Interannual Variations of the Seasonal March in the Southern Hemisphere Stratosphere for 1979–2002 and Characterization of the Unprecedented Year 2002

Abstract

Dynamical features of the interannual variations of the seasonal march in the Southern Hemisphere stratosphere are investigated with the NCEP?NCAR reanalysis dataset from 1979 to 2002, and the unprecedented year 2002, in which a major stratosphere sudden warming occurred, is characterized by comparing it with the other 23 yr. A multiple empirical orthogonal function analysis of the stratospheric mean zonal wind and a composite analysis based on the principal component of the leading mode show that the interannual variations are characterized by early or late deceleration of the polar-night jet, which is well correlated with the variation of a time-averaged upward Eliassen?Palm (EP) flux in the lower stratosphere. The stronger wave activity in the lower stratosphere is associated with the earlier ?shift down? of the jet. The composite difference of the stratospheric mean zonal wind can be traced down to the lower troposphere in September and October. These features are consistent with the variations of the Southern Hemisphere annular mode, although the main disturbance to maintain the variations is different between the stratosphere and troposphere. Some scatter diagrams show the extreme situation of the year 2002. It is far from the cluster of the other 23 yr, but the large deviation in 2002 is consistent with the tendency of the fluctuations in the other years except for its extreme nature.