Formation and Evolution of Pileus Cloud Near the Tropopause

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Thin layers of cirrus are widespread in the tropopause transition layer (TTL) between 14 and 18 km altitude. They have attracted considerable recent attention for their role in climate, stratospheric humidity, and remote sensing. However, because the clouds are very tenuous and very high, their origins remain largely uncertain. This study explores a hypothesis that some TTL cirrus originates as pileus cloud - thin stratiform layers of condensate that form ahead of vigorous convective uplift - that subsequently evolve to cover large areas of the tropics. It appears that, at least in its initial stages, the problem of pileus evolution is essentially one of determining how atmospheric deep convection forces motions in the stratified TTL. A large-eddy-simulation cloud resolving model is used to investigate three main scenarios of the how convection interacts with its environment to form pileus clouds.The broader impacts of this study are derived from the important roles that tropopause transition layer cirrus have in climate and in controlling stratospheric humidity. Moreover, this grant supports one female graduate student.