27 March 2017

A Promising Venue to Improve the Realism of Precipitation Simulations at a Continental Scale

Researchers effectively used convection-permitting modeling and scale-aware representations to improve simulations of U.S. summer precipitation characteristics.

Science

Simulating summer precipitation is a significant challenge for climate models that rely on cumulus representations to simulate moist convection processes that feature deep, saturated updrafts and downdrafts driven by evaporation and precipitation melting. Through systematic evaluation of the effects of model resolution and convective representations, scientists at the U.S. Department of Energy’s Pacific Northwest National Laboratory showed that convection-permitting modeling can more realistically capture the precipitation characteristics in the United States.

Impact

Adept simulations of precipitation are important for modeling the Earth’s water cycle, which supports life and a host of human activities. This study showed a promising venue for significantly improving the realism of precipitation simulations at a continental scale through high-performance computing and convection-permitting climate modeling.

Summary

Simulating summer precipitation has been a long-standing challenge for regional and global climate models. Motivated by recent computing advances that support very high-resolution modeling, this study evaluated the effects of model resolution and convective representations across the gray zone resolutions (approximately between 4 and 15 km). Researchers conducted simulations using the Weather Research and Forecasting model at resolutions of 36 km, 12 km, and 4 km for two summers over the conterminous (lower 48) United States. The convection-permitting simulations at 4 km grid spacing proved to be most capable in reproducing the observed precipitation spatial distributions and sub-daily variability. Researchers found notable differences between simulations with the traditional Kain-Fritsch and scale-aware Grell-Freitas convection schemes. Convection-permitting modeling, in which convection is explicitly resolved, and the use of scale-aware physical representations that are less sensitive to resolution, both improved simulations of the nocturnal timing of precipitation in the Great Plains and North American monsoon regions. As conceptually designed, the scale-aware representation showed reduced sensitivity to model resolution compared with the traditional method. Overall, the research demonstrated notable improvements in simulating summer rainfall and its sub-daily variability through convection-permitting modeling and scale-aware representations, which promise improvements in the water cycle process in climate simulations.

Contact
L. Ruby Leung
Pacific Northwest National Laboratory
Publications
Gao, Y., Leung, L., Zhao, C., & Hagos, S. "Sensitivity of U.S. summer precipitation to model resolution and convective parameterizations across gray zone resolutions." Journal of Geophysical Research: Atmospheres 122, (2017). [10.1002/2016JD025896].