摘要
利用近50年月平均的SODA海洋同化资料和NCEP大气再分析资料,研究了热带太平洋次表层海温异常(SOTA)年代际变率主要分布型以及与之相关的亚洲-北太平洋-北美地区上空异常大气环流场,并揭示了类ENSO模态与中国气候异常之间的联系。得到主要结果:(1)热带太平洋SOTA年代际变率有两种类ENSO模态。第一模为类ENSO事件成熟期热带太平洋年代际SOTA状态;第二模为类ENSO过渡期热带太平洋年代际SOTA状态。二者组合构成类ENSO事件40年左右及其背景下13年左右的周期振荡。(2)类ENSO事件对亚洲-北太平洋-北美上空中高纬和副热带大气系统年代际变化具有重要影响。类El Ni o成熟期间冬季,中高纬地区大气环流经向型发展,贝加尔湖高压脊加强,西太平洋副高偏强、位置偏西,蒙古高原为较强的异常反气旋环流。类El Ni o衰退期(类La Ni a发展期)夏季,贝加尔湖低压槽加深,乌拉尔山高压脊加强,西太平洋副高偏弱,新疆-河套地区为较强的异常反气旋环流距平。类La Ni a事件时相反。(3)热带太平洋类ENSO事件通过影响中高纬和副热带大气系统,造成中国北部地区上空南风距平的年代际变化,进而导致东亚季风和中国气候异常。类El Ni o事件成熟期,中国北部地区上空多异常偏北风,东亚季风弱,华北少雨,长江中、下游多雨;类El Ni o衰退(类La Ni a发展)期,中国北部地区上空亦为异常偏北气流,东亚季风较弱,华北少雨。中国气候异常型主要取决于类ENSO第一模态,而第二模态主要视位相异同来加强或减弱第一模态。两个类ENSO模态的共同作用导致1978年前后中国气候跃变和华北地区持续20余年的干旱。近期类ENSO模的振荡从1998年左右开始转为类La Ni a模态,大致在2018年左右结束。在此期间,华北降水有望增加,长江中、下游降水可能减少。
In the present study,we investigate the decadal variability of the tropical Pacific subsurface ocean temperature anomaly(SOTA) and associated anomalous atmospheric circulation over Asia-North Pacific-North America,through analyzing 50 years of atmosphere-ocean data from the U.S.National Center for Environmental Prediction(NCEP) reanalysis project and Simple Ocean Data Assimilation(SODA).Relationship between ENSO-like modes and climate of China is also revealed.Main results are as follows: (1) Decadal variability of tropical Pacific SOTA has two dominant ENSO-like modes.The primary mode is El Ni?o-like or La Ni?a-like mature phase pattern,and the second mode is associated with the El Ni?o-like/La Ni?a-like developing(La Ni?a-like/El Ni?o-like decaying) phase.These two modes form the cycle of ENSO-like events,which has a background fluctuation of about 40 year's period,superimposed with an oscillation of 13-year's period.(2) The ENSO-like event has significant influence on the decadal variations of Asian-North Pacific-North American and subtropical atmospheric circulation.During the mature phase of El Ni?o-like events,usually in winter,the atmospheric circulation with meridonal pattern in the mid-high latitude develops,a ridge of high pressure over Lake Baikal and a ridge of North American high intensifies,the west Pacific subtropical high strengthens and extends westward,and a strong anomalous anticyclone exists over the Mongolian plateau.When the El Ni?o-like event decays(La Ni?a-like develops),usually in summer,the troughs over the Lake Baikal grow deep,while the west Pacific subtropical high weakens,and an anomalous anticyclone controls the Xinjiang-Hetao region.The case during the La Ni?a-like event is generally opposite.(3) The ENSO-like events in the tropical Pacific Ocean influence the atmosphere system of the mid-high latitude and subtropical regions,resulting in decadal variability of south wind over the northern China,and hence the East Asian monsoon and climate of China.During the mature phase of El Ni?o-like events,the anomalous north wind prevails over the north part of China,the East Asian monsoon weakens,with little rain in the northern China and wet in the middle-lower reaches of the Yangtze River.When the El Ni?o-Like decaying(La Ni?a-like developing),the anomalous north wind also prevails over the north of China,the East Asian monsoon weakens,with drought in the northern China.The result during the La Ni?a-like events is the opposite.The pattern of anomalous climate of China is mainly controlled by the first ENSO-like mode,while the second mode can increase or decrease the contribution of the first one,depending on whether its phase is the same with that of the first mode.The climate shift in China around 1978 and successive occurrence of drought for more than 20 years in north China are primary induced by the influence of the first two ENSO-like modes.The lastest La Ni?a-like phase started from 1998,and will presumably end around 2018,which more rainfall is expected in the northern China and less rainfall in the middle-lower reaches of the Yangtze river.
出处
《热带气象学报》
CSCD
北大核心
2011年第6期785-796,共12页
Journal of Tropical Meteorology
基金
中国科学院知识创新工程重要方向项目(KZCX2-YW-Q11-02)
国家重点基础研究发展计划项目(2012CB417401)
国家自然科学重点基金(40890152)共同资助