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 : 580 & Year : null |
| Title | null | |
| Authors | null | |
| Source | null | |
| Abstract | null | |
| Paper No | 2 | Publication ID : 767 & Year : 2019 |
| Title | Discernment of near Oceanic Precipitating Clouds into Convective or Stratiform based on Z-R Model over an Asian Monsoon Tropical site | |
| Authors | R. Harikumar | |
| Source | Meteorology and Atmospheric Physics (Springer), DOI: 10.1007/s00703-019-00696-3 | |
| Abstract | Type of precipitating near-oceanic clouds are found out and tracked by inferring it from the near-surface empirical relationships of Rainfall rate and Radar reflectivity (Z-R), which are established using a Micro Rain Radar (MRR) and a Joss-Waldvogel Disdrometer at a tropical coastal station Thiruvananthapuram (8.5º N, 76.9ºE), an Asian monsoon near-oceanic site, almost at the tip of Indian peninsula. It is also found out from the vertical variation of Z-R relation that coalescence is prevalent than breakup, as a result of the collision of rain drops, along with evaporation of smaller drops existed as the rain comes down. The DSD/radar-reflectivity/rainfall data from the MRR, Disdrometer and manual rain gauge were inter-compared, and found to have good agreement. The MRR radar Bright Band signature, which is an indication of melting height, is validated using the Wyoming radiosonde data. The whole rain events from March to September 2007 were separated in to Bright Band (BB) and Non- Bright Band (NBB) cases. The variation of Z with R for all the heights (upto 6000m with 200m intervals) is modeled with a function Z=ARb corresponding to both BB and NBB cases; separately for pre-monsoon and southwest monsoon seasons. And, it is realised that there are two distinct fits with different slopes and intercepts are existed for Z-R relations corresponding to BB and NBB cases throughout aloft during both the seasons. It is found out that the presence of Radar BB or NBB signatures, with corresponding distinct Z-R relations even just at near-surface, which can be used as a proxy for discerning the clouds into stratiform or convective respectively. | |
| Paper No | 3 | Publication ID : 578 & Year : 2016 |
| Title | Ground-zero metâ¿¿ocean observations and attenuation of wind energy during cyclonic storm Hudhud | |
| Authors | R. Harikumar, T.M. Balakrishnan Nair, B.M. Rao, P. Rajendra Prasad, P. Ramakrishna Phani, C. Nagaraju, M. Ramesh Kumar, C. Jeyakumar, S.S.C. Shenoi and Shailesh Nayak | |
| Source | CURRENT SCIENCE, VOL. 110, NO. 12, 25 JUNE 2016 | |
| Abstract | Oceanâ¿¿met observations from INCOIS real-time automatic
weather station on-board a ship RV Kaustubh
served as strong ground truth for satellite- and modelderived
forecasts during the very severe cyclonic
storm Hudhud, which made a landfall at Visakhapatnam,
India. The ship recorded maximum wind
speed of 204 km/h (with a minimum central pressure
of 945 hPa), which is the highest (lowest) ever instrumentally
recorded value at a location on the Indian
coastline during any cyclone. Though the global model
forecasts of wind fields have shown good agreement
inland, they failed in representing the reality along the
coasts. Variation in wind energy from ocean towards
inland suggests that it is attenuated exponentially
inland (the maximum wind power density had reduced
by 93,406 W/m2
at Anakapalle (~25 km) compared
to the ocean, and by 7022 W/m2
at Chintapalle
(~100 km inland) compared to Anakapalle). The present
study reinforces the significance of having real time
near-shore oceanâ¿¿met observations, and their
operational usage for evaluation (assimilation) of
(into) oceanâ¿¿met forecast models in real time. | |
| Paper No | 4 | Publication ID : 579 & Year : 2016 |
| Title | Orographic effect on Tropical Rain Physics in the Asian Monsoon region | |
| Authors | Harikumar | |
| Source | Atmospheric Science Letters, (wileyonlinelibrary.com) DOI: 10.1002/asl.692 | |
| Abstract | Effect of orography on tropical rain Drop Size Distribution (DSD), which was not well known, is evidenced through the present study. DSD is the number of raindrops/unit volume/diameter interval, which tells about the underlying physics of rainfall process. Rain DSD was studied, using a Joss-Waldvogel Disdrometer, at three coastal and a hill station in the tropics. The variation in the characteristics of three physically significant parameters derived from the DSD with rain rate clearly unraveled the effect of orography on rain physics. The orographic rain seems to have larger drops compared to non-orographic rains when rain rate is high. | |
| Paper No | 5 | Publication ID : 371 & Year : 2015 |
| Title | Assessment of wind energy potential along the Indian coast using satellite, model and in-situ data for offshore wind farm advisories | |
| Authors | R. Harikumar, L. Sabique, T.M. Balakrishnan Nair and S.S.C. Shenoi | |
| Source | Applied Energy (under review) | |
| Abstract | This paper explains the analysis and assessment of offshore
wind energy along the Indian coast. It identifies the locations of
sustained high winds along the Indian coast using observed winds spanning
over a period of 10 years. The number of windy days having magnitudes > 6
ms-1, > 8 ms-1 and > 10 ms-1 in a year and the associated wind power
density were mapped based on the daily winds derived from a satellite
based scatterometer namely, QuikSCAT (of National Aeronautics and Space
Administration, USA). These maps are very useful to identify the coastal
regions to setup the wind-farms through the erection of wind driven
turbines to generate electricity. Satellite derived winds were first
validated using in situ measurements of winds obtained from 5 moored
buoys (deployed by NIOT/MoES). The in situ measurements were then used to
correct the bias of QuikSCAT winds in the coastal region. Winds at 80 m
are then derived and used for further analysis, as assessment of 80 m
winds are required for wind farming purposes. Such winds were compared
and evaluated using ERA-Interim analysis (~80 m winds) and also using insitu
observations at a similar height, and found to have good agreement.
The southern coast of Tamil Nadu, and the coast of Gujarat-Maharashtra
has the maximum number of windy days. Both regions experience winds above
6 ms-1 for more than 300 days. Southern coast of Tamil Nadu has an
average annual wind power density of 519 Wm-2 and coast of Gujarat-
Maharashtra has a value of 330 Wm-2. The wind power density exceeds 500
Wm-2 along southern Tamil Nadu coast for about 8 months in an year.
However, it exceeds that value only for 3 months along Gujarat-
Maharashtra coast. | |
| Paper No | 6 | Publication ID : 577 & Year : 2015 |
| Title | Validation and inter-comparison of SARAL/AltiKa and PISTACH derived coastal wave heights using in-situ measurements | |
| Authors | Hithin N. K., P.G. Remya, T.M. Balakrishnan Nair, R. Harikumar, Raj Kumar, Shailesh Nayak | |
| Source | IEEE Trans. on Geo Sci. and Rem. sens, 99, pp1-10, DOI: 10.1109/JSTARS.2015.2418251 | |
| Abstract | SARAL/AltiKa, the first Ka-band altimeter, now provides
an opportunity to study wave characteristics in the worldâ¿¿s
coastal ocean with improved accuracy. In the present work, AltiKa-derived significant wave heights (Hs) in the coastal ocean
and inland water bodies have been analyzed using in-situ measurements. Analysis shows that AltiKa measured Hs agree well
with the in-situ measurements with high correlation (0.98), low
bias (6 cm), and low RMSE (19 cm) in the coastal ocean, and
the performance is highly consistent across different coastal zones
in the three tropical oceans. AltiKa performance is found to
be very good (RMSE = 24 cm and correlation = 0.94) near to
the coast (<2 km). In addition to the evaluation of AltiKa Hs,
another coastal altimetry product, Innovative Processing System
Prototype for Coastal and Hydrology Applications (PISTACH)-
derived Hs using Jason-2 altimeter, has also been validated with
in-situ measurements. The OCE3 retracking algorithm provided
in PISTACH is able to improve the Jason-2 Hs in the 100â¿¿25 km
coastal zone. None of the retracking algorithms showed significant
improvement of Hs in the 0â¿¿10 km coastal zone. | |
| Paper No | 7 | Publication ID : 576 & Year : 2015 |
| Title | Ocean State Forecast Along Ship-routes: Evaluation Using ESSO-INCOIS Real-time Ship-Mounted Wave Height Meter and Satellite Observations | |
| Authors | R. Harikumar , N.K. Hithin, T.M. Balakrishnan Nair, P. Sirisha, B. Krishna Parasad, C. Jeyakumar, Shailesh Nayak and S.S.C. Shenoi | |
| Source | J. Atmos. Oceanic Technol., 2015, 32, 2211-2222, DOI: 10.1175/JTECH-D-15-0047.1. | |
| Abstract | Ocean State Forecast (OSF) Along Ship routes (OAS) is an advisory service of Earth System Science Organisation-Indian National Centre for Ocean Information Services (ESSO-INCOIS), which helps the mariners to ensure safe navigation in the Indian Ocean in all seasons as well as in extreme conditions. As there are many users who solely depend this service for their decision making, it is very important to ensure the reliability and accuracy of the service using the available in-situ as well as satellite observations. This study evaluates the significant wave height (Hs) along the ship track in the Indian Ocean using the Shipmounted Wave Height Meter (SWHM), on board Oceanographic Research Vessel Sagar Nidhi, and Cryosat-2 and Jason altimeters. Reliability of the SWHM is confirmed by comparing with collocated buoy and altimeter observations. The comparison along the ship routes using the SWHM shows a very good agreement (correlation coefficient > 0.80) in all the three oceanic regimes, namely, the Tropical Northern Indian Ocean (TNIO), the Tropical Southern Indian Ocean (TSIO) and Extra Tropical Southern Indian Ocean (ETSI) with respect to the forecasts with lead-time of 48 hours. However, the analysis shows ~10% overestimation of forecasted significant wave height in the low wave heights, especially in the TNIO. The forecast is found very reliable and accurate for the three regions during June-September with higher correlation coefficient (average=0.88) and lesser scatter index (average=15%). During other months over-estimation (bias) of lower Hs is visible in the TNIO. | |
| Paper No | 8 | Publication ID : 506 & Year : 2014 |
| Title | Wave forecasting and monitoring during very severe cyclone Phailin in the Bay of Bengal | |
