基于NCEP/NCAR月平均再分析资料， 利用EOF分解方法揭示出1960 -2019年7 -8月亚洲大陆上空西风急流变化的两类主要模态， 并利用合成方法研究了两类模态与东亚大气环流异常的联系及其气候效应。研究结果表明， 夏季亚洲大陆上空西风急流变化的第一模态为纬向风以急流轴为界南北的反位相变化， 主要表现为急流整体的南北移动； 第二模态为纬向风以青藏高原为界在东西方向上的反相变化， 主要表现为急流轴的西南（西北）-东北（东南）向倾斜， 该结论不同于以往大多数研究将第二模态定义为急流的强度变化。通过对大气环流异常的分析发现， 急流的南北移动对应南亚高压同步的南北移动以及西太平洋副热带高压范围的变化， 急流向南移动时， 南亚高压脊线偏南， 同时西太平洋副热带高压向南扩张， 急流向北移动时则相反， 该模态主要影响亚洲地区40°N以南的降水异常以及贝加尔湖一带、 东亚和南亚的温度异常。第二模态即纬向风以青藏高原为界的反相变化主要伴随着南亚高压强度的东西振荡， 急流轴呈西南（西北）-东北（东南）向倾斜时， 南亚高压东侧（西侧）位势高度增强， 该模态与西亚高纬度地区、 中亚以及印度半岛的降水异常有关。此外， 第二模态具有一定的特殊性， 可影响整个欧亚大陆的气温， 并呈现双偶极子型的异常分布。

Based on NCEP/NCAR reanalysis data， the leading modes of the westerly jet over the Asian continent during July-August from 1960 to 2019 and the associated mid-to-high latitude circulations has been investigated in this study.The results show that the first leading mode is characterized by an out-of-phase variation in the south-north direction along the jet axis， resulting in a north-south movement of the jet.The second leading mode exhibits an out-of-phase variation in the east-west direction along the Qinghai-Xizang （Tibetan） Plateau， as a southwest （northwest） - northeast （southeast） tilt of the jet stream axis， which is different from most previous studies emphasizing the intensity variations in the second mode.For the first leading mode， associated with the northward movement of the jet streams， the South Asian High （SAH） moves northward as well as the western Pacific subtropical high （WPSH） northward narrows and vice versa.Furthermore， this first leading mode is associated with the tripolar precipitation pattern over East Asia.Particularly， as the jet stream shifts northward （southward）， the precipitation decreases （increases） in the Jianghuai River and increases （decreases） in South China and North China.As well， the associated temperature variations also show a tripolar pattern over the Eurasian continent， with the boundary of around 20°N and 45°N.It suggests that when the jet stream moves northward， warm （cold） conditions cover East Asia， particularly in the central and eastern regions of China， the Korean Peninsula and Japan， while cold （warm） conditions dominant Lake Baikal， the Indian Peninsula and Indochina Peninsula.As for the second leading mode， the geopotential height in the east （west） side of the SAH increases due to the southwest （northwest）-northeast （southeast） tilt of the jet axis.Additionally， the second mode is related to the precipitation anomalies in the high latitudes of West Asia， Central Asia， and the Indian Peninsula.This mode is particularly important for the double dipole temperature pattern over the Eurasian continent.When the jet stream axis presents a southwest （northwest）-northeast （southeast） tilt， significant positive （negative） temperature anomalies are observed in the middle latitudes of East Asia and specifically in the high latitudes of West Asia.