HR: 0800h
AN: A41D-03    [Abstracts]
TI: Effect of Cloud Microphysics on Storm Dynamics: PRE-STORM Case Study
AU: * Li, X
EM: xli@agnes.gsfc.nasa.gov
AF: Goddard Earth Science and Technology Center, UMBC, Code 613.1 NASA/GSFC, Greenbelt, MD 20770, United States
AU: Tao, W
EM: tao@agnes.gsfc.nasa.gov
AF: NASA Goddard Space Flight Center, Code 613.1 NASA/GSFC, Greenbelt, MD 20770, United States
AU: Khain, A
EM: khain@vms.huiji.ac.il
AF: Hebrew University of Jerusalem, The institute of Earth Sciences, Jerusalem, 91904, Israel
AU: Simpson, J
EM: simpson@agnes.gsfc.nasa.gov
AF: NASA Goddard Space Flight Center, Code 613.1 NASA/GSFC, Greenbelt, MD 20770, United States
AB: A 2D cloud-resolving model, the Goddard Cloud Ensemble (GCE) model, is used to simulate a mid-latitude summertime squall line during the PRE-STORM field campaign on June 10-11, 1985. Two microphysical schemes, a simple bulk scheme and a detailed spectral bin scheme, using identical environmental conditions and initialization, produce storms with different characteristics in terms of storm structures and temporal variations. During the mature stage of the squall line, the bulk scheme produces a multi-cell storm with convective cells, which are remnants of previous leading cells, embedded well into its stratiform region. The leading cell simulated by the bulk scheme has a distinct lifecycle with each new leading cell generated as an independent entity. In contrast, the bin scheme produces a uni-cell storm with a homogeneous stratiform region. The single convective cell at the leading edge has a weak evolution mode with little temporal variation. These characteristics have been observed in storms formed in different environmental conditions, but are simulated here by two self-consistent microphysical schemes. This indicates the significance of cloud microphysics in shaping the storm structure and dynamics. Sensitivity tests using the simple bulk microphysical scheme reveal two major contributors to the sensitivities simulated by the control bulk and bin scheme, that is, the artificial enhancement of the rain evaporation rate simulated in the bulk scheme, and the different partitioning of precipitable ice particles in these two schemes. Strong rain evaporation in the bulk scheme results in a strong near surface cool pool, which overwhelms the horizontal vorticity generated by the near surface wind shear and causes the leading convection to lean backward. The excessive backward tilting is the reason for the splitting and rearward traveling of the leading convection. Reduced rain evaporation in the bulk scheme produces an upright leading convection with little temporal variation, but failed to form an extensive trailing stratiform region due to the assumptions on the forms (hail vs. graupel) and partitioning (snow vs. hail/graupel) of precipitable ice particles. Future work will focus on improving the rain evaporation rate and ice microphysics in the bulk scheme using both the observations and the detailed bin scheme simulations.
DE: 0320 Cloud physics and chemistry
SC: Atmospheric Sciences [A]
MN: 2007 Joint Assembly