春季中国西南降水与青藏高原及周边非绝热加热之间的关系

基于气象观测资料和再分析资料,从西南地区降水年际变化规律入手,运用统计学方法从时空角度分析了与其相伴随的环流型和非绝热加热的关联。结果表明,当西南地区降水偏多时,东西向异常气旋、反气旋分别位于我国长江以南地区上空以及青藏高原西南侧上空对流层中、高层,西南地区对流层高层被异常偏北风控制,低层被异常偏南风控制,中层伴有较强的异常垂直上升运动,且与异常非绝热加热源区基本重合,而青藏高原西南侧上空对流层中层为异常的垂直下沉运动,且与异常非绝热加热汇区基本重合;反之亦然。在此基础上进一步运用气候动力学方法揭示了导致西南降水异常的可能物理过程:高原西南侧爬升流的异常垂直运动通过影响南支气流向下游的水汽输送异常,进而导致西南地区非绝热加热异常,最终实现对西南地区降水的调制作用。

西南地区夏季降水变化与南亚高压的关系

为进一步研究西南地区夏季降水变化与南亚高压的关系,利用1961~2022年6~8月西南地区76个气象观测站的逐日气象观测降水量资料、同期NCEP/NCAR的月平均再分析资料(包括高度场、风场、地面气压场、相对湿度场、比湿场),网格距2.5˚ × 2.5˚,通过合成分析、EOF分解、SVD奇异值分解、南亚高压特征量等方法,详细探讨了西南地区夏季降水变化特征与南亚高压的关系其主要结论如下:(1) 西南地区1961~2022年夏季降水呈负趋势,每10年夏季平均降水量减少4.377 mm,降水量空间分布不均匀,大致为自西北向东南呈增加趋势。(2) 根据EOF分析,前三个模态累计方差贡献率达到了51.6%,能够较好地反映出夏季降水的空间分布类型。第一模态表明西南地区整个地区全年都呈现出多雨(少雨)的趋势。第二模态呈现出正距平区和负距平区交错分布的情况。第三模态呈现出夏季降水从北向南呈“正–负–正”分布类型的情况。(3) 1961~2022年南亚高压特征量不仅存在明显的年际变化,而且也存在明显的年代际变化,除脊线位置外。从1961~2022年,南亚高压的强度在逐渐增强,面积在逐渐增大,东脊点位置逐渐偏西,西脊点位置逐渐偏东,脊线位置逐渐偏南。(4) 从1961~2022年夏季南亚高压各特征参数与西南地区同期降水的点相关分布中可以看出,南亚高压脊线位置、面积指数、强度指数与西南地区同期降水关系最密切。从西南地区夏季降水与同期南亚高压的SVD分解表明:第一模态空间分布型反映了南亚高压偏弱(强)年与西南地区偏旱(涝)年对应关系一般。第二模态空间分布型反映了南亚高压偏弱(强)年与西南地区偏旱(涝)年对应关系较好。

西南地区夏季降水变化与青藏高原大气热源的关系

为进一步研究青藏高原大气热源对西南地区夏季降水的影响,用NCEP/NCAR1961~2022年的月平均再分析资料,网格距2.5˚ × 2.5˚、采用点相关分析、SVD分解、合成分析法及热源计算倒算法对西南地区62年夏季降水的时空分布特征及其与青藏高原大气热源的关系进行了详细研究,结果表明:1) 62年来,整个西南地区的夏季降水有减小的趋势,且西南地区的夏季降水存在三个高值区,高值区分别位于云南的南部地区、四川东部地区和贵州东南部地区,并且在降水高值区附近降水量的梯度也更大。降水量自东向西,自南向北逐渐减少,可以明显看出海拔较高的地区降水量较少。这与西南季风、复杂的地形地貌以及影响西南地区的环流系统等因素有关。2) 在青藏高原在1961~2022年均为大气热源,可以看出大气热源在1961年开始时较弱,随着时间逐渐增强,在70年代中期和80年代末期分别达到强度的最大值,之后大气热源逐渐减弱呈下降趋势,在2020年达到最低值。总体来看,从1961到2022年,青藏高原的大气热源强度呈现由强到弱的变化趋势,且存在一定的年际变化特征。3) 青藏高原地区(26˚00'~39˚47'N,73˚19'~104˚47'E),除东北部的少部分地区为较强冷源外和北部地区为较弱冷源之外,其余大部分地区全年平均均为大气热源,中部地区为较强的大气热源。4) 在青藏高原范围内,与西南地区夏季降水存在显著正相关的地区是高原东部地区的大气热源和高原西部地区大气热源,与西南地区夏季降水存在显著负相关的地区是高原北部地区。总体来说西南地区夏季降水与青藏高原大气热源存在显著的相关性且西南地区夏季降水与青藏高原大气热源具有较高的年际线性相关性。5) 青藏高原大气热源的异常增加会影响西南地区夏季降水的不均变化,部分地区夏季降水量异常增多且存在大值区,部分地区夏季降水量异常减少且存在大值区;而青藏高原大气热源的异常减小时,西南地区夏季降水的增加较均匀。

