Abstract:Based on the ERA-interim, NCEP CFSR daily reanalysis data and daily observation temperature data from 29 stations over middle and low reaches of Yangtze River, the characteristics of the extreme high temperature event,circulation features and its causes over the middle and lower reaches of the Yangtze River during 23 July to 14 August, 2013 were analyzed. Results show that the intensity of the Western Pacific Subtropical High (WPSH) was extremely strong in summer of 2013, and the atmospheric adiabatic heating caused by the enhancing sinking motion in the WPSH controlling zone is the main cause for this high temperature event. Moreover, the extremely enhanced WPSH-related anticyclonic circulation leads to an increasing outflow of the water vapor over the middle and lower reaches of the Yangtze River area to the east, which causes the decreasing of the water vapor content, increasing of downward solar radiation flux at the surface, so this is another cause for this high temperature event. Further analysis indicates that an anomalous enhanced atmospheric heating source over the Maritime Continent is probably the main reason why the WPSH is extremely strong in summer of 2013.