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Ratheesh, Smitha
- Estimating Biological Parameters of a Coupled Physical-Biological Model of the Indian Ocean Using Polynomial Chaos
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PDF Views:79
Authors
Affiliations
1 Oceanic Sciences Division, Atmospheric and Oceanic Sciences Group, Space Applications Centre, Ahmedabad 380 015, IN
1 Oceanic Sciences Division, Atmospheric and Oceanic Sciences Group, Space Applications Centre, Ahmedabad 380 015, IN
Source
Current Science, Vol 110, No 8 (2016), Pagination: 1544-1549Abstract
A statistical emulator technique, namely polynomial chaos, has been used to estimate two time-dependent biological parameters of a coupled physical-biological model of the Indian Ocean. This has been achieved by minimizing a distance function representing misfit between model simulated and satellite-derived surface chlorophyll. First, the parameters have been assumed to be constant in time and optimized values have been found by minimizing a time-averaged distance function. Since no significant improvement in model simulation has been found using a fixed set of optimum parameters, minimization has been carried out daily, assuming the parameters to be time-dependent. Emulation with this set of parameters has led to a significant improvement in the simulated surface chlorophyll. Smoothing of the parameters with singular spectrum analysis has caused less noisy simulations, at the cost of increasing the model data misfit. Time-varying parameters have been found to be more suitable for the hindcast of daily averaged chlorophyll both in the Arabian Sea and the Bay of Bengal.Keywords
Coupled Physical–Biological Model, Distance Function, Polynomial Chaos, Surface Chlorophyll.Full Text
- Seasonal Behaviour of Upper Ocean Freshwater Content in the Bay of Bengal:Synergistic Approach Using Model and Satellite Data
Abstract Views :280 |
PDF Views:110
Authors
Smitha Ratheesh
1,
Rashmi Sharma
1,
K. V. S. R. Prasad
2,
Neeraj Agarwal
1,
Rashmi Sharma
1,
V. S. R. Prasad
2
Affiliations
1 Space Applications Centre, Oceanic Sciences Division, Ahmedabad 380 058, IN
2 Department of Meteorology and Oceanography, Andhra University, Visakhapatnam 530 003, IN
1 Space Applications Centre, Oceanic Sciences Division, Ahmedabad 380 058, IN
2 Department of Meteorology and Oceanography, Andhra University, Visakhapatnam 530 003, IN
Source
Current Science, Vol 115, No 1 (2018), Pagination: 99-107Abstract
Any Change In Precipitation, Evaporation And River Discharge, By Virtue Of Its Impact On The Distribution Of Ocean Salinity, Leaves Its Inevitable Signature On The Freshwater Content (fwc) In The Oceans. In This Study, Synergistic Use Of Satellite Data And Numerical Ocean Circulation Model Is Explored To Examine The Seasonality Of Fwc Of The Upper 30 M Water Column Of The Bay Of Bengal (bob). For This Purpose, First The Sea Surface Salinity (sss) From Aquarius Is Assimilated Into A Model Of The Indian Ocean. Strength Of Assimilation Is Judged By Comparing Simulated Sss With Satellite And Argo Datasets. An Overall Improvement Of 39% Is Observed In Sss Over Free Run Of The Model Without Data Assimilation. Next, The Focus Is Shifted To The Spatial And Temporal Variability Of Fwc Of The Upper 30 M Of Bob In Relation To The Different Components Of Freshwater Forcing. A Delay Of Three Months In The Peak Of Fwc Is Observed With Respect To The Peak Of Net Freshwater Influx For Bob As A Whole. However, The Nature Of The Response Of Fwc To The Total Freshwater Input Forcing In The Major River-dominated Regions Of Bob Is Different From That For The Whole Bob. The Relative Role Of River Influx In Controlling Fwc In These Regions Is Well Brought Out In The Study. For The Ganga–brahmaputra Region, River Run-off Is Observed To Be A Crucial Parameter In Regulating Fwc, Whereas For Both Irrawaddy River Region And Central Bob, Precipitation Dominates The Response. The Response Of Salinity In The Uppermost Part Of The Northern Bob To The Total Freshwater Input Is Much More Rapid Than In The Other Regions.Keywords
Freshwater Content, Sea Surface Salinity, Seasonal Variability, Upper Ocean Region.Full Text
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- Role of Ocean Dynamics on Mesoscale and Sub-Mesoscale Variability of Ekman Pumping for the Bay of Bengal using SCATSAT-1 Forced Ocean Model Simulations
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Authors
Affiliations
1 Oceanic Sciences Division, Space Applications Centre, ISRO, Ahmedabad 380 015, IN
1 Oceanic Sciences Division, Space Applications Centre, ISRO, Ahmedabad 380 015, IN
Source
Current Science, Vol 117, No 6 (2019), Pagination: 993-1001Abstract
Role of ocean dynamics on vertical velocity of Ekman pumping (VVE) is analysed using simulations from very high resolution Ocean General Circulation Model (OGCM) configured for the Bay of Bengal (BoB). For this purpose, OGCM is forced with SCATSAT-1 scatterometer wind fields for 2017. Three mechanisms which modify VVE in the ocean are addressed in this study; the first results from the influence of sea surface temperature (SST) on wind field, and the other two arise from the influence of ocean surface currents (OSCs) on the wind field. Analysis for different length scales ranging from mesoscale to sub-mesoscale is also carried out. The results suggest a significant role of ocean dynamics on VVE, especially over submesoscale range (spatial scales of the order of 2– 10 km). Relative vorticity of OSC-induced Ekman pumping is found to be quite high (~3 m/day) at 2 km length scale, especially along the periphery of mesoscale eddies and along the filament structures. Impact of SST on VVE is least amongst the three factors and is observed to be significant only up to the length scales of 30 km. For length scales less than 10 km, relative vorticity-induced Ekman pumping increases drastically and the total Ekman pumping vertical velocity is predominantly controlled by the relative vorticity of OSC-induced Ekman pumping only.Keywords
Ekman Pumping, Ocean Dynamics, Scatterometers, Vertical Velocity, Wind Field.Full Text
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