Evaluating Model Physics in the Unified Forecast System (UFS): An Exercise of Using the Common Community Physics Package (CCPP) Single-Column Model under the Hierarchical Testing Framework

Abstract:

To inform the development and improvement of the model physics in the Unified Forecast System (UFS), this study applied the hierarchical testing framework, in particular the Common Community Physics Package (CCPP) Single-Column Model (SCM) to investigate the deficiencies in the Developmental Global Forecast System version 16 (GFSv16beta) physics suite, with a special focus on the simulation of the planetary boundary layer (PBL). A Large Eddy Simulation (LES) Atmospheric Radiation Measurement (ARM) Symbiotic Simulation and Observation (LASSO) simulation case with high cloud skill score was selected for evaluating SCM and UFS simulations. Although the UFS simulation captures the evolution and diurnal cycle of the PBL thermodynamics modestly well, large biases exist including a colder, drier, overmixed and deeper PBL along with a slightly out-of-phase diurnal cycle of near-surface temperature. Testing and evaluation with the CCPP SCM, which was observation-constrained, suggested that the GFSv16beta physics suite actually contributed to warmer, overmixed, and deeper PBLs particularly in the afternoon and evening, which was closely related to the PBL and land-surface parameterizations in the suite. Therefore, the cold and dry UFS biases are mostly related to an issue with large-scale advection that may result from errors in the GFS analysis, and/or model physics that lead to upwind errors, such as misplaced synoptic systems. Examining these problems helps to shed light on the longstanding cold bias issue over the CONUS in the GFS.