西南地区夏季降水变化与太平洋海温的关系

为研究西南地区夏季降水变化与太平洋海温的关系,利用中国气象局提供的西南地区76站1961~2022年共62年逐日气象降水观测数据与哈德莱中心网格距为1˚ × 1˚的海温资料、美国国家环境预报中心(NCEP)和国家大气研究中心(NCAR)的网格距为2.5˚ × 2.5˚再分析资料,通过相关分析、合成分析、经验正交函数分解(EOF)、奇异值分解(SVD)等方法,对西南地区夏季降水与太平洋海温的关系进行了详细研究。得到以下结论:(1) 西南地区近60年的夏季降水量呈下降的趋势,降水的空间分布不均,自南向北减少。同时,降水与海温的相关系数表明,西南地区6~8月降水与赤道西太平洋海温关键区(125˚E~175˚W, 15˚S~20˚N)呈显著的正相关,即关键区海温异常偏暖(冷),西南地区夏季降水偏多(少)。(2) EOF及合成分析表明,关键区海温异常偏高时,西南地区的降水偏多且主要集中于四川东部、重庆及贵州地区;而在海温异常偏低的年份时,降水明显偏少。(3) SVD分析表明,关键区前期冬季、春季及当期夏季海温与西南地区夏季降水量均存在显著的正相关关系,即关键区海温异常偏暖(冷),西南地区夏季降水偏多(少),与相关系数分析及合成分析的结果一致。

中国西南夏季降水预测的统计降尺度建模分析

利用BP-CCA方法并结合当前国际先进气候预测模式结果,探讨了如何建立对西南夏季降水具有较高预测技巧的统计降尺度模型及其可预报性来源。结果表明,将热带区域海表温度作为预测因子的降尺度模型的预测能力优于亚洲区域和热带区域500 h Pa位势高度作为预测因子的模型。对模型可预报性来源的分析表明,热带区域海表温度作为预测因子的降尺度模型的预测能力年与年之间的差异主要受热带海表温度EOF第二模态的影响。该模态表现为在热带东南印度洋及西太平洋区域有正载荷值,而在热带中东太平洋区域有负载荷中心,其与影响西南夏季降水的菲律宾和海洋大陆西部对流有较好的相关,并且ECMWF和NCEP业务气候预测模式对其有较好的预测能力。

青藏高原冬春季积雪异常与西南地区夏季降水的关系

选取1961-2007年青藏高原冬、春季积雪日数资料和西南地区夏季降水资料,对高原积雪和降水作奇异值分解(SVD)分析.结果表明:冬春季高原积雪对西南地区夏季旱涝有重要的影响.冬、春季高原积雪的不同分布将造成后期西南地区夏季降水分布出现差异.西南地区夏季降水对冬季高原积雪异常最敏感的区域主要是四川东北部、重庆、西藏中西部,对春季积雪异常最敏感的区域主要位于四川东部、重庆、贵州东北部,以及西藏中东部.与降水敏感区相对应的冬季高原积雪分布的关键区是西藏中西部和青海中南部至四川西北部地区,春季则转变为西藏西部和青海部分地区.总的来说,冬季高原积雪的异常变化比春季对西南地区夏季降水的影响更为明显.因此,前期青藏高原积雪是西南地区夏季降水预测中的一个重要信号,对夏季西南地区降水有一定的指示和预测意义;冬季高原积雪日数尤其具有预报指示意义,可作为一个重要的预测指标.

