ANTARCTIC SEA ICE AND THE POLAR VORTEX INDEX:TEMPORAL AND SPATIAL CHARACTERISTICS AND THEIR RELATIONSHIP^*

The cluster analysis method has been used to divide the Antarctic sea ice variation field into 5 sectors.Then,for each of these sectors,the corresponding indexes of vortex area and vortex intensity on the 500 hPa level have been calculated.These data were used to analyse the temporal and spatial characteristics of both Antarctic sea ice and the vortex index variations and their relationship.Our results show that substantial differences are presented in the climatic pattern and interannual variations of the sea ice data and vortex index in different sectors.The maximum sea ice extent variations appear in sector 1 and sector 4.Oscillation periods of 2-2.5 and 5-7 years exist in the variations of sea ice extent and vortex index in most sectors.A positive trend is only found in sector 1 sea ice extent while the other sectors shown egative trends.The average extent of the Antarctic sea ice as a whole has retreated at a rate of 1.6 latitudes per 100 years.The vortex areas for all sectors have decreased.Nevertheless,the vortex intensities in 3 sectors have increased.The relationship between sea ice and vortex characters in each sector is obvious,but a little complex.Sectors 1 and 5,which are located in the Southeast Pacific and South Atlantic,are the most sensitive areas in terms of sea ice/atmosphere interaction.