Tsunami of 26 December 2004 in the Indian Ocean is described using data from tide gauges along the coast of India. The tsunami struck the Indian east coast around 0330 UTC. The amplitude was 2.0 m above the tide at Chennai and Paradip, 1.5 m at Visakhapatnam and less than a metre at Tuticorin. The tsunami propagated into the Arabian Sea from the south and Kochi was hit at 0541 UTC. The maximum amplitude had decayed to about 80 cm at Kochi and it was less than 10 cm at Okha in Gujarat. All these tide gauges are to the west of the earthquake zone and the detided sea levels show first a rise in sea level with the arrival of the tsunami, and then a sharp decrease. Spectral and wavelet analysis of the residuals shows that the maximum amplitude was at a period of 35-45 min, with another maximum around 20 min. Along the Indian east coast, however, there is another broad peak between 1-2 hours within the first few hours after the first tsunami wave. Numerical simulation of this event is critically dependent on the initial perturbation used to force the model. The extent of the tsunami source region remains a key bottleneck. Arrival times recorded on the tide gauges provide additional constraint on the northern extent of the tsunami source location. Using the newly available tide-gauge data from Paradip, the northernmost station along the Indian east coast and therefore the most critical constraint on the northern extent of the tsunami source region, we investigate the northern extent of the source region of the Indian Ocean tsunami. Using backward ray tracing, it is shown that the tsunami travel times as recorded on the tide gauges at Paradip, Vishakhapatnam, and Chennai imply that the tsunami source region extends to approx. 11 degrees N, implying a source region about 900 km long, about 30% greater than earlier estimates.

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Paper No47Publication ID : 364   &   Year : 2006  
TitleImproved satellite altimetry for the observation of coastal ocean dynamics: A case study for the Northern Indian Ocean
Authors Durand, F.; Shankar, D.; Birol, F.; Shenoi, S.S.C.; Roblou, L.; Lyard, F.; Mnard, Y.
Source Proceedings of SPIE - The International Society for Optical Engineering;6406; 2006; art. no. 64060M
AbstractThe coastal currents in the Northern Indian Ocean are believed to play a prominent role in the heat and salt exchanges between Arabian Sea and Bay of Bengal. Hence it appears timely to carefully monitor their structure and variability at all timescales from intraseasonal to interannual. The objective of this study is to determine to what extent the sea surface height (SSH) variability associated to these coastal processes can be observed with satellite altimetry, in the Northern Indian ocean sector. Indeed, radar altimetry, which allows to measure SSH at centimetric accuracy, has been shown to be a powerful tool to obtain a wealth of information about open-ocean dynamics. Unfortunately, today, the use of standard satellite altimetric products in coastal zones remains challenging. This study explores a newly released coastal altimetric dataset, obtained from a complete reprocessing of the Topex/Poseidon data. We first present an objective method to derive geostrophic current from the raw SSH. Then we present the validation of the altimetric SSH against in situ observations. Finally we briefly analyze the observed variability of the East India Coastal Current at various timescales.

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Paper No48Publication ID : 365   &   Year : 2006  
TitleSeasonal and interannual variability of eddy field and surface circulation in the Gulf of Aden
Authors Al Saafani, M.A., Shenoi, S.S.C.
Source European Space Agency, (Special Publication) ESA SP Issue 614, July 2006, 6p
AbstractThe circulation in the Gulf of Aden is inferred from three different data sets: historical ship drifts, hydrography, and satellite altimeter derived sea level (Topex/Poseidon, Jason and ERS). The circulation in this semi-enclosed basin is marked with strong seasonality with reversals in the direction of flows twice a year following the reversal in monsoonal winds. During the winter monsoon (November - February) there is an inflow from Arabian Sea; an extension of Arabian Coastal Current (ACC). During southwest monsoon (June - August) the flow is generally towards east especially along the northern coast of Gulf of Aden. The geostrophic currents also show that the circulation in the gulf is embedded with mesoscale eddies. These westward propagating eddies appear to enter the Gulf of Aden from the western Arabian Sea in winter. The relative contribution of mesoscale eddies to the circulation in the gulf were estimated using altimeter derived Sea level anomaly (SLA) for the years 1993 to 2003. The effect of these mesoscale eddies extend over the entire water column. The propagation speeds, of these eddies, estimated using weekly spaced altimeter derived SLA (2002 - 2003) is ∼ 4.0 - 5.3 cm S-1. The sum of the speeds of second mode Rossby wave and the mean current (4.8 cm S-1) matches with the propagation speeds of eddies estimated using SLA. Hence, second mode baroclinic Rossby waves appear to be responsible for the westward propagation of eddies in the Gulf of Aden. The presence of these eddies in the temperaturesalinity climatology confirms that they are not transient features.

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Paper No49Publication ID : 90   &   Year : 2005  
TitleHydrography of the eastern Arabian Sea during summer monsoon 2002
Authors Shankar, D.; Shenoi, S.S.C.; Nayak, R.K.; Vinayachandran, P.N.; Nampoothiri, G.; Almeida, A.M.; Michael, G.S.; RameshKumar, M.R.; Sundar, D.; Sreejith, O.P.
Source Journal of Earth System Science,114(5); 2005; pp.459-474.
AbstractHydrographic observations in the eastern Arabian Sea (EAS) during summer monsoon 2002 (during the first phase of the Arabian Sea Monsoon Experiment (ARMEX)) include two approximately fortnight-long CTD time series. A barrier layer was observed occasionally during the two time series. These ephemeral barrier layers were caused by in situ rainfall, and by advection of low-salinity (high-salinity) waters at the surface (below the surface mixed layer). These barrier layers were advected away from the source region by the West India Coastal Current and had no discernible effect on the sea surface temperature. The three high-salinity water masses, the Arabian Sea High Salinity Water (ASHSW), Persian Gulf Water (PGW), and Red Sea Water (RSW), and the Arabian Sea Salinity Minimum also exhibited intermittency: they appeared and disappeared during the time series. The concentration of the ASHSW, PGW, and RSW decreased equatorward, and that of the RSW also decreased offshore. The observations suggest that the RSW is advected equatorward along the continental slope of the Indian west coast.

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Paper No50Publication ID : 89   &   Year : 2005  
TitleEstimating the seaward extent of sea breeze from QuickSCAT scatterometry
Authors Aparna, M.; Shetye, S.R.; Shankar, D.; Shenoi, S.S.C.; Mehra, P.; Desai, R.G.P.
Source Geophysical Research Letters, 32 (13); pp. 1-4
AbstractAn objective method for quantifying the seaward extent of the sea breeze is presented. The underlying assumption is that the offshore decay in the strength of the sea breeze results in an offshore decay of the vector correlation between the wind vectors near and away from the coast. The degradation in the vector correlation coefficient is used to estimate the seaward extent of the sea breeze using QuikSCAT data.

