Application Of A Set Of Circulation Indices For The Polar Vortex In The Boreal Winter On Climate Studies

In this paper, using the monthly mean geopotential height field of NCEP/NCAR reanalysis data, three polar vortex circulation indices of Northern Hemisphere total 12 layers of 500～10hPa in winter from 1948/49 to 2009/10 are defined and calculated, including the area index S, the strength index P, the center position index of longitude/latitude(λc,(?)c).Their series of 62 years are used to analyze the climate characteristics of winter Northern Hemisphere, and to investigate the relationship of them with the arctic sea ice area, sea surface temperature (SST) change and global temperature. The main conclusion:(1)The changes of polar vortex area and strength are different in the vertical height. There is a diversity which month the intra-seasonal maximum appears in. The correlation of polar vortex area and strength is bad, as two relatively independent indices. The inter-decadal trends of them are different between in the upper layers and lower ones, and the abnormal changing regulations are complicated. The change of center positions in the upper layers and lower ones is identical, which are mainly located in the Eastern Hemisphere and the north of 80 degrees north latitude. As polar vortex is around the North Pole, the longitude change is big and the latitude one is small. Interdecadal changing trends of them are significant, especially in the past 10 years, obviously abnormal toward the south. On the whole, the form of center positions from 500hPa to 10hPa is that the radius of counter-clockwise rotation becomes larger with height.(2)Between the S index of winter 500hPa Northern Hemisphere and the sea ice area index (Ia), the two over the same period is a positive correlation, and a significant negative correlation exhibits from 300hPa to 20hPa.The intra-seasonal and seasonal correlation of the P index and the sea ice area index (Ia) is not significant. The center positionλc index from 300hPa to 100hPa and the sea ice area index (Ia) over the same period are significantly correlated. The intra-seasonal and seasonal correlation is significant between the (?)c index and the sea ice area index (Ia) over the same period. In the vertical height, the correlation is smaller and smaller with height increasing. (3)The S index of winter 500-200hPa Northern Hemisphere polar vortex and the SST change over the same period in the central North Pacific and Northwest Pacific are negatively correlated, while the both correlation is bad from 100hPa to 50hPa. The two east-west positive correlation areas appear in the Pacific Ocean near 30°N. In the Atlantic Ocean, both from 500hPa to 100hPa negative correlation region exhibits, however, in the North Atlantic, from 70hPa to 10hPa the correlation zone disappears. From 500hPa to 10hPa, the (?)c index correlates the SST change of the North Pacific over the same period positively. In the equatorial eastern Pacific, the correlation is negative. The correlations between the center position (?)c of the polar vortex upper layers and Indian Ocean's SST index are better than the lower layers.(4)The correlations between the 500-10hPa polar vortex area (S) of winter and the surface temperature over the same period are very good in the middle and lower layer of the polar vortex. In other words, the correlation is positive in the low-latitude and negative in the high-latitude. The correlations between the polar vortex intensity index (P) and the surface temperature over the same period in upper layers are better than lower layers. The correlation is mainly negative in the northern hemisphere and positive in the southern hemisphere, just the relevant regional distribution of different layers is different. The distribution of correlation which is between the (?)c index of winter 500～10hPa and the surface temperature over the same period is different in the vertical height. There is a wide area of positive correlation whose better correlation layer resides in 30°S～30°N. In the northern 30°N of Northern Hemisphere (expect for the north area of the North Ocean), there is a large negative region.