HR: 09:30h
AN: A11D-07 INVITED     [Abstracts]
TI: Effect of Convection on the Tropical Tropopause Layer in a Microphysical Model
AU: * Pfister, L
EM: lpfister@mail.arc.nasa.gov
AF: Earth Sciences Division, NASA/Ames Research Center MS 245-5, Moffett Field, CA 94035-1000 United States
AU: Jensen, E
EM: ejensen@sky.arc.nasa.gov
AF: Earth Sciences Division, NASA/Ames Research Center MS 245-5, Moffett Field, CA 94035-1000 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. Recent observational work has shown that most convection does not penetrate into the TTL, but that the TTL nevertheless contains large sheets of subvisible cirrus clouds. This has led to the conceptual model where TTL control of stratospheric water vapor is achieved largely by in situ formation of clouds and subsequent sedimentation, which arises by horizontal air motion through cold regions. In fact, trajectory-based microphysical models including detailed microphysics and temperature perturbations at all scales, but excluding convective inputs, have successfully simulated the distribution of water vapor near the top of the TTL. But even though most convection does not penetrate into the TTL, convection is probably the TTL's only source of air. Also, water isotope measurements indicate that air cannot be dehydrated by in situ cloud formation alone. The present work includes convective inputs in a trajectory-based microphysical model by using global geostationary satellite imagery. The model calculates ice particle nucleation, growth, evaporation, and sedimentation on a column of air moving along calculated back trajectories. Realistic temperature variations are included, as well as a mean radiatively induced uplift. As the column encounters convection, the air is saturated up to the cloud top as determined by relating satellite brightness temperature to the vertical temperature profile. Sensitivity of the simulated TTL water vapor and cirrus cloud distributions to convective ice crystal inputs and the degree of cloud penetration into the stratosphere are investigated.
DE: 3362 Stratosphere/troposphere interactions
DE: 0320 Cloud physics and chemistry
DE: 0340 Middle atmosphere--composition and chemistry
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting