ESSO - Indian National Centre for Ocean Information Services
(An Autonomous Body under the Ministry of Earth Sciences, Govt. of India)
E-Publications
| Paper No | 1 | Publication ID : 860 & Year : 2023 |
| Title | Wave modulations in the Indian coastal area due to wave?tide interactions. | |
| Authors | Sirisha, P., Remya, P. G., Srinivas, K., & Balakrishnan Nair, T.M. | |
| Source | Journal of Earth System Science, 132(1), 17. | |
| Abstract | The present study highlights the wave?tide interactions in a tide-dominant coast Versova, along the west coast of India. Versova is a macro tidal area and is home to fisheries. Model simulations are carried out to investigate wave?tide interactions with and without incorporating water level (WL) variations in the model setup. The simulation results are compared with the observed data at Versova. Model comparison with wave observation shows that the simulated significant wave height (Hs) reproduced the observed wave heights with an accuracy of scatter index = 8% and correlation = 0.94 with the inclusion of WL variations. The incorporation of WL variations created the energy modulations in the low-frequency part of the wave spectra, raising the periodical modulations in wave height. This low-frequency wave energy modulation is absent in the without WL simulations, resulting in underestimation of energy density which causes underestimation of Hs by ~1 m. Hence this study strongly suggests that water level variations must be incorporated into the wave model to accurately represent wave modulations which are significant during monsoon and extreme events in the tide-dominant coastal areas. | |
| Paper No | 2 | Publication ID : 861 & Year : 2023 |
| Title | Satellite-Based Detection of Noctiluca Bloom in the Coastal Waters of the South-eastern Arabian Sea: A Case Study Implicating Monitoring Needs. | |
| Authors | Samanta, A., Baliarsingh, S.K., Lotliker, A.A., Joseph, S., & Balakrishnan Nair, T.M. | |
| Source | National Academy Science Letters | |
| Abstract | The south-western coast of India recently witnessed an intense bloom of green Noctiluca scintillans (NS) that resulted in water discolouration, scummy surface layer, bioluminescent tides, and mass fish mortality. The Algal Bloom Information Service (ABIS) of the Indian National Centre for Ocean Information Services could efficiently provide information on the spatial extent of the bloom from its occurrence to disintegration. The initiation of the bloom was evidenced on 30 November, attained its peak on 12 December, and waned on 21 December 2021 with chlorophyll-a concentrations of 5.42, 3.01, and 0.33 mg m-3, respectively, and with NS spread area of 3888, 10,608, and 48 Sq Km, respectively. Based on the information generated from ABIS, this manuscript addresses the ecosystem-disrupting algal bloom event and reiterates the need for autonomous coastal water quality observatories as a suitable alternative to field measurements to trace out the underlying factors responsible for the blooms and resultant harmful impacts on the ecosystem. | |
| Paper No | 3 | Publication ID : 862 & Year : 2023 |
| Title | Characteristics of astronomical tides and their modulation on sea level extremes along the Indian coast. | |
| Authors | Mohanty, P.C., Mahendra, R.S., Nayak, R.K., Manche, S.S., Joseph, S., Balakrishnan Nair, T.M., & Srinivasa Kumar, T. | |
| Source | Ocean & Coastal Management, 231, 106398. | |
| Abstract | In this study, long-term hourly sea-level records from 18 tide gauge stations during 1972?2007 were analyzed to study the characteristics of astronomical tides, sea-level trends, and extremes around India's mainland. The de-tided signals were used to estimate these parameters and study tide and surge interaction. The observed sea level depicts significant variability in daily, seasonal, and inter-annual time scales. Semidiurnal tides are the most dominant among the high-frequency tides, with an amplitude of up to 2.5 m for M2 and 0.75 m for S2 tides in the northwestern and northeastern continental shelf and reduced to 0.25 m in the south. The amplitude of diurnal tides (O1 and K1)is relatively weak (<0.25m) at all the stations. The annual harmonics dominate the seasonal cycle, with an amplitude of 0.7 m at Garden Reach in the northeastern continental shelf, decreases to 0.15 m at Tuticorin in the south, and remains small (<0.1 m) along the west coast of India. The amplitude of lunar nodal and perigee tides are significantly high (up to 25 mm) at several stations compared to the long-term global mean sea level trend (~3.3 mm/y). The sea level trend is significantly positive (up to 4 mm/y) for Sagar Island, Diamond Harbor, Haldia, and Mangalore; negative (up to -3 mm/y) for Garden Reach and Okha, and in-significant (0.5 mm/y) for Mumbai, Vishakhapatnam, and Paradip. Interaction between the semidiurnal tides and surges was intense at most stations, with a high probability of surge peaks during the fall-tide conditions in the northern continental shelf, at rising-tidal conditions for the south-eastern and western peninsula, and co-occurring at high tide for southern stations. The degree of tide-surge interaction increases from south to north with an increase in tidal range and significant nodal and perigee tidal modulation. | |
| Paper No | 4 | Publication ID : 854 & Year : 2022 |
| Title | Satellite-Based Marine Ecological Services for the Indian Ocean Region | |
| Authors | Baliarsingh, S.K., Samanta, A., Lotliker, A.A., Mohanty, P.C., Mahendra, R.S., & Balakrishnan Nair, T.M. | |
| Source | India has a vast coastline of ~7,500 km encompassing the west coast (eastern Arabian Sea), east coast (western Bay of Bengal), and islands. The coastal water of India is rich in a wide variety of marine biotic and abiotic resources that support the livelihood of millions through fishery, recreational activities, tourism, marine commerce, maritime logistics, education-research, etc. However, frequent phytoplankton blooms, jellyfish swarming (and beach stranding), and bleaching of coral reefs are exerting adverse impacts on the coastal water quality and ecological services. Indian National Centre for Ocean Information Services (INCOIS), an autonomous body under the Indian Ministry of Earth Sciences, has taken the initiative to monitor and disseminate information/warnings on the above-mentioned perturbations. INCOIS has operationalized satellite-based Algal Bloom Information Service (ABIS) and Coral Bleaching Alert System (CBAS) for monitoring phytoplankton blooms and coral bleaching, respectively. For monitoring jellyfish swarming, environmental triggers have been identified based on favorable conditions and a conceptual framework has been prepared for the possible generation of Jellyfish Aggregation Advisory Service (JAAS). Apart from assisting policymakers/researchers in developing sustainable ocean management strategies, demarcating marine protected areas, and conducting scientific research, these services also complement other satellite-based ecosystem services. | |
| Abstract | Social and Economic Impact of Earth Sciences Springer Nature Singapore (pp. 229-251) | |
| Paper No | 5 | Publication ID : 853 & Year : 2022 |
| Title | The projected changes in extreme wave height indices over the Indian Ocean using COWCLIP2. 0 datasets | |
| Authors | Sardana, D., Kumar, P., Bhaskaran, P. K., & Balakrishnan Nair, T.M. | |
| Source | Climate Dynamics, 1-15 | |
| Abstract | Extreme ocean surface waves can significantly impact the coastal and offshore-related activities, and often cause large-scale destruction to the livelihoods of the coastal population. To potentially reduce the adverse societal impacts and planning operations, it is necessary to assess the futuristic changes in extreme wave climate. This study examined the extreme wave height indices described by the Expert Team on Climate Change Detection and Indices (ETCCDI) for the Indian Ocean (IO) obtained from Coordinated Ocean Wave Climate Projections, Phase 2 (COWCLIP2.0) historical simulations and projected datasets. A multi-model ensemble (MME) approach is employed to study the projected changes under RCP4.5 and RCP8.5 emission scenarios. Substantial increases in rough wave days are projected over the northern sector of the Arabian Sea (AS) and eastern tropical IO (TIO). The projected changes in high wave days and wave-spell-storm duration under both the scenarios are observed in southern IO. On the contrary, widespread projected decreases in rough wave days are evident over the central TIO, and in wave-spell-storm duration for the southern sector of AS. A strong teleconnection between the projected changes in wave extremes in IO is consistent with the projected changes in sea level pressure gradient (SLPG). Further, in southern IO, the Southern Annular Mode (SAM) has strong association with extreme wave indices. | |
| Paper No | 6 | Publication ID : 852 & Year : 2022 |
| Title | Simulating the spatial and temporal distribution of oil spill over the coral reef environs along the southeast coast of Mauritius:A case study on MV Wakashio vessel wreckage, August 2020 | |
| Authors | Prasad, S.J., Balakrishnan Nair, T.M., Joseph, S., Mohanty, P.C. | |
| Source | Journal of Earth System Science, 131 (1), art. no. 42 | |
| Abstract | An oil spill occurred off Mauritius on 6 August 2020, as merchant vessel (MV) Wakashio, with 3896 tons of heavy fuel oil (HFO) on board, struck the coral reef, causing a significant threat to the coral environment. Approximately 1000 tons of HFO leaked from the vessel. The Indian National Centre for Ocean Information Services (INCOIS) set-up an oil-spill trajectory model for the Mauritius domain and generated oil drift patterns during the spill period for 1000 tons of HFO. The simulation showed that Mauritius?s south-east coast was under threat to receive HFO from the stranded vessel. The simulated oil drift pattern was in good agreement with the oil slick signatures obtained from Sentinel-1A data. The affected zone of coral reef environs during the spill period was also estimated using Sentinel-2 datasets. Our analysis showed that on 8 August the oil spread over 14.58 and 5.52 km2 of reef flat and algae/seagrass over the reef, respectively. From 15 August onwards, the oil spread gradually decreased and concentrated along the northern coast of Mauritius over mudflat/mud over reef/turbid water zone. On 8 August, the coastal districts of Grand Port and Flacq were highly affected due to oil spillage. The seaward coral reef zones were least affected by oil spill, compared to the coral reefs adjacent to the coast. | |
| Paper No | 7 | Publication ID : 851 & Year : 2022 |
| Title | Wave induced coastal flooding along the southwest coast of India during tropical cyclone Tauktae | |
| Authors | Ramakrishnan, R., Remya, P. G., Mandal, A., Mohanty, P., Arayakandy, P., Mahendra, R. S., & Balakrishnan Nair, T.M. | |
| Source | Nature-Scientific Reports, 12(1), 19966. | |
| Abstract | The coastal flood during the tropical cyclone Tauktae, 2021, at Chellanam coast, Kerala, India, has invited wide attention as the wave overtopping severely affected coastal properties and livelihood. We used a combination of WAVEWATCHIII and XBeach to study the coastal inundation during high waves. The effect of low-frequency waves and the rise in the coastal water level due to wave setup caused the inundation at Chellanam, even during low tide with negligible surge height. Wave setup raised the water level at the coast with steep slopes to more than 0.6 m and peaked during low tide, facilitating wave breaking at the nearshore region. The coastal regions adjacent to these steep slopes were subjected to severe inundation. The combined effect of long and short waves over wave setup formed extreme wave runups that flooded inland areas. At gently sloping beaches, the longwave component dominated and overtopped the seawalls and damaged households along the shoreline. The study emphasizes the importance of longwave and wave setup and its interaction with nearshore bathymetry during the high wave. The present study shall lead to the development of a coastal inundation prediction system for the low-lying hot spots using the combination of WAVEWATCHIII and XBeach models. | |
| Paper No | 8 | Publication ID : 850 & Year : 2022 |
| Title | Exploring the impact of southern ocean sea ice on the Indian Ocean swells | |
| Authors | Sreejith, M., P. G, R., Kumar, B.P., Raj, A., Balakrishnan Nair, T.M. | |
| Source | Nature-Scientific Reports, 12 (1), art. no. 12360. | |
| Abstract | The present study analyzes the impact of the Southern Ocean (SO) sea ice concentration on the north Indian Ocean (NIO) wave fields through swells using 6 years (2016?2021) of WAVEWATCH III (WWIII) simulations. We did two experimental runs of WWIII, one with sea ice concentration and winds as the forcing (W3with_ice) and the second run with only wind forcing (W3no_ice). Analysis shows the impact of the SO sea ice concentration on northward swell peaks in September?November, coinciding with the maximum sea ice extent in the Antarctic region of the Indian Ocean. W3no_ice simulations are biased more by ~ 60% and ~ 37% in significant wave height and period, respectively, against W3with_ice when compared with NIO mooring data. W3no_ice simulates low-frequency swells and travels fast towards NIO, with implications for operational oceanography. We have shown that the forecasts of the timing of high swell events along NIO coasts can be erroneous by ~ 12 h if the SO sea ice concentration is not included in the model. Further, W3no_ice could potentially produce false swell alerts along southeastern Australian coasts. In summary, our study highlights the importance of the SO sea ice concentration inclusion in the wave models to accurately simulate NIO waves. | |
| Paper No | 9 | Publication ID : 849 & Year : 2022 |
| Title | Advances in Ocean State Forecasting and Marine Fishery Advisory Services for the Indian Ocean Region. Social and Economic Impact of Earth Sciences. | |
| Authors | Balakrishnan Nair, T. M., Srinivas, K., Nagarajakumar, M., Harikumar, R., Nimit, K., Remya, P.G., Francis, P.A., & Sandhya, K. G. | |
| Source | Singapore: Springer Nature Singapore, (pp. 201-227). | |
| Abstract | India is adept in implementing the latest technological advancements and research findings with its fully operational ocean information and advisory services for the Indian Ocean. The operational services viz. Ocean State Forecast (OSF) and Marine Fishery Advisory Services (MFAS) support not only the stakeholders in India, but also those in other neighbouring countries in the region, for safe navigation and cost-effective fishing. The OSF and MFAS programs of the Indian National Centre for Ocean Information Services (INCOIS) have set high standards, with accurate and timely delivery of services. During recent times, INCOIS has made great strides from providing general forecasts to custom-made and impact-based ocean state forecasts, general Potential Fishing Zone (PFZ) advisories to species-specific advisories, based on the user feedback. | |
| Paper No | 10 | Publication ID : 863 & Year : 2022 |
| Title | Improved prediction of oil drift pattern using ensemble of ocean currents | |
| Authors | Prasad SJ, Balakrishnan Nair T.M & Balaji B | |
| Source | Journal of Operational Oceanography | |
