Simulations of Warm Season Extreme Precipitation Events using MPAS-A Runs in the Southeastern US

Much of the most striking weather and climate extremes in midlatitude continental locations occur in the warm season. Local processes in an increasingly warmer climate can intensify the climatic responses of extreme events including maximum rain rates that scale with temperature more strongly than expected from the Clausius-Clapeyron relation. Aside from rain events that are intensified due to storm dynamics associated with greater CAPE, large scale atmospheric dynamics can also work to strengthen or weaken these events. A perquisite of using a global model for this type of analysis.

High resolution (15 km) output from free-running global atmospheric climate simulations, the atmospheric component of the Model for Prediction Across Scales (MPAS-A), was analyzed under current and future climate conditions. Simulation years spanning over 10 years with varying phases of El Niño–Southern Oscillation (ENSO) was selected and integrated for 14.5 months. Sea surface temperature (SST) patterns was analyzed for present-day simulations, and for the future climate simulations we altered present-day SSTs by applying monthly-averaged temperature changes derived from Coupled Model Intercomparison Project phase 5 (CMIP5), and general circulation models (GCMs) following the Representative Concentration Pathway (RCP) 8.5 emissions scenario (Michaelis et al. 2019). With this data, we identify heavy daily precipitation events in the Southeast US using a spatial cluster approach (Moore et al. 2014).

Here we examine the roles of mesoscale and synoptic influences in controlling precipitation morphology, through a case study analysis of the structure and origin of the systems responsible for these extreme precipitation events (EPEs).We compare the current and future simulations for total rainfall amount, location of precipitation maximums, morphology and systematic changes between the events.