HR: 1330h
AN: A53A-04    [Abstracts]
TI: Microphysical sensitivities of cloud-resolving model simulations of KWAJEX
AU: * Blossey, P N
EM: bloss@atmos.washington.edu
AF: University of Washington, Atmospheric Sciences Box 351640, Seattle, WA 98195-1640 United States
AU: Bretherton, C S
EM: breth@atmos.washington.edu
AF: University of Washington, Atmospheric Sciences Box 351640, Seattle, WA 98195-1640 United States
AB: Cloud-resolving model simulations of the conditions around Kwajalein Island during the Tropical Rainfall Measuring Mission (TRMM) Kwajalein Experiment (KWAJEX), July 24--September 15, 1999, are performed to understand the sensitivities of the results to changes in the model's microphysics and radiation parameterizations. An extensive set of observations were collected during KWAJEX, including high quality estimates of precipitation by an S-band ground validation radar. Large-scale forcings for the simulations --- which use cyclic boundary conditions --- have been derived from the observations by Minghua Zhang. The cloud-resolving model used here is the System for Atmospheric Modeling (SAM), developed by Marat Khairoutdinov at Colorado State University, to which the authors have added a second microphysical package (Fu et al 1995) and radiation scheme (from CAM3.0). While the alternate microphysics represents all hydrometeor interactions and has prognostic equations for water vapor, rain, snow, graupel, cloud water and cloud ice, SAM's default microphysics uses temperature to partition the condensate and precipitate among the phases and has prognostic equations only for total water (vapor+cloud) and precipitating water. The simulations are able to track the observed conditions over the full 52 day period without nudging. The different versions of the model generally reproduce the observed precipitation rate, temperature and relative humidity profiles, with mean temperature biases of less than 2K below the tropopause. However, detailed comparisons of simulated ISCCP cloud amounts and radar reflectivities with observations from ISCCP and the ground validation radar reveal important differences that are also reflected in the top-of-atmosphere radiative fluxes. Such discrepancies are strongest in the suppressed periods during KWAJEX, and these are explored in detail to reveal factors that contribute to model biases. The different microphysical and radiation parameterizations can induce substantial changes in the structure of the condensate and precipitate fields but do not qualitatively change the model's biases in the radiative fluxes, ISCCP cloud amounts or radar reflectivities.
DE: 3314 Convective processes
DE: 3337 Numerical modeling and data assimilation
DE: 3374 Tropical meteorology
SC: Atmospheric Sciences [A]
MN: 2005 Joint Assembly