The asymmetric impacts of ENSO modoki on boreal winter climate over the Pacific and its rim

Climate Dynamics - The El Niño–Southern Oscillation (ENSO) Modoki phenomenon has a substantial influence on regional climate. In this study, the results derived from observational and...     

冬季赤道太平洋不同类型海温异常表征指数的再构建

利用1963—2013年Hadley中心月平均海表温度资料,以及NCEP/NCAR再分析资料,根据两类厄尔尼诺事件发生时北半球冬季赤道太平洋地区海温异常的不同空间分布特征,即赤道中太平洋CP型和东太平洋EP型海温异常空间分布,从寻找与之相似的空间型角度出发,设计了一组新的海温异常指数I_(CP)和I_(EP)。与以往ENSO指数相比,新指数组I_(CP)和I_(EP)不仅表示了空间上相互独立的海温异常分布,而且在相同的研究时段内,因时间域上相互独立而能更好地表征和区分两类El Ni?o/La Ni?a事件。据此,采用该新指数组探讨了与中部型和东部型海温异常事件相关的热带太平洋的主要海气耦合特征。结果表明,与传统的东部型El Ni?o事件发生时最大暖海温中心位于赤道东太平洋地区不同,中部型El Ni?o事件,异常增暖中心位于赤道中太平洋。中部型时异常Walker环流的上升支向西偏移,异常降水集中于热带中太平洋,不似东部型时异常限定于赤道东太平洋地区。不论哪类事件,海洋性大陆均可受到影响,即CP或EP型El Ni?o发生时,海洋性大陆区域降水偏少。但比较而言,中部型ENSO对海洋性大陆区域的影响更大。     

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.     

Advances in research of ENSO changes and the associated impacts on Asian-Pacific climate

This review provides a summary on the recent major advances in research of ENSO changes and the associated impacts on Asian-Pacific climate. Achievements in the following topics are summarized: 1) the asymmetry between El Niño and La Niña; 2) the different features of central Pacific (CP) El Niño and eastern Pacific (EP) El Niño; 3) the change of ENSO in a warming world, including analysis of pre-industrial control simulation, historical simulation and climate projections of coupled climate system model; 4) Impact of EP ENSO on warm-pool air-sea interaction and East Asianwestern North Pacific summer monsoon; 5) Impacts of CP ENSO on Asian-Pacific climate, with focus on East Asian seasonal precipitation and tropical cyclones in the western Pacific. Research results published in the recent 5 years are the major sources for this review. Based on the review of the current progresses, some challenging issues needed to be investigated in the future are highlighted.     

中部型ENSO和平流层准两年振荡对冬季北半球平流层臭氧的联合调制作用

利用观测和再分析资料通过合成分析方法,研究了中部型ENSO和平流层准两年振荡（QBO）对冬季北半球平流层臭氧的独立影响和联合调制作用。研究表明,北半球平流层臭氧在中部型厄尔尼诺年增加,而在中部型拉尼娜年减少;准两年振荡东风位相年份,北半球平流层臭氧增加,准两年振荡西风位相结果则相反。相比之下,北半球中、高纬度平流层臭氧异常对准两年振荡活动的响应明显小于其对ENSO活动的响应。进一步研究发现,准两年振荡东风位相会加强中部型厄尔尼诺事件引起的北半球平流层臭氧的增加,而减弱中部型拉尼娜事件造成的平流层臭氧的减少。在准两年振荡西风位相下,中部型厄尔尼诺事件仅导致北半球平流层臭氧含量少量升高,而中部型拉尼娜事件期间臭氧会大幅度减少。因此,准两年振荡东风位相会加强中部型厄尔尼诺事件对北半球平流层臭氧的影响,而减弱中部型拉尼娜事件对北半球平流层臭氧的影响。准两年振荡西风位相会减弱中部型厄尔尼诺而加强中部型拉尼娜事件对北半球平流层臭氧的影响。      

Global seasonal climate predictability in a two tiered forecast system. Part II: boreal winter and spring seasons

