Han, Mei, Scott A. Braun, Toshihisa Matsui, National
Aeronautics and Space Administration, Christopher R. Williams, NOAA/CIRES,
Takamichi Iguchi, NASA/ESSIC
The unique assumptions
of particles size distribution (PSD), number concentration, shape, and fall
velocities in different microphysics schemes in NWP models are critical in
simulating precipitation profiles and microwave radiative properties. Using
observations from a space-borne radiometer and ground-based precipitation
profiling radar, the impact of cloud microphysics schemes in WRF model on the
simulation of brightness temperature, radar reflectivity, and Doppler velocity,
is studied.
Customized simulations
of the radiative properties are conducted for four different schemes in the WRF
model, including GSFC, WSM6, THOM, and MORR. It is found that simulations with
different schemes show large variations in the brightness temperature,
reflectivity, and Doppler velocity. A general bias of ~ 20 K or larger is found
in the (Polarization-Corrected) microwave brightness temperature in these
schemes, which is linked to overestimate of the precipitating ice aloft. The
simulated reflectivity with the THOM scheme appears to agree well with the
observations. We also find a high bias of ~5 and ~10 dBZ in the simulated radar
reflectivity with the GSFC, WSM6, and MORR schemes. These biases are
attributable by the snow intercept parameter, N0s, for the 1-moment schemes,
and by the snow number concentration, Ns, for the 2-moment scheme. Doppler
velocity simulations based on the GSFC scheme show a reasonable agreement with
the observation, while other schemes appear to have a ~ 1 m s-1 high bias.
A spectral bin
microphysics scheme, HUCM, is recently being added into this study. Preliminary results on the reflectivity
and microwave brightness temperature simulations based HUCM will also be
discussed.