Intraseasonal oscillation features of the South China Sea summer monsoon and its response to abnormal Madden and Julian Oscillation in the tropical Indian Ocean

By applying the OLR and wind data,rainfall data and the Madden and Julian Oscillation(MJO)index,the paper deals with intraseasonal oscillation features and inter-annual differences of the South China Sea(SCS)summer monsoon,distribution of its LF circulation and convection fields and rainfall,and path of summer monsoon ISO spreading,as well as impact of tropical Indo-MJO on SCS summer monsoon ISO during 1979-2008.It is found that(1)there are three intraseasonal oscillations of the SCS summer monsoon Intraseasonal Oscillation(ISO)in summer(from May to August)in the climate normal.The SCS summer monsoon ISO goes through six phases(exclusive of weak phase)at every complete fluctuation:developing,the strongest,weakening,restraining,the weakest,and recovering.Due to tropical LC convection spreading to the east and north, the LR convection and circulation fields in the 1st-3rd and 4th-6th phases present the anti-phase in the Arabian Sea-West Pacific latitudinal band.Its corresponding rain bands in the 1st-3rd and 4th-6th phases also present anti-phase roughly.The rain band,mainly in tropical regions in the south of 20°N,moves eastward with LR convection shifting eastward,while the rain band moves northward with LR convection shifting northward in East Asia(EA)subtropical regions in the north of 20°N.(2) The SCS summer monsoon ISO presents significant inter-annual variations in intensity.There are three stronger monsoon in- traseasonal oscillations in summer in the strong SCS monsoon ISO year.The first two oscillations from the tropical Indian Ocean ISO spread northward to the Bay of Bengal first,and then to the South China Sea(SCS)along the 10°-20°N latitudinal band.They are strengthened there and stimulate the ISO moving to the north to form the tropical Indo-ISO.Finally they spread to South China(SC)by relay way in the longitude-latitude direction.Moreover,in the weaker SCS summer monsoon ISO,the oscillation weakens greatly and irregularly in intensity with the weaker ISO spreading in the longitude-latitude direction.In average conditions,the tropical Indian ISO spreads to the SCS by about 20 days(one half ISO periods).(3)MJO1(the first modal of MJO index provided by the CPC)averaged value in the 1st-2nd pentads of April has the negative correlation with the SCS monsoon ISO intensity.The tropical Indo-MJO is slightly stronger in the subsequent May to August when it is more active in the 1st-2nd pentads of April,and the ISO also spreads strongly to the SCS,so that the SCS summer monsoon ISO strengthens.Conversely,the SCS summer monsoon ISO weakens.The abnormal MJO in the 1st-2nd pentads of April contributes to a certain theory basis for us to predict the subsequent SCS summer monsoon ISO intensity and analyze the related regions'abnormal rainfall.