| Authors | T. M. Balakrishnan Nair, P. G. Remya, R. Harikumar, and co-authors | |
| Source | CURRENT SCIENCE, VOL. 106, NO. 8, 25 APRIL 2014, pp.1121-1125. | |
| 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 | 9 | Publication ID : 517 & Year : 2014 |
| Title | An investigation on the consequential features of Southwest Monsoon-2007 Onset and Super cyclone 'Gonu' using Satellite, Model and Ground-based data | |
| Authors | R. Harikumar, Hamza Varikoden, C. A. Babu, R. Vishnu, and G. Mohan Kumar | |
| Source | J. Ind. Geophys. Union ( July 2014 ) v.18, no.3, PP:319-329 | |
| Abstract | Onset features of the Summer monsoon-2007 were analyzed using data from five different sources, namely, the Tropical Rainfall Measuring Mission (TRMM) 3-hourly rainfall, National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) wind reanalysis data set, NOAA Outgoing Longwave Radiation (OLR), cloud imageries from the meteosat satellite,cloud base height and cloud occurrence frequency from a ground-based Vaisala Laser Ceilometer at Thiruvananthapuram. On the day of onset, 33 mm of rainfall was registered by TRMM satellite over south Kerala region with 80% cloud frequency and an averaged cloud base height of 2 km. On the next day, the formation of ¿Gonu¿ super cyclone as a consequence of the convergence of monsoon onset surge in the Arabian Sea has caused the dissipation of cloud bands in the Arabian Sea and in the Bay of Bengal, except over the region of the system. This caused a lull situation for about ten days after the India Meteorological Department (IMD) declared monsoon onset. In fact, the remarkable characteristics of onset, such as deepening of westerlies and strengthening of low level jet streams were observed only after two weeks of IMD declared monsoon onset. Another unique behavior of 2007 monsoon onset was that the Arabian Sea branch of monsoon onset surge has advanced faster than the Bay of Bengal branch in the early stage. | |
| Paper No | 10 | Publication ID : 370 & Year : 2013 |
| Title | Ship-mounted real-time surface observational system on board Indian Vessels for validation and refinement of model forcing fields* | |
| Authors | R. Harikumar, T.M. Balakrishnan nair, G.S. Bhat, Shilesh Nayak, Venkat Shesu Reddem and Shenoi, S.S.C. | |
| Source | J. Atm. Oceanic Tec. (American Meteorological Society), 30, 626¿637.doi: http://dx.doi.org/10.1175/JTECH-D-11-00212.1 | |
| Abstract | A network of ship mounted real-time Automatic Weather Stations integrated with Indian
Geosynchronous satellites INSAT 3A and 3C, named Indian National Centre for Ocean
Information Services Real-time Automatic Weather Stations (I-RAWS) is established.
The purpose of I-RAWS is to measure the surface met-ocean parameters and transmit
the data in real-time in order to validate and refine the forcing parameters (obtained
from different met agencies) of INDian Ocean FOrecasting System (INDOFOS).
Preliminary validation and inter comparison of analyzed products obtained from
National Centre for Medium Range Weather Forecast and European Centre for
Medium-Range Weather Forecasts using the data collected from I-RAWS were carried
out. This I-RAWS was mounted on board Oceanographic Research Vessel Sagar Nidhi
during a cruise across three oceanic regimes viz. Tropical Indian Ocean, Extra Tropical
Indian Ocean and Southern Ocean. The results obtained from such a validation and
inter comparison, and its implications with special reference to the usage of
atmospheric model data for forcing ocean model are discussed in detail. It is noticed
that the performance of analysis products from both atmospheric models are similar
and good, however, European Centre for Medium-Range Weather Forecasts air
temperature over Extra Tropical Indian Ocean and wind speed in Southern Ocean is
marginally better.
Key words: Ship-mounted AWS, INCOIS Real-time AWS (I-RAWS), voluntary observing ships (VOS), INDian Ocean FOrecasting System (INDOFOS), Ocean Observations and Information Services (OOIS) programme, validation, NCMRWF model data, ECMWF model data. | |
| Paper No | 11 | Publication ID : 486 & Year : 2013 |
| Title | Performance of the Ocean State Forecast system at Indian National Centre for Ocean Information Services | |
| Authors | T. M. Balakrishnan Nair, P. Sirisha, K. G. Sandhya, K. Srinivas, V. Sanil Kumar, L. Sabique, Arun Nherakkol, B. Krishna Prasad, Rakhi Kumari, C. Jeyakumar,K. Kaviyazhahu, M. Ramesh Kumar, R. Harikumar , S.S.C. Shenoi and Shailesh Nayak | |
| 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. Spectral Wave model is used for forecasting the wave fields generated by the tropical cyclone and validation of the same is done using real-time automated observation systems. The validation results indicate that the forecasted wave parameters agree well with the measurements. The feedback from user community indicates that the forecast was very reliable and highly useful. Alerts based on this operational ocean state forecast system is thus very 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 | 12 | Publication ID : 470 & Year : 2013 |
| Title | Evaluation of the Global Ocean Data Assimilation System at INCOIS: The Tropical Indian Ocean | |
| Authors | M. Ravichandran, D. Behringer, S. Sivareddy, M. S. Girishkumar, N.Chacko, R. Harikumar | |
| Source | Ocean modelling, Elsevier, 69 (2013), 123-135, DOI: http://dx.doi.org/10.1016/j.ocemod.2013.05.003. | |
| Abstract | A new version of NCEP¿s Global Ocean Data Assimilation System (GODAS), which is based on the Geophysical Fluid Dynamics Laboratory (GFDL) Modular ocean Model version 4.0 (MOM4.0) and a three-dimensional variational (3DVAR) data assimilation scheme, was configured and operationalized at Indian National Centre for Ocean Information Services (INCOIS). The primary objective of the GODAS at INCOIS (INCOIS-GODAS) is to provide an accurate estimate of the ocean state, which will be used to initialize a coupled model for the seasonal monsoon forecast and also to understand the variability of the ocean at different time scales. In this paper, we examine the validation of the INCOIS-GODAS ocean state in the Tropical Indian Ocean (TIO), when it is forced with two different wind products: NCEP/NCAR reanalysis-2 and QuikSCAT scatterometer. The ability of the model to capture the climatological mean state and the intraseasonal and interannual variability of different oceanic parameters, such as sea surface and subsurface temperature, sea surface salinity (SSS), sea surface height anomaly (SSHA) and currents is examined using in situ and satellite data. The analysis reveals that the INCOIS-GODAS provides reasonably accurate simulation of the ocean state in the TIO at both seasonal and interannual time scales. The analysis further shows that there was a considerable improvement in the ocean current field when the model was forced with QuikSCAT winds. | |
| Paper No | 13 | Publication ID : 469 & Year : 2012 |
| Title | Tropical rain Drop Size Distribution and Integral
rain parameters A study using ground-based and satellite measurements | |
| Authors | R. Harikumar | |
| Source | (Book) LAP-Lambert Academic Publishing, ISBN: 978-3-8484-1267-9, 344 pp. (https://www.lap-publishing.com/). | |
| Abstract | This book deals with tropical rain Drop Size Distribution (DSD), rain rate (R)
and radar reflectivity factor (Z). An extensive understanding of rain DSD
and integral rain parameters finds applications in fields like satellite
meteorology, cloud microphysics, soil erosion, micro wave communication
and global climate. DSD and derived rain parameters data from 4 tropical
stations for 10 years, which were measured using a Joss-Waldvogel
Disdrometer and those at different heights, which were collected using a
Micro Rain Radar are used. The Tropical Rainfall Measuring Mission (TRMM)
and other satellite rain rate (3B42-V6) for the same period has also been
used. The major results pertain to the development and testing of a model
for the variation of DSD with rain rate in the tropics. The theoretical
concepts regarding the altitudinal and temporal evolution of rain DSD
could be proved. The evaluation of the vertical profiles of DSD and Z-R
relations for tropical region is another result. This study has also brought
out the need to have a closer look at the satellite retrieval. The behaviour
of the rain rate at tropics and the possible effect of orography on DSD has
also been brought out. | |
| Paper No | 14 | Publication ID : 317 & Year : 2011 |
| Title | Observational study of cloud base height and its frequency over a tropical station, Thiruvananthapuram using Ceilometer | |
| Authors | Hamza Varikoden, R. Harikumar, R. Vishnu, V. Sasi Kumar, S. Sampath, S. Murali Das and G. Mohan Kumar | |
| Source | International Journal of Remote Sensing, Taylor & Francis, 2011, DOI: 10.1080/01431161.2010.542199. | |
| Abstract | The present study aims to bring out the characteristic features of cloud base height
over Thiruvananthapuram during different seasons. Cloud base height data was used for the present work and it was derived from a Vaisala laser ceilometer, CL31 (VLC) installed at the campus of the Centre for Earth Science Studies, Akkulam (8.29◦ N, 76.59◦ E, amsl 15 m). The VLC was in operation from the second week of July 2006 onwards. From the study, we found that cloud base height shows distinct diurnal and seasonal variations in all the seasons (except in rainy days). The diurnal variation for low level clouds was different from that of the mid level clouds. A
cloud free layer is evident in a region between 2.5 and 4 km. This cloud free zone is more prominent during the southwest monsoon period compared to other seasons. Moreover, the monthly variation of cloud frequency and cloud base height were also described in addition to the different periodicities in cloud frequency. The
periodicities found in the cloud frequency were 8-day and 30-day and these are significant at 5% level. Thermodynamic parameters from the radiosonde were also related to the cloud frequency for various seasons and found they are in good agreement. | |
| Paper No | 15 | Publication ID : 318 & Year : 2011 |
| Title | Altitudinal and temporal evolution of Rain Drop Size Distribution observed over a tropical station using a K-band Radar | |
| Authors | R. Harikumar, S. Sampath and V. Sasi Kumar | |
