CROSS-EQUATORIALLY RADIATING STRATOSPHERIC ROSSBY WAVES

Upper Atmosphere Research Satellite observations of constituent distri butions in the middle stratosphere show that extratropical Rossby wave s from the winter hemisphere can, at certain times, radiate across the equator and reach the summer subtropics before they break and are abs orbed. Conditions are most favorable for Rossby waves to radiate into the tropics when the westerlies of the winter hemisphere extend to low latitudes, as usually occurs during November and December in the nort hern hemisphere. Cross-equatorial radiation of quasi-stationary Rossby waves requires westerly equatorial winds, as occurred in the middle s tratosphere in late 1992. Constituent distribution maps show numerous episodes of Rossby-wave radiation across the equator during this early winter period, but not after early January 1993. Wave breaking in bot h the winter and summer subtropics above 22 mb causes constituent exch ange between the tropics and extratropics, including deep tropical in- mixing.