简介：利用1971—2015年云南省124个气象台站雨季开始日期、美国NCEP/NCAR再分析资料和CPC热带太平洋海温指数等数据,运用数理统计方法分析了云南雨季开始期的时空变化特征及其与前期热带太平洋海温的关系。结果表明：（1）云南雨季主要从东、南、西3个方向呈半包围态势向西北腹地推进,具有明显的季风交汇区特征;（2）前期热带太平洋海温对云南雨季开始期的第一空间分布模态（全区一致型）影响显著,即除了雨季开始最早的滇西北、滇西、滇东北和滇东南等少数边缘地区,云南大部分区域的雨季开始期与热带太平洋海温存在显著的正相关关系,其中与前期3—4月Ni1o3.4指数相关性最好;（3）云南雨季开始期对前期3—4月Ni1o3.4指数的响应具有非对称性,对暖事件的响应大于对冷事件的响应;（4）前期热带太平洋海温主要通过影响低纬Walker环流和季风系统进而影响云南雨季的开始。

简介：ThisstudycomparestheimpactsofinterannualArcticseaicelossandENSOeventsonwinterhazedaysinmainlandChinathroughobservationalanalysesandAGCMsensitivityexperiments.Theresultssuggestthat(1)Arcticseaicelossfavorsanincreaseinhazedaysincentral–easternChina;(2)theimpactofENSOisoverallcontainedwithinsouthernChina,withincreased(reduced)hazedaysduringLaNi?a(ElNi?o)winters;and(3)theimpactsfromseaicelossandENSOarelinearlyadditive.Mechanistically,Arcticseaicelosscausesquasi-barotropicpositiveheightanomaliesovertheregionfromnorthernEuropetotheUralMountains(Uralsinbrief)andweakandnegativeheightanomaliesovertheregionfromcentralAsiatonortheasternAsia.TheformerfavorsintensifiedfrequencyoftheblockingovertheregionsfromnorthernEuropetotheUrals,whereasthelatterfavorsanevenairpressuredistributionoverSiberia,Mongolia,andEastAsia.Thislarge-scalecirculationpatternfavorsmorefrequentoccurrenceofcalmandsteadyweatherinnorthernChinaand,asaconsequence,increasedoccurrenceofhazedays.Incomparison,LaNi?a(ElNi?o)exertsitsinfluencealongatropicalpathwaybyinducingacyclonic(anticyclonic)lower-troposphericatmosphericcirculationresponseoverthesubtropicalnorthwesternPacific.Thenortheasterly(southwesterly)anomalyatthenorthwesternrearofthecyclone(anticyclone)causesreduced(intensified)rainfalloversoutheasternChina,whichfavorsincreased(reduced)occurrenceofhazedaysthroughtherain-washingeffect.