Spatial variability of air-sea interaction in the Indian Summer Monsoon from multi-platform measurements

The shallow summertime mixed layer in the Bay of Bengal facilitates relatively rapid adjustment of the upper ocean to surface forcing. Previous work has documented substantial horizontal variations in upper-ocean boundary layer properties on scales of 1-100 km, and provided tantalizing evidence for the importance of air-sea coupling and feedbacks at these small scales. To investigate these processes during the 2019 summer monsoon in the Bay of Bengal, we deployed three deeply drogued surface buoys, carrying high quality surface meteorological instruments and heavily instrumented Wirewalker wave-powered profiling systems. By measuring the ocean surface forcing on minute time-scales concurrently with vertically well-resolved ocean boundary layer variability in time, the detailed relationship between forcing and response can begin to be untangled. In particular, we have characterized ocean boundary layer turbulence, velocity shear, optical properties, and multi-spectral irradiance at time scales that resolve passing clouds, atmospheric cold pool events, and submesoscale ocean variability. Our observations were collected simultaneously from three such deep-drogued buoy systems and by observations collected by the R/V Sally Ride across 10-50 km horizontal separations. We expect that measurements from this array will elucidate the coupling of air-sea variability that projects onto, and improves forecasting of, intraseasonal variability in the southwest monsoon.