Basic structure features of the Arctic stratospheric atmosphere in summer

The influence of stratospheric process on troposphere is one of the hot scientific issues in the present. However, the changes of the summer stratospheric atmospheric circulation in the Arctic and its impact on troposphere have hardly been studied in China. In this paper, NCEP/NCAR reanalysis data are used to analyze the basic structure characteristics of the summer Arctic stratosphere. Results show that there are significant seasonal changes in both stratospheric zonal wind and pressure in the Arctic area (60 degrees N similar to 90 degrees N); moreover, seasonal changes in different altitudes begin at different times. Seasonal transition from winter to summer in the Arctic stratosphere is progressed from top to bottom, while that reverses (from bottom to top) from summer to winter. To take 20 hPa for an example, averagely, the Arctic region is controlled by the polar vortex before the beginning of April; in the middle third of April, the power of high begins to exceed that of low; then the Arctic high completely establishes in the beginning of May, and it is the strongest in July, begins to weaken in August, and terminates in the end of August. The variations of center position of the Arctic high can be divided into three types: North American pattern, Eurasian pattern, and transitional pattern. The structures of wind and pressure in the lower stratosphere are different from those in the middle and upper stratosphere, and the South Asia high is integrated with the Arctic high in the lower stratosphere; in vertical direction, the Arctic high joints the South Asia high at 100 hPa from top to bottom, and the central axis in high is tilted. This study lays a good foundation for the next analyses which include the intraseasonal, interannual and interdecadal variations of the Arctic high strength and summer stratospheric circulation as well as the impact of summer stratospheric anomalies to troposphere.