ENSO与南海SST关系的年代际变化

基于NOAA重建的海面温度（sea surface temperature, SST）资料和NCEP再分析大气资料,研究了ENSO（El Niño-Southern Oscillation）与南海SST关系的年代际变化。结果表明：ENSO影响南海SST的冬、夏季“双峰”现象发生了显著的年代际变化,即冬季的“峰值”自20世纪80年代显著减弱,而夏季的“峰值”稳定持续且在20世纪70年代之后增强;冬季“峰值”的减弱可能与冬季西北太平洋反气旋的年代际变化有关,夏季“峰值”的维持和增强可能与20世纪70年代之后印度洋SST“电容器”效应的增强有关。     

马斯克林高压的周期变化和突变特征分析

利用1948—2015年的NCEP/NCAR月平均再分析资料,对马斯克林高压的周期变化进行研究,客观定义了马斯克林高压的4个特征参数,分析其周期变化特征、季节变化特征及突变检验。结果表明:马斯克林高压季节变化特征明显,其高压中心位置夏、秋季西进、北抬,春季东退;高压中心强度冬、秋季一致增强,冬季达到最强,春季减弱,夏季达到最弱。马斯克林高压的周期变化特征为多波动性,1975年为面积指数和强度指数突变增长年,1975年前后变化明显;马斯克林高压面积指数和强度指数在1948—1985年的主周期为7 a,1985—2015年的主周期为3～5 a。     

东亚冬季风年际变化的ENSO信息 I. 观测资料分析

利用1950～1989年40年的全球月平均资料,详细讨论了东亚冬季风的年际变化特征,分析结果表明东亚冬季风年际变化中包含有明显的ENSO信号,也就是说东亚冬季风活动与ENSO的发生有明显的关系,大多数El Ni?o事件爆发后东亚冬季风偏弱,而大多数La Ni?a爆发后东亚冬季风偏强。通过对这40年间的10次El Ni?o和7次La Ni?a事件的合成分析,结果表明El Ni?o冬半年东亚500 hPa位势高度为正距平、海平面气压为负距平,即东亚冬季风偏弱,阿留申及北美地区呈现出明显的类似PNA型的异常环流形势;La Ni?a冬半年东亚以至于北半球大气环流异常形势与El Ni?o的相反。同时资料分析也表明,在大多数El Ni?o（La Ni?a）爆发前东亚冬季风偏强（弱）。另外,功率谱分析结果表明,东亚冬季风有显著的3～5年和准2年的变化周期,这从另一方面说明了东亚冬季风的年际异常中包含有显著的ENSO信息。     

广东大尺度大气水汽汇的年际及年代际变化特征

用1958～2004年实测降雨量和NCEP／NCAR再分析资料,分析了广东地区大尺度水汽汇的年际和年代际变化特征及其与水汽通量变化的关系。结果表明,气候平均而言,广东春夏季大气向地面输送较多水资源,秋季地气间相互交换的水分相当,冬季由地面向大气输送较多的水资源。四季和年水汽汇的年际分量方差贡献均占主导地位,秋、冬季水汽汇的年际分量有约3年的显著周期。除了显著的年际分量外,冬、春季和年水汽汇的年代际分量方差贡献也较显著,占总方差的40％以上,以30多年的长周期变化为主,目前正处于由正位相向负位相转变的过渡期,预示今后广东有偏旱趋势。广东冬春季水汽汇的异常有显著的同相关系。另外,夏、秋季水汽汇的年代际分量有10～15年的显著周期。广东各季大气水汽汇偏强（弱）是由于从热带低纬输送到南海北部至华南地区的水汽增强（减弱）,并伴随着水汽通量的辐合的增强（减弱）造成,但各季水汽通量异常分布型是有差别的。     

