HR: 1340h
AN: A13A-0891    [Abstracts]
TI: The Role of Deep Convection in Establishing the Isotopic Composition of the Tropical Transition Layer
AU: * Smith, J A
EM: jamisons@lasp.colorado.edu
AF: University of Colorado at Boulder Laboratory for Atmospheric and Space Physics, 392 UCB, Boulder, CO 80309 United States
AU: Ackerman, A S
EM: andrew.ackerman@nasa.gov
AF: NASA Ames Research Center Earth Science Division, Mail Stop 245-4, Moffet Field, CA 94035 United States
AU: Jensen, E J
EM: eric.jensen@nasa.gov
AF: NASA Ames Research Center Earth Science Division, Mail Stop 245-4, Moffet Field, CA 94035 United States
AU: Toon, O B
EM: btoon@lasp.colorado.edu
AF: University of Colorado at Boulder Laboratory for Atmospheric and Space Physics, 392 UCB, Boulder, CO 80309 United States
AU: Toon, O B
EM: btoon@lasp.colorado.edu
AF: University of Colorado at Boulder Program in Atmospheric and Oceanic Sciences, 311 UCB, Boulder, CO 80309 United States
AB: We model the transport of H2O and HDO within deep convection using a 3-D large-eddy simulation (LES) with bin microphysics. The simulations show that Rayleigh fractionation is not a valid description of the isotopologue distribution within deep convection because of lofting of HDO-rich condensate by convective updrafts. A bootstrapping strategy is used to produce a self-replicating correlation of HDO/H2O isotopologue ratio (d) with water vapor mixing ratio (qv) which is qualitatively consistent with the observations. Our results are consistent with two different dehydration mechanisms for air entering the stratosphere in the tropics. Deep convective plumes can detrain into the stratosphere, directly producing d and qv similar to stratospheric observations. Alternatively, air detraining from convection into the tropical transition layer may be gradually dehydrated by cirrus formation during slow ascent through the tropical transition layer (TTL). The production of anomalously dry air in the TTL via convective dehydration (ice condensation and sedimentation from overshoots) is not observed in the simulations, nor is it necessary to explain the observed d in the stratosphere.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0320 Cloud physics and chemistry
DE: 0340 Middle atmosphere: composition and chemistry
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005