9.2 The Kain-Fritsch scheme: Science updates and revisiting gray-scale issues from the NWP and regional climate perspectives

Alapaty, Kirankumar, Russell Bullock, Jr., Jerold Herwehe, Robert Gilliam, Christopher Nolte, Tanya Otte, United States Environmental Protection Agency, John Kain, National Oceanic and Atmospheric Administration, and Jimy Dudhia, National Center for Atmospheric Research

It’s a just matter of time before we see global climate models increasing their spatial resolution to that now typical of regional models. This encroachment brings in an urgent need for making regional NWP and climate models applicable at certain finer resolutions. One of the hindrances using regional models at these finer grid resolutions, particularly between ~10 to 1 km, is the so-called gray-scale issue related to subgrid-scale convection representation. First, the subgrid-scale and radiation interactions need to be implemented before descending on the development of a seamless convection parameterization. This makes clouds, at the least, adequately represented in the regional modeling systems. Then, it is the time to tease few important parameters in a convection parameterization about their scale dependency. These parameters/processes can be: (1) convective adjustment timescale; (2) entrainment of air from the environment; (3) representation of convective cloud microphysics; and (4) evaporation of falling precipitation. We are cognizant that there may be other equally important parameters – but, for now, this is a good start with few in hand. The ultimate goal of this research is to make the Kain-Fritsch scheme used in the WRF model operable at all spatial scales up to about ~1 km grid resolution, thus opening doors for a seamless representation of subgrid-scale convection. We present preliminary results obtained from using various grid resolutions in several test case studies ranging from short- to long-term simulations.