| Abstract | Indian Coast Guard and oil spill responders utilise the operational oil spill advisory services of the Indian National Centre for Ocean Information Services (INCOIS) during the event of oil spills for setting up spill response operations. Oil drifts in marine zones are dominated by ocean currents. Ocean currents generated by numerical models have errors and uncertainties due to model approximations, inaccurate initial and boundary conditions in the model setup. An attempt was made to generate an oil spill advisory using a weighted ensemble of ocean currents. In this study, the oil spill trajectory model, General National Oceanic and Atmospheric Administration (NOAA) Operational Modeling Environment (GNOME) was forced using a weighted ensemble of ocean currents for the Heavy Furnace Oil (HFO) spill reported off Ennore port during 0400 hours (IST) of 28 January 2017. The inverse-variance weighting method was used to estimate weights by comparing zonal and meridional components of individual model ocean currents, with that of High Frequency (HF) Radar currents. The zone of HFO spread obtained while using an ensemble of ocean currents was compared with oil slick signatures obtained from Synthetic Aperture Radar (SAR) data on 0600 hours (IST) of 29 January 2017. It was noted that the trajectory patterns obtained from the weighted ensemble of ocean currents were well within the observed zone of oil slicks, compared to that of individual model ocean currents. | |
| Paper No | 11 | Publication ID : 856 & Year : 2022 |
| Title | Satellite Altimetry Application Case-Studies from The Northern Indian Ocean, in 'Coastal Altimetry: Case Studies for Asian Shelf Seas' | |
| Authors | Nimit K., Mohanty P. C., Mahendra R. S., Nayak R. K., Sudheer J, Nagaraja Kumar M., Swetha N., Balakrishnan Nair T. M, and Srinivasa Kumar, T. | |
| Source | Elsevier Pub. (Eds Stefano Vignudelli and Nurul H Idris) (in press) | |
| Abstract | Altimeters can be useful in marine as well as shoreline studies. In this chapter we present both applications as two separate case-studies from the northern Indian Ocean region. Physical processes in the oceans - such as eddies, gyre, currents and upwelling - have a spatial scale of 10-100 km and lifespan ranging from few days to weeks. Most of these processes are driven by seasonal cycles and often occur at the basin scale. Such episodes determine spatial and vertical structure of water mass in the region with reference to many other properties such as temperature and salinity. As a result, sharp thermal &/or salinity gradients are formed. Upwelling is a phenomenon that brings nutrient rich deeper waters into photic zone (well-lit surface waters). Upwelling and cyclonic eddies form deeper mixed layer which facilitates nutrient entrainment across otherwise stratified waters. These nutrients are lifeline for marine food web. Phytoplankton consume it and blooms (increase in size and numbers) in such favorable conditions. Zooplankton feed upon phytoplankton and planktivorus fishes, on both. Such small (forage) fishes are preyed upon by bigger ones and so on. Nutrients retain along the frontal structure and these areas are proven to be good fishing zones. Such processes can be monitored via altimeters well before a radiometer can detect the same in terms of temperature or ocean color (chlorophyll concentration). With multiple active sensors, current times are best opportunity to harness capabilities of satellite altimetry. Herein we show the importance of Sea Surface Height anomaly (SSHa, retrieved with altimeter) in demarcating potential fishing zones. We also show how SSHa can help predict tuna movements, horizontally as well as vertically in the water column. Moreover, we prove these predictions with positively correlating SSHa to tuna hooking rates. In the end, we list out present and potential future sources from where SSHa can be retrieved in order to provide improved fishery advisories. | |
| Paper No | 12 | Publication ID : 855 & Year : 2022 |
| Title | Satellite-Based Characterization of Phytoplankton Blooms in Coastal Waters of the Northwestern Bay of Bengal. | |
| Authors | Srichandan, S., Baliarsingh, S. K., Samanta, A., Jena, A. K., Lotliker, A. A., Balakrishnan Nair, T.M., & Acharyya, T. | |
| Source | Journal of the Indian Society of Remote Sensing, 50(11), 2221-2228. | |
| Abstract | Phytoplankton blooms are frequent in the coastal waters of the northwestern Bay of Bengal (BoB), with diatom blooms being the most common. For the first time, this study investigated the long-term trend in ocean color satellite-retrieved diatom distribution in coastal waters of the northwestern BoB. A retrospective analogy of phytoplankton bloom events corroborated with earlier in situ observations. The temporal distribution of diatom revealed a bimodal annual trend with peaks during the pre- and post-southwest monsoon periods. This pattern could be attributed to the enhanced degree of phytoplankton growth-promoting nutrient availability along with favorable environmental conditions during both pre- and post-monsoon periods. Diatom distribution indicated a more extensive spatial spread during the post-southwest monsoon. The present study also substantiated diatom availability as a conducive factor for the bloom of heterotrophic Noctiluca scintillans and exudation by Trichodesmium as an excellent source of nutrients for diatom growth. This study suggests developing phytoplankton species-specific satellite retrieval algorithms and ocean color sensors of higher spatiotemporal efficiency, to gain a deeper understanding of the effect of blooms on ecosystem functioning. | |
| Paper No | 13 | Publication ID : 859 & Year : 2022 |
| Title | A Numerical Modelling Approach for Beach Erosion Forecast during the Southwest Monsoon Season | |
| Authors | Ratheesh R, Remya P. G, Ritesh Agrawal, Ch. Venkiteswarlu, B. Gireesh, Amarendra P Balakrishnan Nair T. M and A.S Rajawat, | |
| Source | Journal of Earth System Science | |
| Abstract | Identifying coastal stretches that are likely to erode under high wave conditions is essential to the coastal management community in addressing beach erosion-related issues. The manuscript presents a case study to predict erosion of a selected beach located on the eastern Indian coast during the 2018 southwest (SW) monsoon season. The pre-monsoon beach topography surveyed using DGPS is used as the initial topographic condition in the morphological model. The model simulates subsequent beach erosion during the SW monsoon season, which is forced by forecast waves. Beach erosion advisories that classify the beach as eroding, accreting and no change are disseminated with a lead period of 10 days. During the SW monsoon period, we have monitored the beach using the dumpy level, and the beach topography during the post-monsoon is generated using DGPS surveyed profiles and are used for model validation. The beach area under erosion observed from the model result is homologous with the in-situ observations. The model shows cross-shore sediment transport to dominate during the SW monsoon, particularly in the central and northern sectors of RK beach. The model estimated shoreline position agrees with the DGPS observations, where the central sector has undergone maximum erosion. The comparison shows the model?s ability to simulate beach morphodynamics like landward shifting of the berm crest under a high wave setup and oscillating water levels due to tides. The study highlights the importance of numerical modelling systems that decipher the beach response to the high monsoon waves. | |
| Paper No | 14 | Publication ID : 858 & Year : 2022 |
| Title | Seasonal variation of wave power potentials in the coastal areas of India | |
| Authors | P Sirisha, P G Remya, Jimna Janardhanan, and T M Balakrishnan Nair | |
| Source | Current Science, vol. 122, no. 5, | |
| Abstract | Wave-power generation could be a feasible solution to the huge power requirements of a country like India having a long coastline. The present study provides details of wave characteristics and wave power poten-tial during different seasons along the Indian coast using wave observations. Seasonal average of signifi-cant wave height (Hs) was computed near the coastal areas of India from the measured data. Hs varied in the range 1.62?1.95 m and 1.38?1.39 m along the west and east coastal areas respectively, during summer monsoon. These high waves generate high wave power (>20 kW/m) along the east and west coastal areas of India. The seasonal average of wave power obtained was high (12?19 kW/m) off the west coast of India, suggesting that the west coastal areas are suitable for power generation during summer monsoon. This study highlights that the average wave power is high (12?19 kW/m) during summer monsoon along the west coast and insignificant (<2 kW/m) during non-monsoon. Thus the present study suggests employing a to hybrid arrangement of power generation using solar and ocean wave energies to solve the problem of energy deficit near the coastal areas of India. | |
| Paper No | 15 | Publication ID : 857 & Year : 2022 |
| Title | Analysis of meteorological and oceanic conditions during freak wave events in the Indian Ocean | |
| Authors | Harikumar, R., Sirisha, P., Modi, A., Girishkumar, M.S., Vishnu, S., Srinivas, K., Kumari, R., Yatin, G., Dinesh Kumar, P., Balakrishnan Nair, T.M., Mohapatra, M. | |
| Source | Journal of Earth System Science, 131 (2), art. no. 92 | |
| Abstract | Tropical Cyclone Ockhi was an intense cyclone, with a peculiar and long track, in the Arabian Sea in 2017. It caused severe damage to coastal infrastructure and death of 282 people. Indian National Centre for Ocean Information Services (INCOIS) issued the Joint INCOIS-IMD (India Meteorological Department) bulletins on the Ocean State Forecasts (OSF) and alerts/warnings during Ockhi. Validation of the OSF from INCOIS using buoys reveals that the forecasts were in good agreement with the observations [average correlation 0.9, RMSE <0.8 m (for larger waves), and scatter index <25%]. Climatological analysis of Genesis Potential Index (GPI) suggests that the southeast Arabian Sea, where the TC-Ockhi was intensified, had all the favourable conditions for intensification during November/December. Moreover, it was found that four days before the genesis of Ockhi, the environmental vorticity and relative humidity were more favourable for the cyclogenesis compared to vertical wind shear and potential intensity. The intensification rate was rapid as experienced by earlier cyclones in this region. Also, the cyclone track closely matched the background tropospheric winds. The present study suggests that the forecasters should look into the background dynamic and thermodynamic conditions extensively in addition to multi-model guidance to better predict the genesis, intensity and track of the cyclones. | |
| Paper No | 16 | Publication ID : 848 & Year : 2021 |
| Title | The influence of boreal summer intra-seasonal oscillations on Indo-western Pacific Ocean surface waves | |
| Authors | Srinivas, G., Remya, P.G., Malavika, S., Balakrishnan Nair, T.M. (2020). | |
| Source | Nature-Scientific Reports, 10 (1), art. no. 12631 | |
| Abstract | The present study examines the influence of Boreal Summer Intra-Seasonal Oscillation (BSISO) on Tropical Indian Ocean surface waves using the latest version of ECMWF reanalysis (ERA5) during summer monsoon months June through August (JJA). BSISO is a distinct mode of ISO during JJA having a northward and eastward movement from the equatorial Indian Ocean to the western Pacific Ocean. Composite analysis of anomalies of significant wave heights (SWH), wind sea, swell, and mean wave period for 8 phases of BSISO has been carried out to understand its influence. SWH anomalies in response to BSISO?s are phase-dependent. Negative SWH anomalies are noticed with strong northward and weak eastward propagation during the phases 1?3 in response to the easterly wind anomalies over the north Indian Ocean (NIO). During phases 5?7, high positive SWH anomalies (~?0.5 m) in response to the westerly wind anomalies with northward and weak eastward propagation over NIO. Phases 4 and 8 behave like transition phases. In addition, enhanced (suppressed) SWH anomalies (~?0.5 m) are seen during the active (break) spells of BSISO over NIO. Over the southern tip of India, negative (positive) SWH anomalies prevail during the active (break) conditions. This study clearly suggests that the wave forecast advisories during intra-seasonal time scales would be more useful for offshore and coastal activities during the summer monsoon. | |
| Paper No | 17 | Publication ID : 846 & Year : 2021 |
| Title | Effect of Tidal Cycle on Escherichia coli Variability in a Tropical Estuary | |
| Authors | Baliarsingh, S.K., Lotliker, A.A., Srichandan, S., Basu, A., Balakrishnan Nair, T.M., Tripathy, S.K. | |
| Source | Bulletin of Environmental Contamination and Toxicology, 106 (4), pp. 622-628. | |
| Abstract | A faecal indicator bacteria, Escherichia coli (E. coli), is widely used in monitoring health of estuaries, where tidal amplitude plays a critical role in its variability. Mahanadi estuary, formed at the mouth of a major tropical river Mahanadi, has large socio-economic importance. This anthropogenically stressed estuary remains understudied with respect to E. coli. Hence, this study addressed E. coli variability in Mahanadi estuary with novel sampling strategy that can be implemented at other tropical estuaries. The sampling strategy includes simultaneous measurements, at lesser-saline upper-estuary and higher-saline lower-estuary, over a tidal cycle. Although no significant variability of E. coli was observed between upper and lower-estuary, overall average count was higher during low tide and lower during high tide attributed to salinity fluctuations. Intermittent surpass of E. coli counts above recommended limits in Mahanadi estuary, indicated potential health risk, thus demands for frequent water quality monitoring and management strategies. | |
| Paper No | 18 | Publication ID : 845 & Year : 2021 |
| Title | Did the Coronavirus Disease 2019 Lockdown Phase Influence Coastal Water Quality Parameters off Major Indian Cities and River Basins? | |
| Authors | Lotliker, A.A., Baliarsingh, S.K., Shesu, R.V., Samanta, A., Naik, R.C., Balakrishnan Nair, T.M. | |
| Source | Frontiers in Marine Science, 8, art. no. 648166. | |
| Abstract | The end of the current decade experienced an outbreak of a new strain of coronavirus classified as severe acute respiratory syndrome coronavirus 2 (SARS-CoV2) [coronavirus disease 2019 (COVID-19)] that spread across the globe within a short span of time and was declared as a global pandemic by the World Health Organization. In order to contain the spread of COVID-19, the Indian Government imposed lockdown in various phases, namely, the strict lockdown period (SLP) and relaxed lockdown period (RLP). The present study addresses changes in the magnitude of satellite-derived water quality parameters in the coastal waters off major Indian cities (Mumbai and Chennai) and river basins (Narmada, Mandovi-Zuari, Netravathi, Periyar, Kaveri, Krishna-Godavari, Mahanadi, and Hooghly) along the eastern Arabian Sea (EAS) and western Bay of Bengal (WBoB) during SLP and RLP. The daily climatology (2003?2019) and anomaly (2020) of different water quality parameters, viz., chlorophyll-a (chl-a), downwelling diffused attenuation coefficient (kd490), and particulate organic carbon (POC) were used in the present study to eliminate seasonal biases and to unravel the signature of lockdown-induced changes in the magnitude of the above water quality parameters. During the total lockdown period, the magnitude of the above parameters reduced significantly in the coastal waters of both the EAS and the WBoB. However, this reduction was more significant in the coastal waters of the WBoB, attributed to a reduction in the supply of anthropogenic nutrients. Among different studied locations, the magnitude of water quality parameters significantly decreased off Chennai and Hooghly, during SLP, which subsequently increased during RLP probably due to reduction in anthropogenic material influx during SLP and increase during RLP. During RLP, the coastal waters off Mahanadi showed a maximum decrease in the magnitude of water quality parameters followed by Mandovi-Zuari, irrespective of these regions? quantum of anthropogenic material input, possibly due to the higher response time of the ecosystem to reflect the reduction in anthropogenic perturbations. The satellite-retrieved water quality parameters have provided valuable insight to efficiently describe the changes in the health of the Indian coastal environment in terms of phytoplankton biomass and water clarity. | |
