Joint Effect Of EAP And EU Teleconnections On The Summer Precipitation Pattern In Northeast Aisa

The East Aisa-Pacific(EAP)teleconnection formed by the Rossby source at Northwest Pacific convective activity and the Eurasian(EU)teleconnection that ignites the Rossby source from the North Atlantic Ocean and spreads eastward,both can last for 10-15 days from the development and to the decay of the wather scale,and they also have a very significant climate effect.In the formation of EU teleconnection,the easthigh latitude Rossby source propagating easteard willalso diffuse downstream in the East Asian monsson region,which will affect the formation of EAP teleconnection.Therefore,there is a certain interaction process between EAP teleconnction and EU teleconnection.At the same time,the North Atlantic and Pacific regions serve as the source of these two teleconnection types,and abnormal sea temperature signals will also have a role in teleconnection.Therefore,it is necessary to furtuer study the impact of external forcing on teleconnection type,so as to better understand the summer precipitation in Northeast Asia affected by EU and EAP teleconnections is of great significance to crops and people's production activities.This paper focuses on the impact of EAP teleconnection and EU teleconnection on summer precipitation in Northeast Asia.From the perspective of external forcing and the interaction between the two teleconnections,the effects of EAP and EU teleconnection on summer precipitation in Northeast Asia are explored.Firstly,this paper makes a step-by-step analysis of summer precipitation and circulation in Northeast Asia,and determines that summer precipitation in Northeast Asia will be affected by EAP teleconnection and EU teleconnection.Then the effects of different external forcing(ENSO)and local air-sea interaction(NAO)on EAP teleconnection and EU teleconnection are determined.Then the effects of different phases of EAP and EU teleconnection on summer precipitation in North Asia are pointed out.Finally,the interaction between EAP teleconnection and EU teleconnection is studied from the low frequency scale.The main conclusions of this paper are as follows:(1)Characteristics of summer precipitation and circulation pattern in Northeast AsiaThe traditional summer precipitation is dominanted by the midsummer precipitation.The interannual and interdecadal features and circulation characteristics consistent with the characteristics of midsummer precipitation,and the early summer and midsummer precipitation characteristics and formation mechanism have significant difference.In spatial distribution,the early summer precipitation,midsummer precipitation and traditional summer precipitation all shows the feature of more in the south and less in the north.The first leading mode exhibits a “+-+” meridional tripole pattern in the early summer rainfall,and the first leading mode in the midsummer precipitation and traditional summer precipitation shows the reverse features.In time evolution,the time scale cycle was 5-6a in the early summer and 2-3a in the midsummer,and midsummer precipitation have 2-3a and 5-6a period of oscillation.In the late 1990 s,only the midsummer precipitation and the traditional summer precipitation have undergone significant interdecadal transition in North China and Northeast China.In addition,the anomalous anticyclone over the Western Pacific transport the water vapor to the northern part.And by the Eurasian II teleconnection(EUII)effect caused by early summer precipitation anomalies,which has obvious zonal characteristics.In midsummer,the rainfall is mainly affected by the West Pacific subtropical high extending northward and the strengthen water vapor of the Bay of Bengal and the South China Sea.Eurasia I(EU1)teleconnection pattern and East Asia-Pacific(EAP)teleconnection pattern have significant correlation with the midsummer precipitation in the west of China and the coastal areas.The role of EU teleconnection pattern caused the features of the summer precipitation anomaly center form northwest to southeast.And the EAP teleconnection pattern made the summer precipitation by triode or dipole type to the characteristics.(2)Strengthend relationship between tripole SST over North Atlantic and EU teleconnection patternThe influence of the North Atlantic tripole SST in the spring on the EU teleconnection pattern increased in the early 1990 s,mainly because the North Atlantic tripole SST is more susceptible to the previous winter La Nin?a event before the early 1990 s.The previous winter La Nin?a event responds to the mid-east Pacific sea surface Matsuno-Gill by the atmosphere,forming an anomalous anticyclone in the northeastern Pacific Ocean,which is conducive to the excitation of PNA wave trains,and thus the formation of anomalous anticyclone characteristics in the North Atlantic subtropical region.At the same time,the Walker circulation in the equatorial region strengthened the Hadley circulation in the North Atlantic,which in turn affected the tripole sea temperature of the North Atlantic.After the early 1990 s,NAO made the 850 hPa wind field an anomalous cyclone