The impact of tropical convection and cirrus on upper tropospheric humidity: A Lagrangian analysis of satellite measurements

[1] Geostationary satellite observations are used in conjunction with an objective pattern-tracking algorithm to describe the Lagrangian evolution of convection, clouds and water vapor in the tropical upper troposphere. This analysis reveals that larger convective events within a Lagrangian air mass are associated with larger and longerlived cirrus anvil shields. Convective systems which generate larger cirrus shields are, in turn, associated with higher downstream humidity levels following the anvil’s dissipation. In the absence of cirrus, the clear-sky upper troposphere is shown to dry at a rate consistent with radiatively-driven subsidence. The presence of cirrus anvils following a convective event is shown to reduce the rate of drying and for large anvils can even change its sign. Analysis of the Lagrangian tendencies suggests that this moistening effect is not attributable to the evaporation of cirrus condensate, but instead results from the same dynamical mechanisms responsible for the formation and maintenance of the cirrus anvil.