The cloud condensation nuclei and ice nuclei effects on tropical anvil characteristics and water vapor of the tropical tropopause layer

Cloud anvils from deep convective clouds are of great importance to the radiative energy budget and the aerosol impact on them is poorly understood. In this study, we use a three-dimensional cloud-resolving model with size-resolved cloud microphysics to examine the effects of both cloud condensation nuclei (CCN) and ice nuclei (IN) on cloud anvil properties and water vapor content (WVC) in the tropical tropopause layer (TTL). We find that cloud microphysical changes induced by increases in 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 effects. Our sensitivity study shows that IN have little effect on convective strength but can increase ice number and mass concentrations in cloud anvils significantly under humid conditions. CCN in the planetary boundary layer (PBL) are found to have greater effects on convective strength and mid-tropospheric CCN have negligible effects on convection strength and cloud properties. Convective transport may only moisten the main convective outflow region, and the larger cloud anvil area and more efficient sublimation induced by increasing CCN concentration significantly increase the WVC in the whole TTL domain. This study shows an important role of CCN in the lower troposphere in modifying convection and the upper-level cloud properties. It also shows that the effects of IN and the PBL CCN on the upper-level clouds depend on the humidity, resolving some contradictory results in past studies.