不同年代际背景下南半球冬季马斯克林高压影响因子的比较

利用NCEP/NCAR与ERA-40再分析资料分析了南半球冬季(JJA)马斯克林高压的年际和年代际变化特征,并重点讨论了不同年代际背景下影响马斯克林高压年际变化因子的变化。结果表明,冬季(JJA)马斯克林高压的强度在1976年前后发生了显著的年代际转折,1976年以前强度偏弱,1976年以后强度明显增强。进一步分析显示,影响马斯克林高压年际变化的因子同样也发生了年代际转折。在1976年以前,冬季马斯克林高压与印度洋局地海温和南极涛动(Ant Arctic Oscillation,AAO)表现出显著的相关性;而在1976年以后,冬季马斯克林高压与ENSO和AAO表现出显著的相关性。同时,印度洋局地海温与马斯克林高压的相关性减弱,而ENSO与马斯克林高压的相关性则显著增强。     

夏季低空越赤道气流与ENSO的关系

利用NCEP/NCAR风场和海温等资料,分析了东半球夏季低空各支越赤道气流与ENSO循环的关系及其年代际变化,结果表明:东半球夏季低空越赤道气流强度的年际变化和ENSO循环密切相关,ElNino年夏季马斯克林高压减弱,导致索马里越赤道气流变弱,而澳大利亚高压加强, 105°E及其以东的越赤道气流明显加强,LaNina年则相反;夏季越赤道气流与ENSO的年际关系具有年代际变化特征,索马里越赤道气流与ENSO的关系在 20世纪 70年代末变弱,而 105°E及其以东的越赤道气流与ENSO的关系在 20世纪 60年代末增强。     

热带太平洋海平面高度年际异常及其与中国夏季降水的关系

利用1980—2009年共30a的NCEP逐月GODAS海平面高度（sea surface height,SSH）和中国160站降水资料,系统分析了热带太平洋海平面高度季节变化及年际异常特征,初步探讨了海平面高度年际异常与中国夏季降水年际异常之间的相关关系。结果表明：1）热带太平洋海平面高度气候场总体呈＂V＂型分布,西高东低、西北部高于西南部;西北部高值区稳定少动,春夏季大于0.8m的范围较秋冬季略有扩大;西南部高值区春季范围最大且偏北,夏季最小且偏南;赤道区域海平面高度春秋季高于冬夏季。2）多年平均而言,热带西太平洋、西南太平洋的海平面高度年际异常最强,且冬春季较夏秋季更强,赤道中东太平洋年际异常也较大,且秋冬季异常强度和范围都更大,秋、冬和春季海平面高度年际异常与ENSO事件关系密切。3）当冬季发生ENSO事件,可利用热带太平洋海平面高度异常与中国夏季降水异常之间的同期相关关系,预测次年（ENSO事件衰减年）夏季江南地区特别是洞庭湖和鄱阳湖流域、青藏高原东部、江淮流域、内蒙东部降水可能偏多,黄河中下游流域的河套、华北地区以及华南则降水偏少     

南亚高压的年际和年代际变化

利用1958～1998年NCEP/NCAR再分析月平均100 hPa高度场和风场资料， 依据大气环流观测事实及天气学原理，较客观地定义了描述南亚高压活动的特征参数， 然后对南亚高压的年际及年代际变化特征进行了系统的诊断分析。发现北半球中低纬 100 hPa环流异常具有空间整体性和时间持续性，即北半球中低纬100 hPa环流同时加 强或同时减弱，并且其整体异常具有明显的年代际变化。南亚高压面积和强度的变化 存在3.8年的振荡周期，与ENSO的循环周期一致。南亚高压的中心和脊线在夏季较为稳 定，较大的年际差异出现在春季。高压面积和强度的年际变化最明显，并且面积大、 强度强的年份往往与El Niao年相对应。南亚高压的位置和强度还存 在明显的年代际变化，自1978年以后，冬半年南亚高压脊线南移，中心东移，面积增大， 强度增强，夏半年南亚高压的位置变化不很明显，但是面积和强度也增大增强。这种年代 际异常与低层大气系统及赤道太平洋海温的年代际异常一致。南亚高压强度距平与热带 海洋SSTA密切相关，与印度洋海区的同期相关最好。南亚高压强度异常对印度洋SSTA的 响应时间为0～5个月，对赤道中东太平洋SSTA的响应时间为4～6个月。南亚高压明显的 年际和年代际变化特征表明，可将南亚高压看作气候系统中大气子系统异常的强信号， 通过分析南亚高压的年际及年代际异常可以更直接地研究和预测区域气候异常。     