| Source | International Journal of Remote Sensing, Taylor & Francis, 2011, DOI: 10.1080/01431161.2010.549853. | |
| Abstract | Rain drop size distribution (DSD) measurements at different heights were made using a Micro Rain Radar (MRR) at Thiruvananthapuram (Lat: 8.3 N, Long: 76.9 E). Rain DSD data obtained from the MRR has been compared with a Joss waldvogel impact type Disdrometer (RD-80) deployed nearby and found to have good agreement. The analysis
uses the data during 16 continuous rainfall episodes during the southwest monsoon (JJAS) season. Since all the episodes behaved similarly, a single continuous rainfall episode occurring from Indian Standard Time (IST) 16:10:01 IST to 16:12:31 IST on 12th August 2006 is presented here. The fall velocity of those drops which contribute most to rain rate was more or less constant at different altitudes and also with time
during this episode and the average value is 4.65 m/s. The rain rate was below 5 mm/h for all the heights throughout the time. At the beginning of the rain episode, the number of drops at any given altitude was lower for larger drops. But towards the end of the episode, the number of drops in the smallest size class has reduced at almost all heights, while the number of drops in the larger size classes has increased. This suggests that the larger drops coming from above colliding with smaller drops could coalesce, thus
sweeping out the smaller drops as they fall. The reduction of small drops is seen with a corresponding increase in larger drops and without increase also during the course of
rainfall event. The former is an indication of coalescence while the later is that of evaporation. All these observed phenomena in the natural rain are support for the observational evidence reported by Low and List in 1982. | |
| Paper No | 16 | Publication ID : 468 & Year : 2011 |
| Title | Consultancy service for identification of wind potential zones in western offshore field of ONGC | |
| Authors | R. Harikumar, T.M. Balakrishnan Nair and S.S.C. Shenoi | |
| Source | INCOIS Technical Report, No.: INCOIS-ISG-OSF-TR-2012-07 | |
| Abstract | This report summarises the assessment of wind potential in the western offshore field
of ONGC. It gives a general picture on the wind resource in the entire field and also
identifies the locations of sustained high winds (Wind Potential Zones) with in the field
using observed winds spanning over a period of 10 years. The number of windy days having
magnitudes > 6 ms-1, > 8 ms-1 and > 10 ms-1 in a year, long term average wind speed and the
associated wind power density were mapped based on the daily winds derived from a
satellite based scatterometer namely, QuikSCAT (of National Aeronautics and Space
Administration, USA). These maps are useful to identify the regions to setup the wind-farms
through the erection of wind driven turbines to generate electricity. Satellite derived winds
were first validated using in situ measurements of winds obtained from 5 moored buoys
(deployed by NIOT/MoES). The in situ measurements were then used to correct the bias of
QuikSCAT winds in the coastal region. The analyses for the wind potential assessment have
3
been done in three ways, (1) in a general and an average way to the entire field, (2) specific
wind potential zones (WPZ) with in the field and (3) assessment of wind potential for 0-30
km and 30-50 km from the shore. The annual average wind speed derived using long term
data suggests that the entire field has magnitudes of wind speed ranges from 5 ms-1 to 6 ms-1.
Wind potential map, which gives the number of windy days in a year, suggests that at least
200 and 60 days in a year the wind speed exceeds 6 ms-1 and 8 ms-1 respectively with in the
field. But, the number of days varies from 0 to 25 for wind speeds, which exceed 10 ms-1.
Long tem average annual wind power density in the entire field is more than 300 Wm-2. The
zones identified for high wind potential with in the field based on the assessment using
different maps, are given below. A region bounded with in the co-ordinates 19.2ºN to 19.7ºN
and 70.9ºE to 71.6ºE (ONGC WPZ-1) is found to be having a region of marginally higher
average wind speed and wind potential compared to rest of the field. The interesting aspect is
that five ONGC platforms are situated with in this region. Near-shore region between 18.2ºN
and 19.2ºN (approximately from the place Murud (south) to Uttan Virgin Beach (north)) and
extended from the coast to 72ºE offshore (~70 km away from the coast) (ONGC WPZ-2) is
another region having good wind potential compared to southern near-shore parts of the field.
With in this ONGC WPZ-2, which is a near-shore WPZ, region bounded between 30 and 50
kms away from the coast has wind speeds > 6 ms-1 for ~290 days, while that is only ~275
days for the region bounded between 30 km away from the coast and the coast. | |
| Paper No | 17 | Publication ID : 372 & Year : 2010 |
| Title | A preliminary report on the potential of winds along the Indian coast for offshore wind farming | |
| Authors | R. Harikumar, L. Sabique, T.M. Balakrishnan Nair and S.S.C. Shenoi | |
| Source | INCOIS Report No.: INCOIS-MOG&ISG-OSF-TR-2010-01 | |
| Abstract | This report summarises the analysis of high resolution wind along the Indian coast. It identifies the locations of sustained high winds along the Indian coast using observed winds spanning over a period of 10 years. The number of windy days having magnitudes > 6 ms-1, > 8 ms-1 and > 10 ms-1 in a year were mapped based on the daily climatology of winds derived from a satellite based scatterometer namely, QuikSCAT (of National Aeronautics and Space Administration, USA). The maps are useful to identify the coastal regions to setup the wind-farms for the erection of wind driven turbines to generate electricity. Satellite derived winds were first validated using in situ measurements of winds obtained from 5 moored buoys (deployed by NIOT/MoES). The in situ measurements were then used to correct the bias of QuikSCAT winds in the coastal region. The Coast of Tamil Nadu near Tuticorin, and the coast of Gujarat has the maximum number of windy days. Both regions experience winds above 6 ms-1 for more than 300 days. However, both regions experience winds above 8 ms-1 for less number of days; Tuticorin experiences winds above 8 ms-1 for about 200 days and the coast of Gujarat experiences for about 100 days in a year. Few other locations (but very much localised) also show some wind potential (for example the region south to Vijayawada).
Keywords: QuikSCAT wind data, bias corrections, coastal high resolution wind atlas, wind farm advisories | |
| Paper No | 18 | Publication ID : 271 & Year : 2010 |
| Title | Study on tropical rain with special reference to rain Drop Size Distribution and integral rain parameters using ground-based and satellite measurements | |
| Authors | R. Harikumar | |
| Source | Ph.D. Thesis (Physics), Faculty of Science, Cochin University of Science and Technology, 2010. | |
| Abstract | The main focus of this investigation is to study the tropical rain with special reference to rain Drop Size Distribution (DSD), rain rate (R) and radar reflectivity factor (Z). DSD and other rain parameters data from 4 stations viz. Thiruvananthapuram, Kochi, Munnar and Sriharikota (SHAR) during various monsoon periods from the year 2001, was measured using a Joss-Waldvogel Disdrometer and the data from these measurements are used for this study. Rain DSD data at different heights has been collected using a Micro Rain Radar (MRR) that was installed during September 2005 at Thiruvananthapuram. The Tropical Rainfall Measuring Mission (TRMM) and other satellite rain rate data (3B42-V6) for the period 2001 to 2008 has also been used in the present study.
The thesis is arranged in eight chapters. The major results pertain to the development and testing of an empirical model to represent the variation of DSD with rain rate in the tropics. The theoretical concepts regarding the altitudinal and temporal evolution of rain DSD could be proved experimentally. The evaluation of the vertical profiles of DSD and Z-R relations for our region is another important result of this study. The correlation between satellite measured rainfall and ground based measurements has brought out the need to have a closer look at the satellite retrieval. The behaviour of the intensity of rain fall or rain rate at the four stations and the possible effect of orography on DSD has been also brought out.
The list of publications [6 and under review (5)] including conferences proceedings (24) is given in the beginning. | |
| Paper No | 19 | Publication ID : 374 & Year : 2010 |
| Title | INCOIS-GODAS-MOM: Ocean Analysis for the Indian Ocean: Configuration, Validation and Product Dissemination | |
| Authors | M. Ravichandran, D. Behringer, S. Siva Reddy, M.S. Girishkumar, Neethu Chacko and R. Harikumar | |
| Source | INCOIS Report No.: INCOIS-MOG-TR-2011-06 | |
| Abstract | Recently a new version of NCEP¿s Global Ocean Data Assimilation System
(GODAS), which is based on the Geophysical Fluid Dynamics Laboratory
(GFDL) Modular ocean Model version 4p0 (MOM4p0) and a three-dimensional
variational (3DVAR) data assimilation scheme, was configured at Indian National
Centre for Ocean Information Services (INCOIS). The primary objective of the
GODAS-MOM at INCOIS is to provide an accurate estimate of the ocean state,
which will be used to initialize a coupled model for the seasonal monsoon forecast
and also to understand the variability of the ocean at different time scales. In this
report, we examine the validation of the GODAS-MOM ocean state in the
Tropical Indian Ocean, when it is forced with two different wind products:
NCEP/NCAR reanalysis and QuikSCAT scatterometer. The ability of model to
capture the climatological mean stateand the intraseasonal and interannual
variability of different oceanic parameters, such as sea surface temperature,
salinity, sea surface height anomaly, depth of the 20°C isotherm, currents, mixed
layer depth and isothermal layer depth is examined using in situ and satellite data.
The analysis reveals that the GODAS-MOM provides reasonably accurate
simulation of the ocean state in the TIO at both seasonal and interannual time
scales. The analysis further shows that there was a considerable improvement in
the ocean current field when the model was forced with QuikSCAT winds.
