Features and Possible Causes for the Climate Anomalies in Spring 2018
From March to May 2018, the mean temperature in China ranks the highest since 1961. The temperature is almost above normal in China, with the warmest regions located to the south of the Yangtze River and the central part of northern China. The mean precipitation of China is a little above normal. For eastern China, the precipitation is more than normal to the north of Yangtze River while it is less than normal to the south. As for western China, the positive anomalies of precipitation are observed in most parts of Southwest China, southeastern part of Northwest China and northern and western Xinjiang, while the negative anomalies are mainly in southern Xinjiang, western Qinghai and northwestern Gansu. The zonal wave train stretching from North Atlantic to Northeast Asia via Eurasia Continent at the midhigh latitudes mainly contributes to the climate anomalies in China from March to May 2018, with the trough to the east of Ural Mountains and the ridge over Northeast Asia occupying the key circulations. The anomalous high pressure, especially the ridge over Northeast Asia controls the extensive regions over the midlow latitudes of Asia to cause the higherthannormal temperature over most China from March to May 2018. The trough to the east of Ural Mountains favors the southward outbreak of the cold air, while the ridge over Northeast Asia leads the moisture to transport westward and northward from the western Pacific. Then, the cold and dry air mass merges with the warm and moist one to form the above normal precipitation over the region to the north of the Yangtze River and West China. Meanwhile, the anomalous cyclonic circulation over the South China Sea and the tropical western Pacific contributes to the belownormal precipitation from the region to the south of the Yangtze River to South China. Though a weak La Ni〖AKn~D〗a event occurs during the winter of 2017/2018 and the positive phase of North Atlantic Triple (NAT) mode persists from March to May 2018, they put limited impacts on the 2018s spring rainfall anomalies in China but the circulations dominate. Further analyses present that the intensity of the the trough to the east of Ural Mountains and the ridge over Northeast Asia has high correlations with both temperature and precipitation of China during spring, favoring the abovenormal temperature in most of China and morethannormal precipitation in West China and to the north of the Yangtze River but lessthannormal precipitation to the south. Significant negative correlation exists between the intensity of the two circulations and they are both closely connected with the Eurasian (EU) teleconnection pattern. Moreover, the ridge over Northeast Asia is also highly correlated with the positive phase of AO.