Study On The Space Distribution And Atmospheric Circulation Cause Of Extreme High Temperature Over Eastern China In Summer

On the background of global climate change these years, extreme high temperature events are increasing and becoming stronger, people’s health, agriculture, industry and traffic et al are heavily influenced by them. Based on the CN05 grid datasets from 1961 to 2008, temporal and spatial patterns of extreme high temperature(EHT) days over eastern China in summer were obtained, then three main patterns of EHT days were separated through empirical orthogonal function (EOF) analysis, and the causations of the three patterns especially two’dipole’ patterns were analyzed, in respect of circulation patterns, tele-connection and sea surface temperature anomaly (SSTA). The main results are as follows:(1) The average EHT days over eastern China is increasing remarkably from 1961 to 2008, especially over northeast China and south China, the periodicity of EHT days over eastern China is primarily between 2 and 3 years, except Jiang-huai and Huang-huai area. The mutational year of EHT days over the whole eastern China is 1996, the frequency of large-scare extreme high temperature events is linearly increasing by year, especially after year 2000.(2) Three leading patterns of EHT days over eastern China were obtained by EOF analysis. The EOF1 and PCI show an increasing tendency of EHT days over most areas of eastern China; the EOF2 shows a dipole pattern of EHT days between northeast China and Jiang-huai area; the EOF3 shows a dipole pattern of EHT between north China and south China.(3) The 500 hPa geopotential height (GPH) over northeast China shows a most significant increase since about half a century ago. In typical years of positive EOF2 pattern, there shows positive 500 hPa GPH anomalies over Jiang-huai area while negative GPH anomalies over northeast China, meanwhile, the western Pacific subtropical high (WPSH) is larger and stronger and locates north and west relative to the climate mean field, there are southwesterly anomalies on 850 hPa, the 200 hPa westerly jet is stronger, and there are negative rainfall anomalies over Jiang-huai area while positive rainfall anomalies over northeast China and south China, the anomalous features are almost opposite in the negative phase, respectively. In typical years of positive EOF3 pattern, the WPSH is significantly stronger and locates south relative to the climate mean field, the Okhotsk blocking high is also stronger, there are southwesterly anomalies on 850 hPa, and the 200 hPa westerly jet is stronger, there are positive rainfall anomalies over Jiang-huai area and north China while negative rainfall anomalies over south China, the anomalous features are almost opposite in the negative phase, respectively. The Okhotsk blocking high index, the ridge line index of WPSH and the intensity index of WPSH are all having a positive correlation with EHT days over eastern China.(4) The distribution of Pacific-Japan (PJ) and Euroasia-Pacific (EUP) tele-connection patterns on 500hPa GPH has a correlation with the EOF2 pattern, respectively. The three leading patterns of 500hPa GPH by EOF analysis can partly explain the characteristics of three leading patterns of EHT days by EOF analysis, respectively. Results of the first pattern of EHT days over eastern China and sea surface temperature (SST) on tropical Pacific by singular value decomposition (SVD) analysis show that the raising of SST on most part of tropical Pacific has a close correlation with the increasing of EHT days over eastern China. The SVD2 pattern mainly shows an important influence of El Nino Modoki/La Nina Modoki to the distribution of EHT days over Jiang-huai and Huang-huai area. The SVD3 pattern shows an influence caused by La Nina/El Nino to the distribution of EHT days over eastern China. In year 1998, there are significant positive anomalies over south China on 500hPa GPH, the strong El Nino event in winter between 1997 and 1998 should affect the strength of WPSH in summer of year 1998, and the strengthen El Nino Modoki event since 1998 in summer was maybe in favor of the negative anomalies of EHT days over Jiang-huai and Huang-huai area.Results shown in this thesis, on one hand, can help us to understand the characteristics and mechanism of extreme high temperature, on the other hand, can help the government and relevant departments to draft policies against extreme high temperature, so the results have scientific and practical significance in respect of reducing loss of nation and people’s lives and property.