Modulation of the Ganges-Brahmaputra river plume by the Indian Ocean Dipole and eddies inferred from satellite observations
Event: 2017 Ocean Surface Topography Science Team Meeting
Session: Science III: Mesoscale and sub-mesoscale oceanography
Presentation type: Type Oral
The Bay of Bengal (BoB) receives large amounts of freshwater from the Ganga-Brahmaputra river during the summer monsoon. The resulting upper-ocean freshening influences seasonal rainfall, cyclones, and biological productivity. Ocean currents play a prominent role in the BoB sea surface salinity (SSS) space-time variations, in particular the western boundary current known as the East Indian Coastal Current (EICC). Sparse in-situ observations suggest that the EICC transports these freshwaters southward after the monsoon as a ~200-km wide, 2000-km long “river in the sea” along the East Indian coast. Circulation changes associated with the Indian Ocean Dipole (IOD) and offshore meandering of freshwater due to mesoscale eddies can strongly influence the transport of freshwater within the BoB. SSS from the Soil Moisture Active Passive (SMAP) satellite along with altimetry data, including sea surface height (SSH) and currents, provide unprecedented views of this peculiar “river in the sea” feature from intraseasonal to interannual timescales. The good correspondence in the synergistic use of SSS and altimetry, two independent datasets, shows that SMAP SSS well captures mesoscale features such as eddies. In addition, SMAP SSS agree well with in-situ measurements, capturing the strong cross-shore SSS contrasts (~10-pss) measured along ship transects. Our results further show that remote forcing associated with the negative IOD in the fall of 2016 caused a stronger EICC and “river in the sea” that extended approximately 800 km further south than that in 2015. Moreover, mesoscale eddies induced meandering of this plume, exporting freshwater away from the coast.