On the Sea Surface Temperature variability and mesoscale dispersion in the Bay of Bengal during 2015 and 2019 monsoon as tracked by drifters

Siddhant Kerhalkar, University of Massachusetts Dartmouth, School for Marine Sciences and Technology, New Bedford, MA, United States, Amit Tandon, University of Massachusetts, Dartmouth, Mechanical Engineering, Dartmouth, United States, Emily Shroyer, Oregon State Univ, Corvallis, United States, Luca Raffaele Centurioni, Scripps Institution of Oceanography, University of California San Diego, La Jolla, United States, Jonathan D Nash, Oregon State University, Corvallis, United States, Jennifer A MacKinnon, Scripps Institution of Oceanography, La Jolla, United States, J. Thomas Farrar, Woods Hole Oceanographic Inst, Department of Physical Oceanography, Woods Hole, United States and Leah Johnson, Applied Physics Laboratory University of Washington, Seattle, United States
Abstract:
Indian summer monsoon consists of strong intra-seasonal variability in convection and resulting rain. The periods of active convection are often associated with rain leading to cooling of SSTs, while break periods are marked by absence of rain and warming of SST’s with strong diel cycles in SST. As part of the field program in summer 2019 for Monsoon Intra-Seasonal Oscillations in the Bay of Bengal (MISOBOB), about 30 Surface Velocity Program (SVP) drifters were deployed as a part of the Global Drifter Program. SVP drifters reported the location, Sea Surface Temperature (SST) and Sea Level Pressure (SLP) every 15 minutes. The deployment of the drifters started approximately about 300km off the Indian coast (i.e. in the western side of the Bay of Bengal) with initial distance between drifters being approximately 20 km. Due to the strong eastward mesoscale flow the drifters acted as an excellent tracker for the mesoscale flow. As the drifters tracked the mesoscale flow, most showed SST warming with strong diel cycles, characteristic of the Monsoon break periods. After about 17 days, many of the drifters showed an abrupt end of diel cycling and an SST cooling trend, associated with a depression in the North Bay. At short time scales, the drifter separation can decrease before dispersing on long time scales. This study also considers the impact of mesoscale temporal variability on SST variability, as well as SST gradients during active-break periods. Using remotely sensed (and in some cases in-situ) salinity maps, we also consider the impact of salinity on SST variability in the Bay of Bengal.
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