circulation anomaly and the non-adiabatic heating of the atmosphere is a negative anomaly in the North Atlantic subtropical zone,which weakens the convective activity of the atmosphere,thereby weakening the air-sea interaction and facilitating the warming of the North Atlantic.The southeast wind on the south side of the anomalous anticyclone enhances the climatic anomalous easterly wind and increases the evaporation of the sea surface,which is conducive to the cold sea temperature anomaly in the tropical North Atlantic.The anomalous cyclone in the sub-polar region will increase the amount of cloud over the sub-polar region and reduce the downward radiation,which will make the sea temperature in the sub-polar region a negative anomaly,which will affect the tripole sea temperature of the North Atlantic.At the same time,the interaction between NAO and the North Atlantic SST is strengthened,which weakens the connection between the North Atlantic SST and the previous winter ENSO,which leads to the Rossby source that propagates eastward over the North Atlantic.(3)The influence of winter ENSO on the EAP teleconnection pattern in the summer of the next year is weakendThe effect of the former winter ENSO on the summer EAP teleconnection in the next year was weakened at the end of the 1990 s.In the process of attenuation of the former winter ENSO,due to the memory of the sea temperature itself,the former winter ENSO signal can continue in the Pacific to the spring,while the former winter ENSO can maintain the Indian Ocean sea temperature warmer to the summer by the capacitor charging effect.The tropical Indian Ocean SST continues to warm and accelerates the Kelvin wave to the east.The northwestern Pacific region is a sinking movement accompanied by abnormal divergence,and the abnormal cold sea temperature in the western Pacific region is caused by the "wind-evaporation-SST" effect.At the same time,since the end of the 1990 s,ENSO changed from CP type to EP type,which caused the abnormal warm sea temperature in the central equatorial region to continue,which is not conducive to the maintenance of abnormal cold sea temperature in the western Pacific Ocean.Therefore,the cold sea temperature anomaly in the western Pacific Ocean is not significant,sinking.The westward movement position is not conducive to the maintenance of anomalous anticyclone in the western Pacific.(4)Summer precipitation characteristics in North Asia under different phases of EAP and EU teleconnectionthe configurations of EAP and EU anomalies reflected by EAP and EU indices can be classified into four categories,category I(II)with consistent positive(negative)phases of EAP and EU and category III(IV)with the EAP being a positive(negative)phase and the EU being a negative(positive)phase.Further analyses show that these four categories of EAP and EU anomalies are coherently related to different atmospheric circulations over the mid–latitude region of Eurasian continent,leading to different summer precipitation modes in North Aisa(NA).Category I(II)corresponds to a zonal triple structure of geopotential height at 500-hPa in the region between East Europe and Japan Sea,leading to less(more)precipitation than normal in East Europe,Japan and their surrounding areas,and more(less)precipitation in the region from Central China to Baikal Lake and East Russia.Category III(IV)corresponds to a meridional dipole structure of geopotential height at 500-hPa over NA,leading to more(less)precipitation than normal in the northern part of NA,and less(more)precipitation in most of the southern part of NA.In addition,the EAP teleconnection is positively correlated with the precipitation in the region between the eastern part of the Lake Baikal and the Okhotsk Sea,and is negatively correlated with the precipitation in the region between Northeast China and Japan.Coincidently,the EU teleconnection and precipitation have negative correlations in the Ural and Okhotsk Sea and positive correlations in the Lake Baikal.The respective function of EAP and EU on NA summer precipitation suggests that the northern lobe of EAP overlapped with central and eastern lobes of EU can extend the geopotential anomalies over the Lake Baikal to Far East of Russia,causing the EAP-EU synergistic effect on summer precipitation in NA.(5)The connection between EU and EAP teleconnection on low frequency scale.In this study,by defining the July EU and EAP teleconnection on low frequency scale,and selecting the four years representing the different cases of EU and EAP teleconnection in 2007,1994,1989 and 1993.The results show that the EU "-+-" teleconnection type when it is in the process of development or attenuation,is beneficial to the EAP teleconnection type position shift to the east and north side which is conducive to the propagation of Rossby to the Siberian sky over the North Atlantic.When EU is a "+-+" teleconnection type wave train,it is conducive to the propagation of Rossbepo to the middle and lower reaches,which is not conducive to the formation of positive anomalies in the upper reaches of the Sea of Okhotsk,so that the position of EAP teleconnection is southerly.