| Paper No | 19 | Publication ID : 844 & Year : 2021 |
| Title | Unravelling tidal effect on zooplankton community structure in a tropical estuary | |
| Authors | Srichandan, S., Baliarsingh, S.K., Lotliker, A.A., Sahu, B.K., Roy, R., Balakrishnan Nair, T.M. | |
| Source | Environmental Monitoring and Assessment, 193 (6), art. no. 362 | |
| Abstract | The variability in zooplankton density and species composition in response to tidal oscillations were investigated in the lesser saline upper reaches (E1) and higher saline lower reaches (E2) of the Mahanadi Estuary, located at the mouth of the third largest river in Indian Peninsula. This is the first of its kind high frequency observation over the tidal cycle ranging from highest high tide to lowest low tide in this estuary revealing dynamic variability of zooplankton assemblages. Zooplankton abundance was higher during high tide in comparison to low tide, irrespective of salinity regimes. On the diurnal scale, it was higher at night in comparison to the day at both E1 and E2. The higher abundance of zooplankton groups such as Copepoda, Cladocera, and planktonic larvae during the night at E1 as well as E2 indicating an upward migration. Many of the zooplankton taxa (e.g., Pseudodiaptomus serricaudatus, Pseudodiaptomus sp., Acartia danae, Acrocalanus longicornis, Oithona sp., Corycaeus andrewsi) migrated towards E1 due to tidal effect during high tide and maintained their position even during low tide. In contrast, the prevalence of limnetic taxa (e.g., Brachionus rubens, Polyarthra vulgaris, Bosminopsis deitersi, Moina micrura, Heliodiaptomus sp.) at E2 during low tide indicated a predominant riverine source. The tidal variability of Brachyura (zoea and megalopa) revealed different emergence times that indicated dispersal of zoeas to the adjacent Bay of Bengal and the return of magalopa to the Mahanadi Estuary. Species diversity index was higher during high tide, and prominent at E2. At E1, marine, fresh, marine-brackish, and marine-brackish-fresh zooplankton species dominated during high tide, while brackish-fresh taxa dominated during low tide. Differently, E2 was enriched with marine, marine-brackish, and marine-brackish-fresh taxa during high tide, whereas fresh, brackish-fresh, and marine-fresh dominated during low tide. Salinity and suspended matter influenced the dominant zooplankton taxa at E2 and E1, respectively. Zooplankton assemblages exhibited a pattern of prominent diurnal-spatial variation in comparison to the tidal scale in the Mahanadi Estuary. Overall, this study documented a very high zooplankton diversity (92 taxa belonging to 13 groups) and significant variations in species abundance which highlighted the importance of carrying out sampling over the tidal cycle at contrasting salinity regimes. | |
| Paper No | 20 | Publication ID : 843 & Year : 2021 |
| Title | Holistic approach to assess the coastal vulnerability to oceanogenic multi-hazards along the coast of Andhra Pradesh, India. | |
| Authors | Mahendra, R.S., Mohanty, P.C., Francis, P.A., Sudheer Joseph, Balakrishnan Nair T. M. and Srinivasa Kumar T. | |
| Source | The coastal vulnerability to multi-hazard study aims to assess the coastal zones of Andhra Pradesh that really are vulnerable to various oceanogenic hazards. Using high-resolution coastal elevation, the maximum extent of coastal inundation during extreme high waves of cyclones & tsunamis, shoreline change, and sea-level rise can be computed. Vulnerability impact up to the village level was assessed based on future projection (return period) of multi-hazard impact using a holistic approach with geospatial techniques. The current study results revealed that 706 villages and 8 towns that are completely falling under CMZ are at risk. A total of 9682 km2 of coastal zones of Andhra Pradesh coast are exposed and prone to inundation as recorded under CMZ. Krishna, Godavari, Guntur and Prakasham districts comprise 70% of the total CMZ area are large low-lying areas exposed to ocean hazards. CMZ area along Andhra Pradesh coast recorded a significant negative correlation of - 0.65 with coastal elevation and a positive correlation of 0.34 with coastal exposure index. Shoreline change assessed from 1972 to 2019 across the study area reveals the 7% under high erosion along the headland and low-lying area of Krishna-Godavari delta. The outputs and maps produced in this study provide vital input for coastal disaster management and necessary policy interventions. | |
| Abstract | Environ Earth Sci 80, 651. | |
| Paper No | 21 | Publication ID : 842 & Year : 2021 |
| Title | Evaluation of Winds from SCATSAT-1 and ASCAT Using Buoys in the Indian Ocean | |
| Authors | Modi, A., Munaka, S.K., Harikumar, R., Balakrishnan Nair, T.M., Srinivas, K. | |
| Source | Journal of the Indian Society of Remote Sensing, 49 (8), pp. 1915-1925. | |
| Abstract | Over the data sparse oceanic region, ocean surface winds from scatterometers on-board satellites play a crucial role to make accurate Numerical Weather Prediction model-based analysis. In the present study, ocean surface winds derived from the recently launched SCATSAT-1 for the year 2017 over the Indian Ocean are validated against the winds from the Moored and RAMA buoys. The validation results for ASCAT winds for the same period are also presented. The comparison of SCATSAT-1 (ASCAT) winds against offshore OMNI buoy winds indicates that the mean differences for wind speed and wind direction are 0.5 m/s and ???1.0° (0.39 m/s and ???4.0°), and the RMSEs are 1.44 m/s and 23.0° (1.17 m/s and 25.0°), respectively. For the coastal OMNI buoys, the SCATSAT-1 (ASCAT) indicated that the mean differences for wind speed and wind direction are 1.6 m/s and ???5° (1.15 m/s and ???0.4°), and the RMSEs are 2.65 m/s and 46 deg, (2.1 m/s and 51°), respectively. Quantified differences are almost similar for the comparison of SCATSAT-1/ASCAT with RAMA buoys. Overall, the quantified differences in the wind speed and direction between the SCATSAT-1 and buoys are closer to the satellite?s mission specifications of 1.8 m/s and 20°, respectively, and at par with the ASCAT accuracies. The capability of SCATSAT-1 winds to capture a cyclonic storm OCKHI during December 2017 also is depicted. The present study endorses that the SCATSAT-1 data are accurate and reliable and can be used in Numerical Weather Prediction (NWP) models and also for other applications. | |
| Paper No | 22 | Publication ID : 841 & Year : 2021 |
| Title | Implementation of altimeter data assimilation on a regional wave forecasting system and its impact on wave and swell surge forecast in the Indian Ocean | |
| Authors | Seemanth M, P.G. Remya, Suchandra A Bhowmick, Rashmi Sharma, T.M. Balakrishnan Nair, Raj Kumar and Arun Chakraborty | |
| Source | Ocean Engineering | |
| Abstract | In the present work, we have operationally implemented a data assimilation (DA) scheme in the wave forecasting system at the Indian operational agency, Indian National Centre for Ocean Information Services (INCOIS). Significant Wave Height (SWH) measurements from the SARAL/AltiKa, Jason-2 and Jason-3 altimeters were assimilated using the Optimal Interpolation technique. The impact of altimeter DA towards improving the reliability of wave predictions in the Indian Ocean is evaluated by validating the forecasted wave parameters with buoy observations. The assimilation of altimeter data showed considerable improvement in the wave predictions. SWH forecast in the northern Indian Ocean region improved up to ~15 % in the first 24 h period. The improvement in forecasted wave parameters were due to the correction in swell forecast, which persists throughout the forecast period. For wind-sea forecast, impact of DA was less visible (~4?6% improvement up to forecast lead time of 24 h), as it is primarily driven by local wind fields. The positive impact of DA on the swell forecast is further established considering a swell surge event, named Kallakkadal. | |
| Paper No | 23 | Publication ID : 840 & Year : 2021 |
| Title | Response of phytoplankton biomass to nutrient stoichiometry in coastal waters of the western Bay of Bengal | |
| Authors | Mathew, T., Prakash, S., Kumar Baliarsingh, S., Samanta, A., Lakshmi, R.S., Anandrao Lotliker, A., Chatterjee, A., Balakrishnan Nair, T.M. | |
| Source | Ecological Indicators, 131, art. no. 108119 | |
| Abstract | The hydro-biological parameters such as thermohaline structure, nutrients, and chlorophyll-a (chl-a) during pre-southwest monsoon (PRSWM) and post-southwest monsoon (POSWM) periods of 2017, was investigated and compared along a coastal transect in the western Bay of Bengal (BoB). The impact of cold-core and warm-core eddies on chl-a in the very near coastal waters of the western BoB was analyzed. During PRSWM period, the water column was recharged with phytoplankton growth-promoting nutrients entrained by cold-core eddies that resulted in an increment in chl-a concentration. A three-times increase in chl-a concentration was observed due to the cold-core eddy, whereas the presence of warm-core eddy reduced the chl-a concentration by 87%. However, during POSWM period, despite having higher nitrate concentration and adequate light in the water column, the surface chl-a was substantially lesser than PRSWM. The molar ratio of ambient inorganic macronutrients during POSWM period played a significant role resulting in lower chl-a concentration. Nitrogen to phosphate (N:P) and nitrogen to silicate (N:Si) ratios were less than the Redfield values. The chl-a concentration off Godavari, a biological hotspot, was the lowest during POSWM period. This study highlights phosphate limitation off Godavari during the high river discharge period. | |
| Paper No | 24 | Publication ID : 839 & Year : 2021 |
| Title | Should I stay or should I go? South Indian artisanal fishers? precarious livelihoods and their engagement with categorical ocean forecasts. | |
| Authors | Maxmillan Martin, Abhilash Sukumarapillai, Vijayakumar P.,Harikumar R.,Niyas NT.,TM Balakrishnan Nair Yatin Grover.,Filippo Osella. | |
| Source | Weather, Climate, and Society | |
| Abstract | Ocean State Forecasts contribute to safe and sustainable fishing in India, but their usage among artisanal fishers is often limited. Our research in Thiruvananthapuram district in the southern Indian state of Kerala tested forecast quality and value and how fishers engage with forecasts. In two fishing villages, we verified forecast accuracy, skill, and reliability by comparing forecasts with observations during the 2018 monsoon season (June?September; n = 122). We assessed forecast value by analyzing fishers? perceptions of weather and risks and the way they used forecasts based on 8 focus group discussions, 20 interviews, conversations, and logs of 10 fishing boats. We find that while forecasts are mostly accurate, inadequate forecasting of unusual events (e.g., wind >45 km h-1) and frequent fishing restrictions (n = 32) undermine their value. Fishers seek more localized and detailed forecasts, but they do not always use them. Weather forecasts are just one of the tools artisanal fishers deploy, used not simply to decide as to whether to go to sea but also to manage potential risks, allowing them to prepare for fishing under hazardous conditions. Their decisions are also based on the availability of fish and their economic needs. From our findings, we suggest that political, economic, and social marginality of south Indian fishers influences their perceptions and responses to weather-related risks. Therefore, improving forecast usage requires not only better forecast skill and wide dissemination of tailor-made weather information, but also better appreciation of risk cultures and the livelihood imperatives of artisanal fishing communities. | |
| Paper No | 25 | Publication ID : 838 & Year : 2021 |
| Title | Physicochemical controls on the initiation of phytoplankton bloom during the winter monsoon in the Arabian Sea | |
| Authors | Lakshmi, R.S., Prakash, S., Lotliker, A.A., Baliarsingh, S.K., Samanta, A., Mathew, T., Chatterjee, A., Sahu, B.K., Balakrishnan Nair, T.M. (2021) | |
| Source | Nature-Scientific Reports, 11 (1), art. no. 13448 | |
| Abstract | Occurrence of phytoplankton bloom in the northern Arabian Sea (NAS) during the winter monsoon is perplexing. The convective mixing leads to a deeper and well-oxygenated (>?95% saturation) mixed layer. We encountered low chlorophyll conditions though the nutrient conditions were favorable for a bloom. The mean ratio of silicate (Si) to DIN (Dissolved Inorganic Nitrogen: nitrate?+?nitrite?+?ammonium) in the euphotic zone was 0.52 indicating a ?silicate-stressed? condition for the proliferation of diatoms. Also, the euphotic depth was much shallower (~?49 m) than the mixed layer (~?110 m) suggesting the Sverdrup critical depth limitation in the NAS. We show that the bloom in this region initiates only when the mixed layer shoals towards the euphotic zone. Our observations further suggest that two primary factors, the stoichiometric ratio of nutrients, especially the Si/DIN ratio, in the mixed layer and re-stratification of the upper water column, govern the phytoplankton blooming in NAS during the later winter monsoon. The important finding of the present study is that the Sverdrup?s critical depth limitation gives rise to the observed low chl-a concentration in the NAS, despite having enough nutrients. | |
| Paper No | 26 | Publication ID : 837 & Year : 2021 |
| Title | Potential Fishing Zone characterization in the Indian Ocean by Machine Learning Approach, | |
| Authors | Swarnali Majumder, Sourav Maity, T. M Balakrishnan Nair, Rose P. Bright, Nagaraj Kumar, Naha Shwetha, Nimit Kumar | |
| Source | Advances in Intelligent Systems and computing, Vol 1393, PP 43-54. | |
| Abstract | Potential fishing zone (PFZ) advisory is an essential guideline for the fishing community of India. Several studies have shown that high sea surface temperature (SST) gradient and high chlorophyll concentration in the ocean are the prospective areas for pelagic fish catch. ESSO-INCOIS provides advisories on PFZ on a daily basis using remotely sensed SST and chlorophyll-a data. The limitation of this advisory is that it does not give any information about the probable quantity of the fish. In this study, a hybrid decision tree model is developed for characterizing PFZ in the Indian Ocean. If SST gradient, persistence of SST gradient and chlorophyll concentration of any PFZ are given as the input variables, this model can classify the corresponding PFZ in terms of low, medium or high category of fish catch. According to this study, low SST gradient persistence and high SST gradient indicate possibility of high fish catch. | |
| Paper No | 27 | Publication ID : 836 & Year : 2021 |
