Definition and analysis of the circulation indices of polar vortex at 10 hPa in the Northern Hemisphere

A set of circulation indices are defined and calculated to characterize monthly mean polar vortex at 10 hPa geopotential height chart in the Northern Hemisphere, including area-(S), intensity-(P) and center position (λc, φc)-indices by use of 1948-2007 NCEP/NCAR 10 hPa monthly height data. These indices series are used to investigate the seasonal variation and interannual anomaly of polar vortex, along with the relations with global warming, ozone anomaly and Arctic Oscillation (AO). The results show that (1) there is anticyclonic (cyclonic) from Jun. to Aug. (from Sep. to Mar.). The change of spring circulation pattern is slower than that of autumn. (2) S can be replaced by P due to the interannual synchronal variations of the intensity and area for polar vortex. The interannual (interdecadal) variations of P are significant in Jan. (Jul.). (3) The anomalies of system center position in Jan. are more evident than that in Jul. (4) The variations of mean temperature at mid-stratosphere in the vicinity of pole zone in Jan. are different from that in Jul., but they are synchronal with the corresponding P and not significant correlation with the trend of global warming. However, the relationship between P and total O3 in Jul. are obvious. (5) There is so notable correlation between P and AO that P can represent AO.