DECADAL VARIABILITY OF ATMOSPHERIC CIRCULATION IN THE SOUTHERN MIDDLE AND HIGH LATITUDES

This paper summarizes the long-term and decadal time scale fluctuations of atmospheric circulation in the southern middle and high latitudes. The long time series of Antarctic Oscillation Indices (AOIs) were established for January, April, July and October 4 months based on the historical sea level pressure map and NCAR/NCEP reanalysis surface pressure data set. It was found that the AOI of January increased in a rate of 1.17 hPa/100 a, and July decreased in a rate of -1.49 hPa/100 a since 1871. The method of wavelet analysis was applied to detect the low frequency characteristics of AOIs, and it's clear that there are decadal variations in the time scale of about 20-30 years in all 4 months.Since the averaged value of 4 months could explain most variance of annual AOI, so it's reasonable using the mean AOI of January, April, July and October to represent the annual AOI. The values of annual AOI was much lower in periods of about 1894-1901, 1910-1935, and was much higher in periods of about 1880-1893, 1936-1945. The positive anomaly was significant since 1980 s. Power spectrum of modeled AOIs from Hadley Center Control Integration(HCCI) were compared with the observations, it's found that the inter-annual time scale frequencies were much significant than decadal frequencies. But, there also had the possibility for generating weak decadal fluctuations in some special months and years by the mechanism of Hasselmann.