Relationships between deep convective clouds, cirrus clouds, and the tropical easterly jet over the Indian region observed with Aeolus spaceborne Doppler wind lidar

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 cirrus and deep convective clouds. In this study, we first observe that while the Tropical Easterly Jet (TEJ) is primarily driven by the thermal contrast between warmer land and cooler Indian Ocean, the diverging-rotating outflow around deep convective clouds can strengthen or weaken the TEJ over the Arabian Sea with respect to the wind expected from thermal wind balance, explaining a 3 m s ⁻¹ amplitude variation during the South-Asian Summer Monsoon (SASM). We further focus on disentangling the role of this wind in the formation of cirrus clouds over the Arabian Sea during the SASM, from the roles of temperature and convective intensity variations. We show that from June to October 2020, during the 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 TEJ. Consequently, the cirrus cloud cover over the Arabian Sea is 14 % at 06:00 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 %). These results suggest that the cirrus cloud cover over the Arabian Sea may decrease in the next decades, as the TEJ and the deep convection over the eastern Indian Ocean are expected to decrease in intensity.