| Title | The role of anomalous oceanic features on enhancing flooding duration in Kuttanad region, Kerala (India) | |
| Authors | Modi, A., Balakrishnan Nair, T.M., Remya, P.G., Harikumar, R., Srinivas, K., Srinivas, G. | |
| Source | Journal of Earth System Science, 130 (2), art. no. 111. | |
| Abstract | The present study describes the active role of met-ocean parameters on the heavyCooding thatoccurred during July 2018 in the Kuttanad region, Kerala. The model-derived data as well as obser-vations showed a high anomaly of wave height in July 2018 oAKerala was not correlated with localwind anomaly and indicated possible connection of wave anomalies to swell waves. The high period andhigh amplitude swell waves suggest a wave setup formation near shore forCooding intensiBcation in theKuttanad region. The wave observation at an open ocean location (AD09) also conBrms the presence ofhigh swell waves during the same period. Anomalous elevated non-tidal sea level was evident in the tidegauge data. The narrow opening at Thottappally, is not able to discharge the outCow of the heavyCoodwater and it is further complicated by the wave setup at the entrance caused by long period swellwaves. | |
| Paper No | 28 | Publication ID : 847 & Year : 2021 |
| Title | The impact of Indian Ocean dipole on tropical Indian Ocean surface wave heights in ERA5 and CMIP5 models | |
| Authors | Srinivas, G., Remya, P.G., Kumar, B.P., Modi, A., Balakrishnan Nair, T.M. | |
| Source | International Journal of Climatology, 41 (3), pp. 1619-1632. | |
| Abstract | The present study examines the relationship between the tropical Indian Ocean (TIO) significant wave height (SWH) and Indian Ocean dipole (IOD) during boreal summer season (June through August) in the latest version of European Centre for Medium-Range Weather Forecasts reanalysis (ERA5) and wave simulations forced with surface winds and sea-ice fields from the Coupled Model Intercomparison Project version-5 (CMIP5) models. The interannual variability of SWH shows a significant negative correlation with the IOD over TIO. SWH anomalies display meridional tripole pattern with significant negative (positive) anomalies over eastern equatorial Indian Ocean caused by anomalous easterlies (westerlies), and positive (negative) anomalies over southeastern TIO and the north Bay of Bengal during positive (negative) phase of IOD. The strong wave heights along the east coast of India during positive IOD and the south and southwest coast of India during negative IOD are noticed. CMIP5 models GFDL-CM3, MRI-CGCM3 and the multi-model mean display considerable skill in capturing these teleconnections with substantial magnitude differences. A thorough understanding of the teleconnections between IOD and TIO wave heights is a significant prerequisite for the accurate forecast of surface waves in the Indian Ocean. Hence, this study advocates the importance evaluating the ability of models in representing the SWH and IOD interactions and its implications on Indian coastal regions in the form of inundation, coastal flooding and other vulnerabilities in a changing climate scenario. | |
| Paper No | 29 | Publication ID : 834 & Year : 2020 |
| Title | High-Resolution Operational Ocean Forecast and Reanalysis System for the Indian Ocean | |
| Authors | Francis, P.A, Jithin A. K......Balakrishnan Nair T. M, Pattabhi Rama Rao E, and Satyanarayana B. V | |
| Source | Bulletin of the American Meteorological Society, 101(8), E1340-E1356. | |
| Abstract | A good understanding of the general circulation features of the oceans, particularly of the coastal waters, and ability to predict the key oceanographic parameters with good accuracy and sufficient lead time are necessary for the safe conduct of maritime activities such as fishing, shipping, and offshore industries. Considering these requirements and buoyed by the advancements in the field of ocean modeling, data assimilation, and ocean observation networks along with the availability of the high-performance computational facility in India, Indian National Centre for Ocean Information Services has set up a ?High-Resolution Operational Ocean Forecast and Reanalysis System? (HOOFS) with an aim to provide accurate ocean analysis and forecasts for the public, researchers, and other types of users like navigators and the Indian Coast Guard. Major components of HOOFS are (i) a suite of numerical ocean models configured for the Indian Ocean and the coastal waters using the Regional Ocean Modeling System (ROMS) for forecasting physical and biogeochemical state of the ocean and (ii) the data assimilation based on local ensemble transform Kalman filter that assimilates in situ and satellite observations in ROMS. Apart from the routine forecasts of key oceanographic parameters, a few important applications such as (i) Potential Fishing Zone forecasting system and (ii) Search and Rescue Aid Tool are also developed as part of the HOOFS project. The architecture of HOOFS, an account of the quality of ocean analysis and forecasts produced by it and important applications developed based on HOOFS are briefly discussed in this article. | |
| Paper No | 30 | Publication ID : 833 & Year : 2020 |
| Title | A review of jellyfish aggregations, focusing on India?s coastal waters | |
| Authors | Baliarsingh, S.K., Lotliker, A.A., Srichandan, S., Samanta, A., Kumar, N., Balakrishnan Nair, T.M. | |
| Source | Ecological Processes, 9 (1), art. no. 58 | |
| Abstract | A review of jellyfish aggregations focused on India?s coastal waters was conducted, with the aim to enhance understanding of conducive conditions and subsequent ecological impacts. Jellyfish swarming, as well as their beach strandings, have been reported from many areas of the world?including India?s coastal waters. A variety of natural (winds, tidal fronts, surface currents, water temperature, salinity, turbidity, dissolved oxygen) and anthropogenic (water quality deterioration, overfishing, translocation, habitat modification) factors play pivotal roles in triggering jellyfish aggregations. Jellyfish aggregation events in the forms of their swarming in coastal waters and beach strandings have resulted in ephemeral nuisances such as water quality deterioration, food chain alterations, hindrance in seawater uptake by power plants, clogging of nets during fishing operations, and tourism declines. Several well-known Indian tourist beaches (e.g., Puri, Chennai, Goa, and Mumbai) have experienced beach strandings. Despite recurrence of such events, jellyfishes are relatively less scientifically investigated and monitored in Indian coastal waters. Therefore, it is important to determine the environmental conditions that trigger jellyfish swarming, in order to develop effective monitoring and prediction strategies. This study additionally proposes a conceptual framework towards development of a jellyfish monitoring system for Indian waters using satellite and model data. | |
| Paper No | 31 | Publication ID : 832 & Year : 2020 |
| Title | Impact of tropical and extra tropical climate variability on Indian Ocean surface waves. | |
| Authors | Remya, P.G., Kumar, B.P., Srinivas, G. Balakrishnan Nair T.M., | |
| Source | Climate Dynamic. 54 (11-12), 4919-4933. | |
| Abstract | Understanding the impact of various climate features on wave climate is important for effective coastal climate adaptation and mitigation strategy planning. In the present study, the effect of tropical and extra-tropical climate modes such as Indian Ocean Dipole (IOD), El Niño Southern Oscillation (ENSO) and Southern Annular Mode (SAM) on wind-wave climate of the Indian Ocean (IO) is studied using multiple linear regression of individual climate indices on relevant wind-wave parameters. There are two regions of importance for swell generation in the Indian Ocean - a region between 40° and 60° S in the Southern Ocean (SO) and another region in the Eastern Tropical Indian Ocean (ETIO; 10°?30° S, 60°?100 °E). SAM, the strongest inter-annual mode of the SO, generates swells in the 40°?60°S band throughout the year that eventually propagates to the entire North IO. Both the positive and negative phases of SAM generate swells from SO, but it?s genesis region vary meridionally depending on the phase of SAM. The positive phase of ENSO (LaNiña) generally reduce the westerly wind anomalies in the SO caused by a positive phase of SAM and hence reduce the swell generation from SO, but causes stronger south-easterlies in the ETIO, generating more swells from there. IOD that peaks in September?October?November period has its effect on swell generation limited to eastern equatorial IO. Our analysis suggests that interannual climate features are important in modulating wind-wave climate of IO and a basin-wide model set-up with an accurate representation of various interannual climate features is a prerequisite for accurate wave forecast. | |
| Paper No | 32 | Publication ID : 831 & Year : 2020 |
| Title | Development of small vessel advisory and forecast services system for safe navigation and operations at sea | |
| Authors | Aditya, N.D., Sandhya, K.G., Harikumar, R., Balakrishnan Nair, T.M. | |
| Source | Journal of Operational Oceanography | |
| Abstract | Fishing is the most dangerous profession in the world. To reduce the number of accidents caused by capsizing of vessels, Indian National Centre for Ocean Information Services (INCOIS) has designed and developed an advisory and forecast services system for the Indian ocean regime, which warns users against potential zones and times at which vessel overturning can take place, three days in advance. This paper discusses the development and various aspects of such a system, its decision-making mechanism, and the Standard Operating Procedure (SOP). Warning advisories issued by the system are based upon a newly coined index-Boat Safety Index (BSI). The advisory system is verified with a few real-life incidents of the past. The refinement of the advisory system is planned by updating suitable thresholds for the indices based upon regular feedback from the users. The boats operating along the Indian coast are classified into different categories based upon their beam size, and category-specific advisories are issued. | |
| Paper No | 33 | Publication ID : 835 & Year : 2020 |
| Title | Locally and Remotely Generated Wind Waves in the Southwestern Shelf Sea of India | |
| Authors | Anoop, T.R., Nair, L.S., Prasad, R., Reji, S., Ramachandran, K.K., Prakash, T.N., Balakrishnan Nair, T.M. | |
| Source | Journal of Coastal Research, 89 (sp1), pp. 77-83. | |
| Abstract | The Southwestern Shelf Sea (SWSS) of India has a distinct wave pattern, which makes it different as compared to the adjoining regions. Wave directional spectra during the monsoon season are comparatively broader and double peaked in contrast to that of the western shelf sea. The well-defined directional bi-modality is observed during the south west monsoon which is attributed to the coexistence of the south Indian Ocean swells and the southwest monsoon swells. The shamal swells generated by the shamal wind blowing from the Arabian Peninsula are found to have a significant influence on the wave pattern of the SWSS. In addition, the local sea breeze/land breeze also contributes significantly to the observed changes, particularly to the diurnal variation. A distinct phase lag in occurrence of the maximum significant wave height for the wind sea component is also observed in the northern region of the SWSS during the fair seasons. | |
| Paper No | 34 | Publication ID : 829 & Year : 2019 |
| Title | Numerical simulation and preliminary analysis of spectral slope and tail characteristics using nested WAM-SWAN in a shallow water application off Visakhapatnam | |
| Authors | Umesh, P. A., Bhaskaran, P. K., Sandhya, K. G., & Balakrishnan Nair, T. M. (2019).. | |
| Source | Ocean Engineering, 173, pp. 268-283. | |
| Abstract | Over the past several decades, understanding the nature and slope of high frequency tail in wind-wave modelling studies is extremely important, and its uncertainty amongst -4 and -5 frequency exponent representation was an area of major significance. Hence, an attempt has been made to estimate the slope of the high frequency tail of the wind-wave frequency spectrum off coastal Visakhapatnam using measured data for the period November 2011 to December 2015. The investigation reveals that the high frequency slope of the spectra varied seasonally in the range between -1.80 and -3.77. Annually 75.11% of wave conditions were dominated by swells and the rest 24.89% by wind-seas. Further, the validation of 1D wave spectra at the coastal location utilizing the nested WAM-SWAN setup was promising enough indicating a departure in capturing the peak energies. With the aid of spectral fitting method, the JONSWAP spectra was compared with the measured spectra; which demonstrated significant deviations from the measured spectra revealing high Scatter Index ranging from 0.24 to 1.73. The study aims to report on the uncertainty in the correct slope for the high frequency tail; and the concept of a unified slope at any coastal location remains unpredictable for the oceanographic community. | |
| Paper No | 35 | Publication ID : 830 & Year : 2019 |
| Title | Spectral Modelling on the Characteristics of High Frequency Tail in Shallow Water Wave Spectra at Coastal Puducherry, East Coast of India | |
| Authors | Umesh, P.A., Bhaskaran, P.K., Sandhya, K.G., Balakrishnan Nair, T. M. | |
| Source | Pure and Applied Geophysics, 176 (1), pp. 501-524. | |
| Abstract | About 8 years of measured wave spectra (June 2007?December 2014) off coastal Puducherry located in the east coast of India and bordering the Bay of Bengal were analyzed with an objective to understand the slope of the high frequency tail of the wave spectrum and to determine the occurrence of single peaked, double-peaked and multi-peaked spectra in varying sea states. The temporal and inter-annual variation of the spectral energy density over the years indicates marked variability and the study signifies that wave spectra were multi-peaked from June to October and predominantly double peaked during the rest of the year. Swell and wind sea components have been estimated from the wave spectra by separation frequency method. The analysis shows that swells dominate Puducherry coastal region not only during southwest monsoon (95%), but also during the post-monsoon (100%) and northeast monsoon season. The measured wave spectra were compared with numerical wave model outputs to attain a level of confidence with the buoy data. In addition, analysis on the slope of the high frequency tail of the wave energy spectra shows that its slope varied seasonally in the range of -?1.96 to -?3.27 at the coastal location. Further, the JONSWAP model fitted into measured wave spectra showed high discrepancy between the two, especially in the high frequency tail with Scatter Index ranging between 0.79 and 3.98. The correct slope for the high frequency or even whether a unique slope exists remains elusive for the ocean wave community. | |
| Paper No | 36 | Publication ID : 825 & Year : 2019 |
| Title | Evaluation of the impact of high-resolution winds on the coastal waves | |
| Authors | Sirisha, P., Remya, P.G., Modi, A., Tripathy, R.R., Balakrishnan Nair, T.M., Venkateswara Rao, B. | |
| Source | Journal of Earth System Science, 128 (8), art. no. 226. | |
