Possible Impact Mechanism Of The Interdecadal Variation Of Indian Ocean Sea Surface Temperature On The East Asian Summer Monsoon Precipitatio

The interdecadal variation of sea surface temperature(SST)will have a huge impact on climate change.As one of the three oceans,people have little understanding of the interdecadal change of SST in the Indian Ocean and its impact on climate.Based on multiple sets of reanalysis data and observation data,the paper systematically analyzes and studies the interdecadal variability of the Indian Ocean SST and the East Asian summer monsoon precipitation.First,it starts from the analysis of the climatological characteristics of the East Asian summer monsoon precipitation,and then analyzes the interdecadal variability characteristics of the Indian Ocean SST,and then studies the relevant impact factors and physical mechanisms.And the main conclusions are as follows.(1)There is a significant interdecadal variation of SST in the Indian Ocean,with the largest variability occurring in the boreal summer.The interdecadal variation of the SST in the Indian Ocean is mainly characterized by monopole with the same anomalous signs in basin-scale.The region with the largest interdecadal variation is located in the extratropical southern Indian Ocean.(2)The East Asian summer monsoon has a complex spatial and temporal pattern,which is mainly composed of warm and humid air currents originating from the tropical Indian Ocean and the tropical Pacific Ocean.Observations indicate that East Asian summer precipitation exhibits significant interdecadal variability,with an alternating reverse phase distribution of rainbands from south to north,implying that a rainy band is usually near a dry land.It is shown in the alternation of dipole,tripole and multipole,and the East Asian summer monsoon mainly affects the spatial pattern of meridional tripole precipitation on the interdecadal timescale.(3)When the SST in the extratropical southern Indian Ocean anomalous warms,there will be an abnormal upward movement over the Indian Ocean,which is accompanied by the abnormal sinking movement over the equatorial region,especially over the oceanic continental region,the abnormal weakening of the meridional circulation,and the abnormal upward movement over the subtropical region of the northern hemisphere.The water vapor related to the East Asian summer monsoon precipitation mainly comes from the Northwest Pacific and Indochina Peninsula,most of which comes from the Northwest Pacific and mainly concentrates in the central region of East Asia.When the SST rises,the low-level water vapor input over the southern part of East Asia decreases,while the low-level water vapor from the northwest Pacific enters into the central part of East Asia through the Korean Peninsula.The cloud amount field corresponding to the meridional tripole mode of East Asian summer monsoon precipitation mainly shows that there are a large number of continuous low and medium clouds over the central region of East Asia,while in Northeast Asia,especially in the northern region of the Korean Peninsula,low and medium clouds are relatively small;When the SST rises,the amount of low cloud,medium cloud and high cloud over the central region of East Asia increases,while the amount of low cloud,medium cloud and high cloud over the northeast Asia decreases.(4)In the boreal summer,there are five cross-equatorial flows over the Eastern Hemisphere.Among these five flows,the Somali cross-equatorial flow and the New Guinea cross-equatorial flow play an indispensable role in the process about influencing the East Asian summer monsoon precipitation by the variation of SST in the extratropical southern Indian Ocean.When there is anomalous warming in the extratropical southern Indian Ocean,the Somali crossequatorial flow weakens and then alternating positive and negative waves propagate to central East Asia.It will lead to the increase of precipitation in central East Asia.In contrast,the New Guinea cross-equatorial flow experiences interdecadal enhancement with cyclonic circulation anomalies over the Northwest Pacific and anticyclonic circulation anomalies over the Philippines,the coupling strengthens the water vapor transport from the mid-latitude Northwest Pacific to central East Asia.These circulation anomalies favor the development of a meridional tripole pattern,i.e.a “negative – positive – negative” pattern of East Asian summer monsoon precipitation anomalies on the interdecadal timescale,which is specifically manifested in the abnormal increase of precipitation in central East Asia and the decrease of precipitation in northern and southern East Asia.