The Variation of Compound Warm Dry Extremes Over Eastern China and the Associated East Asian Subtropical Jet in the Boreal Summer

The compound warm dry extremes (CWDEs), which can lead to extreme impacts that are much larger than the sum of the impacts due to the occurrence of individual extremes alone, have frequently hit the land regions. In this study, the spatial-temporal variations of the frequency, warm, and dry intensity of the CWDEs over eastern China and the associated East Asian subtropical jet variations have been investigated. The results show that the first two leading CWDE frequency modes over eastern China are characterized by an increase pattern and a dipole pattern. The increases in the CWDE frequency may be accompanied by both the strong warm and dry in the northern part of China. Whereas, these may be mainly related to the strong warmth in the southern part of China. The dominant increase pattern is associated with the weakened land-branch East Asian subtropical jet, which is maintained by the negative phase of the interdecadal Pacific Oscillation, the warming over high-latitudes of the Atlantic Ocean and the positive phase of the Arctic Oscillation. The dipole pattern is related to the southward shift of the ocean-branch East Asian subtropical jet, which is sustained by the warming in central equatorial Pacific and Indian Oceans, as well as the negative phase of North Atlantic Oscillation and the Pacific-Japan teleconnection. The relative contribution analysis has confirmed the importance of the jet variations to the CWDEs. These results would be helpful for understanding the drivers of the CWDEs. The compound warm dry extremes (CWDEs) have profound economic and social impacts, however, the large-scale circulations driving the CWDEs over eastern China are still unclear. In this study, the role of the upper-level westerly played in the variation of the CWDEs over eastern China has been proposed. The warming over high-latitudes, the Atlantic Ocean, and northwestern Pacific Ocean would benefit the weakened land branch of the westerly, and favor the increases in the occurrences of CWDEs over eastern China. As well, the warming over central equatorial Pacific and Indian Ocean would trigger the southward-movement of the ocean-branch East Asian subtropical jet, and result in the northern-decrease-southern-increase CWDE pattern. These results are helpful for understanding the occurrences of the CWDEs over eastern China and reducing their negative impacts. The leading modes of compound warm dry extreme (CWDE) frequency over eastern China are an increase and dipole patternThe weakened land-branch East Asian subtropical jet and southward movement of the ocean-branch East Asian subtropical jet are the important large-scale circulationsThe sea surface temperature (SST) variations in the North Pacific, Atlantic, and Indian Ocean have physically linked the jet stream and CWDEs over eastern China