Characteristic Differences of CrIS All-Sky Simulations of Brightness Temperature with Different Microphysics Parameterization Schemes

摘要

Influences of cloud liquid water, cloud ice, rain, snow, and graupel on all-sky simulations of the Cross-track Infrared Sounder (CrIS) brightness temperature (TB) are assessed for the 399 data assimilation (DA) channels. The analyses generated by the Gridpoint Statistical Interpolation (GSI) 3D-Var system assimilating conventional and clear-sky satellite radiance observations are used as initial conditions for the Weather Research and Forecasting Model to generate 6-h forecasts with three different microphysics schemes (WSM6, Thompson, and Morrison), which are then used as input to the Community Radiative Transfer Model for all-sky TB simulations. Under all-sky conditions, biases with the WSM6 scheme are negative for all channels and greater in magnitude than -3.5 K. The biases with the Thompson and Morrison schemes vary between -1 and 1 K for all channels. Bias differences among three MP schemes are small in stratus, altocumulus, and cumulus clouds, but large in cirrus and cirrocumulus clouds. The TB simulations in stratus, altocumulus, and cumulus clouds are mostly influenced by the cloud top pressure, while that in cirrus and cirrocumulus clouds depends strongly on cloud optical depth. All-sky TB simulations in cirrus conditions are more positively biased than those under cirrocumulus conditions, probably due to the microphysics schemes producing too thick cirrus clouds. Sensitivity experiments suggest that the TB discrepancies among DA experiments with three MP schemes are mostly caused by the ice or snow type rather than the effective radius of hydrometeor in the upper troposphere. Finally, we propose to combine a cloud-effect parameter with cloud types for modeling observation error characteristics in all-sky DA.