Increased occurrence of two intrinsic atmospheric circulations in Asia during the boreal summer

Abstract

The k-means clustering of reanalysis datasets is used to classify the intrinsic atmospheric circulation in Asia based on the daily geopotential height of 500 hPa during the boreal summer (June, July and August) for 1958–2020. Among the total clusters of atmospheric circulation patterns in Asia, two distinct clusters of atmospheric circulation are characterized by a significant increasing trend in occurrence. They correspond to different zonal wave numbers (1–2 vs. 3–4) of atmospheric circulation in the mid-to-high latitudes of the Northern Hemisphere, and their associated sea surface temperature structures are not the same in the tropical Pacific and the North Atlantic. Further analysis indicates that two clusters of atmospheric circulation alter the amount of summer monsoon precipitation in East Asia, and an increasing amount of precipitation in southern China in recent decades could be explained by the combined effect of an increasing trend in the frequency of occurrence of two clusters of atmospheric circulation. Finally, a long-term simulation of the Community Earth System Model version 2 suggests that anthropogenic forcing may be responsible for the increasing trend of occurrence of the two atmospheric circulations in Asia. © 2024 Royal Meteorological Society.