THE SOUTHERN HEMISPHERE MID-LATITUDE QUASI-40-DAY PERIODIC OSCILLATION WITH ITS EFFECT ON THE NORTHERN HEMISPHERE SUMMER MONSOON CIRCULATION

By using the method of power spectrum combined with band-pass filtering with May-September 1982 grid data from ECMWF,the spatial structure and propagation characteristics are tentatively examined of the SH (Southern Hemisphere) mid-latitude quasi-40-day (ranging from 30-60 days) periodic oscillation (QPO) together with the relation to NH (Northern Hemisphere) summer monsoon,with the result that there exists similar periodicity in the development of baroclinicity and activities of cold air at the same latitudes,and in response to this the zonal wind shows profound QPO with a nearly vertical axis of disturbance and that the air activities can act as periodic external forcing for the monsoon,which intensifies the west wind on the south side of the Mascarene or Australian high,and then the system itself,leading to the reinforcement of the SE trade wind on the north side,followed by the strengthening of cross-equatorial flow that,in turn,causes active monsoon with its northward march over the eastern part of China.The process is responsible for the low-frequency oscillation propagated in a meridional direction,which confirms the speculation of the author.