| Maritime Continent is one of the most important energy source areas in the global sea air system,and changes in atmospheric thermal conditions caused by convective anomalies over it can affect global scale weather and climate.This paper compares the differences in thermal convection characteristics before and after the Maritime Continent rain-dry season transition by using monthly precipitation and Outgoing Longwave Radiation(OLR)from 1979-2019,focusing on revealing the seasonal variation of peripheral precipitation anomalies caused by such thermal differences and explaining their physical mechanisms.In addition,the differences in the effects of Maritime Continent thermal convection anomalies on precipitation in the surrounding areas of South China,South China Sea,and Bay of Bengal in the context of with/without ENSO events are also explored,and the main conclusions are as follows:Before the seasonal transition(March-April),the Maritime Continent strong convective zone is distributed in a band with large intensity and wide range,and the center is mainly located in western Indonesia and north of New Guinea Island;after the seasonal transition(May-June),the Maritime Continent convective strong value zone as a whole is lifted northward and westward,with reduced range,weakened intensity and split into multiple centers,mainly located in the Philippine Islands,eastern Indonesia and Jakarta area.When the Maritime Continent thermal convection anomaly is strong,before the seasonal transition,the anomalous clockwise meridional vertical circulation is excited,resulting in a strong and northerly Hadley circulation,and the Bay of Bengal and South China are mainly controlled by the sinking airflow,with significant negative precipitation anomalies;after the seasonal transition,the Maritime Continent thermal convection anomaly is excited north of the equator,resulting in an anomalous clockwise meridional vertical circulation,which causes the Hadley circulation to shift northward but with a strong intensity.Hadley circulation shifts northward but the intensity is weaker than that before the seasonal transition,the convergence of airflow rises in the northern part of the oceanic continent,and precipitation is high,while the south of China is controlled by the sinking airflow,and precipitation is low.Meanwhile,the presence of net atmospheric non-adiabatic forcing anomalies in the east-central and southern parts of the oceanic continent also favors the establishment and maintenance of Maritime Continent anomalous convection.There are significant differences in the effects of Maritime Continent thermal convection anomalies on peripheral precipitation in the context of with/without ENSO events.Taking the strong heating state of the oceanic continents before the seasonal transition as an example,under the background of ENSO event,the SST gradient between the oceanic continents and the equatorial central-east Pacific is large,the anomalous clockwise latitudinal vertical circulation in the equatorial region is strong,and the Walker circulation is enhanced;meanwhile,the anomalous thermal convection-induced anomalous clockwise meridional vertical circulation causes the Hadley circulation to lift northward,and the positions of the ascending and sinking branches change.The precipitation in the eastern part of the oceanic continent is high while that in southern China is low.In the background of no ENSO event,the strength of the anomalous clockwise latitudinal vertical circulation and the anomalous clockwise meridional vertical circulation weakened,resulting in the weakening of the Walker circulation and the change of the strength and position of the Hadley circulation,which resulted in less precipitation in southern China and more precipitation in the northern part of the South China Sea. |
