PNNL

Abstract

Cloud anvils from deep convective clouds are of great importance to the radiative energy budget and the aerosol impact on them is the least understood. Few studies examined the effects of both cloud condensation nuclei (CCN) and ice nuclei (IN) on anvil properties and water vapor content (WVC) in the Tropical Tropopause Layer (TTL). Using a 3-dimensional cloud-resolving model with size-resolved cloud microphysics, we focus on the CCN and IN effects on cloud anvil properties and WVC in the TTL. We find that cloud microphysical changes induced by CCN/IN play a very important role in determining cloud anvil area and WVC in the TTL, whether convection is enhanced or suppressed. Also, CCN effects on anvil microphysical properties, anvil size and lifetime are much more evident relative to IN. IN has little effect on convection, but can increase ice number and mass concentrations significantly under humid conditions. CCN in the PBL is found to have greater effects on convective strength and mid-tropospheric CCN has negligible effects on convection and cloud properties. Convective transport may only moisten the main convective outflow region but the cloud anvil size determines the WVC in the TTL domain. This study shows an important role of CCN in the lower-troposphere in modifying convection, the upper-level cloud properties. It also shows the effects of IN and the PBL CCN on the upper-level clouds depends on the humidity, resolving some contradictory results in past studies. 2