Exploring Physics Parameterization Development Using an Operationally Based Single-Column Model

While numerical weather prediction (NWP) models are becoming increasingly complex and expensive to develop, use, and test, single-column models (SCMs) offer a simpler and considerably cheaper avenue for testing and developing atmospheric physics. Such models massively reduce the scale of the problem in terms of software, computational expense, and interpretive complexity while maintaining a critical component of the entire system, namely the interaction of atmospheric physics parameterizations assembled within a physics suite. Case studies based on a variety of observational field campaigns can provide initial conditions, model forcing, and comparative data. Where observational gaps exist in the field campaigns, large eddy simulations can be employed to fill them and provide "truth-proxy" data for non-standard variables. Physics developers can utilize SCMs to rapidly develop and test prototype code as well as to tune and explore the parameter space. Given a set of case studies representing a broad enough spectrum of meteorological conditions, a physics scheme's performance within a suite can be characterized readily, although fully three-dimensional testing is necessary to understand a scheme's performance for phenomena where horizontal advection plays a leading role.

SCMs can also be an excellent educational tool. Experiments where individual processes are enhanced or reduced (or eliminated altogether) can be very illuminating and provide students with a hands-on tool for exploring various atmospheric processes from surface-atmosphere interactions to how boundary layer turbulence affects deep convection to cloud-radiative effects. In addition, single column models can provide a platform for learning about the engineering of atmospheric models without the intimidation factor and computational overhead associated with their full-scale three-dimensional counterparts.

Within the Developmental Testbed Center (DTC), as part of the Global Model Test Bed (GMTB) project, an operationally-based SCM has been developed as part of a broader hierarchical physics test harness. It has been developed from the ground up to use physics from the Common Community Physics Package, a collection of vetted and supported physical parameterization schemes from which the NOAA operational community will assemble both operational and pre-operational candidate physics suites for the nascent NOAA Unified Forecast System (UFS) for both NWP and subseasonal applications. In addition, it is packaged with a set of ready-to-run test cases based on Global Atmospheric System Studies (GASS) intercomparison cases and similar datasets from the Atmospheric Radiation Measurement (ARM) program and is readily extendable to user-added cases and data. The connection with the CCPP and the inclusion of "canned" cases allows students and researchers to relatively easily download, build, and test a wide range of physics parameterizations under a range of meteorological conditions and to compare against the current NOAA operational physics suite. The GMTB SCM and its applicability for the educational arena will be demonstrated and discussed.