The Climate Oscillations of the Circumpolar Circulation at 500 hPa in the Northern Hemisphere

In this paper, the climate oscillations of the monthly circumpolar circulation index during 1951—1980 defined as the area enclosed 5520 m, isohypse are studied. It has been found that the circumpolar circulation index not only may easily undergo seasonal variations but also may vary with periodicity of oscillation such as 2—4 months, 5, and 19—20 years. During the period of 30 years from 1951 to 1980, the circumpolar circulation was contracted in the 1950s and expanded in the 1960s, However, during the 1970s, it kept oscillating in the vicinity of the average value. There exists a close relationship between the circumpolar circulation index and the surface air temperature or precipitation in China. When the circumpolar circulation is expanding (contracting), the surface air temperature will decrease (increase) and the precipitation will decrease (increase) in winter, spring and early summer and increase (decrease) in midsummer and autumn. These results can be used to explain the cause of climate change during the past thirty years