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Paper No51Publication ID : 86   &   Year : 2005  
TitleImpact of convection over the equatorial trough on summer monsoon activity over India
Authors RameshKumar, M.R.; Shenoi, S.S.C.; Schultz, J.
Source International Journal of Remote Sensing, 26 (21); 2005; pp. 4747-4762.
AbstractCauses of disruption of rainfall (break in monsoon conditions) over the Indian subcontinent during the monsoon months for the period 1979-1998 are investigated using pentad rainfall data from the Global Precipitation Climatology Project (GPCP). Most (about 73%) of the break in monsoon (BM) events were associated with convective activity (rainfall more than 30 mm/pentad) over the equatorial trough (ET) region. The association between these events and the convective activity over the western (WET) and eastern equatorial trough (EET) regions of the tropical Indian Ocean were further explored. These relationships were tested for different (deficit, normal and excess) monsoon conditions over the Indian subcontinent and the El Nio conditions in the Pacific Ocean. There appears to be a negative and significant correlation between the Central Indian Region (CIR) rainfall and EET during deficit and non-El Nio years. During deficit and El Nio years (1982 and 1987), both CIR and all India rainfall (AIR) exhibited a negative correlation with WET. In the case of years with no breaks, EET was negatively (positively) correlated during the years 1982 and 1992 (1994 and 1997) with AIR. The convective activity was more intense over EET than WET during prolonged BM and also in a deficit and non-El Nino year (1979).

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Paper No52Publication ID : 87   &   Year : 2005  
TitleComment on `The Great Sumatra-Andaman Earthquake of 26 December 2004`
Authors Neetu, S.; Suresh, I.; Shankar, R.; Shankar, D.; Shenoi, S.S.C.; Shetye, S.R.; Sundar, D.; Nagarajan, B.
Source Science: 310(5753); 2005; p. 1431.
AbstractLay et al. (Research Articles, Science 308(5725); 2005; 1127-1133; 20 May 2005), estimated a 600-km length for the tsunami source region. Adding tide-gauge data from Paradip, the northernmost of the Indian east-coast stations and therefore the most critical constraint on the northern extent of the source, it is estimated that its length was greater by approx. 30%.

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Paper No53Publication ID : 91   &   Year : 2005  
TitleOn the accuracy of the simple ocean data assimilation analysis for estimating heat Budgets of the Near-Surface Arabian Sea and Bay of Bengal
Authors Shenoi, S.S.C.; Shankar, D.; Shetye, S.R.
Source Journal of Physical Oceanography,35(3); 2005; pp.395-400.
AbstractThe accuracy of data from the Simple Ocean Data Assimilation (SODA) model for estimating the heat budget of the upper ocean is tested in the Arabian Sea and the Bay of Bengal. SODA is able to reproduce the changes in heat content when they are forced more by the winds, as in wind-forced mixing, upwelling, and advection, but not when they are forced exclusively by surface heat fluxes, as in the warming before the summer monsoon

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Paper No54Publication ID : 88   &   Year : 2005  
TitleHydrography and water masses in the southeastern Arabian Sea during March-June 2003
Authors Shenoi, S.S.C.; Shankar, D.; Michael, G.S.; Kurian, J.; Varma, K.K.; RameshKumar, M.R.; Almeida, A.M.; Unnikrishnan, A.S.; Fernandes, W.; Barreto, N.; Gnanaseelan, C.; Mathew, R.; Praju, K.V.; Mahale, V.P.
Source Journal of Earth System Science, 114(5); 2005; pp.475-491.
AbstractThis paper describes the hydrographic observations in the southeastern Arabian Sea (SEAS) during two cruises carried out in March-June 2003 as part of the Arabian Sea Monsoon Experiment. The surface hydrography during March-April was dominated by the intrusion of low-salinity waters from the south; during May-June, the low-salinity waters were beginning to be replaced by the high-salinity waters from the north. There was considerable mixing at the bottom of the surface mixed layer, leading to interleaving of low-salinity and high-salinity layers. The flow paths constructed following the spatial patterns of salinity along the sections mimic those inferred from numerical models. Time-series measurements showed the presence of Persian Gulf and Red Sea Waters in the SEAS to be intermittent during both cruises: they appeared and disappeared during both the fortnight-long time series. Printed in India.

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Paper No55Publication ID : 92   &   Year : 2005  
TitleRole of ocean in the genesis and annihilation of the core of the warm pool in the southeastern Arabian Sea
Authors Shenoi, S.S.C.; Shankar, D.; Gopalakrishna, V.V.; Durand, F.
Source Mausam: 56(1); 2005; 147-160.
AbstractThe earlier hypothesis, stated in the ARMEX (Arabian Sea Monsoon Experiment) Science Plan, that the ocean plays an important, but passive, role in the genesis of the core of warm pool in the southeastern Arabian Sea (SEAS) is examined in the light of new data collected during Phase 2nd of ARMEX. The new evidence confirms that the ocean plays an important role. This paper summarises the results based on these data, which show that the remotely forced ocean dynamics plays an active, not passive, role not only in the genesis of the core of the warm pool in the SEAS, but also triggers the collapse of the warm pool

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Paper No56Publication ID : 96   &   Year : 2004  
TitleImpact of temperature inversions on SST evolution in the South-Eastern Arabian Sea during the pre-summer monsoon season
Authors Durand, F.; Shetye, S.R.; Vialard, J.; Shankar, D.; Shenoi, S.S.C.; Ethe, C.; Madec, G.
Source Geophysical Research Letters, 31(1); 2004; pp.L01305 1-4.
AbstractTemperature inversions are known to occur in the near-surface ocean regime where salinity stratification is large enough to influence the density field. However, they have not been known as features that alter near-surface processes significantly to influence the sea surface temperature (SST). From the analysis of new observed datasets as well as of state-of-the-art numerical model outputs, this paper shows that heat trapped within a temperature inversion makes significant contribution to warming of the SST in the South-Eastern Arabian Sea during the pre-southwest monsoon season.

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Paper No57Publication ID : 97   &   Year : 2004  
TitleMonsoon onset over Kerala and pre monsoon rainfall peak
Authors RameshKumar, M.R.; Shenoi, S.S.C.; Shankar, D.
Source Proceedings of the National Symposium METOC - 2004 on Emerging Trends in the Fields of Oceanography and Meteorology, 05-06 February 2004. (Natl. Symp. METOC - 2004 on Emerging Trends in the Fields of Oceanography and Meteorology; Kochi; India; 5-6 Feb 2004). ; 2004; 305-307.
AbstractIn the present study the pentad Global Precipitation Climatology Project (GPCP) estimate have been used, which is a blended product of microwave, infrared and in-situ gauge data for the region bounded by 8 degrees - 13 degrees N; 70 degrees - 95 degrees E, from 1st March to 31 May for the years 1979 to 2001. The monsoon onset dates over Kerala, as declared by India Meteorological Department has been used in the present study. For each year, the midday of the pentad with the rainfall peak was looked for in the period from 1st April to 10th May and identified as the Pre Monsoon Rainfall Peak (PMRP). The analysis showed that PMRP exists about seven pentads prior to the onset of the monsoon over Kerala coast. The correlation between PMRP date and the monsoon onset date over Kerala was found to be 0.72, which was statistically significant. Thus, as is felt that the pre monsoon rainfall estimate from the satellite data can be used for predicting the monsoon onset over Kerala coast. The results and the methodology used are briefly presented

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Paper No58Publication ID : 98   &   Year : 2004  
TitleWhy is Bay of Bengal warmer than Arabian Sea during the summer monsoon?
Authors Shenoi, S.S.C.; Shankar, D.; Shetye, S.R.
Source Proceedings of the National Symposium METOC - 2004 on Emerging Trends in the Fields of Oceanography and Meteorology, 05-06 February 2004. (Natl. Symp. METOC - 2004 on Emerging Trends in the Fields of Oceanography and Meteorology; Kochi; India; 5-6 Feb 2004). ; 2004; 87-93.
AbstractThe near-surface Bay of Bengal remains significantly warmer than the Arabian Sea during summer monsoon (June-September). Analysis of the heat budgets of the near-surface Arabian Sea and Bay of Bengal shows significant differences between them during the summer monsoon. In the Arabian Sea, the winds associated with the summer monsoon are stronger and favour the transfer of heat to deeper layers owing to overturning and turbulent mixing. In contrast, the weaker winds over the bay force a relatively sluggish oceanic circulation that is unable to overturn, forcing a heat-budget balance between the surface fluxes and diffusion and the rate of change of heat in the near-surface layer.

