HR: 1340h
AN: A13B-0920    [Abstracts]
TI: Radiative Impacts of Thin Cirrus on the Mesoscale Dynamics Near the Tropical Tropopause
AU: * Ammerman, M C
EM: marie@atmos.washington.edu
AF: Dept. of Atmospheric Sciences, University of Washington, Box 351640, 408 ATG Bldg., Seattle, WA 98195 United States
AU: Durran, D R
EM: durrand@atmos.washington.edu
AF: Dept. of Atmospheric Sciences, University of Washington, Box 351640, 408 ATG Bldg., Seattle, WA 98195 United States
AB: Thin cirrus is a persistent feature of the tropical tropopause layer (TTL), yet it remains uncertain how thin cirrus maintains itself against evaporation and sedimentation. A two-dimensional cloud-resolving model with interactive radiative transfer is used to elucidate the effect of radiation on the longevity of thin cirrus. It is found that radiative heating induces vertical velocities of 7 mm/s for a cloud with an optical depth of 0.05. The magnitude of the vertical motion scales with the optical thickness of the cloud. Evaporation is found to have little effect on the cloud. It is also found that radiative heating of thin cirrus induces gravity waves which produce a circulation that causes the cloud to spread laterally. This self-spreading mechanism may help explain the formation of thin cirrus from deep convective anvils. The thermally forced circulation also spreads potential temperature perturbations away from the cloud edge at the gravity wave phase speed, which exceeds the advective speed of the cloud. Thus, the effect of the radiative heating of thin cirrus is not confined to the location of the cloud, but can impact the thermal balance of the TTL many kilometers away.
DE: 0321 Cloud/radiation interaction
DE: 3362 Stratosphere/troposphere interactions
DE: 3374 Tropical meteorology
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005