| Abstract | This study discusses the impact of high-resolution winds on the coastal waves and analyses the effectiveness of the high-resolution winds in recreating the fine-scale features along the coastal regions during the pre-monsoon season (March?May). The influence of the diurnal variation of winds on waves is studied for the Tamil Nadu coastal region using wind fields from weather research and forecast (WRF) (3 km) and European Centre for Medium-Range Weather Forecasts (ECMWF) (27.5 km). The improvement in the coastal forecast is then quantified with wave rider buoy observations. The high-resolution wind fields simulated fine-scale features like land?sea breeze events and showed good agreement with observation results. The error in the wave height and period is reduced by 8% and 46%, respectively, with the use of high-resolution forcing winds WRF over ECMWF, although the overestimation of wave energy on high frequencies due to overestimated WRF winds remains as a challenge in forecasting. The analysis also shows the importance of accurate wave forecast during a short-duration sudden wind (~12 m/s) occurrence in southern Tamil Nadu near Rameswaram during the pre-monsoon period. Low pressure forms over Tamil Nadu due to the land surface heating, resulting in a sudden increase of winds. High winds and steep waves which cause damage to the property of the coastal community near Rameswaram also were well simulated in the high-resolution forecast system with WRF winds. | |
| Paper No | 37 | Publication ID : 826 & Year : 2019 |
| Title | Oil spill trajectory prediction with high-resolution ocean currents | |
| Authors | Prasad, S.J., Francis, P.A., Balakrishnan Nair, T.M., Shenoi, S.S.C., Vijayalakshmi, T. (2019) | |
| Source | Journal of Operational Oceanography, pp. 1-27. | |
| Abstract | Simulated ocean currents from ocean circulation models along with the surface winds are generally used to force an oil spill trajectory model. Ocean circulation is a key factor in determining the drift of the spilled marine pollutants. The simulations of the drift pattern of spilled oil, when forced by the ocean currents from two ocean models, are presented here. Merchant Vessel (MV) Rak sunk at 72.4865°E, 18.7715°N, on 4 August 2011. As per the information from Indian Coast Guard, approximately 122.5 tons of fuel oil was spilled from the vessel from 5 August 2011 to 12 August 2011. An oil spill trajectory model, General NOAA Operational Modeling Environment (GNOME), was used to simulate the oil drift pattern from MV Rak from 1000 hours of 5 August 2011 to 1300 hours of 12 August 2011. GNOME was forced with winds from European Centre for Medium Range Weather Forecast (ECMWF) and ocean currents from Indian Ocean Forecasting System (INDOFOS) and High-resolution Operational Ocean Forecasting and reanalysis System (HOOFS). We found that the oil drift pattern obtained when forced with ocean currents from HOOFS was in better agreement with the actual track, compared to the one obtained while using INDOFOS currents. | |
| Paper No | 38 | Publication ID : 827 & Year : 2019 |
| Title | Reconstruction of the state space figure of Indian ocean dipole | |
| Authors | Majumder, S., Balakrishnan Nair, T.M., Kiran Kumar, N. | |
| Source | Advances in Intelligent Systems and Computing, 816, pp. 471-482. | |
| Abstract | State space reconstruction is an important index for describing nonlinear time series. However, reconstruction of state space figure is difficult if the data is noisy. Hence, noise reduction is an important step for reconstructing state space figure. In this study, we propose a method which can reconstruct state space picture from a noisy time series. This method is used for reconstructing state space figure from the data of Indian Ocean Dipole. Dimension of the reconstructed attractor is measured by computing correlation dimension. The dynamics of Indian Ocean Dipole is not well understood. The reconstruction of state space figure indicates that there is chaos in Indian Ocean Dipole. Positive Lyapunov exponent reconfirms that the dynamics of Indian Ocean Dipole is chaotic. | |
| Paper No | 39 | Publication ID : 828 & Year : 2019 |
| Title | Maintenance of the southern Bay of Bengal cold pool | |
| Authors | Vinayachandran, P.N., Das, U., Shankar, D., Jahfer, S., Behara, A., Balakrishnan Nair, T.M., Bhat, G.S. (2019) | |
| Source | Deep-Sea Research Part II: Topical Studies in Oceanography, art. no. 104624 | |
| Abstract | The region of relatively cooler water, sitting in the shadow zone of monsoon rainfall, around southern tip of India and around Sri Lanka, is known as the cold pool. A ship-board observations program to the east of Sri Lanka during the summer monsoon of 2009 captured two cooling events within the core of the Summer Monsoon Current (SMC). Time-series of temperature profiles within the cold pool showed a cooling of the sea surface temperature (SST) by about 0.3°C during 22?25 July 2009 and about 0.4°C during 29 July to 2 August 2009. During the cooling periods, both wind speed and mixed layer depth (MLD) increased, but the air-sea heat gain by the ocean remained positive. Efforts were made to estimate the temperature advection term by means of an Operation Advection strategy using CTD data at four locations about 6.5?km away from the time-series location and ship-board acoustic Doppler current profile measurements. Estimates of horizontal temperature advection suggest that these cooling events are induced by the advection of cooler water by the SMC. Simulation using an Indian Ocean model captures such cooling events and the model temperature equation shows that cooling events through the season are driven either by advection or by entrainment. Thus observations and model simulation concurrently demonstrate that cold pool is maintained through the summer monsoon by the SMC in spite of the ocean gaining heat from the atmosphere. | |
| Paper No | 40 | Publication ID : 821 & Year : 2018 |
| Title | Potential influence of the Atlantic Multi-decadal Oscillation in modulating the biennial relationship between Indian and Australian summer monsoons | |
| Authors | Nagaraju, C., Ashok, K., Balakrishnan Nair, T.M., Guan, Z., Cai, W. | |
| Source | International Journal of Climatology, 38 (14), pp. 5220-5230. | |
| Abstract | Using observed and reanalysed data sets, we investigate the potential role of Atlantic Multi-decadal Oscillations (AMO) in weakening the in-phase association between Indian summer monsoon rainfall (ISMR) and following Australian summer monsoon rainfall (ASMR) during the 1932?1966 period. This weakened inter-monsoon link was earlier attributed to a complete breakdown of the El Niño?Southern Oscillation (ENSO) links with the ASMR. We now find that this weakening was associated with strengthening of low-level westerlies and an increase in local low-level convergence in the northern Australia associated with the warm phase of the AMO during this period. This increased background convergence resulted in relatively enhanced ASMR during the El Niño summers during this period. | |
| Paper No | 41 | Publication ID : 820 & Year : 2018 |
| Title | Modelling coastal erosion: A case study of Yarada beach near Visakhapatnam, east coast of India | |
| Authors | Ramakrishnan, R., Agrawal, R., Remya, P.G., NagaKumar, K.Ch.V., Demudu, G., Rajawat, A.S., Balakrishnan Nair, T.M., Nageswara Rao, K. | |
| Source | Ocean & Coastal Management, 156, pp. 239-248. | |
| Abstract | Prediction of coastal erosion is a challenging field of research with immense application potential in coastal management plans. In the present study, we simulated coastal morphological changes that occurred under normal and extreme wave conditions during a four-month winter monsoon period along a pocket beach at Yarada near Visakhapatnam city. We used Xbeach, a process-based numerical model to simulate the morphological changes by forcing the model with buoy observed wave parameters. Initial beach topography was generated from DGPS profiles surveyed in November 2014 at regular spatial intervals. Model simulated changes in the beach elevation due to accretion and erosion are validated by DGPS profiles re-surveyed in March 2015. During the four-month period, the net sediment transport at Yarada is generally southerly and becomes strong during high wave activity inducing erosion at the northern sector and accretion at the southern sector. The model has simulated the changes in elevation with a high degree of accuracy for the eroded northern sector, and with some disparity along the accreted southern sector. The swash and nearshore processes responsible for the coastal erosion were found to exist throughout the simulation period and intensified during the high wave condition. The paper highlights the importance of modelling studies for conceptual understanding of the beach response to normal and extreme conditions, and for identifying vulnerable sectors of a beach so that appropriate measures can be taken to prevent coastal erosion and loss of land. | |
| Paper No | 42 | Publication ID : 824 & Year : 2018 |
| Title | Modification of a linear regression-based multi-model super-ensemble technique and its application in forecasting of wave height during extreme weather conditions | |
| Authors | Majumder, S., Balakrishnan Nair, T.M., Sandhya, K.G., Remya, P.G., Sirisha, P. | |
| Source | Journal of Operational Oceanography, 11 (1), pp. 1-10. | |
| Abstract | In this study, we focus on the improvement of wave forecast of the Indian coastal region using a multi-model ensemble technique. Generally, a number of wave forecast are available for the same region from different wave models. The main objective of this study is to merge the wave forecasts available at Indian National Centre for Ocean Information Services from different wave models to obtain an improved wave forecast using a multi-model super-ensemble method [Krishnamurti et al. 1999. Improved weather and seasonal climate forecasts from multi-model super-ensemble. Science. 285:1548?1550] during extreme weather conditions and to modify Krishnamurthy?s techniques and validate with observations for a better prediction. Here, Multi-grid WAVEWATCH III, Simulating WAves Nearshore and MIKE 21 Spectral Waves are used for the generation of wave forecast. We propose a modification of Krishnamurthy?s linear regression-based ensemble model. By using both of these ensemble techniques, we perform a multi-model ensemble forecasting of significant wave height up to 24-h lead time in the Indian Ocean for three different cyclones (Nilofar, Hudhud and Phailin) and during the southwest monsoon. A comparison of ensemble predictions and individual model predictions with the actual observations showed generally satisfactory performance of the chosen tools. At the time of severe cyclones such as Hudhud and Phailin, our modified technique shows significantly better prediction than the linear regression-based ensemble technique. | |
| Paper No | 43 | Publication ID : 822 & Year : 2018 |
| Title | High Frequency Tail Characteristics in the Coastal Waters off Gopalpur, Northwest Bay of Bengal: A Nearshore Modelling Study | |
| Authors | Umesh, P.A., Bhaskaran, P.K., Sandhya, K.G., Balakrishnan Nair, T.M., | |
| Source | Pure and Applied Geophysics, 175(6), pp. 2351-2379. | |
| Abstract | Over the years, continued uncertainty amid - 4 and - 5 frequency exponent representation observed in the slope of the high-frequency tail of a wind-wave frequency spectrum is a major concern. To comprehend the nature of the high-frequency tail an effort has been made to assess the slope of the high-frequency tail with measured data recorded for 3 years off Gopalpur. The study demonstrates that the high-frequency slope of the spectra varied seasonally in the range of n = - 2.13 to - 3.48. The swell and wind sea parameters calculated by separation frequency method, shows that 64.6% of waves were dominant by swell and the rest 34.9% by sea annually. Single, double and multi-peaked spectra occur 12.23, 71.80 and 15.37% annually. To simulate wave spectra, the nested WAM-SWAN model is forced with ERA-Interim winds and 1D wave spectra comparisons, when performed, proved to be encouraging. From the comparisons of measured and theoretical spectra it is concluded that JONSWAP model could not describe the high-frequency tail of measured spectrum, as indicated by the very high Scatter Index ranging from 0.24 to 1.44. Whether there exists a correct slope for the high-frequency tail is still a question. Moreover, the philosophy of a unique slope at any coastal location remains uncertain for the wave modelling community. | |
| Paper No | 44 | Publication ID : 823 & Year : 2018 |
| Title | An 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. | |
| Abstract | Demand 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. | |
| Paper No | 45 | Publication ID : 819 & Year : 2018 |
| Title | An assessment on oil spill trajectory prediction: Case study on oil spill off Ennore Port | |
| Authors | Prasad, S.J., Balakrishnan Nair T.M., Rahaman H., Shenoi, S.S.C., Vijayalakshmi, T. | |
| Source | Journal of Earth System Science, 127,111. | |
| Abstract | A 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. | |
| Paper No | 46 | Publication ID : 817 & Year : 2017 |
| Title | An assessment on the impact of wind forcing on simulation and validation of wave spectra at coastal Puducherry, east coast of India | |
| Authors | Umesh, P.A., Bhaskaran, P.K., Sandhya, K.G., Balakrishnan Nair, T.M. | |
| Source | Ocean Engineering, 139, pp. 14-32. | |
| Abstract | In context to application of numerical ocean wave prediction, the validation of ocean wave spectra is a research topic of active interest. This study summarizes the results of validation performed with wave spectra using SWAN model off coastal Puducherry, located in the east coast of India. The impact of wind forcing from ECMWF ERA Interim winds and QuikSCAT-NCEP blended winds on resultant wave spectra has also been studied. The study signifies a good correlation between model wave spectra and in-situ observations. Impact of using the two wind field products in predicting extreme wave events was analyzed considering a storm case of November 2008. The numerical results revealed that the blended winds are more suitable in comparison with the ECMWF ERA Interim winds for modeling both normal and extreme events in the coastal Puducherry location. The results also show that wave model output is critically sensitive to the choice of the wind field product, such that the quality of the wind fields is reflected in the quality of the wave predictions. Based on model simulations it is concluded that blended winds generate more realistic wave fields in coastal location and can reproduce the growth and decay of waves in the real-time. | |
| Paper No | 47 | Publication ID : 818 & Year : 2017 |
| Title | An Online Tool for Predicting the Trajectory of the Spilled Marine Pollutant | |
| Authors | Prasad SJ, Balakrishnan Nair T.M, Krishna Prasad B, Kaviyazhahu K, Vijayalakshmi T. | |
| Source | International Journal of Latest Technology in Engineering, Management & Applied Science, 6 (8s), pp.115-120 | |
