Implications of Ural blocking for East Asian Winter Climate in CMIP5 GCMs. Part II: Projection and Uncertainty in Future Climate Conditions

Multiple model ensembles (MME) of Ural blocking frequency in 20 CMIP5 GCMs show no apparent increase or decrease in RCP4.5 and 8.5 runs throughout the 21st century. However, a significant increasing or decreasing trend of the Ural blocking index (UBI) is identified in individual GCMs, and the trend appears to be correlated with the trend of the Siberian high index (SHI), which measures the East Asian winter climate. Regression analyses reveal that the trend of UBI is related to upstream circulation over the Euro-Atlantic region, such as the intensification of the Atlantic jet stream and the propagation of a quasi-stationary Rossby wave across Eurasia.In the late 21st century, the year-to-year variation of UBI appears to show a stronger linkage with the large-scale circulation over the Kara and Laptev Seas. Meanwhile, UB likely exerts a stronger impact on East Asia on synoptic and seasonal timescales. The uncertainty of UB might present a challenge for accurate prediction of the subseasonal and long-term variation of the East Asian winter climate. To further evaluate the uncertainty in projections of UB, additional work should assess the atmospheric response to the sea surface temperature over the Atlantic and the reduction of sea ice.