不同强度El Ni?o的衰减过程.Ⅱ,中等和较弱El Ni?o的衰减过程

在第二部分,我们研究了中等和较弱El Ni?o的衰减过程. 结果表明,对中等El Ni?o而言,在其发展阶段和盛期,负异常信号在西太平洋产生,但由于强度不足,在El Ni?o盛期之后迅速衰减,这是一种夭折的类西太平洋振子过程. 因此,与强El Ni?o不同,中等El Ni?o衰减进入平常态. 而较弱El Ni?o以截然不同的另一种方式进行位相转换,伴随东南太平洋副高的加强和西移,东风异常和海表温度负异常自赤道东太平洋向西扩展,这是一种平流模态过程,导致较弱El Ni?o衰减进入La Nia.     

不同强度El Ni(n)o的衰减过程.Ⅱ,中等和较弱El Ni(n)o的衰减过程

在第二部分,我们研究了中等和较弱El Ni(n)o的衰减过程. 结果表明,对中等El Ni(n)o而言,在其发展阶段和盛期,负异常信号在西太平洋产生,但由于强度不足,在El Ni(n)o盛期之后迅速衰减,这是一种夭折的类西太平洋振子过程. 因此,与强El Ni(n)o不同,中等El Ni(n)o衰减进入平常态. 而较弱El Ni(n)o以截然不同的另一种方式进行位相转换,伴随东南太平洋副高的加强和西移,东风异常和海表温度负异常自赤道东太平洋向西扩展,这是一种平流模态过程,导致较弱El Ni(n)o衰减进入La Ni(n)a.     

不同强度El Ni(n)o的衰减过程.Ⅰ,强El Ni(n)o的衰减过程

将1951～2004年期间的12次El Nino事件分为强、中等、较弱和弱4类,结果发现,强和较弱El Nino衰减进入La Nina,但是中等和弱El Nino衰减进入平常态.因此,El Nino的衰减结果与自身强度之间存在密切的非线性关系.进一步的研究表明,负异常信号自西太平洋向中东太平洋的东传主导了强El Nino事件向La Nina的转变过程,其具体动力过程类似于西太平洋振子理论.热带西北太平洋（WNP）大气异常反气旋在强El Nino位相转变中起核心作用,它的维持和缓慢东移是赤道东风异常维持和发展的原因,而后者通过激发Kelvin波导致了ENSO从El Nino向La Nina的转变.     

1997/1998 El Ni(n)o期间中国南部闪电活动的异常特征

基于近8年卫星观测的全球闪电资料,对中国东南部和中南半岛各季节闪电密度距平场进行EOF分析发现,在这一El Nino事件期间,与NINO3区海表温度正距平升高的同时,1997年春季该地区的闪电活动就出现了显著的正异常,并一直持续到次年春季结束,各季度的正异常区闪电密度距平百分率依次是89%,30%,45%,498%和55%,其中冬季变化幅度最大;正异常区在冬、春季位于中国南部及其沿海地区,而在夏、秋季位于中南半岛南部及泰国湾.与正常年份相比,各季闪电密度正距平中心位置显著偏西,特别是冬、春季同时偏北.另外,中国南部地区的闪电密度和对流性降水量及高CAPE日数三项距平百分比的年际变化分析表明,正异常区和黑潮主干区这三项的距平百分比之间两两相关;在三项中,闪电密度的相对变化率最大,闪电活动对ElNino事件的响应最灵敏.但是,黑潮主干海域、青藏高原和西北、华北-东北等地区的闪电活动对El Nino事件的响应情况更为复杂和多样化.     

1997/1998 El Niño期间中国南部闪电活动的异常特征

基于近8年卫星观测的全球闪电资料, 对中国东南部和中南半岛各季节闪电密度距平场进行EOF分析发现, 在这一El Niño事件期间, 与NINO3区海表温度正距平升高的同时, 1997年春季该地区的闪电活动就出现了显著的正异常, 并一直持续到次年春季结束, 各季度的正异常区闪电密度距平百分率依次是89%, 30%, 45%, 498%和55%, 其中冬季变化幅度最大; 正异常区在冬、春季位于中国南部及其沿海地区, 而在夏、秋季位于中南半岛南部及泰国湾. 与正常年份相比, 各季闪电密度正距平中心位置显著偏西, 特别是冬、春季同时偏北. 另外, 中国南部地区的闪电密度和对流性降水量及高CAPE日数三项距平百分比的年际变化分析表明, 正异常区和黑潮主干区这三项的距平百分比之间两两相关; 在三项中, 闪电密度的相对变化率最大, 闪电活动对El Niño事件的响应最灵敏. 但是, 黑潮主干海域、青藏高原和西北、华北-东北等地区的闪电活动对El Niño事件的响应情况更为复杂和多样化.     