We examine the Florida Climate Institute–Florida State University Seasonal Hindcast (FISH50) skill at a relatively high (50 km grid) resolution two tiered Atmospheric General Circulation Model (AGCM) for boreal winter and spring seasons at zero and one season lead respectively. The AGCM in FISH50 is forced with bias corrected forecast sea surface temperature averaged from two dynamical coupled ocean–atmosphere models. The comparison of the hindcast skills of precipitation and surface temperature from FISH50 with the coupled ocean–atmosphere models reveals that the probabilistic skill is nearly comparable in the two types of forecast systems (with some improvements in FISH50 outside of the global tropics). Furthermore the drop in skill in going from zero lead (boreal winter) to one season lead (boreal spring) is also similar in FISH50 and the coupled ocean–atmosphere models. Both the forecast systems also show that surface temperature hindcasts have more skill than the precipitation hindcasts and that land based precipitation hindcasts have slightly lower skill than the corresponding hindcasts over the ocean.     

Simulation of the westerly jet axis in boreal winter by the climate system model FGOALS-g2

The major features of the westerly jets in boreal winter, consisting of the Middle East jet stream (MEJS), East Asian jet stream (EAJS) and North Atlantic jet stream (NAJS), simulated by a newly developed climate system model, were evaluated with an emphasis on the meridional location of the westerly jet axis (WJA). The model was found to exhibit fairly good performance in simulating the EAJS and NAJS, whereas the MEJS was much weaker and indistinguishable in the model. Compared with the intensity bias, the southward shift of the WJA seems to be a more remarkable deficiency. From the perspective of Ertel potential vorticity, the profiles along different westerly jet cores in the model were similar with those in the reanalysis but all shifted southward, indicating an equatorward displacement of the dynamic tropopause and associated climatology. Diagnosis of the thermodynamic equation revealed that the model produced an overall stronger heating source and the streamfunction quantifying the convection and overturning Hadley circulation shifted southward significantly in the middle and upper troposphere. The two maximum centers of eddy kinetic energy, corresponding to the EAJS and NAJS, were reproduced, whereas they all shifted southwards with a much reduced intensity. A lack of transient eddy activity will reduce the efficiency of poleward heat transport, which may partially contribute to the meridionally non-uniform cooling in the middle and upper troposphere. As the WJA is closely related to the location of the Hadley cell, tropopause and transient eddy activity, the accurate simulation of westerly jets will greatly improve the atmospheric general circulation and associated climatology in the model.     

夏季厄尔尼诺-Modoki和东部型ENSO海表温度异常分布型特征及其与海洋性大陆区域气候异常的联系

2007年,Ashok等揭示了赤道太平洋区域存在一种三极型分布海表温度异常并称之为厄尔尼诺-Modoki,同时定义了相应的海表温度异常指数EMI（记为I_EM）。在此基础上,利用英国哈得来中心逐月海表温度资料、美国NCEP/NCAR月平均再分析数据集、美国国家海洋和大气管理局（NOAA）逐月降水资料（CMAP）,通过在太平洋海表温度异常中扣除厄尔尼诺-Modoki信号后,在Nino1+2区域上定义了东太平洋型海表温度异常指数EPNI（I_EPN）。据此,由I_EPN和I_EM可构成描述热带太平洋海表温度异常变化的一对指数。分析了两个指数相应的海气状态及对海洋性大陆区域气候异常的影响。结果表明,厄尔尼诺-Modoki和东太平洋型海表温度异常及其影响存在显著差异。在北半球夏季,当I_EM处于正位相时,热带太平洋海表温度异常呈现“负-正-负”的结构,海洋性大陆大部分区域海表温度异常为负,此时对流层低层太平洋地区辐合,海洋性大陆地区辐散,对流层高层太平洋地区辐散,海洋性大陆地区辐合。对应于辐合辐散中心,存在着自赤道中太平洋分别向赤道东太平洋和海洋性大陆中东部地区的异常垂直环流圈,同时也存在自海洋性大陆西部向印度洋西部的垂直环流。大气在海洋性大陆区域北部加热,南部冷却;在太平洋地区西部加热而东部冷却;在海洋性大陆区域10°N以南降水偏少,而10°N以北降水偏多。当I_EPN处于正位相时,热带太平洋海表温度异常呈现“西负东正”分布型,海洋性大陆区域海表温度异常呈现“西正东负”分布,对流层低层海洋性大陆地区辐散中心范围偏大、位置偏东、强度偏强,太平洋地区辐合中心范围偏小、位置偏东,热带环流异常在垂直方向上呈斜压结构,海洋性大陆区域北部大气加热而南部冷却,太平洋地区大气均呈加热正异常,海洋性大陆大部分区域降水均偏少,赤道太平洋降水偏多。以上这些结果有利于深刻理解热带太平洋海表温度异常的特征及其对海洋性大陆区域气候的影响。     

