Evaluation of the Simulation of ENSO Teleconnections to Precipitation Extremes Over the U.S. in High-Resolution Version (25 km) of E3SMv1
High-resolution Earth System Models provide the opportunity to investigate details of regional climate extremes where they are coupled to and embedded in the large-scale environment driving them. In this study, extreme value analysis of a century-long control simulation of the high-resolution version of E3SM (E3SMv1-HR, 25 km nominal horizontal resolution of the atmosphere model) is conducted to evaluate the simulation of ENSO teleconnections to winter precipitation extremes over the US. The role of large-scale drivers in generating model bias in ENSO dependence of extremes is also identified.
E3SMv1-HR reduces low-resolution model’s (110 km) bias over Southeast US by simulating stronger El-Niño associated extremes. This is due to improved simulation of ENSO-associated moisture variability over the region and stronger vertical velocities in E3SMv1-HR. Over the Pacific Northwest, E3SMv1-HR simulates stronger than observed La Niña associated extremes despite weaker simulation of ENSO-dependent extra-tropical storm track activity. This is due to a stronger than observed influx of moisture from the Pacific Ocean during La Niña events in E3SMv1-HR.
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 LR's model bias. Both LR and HR produce weaker than the 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.