Analysis Of The Extremely High Temperature Event In The Middle And Lower Reaches Of The Yangtze River In The Summer Of 2013

Based on the ERA-interim daily reanalysis data, NCEP CFSR daily ground flux data, NCAR/NOAA OLR data, NCEP GFS FNL global reanalysis data, NCEP RTG_SST sea temperature data, CMA-STI tropical cyclone best track database and 29-station observation data, the characteristics and courses of the extreme high temperature event in the middle and lower reaches of the Yangtze River in the summer of 2013 are analyzed. Main conclusions are reached as follows:(1)The intensity of the Western Pacific subtropical high (WPSH) is extremely strong in the summer of 2013, and its associated atmospheric adiabatic heating due to the enhanced sinking motion is one of the causes for this high temperature event. At the same time, the extremely enhanced WPSH-related anticyclonic circulation over the middle and lower reaches of the Yangtze River area leads to an increase in the water vapor outflow from its north and east boundaries. As a result, this decrease in water vapor content results in an increase in downward solar radiation flux at the surface, which is another cause for this high temperature event.(2)The anomalous enhanced atmospheric heating source over the Maritime Continent is probably one of the reason why the Western Pacific Subtropical high is extremely strong in the summer of 2013.the eastward shift of the South Asian High (SAH) is accompanied with the northwestward development of the WPSH, and vice versa. SAH will influence the short-term variation of WPSH under the influence of both dynamic and thermodynamic factors. This relationship is pretty clear in the summer of 2013, which is probably another important factor that leads to the westward development and enhancement of the WPSH.(3)Under the influence of severe typhoon Utor (No.1311), there appears cyclonic circulation anomaly over the middle and lower reaches of the Yangtze River area, which leads to the decrease in both surface air temperature and WPSH-related anticyclonic circulation. This proves that Utor is the factor which leads to the end of the high temperature process.