Characteristics Of SST Anomalies In The Maritime Continental Region In The Northern Hemisphere In Summer And Their Relationship With Climate Anomalies In The Asian-Australian Regio

The sea surface temperature anomalies（SSTA）in the Maritime Continent（MC）region are mainly related to the climate anomaly in Asia-Australia region.This paper mainly uses the daily and monthly averaged data of NCEP/NCAR,CMAP,GODAS,OISST,etc.of the National Oceanic and Atmospheric Administration（NOAA）and the precipitation grid data of China in CN05.1 to systematically study the characteristics of sea surface temperature anomalies in the boreal summer（June–August）in the Maritime Continent（MC）region,their changes after filtering ENSO and IOD signals in turn,and the occurrence characteristics and causes of Marine Heatwave（MHW）events in this region.The influence of SSTA on climate anomaly in Asia-Australia region is analyzed.The results show that the different change modes of sea surface temperature in MC region have different effects on the precipitation in Asia-Australia region through air-sea interaction.The main conclusions are as follows:（1）The SSTA in the MC region in the boreal summer is closely related to the summer climate anomaly in East Asia.Singular value decomposition（SVD）and other methods are used to study the characteristics of the first two modes of the sea surface temperature anomaly（SSTA）in the MC region in summer and the sea level pressure anomaly（SLPA）in East Asia,and their effects on the climate anomaly.The results show that the SSTA in the MC region of SVD1 is a warm SSTA in the whole region.At this time,the SLPA in East Asia is a positive anomaly in the whole region.The SSTA in the MC region in SVD2 is east-west reverse,warm anomaly in the east,cold anomaly in the west,and the SLPA in East Asia is south-north reverse,positive anomaly in the north,and negative anomaly in the south.The formation of the SSTA of the two modes is jointly determined by ocean dynamics and heat flux changes.The mode of SLPA in East Asia is shown as an abnormal anticyclone in the northwest Pacific Ocean in SVD1,and a circulation anomaly similar to PJ/EAP in the western Pacific Ocean in SVD2.Under the influence of different circulation configurations,when PC1is in a positive phase,the precipitation in the middle and lower reaches of the Yangtze River in China and in the south of the Yunnan Guizhou Plateau is positive,while the precipitation in central and northeast China is negative.When PC2 is in a positive phase,the precipitation in most areas in the middle and lower reaches of the Yangtze River,Hetao area and southwest China is positive,while that in Huaibei region and northeast China is negative.（2）The sea surface temperature anomalies（SSTA）in the Maritime Continent（MC）region are mainly related to local variability,ENSO,and Indian Ocean dipole.Using the reanalysis from NOAA and NCEP/NCAR,by employing the Empirical Orthogonal Function（EOF）analysis,we have explored the principal mode of ENSO-independent SSTA in the MC in summer and its associations with regional climate anomalies.After ENSO signals have been removed,the leading mode of SSTA in the MC is a unipolar warm SSTA distribution,which mainly varies on interannual timescale.The maintenance mechanisms of the ENSO-independent SSTA are different in different sub-regions,especially over south of Java and the tropical northwestern Pacific.When the time-coefficient of the first leading EOF mode（EOF1）is in positive,warmer SSTA are observed in area south of Java.The oceanic dynamic heating there facilitates the warmer SSTA.Thus,the Gill-type response of the atmosphere is found over the region south of Java,inducing the upward motion as a result.The diabatic cooling in the atmosphere is dominant over the tropical northwestern Pacific,where the warmer SSTA is maintained by the absorption of solar radiation due to less cloud there.A tilted vertical circulation is hence formed,linking the tropical southeastern Indian Ocean with the tropical northwestern Pacific.The anomalous circulations in Asian-Australian monsoon region are affected by this ENSO-independent SSTA mode,resulting in decreased summer rainfall anomaly in the region near the southeast coast of China and increased winter precipitation anomaly over the extra-tropical region of Australia.（3）On the basis of filtering the ENSO signal and further filtering the IOD signal,the leading mode of the SSTA in the MC region in summer is still the unipolar warm SSTA distribution.When PC1 is in the positive phase,the large value area of the warm SSTA is located in the sea area west of New Guinea Island,and it is mainly the annual variation component,with a period of about 11 years.The MC regional average SST anomaly index is defined I_FEI,which is highly correlated with EOF1 mode.When the time coefficient of I_FEI is in positive phase,the dominant factors that maintain the warm SSTA in various regions of MC region are different.The northeast sea area of MC is mainly affected by short wave radiation anomaly of the ocean subsurface layer,while the Bay of Bengal and the sea area west of the New Guinea Island is mainly affected by the short wave and long wave radiation anomalies.The SSTA further affected the circulation anomaly.The abnormal diabatic heating of the atmosphere near Java Island and the abnormal diabatic cooling of the equatorial region east of New Guinea Island forced the atmosphere to produce an easterly anomaly near the equator,and formed a significant abnormal anticyclone circulation in the northwest Pacific.Affected by the circulation anomaly field,the precipitation in the southwest of MC region increased,the precipitation in the northwest Pacific region decreased,especially near the Philippines.The precipitation in southern China increased significantly.（4）The occurrence of Marine heatwave（MHW）in MC region is mainly affected by the abnormal warming of summer mean sea temperature.This includes not only the influence of local SST warming trend caused by global warming,but also the influence of interannual SST mode caused by air-sea interaction.The amplitude of the duration days of the MHW in the MC region is increasing with global warming.The main mode of the total day anomaly of MHW not only has a long-term trend of change,but also has significant interannual characteristics.After filtering out the interdecadal signals,when PC1 is in positive phase,the total number of days of MHW in the north of the equator in MC region increases abnormally,and the maximum value area is located in the South China Sea area and the western Pacific area north of New Guinea Island.The anomaly of ocean current in the sea area near Java Island promotes the gathering of warm water here,which is conducive to the rise of sea temperature in the region,and thus to the occurrence of a single long-lasting MHW in the region.In the Northwest Pacific Ocean,the ocean is warmed by receiving more heat flux,which is conducive to the continuous occurrence of MHW.Under this mode,the precipitation decrease in the northeastern part of the MC region,and increase in the southwestern part.The precipitation in southeast China,North China Plain and Korean Peninsula also increased.These results are conducive to deepening the understanding of the characteristics of the SSTA in the MC region and its relationship with the climate anomaly in Asia and Australia,and provide some clues for further research on the climate anomaly in Asia and Australia.