The Influence Of The Western Pacific Warm Pool SST On The Synergistic Changes Of Dry And Wet In Eurasia Since The Little Ice Age

Research based on instrumental records found that the Western Pacific Warm Pool(WP),as the region with the highest global sea surface temperature(SST),has an important influence on the wet and dry synergistic changes in Eurasia.However,the Little Ice Age(LIA,1250-1850)serves as the background of the current warm period(CWP),the synergistic changes in dry and wet conditions in Eurasia and its response to WP warming remain unclear.The effects of WPSST on precipitation in Eurasia during the instrumental period were studied using sea temperature,precipitation,and 1625tree-ring width records from Eurasia.The dipole pattern of precipitation in Eurasia is discussed as coexisting in precipitation and tree ring chronology.At the same time,the re-analysis data were used to analyze the spatial-temporal characteristics of atmospheric circulation affecting precipitation dipoles.Finally,the tree-ring chronology was used to reconstruct the precipitation dipoles since the LIA,and the reconstruction data were used to find various possible factors affecting the dipole changes.The results show:(1)Annual precipitation in Southern Europe and Mongolia was negatively correlated with WPSST(p <0.1);annual precipitation in Central Asia and Northern Europe was positively correlated with WPSST(p <0.1).A pair of precipitation dipoles regulated by WPSST exist in Europe and Asia.In Asia is the Central Asia / Mongolia(CAMO)dipole.This dipole is characterized by a positive correlation between precipitation in Central Asia and WPSST,and a negative correlation between precipitation in Mongolia and WPSST.In Europe,it is a Nordic / Southern European(NESE)dipole.This dipole is characterized by a positive correlation between WPSST and precipitation in Northern Europe,and a negative correlation with precipitation in Southern Europe.When WPSST rises,precipitation increases in Central Asia and Northern Europe,and decreases in Mongolia and Southern Europe.When an El Ni(?)o-Southern Oscillation(ENSO)positive(negative)phase event occurs,it is usually accompanied by a decrease(increase)in WPSST,The magnitudes of precipitation change in Central Asia,Mongolia,Northern Europe and Southern Europe have all increased.The more obvious the WPSST change,the stronger the CAMO and NESE dipoles are.(2)From the perspective of the 500 h Pa geopotential height field and wind field,the North Atlantic Oscillation(NAO)and Pacific Interdecadal Oscillation(PDO)events are interannual signals that WPSST affects precipitation changes in Eurasia.When the WPSST is abnormal,the atmospheric circulation changes in summer,autumn,and winter in Europe are obvious.When WPSST is high,the northern European sea level air pressure is weak,and there is an abnormally convergent rising area of cyclonic wind field at 700 h Pa.South European sea level air pressure is strong,700 h Pa has anticyclonic wind field abnormally divergent sinking area.In Central Asia,there are obvious differences in atmospheric circulation in spring,summer,and autumn.When WPSST is high,the northeast airflow from the western Pacific and the southwest airflow from the Indian Ocean Intersection in Southeast Asia,and met cold air from high latitudes in Central Asia.In Mongolia,there is a positive pressure swing and anticyclone anomalous circulation.In the context of ENSO,these circulation differences are enhanced to varying degrees.From the perspective of water vapor transport,when the WPSST is warm,the 850 h Pa zonal water vapor flux anomaly is negative in the Pacific Ocean and the Indian Ocean is positive;in Mongolia,the 850 h Pa meridional water vapor flux anomaly is negative.Abundant water vapor is concentrated in Central Asia,and Mongolia's water vapor conditions are poor.In Europe,there is a 850 h Pa zonal water vapor flux anomaly centered at(50 ° N,0 ° E).The 850 h Pa meridional water vapor flux anomaly is positive in Northern Europe and negative in Southern Europe,and its range and intensity increase when the ENSO event occurs,making the humidity transport in Southern Europe weaker,and the humidity transport in Northern Europe stronger.(3)Among the CAMO dipoles from 1280 to 1990 reconstructed from the tree-ring chronology,the CAMO dipoles are only significant on the interdecadal scale.Significant periods include the early 14 th century,early 15 th century,mid 17 th century,18 th century,and since the 20 th century.Since the LIA,the intensity of the CAMO dipole has increased with increasing solar radiation and northern temperature,and has weakened with increasing PDO.However,in the 20 th century,the positive correlation between the intensity of CAMO and solar radiation weakened.(4)Among the 1801-1990 NESE dipoles reconstructed from the tree-ring chronology,the NESE dipoles are more significant on the interdecadal scale.Significant periods occurred between the 1830 s and 1950 s and since the 20 th century.When the solar radiation increases,the temperature of the northern hemisphere increases,and NAO increases,the intensity of the NESE dipole increases.