Relationships between Thin clouds, Opaque Clouds, and the Tropical Easterly Jet over the Indian Region observed with Aeolus Spaceborne Doppler Wind Lidar

Abstract. Direct wind observations used to be rare over the Arabian Sea and the Bay of Bengal. Since the launch of ESA's Aeolus Doppler Wind Lidar, profiles of horizontal wind are acquired every day and are perfectly co-located with profiles of thin and opaque clouds. In this study, we show that from June to October 2020, during the South-Asian Summer Monsoon (SASM), high altitude clouds formed over the Bay of Bengal by deep convection in the afternoon are advected westward towards the Arabian Sea in the morning by the fast winds of the Tropical Easterly Jet (TEJ). Consequently, the thin high cloud cover over the Arabian Sea is 14 % at 06 LT on days where westward winds are faster than 23.6 m s^-1 between 14 and 17 km of altitude, more than twice as much than on days where westward winds are slower than 23.6 m s^-1 (6 %). While the TEJ is primarily driven by the thermal contrast between warm land and cooler Indian Ocean, we observe that the diverging-rotating outflow around deep convective (opaque) clouds can strengthen or weaken the TEJ over the Arabian Sea with respect to the thermal wind, explaining a 3 m s^-1 amplitude variation during the SASM. These results suggest that the cirrus cloud cover over the Arabian Sea may decrease in the next decades, as the TEJ and the convection over the Eastern Indian Ocean are expected to decrease in intensity.