Quantifying the Radiative Impact of Clouds on Tropopause Layer Cooling in Tropical Cyclones

Abstract

AbstractA ubiquitous cold signal near the tropopause, here called “tropopause layer cooling” (TLC), has been documented in deep convective regions such as tropical cyclones (TCs). Temperature retrievals from the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) reveal cooling of order 0.1–1 K day−1on spatial scales of order 1000 km above TCs. Data from the Cloud Profiling Radar (onboardCloudSat) and from the Cloud–Aerosol Lidar with Orthogonal Polarization [onboard theCloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations(CALIPSO)] are used to analyze cloud distributions associated with TCs. Evidence is found that convective clouds within TCs reach the upper part of the tropical tropopause layer (TTL) more frequently than do convective clouds outside TCs, raising the possibility that convective clouds within TCs and associated cirrus clouds modulate TLC. The contribution of clouds to radiative heating rates is then quantified using theCloudSatandCALIPSOdatasets: in the lower TTL (below the tropopause), clouds produce longwave cooling of order 0.1–1 K day−1inside the TC main convective region, and longwave warming of order 0.01–0.1 K day−1outside; in the upper TTL (near and above the tropopause), clouds produce longwave cooling of the same order as TLC inside the TC main convective region, and up to one order of magnitude smaller outside. Considering that clouds also produce shortwave warming, it is suggested that cloud radiative effects inside and outside TCs only explain modest amounts of TLC while other processes must provide the remaining cooling.