| Abstract | An online oil spill advisory (OOSA) system was developed for the first time in India, at Indian National Centre for Ocean Information Services (INCOIS) to serve the coastal community, regulatory authority and oil spill responders. It is achieved by triggering the oil spill trajectory model through web-interface. OOSA receives the inputs from the users in html feeds. Once after the submission of inputs, it automatically triggers the oil spill trajectory model and delivers the drift pattern of the pollutant at regular intervals, without the support from modeling community or officials of INCOIS. It is completely an automated set up. The system comprised the diagnostic mode of General National Oceanic and Atmospheric Administration (NOAA)Operational Modeling Environment(GNOME)in batch, which is triggered through web interface with the details such as, location, date& time of the spill, quantity, type of the oil spilled. The forecasted wind forcing and the current forcing obtained from our ocean state forecast (OSF)laboratory, were tuned and set in the prescribed format on daily operational basis. The generated trajectory is layered automatically on a web map, so that the zones that are likely to get affected are known. Trajectory predictions were made online for the oil spill occured at Sundarbans delta during 09.12.2014 to 15.12.2014. The oil slicks were noticed within 1.3 km from the predicted locations. This paper explains the simulation of an oil spill trajectory model for getting the drift pattern of the pollutant at Sundarbans delta, through web interface. The method of interpreting the results are also explained. This OOSA system is made available online, so that the users can utilize this during oil spills, mock drills and for preparing the local contingency plans. This system will also guide the oil spill responders, to manage and plan the response activities during the event of an actual or a hypothetical oil spill. | |
| Paper No | 48 | Publication ID : 816 & Year : 2017 |
| Title | Evaluation of wave forecast in the north Indian Ocean during extreme conditions and winter monsoon | |
| Authors | Sirisha, P., Sandhya, K.G., Balakrishnan Nair, T.M., Venkateswara Rao, B | |
| Source | Journal of Operational Oceanography, 10 (1), pp. 79-92. | |
| Abstract | The accuracy of the operational ocean state forecast system at ESSO-INCOIS during extreme events as well as calm conditions for a lead time of 24, 72 and 144 h is evaluated in this paper. Forecasted wave parameters (significant wave height, mean wave period and mean wave direction) are compared with in situ data for three cyclones (Sidr, Khai Muk and Nisha) that occurred in the Bay of Bengal (BoB). Forecasts obtained for 24 and 72 h showed good agreement with in situ data. Error statistics obtained during extreme events (SI??.75) suggests the good quality of the wave forecasts, which could be used for issuing high wave alerts. The two-dimensional energy spectra from the wave model during the Sidr cyclone period showed the capability of the model to simulate wind seas and swells even under cyclonic conditions. During winter monsoon, the error statistics obtained in the BoB suggests, good quality of 24- and 72-h wave forecasts. Thus the wave model is good at simulating the wave conditions for different wave height ranges and for a lead time of up to 72 h and hence a reliable tool for generating operational ocean state forecasts. | |
| Paper No | 49 | Publication ID : 813 & Year : 2016 |
| Title | Wave hindcast studies using SWAN nested in WAVEWATCH III - Comparison with measured nearshore buoy data off Karwar, eastern Arabian Sea | |
| Authors | Amrutha, M.M., Kumar, V.S., Sandhya, K.G., Balakrishnan Nair, T.M., Rathod, J.L. | |
| Source | Ocean Engineering, 119, pp. 114-124. | |
| Abstract | Waves in the nearshore waters (~15 m water-depth) of eastern Arabian Sea were simulated using SWAN nested in WAVEWATCH III (WW3) for the year 2014. The sensitivity of the numerical wave model WW3 towards different source term (ST) packages was tested. The performance of WW3 was evaluated with the measured deep water buoy data at 15.0000° N, 69.0000° E. Overall, the WW3 wave hindcast results using ST4 physics in deep water show a reasonable match (r=0.97 and SI=0.16) with the measured significant wave height (Hs). In deep water, a large overestimation (~23.7%) of mean wave period was observed using ST2 compared to ~8.2% using ST4. Komen et al. (1984) whitecapping formulation was found suitable based on the sensitivity studies of SWAN. Simulated Hs using nested SWAN model shows good correlation (r=0.96) with the nearshore measured data. During high sea state (Hs>2 m), an overestimation (~19.8% for ST2 and ~21.4% for ST4) and during low sea state (Hs<1 m), an underestimation (~16.1% for ST2 and ~31.5% for ST4) in mean wave period was observed in the nearshore. WW3 model forced by modified wind field (speed increased by 5%) during June and July resulted in a reduction in underestimation of Hs from 8.6% to 2.2%. | |
| Paper No | 50 | Publication ID : 814 & Year : 2016 |
| Title | Cyclone and monsoonal wave characteristics of northwestern Bay of Bengal: long-term observations and modeling | |
| Authors | Patra, S.K., Mishra, P., Mohanty, P.K., Pradhan, U.K., Panda, U.S., Ramana Murthy, M.V., Sanil Kumar, V., Balakrishnan Nair, T.M. | |
| Source | Natural Hazards, 82(2), pp. 1051-1073. | |
| Abstract | Long-term wave data play a crucial role in arriving the wave criteria for ports and harbors and shore protection structures. Seasonal and annual wave characteristics are studied based on wave data collected for the year 1994, 2008?2009 and 2013?2014 off Gopalpur, northwestern Bay of Bengal (BoB). The tropical cyclones ensued in BoB hit the coast frequently causing severe erosion due to extreme waves. The sea and swell waves are separated by wave steepness method, and the significant wave height (H s), zero-crossing period and mean wave direction are examined. The results indicate a distinct shift in sea direction by 90° during mid-November to mid-February compared with rest of the year. Throughout the year, predominant swell direction is 160°. In an annual cycle, the contribution of swells in wave height is slightly higher than that of the seas. Annual occurrences of single-, double- and multi-peaked spectra are 22, 40 and 38 %, respectively. The waves are predominant southerly during the southwest monsoon (June, July, August and September) and south-southeasterly for rest of the year, and the variations of wave parameters for three different years are trivial. The spectral wave model MIKE 21 is used to simulate wave characteristics using reanalyzed NCEP wind data for the period June 2008 to May 2009 which exhibits good agreement with a correlation coefficient (R) of 0.86 for H s. The design significant wave height of 7.1 m and 7.8 m is calculated for 10 and 100 years of return periods, respectively, by Weibull distribution. | |
| Paper No | 51 | Publication ID : 815 & Year : 2016 |
| Title | On the co-existence of high-energy low-frequency waves and locally-generated cyclone waves off the Indian east coast | |
| Authors | Sandhya, K.G., Remya, P.G. Balakrishnan Nair, T.M., Arun, N. | |
| Source | Ocean Engineering, 111, pp. 148-154. | |
| Abstract | The evolution of wave energy spectra obtained from a directional waverider buoy at the landfall location (Gopalpur) of the very severe cyclonic storm Phailin in the Bay of Bengal is discussed. The study reveals that swells generated approximately 8600 km away from the buoy location in the southern ocean (at 12 UTC on 3 October, 2013) travelled at a speed of 15.6 m/s and contributed to create a complex wave field at Gopalpur during cyclone Phailin. The rare co-existence of the low-frequency (0.055 Hz), high-energy (21.37 m^2/Hz) southern ocean swells with local cyclone-generated swells during the period (8?12 October, 2013) is reported. | |
| Paper No | 52 | Publication ID : 812 & Year : 2016 |
| Title | Ground-zero met?ocean observations and attenuation of wind energy during cyclonic storm Hudhud | |
| Authors | Harikumar, R., Balakrishnan Nair, T. M., Rao, B. M., Prasad, Rajendra, Ramakrishna Phani, P., Nagaraju, C., Ramesh Kumar, M., Jeyakumar, C., Shenoi, S.S.C., Nayak, Shailesh, | |
| Source | Current Sciences, 10 (12), pp. 2245-2252. | |
| Abstract | Ocean?met observations from INCOIS real-time automatic weather station on-board a ship RV Kaustubh served as strong ground truth for satellite-and model-derived forecasts during the very severe cyclonic storm Hudhud, which made a landfall at Visakha-patnam, 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/m 2 at Anakapalle (~25 km) compared to the ocean, and by 7022 W/m 2 at Chintapalle (~100 km inland) compared to Anakapalle). The present study reinforces the significance of having real-time near-shore ocean?met observations, and their operational usage for evaluation (assimilation) of (into) ocean?met forecast models in realtime. | |
| Paper No | 53 | Publication ID : 809 & Year : 2016 |
| Title | Teleconnection between the North Indian Ocean high swell events and meteorological conditions over the Southern Indian Ocean | |
| Authors | Remya, P. G., S. Vishnu, B. Praveen Kumar, Balakrishnan Nair, T.M., and B. Rohith, (2016) | |
| Source | Journal of Geophysical Research:Oceans, 121(10) pp. 7476-7494 | |
| Abstract | The link between North Indian Ocean (NIO) high swell events and the meteorological conditions over the Southern Indian Ocean (SIO) is explored in this article, using a combination of in situ measurements and model simulations for the year 2005. High waves, without any sign in the local winds, sometimes cause severe flooding events along the south-west coast of India, locally known as the Kallakkadal events and cause major societal problems along the coasts. In situ observations report 10 high swell events in NIO during 2005. Our study confirms that these events are caused by the swells propagating from south of 30°S. In all cases, 3?5 days prior to the high swell events in NIO, we observed a severe low-pressure system, called the Cut-Off Low (COL) in the Southern Ocean. These COLs are quasistationary in nature, providing strong (~25 ms-1) and long duration (~3 days) surface winds over a large fetch; essential conditions for the generation of long-period swells. The intense equator ward winds associated with COLs in the SIO trigger the generation of high waves, which propagate to NIO as swells. Furthermore, these swells cause high wave activity and sometimes Kallakkadal events along the NIO coastal regions, depending on the local topography, angle of incidence, and tidal conditions. Our study shows that such natural hazards along the NIO coasts can be forecasted at least 2 days in advance if the meteorological conditions of the SIO are properly monitored. | |
| Paper No | 54 | Publication ID : 810 & Year : 2016 |
| Title | A Coupled Numerical and Artificial Neural Network Model for Improving Location Specific Wave Forecast | |
| Authors | Londhe, S.N., Shah, S., Dixit, P.R., Balakrishnan Nair, T.M., Sirisha, P., Jain, R. | |
| Source | Applied Ocean Research, 59 pp. 483-491. | |
| Abstract | As more than a quarter of India?s population resides along the coastlines, it is of utmost importance to predict the significant wave height as accurately as possible to cater the needs of safe and secure life. Presently Indian National Centre for Ocean Information Services (INCOIS) provides wave height forecasts on regional as well as local level ranging from 3 hours to 7 days ahead using numerical models. It is evident from numerical model forecasts at specific locations that the significant wave heights are not predicted very accurately. The obvious reason behind this is the ?wind? used in these models as a forcing function is itself forecasted wind (ECMWF wind (European Centre for Medium-range Weather Forecasting)) and hence many times the forecasts, differ very largely from the actual observations. These models work on larger grid size making it as major impediment in employing them particularly for location specific forecasts even though they work reasonably well for regional level. Present work aims in reducing the error in numerical wave forecast made by INCOIS at four stations along Indian coastline. For this ?error? between forecasted and observed wave height at current and previous time steps was used as input to predict the error 24 hr ahead in advance using ANN since it has been effectively used for wave forecasting (univariate time series forecasting in general) since last two decades or so. This predicted error was then added or subtracted from numerical wave forecast to improve the prediction accuracy. It is observed that numerical model forecast improved considerably when the predicted error was added or subtracted from it. This hybrid approach will add to the usefulness of the wave forecasts given by INCOIS to its stake holders. The performance of improved wave heights is judged by correlation coefficient and other error measures like RMSE, MAE and CE. | |
| Paper No | 55 | Publication ID : 811 & Year : 2016 |
| Title | Neural-Network-Based Data Assimilation to Improve Numerical Ocean Wave Forecast | |
| Authors | Deshmukh A. N., Deo M. C., Bhaskaran P. K., Balakrishnan Nair T. M., Sandhya K.G. | |
| Source | IEEE Journal of Ocean Engineering, 99, | |
| Abstract | This paper demonstrates the skill level of a wavelet neural network in improving numerical ocean wave predictions of significant wave height (H 8 ) and peak wave period (T p ) having practical applications in operational centers. The study uses data of H 8 and T p for a coastal region off Puducherry located in the east coast of India, and obtained from a high-resolution wave model resulting from nesting of the SWAN model with the WW3 model. A wave rider buoy located off Puducherry provided data for a period of 25 months during the period from June 2007 until July 2009 used in this study. The time series of error between numerical and corresponding measured values was first constructed, and using a wavelet neural network, the errors were predicted for future time steps. The predicted errors when incorporated into the model values provided the updated prediction of H 8 and T p . The study signifies that numerical estimations could be significantly improved using this procedure. The results provide quite satisfactory predictions with a lead time varying from 3 to 24 h. The study points out that adequate training of the neural network is an essential prerequisite to obtain good performance and skill levels. A comparison between the suggested prediction method with the standalone neural network model trained with measured data off Puducherry showed that the former approach is preferred over the latter in obtaining a sustained prediction performance. | |
| Paper No | 56 | Publication ID : 775 & Year : 2015 |
| Title | Ocean State Forecast Along Ship-routes: Evaluation Using ESSO-INCOIS Real-time Ship-Mounted Wave Height Meter and Satellite Observations | |
| Authors | 23. Harikumar, R., N. Hithin, T. Balakrishnan Nair, P. Sirisha, B. Krishna Prasad, C.Jeyakumar, S. Nayak, and S. Shenoi | |
| Source | Journal of Atmospheric and Oceanic Technology, 32, pp. 2211-2222. | |
| Abstract | -- | |
| Paper No | 57 | Publication ID : 771 & Year : 2015 |
| Title | Analysis of SARAL/AltiKa Wind and Wave over Indian Ocean and its Real-time Application in Wave Forecasting System at ISRO | |
| Authors | 27. Bhowmick, S.A., Modi, R., Sandhya, K.G., Seemanth, M., Balakrishnan Nair, T.M., Kumar, R., Sharma, R. | |
| Source | Marine Geodesy, 38 pp. 396-408 | |
| Abstract | -- | |
| Paper No | 58 | Publication ID : 772 & Year : 2015 |
| Title | Coastal sea level response to the tropical cyclonic forcing in the northern Indian Ocean. | |
| Authors | 26. Mehra, P., Soumya, M., Vethamony, P., Vijaykumar, K., Balakrishnan Nair, T.M., Agarvadekar, Y., Jyoti, K., Sudheesh, K., Luis, R., Lobo, S. and Harmalkar, B | |
| Source | Ocean Science, 11. pp. 159-173. | |
| Abstract | -- | |
| Paper No | 59 | Publication ID : 773 & Year : 2015 |
| Title | "Validation and Intercomparison of SARAL/AltiKa and PISTACH-Derived Coastal Wave Heights Using In-Situ Measurements," Selected Topics in Applied Earth Observations and Remote Sensing | |