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Paper No59Publication ID : 95   &   Year : 2004  
TitleRemote forcing annihilates barrier layer in southeastern Arabian Sea
Authors Shenoi, S.S.C.; Shankar, D.; Shetye, S.R.
Source Geophysical Research Letters,31(5);2004;pp.L05307 1-4.
AbstractTime-series measurements of temperature and salinity profiles were made every two hours at 74 degrees 30 minutes E, 9 degrees 13 minutes N in the southeastern Arabian Sea (SEAS) during 22-March-7-April and 23-May-7-June 2003 as part of the Arabian Sea Monsoon Experiment (ARMEX). The observations show that a 20 m thick barrier layer (BL) exists during March-April owing to a surface layer of low-salinity waters advected earlier during December-January from the Bay of Bengal. The BL is almost annihilated by 7 April owing to upwelling. The relic BL that survives is annihilated later in May by upwelling, and by the inflow of high-salinity waters from the north and by mixing due to stronger winds, which deepen the mixed layer. Evidence from satellite data and arguments based on existing theories are presented to show that both the upwelling and the advection of high-salinity waters are remotely forced.

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Paper No60Publication ID : 93   &   Year : 2004  
TitleSeasonal cycle of hydrography in the Bab el Mandab region, southern Red Sea
Authors AlSaafani, M.A.; Shenoi, S.S.C.
Source Proceedings of the Indian Academy of Sciences, Earth and Planetary Sciences 113 (3); 2004; pp.269-280.
AbstractThe seasonal cycle of temperature - salinity variations in the Bab el Mandab region (southern Red Sea) is described using CTD data collected during four cruises spread over the period May 1995-August 1997. A two layer system exists during early summer, winter and spring while a three layer system exists during summer. During summer, a large amount of the Gulf of Aden water intrudes into the Bab el Mandab region; up to the northern limit (14.5N). The quantity of Red Sea water that flows into the Gulf of Aden is maximum during the winter and minimum during the summer

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Paper No61Publication ID : 94   &   Year : 2004  
TitleObservational evidence for westward propagation of temperature inversions in the southeastern Arabian Sea
Authors Shankar, D.; Gopalakrishna, V.V.; Shenoi, S.S.C.; Durand, F.; Shetye, S.R.; Rajan, C.K.; Johnson, Z.; Araligidad, N.; Michael, G.
Source Geophysical Research Letters,31(8); 2004; pp. L08305 1-4.
AbstractA warm pool forms in the southeastern Arabian Sea (SEAS) prior to the onset of the summer monsoon over India in early June; the core of this warm pool is in the Lakshadweep Sea (LS). XBT and surface salinity data collected in the LS during May-2002-April-2003 show that temperature inversions occur off the southwest coast of India in early December with the arrival of low-salinity waters from the Bay of Bengal. The low-salinity waters and the inversions propagate westward along with the downwelling Rossby waves that constitute the Lakshadweep sea-level high; inversions occur in the western LS (approx. 73 degrees E) about 40 days after they occur near the coast in the eastern LS (approx. 75.5 degrees E). They disappear in April, when the Tropical Convergence Zone moves over the SEAS and the warm pool engulfs the region. Ocean dynamics and air-sea fluxes are together responsible for the formation and westward propagation of the inversions

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Paper No62Publication ID : 101   &   Year : 2002  
TitleDifferences in heat budgets of the near-surface Arabian Sea and Bay of Bengal: Implications for the summer monsoon
Authors Shenoi, S.S.C.; Shankar, D.; Shetye, S.R.
Source Journal of Geophysical Research C: Oceans 107 (6), pp. 5.1-5.14
AbstractAn analysis of the heat budgets of the near-surface Arabian Sea and Bay of Bengal shows significant differences between them during the summer monsoon (June- September). In the Arabian Sea the winds associated with the summer monsoon are stronger and favor the transfer of heat to deeper layers owing to overturning and turbulent mixing. In contrast, the weaker winds over the bay force a relatively sluggish oceanic circulation that is unable to overturn, forcing a heat budget balance between the surface fluxes and diffusion and the rate of change of heat in the near-surface layer. The weak winds are also unable to overcome the strong near-surface stratification because of a low- salinity surface layer. This leads to a shallow surface mixed layer that is stable and responds quickly to changes in the atmosphere. An implication is that sea surface temperature (SST) in the bay remains higher than 28C, thereby supporting large-scale deep convection in the atmosphere during the summer monsoon. The atmospheric heating associated with the convection plays a critical role in sustaining the monsoon winds, and the rainfall associated with it, not only over the bay but also over the Indian subcontinent, maintains a low-salinity surface layer. In the Arabian Sea the strong overturning and mixing lead to lower SST and weak convective activity, which in turn, lead to low rainfall and runoff, resulting in weak stratification that can be overcome easily by the strong monsoon winds. Thus, in both basins, there is a cycle with positive feedback, but the cycles work in opposite directions. This locks monsoon convective activity primarily to the bay.

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Paper No63Publication ID : 103   &   Year : 2002  
TitlePreface to: Pan Ocean Remote Sensing Conference (PORSEC)
Authors Desa, E.; Brown, R.; Shenoi, S.S.C.; Joseph, G. eds.
Source Pan Ocean Remote Sensing Conf.; Dona Paula, Goa; India; Dec 2000). (Proc. Indian Acad. Sci. (Earth Planet. Sci.)). : 111(3); 2002; 187-378.
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Paper No64Publication ID : 102   &   Year : 2002  
TitleDaily SST fields produced by blending infrared and microwave radiometer estimates
Authors Sreejith, O.P.; Shenoi, S.S.C
Source Proceedings of The Sixth Pan Ocean Remote Sensing Conference (PORSEC) Bali, 3-6 September 2002: Remote sensing and ocean science for marine resources exploration and environment. Vol. 2. eds. by: Pasaribu, B.P.; Kaswadji, R.; Nurjaya, I.W.; Gaol, J.L.(6. Pan Ocean Remote Sensing Conf. (PORSEC); Bali; Indonesia; 3-6 Sep 2002). PORSEC 2002 Secretariat; Bogor; Indonesia; 2002; 567-570.
AbstractMeasurement of Sea Surface Temperature (SST) using satellite based sensors have matured during the last decade. The infrared measurements, using the AVHRR sensor, flown onboard the NOAA satellites, have been used for the generation of high resolution operational products on daily basis, since 1982. However, the intrinsic problem of the infrared radiation prevents the retrieval of SST in the presence of clouds. This causes heavy loss of SST data over the north Indian Ocean especially during the summer monsoon (June-September). The recent advances in the microwave remote sensing of SST provides an alternative for the retrieval of SSTs in the presence of clouds. The microwaves, though they can measure the SSTs in the presence of clouds, their spatial resolution is poorer than that of infrared measurements. Near land boundaries the retrievals of the SSTs using microwaves are inferior due to the contamination from the emissions from land. In this study we take the advantage of the SST retrievals from infrared (NOAA/AVHRR) and microwave (TRMM/TMI) sensors and produce a new SST filed. An objective analysis scheme is used to combine the SSTs retrieved using AVHRR (9 km daily ascending and descending passes) and TMI (25 km ascending and descending passes) sensors to produce a daily field at a spatial resolution of 18 km. The new SST fields when compared with in situ measurements (drifting buoy SSTs) showed improvement (Root Mean Square Error of 0.659 degrees C). The corresponding root mean square error of the SSTs derived from AVHRR and TMI were 0.642 degrees C, and 0.783 degrees C respectively.