近20年全球冬、夏季海平面气压场和500 hPa高度场年代际变化特征分析

利用1958－1997年全球海平面气压场和500hPa高度场的月平均资料分析了70年代中后期年代际突变前后16a平均的冬、夏海平面气压场和500hPa高度场的变化特征。结果表明，发生在70年代中后期的年代际气候突变是全球性的；突变后与突变前相比，冬季海平面气压场上的阿留申低压增强并发生了东移，与之对应的冬季500hPa高度场上的东亚大槽减弱，同时也发生了明显的系统性东移；冬季，蒙古高压北部减弱，南部稍有增强；夏季，印度低压和东亚的季风低压均减弱；而副热带高压系统普遍增强。     

山东省冬夏季气温异常的季风特征

利用山东省80个代表站1961~2003年月平均气温资料和同期NCAR/NCEP再分析资料,运用统计学方法,分析了季风背景下冬、夏季气温异常的年际、年代际变化和周期特征及变温的空间分布,并研究了东亚冬、夏季风对气温变化的影响。结果表明,冬夏季气温变化趋势明显不同,冬季增温趋势显著,夏季无明显增温趋势;2~6年的周期振荡在不同时期通过了0.05信度检验,小波分析2004年夏季气温不会偏高推断得到证实。冬、夏季气候具有明显的季风特征,季风与气温关系密切,即强(弱)冬季风山东易冷(暖)冬;强(弱)夏季风,易暖(冷)夏。冬季风比夏季风对同期气温作用更显著。季风的隔季相关性质对气温的变化有一定影响。     

Understanding the wet season variations over Florida

The wet season of Florida is well defined and is invariably centered in the boreal summer season of June–July–August. In this observational study we objectively define the Length of the Wet Season (LOWS) for Florida and examine its variations with respect to El Niño and the Southern Oscillation (ENSO) and the Atlantic Warm Pool (AWP). Our study reveals that ENSO variability has a profound influence on the LOWS especially over south Florida and parts of panhandle Florida prior to 1976. In the post-1976 era the influence of ENSO has significantly diminished. Our results show that in this pre-1976 era, warm (cold) ENSO events in the boreal winter are followed by long (short) LOWS over the region. This variation is consistent with warm (cold) ENSO events influencing early (late) onset of the wet season in the region. There is significant relationship of the LOWS in south and northeast Florida with the variation of the AWP. Unlike the teleconnection with ENSO the relationship of the demise of the wet season with AWP is stronger in the post-1976 period compared to the pre-1976 period. Furthermore the variability of the LOWS has increased in the post-1976 period.     

季风与ENSO的选择性相互作用:年循环和春季预报障碍的影响

本文主要基于对Webster and Yang（1992）一文的回顾,讨论了年循环在季风和ENSO相互作用中的作用、春季预报障碍（SPB）、Webster-Yang指数（WYI）、以及亚洲夏季风的前期讯号等内容。亚洲季风和ENSO作为全球天气和气候变率的主要来源,它们之间的相互作用存在明显的年变化和季节“锁相”特征:在北半球秋冬季,亚洲季风对流活动最弱,此时ENSO的信号最强;但是到了北半球春季,亚洲季风对流快速爆发,而此时的ENSO信号却迅速衰减。亚洲季风和ENSO位相的错位变化使得热带海—气系统的不稳定性在北半球春季达到最大,此时任意一个微小的扰动都容易快速增长,最终导致基于ENSO的预报技巧减小。亚洲夏季风环流本质上可以看成是大气对副热带地区潜热加热的低频罗斯贝波响应,它具有很强的垂直风切变,这是WYI定义的物理基础。WYI数值越大,代表垂直东风切变越大,即亚洲季风环流增强,反之亦然。利用WYI与前期大气环流场、欧亚雪盖、土壤湿度等物理量进行回归分析,结果表明:当亚洲夏季风增强时,前期冬季和春季,在北印度洋和亚洲副热带地区上空出现东风异常,同时在更高纬度地区伴随出现西风的异常;此外,副热带地区如印度次大陆、中南半岛和东亚的土壤湿度增大;中纬度地区尤其是青藏高原中西部的积雪密度明显减小。这些前期讯号的发现有助于我们构建动力统计模型,进而提高对亚洲夏季风的季节预报水平。     

