Evaluation of a single-moment bulk microphysics scheme using a satellite simulator and TRMM data

Abstract:

Tropical precipitation systems make important contributions to the global energy budget and play a key role in climate and weather modeling. One important issue in a cloud modeling is the parameterization of the microphysical processes of hydrometeors. Single-moment schemes that calculate only the mass concentrations of hydrometeors have been widely used for large-scale experiments and long-term cloud simulations.

Several studies have examined the role of microphysics parameterizations in tropical convective systems. We investigate how the results are evaluated using more realistic size distributions of microphysics.

In this study, the cloud microphysics of deep convective systems is evaluated over the tropical open ocean simulated by a cloud system resolving model using a satellite simulator. We evaluate the horizontal distribution of cloud sizes, the joint probability distributions of cloud-top temperature, precipitation-top height, and CFADs of radar reflectivities for each category in cloud-system-resolving simulations using a TRMM precipitation radar (PR) and infrared scanner following the approach proposed by Masunaga and Kummerow (2006) and Matsui et al. (2009). The control experiment shows biases related to underestimation of stratiform precipitation and a higher frequency of precipitating deep clouds whose top height is higher than 12 km compared with the TRMM data, although it shows good agreement for the horizontal distribution and statistical cloud size distributions of deep convective systems. The biases in the joint histogram are improved by changing the cloud microphysics parameters in the framework of a single-moment bulk microphysics scheme. In particular, the effects of the size distribution of precipitating hydrometeors are examined. Global cloud system resolving simulations with a 3.5 km horizontal resolution are done and analyzed using TRMM and CloudSat. The T3EF structure is similar to the regional cloud system resolving results. The modified microphysics improves the joint histogram structures. The OLR of the modified simulation is lower than the control run with a wide range of anvil clouds. The bias of upper troposphere is improved and precipitation system is well organized in the modified simulation. The regional differences of T3EF are examined.