冬季北大西洋涛动与中国西南地区降水的不对称关系

利用1951—2010年NCEP/NCAR再分析资料和中国160个站逐月降水资料,探讨了冬季北大西洋涛动(NAO)与同期中国西南地区降水的关系。结果表明,冬季北大西洋涛动与西南地区降水存在显著的正相关关系,并且,正相关具有不对称性,即当冬季北大西洋涛动处于负位相时,东亚地区环流形势不利于中国西南地区降水的形成,对应着中国西南地区冬季降水的显著减少。而当冬季北大西洋涛动处于正位相时,北大西洋涛动与中国西南地区降水的正相关关系并不显著。进一步的分析表明,与中国西南冬季降水变化密切相关的主要环流结构是里海和中东—阿拉伯海—青藏高原及其下游的遥相关型(CAT遥相关型)。北大西洋涛动与里海和中东—阿拉伯海—青藏高原及其下游的遥相关结构存在不对称关系,两者的关系仅在北大西洋涛动负位相时显著。冬季北大西洋涛动高、低指数年分别合成的波射线和波作用通量的结果表明,当冬季北大西洋涛动为负位相时,冬季地中海地区的扰动源会形成与里海和中东—阿拉伯海—青藏高原及其下游的遥相关路径一致的波射线,同时波作用通量的结果表明,定常波由里海和中东、阿拉伯海一直传播到青藏高原及下游地区,而冬季北大西洋涛动高指数年,地中海地区的扰动源所形成的波射线偏北,波动传播到达印度半岛地区之后不再向下游传播。冬季北大西洋涛动对里海和中东—阿拉伯海—青藏高原及其下游的遥相关波列的不对称影响决定了北大西洋涛动与西南冬季降水的不对称关系。

近几十年青藏高原热源影响西南地区夏季降水的研究进展

本文对近几十年关于青藏高原热源、西南地区降水变化以及二者之间的影响研究进行了回顾。结果表明:1)青藏高原热源的变化存在明显的区域性、季节性和时间阶段性。不同来源和时间长度的资料,对热源计算结果有一定影响,但对于夏季热源的结论都比较一致。2)西南川渝地区的降水,在川西高原、云南中部以北高海拔地区年总降水量呈明显增加趋势,而在四川盆地、贵州东部丘陵地区年降水量呈减少趋势。降水的减少和增加存在明显的时空分布特征,区域性和季节性变化明显。3)青藏高原热源与西南地区降水之间有明显的关联。但对于不同热源区对于西南地区降水的影响研究较少。

ENSO事件的季节演变对西南夏季降水异常的影响分析

采用西南120站逐月夏季降水,美国CPC年逐月Nino3.4指数,NCEP/NCAR逐月环流等资料,分析了ENSO事件的季节演变对西南夏季降水的影响及其机制。结果表明,ENSO事件衰减对西南降水有重要影响,这种影响主要由赤道中东太平洋海温影响菲律宾对流活动进而持续调制西太平洋副热带高压(简称西太副高)实现,与ENSO事件的结束季节有重要关联。在El Nino(La Nina)衰减年,随着事件结束时间从冬季向春、夏季推迟,赤道中东太平洋海温释放能量增大(减弱),西太副高向大强西南(小弱东北)的方向发展,加强(抑制)南海的水汽输送,影响着孟加拉湾水汽输送,从而影响西南降水异常分布,其显著区域随着事件结束季节的推迟而扩大,在El Nino衰减次年更为突出。依据能量累积释放效应,从前一年9月开始的逐月Nino3.4区累积海温能更好指示夏季西太副高的强弱和大小,当4-5月的累积海温超过±0.5时,与夏季副高面积、强度指数的符号一致率为100%。因此,能够依据累积海温判断夏季西太副高强弱、大小,从而判断西南夏季降水的异常趋势。

