Projected Warm Season Intensification of the Great Plains Low Level Jet in CMIP6 Simulations

Abstract:

The Great Plains low-level jet (GPLLJ) is an atmospheric warm season-induced wind feature and an important driver of precipitation across the U.S. Great Plains and Midwest. We analyzed simulations from 24 Coupled Model Intercomparison Project (CMIP6) coupled atmosphere-ocean global climate models to understand warm season variations in the climatological GPLLJ and hydrological changes resulting from anthropogenic climate change during the twenty first century. CMIP6 simulations were then compared with two reanalysis products throughout the 20^th century. Long-term historical simulations demonstrate skill among CMIP6 models, through a multi-model average, in reproducing characteristics of the GPLLJ.

Our results show that future climate simulations, based on two shared socioeconomic pathways (SSP3.70 and SSP5.85), produce an intensification of the GPLLJ during the transition months from spring to summer (April, May, June). The jet strengthening is supported by the continued building of the North Atlantic Subtropical High to the west, due to increasing temperature and pressure gradients between the continental United States and subtropical Atlantic. Destabilization of the atmosphere over the Midwest, coupled with low level advection from the Gulf of Mexico, contribute to the precipitation enhancement and wetter soil moisture characteristics over the Midwest during the months of April and May. Additionally, projections illustrate a decrease in summer precipitation in the southern Great Plains linked to anomalous large-scale circulation and a change in GPLLJ patterns. Anomalously strong GPLLJs, based on an extreme jet frequency analysis relative to the historical time period, are projected to occur more often in the future during transition months, enhancing the probability of hazardous flood conditions. Overall, these results align with previous CMIP5 modeling studies surrounding the GPLLJ, showing a modification in spatial precipitation characteristics due to a strengthened GPLLJ and changing large-scale dynamics under a continued warming world.