冬/夏季热带太平洋与印度洋海表温度年际异常关系的年代际变化

利用NCEP/NCAR再分析资料、全球海温海冰GISST 2.3b资料, 用EOF技术分析了热带太平洋海表温度的年际异常 (SSTA) 变化特征表明:可用Ni?o3指数表示热带太平洋SSTA, 并用该指数来讨论热带太平洋、热带印度洋SSTA间的关系。分季节分析表明:冬季Ni?o3指数与热带印度洋SSTA间的关系表现为热带印度洋整体相关系数为正的单极形态, 且1976年以后两者的关系减弱, 其原因是冬季为ENSO事件的盛期, 另外, 冬季西太平洋暖水区东移导致太平洋Walker环流上升支强盛处的东移, 造成两洋的垂直纬向环流耦合减弱。夏季两者关系表现为偶极形态 (热带西印度洋与Ni?o3指数同相变化, 热带东印度洋则相反), 但1976年以后两者的关系有所加强, 是因为夏季为偶极子盛期, 也是ENSO事件的发展期, 同时夏季西太平洋暖水区东移并未引起太平洋Walker环流上升支强盛处的明显东移, 且印度洋季风环流、太平洋Walker环流的上升支强盛处的强度增大了, 造成两洋的垂直纬向环流耦合更强烈。即1976年以后, 冬季热带两洋SSTA间的关系减弱了, 而夏季两者关系则变得更密切。     

What controls phase-locking of ENSO to boreal winter in coupled GCMs?

In this study, the phase-locking of El Nino Southern Oscillation (ENSO) in a coupled model with different physical parameter values is investigated. It is found that there is a dramatic change in ENSO phase-locking in response to a slight change in the Tokioka parameter, which is a minimum entrainment rate threshold in the cumulus parameterization. With a smaller Tokioka parameter, the model simulates ENSO peak in the boreal summer season rather than in the winter season as observed. It is revealed that the differences in climatological zonal sea surface temperature (SST) gradient and its associated mean state changes are crucial to determine the phase-locking of ENSO. In the simulations with smaller Tokioka parameter values, climatological zonal SST gradient during the boreal summer is excessively large, because the zonally-asymmetric SST change (i.e., SST increase is relatively smaller over the eastern Pacific) is maximum during the boreal summer when the eastern Pacific SST is the coolest of the year. The enhanced climatological zonal SST gradient in boreal summer reduces the convection over the eastern Pacific, which leads to a weakening of air–sea coupling strength. The minimum coupling strength during summer prevents SST anomalies from further development in the following season, which favors SST maximum during summer. In addition, enhanced zonal SST gradient and resultant thermocline shoaling over the eastern Pacific lead to excessive zonal advective feedback and thermocline feedback. Atmospheric damping is also weakened during boreal summer season. These changes due to feedback processes allow an excessive development of SST anomalies during the summer time, and lead to a summer peak of ENSO. The importance of basic state change for the ENSO phase-locking is also validated in a multi-model framework using the Coupled Model Intercomparison Project phase-3 archive. It is found that several of the climate models have the same problem in producing a summer peak of ENSO. Consistent with the simulations with different physical parameter values, these models have minimum air–sea coupling strength during the boreal summer season. Also, they have stronger climatological zonal SST gradient and shallower climatological thermocline depth over the eastern Pacific during the boreal summer season.     

