Satellite cloudy radiances are rarely used in the data assimilation system because of uncertainty in cloud properties predicted by NWP models. This study will investigate this uncertainty by simulating satellite radiances using a cloud model and comparing with the measurements from satellite microwave sensors. In the cloud model, the prognostic equations of hydrometeors and explicit microphysics parameterization schemes can provide cloud information (Li et al. 1999). A microwave radiative transfer model developed by Liu and Weng (2002) is used to simulate radiances at the AMSU frequencies with cloud resolving model outputs. Sensitivity tests are conducted to test the response of cloud hydrometeors to the accretion of snow by graupel (PGACS). It is found that the experiment without PGACS shows significant increase of snow and decrease of graupel compared to the experiment with PGACS. As a result, the radiance variability in the simulated domain becomes larger in the experiment without PGACS than that with PGACS. The signals of radiance differences between simulations and observations are much significant at AMSU channels 16 and 17 that are sensitive to ice clouds. This comparison indicates that PGACS may suppress the development of precipitation ice unrealistically.

Cloud microphysics budgets in the tropical deep convective regime simulated with a cloud resolving model are analyzed to identify dominant cloud microphysical processes associated with tropical precipitation and propose a simplified set of cloud microphysics parameterization schemes for tropical rainfall modeling. It is found that the collection of cloud water by raindrops and the riming of cloud water by precipitation ice particles are associated with convective and stratiform precipitation, respectively. These relations may lead us to estimate the conversion rate of the dominant cloud microphysical processes when reliable precipitation type/rate are available from satellite retrievals.

Li, X., C.-H. Sui, and K.-M. Lau, 1999: Large-scale forcing and cloud-radiation interaction in the tropical deep convective regime. J. Atmos. Sci., 56, 3028-3042.

Liu, Q., and F. Weng, 2002: A microwave polarimetric two-stream radiative transfer model, J. Atmos. Sci., 59, 2396-2402.