H. Aoki et al., INTERANNUAL VARIABILITY OF THE TROPOSPHERIC CIRCULATION AND ITS RELATION TO THE STRATOSPHERE IN THE SOUTHERN-HEMISPHERE, Journal of the Meteorological Society of Japan, 74(4), 1996, pp. 509-523
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.