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—September1982 grid data from ECMWF,the spatial structure and propagation characteristics are tentatively examinedof the SH (Southern Hemisphere) mid-latitude quasi-40-day (ranging from 30—60 days) periodic oscilla-tion (QPO) together with the relation to NH (Northern Hemisphere) summer monsoon,with the result thatthere 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 thatthe air activities can act as periodic external forcing for the monsoon,which intensifies the west wind on thesouth side of the Mascarene or Australian high,and then the system itself,leading to the reinforcement of theSE trade wind on the north side,followed by the strengthening of cross-equatorial flow that,in turn,causesactive monsoon with its northward march over the eastern part of China.The process is responsible for thelow-frequency oscillation propagated in a meridional direction,which confirms the speculation of theauthor.