The impact of different WRF model physical parameterizations and their interactions on warm season MCS rainfall

In recent years, a mixed physics ensemble approach has been investigated as a method to better predict Mesoscale Convective System (MCS) rainfall. For both mixed physics ensemble design and interpretation, knowledge of the general impact of various physical schemes and their interactions on warm season MCS rainfall forecasts would be useful. To pursue this goal, a matrix of 18 WRF model configurations, created using different physical scheme combinations, was run with 12 km grid spacing for 8 International H2O Project (IHOP) MCS cases. For each case, 3 different treatments of convection (Betts-Miller-Janjic scheme, Kain-Fritsch scheme and no convective scheme), 3 different microphysical schemes (NCEP class 5, Lin et al., and Ferrier) and 2 different planetary boundary layer schemes (MRF and ETA) were used. In order to quantify in detail the impacts of the variation of two different physical schemes and their interaction on the simulated rainfall the factor separation method was used.

The general findings obtained through use of the factor separation method will serve as a foundation for a more detailed investigation of the physical parameterizations' impacts on simulated rainfall when certain adjustments within the parameterizations have been performed. Some examples include the impact of increased mixing within the ETA PBL scheme as well as its interaction with different convective treatments on simulated MCS rainfall, and the impacts of changes to parameters within the Betts-Miller-Janjic convective scheme.