| Authors | 25. Hithin, N.K.; Remya, P.G.; Balakrishnan Nair, T.M.; Harikumar, R.; Kumar, R.; Nayak, S | |
| Source | IEEE Journal, Vol no.99, pp.1,10 | |
| Abstract | -- | |
| Paper No | 60 | Publication ID : 774 & Year : 2015 |
| Title | Numerical simulation and observations of very severe cyclone generated surface wave fields in the north Indian Ocean | |
| Authors | 24. Sirisha, P., Remya, P.G., Balakrishnan Nair, T.M., Rao, B Venkateswara | |
| Source | Journal of Earth System Science, pp. 1-13. | |
| Abstract | -- | |
| Paper No | 61 | Publication ID : 350 & Year : 2014 |
| Title | Validation of altimeter-derived significant wave heights in the Northern Indian Ocean during monsoon and extreme conditions | |
| Authors | Sabique, L., Balakrishnan Nair, T. M., Srinivas, K., Shailesh Nayak | |
| Source | Marine Geodesy (under Review). | |
| Abstract | -- | |
| Paper No | 62 | Publication ID : 507 & Year : 2014 |
| Title | Spectral wave characteristics off Gangavaram, Bay of Bengal | |
| Authors | Kumar, V.S., Dubhashi, K.K., Balakrishnan Nair, T.M., | |
| Source | Journal of Oceanography, pp. 1-15. Article in Press. | |
| Abstract | Spectral wave characteristics were studied based on waves measured for 1 year during 2010 off Gangavaram, Bay of Bengal. Maximum wave height of 5.2 m was observed on 19 May 2010 due to the influence of cyclonic storm LAILA. The wave spectrum was single-peaked during 57 % of the time and the double-peaked spectrum observed was mainly swell-dominated. Low-frequency waves (0.05-0.15 Hz) were predominantly from 150° to 180°, whereas high-frequency waves (>0.15 Hz) during November-January were mainly from 90° to 120°, and during July and August from 180° to 210°. Annual average significant wave height was similar to the value (1 m) observed in the eastern Arabian Sea. | |
| Paper No | 63 | Publication ID : 509 & Year : 2014 |
| Title | Wave forecasting and monitoring during very severe cyclone Phailin in the Bay of Bengal | |
| Authors | 3. Balakrishnan Nair, T.M., Remya, P.G., Harikumar, R., Sandhya, K.G., Sirisha, P., Srinivas, K., Nagaraju, C., Nherakko, A., Krishna Prasad, B., Jeyakumar, C., Kaviyazhahu, K., Hithin, N. K., Kumari, Rakhi., Sanil Kumar, V., Ramesh Kumar, M., Shenoi, S.S.C., Nayak, Shailesh., | |
| Source | Current Science,106 (Article in press) | |
| Abstract | Wave 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 Indian Ocean swells with a peak period of 20¿22 s
hitting Gopalpur coast along with the cyclone generated waves. | |
| Paper No | 64 | Publication ID : 508 & Year : 2014 |
| Title | Wave forecasting system for operational use and its validation at coastal Puducherry, east coast of India | |
| Authors | Sandhya, K.G., Balakrishnan Nair, T.M., Bhaskaran, P.K., Sabique, L., Arun, N., Jeykumar, K. | |
| Source | Ocean Engineering, (Article in Press) | |
| Abstract | An incredible demand for coastal sea-state forecast in recent years has led to development and implementation of wave forecasting system in operational centers, having wide practical applications relevant to marine industry. The wave forecasting system takes advantage of parametric techniques, by nesting global ocean wave models to coastal and near-shore high-resolution wave models. The Indian National Centre for Ocean Information Services (INCOIS) at Hyderabad has a mandate for operational marine weather forecast services that envisages integration and coupling state-of-the-art weather models for operational oceanographic needs. In the present study, two state-of-art wave models viz; WAVEWATCH III (WW3) and Simulating WAves Nearshore (SWAN) are nested and forced with French Research Institute for Exploitation of the Sea/Laboratory of Oceanography From Space (IFREMER/CERSAT) blended surface winds. The objective is to investigate wave evolution at a coastal location off Puducherry in the east coast of India. To evaluate model performance, a detailed validation study is performed by comparing model-simulated wave parameters and wave spectra with corresponding in-situ wave rider buoy observations for four prominent seasons viz; northeast monsoon, southwest monsoon, pre- and post-monsoon. The study signifies applicability of nested wave model for operational use during normal weather condition at coastal Puducherry | |
| Paper No | 65 | Publication ID : 516 & Year : 2013 |
| Title | Influence of winds on temporally varying short and long period gravity waves in the near shore regions of the eastern Arabian Sea | |
| Authors | Glejin,J., Sanil Kumar,V., Balakrishnan Nair, T.M., Singh,J., | |
| Source | Ocean Science, 9, pp.343¿353 | |
| Abstract | Wave data collected off Ratnagiri, west coast of India, during 1 May 2010 to 30 April 2012 are used in this study. Seasonal and annual variations in wave data controlled by the local wind system such as sea breeze and land breeze, and remote wind generated long period waves are also studied. The role of sea breeze on the sea state during pre-and postmonsoon seasons is studied and it is found that the maximum wave height is observed at 15:00 UTC during the premonsoon season, with an estimated difference in time lag of 1-2 h in maximum wave height between premonsoon and postmonsoon seasons. Observed waves are classified in to (i) short waves (Tp <8 s), (ii) intermediate waves (8 < Tp< 13 s), and (iii) long waves (period (Tp) and the percentages of occurrence of each category are estimated. Long period waves are observed mainly during the pre-and the postmonsoon seasons. During the southwest monsoon period, the waves with period > 13 s are a minimum. An event during 2011 is identified as swells propagated from the Southern Ocean with an estimated travelling time of 5-6 days. The swells reaching the Arabian Sea from the south Indian Ocean and Southern Ocean, due to storms during the pre-and postmonsoon periods, modify the near surface winds due to higher phase wave celerity than the wind speed. Estimation of inverse wave age using large-scale winds such as NCEP (National Centers for Environmental Prediction) reflects the presence of cyclonic activity during pre-and postmonsoon seasons but not the effect of the local sea breeze/land breeze wind system. | |
| Paper No | 66 | Publication ID : 515 & Year : 2013 |
| Title | Comparison of Grid Averaged Altimeter and Buoy Significant Wave Heights in the Northern Indian Ocean | |
| Authors | Sabique, L., Balakrishnan Nair, T.M., Srinivas, K., Nayak, N.S. | |
| Source | Marine Geodesy, 36 (1), pp. 72-85 | |
| Abstract | A quantitative comparison of the collocated inter-annual significant wave height (SWH) data collected between 2006 and 2009 from buoys and altimeters at nine buoy locations (total n = 2241) in the Northern Indian Ocean is attempted for assessing the validity of daily averaged gridded altimeter significant wave height (ASWH) provided by AVISO for operational use. ASWH is underestimated by 0.20 m, the root-mean-square error (RMSE) is less than 0.30 m, the Scatter Index is less than 20%, and the correlation coefficient is greater than 0.90. Further, at three locations, the examination of the above statistics showed that the bias and RMSE is high during the southwest monsoon season compared with the Northeast monsoon. Scatter Index showed only slight variation (14-18%) for different ranges of SWH. The response of the daily average gridded ASWH data during extreme conditions (cyclones) in the vicinity of the buoy locations is poor at all compared buoy locations. The gridded ASWH from different satellite missions provided by AVISO can be used for basin scale validation experiments of the wave model and for climatological studies in the Indian Ocean, except during cyclone conditions | |
| Paper No | 67 | Publication ID : 513 & Year : 2013 |
| Title | Wave power potential at a few shallow water locations around Indian coast | |
| Authors | Sanil Kumar V., Dubhashi, K.K. Balakrishnan Nair, T.M., Singh, J. | |
| Source | Current Science, 104 (9), | |
| Abstract | Variations in nearshore wave power at four shallowwater locations along the east and west coast of India are examined based on the measured wave data for one-year period. The study shows that along the west coast of India, 83¿85% of the annual wave power is during the summer monsoon period (June¿September), whereas at Visakhapatnam (on the east coast), 55% of the annual wave power is during the summer monsoon period. Along Puducherry coast in the east, wave power is relatively less with maximum value of 31.8 kW m¿1. The average wave power during the summer monsoon is high (15.5¿19.3 kW m¿1) along the west coast of India. The study shows that the annual average wave power (1.8¿7.6 kW m¿1) along the locations studied is much lower than that available for temperate zones. | |
| Paper No | 68 | Publication ID : 599 & Year : 2013 |
| Title | Waves off Puducherry, Bay of Bengal, during cyclone THANE | |
| Authors | Sanil Kumar, V., Johnson, G., Dubhashi, K.K., Balakrishnan Nair, T.M., | |
| Source | Natural Hazards, 69 (1), pp. 509-522. | |
| Abstract | We studied the wave characteristics during the very severe cyclonic storm THANE which crossed the east coast of India between Puducherry and Cuddalore based on waves measured at a location in Bay of Bengal at 14 m water depth. Objective of the paper is to document the highest wave height measured in the nearshore waters of east coast of India. On 29 December 2011, cyclone passed within 77-315 km of the wave measurement location with maximum wind speed of 46.3 m/s (90 knots) and resulted in maximum wave height of 8.1 m. Maximum wave height recorded is 0.54 times the water depth, and the ratio of crest height to wave height of the highest wave recorded is 0.65. Maximum value of significant wave height estimated using the parametric wave model for deep-water conditions is 6.4 m, whereas the measured value is 6 m indicating that parametric wave model estimates the wave height reasonably well (within 8 % error) during the cyclone period | |
| Paper No | 69 | Publication ID : 612 & Year : 2013 |
| Title | Influence of winds on temporally varying short and long period gravity waves in the near shore regions of the eastern Arabian Sea | |
| Authors | Glejin, J., Sanil Kumar, V., Balakrishnan Nair, T.M., Singh, J. | |
| Source | Ocean Science, 9 (2), pp. 343-353 | |
| Abstract | Wave data collected off Ratnagiri, west coast of India, during 1 May 2010 to 30 April 2012 are used in this study. Seasonal and annual variations in wave data controlled by the local wind system such as sea breeze and land breeze, and remote wind generated long period waves are also studied. The role of sea breeze on the sea state during pre-and postmonsoon seasons is studied and it is found that the maximum wave height is observed at 15:00 UTC during the premonsoon season, with an estimated difference in time lag of 1-2 h in maximum wave height between premonsoon and postmonsoon seasons. Observed waves are classified in to (i) short waves (Tp <8 s), (ii) intermediate waves (8 < Tp< 13 s), and (iii) long waves (period (Tp) and the percentages of occurrence of each category are estimated. Long period waves are observed mainly during the pre-and the postmonsoon seasons. During the southwest monsoon period, the waves with period > 13 s are a minimum. An event during 2011 is identified as swells propagated from the Southern Ocean with an estimated travelling time of 5-6 days. The swells reaching the Arabian Sea from the south Indian Ocean and Southern Ocean, due to storms during the pre-and postmonsoon periods, modify the near surface winds due to higher phase wave celerity than the wind speed. Estimation of inverse wave age using large-scale winds such as NCEP (National Centers for Environmental Prediction) reflects the presence of cyclonic activity during pre-and postmonsoon seasons but not the effect of the local sea breeze/land breeze wind system. | |
| Paper No | 70 | Publication ID : 510 & Year : 2013 |
| Title | Performance of the Ocean State Forecast system at Indian National Centre for Ocean Information Services | |
| Authors | Balakrishnan Nair, T.M., Sirisha, P., Sandhya, K.G., Srinivas, K., Sanil Kumar, V., Sabique, L., Nherakkol, A., Krishna Prasad, B., Kumari, R., Jeyakumar, C., Kaviyazhahu, K., Ramesh Kumar, M., Harikumar, R., Shenoi, S.S.C., Nayak, S. | |
| Source | Current Science,105(2), pp.175-181 | |
| Abstract | The 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. Spec-tral wave model is used for forecasting the wave fields generated by the tropical cyclone and vali-dation 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 | |
| Paper No | 71 | Publication ID : 538 & Year : 2013 |
| Title | Monsoon and cyclone induced wave climate over the near shore waters off Puduchery, South Western Bay of Bengal | |
| Authors | Glejin J., Sanil Kumar V,. Balakrishnan Nair, T.M., | |
| Source | Ocean Engineering, 72, pp. 277¿286 | |
| Abstract | Seasonal and annual variations in wave characteristics are studied based on measurements during 2009-2011 using wave rider buoy. Presence of swells generated by the south Indian Ocean cyclones are found over the south western Bay of Bengal during pre-monsoon season. Maximum significant wave height is measured 6 m during Thane cyclone in December, 2011. Long period waves are observed mostly during the summer (SW) monsoon and are negligible in the winter (NE) monsoon period. Short period waves dominate (63%) the wave climate during the NE monsoon. Wave spectra during the SW monsoon are multi peaked whereas during the post monsoon season single peaked spectra are found. Single peaked spectra observed during SW monsoon of 2011 coincides with the presence of positive Indian Ocean Dipole. Waves during the pre monsoon and SW monsoon season are influenced by sea breeze. Analysis indicates that directional width is minimum for waves from the NE since they are wind waves and maximum for waves from SE since they are swells. Study indicates that wave climate of the south western Bay of Bengal is in contrast to that in eastern Arabian Sea during the SW monsoon | |
| Paper No | 72 | Publication ID : 351 & Year : 2011 |
| Title | Oxycline variability in the central Arabian Sea: An Argo-Oxygen Study | |
| Authors | Satya Prakash, T.M. Balakrishnan Nair, T.V.S. Udaya Bhaskar and Prince Prakash | |
| Source | Journal of Sea Research (under Review). | |
| Abstract | -- | |
| Paper No | 73 | Publication ID : 339 & Year : 2011 |
| Title | Validation of Mixed Layer Depth Derived using Satellite Data and Wave Model with In-Situ Observations | |
| Authors | K. Annapurnaiah, T.V.S. Udaya Bhaskar, T.M. Balakrishnan Nair and Satyabana Das | |
| Source | International Journal of Oceans and Oceanography, 5 (1) 23-34. | |
| Abstract | The seasonal variability of mixed layer depth (MLD) in the northern Indian
Ocean (40°E ¿ 105°E and 2°S ¿ 30°N) was estimated from empirical relation using wind speed from QuickSCAT and wave parameters (significant wave height and wave period) obtained from MIKE-21 SW model. MLD estimated from this empirical model is compared with MLD estimated from Argo temperature and salinity profiles. The extent of mechanical mixing with in the top layer of water by local wind and wave activity is studied using this simple statistical predictive method. The correlation coefficient (R) between in-situ MLD and model MLD is found to be 0.52, 0.67, 0.34 and 0.04 for premonsoon, southwest monsoon, post-monsoon and northeast monsoon respectively. By and large, the proposed empirical model could be used to simulate the MLD and its trend by considering wind and wave parameters, and can act as a useful tool at times when there are sparse in-situ observations.
