85th AMS Annual Meeting

Tuesday, 11 January 2005
The effects of cold microphysical processes on surface precipitation variability. Part II: Tropical Precipitation
Jianzhong Wang, Hydrologic Research Center, San Diego, CA; and K. P. Georgakakos
Hydrological Research Center 12780 High Bluff Drive, Suite 250 San Diego, CA 92130 Tel: 858-794-2726; Fax: 858-792-2519; E-mail: jwang@hrc-lab.org

On the basis of the precipitation and microphysics verification of the MM5 model high resolution numerical simulation of two KWAJEX precipitation events occurring in the tropical ocean, the roles of cold microphysical processes in the surface precipitation variability are investigated and the sensitivity tests of surface precipitation to various microphysical factors associated with cold microphysical processes are made.

Though the verification of the simulated mean area precipitation and estimated radar reflectivity, MM5 model is found to be capable to simulate the observed precipitation features in these two tropical precipitation cases. The model initialization with the intensive sounding and surface observation acquired in the KWAJEX field experiment is crucial to the success of the precipitation simulation in terms of the amount and timing of the peak mean area precipitation in the Kwajelean Island for the 8/11/1999 case. The incorporation of cloud droplet spectrum features of tropical cloud into the mesoscale model proves substantial to the simulated peak rainfall especially for the less severe tropical precipitation case of 08/19/1999, with the simulated peak 6hr mean area rainfall with the continental cloud 24% less than that with the maritime cloud.

Besides the verification of the simulated precipitation for these two tropical precipitation cases, the verification of the microphysical properties simulated by the GSFC ice microphysics scheme in the MM5 model is also made by comparing the observed ice concentration from the cloud microphysical probe such as 2D-C in the anvil cloud with the 2D-C ice concentration estimated from the simulation. It was found that the magnitude of the simulated ice concentration is close to the detected.

The comparison between the simulations of with/without cold microphysical process reveals that the graupel-related cold microphysical processes in the model microphysics scheme are vital. It not only modifies the magnitude of surface precipitation but also the spatial distribution of surface precipitation. The maximum precipitation predicted by the warm rain scheme doubles the one simulated by the ice microphysics. Further investigation points to the different dealing of supercooled raindrops in these two microphysics schemes responsible for the significant difference in the simulated maximum precipitation from these two schemes.

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