HR: 13:40h
AN: A12D-01    [PDF]
TI: Evaluation of the Adapative Infrared Iris Hypothesis Using TRMM Satellite Measurements
AU: * Rapp, A D
EM: rapp@atmos.colostate.edu
AF: Dept. of Atmospheric Science, Colorado State University, Fort Collins, CO 80523 United States
AU: Kummerow, C
EM: kummerow@atmos.colostate.edu
AF: Dept. of Atmospheric Science, Colorado State University, Fort Collins, CO 80523 United States
AU: Berg, W
EM: berg@atmos.colostate.edu
AF: Dept. of Atmospheric Science, Colorado State University, Fort Collins, CO 80523 United States
AU: Griffith, B
EM: brian@atmos.colostate.edu
AF: Dept. of Atmospheric Science, Colorado State University, Fort Collins, CO 80523 United States
AB: Significant controversy surrounds the adaptive infrared iris hypothesis put forth by Lindzen et al. (2001), whereby tropical anvil cirrus detrainment is dependent on the underlying temperature and this dependence acts as an iris to inhibit changes in the surface temperature. This hypothesis implies increased precipitation efficiency in regions of higher sea surface temperatures (SSTs) which reduces cirrus detrainment. Tropical Rainfall Measuring Mission (TRMM) satellite measurements are used to investigate the adaptive infrared iris hypothesis. Pixel-level Visible and Infrared Scanner (VIRS) 10.8 $\mu$m brightness temperature data and Precipitation Radar (PR) rainrate data from TRMM are collocated and matched to determine individual convective cloud boundaries. Each cloudy pixel is then matched to the underlying SST. This study examines clouds with a single convective core to determine if a relationship exists between the size of convective clouds and the underlying SSTs. In doing so, we address some of the criticisms of the Lindzen et al. study by eliminating the cloud-weighted SST and limiting ourselves to only clouds identified as convective by the PR. The proposed mechanism for the iris hypothesis is also examined using cloud size and rainfall information. Normalizing cloud size by the amount of rainfall from the cloud provides information on whether or not the cloud size decreases at higher SSTs with increasing rainfall. Preliminary results support the adaptive infrared iris hypothesis and mechanism. It should be noted, however, that the strength of support for the iris is dependent on the brightness temperature threshold chosen for the cloud boundaries. Regressions of cloud size with SST show negative slopes and correlations signifying that cloud size decreases with increasing SST as proposed by Lindzen et al. Normalized cloud size by rainfall regressed against SST also shows a negative slope and correlation, indicating that the amount of rainfall from a cloud does increase as the cloud size decreases at higher SSTs.
DE: 1640 Remote sensing
DE: 1704 Atmospheric sciences
DE: 3314 Convective processes
DE: 3339 Ocean/atmosphere interactions (0312, 4504)
DE: 3359 Radiative processes
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting