Changes in the Convective Population and Thermodynamic Environments in Convection-Permitting Regional Climate Simulations over the United States

Novel high-resolution convection-permitting regional climate simulations over the U.S. employing the pseudo-global warming approach are used to investigate changes in the convective population and thermodynamic environments in a future climate. Two sets of continuous 13-year simulations for the period 1 October 2001 – 30 September 2013 are conducted using (1) ERA-Interim reanalysis forcing (CTRL) and (2) ERA-Interim reanalysis forcing plus a climate perturbation derived from a 19-model CMIP5 ensemble monthly mean climate change signal for the RCP8.5 scenario (PGW). The high-resolution simulations closely match the observed precipitation diurnal cycle, indicating that they reproduce organized and propagating convection that most climate models cannot adequately represent. Results from this study show that weak to moderate convection will decrease in frequency and strong convection will increase in frequency in a future climate. The thermodynamic environments supporting convection are analyzed and show that convective available potential energy (CAPE) increases and convective inhibition (CIN) also increases downstream of the Rockies in a future climate. Previous studies suggest that CAPE will increase in a future climate, however a corresponding increase in CIN acts as a balancing force to shift the convective population by suppressing weak to moderate convection and also provides an environment where CAPE can build to extreme levels and may result in more frequent severe convection. An idealized investigation of fundamental changes in the thermodynamic environment was conducted by shifting a standard atmospheric profile by ± 5°C. When temperature is increased, both CAPE and CIN increase in magnitude, while the opposite is true for decreased temperatures. Thus, even in the absence of synoptic and mesoscale variations, a warmer climate will provide more CAPE and CIN that will shift the convective population, likely impacting the water and energy budgets on Earth.