Southern Hemisphere extra-tropical forcing: a new paradigm for El Ni?o-Southern Oscillation

The main goal of this paper is to shed additional light on the reciprocal dynamical linkages between mid-latitude Southern Hemisphere climate and the El Ni?o-Southern Oscillation (ENSO) signal. While our analysis confirms that ENSO is a dominant source of interannual variability in the Southern Hemisphere, it is also suggested here that subtropical dipole variability in both the Southern Indian and Atlantic Oceans triggered by Southern Hemisphere mid-latitude variability may also provide a controlling influence on ENSO in the equatorial Pacific. This subtropical forcing operates through various coupled air?Csea feedbacks involving the propagation of subtropical sea surface temperature (SST) anomalies into the deep tropics of the Atlantic and Indian Oceans from boreal winter to boreal spring and a subsequent dynamical atmospheric response to these SST anomalies linking the three tropical basins at the beginning of the boreal spring. This atmospheric response is characterized by a significant weakening of the equatorial Atlantic and Indian Inter-Tropical Convergence Zone (ITCZ). This weakened ITCZ forces an equatorial ??cold Kelvin wave?? response in the middle to upper troposphere that extends eastward from the heat sink regions into the western Pacific. By modulating the vertical temperature gradient and the stability of the atmosphere over the equatorial western Pacific Ocean, this Kelvin wave response promotes persistent zonal wind and convective anomalies over the western equatorial Pacific, which may trigger El Ni?o onset at the end of the boreal winter. These different processes explain why South Atlantic and Indian subtropical dipole time series indices are highly significant precursors of the Ni?o34 SST index several months in advance before the El Ni?o onset in the equatorial Pacific. This study illustrates that the atmospheric internal variability in the mid-latitudes of the Southern Hemisphere may significantly influence ENSO variability. However, this surprising relationship is observed only during recent decades, after the so-called 1976/1977 climate regime shift, suggesting a possible linkage with global warming or decadal fluctuations of the climate system.     

Role of the southern Indian Ocean in the transitions of the monsoon-ENSO system during recent decades

The focus of this study is to document the possible role of the southern subtropical Indian Ocean in the transitions of the monsoon-ENSO system during recent decades. Composite analyses of sea surface temperature (SST) fields prior to El Niño-Southern Oscillation (ENSO), Indian summer monsoon (ISM), Australian summer monsoon (AUSM), tropical Indian Ocean dipole (TIOD) and Maritime Continent rainfall (MCR) indices reveal the southeast Indian Ocean (SEIO) SSTs during late boreal winter as the unique common SST precursor of these various phenomena after the 1976–1977 regime shift. Weak (strong) ISMs and AUSMs, El Niños (La Niñas) and positive (negative) TIOD events are preceded by significant negative (positive) SST anomalies in the SEIO, off Australia during boreal winter. These SST anomalies are mainly linked to subtropical Indian Ocean dipole events, recently studied by Behera and Yamagata (Geophys Res Lett 28:327–330, 2001). A wavelet analysis of a February–March SEIO SST time series shows significant spectral peaks at 2 and 4–8 years time scales as for ENSO, ISM or AUSM indices. A composite analysis with respect to February–March SEIO SSTs shows that cold (warm) SEIO SST anomalies are highly persistent and affect the westward translation of the Mascarene high from austral to boreal summer, inducing a weakening (strengthening) of the whole ISM circulation through a modulation of the local Hadley cell during late boreal summer. At the same time, these subtropical SST anomalies and the associated SEIO anomalous anticyclone may be a trigger for both the wind-evaporation-SST and wind-thermocline-SST positive feedbacks between Australia and Sumatra during boreal spring and early summer. These positive feedbacks explain the extraordinary persistence of the SEIO anomalous anticyclone from boreal spring to fall. Meanwhile, the SEIO anomalous anticyclone favors persistent southeasterly wind anomalies along the west coast of Sumatra and westerly wind anomalies over the western Pacific, which are well-known key factors for the evolution of positive TIOD and El Niño events, respectively. A correlation analysis supports these results and shows that SEIO SSTs in February–March has higher predictive skill than other well-established ENSO predictors for forecasting Niño3.4 SST at the end of the year. This suggests again that SEIO SST anomalies exert a fundamental influence on the transitions of the whole monsoon-ENSO system during recent decades.     

