Using the Global Modeling TestBed Single Column Model to Test a Newly Developed Convective Parameterization

The initial focus of the Global Modeling TestBed (GMTB), a collaborative project between NOAA GSD and NCAR through the Developmental Testbed Center, is to develop a framework to evaluate advancements in physics parameterizations for future use in operational NWP. Such a framework consists of an Interoperable Physics Driver (IPD), a Common Community Physics Package (CCPP), and a physics test harness. The IPD is an evolving software layer between an atmospheric dycore and an atmospheric physics suite. It was initially designed to serve as a singular interface to the GFS physics suite, but is being generalized to accommodate potentially many dycores and physics suites to function as a standardized interface. The CCPP is a limited collection of physics suites that will be supported by the DTC and curated by physics experts from the research community, the DTC, and NOAA EMC. Suites within the CCPP will serve as benchmarks with which to judge parameterization advancements and as starting points for future modification. The physics test harness consists of the data and tools required to uniformly test and evaluate physics parameterizations and suites. It encompasses many testing and evaluation paradigms, from individual parameterization simulators, to single-column modeling, to limited-domain 3D modeling, to medium-resolution global forecasts. Evaluation of a new physics parameterization is facilitated through connection of the parameterization source code to the IPD. Use of the test harness and comparison to the schemes and suites within the CCPP follows easily.

The single-column model layer of the test harness can be a particularly cost effective physics evaluation tool. Although evaluation of physics parameterizations in a global model setting cannot be replaced, interpretation of results can be hampered both by errors introduced by the dycore and advection of the errors produced by the physics suite itself, not to mention the large relative computational cost. With a single column model, such errors are eliminated and interpretation can be more straightforward. In addition, single-column models can be run in seconds on a desktop-class processor, allowing for exploration of a wide set of meteorological conditions and tuning parameters quickly. The single-column model developed as part of the GMTB physics test harness uses the latest version of the IPD, can be driven using any of the forcing methods found in Randall and Cripe (1999), and can be initialized and forced using either field campaign observationally-based cases or gridded GFS output. A scale-aware convective parameterization developed by Grell and Freitas (2014) was recently connected to the IPD and tested using the GMTB test harness. An evaluation of this scheme compared to the operational GFS convective scheme (simplified Arakawa-Schubert) was performed to demonstrate the usefulness of the physics testbed. Results from this evaluation will be presented.