西南夏季降水多因子降维客观预测方法研究

本文改进了现有的多模态时间稳定性判别标准,提出一种筛选稳定高相关预测信号的思路,对1981~2016年西南夏季降水距平百分率多模态的时间稳定性、时空特征和可预测模态关键信号等进行了分析研究,在此基础上构建了多因子降维预测模型。结果表明,前9个模态在预测时效为3年和近10年内稳定,累计方差贡献率占70%,是西南夏季降水的主要模态。结合稳定高相关概念和最优子集回归方法得到主模态PC(Principal Component)系数的最优预测信号和预测方程。回报检验结果表明,各方程对PC系数有较好的拟合效果,复相关系数为0.62~0.84,均通过了99.99%的显著性检验,同号率均大于69%。构建的多因子降维预测模型对西南夏季降水的空间分布,正负趋势和异常级有较好的回报效果:距平相关系数(Anomaly Correlation Coefficient,简称ACC)平均值为0.58;时间相关系数(Temporal Correlation Coefficient,简称TCC)在除零星站点外的整个区域通过90%的显著性检验,且大部分区域通过99.9%的显著性检验;趋势异常综合评分(PS)平均分为84,其中区域降水最异常的十年,PS平均分为87.1。经过13年(1971~1980年和2017~2019年)的预报检验,该模型的PS平均分为72。其中2017~2019年的PS均分为77,优于发布预测评分。

初夏西北太平洋副高东西变动对中国南部降水东西差异的影响

西北太平洋副热带高压(以下简称副高)是影响中国气候的大尺度环流系统,为了进一步了解副高对中国气候的影响,本文利用站点观测资料和大气环流再分析资料,通过资料诊断分析和数值模拟方法,探讨了6月副高东西变动对中国南部降水的影响,以及影响副高东西变动的前期海洋因子.结果表明副高东西变动对中国西南和华南地区降水的影响明显不同:副高偏东有利于降水西南偏多而华南偏少,偏西则降水变化刚好相反.其原因与副高东西变化引起的环流差异有关,华南降水与副高东(西)变动时西太平洋地区副高西北侧的东北(西南)风异常以及东亚中低纬度地区异常经向波列的变化直接有关,而西南降水异常不仅与副高东西变动在东南亚地区引起的纬向风异常有关,与青藏高原大地形动力作用对副高北侧异常纬向风的变化也有十分密切的联系.此外,副高东西变动时影响西南和华南地区的水汽来源不同,影响西南的水汽主要来源于赤道印度洋80°E附近越赤道气流,而影响华南的水汽主要来源于副高南侧偏东气流从西北太平洋地区输送的水汽.进一步分析发现前期冬春季热带西北太平洋和赤道西太平洋海温变化的偶极差异与后期初夏副高东西变动有密切联系,冬春季西北太平洋暖海温和赤道西太平洋冷海温变化有利于后期初夏副高偏西,相反则有利于副高偏东,数值模拟结果在一定程度证实了资料诊断分析结果.

2022年春季我国气候异常特征及成因分析

利用气象台站观测资料、NCEP/NCAR大气再分析资料和NOAA的海温资料,采用相关、合成分析等方法分析和讨论了2022年春季我国的气候主要特征和成因诊断。2022年春季,我国季风雨带进程总体呈现偏早的特点。全国平均气温为12.1℃,为1961年以来历史同期最高值。全国平均降水量为154 mm,接近常年同期,但旱涝分布差异显著,其中西南地区降水量为1961年以来历史同期最高值。通过对同期的环流分析发现,对流层中高层形成的自乌拉尔山以北经青藏高原至中南半岛“―+―”的西北—东南向异常环流形势,使得低层风场上低纬异常偏东气流及南下的异常东北—偏北气流在西南地区辐合,有利于水汽向西南地区的输送和冷暖空气在西南地区的交汇,从而导致2022年春季西南地区降水的异常偏多。此外,自2021年秋季开始并一直持续发展的中东太平洋拉尼娜事件是西南地区春季降水异常偏多的重要外强迫因子,而拉尼娜事件结束的早晚会对春季西南地区降水异常产生不同的影响。2022年春季持续发展的拉尼娜事件使得上述异常环流型更为典型,更有利于西南地区的降水偏多。

The increasing predominance of extreme precipitation in Southwest China since the late 1970s

Extreme precipitation events cause severe environmental and societal damage worldwide.Southwest China(SWC)is sensitive to such effects because of its overpopulation,underdevelopment,and fragile ecosystems.Using daily observations from 108 rain-gauge stations,the authors investigated the frequency of extreme precipitation events and their contribution to total precipitation in SWC since the late 1970 s.Results indicate that total precipitation is decreasing insignificantly,but rainfall-events frequency is decreasing significantly,whereas the region is experiencing more frequent and intense extreme precipitation events.Note that although fewer stations are statistically significant,about 60%of the rain-gauge stations show an increasing trend in the frequency and intensity of extreme precipitation.Furthermore,there is an increasing trend in the contribution of total extreme precipitation to total precipitation,with extreme precipitation becoming dominant in the increasingly arid SWC region.The results carry important implications for policymakers,who should place greater emphasis on extreme precipitation and associated floods and landslides when drafting water-resource management policies.

