Abstract: The characteristics and causes of an extreme high-temperature event in the summer of 2013 in Zhejiang Province were analyzed using the conventional automatic weather station observations and the European Center for Medium-Range Weather Forecasts (ECMWF) Re-Analyses (ERA) Interim reanalysis data (resolution with 0.75°×0.75°).The results show that the highest temperature appears in the summer of 2013 since 1951 over Zhejiang Province.Its mean value of temperature in July and August,the number of the high-temperature days and extreme value of the maximum temperature all break the highest records since 1951.The short-time period of Meiyu and less impact of the typhoon are the backgrounds for this high-temperature weather.Among its six high-temperature stages,the fourth is the one that lasts the longest and has the strongest intensity.The main reasons for the high temperature are as follows.First,the stronger westward subtropical high and stronger eastward South Asia high in the summer together control the high and low levels over Zhejiang region.It leads to the convective activity is inhibited by the sinking airflow.Second,the center of polar vortex tends to the north of the North America.So the cold air coming from the polar vortex is weak at Zhejiang region.Meanwhile,the troughs in the middle and high latitudes are relatively shallow.It is not favorable for the cold air to move southwards.Furthermore,the subtropical high occupies over the middle and lower reaches of the Yangtze River from mid-July and then forms a banding high-pressure dam in early August.Under this situation,the convergence zone of cold and warm airs is located northwards,and the precipitation areas are also northward.Third,the westerly jet lies northward.It impedes the subtropical high moving westwards.Under the influence of the sinking airflow,it leads to the temperature increasing at this region.

Key words: High temperature, Subtropical high, South Asia high, Polar vortex, Westerly jet