Investigating the relationship between aerosols, convective ice and detrained water vapor in the upper troposphere

Recent studies have shown that tropical ice clouds with smaller effective radii have the potential to increase the water vapor mixing ratio in the upper troposphere (UT) within seasonal time scales. This has serious implications for climate because UT water vapor is a significant source of lower stratospheric (LS) moisture, which in turn is an important greenhouse-forcing agent. Observations have also shown that the average effective radius of ice clouds is smaller when formation occurs in a polluted environment. Thus, an important question to ask is do anomalous aerosol conditions change ice microphysics to the point where there is an impact on UT moisture? To this end, this study uses a combination of passive and active A-Train satellite retrievals and atmospheric reanalysis to investigate the relationship between aerosol conditions, ice cloud properties and moisture in the UT/LS. Ice clouds are identified using the combined CALIOP lidar and CloudSat radar 2C-ICE product, and separated into convective and non-convective clouds using a vapor mixing ratio threshold derived from MLS Level 2 data. Case studies of convective ice in different regions will be presented showing the evolution of the effective radius and water vapor mixing ratio following the cloud for heavy and light aerosol conditions. In general, there is an increase in the relative humidity of UT air layers post-convective detrainment of clouds with smaller effective radii. This result indicates that small ice particles caused by an increase in aerosol loading have the ability to moisten the UT and subsequently affect the radiative forcing by water vapor.