Regional differences in rainfall frequency and amount over southwestern China

In this paper,the rainfall features in southwestern China are studied using daily rainfall station data.The rainfall features are distinct along the eastern and western edges of the Hengduan Mountains and over the mountains,especially in terms of rainfall frequency.The rainfall amounts and frequencies are much higher along the eastern and western edges than over the mountains,particularly during spring,which is partly contributed by the number and duration of rainfall events.The differences are more obvious in the nocturnal rainfall than in the daytime rainfall.The rainfall differences over the three regions could be affected by the large-scale environment.By analyzing reanalysis data,the large-scale circulations linked to the different rainfall features over southwestern China,and the interactions of these circulations with the topography are also discussed.

Evaluation of the WRF Model with Different Land Surface Schemes: A Drought Event Simulation in Southwest China during 2009–10

The authors examined the performance of version 3.4.1 of the Weather Research and Forecasting Model(WRF) with various land surface schemes in simulating a severe drought event in Southwest China. Five numerical experiments were completed using the Noah land surface scheme, the Pleim-Xiu land surface scheme, the Noah-MP land surface schemes, the Noah- MP scheme with dynamic vegetation, and the Noah-MP scheme with dynamic vegetation and groundwater processes. In general, all the simulations reasonably reproduced the spatial and temporal variations in precipitation, but significant bias was also found, especially for the spatial pattern of simulated precipitation. The WRF simulations with the Noah-MP series land surface schemes performed slightly better than the WRF simulation with the Noah and Pleim-Xiu land surface schemes in reproducing the severe drought events in Southwest China. The leaf area index(LAI) simulated by the different land surface schemes showed significant deviations in Southwest China. The Pleim-Xiu scheme overestimated the value of LAI by a factor of two. The Noah-MP scheme with dynamical vegetation overestimated the magnitude of the annual cycle of the LAI, although the annual mean LAI was close to observations. The simulated LAI showed a long-term lower value from autumn 2009 to spring 2010 relative to normal years. This indicates that the LAI is a potential indictor to monitor drought events.

Characteristic Analysis of One Heavy Precipitation Synoptic Process in the South-west of Shandong Province

[Objective] This paper aimed to explore the formulation mechanism of one heavy precipitation synoptic process in the south-west of Shandong Province from June 16th to June 17th in 2010. [Method] Based on information of circulation forms and physical quantity field, data of radar echo evolution and numerical prediction test, a heavy precipitation synoptic process in southwest Shandong during June 16th to June 17th in 2010 was analyzed to explore the formation mechanism of this synoptic process. [Result] The results showed that under the condition of relatively large circulation radial degree in eastern China, high-altitude cold vortex in Mongolia split, moved towards the south and impacted southwest air current at the edge of subtropical high from the west side. Cold vortex and shear line at the edge of subtropical high were the major impact system for the formulation of heavy precipitation synoptic process. The transportation of the southwest jest stream to the warm moist airflow provided water vapor conditions for the heavy precipitation, the high and low level jet stream and low level shear line provided strong dynamic lifting for this precipitation. [Conclusion] This study provided reference for heavy precipitation forecast.

Strengthened influence of the East Asian trough on spring extreme precipitation variability over eastern Southwest China after the late 1980s

The relationship between variations in the East Asian trough(EAT)intensity and spring extreme precipitation over Southwest China(SWC)during 1961-2020 is investigated.The results indicate that there is an interdecadal increase in the relationship between the EAT and spring extreme precipitation over eastern SWC around the late1980 s.During the latter period,the weak(strong)EAT corresponds to a strong and large-scale anomalous anticyclone(cyclone)over the East Asia-Northwest Pacific region.The EAT-related anomalous southerlies(northerlies)dominate eastern SWC,leading to significant upward(downward)motion and moisture convergence(divergence)over the region,providing favorable(unfavorable)dynamic and moisture conditions for extreme precipitation over eastern SWC.In contrast,during the former period,the EAT-related circulation anomalies are weak and cover a relatively smaller region,which cannot significantly affect the moisture and dynamic conditions over eastern SWC;therefore,the response in extreme precipitation over eastern SWC to EAT is weak over the period.The interdecadal change in the relationship between eastern SWC spring extreme precipitation and the EAT could be related to the interdecadal change in the EAT variability.The large(small)variability of the EAT is associated with significant(insignificant)changes in spring extreme precipitation over eastern SWC during the latter(former)period.

