Reinvestigations on the East Asian Subtropical Monsoon and Tropical Monsoon

The East Asian monsoon consists of the subtropical monsoon and the tropical monsoon,whose interaction has not been paid attention to.NCEP/NCAR reanalysis dataset and CMAP(Climate Prediction Center Merged Analysis of Precipitation) rain data are used to investigate differences and relationship between the East Asian subtropical monsoon and the tropical monsoon in order to discuss the essence of the subtropical monsoon.Analyses find that the onset of the subtropical monsoon is in middle March,earlier than that of the tropical monsoon.They are independent on each other,the subtropical monsoon is not the northward branch of the tropical monsoon,by contraries,the former onset is propitious to the latter breakout.The subtropical monsoon sets up step by step but retreats rapidly,while the tropical monsoon breaks out suddenly but withdraws slowly.The subtropical/tropical monsoon onset is characterized by southerly/westerly beginning,which lies on zonal/meridional land-sea thermal contrast reverse.Heating source over the Tibetan Plateau and zonal land-sea thermal difference play important roles not only in the subtropical monsoon,but also in the tropical monsoon.