The CCN and IN Effects on Tropical Anvil Characteristics and Water Vapor of the Tropical Tropopause Layer (TTL)

Cloud anvils from deep convective clouds are of great importance in the radiative budgets and the aerosol effect on them is the least understood. Few studies examined the effects of both cloud condensation nuclei (CCN) and ice nuclei (IN) on anvil macrophysical and microphysical 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, based on two real thunderstorm cases that developed in contrasting dynamic, thermodynamic, and aerosol environments. We find the CCN effects on anvil microphysical properties, anvil size and lifetime are much more evident relative to IN, mainly due to significant changes on the cloud microphysical properties induced by CCN. Increasing CCN always increases anvil size, especially in dry environment. We also find that CCN in the PBL has greater effects on convective updraft velocity in both humid and dry cases. Similar pattern is found for CCN and IN effects on the WVC in the TTL clear air. This study shows that cloud microphysical properties that could be greatly changed by CCN are the key factors in determining cloud anvil macro- and micro- properties and WVC in the TTL clear air, indicating an important role of CCN in the lower-troposphere in modifying the upper-levels clouds and air compositions. The anvils and WVC in the TTL clear air are more susceptible to CCN in the dryer environment, and anvil properties in the humid environment are much more susceptible to IN relative to the dry environment.