Keywords: Ocean modelling, Data assimilation, Ocean general
circulation model, MOM-GODAS, Ocean Analysis product, Indian Ocean | |
| Paper No | 20 | Publication ID : 373 & Year : 2010 |
| Title | Report on the assessment of wind energy potential along the Indian coast for offshore wind farm advisories | |
| Authors | R. Harikumar, L. Sabique, T.M. Balakrishnan Nair and S.S.C. Shenoi | |
| Source | INCOIS Report No.: INCOIS-MOG&ISG-TR-2011-07 | |
| Abstract | This report summarises the analysis of high resolution wind along the Indian coast. It identifies the locations of sustained high winds along the Indian coast using observed winds spanning over a period of 10 years. The number of windy days having magnitudes > 6 ms-1, > 8 ms-1 and > 10 ms-1 in a year and the associated wind power density were mapped based on the daily winds derived from a satellite based scatterometer namely, QuikSCAT (of National Aeronautics and Space Administration, USA). These maps are useful to identify the coastal regions to setup the wind-farms through the erection of wind driven turbines to generate electricity. Satellite derived winds were first validated using in situ measurements of winds obtained from 5 moored buoys (deployed by NIOT/MoES). The in situ measurements were then used to correct the bias of QuikSCAT winds in the coastal region. The southern coast of Tamil Nadu, and the coast of Gujarat-Maharashtra has the maximum number of windy days. Both regions experience winds above 6 ms-1 for more than 300 days. However, both regions experience winds above 8 ms-1 for less number of days; southern coast of Tamil Nadu experiences winds above 8 ms-1 for about 200 days and the coast of Gujarat-Maharashtra experiences for about 100 days in a year. Southern coast of Tamil Nadu has an average annual wind power density of 519 Wm-2 and coast of Gujarat-Maharashtra has a value of 330 Wm-2. The WPD exceeds 500 Wm-2 along southern Tamil Nadu coast for about 8 months in an year. However, it exceeds that value only for 3 months along Gujarat-Maharashtra coast. Few other locations (but very much localised) also show some wind potential (for example the region south to Vijayawada).
Keywords: QuikSCAT wind data, bias corrections, coastal high resolution wind atlas, wind farm advisories, wind potential maps, wind power density | |
| Paper No | 21 | Publication ID : 247 & Year : 2010 |
| Title | Variation of rain drop size distribution with rain rate at a few coastal and high altitude stations in southern peninsular India | |
| Authors | R. Harikumar, S. Sampath, V. Sasi Kumar | |
| Source | Advances in Space Research, Elsevier, 45 (2010), 576¿586 | |
| Abstract | Rain drop size distribution (DSD) was measured at four places in Southern India {Thiruvananthapuram, Kochi, Munnar and Sriharikota
(SHAR)} using a Joss¿Waldvogel (JW) impact type disdrometer. The data for each minute were corrected for dead time errors
and rain rate was computed from the corrected data. The data for a whole month were then sorted according to rain rate (R) into several
classes ranging from 0.1 to >100 mm/h. The average DSD in each class was computed, and the lognormal distribution function was fitted
to the average. In all the cases, the function fitted the data very well. The fit parameters were found to have dependence on rain rate. The
total number of drops (NT), the geometric mean diameter (Dg) and the standard geometric deviation (r) were also computed from the fit
parameters. The standard geometric deviation (r) was found to be more or less constant with rain rate at all the sites and in all months.
The other two parameters (NT and Dg) were found to vary exponentially with rain rate except in Munnar, a high altitude station. At
Thiruvananthapuram, in most of the months, NT increased exponentially with rain rate up to some value of R, which was different
in different months, and then remained more or less constant or decrease slightly. In all cases, the variation of NT and Dg was such that
NTDg3 increased linearly with rain rate. | |
| Paper No | 22 | Publication ID : 309 & Year : 2010 |
| Title | Vertical profiles of Rain Drop Size Distribution at a tropical station using a k-band Doppler Radar | |
| Authors | Harikumar, R., Sampath, S., Sasi Kumar V. | |
| Source | Proc. 38th COSPAR Scientific Assembly 2010, p.116, Bremen, Germany, July-2010. | |
| Abstract | Rain drop size distribution measurements are being carried out at CESS, Thiruvananthapuram
(Lat: 8.3 N, Long: 76.9 E) using a Joss-Waldvogel disdrometer and a micro rain radar. The
disdrometer, an electromechanical instrument, gives the DSD at the surface. The micro rain
radar, a Doppler radar, gives the DSD at di erent heights, starting from 200 m. Both the
instruments are deployed at the same site. Measurements made during a few rainfall events are
compared and the general characteristics are derived. The DSD measured at the surface and at
200m with short term averaged follows a log-normal distribution. But the radar measurements
di er from the log-normal distribution, irrespective of the averaging time above 400m altitude.
The smaller drop sizes show an exponential decrease with increasing drop diameter rather than
the increase as expected from a log-normal distribution. The presence of a large number of
smaller drops above 400 m and their relative absence below this altitude are presented and
discussed. This point out that the larger drops coming from above colliding with smaller drops
could coalesce, thus sweeping out the smaller drops as they fall. All these observed phenomena
in the natural rain are the observational evidence for the ndings by Low and List in 1982. | |
| Paper No | 23 | Publication ID : 310 & Year : 2010 |
| Title | Evidence of the orographic effect on Rain from Rain Drop Size Distribution at coastal and high altitude tropical stations | |
| Authors | Harikumar, R., Sampath, S., Mohan Kumar, G. | |
| Source | Proc. 38th COSPAR Scientific Assembly 2010, p.116, Bremen, Germany, July-2010. | |
| Abstract | Rain Drop Size Distribution (DSD) is the number of raindrops/unit volume/diameter interval.
DSD was studied using a Joss-Waldvogel Disdrometer operated at stations, Thiruvananthapu-
ram (8.3oN, 76.6oE; 4 m amsl), Kochi (9.6oN, 76.2oE; 5 m), Munnar ( 10.1oN, 77.1oE; 1500 m)
and Sriharikota (13.6oN, 80.3oE; 3 m). Kochi and Thiruvananthapuram are west coast stations
and Sriharikota is an east coast station. Munnar is a hill station about 130 km east of Kochi on
the Western Ghats. The entire data were divided into periods of di erent rain rate. The mean
DSD for each rain rate range was computed. The DSD values were tted with the log-normal
distribution function of the form N(D)=(a0/D)*Exp[-0.5((ln( D)-a1)/a2)**2] Where N(D) is the number of drops per cubic metre per mm interval of diameter, D is the drop diameter and a0, a1 and a2 are t parameters. Three physically signi cant parameters, viz. Total number of drops (NT), Geometric mean diameter (Dg) and Standard geometric deviation () were derived from the t parameters. We tted the values with the expression NT=aRb, as suggested by Verma and Jha (1996). The t was good for the stations other than Munnar. For Munnar, NT increases up to around 3 mm/hr and then decrease with rain rate. The Dg values were also tted with a similar expression. We found that, at Thiruvananthapuram, Kochi and Sriharikota, Dg increases with rain rate. But at Munnar, Dg remains more or less constant for rain rates up to about 3 mm/hr and then increases exponentially. did not show any dependence on rain rate. The characteristics of these three parameters with rain rate clearly unravelled the dependence of orography on rain. | |
| Paper No | 24 | Publication ID : 267 & Year : 2009 |
| Title | Simultaneous Evidence for the origin of rain from Stratiform or Convective Clouds from the Micro Rain Radar Bright Band Signature and the Vertical profiles of Z-R Empirical relation | |
| Authors | Harikumar, R., Sampath, S., Mohan Kumar, G., Sasi Kumar, V. | |
| Source | Proceedings, International Conference on Megha-Tropiques Science and Applications, pp. 109-113, Bangalore, India, March-2009. | |
| Abstract | A Micro Rain Radar (MRR) and a Joss-Waldvogel type impact type Disdrometer have been operated at the premises of the Centre for Earth Science Studies, Thiruvananthapuram (8.5º N, 76.9ºE, 4 m amsl). The data from MRR has been validated with disdrometer data and found agreement1. The rain Drop Size Distribution (DSD) and the integral rain parameters up to an altitude of 6000 m with a height resolution of 200 m and the radar bright band can have from the MRR. The radar Bright Band signature, which is an indication of freezing height2, is validated with the Wyoming radiosonde data that can be downloaded from the web.
The whole rain events (1 minute output of integral rain parameters from the MRR) from March to September 2007 were separated in to Bright Band (BB) and Non- Bright Band (NBB) cases. The presence of bright band is very clear from the vertical profile of rain rate obtained from the MRR. The variation of radar reflectivity factor (Z) with rain rate for all the heights is fitted with a function of the form Z=aRb corresponding to the BB and NBB cases separately for Pre-monsoon and Southwest monsoon seasons. Clearly, two distinct fits with different slopes are obtained for BB and NBB cases during both the seasons (Fig. 1.). Since the possible effect of radar ground clutter is there, the data from 200 metre height is not used in the analysis. The fit has good correlation coefficient of nearly 1 for all the Z-R relations during BB and NBB cases during both the seasons at all the heights. But in the NBB cases, there is a saturation in the radar reflectivity values beyond some rain rates at all the heights.
The values of these fit parameters for BB and NBB corresponding to each altitude has been tabulated and studied the altitudinal variation of these fit parameters for different seasons (Fig. 2). In both the seasons and for BB and NBB, both a and b are decreasing with altitude except for southwest BB case. In the southwest BB case, a and b are varying sinusoidal with altitude having an approximate phase difference of 180 degrees in the variation of a and b. The reason for such a difference could be brought out with more data.
A similar distinct difference in the slopes of the BB and NBB Z-R relation is there through out aloft. Any way, the analyses were limited to a height of 3200 m due to possible pollution in the data due to the effect of radar bright band signature in the back-scattered radar spectrum.
