Riverine freshwater plume variability in the Bay of Bengal using wind sensitivity experiments

Abstract

The role of winds in determining the dispersal pattern of the freshwater plume in the Bay of Bengal (BoB) is investigated using a high-resolution regional ocean model with realistic coastline, bathymetry, and river discharge data. Multiple experiments are carried out with idealized winds of different directions and speeds representing the seasonal wind patterns in the BoB. Monthly climatology of freshwater discharge from the major rivers in the domain is included at the geographic locations. The freshwater plume is channelled along the coast in cases of southeasterly and northeasterly winds but is forced towards the central BoB under southwesterly winds. The variations in equivalent depth of freshwater suggest that the high winds tend to confine the low-saline water in the northern and northeastern parts of the BoB. The momentum analysis shows that geostrophic balance dominates throughout the vertical section in the plume. The vertical viscosity also plays an important role in the upper ocean in response to the varying wind directions. The high wind condition in the bay confines the freshwater in its northernmost parts with equivalent depth >8 m. An increase in wind speed from 2 to 8 m s−1 results in the enhancement of southward meridional surface salt advective flux (SSAF) from 2 to 10 kg m−2 s−1 along the western boundary of the BoB. Thus, the distinct roles of wind speed and direction on the characteristics of the freshwater plume in the BoB are demonstrated using idealized numerical experiments.