Intraseasonal Inconsistency of Interdecadal Variations of Summer High Temperature in Yangtze River Basin and the Corresponding Atmospheric Circulation Anomaly
Using the maximum temperature observation data, Meiyu data and NCEP/NCAR reanalysis data, we analyze the interdecadal variation characteristics of high temperature stations in Yangtze River Basin and the corresponding atmospheric circulation anomaly at different periods of summer from 1961 to 2020. The results show that high temperature events mainly occurred in the middle-east part (east of 105°E) of the Yangtze River Basin. There existed an abrupt mutation in the summer high temperature across this basin around 2002. Relative to the 35℃ threshold, the increments of high temperature stations at 37℃ and 40℃ were more obvious before and after the mutation. But interdecadal variation characteristics at different periods of summer were inconsistent, and they can be divided into two categories: the slow increasing periods without significant interdecadal turnings and the quick increasing periods, in which an abrupt mutation occurred around 2002 and the interdacadal relative change rates were higher than that of the whole season of summer. The Eurasian teleconnection, the East Asia-Pacific teleconnection and the end time of Meiyu were the major contributors to the intraseasonal inconsistency. During the quick increasing periods, the significant interdecadal increase of high temperature was always accompanied by abnormal intensification of East Asia-Pacific teleconnection. The circulations in the mid-high latitude over Eurasia were significantly different between the two periods with the largest relative change rates. During the slow increasing periods, however, Eurasian teleconnection strengthened at a lower magnitude, while East Asia-Pacific teleconnection was weakened. The slow increase of high temperature stations in 9-19 July was related to the late end of Meiyu.