中国华北雾霾天气与超强El Ni?o事件的相关性研究

2015年11—12月,全国接连发生七次大范围、持续性雾霾天气过程,其中,11月27日—12月1日的雾霾天气过程持续时间长达五天,成为2015年最强的一次重污染天气过程;12月19-25日重度雾霾再次发展,影响面积一度达到35.2万km~2.本文利用多种数据资料通过个例对比和历史统计详细分析了超强El Ni?o背景下雾霾天气频发的天气气候条件.其结果清楚表明:2015年11—12月欧亚中高纬度以纬向环流为主,东亚冬季风偏弱,使得影响我国的冷空气活动偏少,我国中东部大部地区对流层低层盛行异常偏南风,大气相对湿度明显偏大,并且大气层结稳定,对流层底层存在明显逆温.上述大气环流条件使得污染物的水平和垂直扩散条件差,因此在有一定污染排放的情况下,造成了重度雾霾天气过程的频发.由此,超强El Ni?o事件所导致的大尺度大气环流异常是我国中东部,尤其华北地区冬季雾霾天气频发的重要原因之一.     

Conceptual model about the interaction between El Nio/Southern Oscillation and Quasi-Biennial Oscillation in far west equatorial Pacific

In the tropical Pacific region, El Ni?o/Southern Os- (COADS SST from 1945 to 1993) in the eastern cillation (ENSO) and the Quasi-Biennial Oscillation in (150°W-90°W, 5°S-5°N) and the observed SST far west equatorial Pacific (QBOWP) are two most and zonal wind in the far western equatorial Pacific prominent interannual variation phenomena. The for- (120°-140°E, 0°-10°N) (Fig.1), in the eastern Pa- mer is characterized by coupled SST-wind variability cific the period of S…     

Using CMIP5 model outputs to investigate the initial errors that cause the “spring predictability barrier” for El Nio events

Most ocean-atmosphere coupled models have difficulty in predicting the El Nio-Southern Oscillation(ENSO) when starting from the boreal spring season. However, the cause of this spring predictability barrier(SPB) phenomenon remains elusive. We investigated the spatial characteristics of optimal initial errors that cause a significant SPB for El Nio events by using the monthly mean data of the pre-industrial(PI) control runs from several models in CMIP5 experiments. The results indicated that the SPB-related optimal initial errors often present an SST pattern with positive errors in the central-eastern equatorial Pacific, and a subsurface temperature pattern with positive errors in the upper layers of the eastern equatorial Pacific, and negative errors in the lower layers of the western equatorial Pacific. The SPB-related optimal initial errors exhibit a typical La Ni-a-like evolving mode, ultimately causing a large but negative prediction error of the Nio-3.4 SST anomalies for El Nio events. The negative prediction errors were found to originate from the lower layers of the western equatorial Pacific and then grow to be large in the eastern equatorial Pacific. It is therefore reasonable to suggest that the El Nio predictions may be most sensitive to the initial errors of temperature in the subsurface layers of the western equatorial Pacific and the Nio-3.4 region, thus possibly representing sensitive areas for adaptive observation. That is, if additional observations were to be preferentially deployed in these two regions, it might be possible to avoid large prediction errors for El Nio and generate a better forecast than one based on additional observations targeted elsewhere. Moreover, we also confirmed that the SPB-related optimal initial errors bear a strong resemblance to the optimal precursory disturbance for El Nio and La Nia events. This indicated that improvement of the observation network by additional observations in the identified sensitive areas would also be helpful in detecting the signals provided by the precursory disturbance, which may greatly improve the ENSO prediction skill.     

The critical role of Indian summer monsoon on the remote forcing between Indian and Northwest Pacific during El Nio decaying year

Recent studies have found a connection between Indian Ocean Basin Warming and the anomalous Northwest Pacific Anticyclone(ANPWA) during El Ni?o decaying year.This study focuses on the necessary condition for this connection by using observation and numerical simulation.The seasonal transition of the Indian Ocean sea surface wind is critical to the climatic effect of Indian Ocean Basin Warming.When the South Asian Summer Monsoon reaches its peak,the background wind becomes desirable for basin warming,which then affects the climate in the Northwest Pacific.Via the Kelvin waves and Ekman divergence,the wind anomalies exist in the lower atmosphere east of the Indian Ocean warm Sea Surface Temperature(SST) anomalies,and intensify and sustain the ANWPA throughout the El Nio decaying summer.This impact plays an important role in the inter-annual variability of the East Asian Summer Monsoon.