Paleoclimate simulations of the mid-Holocene and last glacial maximum by FGOALS

Paleoclimate simulations of the mid-Holocene (MH) and Last Glacial maximum (LGM) by the latest versions of the Flexible Global Ocean-Atmosphere-Land System model, Spectral Version 2 and Grid-point Version 2 (FGOALS-s2 and g2) are evaluated in this study. The MH is characterized by changes of insolation induced by orbital parameters, and the LGM is a glacial period with large changes in greenhouse gases, sea level and ice sheets. For the MH, both versions of FGOALS simulate reasonable responses to the changes of insolation, such as the enhanced summer monsoon in African-Asian regions. Model differences can be identified at regional and seasonal scales. The global annual mean surface air temperature (TAS) shows no significant change in FGOALS-s2, while FGOALS-g2 shows a global cooling of about 0.7 C that is related with a strong cooling during boreal winter. The amplitude of ENSO is weaker in FGOALS-g2, which agrees with proxy data. For the LGM, FGOALS-g2 captures the features of the cold and dry glacial climate, including a global cooling of 4.6 C and a decrease in precipitation by 10%. The ENSO is weaker at the LGM, with a tendency of stronger ENSO cold events. Sensitivity analysis shows that the Equilibrium Climate Sensitivity (ECS) estimated for FGOALS ranges between 4.23 C and 4.59 C. The sensitivity of precipitation to the changes of TAS is～2.3% C-1 , which agrees with previous studies. FGOALS-g2 shows better simulations of the Atlantic Meridional Overturning Circulation (AMOC) and African summer monsoon precipitation in the MH when compared with FGOALS-g1.0; however, it is hard to conclude any improvements for the LGM.     

ENSO phase-locking to the boreal winter in CMIP3 and CMIP5 models

In this study, the El Nino-Southern Oscillation (ENSO) phase-locking to the boreal winter in CMIP3 and CMIP5 models is examined. It is found that the models that are poor at simulating the winter ENSO peak tend to simulate colder seasonal-mean sea-surface temperature (SST) during the boreal summer and associated shallower thermocline depth over the eastern Pacific. These models tend to amplify zonal advection and thermocline depth feedback during boreal summer. In addition, the colder eastern Pacific SST in the model can reduce the summertime mean local convective activity, which tends to weaken the atmospheric response to the ENSO SST forcing. It is also revealed that these models have more serious climatological biases over the tropical Pacific, implying that a realistic simulation of the climatological fields may help to simulate winter ENSO peak better. The models that are poor at simulating ENSO peak in winter also show excessive anomalous SST warming over the western Pacific during boreal winter of the El Nino events, which leads to strong local convective anomalies. This prevents the southward shift of El Nino-related westerly during boreal winter season. Therefore, equatorial westerly is prevailed over the western Pacific to further development of ENSO-related SST during boreal winter. This bias in the SST anomaly is partly due to the climatological dry biases over the central Pacific, which confines ENSO-related precipitation and westerly responses over the western Pacific.     

Multi-scale climate variability of the South China Sea monsoon: A review

This review recapitulates climate variations of the South China Sea (SCS) monsoon and our current understanding of the important physical processes responsible for the SCS summer monsoon's intraseasonal to interannual variations. We demonstrate that the 850 hPa meridional shear vorticity index (SCSMI) can conveniently measure and monitor SCS monsoon variations on a timescale ranging from intraseasonal to interdecadal. Analyses with this multi-scale index reveal that the two principal modes of intraseasonal variation, the quasi-biweekly and 30–60-day modes, have different source regions and lifecycles, and both may be potentially predicted at a lead time longer than one-half of their corresponding lifecycles. The leading mode of interannual variation is seasonally dependent: the seasonal precipitation anomaly suddenly reverses the sign from summer to fall, and the reversed anomaly then persists through the next summer. Since the late 1970s, the relationship between the SCS summer monsoon and El Niño-Southern Oscillation (ENSO) has significantly strengthened. Before the late 1970s, the SCS summer monsoon was primarily influenced by ENSO development, while after the late 1970s, it has been affected mainly in the decaying phase of ENSO. The year of 1993 marked a sudden interdecadal change in precipitation and circulation in the SCS and its surrounding region. Over the past 60 years, the SCS summer monsoon's strength shows no significant trend, but the SCS winter monsoon displays a significant strengthening tendency (mainly in its easterly component and its total wind speed). A number of outstanding issues are raised for future studies.