HR: 0800h
AN: A41B-0049    [Abstracts]
TI: The Effect of Convection and In-situ Dehydration on the Tropical Tropopause Layer
AU: * Pfister, L
EM: lpfister@mail.arc.nasa.gov
AF: NASA/Ames Research Center, Moffett Field, California, Moffett Field, CA 94035-1000 United States
AU: Jensen, E
EM: ejensen@sky.arc.nasa.gov
AF: NASA/Ames Research Center, Moffett Field, California, Moffett Field, CA 94035-1000 United States
AU: Read, W G
EM: bill@mls.jpl.nasa.gov
AF: NASA Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109 United States
AB: The Tropical Tropopause Layer (TTL), a region that surrounds the thermal tropical tropopause and extends from about 14 to 18 km, controls the input of water vapor into the lower tropical stratosphere. Though most convection does not penetrate the TTL, the convective turnover time is comparable to the radiatively driven vertical transit time. This makes the process of dehydrating tropospheric air to stratospheric values a complex mix of convective hydration (or dehydration) and in-situ dehydration by subvisible cirrus cloud sheets. Previous work has simulated water vapor and cloud distributions with reasonable success (based on comparisons with HALOE water and SAGE cloud data) using only in-situ dehydration processes. This work examines both convective and in-situ processes by use of a one-dimensional, trajectory based microphysical model with convective injection. Convective injection is based on geostationary satellite imagery, and the convective turnover times derived from our formulation are reasonably consistent with other estimates using independent methods. Results so far include: (1) convection hydrates the lower part of the TTL (below 365K) by 50 to 100 percent, with 10 percent hydration at higher levels; (2) convective hydration is reduced substantially because of subsequent in-situ dehydration; (3) hydration due to convection appears reasonably uniformly distributed throughout the tropics; and (4) cloud distributions are improved by using the convective formulation. At this point, comparisons of model results have been with long-term averages obtainable with solar occultation satellites. Use of actual observed convection to inject water (or produce cold dry air) makes comparisons of trajectory calculations ending at a particular time with long-term averages problematic. Newer water vapor measurements from the MLS instrument aboard EOS Aura will facilitate comparisons on a more frequent basis for the winter of 2004-05. This paper will discuss these comparisons.
DE: 0322 Constituent sources and sinks
DE: 0341 Middle atmosphere: constituent transport and chemistry (3334)
DE: 3362 Stratosphere/troposphere interactions
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005