HR: 09:30h
AN: A51C-05    [Abstracts]
TI: Interactions of Cloud Microphysics and Dynamics Simulated in a PRE-STORM Squall Line Case
AU: * Li, X
EM: xli@agnes.gsfc.nasa.gov
AF: GEST Center, U of Maryland, Baltimore County, Code 613.1, NASA/Goddard Space Flight Center, Greenbelt, MD 20771 United States
AU: Tao, W
EM: tao@agnes.gsfc.nasa.gov
AF: Code 613.1, NASA/GSFC, NASA Goddard Space Flight Center, Greenbelt, MD 20771 United States
AU: Khain, A
EM: khain@vms.huji.ac.il
AF: The Hebrew University of Jerusalem, The Institute of Earth Sciences, Givat Ram, 91904 Israel
AU: Simpson, J
EM: simpson@agnes.gsfc.nasa.gov
AF: Code 613.1, NASA/GSFC, NASA Goddard Space Flight Center, Greenbelt, MD 20771 United States
AB: The Goddard Cumulus Ensemble (GCE) Model is used to simulate the June 10-11, 1985 PRE-STORM squall line. The 2-D version of the GCE model initialized with a cool pool is integrated for 12 hours until the storm develops into a semi-steady state. It is found that, with all environmental conditions identical, the strength of the rain evaporation affects the steady state storm dynamics significantly. When the rain evaporation is weak, the negative vorticity generated by the surface cool pool nearly balances the positive vorticity of the ambient wind shear. The leading convective cell in this type of squall system is upright and tall. The air detrained from the leading convective cell loses most of its buoyancy. It brings the ice particles back to the stratiform region without developing any weak convective cells, producing uniform weak ascending and more homogeneous stratiform rain with a prominent bright band in the simulated radar reflectivity pattern. On the other hand, when the rain evaporation rate is strong, the cool pool is strong, too. The negative vorticity generated by the cool pool overpowers the ambient near surface positive vorticity. The resulted leading cell tilts downshear. The updraft in the leading cell is cut by the downdraft produced by rain evaporation. The remained buoyant air parcel continues to rise while moving into the stratiform region, forming weak convective cells in the stratiform region. The differences in evaporation strengths simulated in the GCE Model are produced by two self-consistent microphysical schemes, one is a bulk type, and the other is an explicit bin model. The assumption in the bulk scheme that the intercept of the raindrop size distribution is a fixed value results in stronger rain evaporations, especially in the downdraft cores. In a dry and unstable summer time mid-latitude environment, this produces significant differences in storm structure, rainfall pattern, and rain efficiencies. This study suggests that under certain circumstances, small differences in cloud microphysical processes may have comparable sensitivities as changing some of the environmental conditions. In addition to the rain evaporation, the terminal fall velocity of precipitable ice particles also plays an important role in shaping the stratiform rain in this squall line case. When the fall velocities of ice particles are reduced, significantly more stratiform rain is produced by the squall line. The wind and pressure patterns of the squall line changes accordingly, too.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0320 Cloud physics and chemistry
SC: Atmospheric Sciences [A]
MN: 2005 Joint Assembly