Wintertime internal climate variability over Eurasia in the CESM large ensemble

Abstract

Based on outputs of historical runs of 38 members from the Community Earth System Model (CESM) Large Ensemble Project, this study evaluates the capability of the model to simulate the winter climate over the Northern Hemisphere, with an emphasis on Eurasia. The climatology and interannual variability of the wintertime circulation and surface air temperature (SAT) can be well reproduced. The multi-member mean of the long-term trends of sea level pressure (SLP) and SAT resemble the observations, suggesting the capability of CESM to reproduce the forced component of the observed trends. Meanwhile, the trends of SLP and SAT show large diversity among the 38 members, implying the importance of low-frequency variability in the observed trends. Considering the high skill of the CESM to simulate the observed climate, the internal climate variability described by the inter-member spread is further examined. It reveals that the internal climate variability of wintertime SLP over Eurasia can be captured by analyzing the inter-member spread of their climatology, interannual variability, or long-term trend. Moreover, the variations of the inter-member spread are regulated by the same mechanism as that of the observed interannual variability, implying the feasibility of explaining the characteristics and mechanism of the inter-member spread with the corresponding interannual variability in observations.