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Paper No65Publication ID : 100   &   Year : 2002  
TitleAn evaluation of satellite and in situ based sea surface temperature datasets in the north Indian ocean region
Authors Sreejith, O.P.; Shenoi, S.S.C
Source International Journal of Remote Sensing, 23(24);2002;pp.5165-5175.
AbstractSatellite based daily fields of Pathfinder SST (PFSST) and blended-analysed fields like National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) and Reynolds weekly SST data were compared with the in situ measurements obtained from several drifting buoys and a moored buoy in the north Indian Ocean. The mean differences (bias) and scatter (root mean square deviation (RMSD)) were higher than the ideally expected values of <0.01C and 0.5C for all three datasets. There was very little difference in the error statistics from one region to another. The error statistics differed significantly from year to year. The PFSST fields reported cooler SSTs ∼0.5C, during August 1991 to April 1992, due to the increased input of aerosols in the atmosphere caused by the eruption of Mount Pinatubo. Being a high resolution dataset, the PFSST is best able to mimic the sudden changes in the in situ SSTs that happen over a couple of days to a couple of weeks. Neither NCEP/NCAR data nor the Reynolds data were able to mimic the changes in SST that occur over a period of a few days. All three datasets are useful for the analysis of low frequency oscillations like annual and semi-annual cycles. PFSST and NCEP/NCAR SSTs are also useful for the analysis of higher frequency oscillations in the SST fields such as the 26-day period oscillations in the equatorial Indian Ocean.

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Paper No66Publication ID : 132   &   Year : 2000  
TitleThe Fifth Pacific Ocean Remote Sensing Conference (PORSEC), 5-8 December 2000. Proceedings of PORSEC 2000. Vol. 1-2
Authors Desa, E.; Shenoi, S.S.C.; Bhat, S.R.; Pankajakshan, T.; Muraleedharan, P.M.; Desa, E.; Rao, L.V.G. Eds.
Source 5th. Pacific Ocean Remote Sensing Conference (PORSEC); Dona Paula, Goa; India; 5-8 Dec 2000). Natl. Inst. of Oceanography; Goa; India; 2000; xviii+ 900 pp.
Abstract...

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Paper No67Publication ID : 104   &   Year : 2000  
TitleInertial currents in the Indian Ocean derived from satellite tracked surface drifters
Authors Saji, P.K.; Shenoi, S.S.C.; Almeida, A.M.; Rao, L.V.G.
Source Oceanologica Acta,23(5);2000; pp.635-640.
AbstractSatellite-tracked surface drifters were used to analyze the characteristics of inertial currents in the tropical Indian Ocean. The drifters were drogued at 15 m depth and had wind-produced slips less than 0.1% of the wind speed. The rotary spectra of surface velocity components indicated the significance of intertial currents. They are circular (rotary coefficient > 0.5), highly intermittent and contribute up to 46% to the total kinetic energy of the surface flow field. Events of intertial activity, either triggered by the passage of atmospheric disturbances or by the local fluctuations in the atmospheric pressure (winds), did not last for more than 4 to 5 intertial cycles. The observed intertial frequency exhibited a shift towards the red end of the spectrum by 12%. Cyclonic storm induced inertial events even at a location 300 km away from it

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Paper No68Publication ID : 108   &   Year : 1999  
TitleOn the suitability of global algorithms for the retrieval of SST from the north Indian Ocean using NOAA/AVHRR
Authors Shenoi, S.S.C.
Source International Journal of Remote Sensing: 20(1); 1999; pp.11-29.
AbstractThe errors associated with the SST retrievals from the north Indian Ocean, using global multichannel sea surface temperature (MCSST), nonlinear sea surface temperature (NLSST), and Pathfinder sea surface temperature (PFSST) algorithms are analysed using satellite-sea-truth matchups for NOAA-9 and NOAA-11. The trends associated with the SST retrievals with respect to various independent parameters and simple statistics are analysed to assess the performance of the algorithms. The MCSST and NLSST retrievals have undesirably large trends assocaited with surface temperature, satellite, scan geometry and scan time (day/night); SST retrievals using PFSST show the lowest trends. The simple statistics, mean, and RMSD, are worst for MCSST (0.6 and 1.3~'C); they are unsatisfactory for NLSST (0.4 and 0.7~'C) and PFSST (0.4 and 0.7~'C) also. Considerable improvement in statiscs and trends are achievable by regionally optimizing the algorithm coefficients. The mean and RMSD of residuals drop to more than 50% of the values obtained by the use of global coefficients. Regionally optimized NLSST appear to be the better algorithm for the north Indian Ocean in the absence of time-dependent regional coefficients suggested by PFSST

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Paper No69Publication ID : 106   &   Year : 1999  
TitleOn the role of the cross equatorial flow on summer monsoon rainfall over India using NCEP/NCAR reanalysis data
Authors RameshKumar, M.R.; Shenoi, S.S.C.; Schluessel, P
Source Meteorology and Atmospheric Physics, 70(3-4); 1999; pp. 201-213.
AbstractThe role of the cross equatorial flow from the southern Indian Ocean on the Indian Summer monsoon is examined using the National Centre for Environmental Prediction (NCEP)/National Centre for Atmospheric Research (NCAR) data for the period January 1982 to December 1994. A comparison of NCEP/NCAR data with the satellite data retrieved from the Special Sensor Microwave Imager (SSM/I) sensor onboard the Defense Meteorological Satellite Program (DMSP) exhibited a negative bias for the wind speeds greater than 4 m/s whereas in the case of specific humidity. SSMI values exhibited a positive bias and the precipitable water derived from the satellite data exhibited a negative bias. The NCEP reanalysis is able to depict the mean annual cycle of both the cross equatorial flow and moisture flow into the Indian subcontinent during the monsoon season, but it fails to depict these differences during excess (1983, 1988, 1994) and deficit monsoon (1982, 1986, 1987) composites. Further, it is seen that inter hemispheric flow far exceeds the excess moisture available over the Arabian Sea indicating that it is the cross equatorial flow which decides the fate of the Indian summer monsoon

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Paper No70Publication ID : 105   &   Year : 1999  
TitleNear-surface circulation and kinetic energy in the tropical Indian Ocean derived from lagrangian drifters
Authors Shenoi, S.S.C.; Saji, P.K.; Almeida, A.M.
Source Journal of Marine Research, 57(6); 1999; pp. 885-907.
AbstractTrajectories of 412 satellite-tracked drifting buoys deployed in the tropical Indian Ocean have been analyzed to document the surface circulation and kinetic energy field. Only drifters drogued at 15 m depth and having drag area ratio greater than 35 are used to estimate current velocities. Unlike in earlier studies, the widening of the Equatorial Jet in the eastern equatorial Indian Ocean and the westward flow at the equator during July-August are apparent in the present data set. The comparison of drifter data with the seasonal mean dynamic topography (0/1000 db) shows that the surface circulation pattern inferred from dynamic topography does not always represent the surface currents in the Indian Ocean. Both compare well for the South Equatorial Current, the Equatorial Counter Current, and the southwestward current along the Indonesian Islands; they differ in the Bay of Bengal during the southwest monsoon, but are similar during the northeast monsoon. Maps of mean and eddy kinetic energy show maxima in the regions of western boundary currents and equatorial currents and minima in the Arabian Sea, the Bay of Bengal, and south of 20'S