| |
| Paper No | 74 | Publication ID : 352 & Year : 2011 |
| Title | Monthly variations of beach morphology and sediment characteristics along Visakhapatnam to Bheemunipatnam Coast, Andhra Pradesh | |
| Authors | K. S. N. Reddy, K. N.V.V.Murthy, K. Durga Prasad, T. N. Lakshmi, K. Gopala Reddy and T. M. Balakrishnan Nair | |
| Source | Indian Journal of Geo-marine Sciences (under Review). | |
| Abstract | -- | |
| Paper No | 75 | Publication ID : 353 & Year : 2011 |
| Title | Preliminary Inter-comparison and Validation of the NCMRWF and ECMWF data over Indian Ocean and Southern Ocean using data from the INCOIS Real-time ship-mounted Automatic Weather Station (IRAWS) programme (communicating). | |
| Authors | R. Harikumar, T.M. Balakrishnan Nair, G.S. Bhat, Shilesh Nayak, S.S.C. Shenoi and Venkat Shesu Reddem | |
| Source | -- | |
| Abstract | -- | |
| Paper No | 76 | Publication ID : 354 & Year : 2011 |
| Title | A multi-grid WAVEWATCH III operational model for Indian ocean - Model setup and validation (communicating). | |
| Authors | Sabique, L. Balakrishnan Nair, T. M., Shenoi S. S. C and Shailesh Nayak | |
| Source | -- | |
| Abstract | -- | |
| Paper No | 77 | Publication ID : 355 & Year : 2011 |
| Title | Operational Wave Forecasting during NE monsoon in Indian Ocean using a finite element wave model. (Communicating). | |
| Authors | Sirisha P, Sandhya K. G. Balakrishnan Nair. T. M., Annapurnaiah. K, Shailesh Nayak and Sanil Kumar | |
| Source | -- | |
| Abstract | -- | |
| Paper No | 78 | Publication ID : 340 & Year : 2010 |
| Title | Wind sea and Swell Characteristics off East coast of India During Southwest Monsoon | |
| Authors | Suresh, RRV and Annapurnaiah, K and Reddy, KG and Lakshmi, TN and Balakrishnan Nair, TM | |
| Source | International Journal of Oceans and Oceanography, 4 (1) 35-44 | |
| Abstract | The waves along the east coast of India during south-west monsoon have great importance due to the prevailing rough conditions. Significant Wave height (Hs) and other wave conditions are measured at a location of 20m water depth off east coast of India during south-west monsoon 2009. Wind-sea (Hsw) and swell (Hss) components are separated from the measured data, to look into the characteristics of the waves at the measured location. It is observed that the sea-state is dominated by swells arriving from south-east (SE) to south (S). The maximum measured Hs is 2.62 m. Good positive correlation of 0.84 is observed between Hss and Hs. The contribution of Hss to Hs is 63.2 % and remaining is due to Hsw. Wave age shows the presence of young sea with significant occurrence of swell. The spectral band width parameter (e), calculated from the measured data indicates that the wave components cover wide range of frequencies. The high values of spectral narrowness parameter (v) and peakedness parameter (Qp) are observed during the study period. | |
| Paper No | 79 | Publication ID : 341 & Year : 2010 |
| Title | Simulation of coastal winds along the central west coast of India using the MM5 mesoscale model | |
| Authors | Pushpadas, Dhanya and Vethamony, P and Sudheesh, K and George, Smitha and Babu, MT and Balakrishnan Nair, TM | |
| Source | Meteorology and Atmospheric Physics, 109 (3-4) 91-106 0.872 | |
| Abstract | A high-resolution mesoscale numerical model (MM5) has been used to study the coastal atmospheric circulation of the central west coast of India, and Goa in particular. The model is employed with three nested domains. The innermost domain of 3 km mesh covers Goa and the surrounding region. Simulations have been carried out for three different seasons¿northeast (NE) monsoon, transition period and southwest (SW) monsoon with appropriate physics options to understand the coastal wind system. The simulated wind speed and direction match well with the observations. The model winds show the presence of a sea breeze during the NE monsoon season and transition period, and its absence during the SW monsoon season. In the winter period, the synoptic flow is northeasterly (offshore) and it weakens the sea breeze (onshore flow) resulting in less diurnal variation, while during the transition period, the synoptic flow is onshore and it intensifies the sea breeze. During the northeast monsoon at an altitude of above 750 m, the wind direction reverses, and this is the upper return current, indicating the vertical extent of the sea breeze. A well-developed land sea breeze circulation occurs during the transition period, with vertical extension of 300 and 1,100 m, respectively. | |
| Paper No | 80 | Publication ID : 342 & Year : 2010 |
| Title | Waves in shallow water off west coast of India during the onset of summer monsoon | |
| Authors | Sanil Kumar, V and Philip, C Sajiv and Balakrishnan Nair, TM | |
| Source | Annales Geophysicae, 28 p.817-824 | |
| Abstract | The wave growth characteristics during the onset of summer monsoon in a swell dominated open ocean at a location off the west coast of India at 14 m water depth are studied. 67% of the measured waves are due to the swells arriving from south and south-west and the balance was due to the seas from south-west to north-west. Wave age of the measured data indicates that the measured waves are young sea with presence of swells. Even when the wind speed reduced to less than 3 m/s, significant wave height more than 2 m is present due to the swells in the Arabian Sea. The maximum wave height increased from 2 to 8 m within 60 h. The mean wave directions at the high frequencies align with the westerly wind direction and gradually shift to south-westerly swell direction at low frequencies during the wave growth. The strong westerly winds present between longitude 72° and 72.5° at latitude 12.5° has created the high waves (Hm0 upto 5.65 m) during the measurement period. | |
| Paper No | 81 | Publication ID : 343 & Year : 2009 |
| Title | Forecasting the oceans: The oceanographic services from the Indian National Centre for Ocean Information Services | |
| Authors | S.S.C. Shenoi, T. Srinivasa Kumar, Balakrishnan Nair, TM E. Pattabhi Rama Rao, M. Nagaraja Kumar, Ch. Patanjali Kumar, E. Uma Devi, K.G. Sandhya and K. Annapuraiaha | |
| Source | Mausam, p.225-238 | |
| Abstract | Ministry of Earth Sciences (formerly Department of Ocean Development) established Indian National Centre for Ocean Information Services in Hyderabad to provide the best possible ocean information and advisory services to the society, industry, government and scientific community through sustained ocean observations
and constant improvements through systematic and focused research In pursuit of this goal, INCOIS is engaged in providing the information and value-added services on the oceanic realm to the coastal community, maritime boards, industry, etc. In this 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.
| |
| Paper No | 82 | Publication ID : 344 & Year : 2008 |
| Title | WFS for Indian seas, an INCOIS experience (2008) | |
| Authors | Balakrishnan Nair T. M, Annapurnaiah K, Satyabana Das, Kali Prasad and Shailesh Nayak | |
| Source | Geospatial Today, 22-25 | |
| Abstract | -- | |
| Paper No | 83 | Publication ID : 345 & Year : 2006 |
| Title | Monsoon control on trace metal fluxes in the deep Arabian Sea | |
| Authors | Balakrishnan Nair, TM | |
| Source | Journal of Earth System Science 115 (4) p.461- 472 | |
| Abstract | Particulate fluxes of aluminium, iron, magnesium and titanium were measured using six time-series sediment traps deployed in the eastern, central and western Arabian Sea. Annual Al fluxes at shallow and deep trap depths were 0.47 and 0.46 g m-2 in the western Arabian Sea, and 0.33 and 0.47 g m-2 in the eastern Arabian Sea. There is a difference of about 0.9-1.8 g m-2 y-1 in the lithogenic fluxes determined analytically (residue remaining after leaching out all biogenic particles) and estimated from the Al fluxes in the western Arabian Sea. This arises due to higher fluxes of Mg (as dolomite) in the western Arabian Sea (6-11 times higher than the eastern Arabian Sea). The estimated dolomite fluxes at the western Arabian Sea site range from 0.9 to 1.35 g m-2 y-1. Fe fluxes in the Arabian Sea were less than that of the reported atmospheric fluxes without any evidence for the presence of labile fraction/excess of Fe in the settling particles. More than 75% of Al, Fe, Ti and Mg fluxes occurred during the southwest (SW) monsoon in the western Arabian Sea. In the eastern Arabian Sea, peak Al, Fe, Mg and Ti fluxes were recorded during both the northeast (NE) and SW monsoons. During the SW monsoon, there exists a time lag of around one month between the increases in lithogenic and dolomite fluxes. Total lithogenic fluxes increase when the southern branch of dust bearing northwesterlies is dragged by the SW monsoon winds to the trap locations. However, the dolomite fluxes increase only when the northern branch of the northwesterlies (which carries a huge amount of dolomite accounting 60% of the total dust load) is dragged, from further north, by SW monsoon winds. The potential for the use of Mg/Fe ratio as a paleo-monsoonal proxy is examined. | |
| Paper No | 84 | Publication ID : 346 & Year : 2005 |
| Title | Settling barium fluxes in the Arabian Sea: Critical evaluation of relationship with export production | |
| Authors | Balakrishnan Nair, TM; Ittekkot, L; Shankar, L;Guptha, MVS | |
| Source | Deep Sea Research Part II 52 (14-15) p.1930-1946. | |
| Abstract | Time series measurement of biogenic and barium fluxes was made using nine sediment traps deployed in the western, central and eastern part of the Arabian Sea with the objective of evaluating barium as a proxy for surface ocean productivity. Our observations show a strong linear correlation between Ba excess fluxes and biogenic opal and organic carbon (Corg) fluxes, indicating a biogenic origin of particulate Ba. However, the correlation between biogenic and Baexcess fluxes is remarkably strong in areas of uniform productivity like the central Arabian Sea, when compared to regions of episodic productivity. The processes that precipitate particulate Ba appear to be less active during periods of high biogenic flux. A large discrepancy is documented between the export flux calculated from the barium-based algorithm [Francois, R., Honjo, S., Manganini, S.J., Ravizza, G.E., 1995. Biogenic barium fluxes to the deep sea: implications for paleoproductivity reconstruction. Global Biogeochemical Cycles 9, 289-303] and from Corg fluxes [Sarnthein, M., Winn, K., Duplessy, J.C., Fontugne, M.R., 1988. Global variations of surface ocean productivity in low and mid latitudes: influence on CO2 reservoirs of the deep ocean and atmosphere during the last 21,000 years. Paleoceanography 3, 361-399] at different depths. However, ∼35% increase in Ba fluxes and a concomitant increase in Ba/Corg ratios are documented between 919 and 2002 m water depth in the western Arabian Sea. This increase may be due either to barite formation within the fecal pellets of mesozooplankton thriving at deeper levels or to scavenging of Ba by Mn oxyhydroxides. Manganese oxyhydroxides seem to act as a prominent scavenging phase for particulate Ba when the Mnexcess content in the settling particles exceeds ∼200 ppm, especially in the western and central Arabian Sea where in situ precipitation of Mn oxides is reported. The estimated preservation efficiency of Ba in the Arabian Sea sediments ranges between 50% and 61%. This is two-fold higher than the global average, suggesting that Ba may be a promising proxy for paleoproductivity estimation. | |
| Paper No | 85 | Publication ID : 347 & Year : 2000 |
| Title | Lithogenic and Associated Elemental -Fluxes in the Arabian Sea and Some Paleomonsoonal Implications | |
| Authors | Balakrishnan Nair. T. M | |
| Source | Journal of Indian Association of Sedimentologists. | |
| Abstract | -- | |
| Paper No | 86 | Publication ID : 349 & Year : 1999 |
| Title | Factors Controlling Vertical Flux of Particles in the Arabian Sea | |
| Authors | Balakrishnan Nair,.T. M., Ramaswamy, V., Parthiban, G. and Shankar, R. | |
| Source | Journal of Geological Society of India, 54, 369-378. | |
| Abstract | Particle fluxes were measured using six time-series sediment traps at three sites in the western (16°20' N; 60°30' E), central (14°31' N; 64°46' E) and eastern (15°31' N; 68°43' E) Arabian Sea. Trap deployment depths were between 900 and 3000 m and collection period was from December 1992 to February 1994. Annual particle fluxes showed an east-west trend with minimum fluxes (22.25 g m-2) in the eastern Arabian Sea and maximum fluxes (69.81 g m-2) in the western Arabian Sea. Carbonates, contributed mainly by foraminifers and coccolithophorids, are the dominant component in all the traps. Opal fluxes were maximum in the western Arabian Sea. At all the locations, lithogenic percentages increased with depth whereas organic carbon percentages decreased. Particle flux patterns show a strong seasonality with peak fluxes during the southwest (SW) monsoon (June to September). Relatively high fluxes were also observed during the northeast (NE) monsoon (December to February). In the western Arabian Sea, particle fluxes are dominated mainly by carbonates during the early SW monsoon but by biogenic silica during the late SW monsoon. The increase in particle fluxes during the early SW monsoon is related to variations in the mixed layer depth which, in turn, is controlled by the strength of the Findlater Jet and the curl of the wind stress. The increase in biogenic silica fluxes during the late SW monsoon is related to the advection of nutrient-rich water from the Oman and Somali upwelling areas. In the eastern Arabian Sea, particle fluxes are high during the NE monsoon due to the effects of winter cooling. | |
| Paper No | 87 | Publication ID : 348 & Year : 1999 |
| Title | Seasonal and spatial variation in settling manganese fluxes in the northern Arabian Sea | |
| Authors | Balakrishnan Nair, T. M., Ramaswamy, V., Shankar, R. and Ittekkot, V. | |
| Source | Deep-Sea Research I, 46 1827-1839. | |
| Abstract | Particulate manganese Mn fluxes measured with six time series sediment traps showed that the annual settling fluxes were 3-6 times higher in the west compared to those in the east and central Arabian Sea. Annual detrital Mn Mndt flux was nearly the same in the eastern and western Arabian Sea, but excess Mn Mnex fluxes were much higher 4 times in the western Arabian Sea. Atmospheric inputs cannot account for these high-Mn fluxes. Central and eastern Arabian Sea traps are overlain by a thick and intense denitrification layer, which may cause reductive dissolution of Mn oxides from settling particles and consequently low Mnex fluxes. As the exchange of intermediate waters between the Arabian Sea and the rest of the Indian Ocean is confined largely to the western Arabian Sea, relatively more toxic and dynamic conditions prevail in this region. Increased oxidizing conditions coupled with higher inputs of dissolved Mn through intermediate and surface advective processes might have led to in situ oxidation of Mn, thus resulting in higher vertical fluxes of Mnex. Mnex fluxes in traps at ~ 1000 m depth exhibited seasonal variability with a minimum during the winter monsoon January-February and maximum during the pre- and early- south-west monsoon March-June. This variation is correlated with water mass movements and bacterial abundance observed during the Joint Global Ocean Flux Study JGOFS. The possible involvement of bacteria and the microbial loop is suggested for the concentration and vertical transport of excess Mn. | |