Characteristics of blocking high in Northeast Asia and other areas of the northern Hemisphere and their relationships during May to June in recent 40 years

KeyWord:May to June;Northern Hemisphere blocking high;Northeast Asia blocking high;North Tibetan Plateau blocking high;Characteristics;Information flow

Abstract:

      Based on NCEP/NCAR-Ⅰ reanalysis and the internationally accepted definition of blocking high, the northern Hemisphere blocking high distribution maps were obtained from May to June over the 40-year period of 1979—2018 using subjective and objective detection methods. Linear correlation and information flow statistical methods are used to study interannual and interdecadal relationships between anomalous variations of blocking highs over Northeast Asia and other areas in the northern Hemisphere. According to the concentration of blocking high activities and their percentages of total days in the northern Hemisphere, 8 major areas in May and 10 major areas in June are selected. In May, the North Pacific blocking, the North America blocking, and the Ural blocking are the top three. In June, the number of days for the Northeast Asia blocking jumps to the top. It is worth noting that in the early summer, there is a significant increase in blocking to the south of the Baikal Lake and north of the Tibetan Plateau, which is called the North Tibetan Plateau blocking high. The latitude distribution of the northern Hemisphere blocking high activity centers in May and June shows a "sine wave" characteristic. Although the 500 hPa height field anomalies caused by blockings in their main active areas in the northern Hemisphere show different characteristics in May and June, they demonstrate teleconnection characteristics. The interannual variation of the Northeast Asia blocking high in May and June shows an obvious independence. The Northeast Asia blocking high in May is a source of the interannual variation of Lake Baikal blocking high in June; it is also an unstable source of the interannual variation of the North Tibetan Plateau blocking high in June. The North Pacific blocking in May is the only stable source of the interannual variation of the Northeast Asia blocking in June. In June 2019, the area of most frequent and abnormal blocking high activities in the northern Hemisphere remains in Europe for 19 d, which is 2.7 times the climatological average of 7 d. The blockings are also the main influence system leading to the early summer high temperature in Europe.