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Paper No71Publication ID : 107   &   Year : 1999  
TitleOn the sea surface temperature high in the Lakshadweep Sea before the onset of the southwest monsoon
Authors Shenoi, S.S.C.; Shankar, D.; Shetye, S.R.
Source Journal of Geophysical Research C: Oceans, 104(C7);1999;pp.15703-15712.
AbstractThe north Indian Ocean becomes the warmest area of the world oceans prior to the onset of southwest monsoon in June. During this period a zonal band of high sea surface temperature (SST), the "thermal equator" (TE), moves over this region concurrently with the Intertropical Convergence Zone (ITCZ). Using a weekly SST data set, it is shown that another SST high develops off southwest India in the Lakshadweep Sea in March, well before the TE moves in to the area, and that it continues to retain its identity until the onset of monsoon. The SST high has its genesis about 6 months earlier in the Bay of Bengal. The collapse of the southwest monsoon in October and the onset of the northeast monsoon trigger downwelling coastal Kelvin waves that propagate along the periphery of the Bay of Bengal, forcing an equatorward East India Coastal Current, which brings low-salinty water from the bay to the southeastern Arabian Sea during the northeast monsoon (November-January). As the Kelvin waves propagate poleward along the west coast of India after turning around Sri Lanka, they radiate downwelling Rossby waves that produce a "high" in sea level off southwest India. The downwelling and the surface layer of low-salinity water provide a breeding ground for the formation of a SST high in January. by March, with the increase in solar insolation due to the northward march of the Sun and the deep stable surface layer, the high reaches a mature phase clearly evident in the Lakshadweep Sea. By, May, when the thermal equator and ITCZ move over the region, the high can be seen embedded in the TE. It is speculated that at this time the high helps in producing conditions that are conducive for genesis of the monsoon onset vortex

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Paper No72Publication ID : 109   &   Year : 1996  
TitleHydrography and circulation in the western Bay of Bengal during the northeast monsoon
Authors Shetye, S.R.; Gouveia, A.D.; Shankar, D.; Shenoi, S.S.C.; Vinayachandran, P.N.; Sundar, D.; Michael, G.S.; Nampoothiri, G.
Source Journal of Geophysical Research C: Oceans, 101(C6);1996; pp.14011-14025.
AbstractThe Bay of Bengal, a semienclosed tropical basin that comes under the influence of monsoonal wind and freshwater influx, is distinguished by a strongly stratified surface layer and a seasonally reversing circulation. We discuss characteristics of these features in the western Bay during the norteast monsoon, when the East India Coastal Current (EICC) flows southward, using hydrographic data collected during December 1991. Vertical profiles show uniform temperature and salinity in a homogeneous surface layer, on average, 25 m deep but shallower northward and coastward. The halocline, immediately below, is approximately 50 m thick; salinity changes by approximately 3 parts per thousand. About two thirds of the profiles show temperature inversions in this layer. Salinity below the halocline hardly changes, and stratification is predominantly due to temperature variation. The halocline is noticeably better developed and the surface homogeneous layer is thinner in a low-salinity plume that hugs the coastline along the entire east coast of India. The plume is, on average, 50 km wide, with isohalines sloping down toward the coast. Most prominent in the geostrophic velocity field is the equatorward EICC. Its transport north of about 13~'N, computed with 1000 dbar as the level of reference, varies between 2.6 and 7.1 x 10@u6@@ m@u3@@ s@u-1@@; just south of this latitude, a northwestward flow from offshore recurveys and merges with the coastal current. At the southern end of the region surveyed, the transport is 7.7 x 10@u6@@ m@u3@@ s@u-1@@. Recent model studies lead us to conclude that the EICC during the northeast monsoon is driven by winds along the east coast of India and Ekman pumping in the interior bay. In the south, Ekman pumping over the southwestern bay is responsible for the northwestward flow that merges with the EICC

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Paper No73Publication ID : 111   &   Year : 1994  
TitleCirculation and water masses of the Arabian Sea
Authors Shetye, S.R.; Gouveia, A.D.; Shenoi, S.S.C.
Source Proceedings of the Indian Academy of Sciences - Earth and Planetary Sciences 103 (2), 1994; pp. 107-123
AbstractThe circulation in the coastal region off Oman is driven mainly by local winds and there is no remotely driven western boundary current. Local wind-driving is also important to the coastal circulation off western India during the southwest monsoon but not during the northeast monsoon when a strong (approximately 7 x 10@u6@@ m@u3@@/sec) current moves poleward against weak winds. This current is driven by a pressure gradient which forms along this coast during the northeast monsoon due to either thermohaline-forcing or due to the arrival of Kelvin waves from the Bay of Bengal. The present speculation about flow of bottom water (deeper than about 3500 m) in the Arabian Sea is that it moves northward and upwells into the layer of North Indian Deep Water (approximately 1500-3500 m). It is further speculated that the flow in this layer consists of a poleward western boundary current and a weak equatorward flow in the interior. It is not known if there is an annual cycle associated with the deep and the bottom water circulation

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Paper No74Publication ID : 114   &   Year : 1993  
TitleSalinity extrema in the Arabian Sea
Authors Shenoi, S.S.C.; Shetye, S.R.; Gouveia, A.D.; Michael, G.S.
Source Monsoon biogeochemistry. eds. by: Ittekkot, V.; Nair, R.R.; eds.(Mitteilungen des Geologisch-Palaon- tologischen. Instituts der Universitat Hamburg 76;1993; pp.37-49.
AbstractLevitus (1982) climatology has been used to identify four extrema, three maxima and one minimum, in the vertical salinity profiles in the Arabian Sea. Their geographical distribution, depths, theta-S characteristics, and seasonal variability are described. Two of the maxima arise from the influence of Red Sea and the Persian Gulf Water. The third, which lies at the bottom of the Equatorial Surface Water, forms due to freshening at the surface of high salinity Arabian Sea near-surface waters. The dominant factors leading to the dormation of the little known subsurface salinity minimum appear to be, (1) transport of the low salinity water by the northeast monsoon coastal current along the west coast of India and subsequent increase in the surface salinity of this water due to evaporation in the North Arabian Sea, (2) poleward coastal undercurrent along the west coast of India during the southwest monsoon. The theta-S characteristics of the four salinity extrema are used to put into perspective the structure of the Arabian Sea water masses

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Paper No75Publication ID : 112   &   Year : 1993  
TitleThe western boundary current of the seasonal subtropical gyre in the Bay of Bengal
Authors Shetye, S.R.; Gouveia, A.D.; Shenoi, S.S.C.; Sundar, D.; Michael, G.S.; Nampoothiri, G.
Source Journal of Geophysical Research, 98(1); 1993; pp. 945-954.
AbstractHydrographic data collected during March-April 1991 show the presence of a poleward current along the western boundary of the Bay of Bengal of about 10~'N carrying warmer waters of southern origin. The inshore side of the current was marked by cooler, more saline waters brought to the surface due to the presence of the current which transported approximately 10 x 10@u6@@m@u3@@/s. The hydrography is suggestive of many of the features that have been associated with the western boundary currents of the subtropical gyres of the world oceans:a recirculation zone, waves, eddies, etc. These features, however, were not satisfactorily resolved in the data. Using available climatologies of monthly mean ship drifts, seasonal hydrography, and monthly mean wind stress, we propose that the poleward current is the western boundary current of a seasonal anticyclonic subtropical gyre which forms in the Bay during January, is best developed during March-April, and decays by June. The gyre and the western boundary current are unique because of their seasonal character. The pattern of circulation leading to formation and decay of the gyre is reproduced reasonably well in the computation of the monthly mean barotropic transport induced by the curl of wind stress, which has a well-defined annual cycle due to the monsoon and which is conductive to the formation of an anticyclonic gyre only during the months of January-May. The pattern of circulation due to barochlinic transport induced by the wind stress, however, is not known at present, and this makes it difficult to conclude unequivocally that e wind stress curl over the bay is the sole mechanism to force the gyre.

