Variation Features and the Impact of the Latitudinal Position of the Western Pacific Subtropical High in Summer

The geopotential height, wind field(u, v, w), temperature, relative humidity, maximum temperature, and SST fields in the ECMWF reanalysis data sets and the observational precipitation data in China are used to study the dynamic climate features and the evolution of subtropical high over the northwestern Pacific in July. Two processes which describe the south and north positions of subtropical high are defined (south or north position lasting for more than six days is defined as one process) and the correspondence composite analysis are completed. The results show that the intraseasonal oscillation is obvious both in the south and north processes, and the most typical oscillation occurs in July. Corresponding to the south and north processes of the subtropical high, there are evident different features and evolutions in atmospheric circulation, the distribution of precipitation, the maximum temperature in China, and the SST anomaly in the northwestern Pacific. This means that it is necessary to study and understand the dynamic characteristic of weather and climate based on the variability of the atmospheric system even though just in July as a short period. Through the analysis of process evolutions, some interesting results on the premonition characteristic, variation features during and after the north, south processes of subtropical high are indicated, which are undiscovered in previous studies.