Sensitivity of the Bay of Bengal Upper Ocean to Precipitation and River Runoff
Adamas University, Kolkata
Department of Mathematics, Adamas University Kolkata, West Bengal, India Pincode: 700126 Mobile: 9775576844 E-mail: email@example.com
The Bay of Bengal (BoB) is uniquely distinguishable from other parts of the tropical world ocean for its intense spatio-temporal salinity contrast caused by the enormous amount of freshwater input, mostly in its northern sector, from monsoon rain and river runoff. This study investigates the sensitivity of the BoB upper ocean characteristics to these two freshwater sources using the Regional Ocean Modeling System (ROMS). A set of four long-term eddy-resolving simulations is carried out using different combinations of the two freshwater components, while keeping all other forcing unchanged. Simulated fields show that the freshwater inputs largely affect the thermohaline structure, circulation, and the upwelling along the western boundary of the BoB. The impact of freshwater on sea surface temperature (SST) is very small compared to the impact on sea surface salinity (SSS). The presence of freshwater in the surface layers marginally reduces the SST mostly in the northern BoB during the post-monsoon and winter season. The major impact of freshwater on temperature is realized in the subsurface layers - heating within the barrier layer and cooling in the layers underneath. The precipitation reduces the SSS over the entire domain throughout the year; however, it is not sufficient to maintain the SSS contrast observed in the BoB. The river runoff impacts regionally over the plume areas (maximum near the river mouths) and plays the dominant role in maintaining the spatial and seasonal salinity contrast. In addition, the river runoff is found to be the primary factor behind the formation of the near surface stratification, barrier layer and temperature inversions observed in the northern BoB. The freshwater input increases the SSH and shoals the D20 of the domain. The formation, maintenance and intensity of the southward flowing current along the northwest coast during the summer monsoon, followed by the southward flowing east India coastal current (EICC) along the western boundary are substantially affected by the freshwater input, especially from river runoff.