Demonstration of Hierarchical System Development Using Common Community Physics Package and Its Companion Single-Column Model to Inform Physics Development: An Example from An ARM SGP Case on June 11 2016

This study demonstrates an application of the hierarchical system development (HSD) testing and evaluation approach to inform model physics development of the Unified Forecast System (UFS). By investigating a nonprecipitating shallow cumulus case at the Atmospheric Radiation Measurement Southern Great Plains atmospheric observatory, the work is focused on taking advantage of the Common Community Physics Package (CCPP) single-column model (SCM) to conduct hypothesis testing for understanding physics-related, operation-relevant forecast issues and elucidating whether and how these issues are attributable to model physics. The prevailing cold, dry lower troposphere in the UFS global forecast is investigated and found to be attributable to problematic synoptic flow over the studied site, which also contributes to an earlier collapse of the daytime planetary boundary layer (PBL), insufficient nocturnal PBL transitions, and a lack of decoupling between the stable boundary layer and the overlying residual layer late in the afternoon. Testing and evaluation using the CCPP SCM experiments conducted with the same physics as used in the global model, however, indicates that the model physics tends to generate an excessively warm (unlike the cold UFS global forecast), deep PBL, which in part results from overestimated surface heat fluxes that are tied to the land surface model, misrepresented PBL processes such as enhanced alternating thermals, and scarce clouds, which are related to the PBL and microphysics. The longstanding problem of weak nocturnal surface-driven temperature inversion is connected to overly cooled and windy condition near the surface, both of which are largely induced by the PBL parameterization. The investigation suggests room for improvement in the representations of the surface conditions, PBL processes, and the land-atmosphere-cloud interactions in the physics suite examined. The work introduces an avenue for the broader community to engage into the application of HSD for facilitating physics development while achieving forecast improvement of the UFS.