EFFECT OF PLANETARY AND SYNOPTIC SCALE WAVES IN MAINTAINING MERIDIONAL CIRCULATIONS AT MID AND LOW LATITUDES^*

Following Wu and Chen(1989), in terms of the elliptical differential equation with mean meridional stream function, an equation similar in form to that developed by Kuo(1956) and by use of time average statistics of atmospheric circulation in wavenumber domains at the same intervals of time, a study is made of the contribution of the internal forcing of the atmosphere in two space scales to mean meridional circulation. Results show that planetary waves have considerable influence on the intensity of the upper center of the bi-Hadley cell, and, in contrast, synoptic-scale waves exert vital effect on the Ferrel cell, and that in the Northern Hamisphere(NH) such internal forcings by planetary- and synoptic-scale waves are comparable on mean meridional circulations whereas the latter contribute far more than the former in the Southern Hemisphere(SH).Further, in the northern winter(summer) the contribution of heat(angular momentum) transport of planetary waves allows the descending(ascending) branch to occur as far as around 40°N, some kind of effect that makes quite important contribution to the winter(summer) monsoon circulation in eastern Asia.