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Paper No76Publication ID : 113   &   Year : 1993  
TitleOn the flow, thermal field and winds along the western continental shelf of India
Authors Antony, M.K.; Shenoi, S.S.C.
Source Continental Shelf Research, 13(4);1993; pp.425-439.
AbstractShort duration current meter recordings during May 1984, March 1986 and November 1986 along with wind and hydrographic data at a point (1508′N and 7316′E) in the western continental shelf of India were analysed for mean flow characteristics and for their possible relationship with wind and mass field. The analyses show that the mean alongshore flows (V) during May and March are towards south and during November, towards north. The barotropic and baroclinic components of the observed flow and the correspondence between the alongshore components of the flow and the wind stress suggest that the alongshore flows are mainly barotropic and wind driven. The correlation coefficients computed between pairs of U and V components also support this proposition. The mass field is found to be in agreement with the observed alongshore flow during May, but it does not favour the observed northward flow during November. This discrepancy during November is explained as due to the time lag in the adjustment of the mass field to the wind driven flow during the transition phase. It is further suggested that along the west coast of India, the impulse needed to trigger the flow reversal during October-November is provided by the wind. The process of flow reversal starts near the coast first and propagates slowly offshore.

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Paper No77Publication ID : 118   &   Year : 1992  
TitleDoes winter cooling lead to the subsurface salinity minimum off Saurashtra, India?
Authors Shetye, S.R.; Gouveia, A.D.; Shenoi, S.S.C.
Source Oceanography of the Indian Ocean. Desai, B.N. ed.; 1992; pp.617-625.
AbstractCold and dry winds of the northeast monsoon cool the northern Arabian Sea during November-January. The intensity of cooling is highest in the proximity of the peninsula of Saurashtra, India. Using hydrographic data, we propose that the cooling in this region, particularly during cold outbreaks, increases the density of shelf waters sufficiently to form a water mass which sinks and spreads at a depth of about 150 m and is characterized by a weak salinity minimum with sigma-theta in the range of 25.5-26.6 gm/cm super(3). It appears that the advection of lower salinity water into the basin by the northeast monsoon coastal current and subsequent evaporation in the mixed-layer also plays a role in recharge of the salinity minimum

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Paper No78Publication ID : 116   &   Year : 1992  
TitleDiurnal and semi-diurnal tidal currents in the deep mid-Arabian sea
Authors Shenoi, S.S.C.; Gouveia, A.D.; Shetye, S.R.
Source Proceedings of the Indian Academy of Sciences - Earth and Planetary Sciences 101 (2); 1992; pp. 177-189
AbstractCurrent meter records from two depths, approximately 1000 m, at three mooring in the deep mid-Arabian Sea were used to study tidal components. Tidal ellipses for the semi-diurnal (M2, S2 and K2) and the diurnal (K1 and P1) tidal constituents have been determined using the currents recorded at hourly intervals during May 1986-May 1987. The clockwise rotating M2 tidal currents were the strongest. The maximum horizontal velocities due to M2, S2 and K1 tides were 2.2 cm/s, 1.0 cm/s and 0.89 cm/s respectively. The amplitudes of the other two constituents (P1 and K2) were much smaller. The barotropic M2 ellipses have been estimated by averaging the M2 tidal currents at the upper and lower levels. Although the amplitudes of computed ellipses are lower than those that have been predicted using numerical models of global tidal model, their orientations are the same

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Paper No79Publication ID : 115   &   Year : 1992  
TitleSatellite observations of the northeast monsoon coastal current
Authors Shenoi, S.S.C.; Gouveia, A.D.; Shetye, S.R.; Rao, L.V.G.
Source Proceedings of the PORSEC-'92 in Okinawa, Conference for Pacific Ocean Environments and Probing, 25-31 August, 1992, Okinawa, Japan. Vol. 2, pp.796-801.
AbstractSatellite Infrared observations, from Advanced Very High Resolution Radiometer (AVHRR), during November 1987-February 1988 and hydrographic data from the eastern Arabian Sea are used to describe the poleward flowing coastal current in the eastern Arabian Sea during the northeast monsoon. The current, identified by a band of warm water, forms in November in the south, and is best developed during December-January when it can be traced along the entire coast of the eastern Arabian Sea. Off the southwest coast of India (10 degrees N) the current was approximately 400 km wide. At about 22 degrees N, the flow was restricted mainly to the vicinity of the continental slope and the current was a narrow jet of about 150 km width. Further north the core of the current narrowed down to about 50 km and turned west following the shelf off Pakistan. The current carried warmer waters (greater than 29 degrees C) of southern origin to the North Arabian Sea. In the northern half of the coastline (north of 15 degrees N), the temperature within the core of the current was about 1 degrees C above the ambient temperatures

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Paper No80Publication ID : 110   &   Year : 1992  
TitleM sub(2) tidal currents on the shelf off Goa, west coast of India
Authors Shenoi, S.S.C.; Gouveia, A.D.; Shetye, S.R.
Source Ocean technology: Perspectives. eds. by: Sushilkumar; Agadi, V.V.; Das, V.K.; Desai, B.N.(Symp. on Ocean Technology; National Institute of Oceanography, Goa; India; 27-29 Aug 1992). Publ. and Inf. Dir.; New Delhi; India; 1994; pp.415-427.
AbstractCurrent meter records collected during three different months from a site off Goa (15 degrees 08'N, 73 degrees 16'E) over the western continental shelf of India have been used to describe the M sub(2) tidal structure in a water column of depth about 100 m. Tidal ellipse parameters and Greenwich phases were estimated using the least squares fit technique. M sub(2) tidal currents have shown significant variations from one season to another (15 cm/s during May 1984 to 3.7 cm/s during November 1986). The baroclinic M sub(2) tide have been interpreted in terms of linear internal wave dynamics. The results show that the M sub(2) baroclinic tide is dominatEd. by the first mode. The horizontal wavelength over the shelf predictEd. by this method is about 22 km. This is smaller than the shelf width of about 110 km. The group velocity for the first baroclinic mode is about 0.45 m/s, which means that energy takes approximately two and a half days to cross the shelf. Evidence presented here suggests that stratification over the continental shelf and the adjacent slope has influenced the amplitude of internal tidal currents. The bottom slope switches from being supercritical to subcritical in the shelf break region during May and remains subcritical all over the shelf and the slope during November

