Improving the Rapid Refresh (RAP) and High Resolution Rapid Refresh (HRRR) Physics to Better Perform Across a Wide Range of Spatial Scales
The RAP currently employs a modified form of the Mellor-Yamada-Nakanishi-Niino (MYNN) PBL scheme, which is an improved TKE-based scheme tuned to match large-eddy simulations. Modifications have been performed to better match observations at 13 km (RAP) grid spacing but more multi-scale testing is required before modifications are introduced to make it scale-aware. A scale-aware convective parameterization, the Grell-Freitas scheme, has been developed to better handle the transition in behavior of the sub-grid scale convective processes through the grey zone. This study examines the change in behavior of both schemes across the grey zone. Their transitional behavior is characterized and strategies to improve each scheme is explored. Further tests are performed to elucidate the impacts of specific model parameters that may improve weather prediction across the grey zone.