Tiny Processes in Clouds Drive Storm System Longevity over the Central United States
With improved cloud microphysics representing observed storm structures, models can better simulate long-lasting storms prone to produce flooding.
Mesoscale convective systems (MCSs) are a form of massive organized thunderstorms that can last up to 24 hours, and are projected to increase in both frequency and rainfall amount across the U.S. by the end of this century. While climate models with spatial resolution comparable to regional weather forecasting models can simulate the large-scale storm environment, details of how to represent cloud microphysical processes remain uncertain.
To assess the significance of microphysical processes, researchers at the U.S. Department of Energy's Pacific Northwest National Laboratory analyzed season-long simulations of MCSs with two different representations of cloud microphysics. They found that the cloud microphysical treatment with more slow-falling snow particles produced more realistic storm rainfall areas and longer-lived storms with greater flood potential, which indicates microphysical processes have important effects on the evolution of the storms.
As next-generation climate models continue to increase in resolution and complexity, physical processes such as cloud microphysics play a more prominent role in model uncertainties. This study suggests that cloud microphysics will greatly affect simulations of the hydrological cycle and extreme precipitation events in the climate system. Understanding the interactions and feedbacks between microphysics in MCSs and large-scale environments is important for better understanding and projecting the effects of warming temperatures on changes in hydrological extremes associated with MCSs.
Reference: Z. Feng, L.R. Leung, R.A. Houze, S. Hagos, J. Hardin, Q. Yang, B. Han, J. Fan, "Structure and Evolution of Mesoscale Convective Systems: Sensitivity to Cloud Microphysics in Convection-Permitting Simulations over the U.S." Journal of Advances in Modeling Earth Systems10, 1470-1494 (2018). [DOI: 10.1029/2018ms001305]