摘要
本文利用1979～2018年NCEP逐日再分析资料,探讨了夏季欧亚中高纬地区10～30天大气季节内振荡(ISO)的时空演变及其对欧洲阻塞频率的影响,并探讨了两者对欧亚极端高温发生频率的协同作用.研究表明,欧亚中高纬10～30天大气ISO表现出东传和西传两种模态.东(西)传模态下,对流层西北—东南向倾斜的四极型(东西向分布的偶极型)准正压位势高度异常耦合温度异常同时向东南方向(向西)传播.位相合成表明,在两个模态下,中高纬低频Rossby波列在传播过程中能够显著影响欧洲阻塞的发生.东(西)传模态位相6～7(5～6)期间,欧洲阻塞发生最频繁.在东(西)传模态位相6～7(5～6)期间,欧洲西部、东欧平原、乌拉尔山以及我国东北平原(欧洲和乌拉尔山)地区分别受准正压的+-+-(+-)高度异常控制.有阻塞发生时,东传模态下,欧洲西部的正高度异常强度明显增强,乌拉尔山地区,东欧平原以及我国东北平原地区的高度异常强度均有所减弱.同时,欧洲以南出现负的高度异常;西传模态下,偶极型高度异常强度均增强,欧洲以南和我国东北平原分别出现负的和正的高度异常.可见,在两个模态阻塞频发位相下,阻塞的发生增加了欧洲和我国东北地区极端高温事件的发生频率,降低了欧洲以南和乌拉尔山地区极端高温事件的发生频率.因此,欧洲阻塞活动显著调控了欧亚中高纬地区大气ISO两个传播模态对极端高温事件的影响.
Abstract
Using the NCEP reanalysis daily data during 1979-2018,the spatiotemporal evolution of the 10-30-day atmospheric intraseasonal oscillations(ISOs)over the mid-high latitudes of Eurasia and their effects on the European blocking frequency are examined.Furthermore,the co-effect of the blocking and ISOs on extreme hot event frequency is studied.The ISO shows two modes,namely,the eastward and westward propagating modes.During the eastward(westward)propagating mode,the northwest-southeast tilted quadrupole(east-west dipole)quasi-barotropic geopotential height anomaly,together with the air temperature anomaly at the troposphere,propagates southeastward(westward).Phase composite reveals that,during both modes,the mid-high latitude low-frequency Rossby wave trains substantially influence the European blocking frequency during the propagating journey.The most frequent European blocking emerges in phases 6-7(5-6)during the eastward(westward)mode,which is referred to as E-P67(W-P56).During E-P67(W-P56),western Europe,the eastern European plain,the Ural Mountains,and the northeast plain of China(Europe and the Ural Mountains)are controlled by quasi-barotropic+-+-(+-)height anomalies,respectively,thereby resulting in considerable positive frequency anomalies of extreme hot events over western Europe and the Ural Mountains(Europe)and negative anomalies over the eastern European plain and the northeast plain of China(Ural Mountains).If blocking occurs during E-P67,the positive height anomaly intensity over western Europe increases substantially,and the positive or negative ones over the Ural Mountains,eastern European plain,and northeast plain of China weaken;meanwhile,a negative height anomaly emerges in the south of Europe,causing a negative extreme hot frequency anomaly.During W-P56,the positive and negative height anomalies are increased,and they materialize over the northeastern plains of China and south of Europe,decreasing and increasing the hot events in the two regions,respectively.Therefore,during E-P67 and W-P56,the European blocking increases(decreases)the frequency of extreme hot events in Europe and the northeast plains of China(south of Europe and the Ural Mountains).Thus,European blocking activities considerably control the influences of the two propagating ISO modes on the extreme hot events over the mid-high latitudes of Eurasia.
基金项目
国家重点研发计划(2023YFF0805404)
国家自然科学基金(42305043)
江苏省自然科学基金(BK20210660)
新疆维吾尔自治区自然科学基金青年基金(2023D01B06)
维普
万方数据