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Paper No81Publication ID : 117   &   Year : 1992  
TitleSeasonally reversing current bands across 15 degrewes N in the Arabian Sea and their implications
Authors Antony, M.K.; Shenoi, S.S.C.; Gopalakrishna, V.V.; Murty, C.S.; Rao, D.P.; Murty, V.S.N.; Sastry, J.S
Source Indian Journal of Marine Sciences, 21; 1992; pp.46-51.
AbstractGeostrophic currents computed from hydrographic data collected in different months from a section along 15 degrees N in the Arabian Sea show alternate N-S current bands. Flow directions of these bands are found to reverse with the change in season. Analysis of ship drift data (KNMI atlas) supports the existence of such bands in this area. Evidences suggest the possibility that these current bands can be due to westward propagation of planetary (Rossby) waves of annual periodicity with a probable speed of 1-2 cm.sec/1 and wave length varying between 200 and 500 km. Generation of these waves is thought to be linked to the SW and NE monsoon winds in this region

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Paper No82Publication ID : 120   &   Year : 1991  
TitleWind-driven coastal upwelling along the western boundary of the Bay of Bengal during the southwest monsoon
Authors Shetye, S.R.; Shenoi, S.S.C.; Gouveia, A.D.; Michael, G.S.; Sundar, D.; Nampoothiri, G.
Source Continental Shelf Research 11(11);1991; pp.1397-1408
AbstractA hydrographic survey during the southwest monsoon (July-August 1989) showed that along most of the western boundary of the Bay of Bengal, in an approximately 40 km wide band, isopycnals from depths up to about 70 m surfaced due to upwelling forced by local winds, in a fashion similar to that observed along eastern boundaries. Below the upwelling band there were often signatures of downwelling, suggestive of an undercurrent. There were no indications of a large-scale remotely forced western boundary current. Geostrophic velocity in the upwelling band was in the direction of the winds. The dynamic topography outside the upwelling band had cellular structures possibly indicating the presence of shelf waves with longshore wavelength of 400-500 km. The near-surface stratification was dominated by salinity, a consequence of high freshwater input to the Bay. The upwelling led to a coastward increase in salinity, except near the northern end where the freshwater influx from the Ganges and the Brahmaputra rivers overwhelmed other processes and gave rise to a freshwater plume offshore of the upwelling band. This plume moved equatorward against local winds

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Paper No83Publication ID : 121   &   Year : 1991  
TitleThe coastal current off western India during the northeast monsoon
Authors Shetye, S.R.; Gouveia, A.D.; Shenoi, S.S.C.; Michael, G.S.; Sundar, D.; Almeida, A.M.; Santanam, K.
Source Deep Sea Research Part A, Oceanographic Research Papers, 38 (12); 1991; pp.1517-1529.
AbstractHydrographic data collected during December 1987 and January 1988 are used to describe the poleward coastal current along the west coast of India that flows against weak winds during the northeast monsoon. Near the southern end of the coast, at about 10 degrees N, the current was approximately 400 km wise, 200 m deep and carried the low salinity Equatorial Surface Water. The isopycnals tilted down on approaching the coast. Near the northern end of the coast, at about 22 degrees N, the flow was restricted mainly to the vicinity of the continental slope; the current was a narrow (100 km), 400m deep jet with a transport of about 7 x 106 m3 s-1. Along most of the coastline, a southward moving undercurrent was inferred from the distribution of salinity, temperature and dynamic topography. To understand the driving mechanism of the current, the annual cycle of the contribution of the longshore pressure gradient and that of the winds to the near-surface momentum balance was examined using available climatologies.

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Paper No84Publication ID : 122   &   Year : 1991  
TitleCurrent measurements over the western continental shelf of India
Authors Shenoi, S.S.C.; Antony, M.K.
Source Continental Shelf Research,11; 1991; pp.81-93
AbstractCurrent meter observations obtained from a site off Goa (15 degrees 08'N, 73 degrees 16'E) over the western continental shelf of India are presented. Data were collected from the site during three different months in a water column of depth about 100 m. The nature of flows are described by means of visual display, linear regression and spectral analysis. The flows are a result of the superimposition of oscillations of wide-ranging frequencies over a weak mean flow. The mean flow was towards south during May and March and towards north during November. The spectral analysis indicates that the inertial and semidiurnal frequency motions are the major contributors to the current structure. The inertial currents were concentrated near the surface with a rapid decay towards the bottom. The analysis also indicates that the diurnal and semidiurnal motions are mainly due to baroclinic internal tides rather than due to barotropic surface tides. Above the semidiurnal frequencies the currents were composed mainly of high-frequency oscillations of comparatively low magnitudes. These motions are strongly time-dependent and they may be related to internal waves in coastal waters

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Paper No85Publication ID : 119   &   Year : 1991  
TitleObserved low-frequency currents in the deep mid-Arabian sea
Authors Shetye, S.R.; Shenoi, S.S.C.; Sundar, D.
Source Deep-Sea Research, 38; 1991; pp.57-65.
AbstractCurrent meter records form approximately 1000 and 3000 m at three moorings with a zonal separation of about 5 degrees along the 15 degrees N latitude in the mid-Arabian Sea during May 1986 to May 1987 have used to described the low-frequency currents in the area. Although the spectra for the six time series have similar shapes, their energy levels differ. There was no significant coherence between upper and the lower currents at any mooring, nor between currents at adjacent moorings. Energies dropped from the west to the east both at the upper and the lower levels, but the drop was much larger in the deeper currents. In fact, the energy in the deeper currents for periods from 1 to 4 weeks was higher than that at the upper level at the western mooring, marginally higher at the central mooring, and not significant at the eastern mooring

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Paper No86Publication ID : 123   &   Year : 1990  
TitleHydrography and circulation off the west coast of India during the southwest monsoon 1987
Authors Shetye, S.R.; Gouveia, A.D.; Shenoi, S.S.C.; Sundar, D.; Michael, G.S.; Almeida, A.M.; Santanam, K.
Source Journal of Marine Research,48; 1990; pp. 359-378.
AbstractDuring June-August 1987 thirteen hydrographic sections, each approximately perpendicular to the coast, covered the coastal region off western India. The southernmost section showed occurrence of upwelling, the nearshore surface temperature being about 2.5 degrees C lower than farther offshore. There was a shallow (approximately 75 to 100 m deep) equatorward surface current, below which there were signatures of downwelling indicative of a poleward undercurrent hugging the continental slope. T-S characteristics showed that the undercurrent carried low salinity water found in the southwestern Bay of Bengal. Conditions similar to those found at this section existed up to around 15N but the intensify if upwelling, and the signatures of the surface current and the undercurrent grew weaker progressively from the south to the north, and ceased to be noticeable at about 20 N. The width of the surface current was about 150 km, whereas the undercurrent was about 40 km wide. The transport in the equatorward surface current increased from less than 0.5 x 106 m3/s to about 4 x 106 m3/s from the north to the southern end of the coast

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Paper No87Publication ID : 124   &   Year : 1989  
TitleWave refraction and longshore current patterns along Calangute beach (Goa), west coast of India
Authors Krishnakumar, V.; Murty, C.S.; Shenoi, S.S.C.; Heblekar, A.K.
Source Indian Journal of Marine Science,18; 1989; pp. 184-188.
AbstractWave refractions study for most predominant waves with 6,8,10 and 12 sec period and approaching from directions WNW, W and WSW has been carried out along the Calangute beach. The energy distribution and probable longshore/offshore current pattern are qualitatively assessed. The degree of refraction is less and no abnormal energy concentrations occur along this stretch. The waves after breaking give rise to many opposing flows forming circulation cells along the entire stretch. Zones of quasi-permanent rip currents are identified at Calangute and Candolim sections for 10 sec period waves approaching from WNW and W.

