Evaluating Mesoscale Convective Systems Over the US in Conventional and Multiscale Modeling Framework Configurations of E3SMv1

Abstract

Organized mesoscale convective systems (MCSs) contribute a significant amount of precipitation in the Central and Eastern US during spring and summer, which impacts the availability of freshwater and flooding events. However, current global Earth system models cannot capture MCSs well and misrepresent the statistics of precipitation in the region. In this study, we investigate the representation of MCSs in three configurations of the Energy Exascale Earth System Model (E3SMv1) by tracking individual storms based on outgoing longwave radiation using a new application of TempestExtremes. Our results indicate that conventional parameterizations of convection, implemented in both low (LR; ∼150 km) and high (HR; ∼25 km) resolution configurations, fail to capture almost all MCS‐like events, in‐part because they underestimate high‐level cloud ice associated with deep convection. On the other hand, the multiscale modeling framework (MMF; cloud‐resolving models embedded in each grid‐column of ∼150 km resolution E3SMv1) configuration represents MCSs and their annual cycle better. Nevertheless, relative to observations, the E3SMv1‐MMF spatial distribution of MCSs and associated precipitation is shifted eastward, and the diurnal timing is lagged. A comparison between the large‐scale environment in E3SMv1‐MMF and ERA5 reanalysis suggests that the biases during the summer in E3SMv1‐MMF are associated with biases in low‐level humidity and meridional moisture transport within the low‐level jet. The fact that conventional parameterizations of convection, even with high‐resolution, cannot capture MCSs over the US suggests that methods with explicit representation of kilometer‐scale convective organization, such as the MMF, may be necessary for improving the simulation of these convective systems.

Realistic Precipitation Diurnal Cycle in Global Convection‐Permitting Models by Resolving Mesoscale Convective Systems

“…The atmospheric convection parameterization is frequently cited as a primary reason why GCMs struggle to accurately simulate the diurnal cycle of precipitation (Dai & Trenberth, 2004;Liang et al, 2004;Tao et al, 2023;Xie et al, 2019). With advances in tracking MCSs in observations and simulations, recent studies found that most GCMs with convection parameterizations (even with a relatively high resolution, e.g., 25 km) cannot simulate MCSs well, which exhibit a distinct diurnal cycle (e.g., Dong et al, 2021;Feng et al, 2021;Hsu et al, 2023;Vergara-Temprado et al, 2020). As MCSs contribute to about half of the total precipitation in the tropics and subtropics and many critical processes that initiate and maintain MCSs are not resolved or correctly parameterized in GCMs (Fan et al, 2017;Houze et al, 1989;Moncrieff, 1992;Slingo et al, 2022;Varble et al, 2014;Q.…”