Quasi-stationary planetary waves in the southern hemisphere troposphere

By using the NCEP/NCAR Reanalysis dataset for 17 years (1979-1995), the structure and behaviour of quasi-stationary planetary waves (QSPWs) in the Southern Hemisphere winter were studied in relation to the tropospheric zonal wind variations shown by Aoki et al. (1996). An empirical orthogonal function (EOF) analysis was made of 300 hPa height fields to detect the fluctuation of horizontal QSPW structure. The composite analysis based on the EOF analysis indicated that the QSPWs change their amplitude in the eastern hemisphere and phase in the western hemisphere between the single-jet and double-jet profiles. The wave activity flux diagnosis suggests poleward propagation from the subtropics during the period of single-jet and the equatorward propagation from polar latitudes during the double-jet period. It is shown that the horizontal EP flux divergence by total waves, especially due to high-frequency disturbances, prays an essential role in the maintenance of the difference between the two jet profiles. As regards the total (horizontal and vertical) divergences, the contribution of the QSPWs to forcing of the zonal-mean zonal wind anomalies is important in higher latitudes around 60 degrees S.