Abstract:
A 2-month (August–September) regime of the year 2007 West African monsoon (WAM) was simulated with 27 physics
combinations using the Weather Research and Forecasting model at 20-km horizontal grid. The objective is to examine WAM
sensitivity to parameterization of microphysical, convective, and boundary layer processes for long-term simulation. The model
precipitation was evaluated against the TRMM, CMORPH, and GPCP satellite rainfall products. The surface temperature was
compared against the ERA-Interim, NCEP, MERRA, and global surface air temperature, an ensemble of the three reanalysis
datasets. Model skill score (MSS) computed from a synthesis of the normalized correlation coefficient, mean bias, and mean
absolute error was used to rank the model performance. Results show the model adequately simulates the diurnal cycles of
surface temperature than precipitation, as well as the westward propagation of intense precipitation associated with the African
easterly waves. The new Grell-Freitas (nGF) cumulus parameterization scheme (CPS) outperforms its predecessor especially
when combined with the Mellor-Yamada-Nakanishi-Niino 2.5 (MYNN) planetary boundary layer scheme. The new simplified
Arakawa-Schubert (nSAS) and Tiedtke CPSs produced better simulation of precipitation and surface temperature, respectively.
The simulation of observed peak of diurnal precipitation in nSAS and nGF highlights success made towards a more realistic
representation of convective processes by the schemes. Goddard microphysics and MYNN performed better for both variables.
Based on the MSS, some relatively good and poorly performing combinations for precipitation and surface temperature were
identified. The optimal combinations are however not separated in a statistically significant way and, thus, could be used for longterm
simulation of WAM.
