Mixed layer evolution in high and low sea level anomaly features in the Bay of Bengal

Abstract

Argo temperature and salinity profiles from 2015 through 2018 in the Bay of Bengal are combined with satellite altimetry and reanalysis data to compare surface layer evolution within regions of high and low sea level anomaly (SLA), which includes mesoscale eddies, with emphasis on the period May through October spanning the transition into and through the summer monsoon. The seasonality of the high-SLA group is especially pronounced, with warmer sea surface temperature (SST) during the pre-summer monsoon; deeper mixed layer depth (MLD) during the summer monsoon; lower sea surface salinity (SSS) during the post-summer monsoon; and increased in barrier layer thickness (BLT) during the winter monsoon. Summer monsoon heat flux estimated from integrated upper ocean heat content is negative (heat flux out of the water column) in both SLA cases. However, the high-SLA heat loss for the upper 70 m is about 3 times greater in magnitude than the low-SLA group: 22 W/m2 versus 8 W/m2. On comparison to the air-sea heat flux from ERA5 reanalysis, we find that heat convergence by ocean processes into the water column account for about 67% of the heat lost via air-sea exchange in the high-SLA group and about 86 % of the heat lost via air-sea heat flux in the low-SLA group.