Using Clustering to Evaluate the CESM1 Large Ensemble's Ability to Simulate Regional Variations in Heat Waves

Nighttime heat waves are known to kill people, as they prevent the public from recovering from the daytime heat. We evaluated the ability of the Community Earth System Model version 1 (CESM1) Large Ensemble Project (LE) to simulate regional variations in nighttime heat waves over North America. We also investigated any possible reasons for deficiencies of the simulations. The model results were compared to observations from the Global Historical Climatology Network – Daily. A nighttime heat wave was defined as the 90^th percentile exceedance of the departure from the average summer (JJA) daily minimum temperature. We employed hierarchical clustering analysis to identify regions that behave similarity in the observations and the LE members. The observations and LE members were found to be most similar for smaller numbers of clusters. When comparing, The LE simulated the North American East-West boundary farther east than observed. This appears to be associated with a dry bias over mountains in the LE. The LE simulated the eastern North American boundary farther north than observed. This appears to be due to errors in the simulated position and strength of the Bermuda High.