Characteristics of Cool Summer Events and Atmospheric Circulation in Last 55 Years over Hubei Province
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Abstract:
The threshold of cool summer is defined as -10 times the standard deviation of average summer air temperature anomaly, and singlestation cool summer is divided into two intensity grades: weak cool summer and strong cool summer. On the basis of the division method for singlestation cool summer, the definition method and classification standards for regional and provincial cool summer are defined, and regional and provincial cool summer intensity are identified by the percentile rank of cool summer stations respectively. The analysis of the spatial and temporal distribution characteristics of the cool summer events in Hubei Province from 1961 to 2015 shows that the cool summer event occurred more frequently in the southern and eastern Hubei than in northern and western parts. The frequency of cool summer over the southeastern Hubei was the highest while lowest in northwestern area. There occurred 7 cool summer years across Hubei over the last 55 years, including three strong years. The cool summer events occurred mainly in the 1980 s and 1990 s. Afterwards the variability of cool summer index tends to increase after the 1980s, and the provincial cool summer events still occurred in the background of global warming. By use of the NECP/NACR reanalysis dataset, the atmospheric circulation backgrounds of the cool summer years and the warm summer years and the rainy summer years are analyzed. The wave trains of mean geopotential height anomalies at 500 hPa and 100 hPa show as negative phase spatial distribution in cool summer years in the midlatitude region of the East Asia coast, and vice versa in warm summer years. The ridge line of the subtropical high was southward by 3 to 5 latitudes in cool summer years than those in warm summer years, and the ridge line of the South Asia high was southward by 2 to 3 latitudes in cool summer years than those in warm summer years. In cool summer years, there were more circulation fluctuations in at middle to high latitudes with a circulation background of two troughs and one ridge, and southward westerlies circulation. The wave trains of mean geopotential height anomaly at 500 hPa showed a “-+” distribution in cool summer years from Northeast China to South China, but the negative anomaly center was westward. Some cool summer years were also rainy summer years. There existed contemporary negative correlation and nonsignificant lag between SST Ni〖KG-*5〗n〖DD（-1*2〗〖HT〗＾〖DD)〗o 34 index of the Equatorial Middle East Pacific and the summer temperature anomaly index in Hubei Province, generally cool summer years corresponding with warm events in the Equatorial Middle East Pacific.
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Supported by:Beijing E-Tiller Technology Development Co., Ltd.
Supported by:Beijing E-Tiller Technology Development Co., Ltd.