Since the radar BB signature is an indication of rain originated from stratiform clouds2 and NBB is an indication of rain originated from non-stratiform clouds and also the mentioned simultaneous transition of the slope of the Z-R relation gives a new clear-cut method for classification of tropical precipitation as stratiform or convective origin using a Micro Rain Radar.
| |
| Paper No | 25 | Publication ID : 266 & Year : 2009 |
| Title | Evidence of the orographic effect on rain from rain drop size distribution at coastal and high altitude stations | |
| Authors | Harikumar, R., Sampath, S., Mohan Kumar, G. | |
| Source | Proceedings, 46th Annual convention and meeting of Indian Geophysical Union, pp. 82, Dehradun, India, October 2009. | |
| Abstract | Rain Drop Size Distribution (DSD) is the number of raindrops/unit volume/diameter interval. DSD was studied using a Joss-Waldvogel Disdrometer operated at stations, Thiruvananthapuram (8.3ºN, 76.6ºE; 4 m amsl), Kochi (9.6ºN, 76.2ºE; 5 m), Munnar ( 10.1ºN, 77.1ºE; 1500 m) and Sriharikota (13.6ºN, 80.3ºE; 3 m). Kochi and Thiruvananthapuram are west coast stations and Sriharikota is an east coast station. Munnar is a hill station about 130 km east of Kochi on the Western Ghats.
The entire data were divided into periods of different rain rate. The mean DSD for each rain rate range was computed. The DSD values were fitted with the log-normal distribution function.
Three physically significant parameters, viz. Total number of drops (NT), Geometric mean diameter (Dg) and Standard geometric deviation (σ) were derived from the fit parameters. We fitted the values with the expression NT=aRb, as suggested by Verma and Jha (1996). The fit was good for the stations other than Munnar. For Munnar, NT increases up to around 3 mm/hr and then decrease with rain rate. The Dg values were also fitted with a similar expression. We found that, at Thiruvananthapuram, Kochi and Sriharikota, Dg increases with rain rate. But at Munnar, Dg remains more or less constant for rain rates up to about 3 mm/hr and then increases exponentially. σ did not show any dependence on rain rate. The characteristics of these three parameters with rain rate clearly unravelled the dependence of orography on rain.
| |
| Paper No | 26 | Publication ID : 265 & Year : 2009 |
| Title | Altitudinal variation of Radar Reflectivity Factor-Rain rate (Z¿R) relation at a tropical site observed using a Micro Rain Radar: A valuable information for remote sensing of rain | |
| Authors | Harikumar, R., Sampath, S., Mohan Kumar, G. | |
| Source | Proceedings, Seminar on Climate Change, Causes, Measures and Preparedness, pp. 60-61, Hyderabad, India, August 2009. | |
| Abstract | The vertical profiles of Radar Reflectivity Factor-Rain rate (Z-R) relations are mandatory for accurate retrieval of rain parameters from radar back-scattered spectrum. This paper presents such a study that deals with the altitudinal variation of Z-R relation during different monsoon seasons for different types of rain at a tropical station. A Micro Rain Radar (MRR) and a Joss-Waldvogel impact type Disdrometer have been operated at the premises of the Centre for Earth Science Studies, Thiruvananthapuram (8.5º N, 76.9ºE, 4 m amsl). The data from MRR has been validated with disdrometer data and found to have good agreement1. The rain Drop Size Distribution (DSD) and the integral rain parameters up to an altitude of 6000 m with a height resolution of 200 m can be obtained from the MRR.
The rain events (1-minute output of integral rain parameters from the MRR) from March to September 2007 were separated in to Bright Band (BB) and Non-Bright Band (NBB) cases. The radar Bright Band signature, which is an indication of freezing height2, is validated with the Wyoming radiosonde data3.
The presence of bright band is clearly discernible from the vertical profile of rain rate obtained from the MRR. The variation of radar reflectivity factor (Z) with rain rate for all the heights is fitted with a function of the form Z = a R b corresponding to the BB and NBB cases separately for Pre-monsoon and Southwest monsoon seasons. Clearly, two distinct fits with different slopes are obtained for BB and NBB cases during pre-monsoon and southwest monsoon seasons (Fig. 1). The Z-R relations obtained are also shown in the figure. The MRR data above 200 m alone is used in the analysis to eliminate the possible effect of radar ground clutter. The fit has good correlation coefficient of nearly 1 for all the Z-R relations during BB and NBB cases during both the seasons at all the heights. But in the NBB cases, it is noted that there is saturation in the radar reflectivity values beyond some rain rates at all the heights.
The values of these fit parameters for BB and NBB corresponding to each altitude has been studied for the altitudinal variation of these fit parameters for different seasons. In both the seasons and for BB and NBB, both a and b are decreasing with altitude except for southwest BB case. By incorporating the expressions of a and b for each case in the basic Z-R relation (Z = a R b ), an empirical relation for the variation of Z-R relation with altitude could be derived. In the southwest BB case, a and b are almost constant with little variation with altitude. The reason for such a difference in behavior of BB during the SW monsoon needs to be looked into in detail.
The analyses were limited to a height of 3200 m to avoid possible pollution in the data due to the effect of radar bright band signature in the back-scattered radar spectrum.
The Z-R relation gives a new clear-cut method for classification of tropical precipitation as stratiform or convective origin using a Micro Rain Radar from the BB and NBB detections.
| |
| Paper No | 27 | Publication ID : 268 & Year : 2009 |
| Title | Spatial Variability of Rain Drop Size Distribution-Study at High Altitude and Coastal Tropical Stations in Peninsular India | |
| Authors | Harikumar, R., Sampath, S., Mohan Kumar, G. | |
| Source | Proceedings, International Conference on Megha-Tropiques Science and Applications, pp. 114-17, Bangalore, India, March-2009. | |
| Abstract | Rain drop size distribution (DSD) was studied using a Joss-Waldvogel type Disdrometer installed at four tropical stations, Thiruvananthapuram (Lat: 8.29º N, Long: 76.59º E), Kochi (9.58º N, 76.17º E), Munnar ( 10.08º N, 77.07º E) and Sriharikota-SHAR (13.58º N, 80.29º E). Thiruvananthapuram is on the west coast at the tip of peninsular India. Kochi is an important commercial city in Kerala situated on the western coast on the shores of the state¿s largest estuary. Munnar is a hill station about 130 km east of Kochi on the Western Ghats in South India (at about 1500 m amsl) and Sriharikota is on the eastern coast. Thiruvananthapuram, Kochi and Sriharikota experience rain rates (R) greater than 100 mm/hr while the rain rate in Munnar is rarely close to 100 mm/hr.
The entire data were divided into periods of different rain rate. The rain rate ranges used were from < 0.01 mm/hr to >100 mm/hr with boundaries of 0.02, 0.05, 0.1, 0.2, 0.5, 1, 2, 5, 10, 20, 50 and 100 mm/hr. The mean DSD for each rain rate range was computed. The DSD values were fitted with the lognormal distribution function.
Three physically significant parameters, namely, total number of drops (NT), geometric mean diameter (Dg) and standard geometric deviation (σ), were derived from the fit parameters. We found that NT increases gradually with rain rate at Kochi and Sriharikota (Fig. 2.a) for all rain rates (Harikumar et al. 2007). But at Munnar, it increases with rain rate up to around 3 mm/hr and then decreases at higher rain rates with an accompanying increase in Dg. At Thiruvananthapuram, the variation up to 3 mm/hr follows the normal pattern, but then NT remains more or less constant or starts decreasing. We fitted the values with the expression NT = aRb, as suggested by (Verma and Jha 19961), except Munnar. The fit was good for all the 3 stations other than Munnar. The geometric mean diameter values were also fitted with a similar expression. We found that, at Thiruvananthapuram, Kochi and Sriharikota, Dg increases with rain rate (Fig.2.b). But at Munnar, Dg remains more or less constant for rain rates up to about 3 mm/hr and then increases exponentially. The standard geometric deviation (σ) did not show any significant dependence on rain rate.
The characteristics of rain in terms of the three parameters for coastal stations on the west coast, i.e., Thiruvananthapuram and Kochi, are similar. But the characteristic at Sriharikota, a station on the east coast, is slightly different from that at Kochi and Thiruvananthapuram. At Sriharikota, NT increases faster with rain rate than at Kochi. In fact, for any given rain rate, NT is higher at Sriharikota than at Kochi. Dg increases with rain rate at both the places. But for any given rain rate, the Dg at Kochi is higher than that at Sriharikota. Thus, for a rain with a given rain rate, there are less number of drops at Kochi than at Sriharikota, and the drops are generally larger in size. In other words, rainfall at Sriharikota is made up of more number of smaller drops compared to Kochi.
