Simulation of ENSO teleconnections to precipitation extremes over the US in the high resolution version of E3SM

Abstract

Abstract We evaluate the simulated teleconnection of El Niño Southern Oscillation (ENSO) to winter season precipitation extremes over the United States in a long (98 years) 1950-control high resolution version (HR, 25 km nominal atmosphere model horizontal resolution) of US Department of Energy’s (DOE) Energy Exascale Earth System Model version 1 (E3SMv1). Model bias and spatial pattern of ENSO teleconnections to mean and extreme precipitation in HR overall are similar to the low-resolution model’s (LR, 110 km) historical simulation (4-member ensemble, 1925-1959). However, over the Southeast US (SE-US), HR produces stronger El Niño associated extremes, reducing upon LR’s model bias. Both LR and HR produce weaker than observed increase in storm track activity during El Niño events there. But, HR improves the ENSO associated variability of moisture transport over SE-US. During El Niño, stronger vertical velocities in HR produce stronger large-scale precipitation causing larger latent heating of the troposphere that pulls in more moisture from the Gulf of Mexico into the SE-US. This positive feedback also contributes to the stronger mean and extreme precipitation response in HR. Over the Pacific Northwest, LR’s bias of stronger than observed La Niña associated extremes is amplified in HR. Both models simulate stronger than observed moisture transport from the Pacific Ocean into the region during La Niña years. The amplified HR bias there is due to stronger orographically driven vertical updrafts that create stronger large scale precipitation, despite weaker La Niña induced storm track activity.