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Paper No88Publication ID : 125   &   Year : 1988  
TitleSeasonal cycle of surface circulation in the coastal North Indian Ocean
Authors Shetye, S.R.; Shenoi, S.S.C.
Source Proceedings of the Indian Academy of Sciences - Earth and Planetary Sciences, 97(1);1988;pp.53-62.
AbstractMonthly-mean winds and currents have been used to identify the driving mechanisms of seasonal coastal circulation in the North Indian Ocean. The main conclusions are: (i) the surface circulation off Arabia is typical of a wind-driven system with similar patterns of longshore current and wind stress; (ii) circulation off the west coast of India is consistent with the dynamics of a wind-driven eastern boundary current only during the southwest monsoon. During the northeast monsoon it is possible that the influence of the interior flow is important. (iii) There are at least three mechanisms that influence the surface circulation off the east coast of India; wind-stress, influence of fresh-water run off and contribution of the interior flow. It is difficult at present to assess the relative importance of these three processes

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Paper No89Publication ID : 126   &   Year : 1988  
TitleNature of the observed oscillatory flows in shelf waters of the western continental shelf of India
Authors Shenoi, S.S.C.; Antony, M.K.; Sundar, D.
Source Journal of Coastal Research: 4(4);1988; pp.617-626
AbstractTime series data on currents obtained from three Aanderaa current meters moored at a station depth of 92 m in the waters of the western continental shelf of India during May 1984 indicated the presence of oscillatory flows. The spectral computations revealed maximum in the semidiurnal frequency band with its magnitude higher by one order compared to that of the other bands. An analysis of phase differences together with coherence of flows at different levels and their amplitudes showed dominance of internal waves with frequencies close to semidiurnal period (internal tide) controlling the flow structure. The temperature records at these levels together with the B.T. time series data collected in the vicinity of mooring site supported the presence of internal waves. Semidiurnal characteristics computed from hydrographic data collected during the period of mooring across the shelf combined with the distribution of phases and amplitudes of horizontal velocities are found to be consistent with the generation of internal tides along the slope region. The barotropic and baroclinic nature of these currents separated and decomposed by averaging the data from all sensors and using empirical orthogonal functions respectively revealed the dominance of the former in the longshore component and the latter in the cross-shore component

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Paper No90Publication ID : 127   &   Year : 1987  
TitleMonsoon induced seasonal variability of sheltered versus exposed beaches along the west coast of India
Authors Shenoi, S.S.C.; Murty, C.S.; Veerayya, M.
Source Marine Geology: 76; 1987; pp.117-130.
AbstractChanges in profile configuration of the beaches at different locations along the west coast of India have been quantitatively compared by means of Empirical Orthogonal Function (EOF) analysis. These beaches, though exposed to similar monsoonal forcings, respond through variable changes depending on their individual geographical/geomorphological setting. The analysis suggests that, for the period of study, the beaches are stable as revealed by the temporal dependence of the first eigenfunction. The second function reveals the significant erosional/accretional phases with a well defined cyclicity of one year associated with monsoonal wind and wave climate. The second spatial function efficiently expresses a"pivot point" for the seasonal shore-normal movement of sand. The depth at which this pivot point occurs is inversely related to the width of the beach. The differential energy environments, even over short distances, are found to be the prime factors that determine the magnitude of temporal beach variability. Unprotected beaches showed higher magnitudes of variability. These results suggest that the second eigenfunction and the variance of the data set are more useful than the other order eigenfunctions for a comparative study of this kind

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Paper No91Publication ID : 128   &   Year : 1986  
TitleViscous damping of solitary waves in the mud banks of Kerala, West coast of India
Authors Shenoi, S.S.C.; Murty, C.S.
Source Indian J. Mar. Sci.: 15; 1986; pp.78-83.
AbstractAnalysis of wave damping in mud bank region following the process of transfer of wave energy to the interior of fluid column through the boundary layer and the energy loss computations owing to viscous shear beneath the solitary wave over a smooth horizontal surface are presented. It is shown that waves can almost or completely be dissipated over a mud bank of width about 3 - 4 km when the kinematic viscosity increases to 1 cm2 sec -1. Waves of higher amplitude are dissipated much faster than those of lower amplitude

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Paper No92Publication ID : 129   &   Year : 1985  
TitleMorphology and grain-size characteristics of a log-spiral beach at Nagwa (Diu), west coast of India
Authors Veerayya, M.; Shenoi, S.S.C.; Murty, C.S.
Source Indian Journal of Marine Sciences,14; 1985; pp.127-132.
AbstractSediment samples collected along 6 beach profiles of a log-spiral shaped beach and nearby dunes have been studied for particle size distribution in relation to wave refraction patterns. The results reveal that the foreshore sediments are in the coarse to fine sand grade (M Gamma 0.84 to 2.96 phi), well to poorly sorted 0.45 to 1.73 phi) and positive to negatively skewed (0.25 to -0.54 ski) classes. Sediments at profile st 1 in E are coarser and poorly sorted while they are fine-grained and better sorted in W as well as along the curved section of the beach. Alongshore variations in grain-size characteristics of beach sediments which have been discussed in relation to beach topography, wave induced littoral flows and prevaling meteorological and oceanographic conditions indicate clearly the suitability of the area close to st 6 in the curved part of the bay for developmental activities related to coastal zone

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Paper No93Publication ID : 130   &   Year : 1985  
TitleMonthly mean wind stress along the coast of the north Indian Ocean
Authors Shetye, S.R.; Shenoi, S.S.C.; Antony, M.K.; Krishnakumar, V.
Source Proceedings of the Indian Academy of Sciences - Earth and Planetary Sciences, 94 (2);1985;pp. 129-137.
Abstracthave been computed using the bulk aerodynamic method for each of a string of 36 two-degree-latitude by two-degree-longitude squares along the coast of the north Indian Ocean. The data source of the computation is the sixty-year mean resultant winds of Hastenrath and Lamb. The main features exhibited by the components, taking the longshore components as positive (negative) when the Ekman transport is away from (towards) the coast, are: (1) Along the coasts of Somalia and Arabia, the magnitude of the wind stress is among the highest in the north Indian Ocean, and its direction is generally parallel to the coastline. This results in a longshore component which is large (as high as 2.5 dyne/cm2) and positive during the southwest monsoon and weaker (less than 0.6 dyne/cm2) and negative during the northeast monsoon. (2) Though weak (less than 0.2 dyne/cm2) during the northeast monsoon, the monthly-mean longshore component along the west coast of India remains positive throughout the year. The magnitude of the offshore component during the southwest monsoon is much larger than that of the longshore component. (3) The behaviour of the wind stress components along the east coast of India is similar to that along the Somalia-Arabia coast, but the magnitudes are much smaller

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Paper No94Publication ID : 131   &   Year : 1983  
TitleLittoral drift along shoreline between Munambum and Anthakaranazhi, Kerala coast
Authors PrasannaKumar, S.; Shenoi, S.S.C.; Kurup, P.G.
Source Indian Journal of Marine Sciences.: 12; 1983; pp.209-212.
Abstract...

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