Munnar behaves very differently compared to other three coastal stations. Up to a rain rate of around 3 mm/hr, NT increases first and then decreases beyond with rain rate while Dg remains more or less constant up to 3 mm/hr and then increases exponentially beyond with rain rate. The effect of orography on rain is very clear from such a difference in rain DSD at Munnar, a high altitude station (1500 m amsl) from all other coastal stations. The difference in the DSD behaviour shown by Munnar and SHAR (which are far from the west coasts) at least during southwest monsoon period (when south-westerlies are prevailing) ensures the lack of influence of the anthropogenic aerosols on rain DSD. If it was so, DSD at Munnar and SHAR should behave similarly. Ie, effect of orography is the only one reason for the spatial variability of rain DSD.
| |
| Paper No | 28 | Publication ID : 249 & Year : 2009 |
| Title | An empirical model for the variation of rain drop size distribution with rain rate at a few locations in southern India | |
| Authors | R. Harikumar, S. Sampath, V. Sasi Kumar | |
| Source | Advances in Space Research, Elsevier, 43 (2009), 837¿844 | |
| Abstract | A Joss¿Waldvogel impact type disdrometer was installed at four different locations in the Indian peninsula during various periods from 2001 till date. The data are analysed to study the nature of rain drop size distribution (DSD) in this region. Out of the three well known distributions that describe DSD, namely, the Marshall¿Palmer, Gamma and Lognormal, it has been found that Lognormal distribution
fits the DSD in this region better than the other ones. Lognormal distributions for different rain rates were then derived by fitting the lognormal function to the data using a curve fitting software. Then the variation of fit parameters with rain rate was evaluated. Incorporating these variations, into the Lognormal distribution, an empirical equation that describes the DSD in this region for different
rain rates was derived. Then this equation was tested with sample data from each of these stations. The data used for validation were not
used for fitting lognormal equation to derive the fit parameters. The correlation between the DSD measured and derived using the empirical model was found to be quite good (0.9) except in some cases where the coefficient dropped to 0.75. The empirical model can be updated when more data are available. | |
| Paper No | 29 | Publication ID : 250 & Year : 2009 |
| Title | Properties of cloud base height during southwest monsoon period over a tropical station, Thiruvananthapuram | |
| Authors | Hamza Varikoden, R. Harikumar, V. Sasi Kumar, S. Murali Das, S. Sampath and G. Mohan Kumar | |
| Source | Current Science, Vol. 96, No. 4, 25 February 2009, 562-568 | |
| Abstract | The study of the clouds and their properties has remained unexplored, especially during the southwest (SW) monsoon season due to the unavailability of reliable data sets. Here we made an attempt to study the cloud base height (CBH) and its characteristics during the SW monsoon period of 2007 using CBH data obtained
by a Vaisala Laser Ceilometer (VLC). The VLC
was made operational at Thiruvananthapuram since
July 2006 to monitor the CBH every 15 s. The relation of CBH with meteorological parameters is studied using the radiosonde observations. We found that clouds during the SW monsoon season have mainly concentrated below 2500 m. A layer with relatively void clouds was present between 2500 and 4000 m. We call this region as cloud-free zone. The amplitude of variability
of CBH was less compared to the variability of
the cloud frequency. Active monsoon is when the
cloud frequency exceeds 70% and break phase is when it is less than 40%. The cloud frequency increases when the wind shear increases in the lower levels. Similarly, temperature is more during break phase of monsoon however, the relative humidity shows an increase during active phase of monsoon. Multiple clouds were also noticed during active phase, but it was negligible during break phases of monsoon. | |
| Paper No | 30 | Publication ID : 253 & Year : 2008 |
| Title | Comparison of TRMM precipitation data with Micro Rain Radar and Disdrometer data during different monsoon seasons | |
| Authors | R, Harikumar; Varikoden, Hamza; S, Sampath; G, Mohan Kumar; M, Gairola R. | |
| Source | Proceedings, 37th COSPAR Scientific Assembly. Held 13-20 July 2008, in Montréal, Canada., p.2535 (SAO/NASA ADS Astronomy Abstract Service) | |
| Abstract | Active radar observations from the TRMM Precipitation Radar provide high resolution satellitebased rainfall estimates. To understand these measurements, it would be needed to compare with ground-based measurements and also be awared of the seasonal dependance of the satellite measurements. This paper presents such a comparison carried out for Thiruvananthapuram (Lat: 8.523, Long: 76.910). A Micro Rain Radar and an impact type Joss- Waldvogel Disdrometer have been deployed in the premises of Centre for Earth Science Studies (CESS), Thiruvananthapuram to study the characterization of tropical rainfall. Rain drop size distribution (DSD) and rain rate are obtained at the surface from the disdrometer data and at different heights from the Micro Rain Radar. The data from the disdrometer and that from micro rain radar corresponding to a height of 35 metre from the surface are taken here for comparison with the TRMM data. TRMM rain rate is available as 3 hourly data over a 0.25o X 0.25o grid. The grid that corresponds to Thiruvananthapuram (Lat: 8.375o N to 8.625o N, Long: 76.875o E to 77.125o E) is chosen for the comparison. The analysis uses the rain rate data during the year 2006 obtained from the TRMM satellite, the disdrometer and the MRR. The correlation of the three hourly rainfall data between TRMM and disdrometer and TRMM and micro rain radar have been found to be significant. For the southwest and the northeast monsoon periods, the correlation between the data from the TRMM and disdrometer is 0.6. But from December to third week of May (non-monsoonal period), the data does not compare well. This may be due to the localized effects of rainfall due to local convection. Only 40% could be detected together by the TRMM and disdrometer sensors, out of the total number of events where at least any one of the sensors detect rain. Some of the events which could be detected by TRMM alone, could not be detected by the disdrometer and vice-versa. For rainfall events detected both by the satellite and ground based sensors, the TRMM rainfall appears to be under estimated in magnitude, on an average, up to 50%. This is due to the fact that the satellite comprises an area averaged data for the 0.25o X 0.25o grid. The number of events detected by single sensor only is being high indicates that the rainfall is not uniform even over a small grid size of 0.25X0.25 degrees. This also indicates the need to have closely knit network of ground stations for a more meaningful comparison. | |
| Paper No | 31 | Publication ID : 256 & Year : 2008 |
| Title | Study of Asian summer monsoon onset phase using satellite and ground based measurements | |
| Authors | Hamza Varikoden, R. Harikumar, S. Murali das, S. Sampath and G. Mohan Kumar | |
| Source | Proceedings, 37th COSPAR Scientific Assembly. Held 13-20 July 2008, in Montréal, Canada., p.3298 | |
| Abstract | Indian summer monsoon is a global phenomenon and is caused by the large convective heat source on the ITCZ (inter tropical convergence zone) in the northern hemisphere tropics extending from the Arabian Sea to the West Pacific Ocean. The convective heat source lasts for more than one hundred days. The convection marks the beginning of rainy season and the date on which a marked increase in rainfall is observed is known as the monsoon onset. The mean date of this onset of the Indian monsoon is 1st June, with a standard deviation of 8 days. The features of onset phase of southwest monsoon was analyzed from 2002 to 2007 with giving importance to 2007 monsoon onset because it has a double monsoon onset like characteristics. We analyzed the onsets using data from four different sources, namely, the TRMM (Tropical Rainfall Measuring Mission) 3 hourly rainfall (spatial resolution 0.25° X 0.25° latitudelongitude), meteorological parameters from NCEP/NCAR reanalysis data set, NOAA OLR (spatial resolution 2.5° X 2.5° latitude-longitude) and cloud base height from a Vaisala Laser Ceilometer installed at Trivandrum. The VLC data is available only for the last year. On the day of onset in 2007, rainfall reported by TRMM over the south Indian region is about 50 mm and the cloud occurrence of the day is 85% with an average cloud base height of 2 km. Out of it more than 65% is low level clouds with average cloud height is 1 km. During the onset phase, the convection is confined to south of 12° N and thereafter it weakens. Another band of convection is formed after the onset phase is leading to the northwards propagation of the monsoon surge. The characteristics of onset, such as deepening and strengthening of westerlies are shown only during the onset phase in 2007 and the monsoon circulation was built up again only after 10 to 12 days over the Kerala region after the onset phase. | |
| Paper No | 32 | Publication ID : 254 & Year : 2008 |
| Title | Altitudinal and Temporal Evolution of Rain Drop Size Distribution Observed Over a Tropical Station Using a Micro Rain Radar | |
| Authors | R. Harikumar and S. Sampath | |
| Source | Proceedings, 37th COSPAR Scientific Assembly. Held 13-20 July 2008, in Montréal, Canada., p.2534 (SAO/NASA ADS Astronomy Abstract Service) | |
| Abstract | Rain drop size distribution (DSD) measurements at different heights were made using a Micro Rain Radar (MRR-2) at Thiruvananthapuram (8.3 N, 76.9 E). The rain DSD data obtained from MRR has been compared with a Joss waldvogel impact type Disdrometer (RD-80) deployed nearby and they are in good agreement. The analysis uses the data for different rain episodes. Here presents the data during a continuous rainfall episode from 16:10:01 hrs to 16:12:31 hrs on 12th August 2006 only. The fall velocity (velocity of those drops which contribute most to rain rate) was more or less constant at different altitudes and also with time and the average value is 4.6 m/s. The rain rate was below 5 mm/hr for all the heights throughout the time. At the beginning of the rain episode, the number of drops at any given altitude was higher for smaller drops and lower for larger drops. But towards the end of the episode, the number of drops in the smallest size class has reduced at almost all heights, while the number of drops in the larger size classes has increased. This means that the larger drops coming from above collide with smaller drops and coalesce, thus sweeping out the smaller drops as they fall. It is also observed that, the number of drops falls exponentially with diameter at all heights. The number of drops at the small diameter end is very high at the highest altitude and decreases drastically as altitude decreases. This also suggests that, coalescence is more predominant than break-up during collisions of the rain drops as they fall. | |
| Paper No | 33 | Publication ID : 255 & Year : 2008 |
| Title | An Empirical Model for the variation of Rain Drop Size Distribution with Rain Rate at a few locations in Southern India | |
| Authors | R. Harikumar and S. Sampath | |
| Source | Proceedings, 37th COSPAR Scientific Assembly. Held 13-20 July 2008, in Montréal, Canada., p.2536 | |
| Abstract | Raindrop size distribution measurements have been made for varying periods at four different stations in the Southern Indian region using an electromechanical disdrometer. The stations
are Thiruvananthapuram (8.29 N, 76.59 E; 4 m amsl) and Kochi (9.58 N, 76.17 E; 5 m amsl),
which are west coast stations; Munnar (10.08 N, 77.07 E; 1500 m amsl), a high altitude station
in the western ghats and Sriharikota-SHAR (13.58 N, 80.29 E), an east coast station. The data
has been used to study the variation of number of raindrops with the drop size. The analysis
of the data has been done after grouped based on the season. The log-normal distribution
expresses the behaviour better than the gamma distribution in the entire rain rate or intensity
range. The variation of this log-normal distribution with rain rate or intensity has been studied. Using this, an empirical model for raindrop size distribution in terms of drop diameter and rain rate has been derived of the form
N(D,R) = [(A0 + A1R + A2LnR)/D]exp[−0.5(LnD − (B0 + B1R + B2LnR)/C)2]
Where D is the drop diameter, R is the rain rate and A0,A1,A2,B0,B1,B2 and C are fit
parameters. These fit parameters are found by iterative method for all the seasons in each
station. The empirical model has been tested with measurements and found a correlation coefficient
of above 0.9 for all the seasons in all the stations, except for the station SHAR. The
correlation coefficient for SHAR decreases as intensity increases. The correlation coefficient is 0.98 for the lowest rain rate and it is 0.72 for the highest observed rain rate. | |
| Paper No | 34 | Publication ID : 251 & Year : 2007 |
| Title | Comparison of drop size distribution between stations in Eastern and Western coasts of India | |
| Authors | R.Harikumar, V.Sasi Kumar, S.Sampath and P.V.S.S.K.Vinayak | |
| Source | J. Ind. Geophys. Union ( April 2007 ), Vol.11, No.2, pp.111-116 | |
| Abstract | A Joss-Waldvogel type disdrometer was installed at Thiruvananthapuram, Kochi, and Sreeharikotta
(SHAR) during various periods. This paper presents results from the analysis of the data.
