Interannual And Interdecadal Variation Characteristics And Related Dynamic Mechanisms Of Winter Precipitation In The Three-River Headwaters Region

This study investigates the interannual and interdecadal variations of monthly precipitation over the Three River Source(TRS)region in China based on precipitation observations collected at stations in the TRS region from 1980/1981 to 2014/2015,gridded CN05.1 data from 1961/1962 to 2016/2017 and reanalysis datasets.(1)The interannual variations of TRS monthly precipitation are different in different months of winter over the period of 1980/1981–2014/2015.In winter,the precipitation over the TRS region showed significant interdecadal variability for the period of 1961–2016.The precipitation was less than normal from 1960 s to mid-1980 s,and more than normal from the late 1980 s to the early 21 st century.The TRS winter precipitation experienced a significant interdecadal increase after the mid-1980 s.(2)The interannual variability of TRS precipitation in November is modulated by an anomalous westerly water vapor transport(WVT)branch.This anomalous WVT branch is related to a North Atlantic-Europe-Tibetan Plateau wave-train that originates in the North Atlantic due to the ocean-atmosphere interaction.In December,a circum-global teleconnection(CGT)wave-train can induce anomalous westerly WVT in the TRS region,resulting in increased precipitation there.This CGT wave-train is triggered by warm SST anomalies in the central-eastern tropical Pacific associated with the El Ni(?)o-Southern Oscillation.The interannual variability of TRS precipitation in January and February is affected by southwesterly WVT anomalies over the TRS region,which are associated with a southeastward propagating wave-train over Eurasia caused by the North Atlantic Oscillation(NAO).In March,the interannual variability of TRS precipitation is modulated by the leading mode of the Eurasian circulation that resembles the Scandinavian(SCAND)pattern,which can cause anomalous southwesterly WVT in the TRS region.In winter,the characteristics of sea surface temperature(SST)anomalies and atmospheric circulations associated with interannual variations of monthly precipitation over the TRS region are different for individual winter months.(3)The interdecadal increase of winter precipitation occurred in the TRS region during1961–2016,which is associated with the water vapor convergence and the development of convective activities.The anomalous low over the Ural Mountains and the anomalous high extending from Lake Baikal to Northeast China are affected by the circum-global zonal wavetrain associated with the NAO.The anomalous low and high may induce enhanced and southward movement of the temperate jet stream,which caused the upper-level divergence and development of convection over the TRS region.The anomalous easterly wind over the TRS region is mainly affected by an anomalous high extending from Lake Baikal to Northeast China,which induces water vapor convergence and increased water vapor over the TRS region.The decadal variation of NAO may be associated with North Atlantic warm SST anomalies.In addition,the decrease of Arctic sea ice may induce the interdecadal increase of winter precipitation over the TRS region by affecting the temperate jet stream.