Study On The Extreme High Temperature Events In Summer And Its Mechanism In Recent 30 Years In North China

In this paper, based on the daily data of ground-based observations in North China, and the NCEP/NCAR reanalysis data from 1980 to 2010, the distributions and characteristics of extreme high temperature(EHT) changes in the past 30 years were studied in North China. Further discussions of the abnormal characteristics of atmospheric circulations and sea surface temperature when extreme temperature events happen show that there are relations among these facts. In the last part, the high-temperature weather during June 29 to July 2 in 2000 of Beijing was discussed.Either the days or the mean temperature of the high-temperature increased with age in North China. The geographical distributions of high-temperature days presented this characteristic:more EHT is in.the North and South, less is in the middle region. The distribution of the maximum of EHT is mainly in the middle region of east of the Taihang mountains. The variation characteristics of EHT with age:the number of occurrence of EHT increased with age. Meantime, the geographical distribution show that:in the 80s, days of EHT were mainly in the south of North China and the area of Henan, Shandong Etc. The number of occurrences of EHT in the 1990s increased significantly than1980s in the region of Hebei and the middle area of Shanxi.2000 years later, the days of EHT increased in north of Hebei, Beijing, Tianjin and Neimenggu. During the past 30 years, the days of EHT has especially increased significantly in the north of North China, less in the middle area, and relatively stable in the south region. Through the statistical analysis of the days of EHT in North China, the corresponding atmospheric circulations were also analyzed in this paper. Results show that:the EHT in North China is mainly influenced by Continental High Pressure, Western Pacific Subtropical high pressure(WPSHP) and Sea Surface Temperature Abnormal. The probability of EHT in North China increased when the WPSHP was stronger with a westward ridge point and a northward ridge line. The same situation occurs when Continental High Pressure was stronger, the North China was controlled by its ridge line, there’s a warm area which temperature is larger than 25℃, and simultaneously Northwest winds are dominant in high altitude. Furthermore, the EHT in North China is also closely related with Sea Surface Temperature Abnormal. When during the period of ENSO or ENSO Modoki, there appear significant differences of the maxmum temperature of North China. Based on the relationship, ENSO Modoki has a larger significant region when associated with EHT of North China, and is more relevant. The relationship between ENSO Modoki and EHT of North China is strongest in autumn. And during the same period, ENSO is more relevant in summer. In the last part, based on the example of extreme high temperature appeared in Beijing during June 29 to July 2 in 2000, the atmospheric circulations and other physical amounts in this weather process were discussed. Results show that:Continental High Pressure and WPSHP have the most contributions to this weather process. And temperature advection is more essential, followed in solar radiation for EHT.