Temperature and Precipitation Variations at Two Meteorological Stations on Eastern Slope of Gongga Mountain,SW China in the Past Two Decades

Gongga Mountain, locates on the eastern edge of Tibetan Plateau of China, is the highest mountain in China except summits in Tibet. Only limited meteorological data on Gongga Mountain have been published so far. Here we present the meteorological records from two stations, Moxi Station （at 1,621.7 m above sea level （a.s.1.）, 1992- 2010） and Hailuogou Station （at 2,947.8 m a.s.l., 1988-2010）, on the eastern slope of Gongga Mountain. In the past two decades, the annual precipitation decreased while the annual mean temperature increased at Hailuogou Station. Both precipitation and temperature increased at Moxi Station. The precipitation variation on the eastern slope of Gongga Mountain is influenced by both East Asian Monsoon and Indian Monsoon, so that the precipitation concentrated between May and October. The temperature variation on the eastern slope of Gongga Mountain in the past two decades showed similar trends as that of the northern hemispheric and global. In the past two decades, the temperature increased o.35℃ and o.3℃/decade at Hailuogou Station and Moxi Station respectively, which was higher than the increase extents of northern hemispheric and global temperature. The most intense warming occurred at the first decade of 21St century. The winter temperature increased more at Hailuogou Station than at Moxi Station. A remarkable increase of temperature in March was observed with only a little precipitation at both high and low altitude stations.

Modeling of the Second Indirect Effect of Anthropogenic Aerosols in East Asia

This study investigated the second indirect climatic effect of anthropogenic aerosols,including sulfate,organic carbon(OC) ,and black carbon(BC) ,over East Asia.The seasonal variation of the climatic response to the second indirect effect was also characterized.The simulation period for this study was 2006.Due to a decrease in autoconversion rate from cloud water to rain as a result of aerosols,the cloud liquid water path(LWP) ,and radiative flux(RF) at the top of the atmosphere(TOA) changed dramatically,increasing by 14.3 g m-2 and decreasing by-4.1 W m-2 in terms of domain and annual average.Both LWP and RF changed most in autumn. There were strong decreases in ground temperature in Southwest China,the middle reaches of the Yangtze River in spring and autumn,while maximum cooling of up to-1.5 K occurred in the Chongqing district.The regional and annual mean change in ground temperature reached-0.2 K over eastern China.In all seasons except summer,precipitation generally decreased in most areas north of the Yangtze River,whereas precipitation changed little in South China.Precipitation changed most in summer,with alternating bands of increasing(～40 mm) and decreasing(～40 mm) precipitation appearing in eastern China.Precipitation decreased by 1.5-40 mm over large areas of Northeast China and the Huabei Plain.The domain and annual mean change in precipitation was approximately-0.3 mm over eastern China.The maximum reduction in precipitation occurred in summer,with mean absolute and relative changes of-1.2 mm and-3.8%over eastern China.This study revealed considerable climate responses to the second indirect effect of aerosols over specific regions of China.

Weakening of Winter North Atlantic Oscillation Signal in Spring Precipitation over Southern China

In this study,the relationship between the North Atlantic Oscillation （NAO） in winter （DecemberFebruary） and the precipitation over southem China （SCP） in the following spring （March-May） was investigated.Results showed an interdecadal change,from strong to weak connection,in their connection.Before the early 1980s,they were highly correlated,with a strong （weak） winter NAO followed by an increased （decreased） spring SCP.However,after the early 1980s,their relationship was weakened significantly.This unstable relationship may be linked to the climatological change of East Asian jet.Before the early 1980s,the wave train along the Asian jet propagated the NAO signal eastward to East Asia and affected local upper-tropospheric atmospheric circulation.A strong NAO in winter led to an anomalous anticyclonic circulation at the south side of 30°N in East Asia in spring,resulting in an increase of SCP.In contrast,after the early 1980s,the wave train pattern along the Asian jet extended eastward due to strengthening of the climatological East Asian jet.Correspondingly,the NAO-related East Asian atmospheric circulations in the upper troposphere shifted eastward,thereby weakening the linkage between the spring SCP and the winter NAO.