Summertime Near‐Surface Temperature Biases Over the Central United States in Convection‐Permitting Simulations.

Convection‐Permitting Model (CPM) simulations of the Central United States climate for the summer of 2011 are studied to understand the causes of warm biases in 2‐m air temperature (T2m) and related underestimates of precipitation including that from mesoscale convective systems (MCSs). Based on 10 CPM simulations and 9 coarser‐resolution model simulations, we quantify contributions from evaporative fraction (EF) and radiation to the T2m bias with both types of models overestimating T2m largely because they underestimate EF. The performance of CPMs in capturing MCS characteristics (frequency, rainfall, propagation) varies. The pre‐summer precipitation bias has large correlation with mean summertime T2m bias but the relationship between summertime MCS mean rainfall bias and T2m bias is non‐monotonic. Analysis of lifting condensation level deficit and convective available potential energy suggests that models with T2m warm biases and low EF have too dry and stable boundary layers, inhibiting the formation of clouds, precipitation and MCSs. Among the CPMs with differing model formulations (e.g., transpiration, infiltration, cloud macrophysics and microphysics), evidence suggests that altering the land‐surface model is more effective than altering the atmospheric model in reducing T2m biases. These results demonstrate that land‐atmosphere interactions play a very important role in determining the summertime climate of the Central United States. Plain Language Summary: It is challenging for conventional coarse‐resolution weather and climate models to simulate summertime near‐surface air temperature (T2m) over the central United States. We thought that a large reduction in the warm T2m bias would occur only when the model resolution was sufficiently fine to resolve mesoscale convective systems (MCSs), which are responsible for around 30%–70% of summertime rainfall. Here, we examined T2m, MCSs, and other climatic features in a collection of kilometer‐scale model simulations which have the necessary resolution to simulate MCSs. However, we found that these models also simulate a warm T2m bias and the relationships with other variables are very similar to that of the coarse‐resolution models. In particular, variations in the warm bias are well related to variations in evaporative fraction, which is the fraction of surface heat fluxes that are in latent heat form as opposed to sensible heat. Our analysis suggests that land‐atmosphere interactions play an important role for kilometer‐scale models to simulate realistic summertime T2m and precipitation over the Central United States. Key Points: Convection Permitting Models have surface warm biases mainly because of evaporation underestimation, similar to coarser‐resolution modelsThe simulations of mesoscale convective systems can be degraded by the evaporative fraction biases, which also influence surface warm biasesThe land surface impacts precipitation via its influence on evapotranspiration whereas spring precipitation impacts summertime soil moisture [ABSTRACT FROM AUTHOR]