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 20-Year satellite climatology of ocean circulation in the Northern Indian Ocean.
Poster Title: 20-Year satellite climatology of ocean circulation in the Northern Indian Ocean.
Submitted on 05 Apr 2022
Author(s): Dhage, L., Strub, T., Durland, T., Matano, R., & Somayajulu, Y. K.
This poster was presented at 6th Coastal Altimetry Workshop. Lake Garda, Italy.
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Poster Information
Abstract: Previous studies have shown that Downwelling Kelvin Waves can propagate from the Equator to the Bay of Bengal (BoB) and around Sri Lanka to the west coast of India, while Upwelling Kelvin Waves propagate only to the BoB. Modeling experiments suggest that upwelling along India’s SW coast is forced by winds along India’s east coast. Here we correlate the upwelling and downwelling sea level signals (AVISO gridded Sea Level Anomalies, SLA) along India’s southwest coast to alongshore winds in coastal bands along the wave guide connecting the equator to western India. We examine two periods: 1) The Summer Monsoon (Upwelling: June-September); and 2) The Winter Monsoon (Downwelling: November-March). During Downwelling, high SLA along the southwest coast of India are highly correlated with the winds from India’s southern tip to its northeast coast, suggesting the importance of wind forcing along this entire path. During Upwelling, low SLA along the southwest coast are highly correlated with the winds from the west coast of India to eastern Sri-Lanka, suggesting forcing by alongshore winds in a smaller, more local domain than for downwelling. Lagged correlations of sea level from the southwest coast of India with the sea level from the east and west coast of India support a hypothesis that the upwelling signal first appears at the tip of Sri-Lanka and southern India and then slowly progresses west and northward along the west coast of India.Summary: Downwelling: Low correlations between SLA off SW India and winds for Box 1 and significant correlations with increasing lag as we travel from Box 2 to Box 5 suggest the importance of remote forcing for the downwelling signal, especially from the east coast of India. These correlations reduce quite a bit for Box 4 and Box 5 during positive Indian Ocean Dipole (IOD) years [94,97,06], suggesting weakening of the progression for downwelling signal during IOD years.

References: 1. Rao, R.R., M.S. Girish Kumar, M. Ravichandran, A.R. Rao, V.V. Gopalakrishna and P. Thadathil (2010), Interannual variability of Kelvin wave propagation in the wave guides of the equatorial Indian Ocean, the coastal Bay of Bengal and the southeastern Arabian Sea during 1993-2006, Deep-Sea Res (114), I:57, 1-13/

2. D. Shankar and S.R. Shetye (1997), On the dynamics of Lakshadweep high and low in the southeastern Arabian Sea, J. Geophys. Res. (102), 0148-0227/97/97JC00465

3. J. Vialard, S.S.C. Shenoi, J. P. McCreary, D. Shankar, F. Du-rand, V. Fernando, and S. R., Shetye (2009), Intraseasonal response of Northern Indian Ocean coastal waveguide to the Madden-Julian Oscillation, Geophys. Res. Lett. (36), L14606, doi:10.1029/2009GL038450

4. Durand, F., Shankar, D., Birol, F. and S.S.C. Shenoi (2009), Spatio-temporal structure of the East India Coastal Currrent from satellite altimetry, J. Geophys. Res. (114), C02013, doi:10.1029/2008JC004807/
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