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

Abstract

Cloud anvils from deep convective clouds are of great importance to the radiative energybudget and the aerosol impact on them is poorly understood. In this study, we use athree-dimensional cloud-resolving model with size-resolved cloud microphysics to examinethe effects of both cloud condensation nuclei (CCN) and ice nuclei (IN) on cloud anvilproperties and water vapor content (WVC) in the tropical tropopause layer (TTL). We findthat cloud microphysical changes induced by increases in CCN/IN play a very importantrole in determining cloud anvil area and WVC in the TTL, whether convection isenhanced or suppressed. Also, CCN effects on anvil microphysical properties, anvilsize and lifetime are much more evident relative to IN effects. Our sensitivitystudy shows that IN have little effect on convective strength but can increaseice number and mass concentrations in cloud anvils significantly under humidconditions. CCN in the planetary boundary layer (PBL) are found to have greatereffects on convective strength and mid-tropospheric CCN have negligible effects onconvection strength and cloud properties. Convective transport may only moisten themain convective outflow region, and the larger cloud anvil area and more efficientsublimation induced by increasing CCN concentration significantly increase the WVCin the whole TTL domain. This study shows an important role of CCN in thelower troposphere in modifying convection and the upper-level cloud properties. Italso shows that the effects of IN and the PBL CCN on the upper-level cloudsdepend on the humidity, resolving some contradictory results in past studies.