The ultimate goal of the Physics Working Group is the development of a unified suite of atmospheric physical parameterizations that can be applied with minimal modification across convection-permitting to sub-seasonal to seasonal scales in the UFS. Model physical parameterizations describe the changes to variables at model grid-scales in forecast variables due to sub-grid scale diabatic processes, as well as resolved-scale physical processes. Physical parameterization development has been a critical driver of increased forecast accuracy of global and regional models, as more processes are accounted for with sophistication appropriate for the model resolution and vertical
domain. Key atmospheric processes that are parameterized in current global models include subgrid turbulent mixing in and above the boundary layer, cloud microphysics and ‘macrophysics’ (subgrid cloud variability), cumulus convection, radiative heating, and gravity wave drag. Parameterizations of surface heat, moisture, and momentum fluxes over land, ocean, and other bodies of water/ice, subgrid mixing within the ocean due to top and bottom boundary layers, gravity waves and unresolved eddies, land surface and sea ice properties are also important on weather and seasonal time scales. Accurately yet efficiently incorporating this diversity of diabatic and transport effects in a global or regional forecast model is extremely demanding, requiring careful parameterization design that respects physical realism while
supporting the range of model resolutions that will be used and a diagnosis of initialization and forecast errors that is tightly connected with the data assimilation system. Moreover, the interactions between various physical parameterizations play a major role in the prediction system forecast skill.