Interannual Variability in Clouds and Aerosols During the Asian Monsoon as Observed by CALIOP

The Asian monsoon (AM) dominates Upper Tropospheric/Lower Stratospheric (UT/LS) cloudiness during the Boreal Summer. Recent measurements of aerosols by satellite, balloon and airborne instruments as well as modeling studies of the Asian summer monsoon anticyclone suggest the presence of cloud nucleating particles containing ammonium, sulfate and nitrate. The predominate source of these aerosols are both natural and anthropogenic emissions from the Indian subcontinent and from China. Emissions near the ground are transported by deep convection into the UT/LS, with an apparently long lifetime within the resulting Asian tropopause aerosol layer (ATAL). Additionally, dust and carbonaceous aerosols can be transported into the ATAL by deep convection. The Cloud and Aerosol Lidar with Orthogonal Polarization (CALIOP) on the CALIPSO satellite has been observing clouds and aerosols in the ATAL for 13 years. We show time series of the total cloud fraction, convective cloud fraction, cloud top heights and ice water path between 14 and 20 km observed by CALIOP, as well as variability in 532 nm depolarization and attenuated 1064 nm/532 nm backscatter ratio of both aerosols and clouds. We also decompose the time series into time periods when the monsoon is developing, and when the monsoon convection peaks each year from 2006 through 2019. An avenue of investigation is to show whether we can trace observed variability in clouds to anthropogenic aerosol source regions over India and China.