HR: 08:00h
AN: A11D-01    [Abstracts]
TI: Fluctuations of Cloud, Humidity, and Thermal Structure Neare the Tropical Tropopause
AU: * Salby, M L
EM: gratrix@colorado.edu
AF: The University of Colorado, 311 UCB, Boulder, CO 80309 United States
AU: Sassi, F
EM: sassi@ucar.edu
AF: Atmospheric Systems and Analysis, 12995 Sheridan Blvd. Suite 204, Broomfield, CO 80020 United States
AU: Sassi, F
EM: sassi@ucar.edu
AF: National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307 United States
AU: Callaghan, P F
EM: paddy@asac.org
AF: Atmospheric Systems and Analysis, 12995 Sheridan Blvd. Suite 204, Broomfield, CO 80020 United States
AU: Read, W
EM: bill@mls.jpl.nasa.gov
AF: Jet Propulsion Laboratory, 4800 Oak Grove Drive , Pasadena, CA 91109-8099 United States
AU: Pumphewy, H
EM: Hugh.Pumphrey@ed.ac.uk
AF: University of Edinburgh, School of Geosciences The King's Buildings West Mains Road , Edinburgh, EH9 3JG United Kingdom
AB: Thermal and humidity structure near the tropical tropopause are studied in microwave satellite retrievals of water vapor from MLS, along with contemporaneous dynamical structure in ECMWF analyses and cold cloud in high resolution Global Cloud Imagery. These fields all vary coherently with the outflow from convective centers -- in the upper troposphere as well as in the lowermost stratosphere. The outbreak of deep convection is accompanied by diabatic heating below a level between 250 and 150 mb, but by diabatic cooling at higher levels. The reversal from heating to cooling is broadly consistent with cumulus detrainment. Through irreversible mixing, that process serves as a heat source for the environment below the Level of Neutral Buoyancy (LNB), but as a heat sink at higher levels. Calculations, inclusive of entrainment, place the LNB very near the observed reversal from heating to cooling. The outbreak of convection is also accompanied humidification below 125 mb, but by dehydration at higher levels. The reversal from humidification to dehydration coincides with levels where environmental conditions approach saturation. Those conditions suggest the efficient removal of total water from cumulus updrafts, leaving dessicated air to ventilate higher levels. Cumulus detrainment then acts to humidify the environment beneath the zone of nearly-saturated environmental conditions, but to dehydrate it at higher levels. Dry air emerges from the region of coldest cloud. It then extends into the winter hemisphere, along streamlines that characterize the Hadley circulation. Coinciding with diabatic cooling are stratospheric convergence and downwelling. These features of stratospheric motion amplify simultaneously with divergence at tropospheric levels, which represents the major outflow from deep convection. The deepest convection, found over the equatorial Pacific, coincides with the highest moist static energy. The latter yields an LNB that is some 3 km higher over the equatorial Pacific than elsewhere, in agreement with the observed reversal from heating to cooling. Observed brightness temperatures place the level at which cumulus anvils are most extensive very near the cold point over the equatorial Pacific. This, in turn, lies near the tropical tropopause throughout the tropics. Collectively, these features suggest that the coldest cloud, found over the equatorial Pacific, plays a key role in maintaining temperature and humidity near the tropical tropopause.
DE: 0320 Cloud physics and chemistry
DE: 0322 Constituent sources and sinks
DE: 0368 Troposphere--constituent transport and chemistry
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting