Interannual Variations in the Southern Hemisphere Circulation

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Abstract
An analysis has been made of variations in the atmospheric circulation with periods of more than 50 days occurring in the Southern Hemisphere between 1980 and 1986, using analyses produced by the European Centre for Medium Range Weather Forecasts (ECMWF), mainly at the 500 hPa level. A smoothed mean annual cycle was removed from the data to define anomalies which were then filtered to retain variations with periods greater than 50 days. The >50 day period variations account for 20%–30% of the variance of daily 500 hPa geopotential anomalies at midlatitudes, up to 50% over Antarctica and more than 70% in the tropics. The total variance was found to be more uniform at high latitudes over the southern oceans than reported in previous studies, possibly reflecting the more comprehensive dataset used in the ECMWF analyses. The first three empirical orthogonal functions (EOFs) of the geopotential height anomalies amounted for 40% of the low-pass filtered fields. The first is a zonal field with the sign ... Abstract An analysis has been made of variations in the atmospheric circulation with periods of more than 50 days occurring in the Southern Hemisphere between 1980 and 1986, using analyses produced by the European Centre for Medium Range Weather Forecasts (ECMWF), mainly at the 500 hPa level. A smoothed mean annual cycle was removed from the data to define anomalies which were then filtered to retain variations with periods greater than 50 days. The >50 day period variations account for 20%–30% of the variance of daily 500 hPa geopotential anomalies at midlatitudes, up to 50% over Antarctica and more than 70% in the tropics. The total variance was found to be more uniform at high latitudes over the southern oceans than reported in previous studies, possibly reflecting the more comprehensive dataset used in the ECMWF analyses. The first three empirical orthogonal functions (EOFs) of the geopotential height anomalies amounted for 40% of the low-pass filtered fields. The first is a zonal field with the sign ...

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