HR: 11:50h
AN: A12A-05    [Abstracts]
TI: The Effect of Tropical Cirrus on the Humidity Distribution in the Tropical Troposphere
AU: * Zhang, Y
EM: zyuying@met.utah.edu
AF: Department of Meteorology University of Utah, WBB Rm819 135S 1460E, Salt Lake City, UT 84112-0110 United States
AU: Mace, G J
EM: mace@met.utah.edu
AF: Department of Meteorology University of Utah, WBB Rm819 135S 1460E, Salt Lake City, UT 84112-0110 United States
AU: Krueger, S
EM: skrueger@met.utah.edu
AF: Department of Meteorology University of Utah, WBB Rm819 135S 1460E, Salt Lake City, UT 84112-0110 United States
AU: Zulauf, M
EM: mazulauf@met.utah.edu
AF: Department of Meteorology University of Utah, WBB Rm819 135S 1460E, Salt Lake City, UT 84112-0110 United States
AB: Water vapor is the principal contributor to the greenhouse effect due to the dominance of infrared absorption (Jones and Mitchell, 1991), and the Outgoing Longwave Radiation (OLR) at TOA is more sensitive to the water vapor in upper troposphere where the climatological humidity is relatively low (Udelhofen and Hartmann, 1995; Schneider, 1999; Jensen et al. 1991; Fasullo and Sun, 2001). Sherwood (1999) indicated that at sufficient distances from active convection direct moistening of the environment by the sublimation of ice has significantly less impact on vapor distributions than cloud-radiative-dynamic effects, while Salathe and Hartmann (1997) showed that cirrus beyond the vicinity of deep convection systems play a minor role for the upper-tropospheric humidity (UTH) distribution. Using observations from a geostationary satellite (GMS), it is shown that UTH is highly correlated with cirrus-cloud coverage, especially in the regions without active convection. Due to the high coverage of cirrus clouds and low coverage of deep convection systems, this result supports that cirrus is not a minor role to control the UTH distribution in the tropical region. Combining the pattern-tracking technique to trace UTH features from sequential images (Soden, 1998) and the split-window method to identify the pixels for different cloud type (Inoue, 1987), the UTH tendency change with cirrus is explored from a Lagrangian perspective. The results show that thick cirrus is associated with higher moistening rate than thin cirrus and clear-sky conditions, and the periods of cirrus growth are related to enhanced moistening of the upper troposphere compared with periods of cirrus decay. Cirrus microphysical properties are related to the UTH changes, and the large scatter and the large range of humidity indicate that cloud properties alone can not explain the variability of tropical moisture. It is also shown by a simulation from a large-eddy model that cirrus, through their radiative effects, cause the redistribution of the upper-tropospheric water vapor to moisten cloud column.
DE: 0321 Cloud/radiation interaction
DE: 1836 Hydrological cycles and budgets (1218, 1655)
DE: 3310 Clouds and cloud feedbacks
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005