Drop Size Distribution (DSD) and rainfall rate for each minute were computed from the disdrometer data, and the entire data for each month were sorted by rainfall rate. The data were
then divided into different ranges of rainfall rate and DSD computed for each. The average DSD
for each range was fitted with a lognormal distribution function of the form
N(D) = (a0/D) exp (-0.5(ln( D)-a1)/a2)2
where D = drop diameter, N(D) = number of drops/m3/mm interval.
The results show the following: For the lowest rainfall intensity, the distribution is narrow
and is dominated by small drops. With increase in intensity, the distribution spreads out and more
larger drops appear. However, in some cases, the data does not follow the lognormal distribution.
The total number of drops, NT, geometric mean diameter, Dg and standard geometric deviation,
σ was derived from the ai. NT showed a tendency to increase slightly with rainfall rate. Dg followed a simple power relationship of the form Dg = b0Rb1. The standard geometric deviation did not show any significant dependence on rainfall rate.
The characteristics of rainfall in terms of the three parameters for coastal stations on the
west coast are similar. The rate of increase of NT is higher at SHAR than at Kochi. NT is higher at SHAR than at Kochi for any particular rainfall rate, indicating that, unlike Kochi and other stations on the western coast, rainfall at SHAR is made up of more number of smaller drops. | |
| Paper No | 35 | Publication ID : 257 & Year : 2007 |
| Title | Investigation on the variation of rain Drop Size Distribution with rainfall intensity at tropical stations in peninsular India | |
| Authors | R. Harikumar, S. Sampath and V. Sasi Kumar | |
| Source | Proceedings, TROPMET 2007, Bhopal, December-2007. | |
| Abstract | Rain drop size distribution (DSD) was studied using a Joss-Waldvogel type Disdrometer installed at four tropical stations, Thiruvananthapuram (Lat: 8.29º N, Long: 76.59º E), Kochi (9.58º N, 76.17º E), Munnar ( 10.08º N, 77.07º E) and Sriharikota-SHAR (13.58º N, 80.29º E). Thiruvananthapuram is on the west coast at the tip of peninsular India. Kochi is an important commercial city in Kerala situated on the western coast on the shores of the state¿s largest estuary. Munnar is a hill station about 130 km east of Kochi on the Western Ghats in South India (at about 1500 m amsl) and Sriharikota is on the eastern coast. Thiruvananthapuram, Kochi and Sriharikota experience rainfall intensities (R) greater than 100 mm/hr while the rainfall intensity in Munnar is rarely close to 100 mm/hr.
The entire data were divided into periods of different rainfall intensity. The intensity ranges used were from < 0.01 mm/hr to >100 mm/hr with boundaries of 0.02, 0.05, 0.1, 0.2, 0.5, 1, 2, 5, 10, 20, 50 and 100 mm/hr. The mean DSD for each intensity range was computed. The DSD values were fitted with the log-normal distribution function
Three physically significant parameters, namely, total number of drops (NT), geometric mean diameter (Dg) and standard geometric deviation (σ), were derived from the fit parameters. We found that NT increases gradually with rainfall intensity at Kochi and Sriharikota (Fig. 2) for all intensities (Harikumar et al. 2007). But at Munnar, it increases with intensity up to around 3 mm/hr and then decreases at higher intensities with an accompanying increase in Dg. At Thiruvananthapuram, the variation up to 3 mm/hr follows the normal pattern, but then NT remains more or less constant or starts decreasing. We fitted the values with the expression NT = aRb, as suggested by (Verma and Jha 1996). The fit was good for the stations other than Munnar. The geometric mean diameter values were also fitted with a similar expression. We found that, at Thiruvananthapuram, Kochi and Sriharikota, Dg increases with rainfall intensity (Fig. 3). But at Munnar, Dg remains more or less constant for intensities up to about 3 mm/hr and then increases exponentially. The standard geometric deviation (σ) did not show any significant dependence on rainfall intensity.
The characteristics of rainfall in terms of the three parameters for coastal stations on the west coast, i.e., Thiruvananthapuram and Kochi, are similar. But the characteristic at Sriharikota, a station on the east coast, is different from that at Kochi and Thiruvananthapuram. At Sriharikota, NT increases faster with rainfall intensity than at Kochi. In fact, for any given rainfall intensity, NT is higher at Sriharikota than at Kochi. Dg increases with rainfall intensity at both the places. But for any given intensity, the Dg at Kochi is higher than that at Sriharikota. Thus, for a given intensity of rainfall, there are less number of drops at Kochi than at Sriharikota, and the drops are generally larger in size. In other words, rainfall at Sriharikota is made up of more number of smaller drops compared to Kochi. | |
| Paper No | 36 | Publication ID : 252 & Year : 2007 |
| Title | Rainfall intensity characteristics at coastal and high altitude stations in Kerala | |
| Authors | V Sasi Kumar, S Sampath, P V S S K Vinayak and R Harikumar | |
| Source | J. Earth Syst. Sci., Springer, 116, No. 5, October 2007, pp. 451¿463 | |
| Abstract | Rainfall intensities measured at a few stations in Kerala during 2001¿2005 using a disdrometer were found to be in reasonable agreement with the total rainfall measured using a manual rain gauge.
The temporal distributions of rainfall intensity at different places and during different months
show that rainfall is of low intensity (<10mm/hr), 65% to 90% of the time. This could be an indication of the relative prevalence of stratiform and cumuliform clouds. Rainfall was of intensity <5mm/hr for more than 95% of the time in Kochi in July 2002, which was a month seriously
deficient in rainfall, indicating that the deficiency was probably due to the relative absence of cumuliform clouds. Cumulative distribution graphs are also plotted and fitted with the Weibull distribution. The fit parameters do not appear to have any consistent pattern. The higher intensities also contributed significantly to total rainfall most of the time, except in Munnar (a hill station).
In this analysis also, the rainfall in Kochi in July 2002 was found to have less presence of high
intensities. This supports the hypothesis that the rainfall deficiency was probably caused by the
absence of conditions that favoured the formation of cumuliform clouds. | |
| Paper No | 37 | Publication ID : 259 & Year : 2007 |
| Title | An extensive study on Rain DSD over tropical stations in Peninsular India using a J-W Disdrometer | |
| Authors | R. Harikumar, S. Sampath and V. Sasi Kumar | |
| Source | Proc. Geophysical Research Abstracts, Vol. 9, 00790, 2007, SRef-ID: 1607-7962/gra/EGU2007-A-00790, European Geosciences Union Assembly-2007, Vienna, Austria, April-2007. | |
| Abstract | Rain drop size distribution (DSD) was studied using a Joss-Waldvogel type Disdrometer
installed at four tropical stations, Thiruvananthapuram (Lat: 8.29 N, Long: 76.59
E), Kochi (9.58 N, 76.17 E), Munnar ( 10.08 N, 77.07 E) and Sriharikota (13.58 N,
80.29 E). Thiruvananthapuram is on the west coast at the tip of peninsular India. Kochi
is an important commercial city in Kerala situated on the western coast on the shores
of the state¿s largest estuary. Munnar is a beautiful hill station about 130 km east of
Kochi on the Western Ghats in South India (at about 1500 m amsl) and Sriharikota is
on the eastern coast. Thiruvananthapuram, Kochi and Sriharikota experience rainfall
intensities greater than 100 mm/hr while the rainfall intensity in Mannar is rarely close
to 100 mm/hr. The entire data were divided into periods of different rainfall intensity. The intensity ranges used were from < 0.01 mm/hr to >100 mm/hr with boundaries of 0.02, 0.05,
0.1, 0.2, 0.5, 1, 2, 5, 10, 20, 50 and 100 mm/hr. The mean DSD for each intensity range
was computed. The DSD values were fitted with the log-normal distribution function of the form
N(D) = (a0/D) exp (-0.5((ln(D) − a1)/a2)2)
Three physically significant parameters, namely, total number of drops (NT ), geometric
mean diameter (Dg) and standard geometric deviation (), were derived from the
fit parameters. We found that NT increases gradually with rainfall intensity at Thiruvananthapuram, Kochi and Sriharikota for all intensities. But at Munnar, it increases
with intensity up to 1 mm/hr and then decreases at higher intensities. We fitted the values with the expression NT= aRb, as suggested by Verma and Jha (Raindrop size distribution model for Indian climate, Indian J. Radio Spa Phys, vol. 25, 15-21, 1996). The fit was good for the stations other than Munnar. The geometric mean diameter values were also fitted with a similar expression. We found that, at Thiruvananthapuram,
Kochi and Sriharikota, Dgincreases with rainfall intensity. But at Munnar, Dgremains
more or less constant for intensities up to about 1 mm/hr and then increases exponentially.
The standard geometric deviation did not show any significant dependence on rainfall intensity.
The characteristics of rainfall in terms of the three parameters for coastal stations on
the west coast, i.e., Thiruvananthapuram and Kochi, are similar. But the characteristic
at Sriharikota, a station on the east coast, is different from that at Kochi and Thiruvananthapuram. At Sriharikota, NT increases faster with rainfall intensity than
at Kochi. In fact, for any given rainfall intensity,NT is higher at Sriharikota than at
Kochi.Dg increases with rainfall intensity at both the places. But for any given intensity,
theDgat Kochi is higher than that at Sriharikota. Thus, for a given intensity of rainfall, there are less number of drops at Kochi than at Sriharikota, and the drops are generally larger in size. In other words, rainfall at Sriharikota is made up of more number of smaller drops compared to Kochi. | |
| Paper No | 38 | Publication ID : 258 & Year : 2007 |
| Title | Spatial and temporal evolution of rain drop size distribution | |
| Authors | R. Harikumar, V. Sasi Kumar and S. Sampath | |
| Source | Proceedings, METOC-2007, pp. 159-163, Kochi, May 2007. | |
| Abstract | Rain drop size distribution measurements at different heights were made using a Micro Rain Radar (MRR-2) at Thiruvananthapuram. The analysis uses the data during a continuous rainfall episode from 16:10:01 hrs to 16:12:31 hrs on 12th August 2006. The fall velocity (velocity of those drops which contribute most to rainrate) was more or less constant at different altitudes and also with time and the average value is 4.648 m/s. The rain rate was below 5 mm/hr for all the heights throughout the time. At the beginning of the rain episode, the number of drops at any given altitude was lower for larger drops. But towards the end of the episode, the number of drops in the smallest size class has reduced at almost all heights, while the number of drops in the larger size classes has increased. The larger drops coming from above collide with smaller drops and coalesce, thus sweeping out the smaller drops as they fall. | |
| Paper No | 39 | Publication ID : 261 & Year : 2006 |
| Title | Rain Drop Size Distribution studies using a Disdrometer and a Micro rain radar | |
| Authors | R. Harikumar, V. Sasi Kumar, P.V.S.S.K.Vinayak & S. Sampath | |
| Source | Proceedings, National Space Science Symposium (NSSS-2006), pp. 59, Visakhapatnam, February-2006. | |
| Abstract | Rain drop size distribution measurements are being carried out at CESS, Thiruvananthapuram using a Joss-Waldvogel disdrometer and a micro rain radar. The disdrometer, an electromechanical instrument, gives the DSD at the surface. The micro rain radar, a Doppler radar, gives the DSD at different heights, starting from 200 m. Both the instruments are deployed at the same site. Measurements made during a few rainfall events are compared and the general characteristics are derived.
The DSD measured at the surface and at 200m follows a log-normal distribution, as shown in Figure 1. But the radar measurements differ from the log-normal distribution above 400m altitude, as shown in Figure 2. The smaller drop sizes show an exponential decrease with increasing drop diameter rather than the increase as expected from a log-normal distribution. The presence of a large number of smaller drops above 400 m and their relative absence below this altitude are presented and discussed. | |
| Paper No | 40 | Publication ID : 262 & Year : 2006 |
| Title | Rain Drop Size at different heights | |
| Authors | R. Harikumar, V. Sasi Kumar, S. Sampath and P.V.S.S.K. Vinayak | |
| Source | Proceedings, 18th Kerala Science Congress-2006, pp. 244-245, Thiruvananthapuram, January-2006. | |
| Abstract | Rain drop size distributions at different heights, and at the surface, were measured using a Micro Rain Radar and a disdrometer at Thiruvananthapuram. The data obtained for a continuous rainfall event of one hour duration on 12th October are presented and discussed. The data from both instruments are in agreement. The number of drops falls exponentially with diameter at all heights. The number of drops at the small diameter end is very high at the highest altitude and decreases drastically as altitude decreases. At the surface, the DSD follows a lognormal distribution, as observed earlier also. | |
| Paper No | 41 | Publication ID : 260 & Year : 2006 |
| Title | Rainfall intensity and DSD at sea level and at 1500 m altitude in southern India - studies using TRMM and Disdrometer data | |
| Authors | Harikumar, R.; Sasikumar, V.; Sampath, S. | |
| Source | Proceedings, 36th COSPAR Scientific Assembly. Held 16 - 23 July 2006, in Beijing, China. Meeting abstract from the CDROM, #1027 (SAO/NASA ADS Astronomy Abstract Service) | |
| Abstract | Rainfall intensity and rain drop size distribution were studied using TRMM data and a Joss-Waldvogel type disdrometer installed at Kochi Lat 9 9 N Long 76 2 E 15 m amsl and Munnar Lat 10 1 N Long 77 1 E 1500 m amsl during the south-west monsoon period The stations are situated in Kerala an elongated coastal state in the south-west tip of peninsular India Kochi is an important commercial city in Kerala situated close to the western coast and on the shores of the state s largest estuary Munnar is a beautiful hill station about 130 km east of Kochi on the Western Ghats in South India The average annual rainfall is 310 cm at Kochi and 380 cm at Munnar The TRMM data were retrieved for Kochi and Munnar regions and the 3-hourly intensity values obtained The data from the disdrometer were used to compute rainfall intensities and were compared with the intensities from the TRMM data Generally above 95 of the rain events has rainfall intensity less than 5 mm hr for both the stations Kochi experiences intensities greater than 100 mm hr while the rainfall intensity in Munnar is rarely close to 100 mm hr The disdrometer data were also used to derive rain drop size distribution at the two stations Rain drop size distributions for different intensity ranges from the disdrometer data The entire data were divided into periods of different rainfall intensity The intensity ranges used were from 0 01 mm hr to 100 mm hr with boundaries of 0 02 0 05 0 1 0 2 0 5 1 2 5 10 20 and 50 mm hr The mean DSD for each intensity range was computed The DSD values | |
| Paper No | 42 | Publication ID : 375 & Year : 2005 |
| Title | Ambient carbon monoxide measurements in the ISRO-GBP land campaign at Jaduguda by Centre for Earth Science Studies | |
| Authors | G. Mohan kumar, V.S. Jeena, R. Harikumar and S. Sampath | |
| Source | Technical report submitted to ISRO | |
| Abstract | . | |
| Paper No | 43 | Publication ID : 263 & Year : 2005 |
| Title | Comparison of Drop Size Distribution between stations in Eastern and Western coasts of India | |
| Authors | R. Harikumar, V. Sasi Kumar, S. Sampath and P.V.S.S.K. Vinayak | |
| Source | Proceedings, 42nd Annual Convention of the Indian Geophysical Union-2005, pp. 32-33, Bhopal, December-2005. | |
| Abstract | A Joss-Waldvogel type disdrometer was installed at Thiruvananthapuram, Kochi, and Sreeharikotta (SHAR) during various periods. This paper presents results from the analysis of the data.
DSD and rainfall rate for each minute were computed from the disdrometer data, and the entire data for each month were sorted by rainfall rate. The data were then divided into different ranges of rainfall rate and DSD computed for each. The average DSD for each range was fitted with a lognormal distribution function.
The results show the following: For the lowest rainfall intensity, the distribution is narrow and is dominated by small drops. With increase in intensity, the distribution spreads out and more larger drops appear. However, in some cases, the data does not follow the lognormal distribution.
The total number of drops, NT, geometric mean diameter, Dg, and standard geometric deviation, σ were derived from the ai. NT showed a tendency to increase slightly with rainfall rate. Dg followed a simple power relationship of the form Dg = b0Rb1.The standard geometric deviation did not show any significant dependence on rainfall rate.
The characteristics of rainfall in terms of the three parameters for coastal stations on the west coast are similar. The rate of increase of NT is higher at SHAR than at Kochi. NT is higher at SHAR than at Kochi for any particular rainfall rate, indicating that, unlike Kochi and other stations on the western coast, rainfall at SHAR is made up of more number of smaller drops.
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| Paper No | 44 | Publication ID : 264 & Year : 2004 |
| Title | A Study on Rain Drop Size Distribution | |
| Authors | R. Harikumar, V. Sasi Kumar, S. Sampath and P.V.S.S.K. Vinayak | |
| Source | Proceedings, 14th Swadeshi Science Congress-2004, pp. 51, Thekkady, November-2004 | |
| Abstract |
Rain is an important part of climate and even a part of life in kerala. But, studies on rain has not been done much so far in Kerala. Most of the centres here measures the rainfall over a period of one day. Because, the features of the rainfall with a durartion of less than a day as well as the size of rain drops have not been studied yet. The detailed studies of the size of the raindrops, rain rate and the relation between these two are explained in this paper.
The rain drop size distribution measurements have been done at Thiruvananthapuram and Kochi using an instrument viz. Disdrometer. These data will be logged into a computer every minute automatically. The number of drops in every 20 diamter classes will be logged into a computer. The rain rate could be found out from these data. This data has been classified on the basis of the rain rate. The average number of drops in these 20 diameter classes corresponding to each rain rate ranges has been found out and fitted with a lognormal distribution function. The 'Total number of drops' and 'Geometric mean diameter' has been derived from this fit. The variation of these two parameters with rain rate has been found out. It is found out that these variations have differences at Thiruvananthapuram and Kochi. The results will presented and discussed in detail in the paper.
(This abstract in this proceedings is in malayalam, which is the mother toungue of Kerala. This paper has been presented in Malayalam too)
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