INTERANNUAL VARIABILITY OF THE TROPOSPHERIC CIRCULATION AND ITS RELATION TO THE STRATOSPHERE IN THE SOUTHERN-HEMISPHERE

The interannual variability of the seasonal evolution of the zonal mea n wind and wave activity in the southern hemisphere troposphere is inv estigated, using a global analysis data-set for 1979-1993 provided by the National Meteorological Center (NMC), to understand the dynamical coupling between the troposphere and the stratosphere. The interannual variance of the zonal mean wind at 300 hPa calculated for each calend ar day has maxima at 60 degrees S and 40 degrees S almost all year rou nd. W;Ve found that a zonal wind index defined by the difference of th e zonal wind speed between 60 degrees S and 40 degrees S is a sensitiv e indicator of two typical latitudinal profiles of the zonal mean wind in the southern hemisphere troposphere: the single-jet and the double -jet profiles. The seasonal evolution of zonal wind indices is separat ed into two groups, i.e., DS (double-single) years and SD (single-doub le) years. DS years are characterized by a double-jet structure in ear ly winter and a single-jet in late winter, while in SD years the zonal mean wind has a single-jet structure in early winter and changes its profile into a double-jet in late winter. The appearance of DS and SD years is similar to that of the two categories of the westerly jet pro file in the southern hemisphere upper stratosphere in Shiotani et al. (1993). Wave activity is diagnosed by the Eliassen-Palm (E-P) flux. Cl ear differences are seen in May-June between DS and SD years in the ho rizontal component of E-P flux. Variation of the horizontal component precedes change in the zonal mean wind, indicating its importance in t ransitions between the single- and double-jet. The zonal wind structur e has influence on planetary wave 1 activity. The vertical component o f wave 1 E-P flux is small (large) at 60 degrees S and 500 hPa when th e zonal wind has a double-jet (single-jet) structure during winter. Th e weak flux at 500 hPa in the years with a double-jet structure yields weak wave 1 activity in April-June but gives strong wave 1 activity t hrough more efficient propagation in August-November at 100 hPa relati ve to the years with a single-jet structure.