夏季厄尔尼诺-Modoki和东部型ENSO海表温度异常分布型特征及其与海洋性大陆区域气候异常的联系

2007年,Ashok等揭示了赤道太平洋区域存在一种三极型分布海表温度异常并称之为厄尔尼诺-Modoki,同时定义了相应的海表温度异常指数EMI（记为I_EM）。在此基础上,利用英国哈得来中心逐月海表温度资料、美国NCEP/NCAR月平均再分析数据集、美国国家海洋和大气管理局（NOAA）逐月降水资料（CMAP）,通过在太平洋海表温度异常中扣除厄尔尼诺-Modoki信号后,在Nino1+2区域上定义了东太平洋型海表温度异常指数EPNI（I_EPN）。据此,由I_EPN和I_EM可构成描述热带太平洋海表温度异常变化的一对指数。分析了两个指数相应的海气状态及对海洋性大陆区域气候异常的影响。结果表明,厄尔尼诺-Modoki和东太平洋型海表温度异常及其影响存在显著差异。在北半球夏季,当I_EM处于正位相时,热带太平洋海表温度异常呈现“负-正-负”的结构,海洋性大陆大部分区域海表温度异常为负,此时对流层低层太平洋地区辐合,海洋性大陆地区辐散,对流层高层太平洋地区辐散,海洋性大陆地区辐合。对应于辐合辐散中心,存在着自赤道中太平洋分别向赤道东太平洋和海洋性大陆中东部地区的异常垂直环流圈,同时也存在自海洋性大陆西部向印度洋西部的垂直环流。大气在海洋性大陆区域北部加热,南部冷却;在太平洋地区西部加热而东部冷却;在海洋性大陆区域10°N以南降水偏少,而10°N以北降水偏多。当I_EPN处于正位相时,热带太平洋海表温度异常呈现“西负东正”分布型,海洋性大陆区域海表温度异常呈现“西正东负”分布,对流层低层海洋性大陆地区辐散中心范围偏大、位置偏东、强度偏强,太平洋地区辐合中心范围偏小、位置偏东,热带环流异常在垂直方向上呈斜压结构,海洋性大陆区域北部大气加热而南部冷却,太平洋地区大气均呈加热正异常,海洋性大陆大部分区域降水均偏少,赤道太平洋降水偏多。以上这些结果有利于深刻理解热带太平洋海表温度异常的特征及其对海洋性大陆区域气候的影响。      

Northern poleward edge of regional Hadley cell over western Pacific during boreal winter: year-to-year variability,influence factors and associated winter climate anomalies

Compared to the zonal-mean Hadley cell (HC), our knowledge of the characteristics, influence factors and associated climate anomalies of the regional HC remains quite limited. Here, we examine interannual variability of the northern poleward HC edge over western Pacific (WPHCE) during boreal winter. Results suggest that interannual variability of the WPHCE is impacted by the El Niño-Southern Oscillation (ENSO) Modoki, North Pacific Oscillation (NPO) and North Atlantic Oscillation (NAO). The WPHCE tends to shift poleward during negative phase of the ENSO Modoki, and positive phases of the NPO and NAO, which highlights not merely the tropical forcing but also the extratropical signals that modulate the WPHCE. ENSO modoki, NPO and NAO modulate the WPHCE via inducing atmospheric anomalies over the western North Pacific. We further investigate the climatic impacts of the WPHCE on East Asia. The poleward shift of the northern descending branch of the WPHC results in anomalous upward (downward) motions and upper-level divergence (convergence) anomalies over south-central China (northern East-Asia), leading to increased (decreased) rainfall there. Moreover, pronounced cold surface air temperature anomalies appear over south-central China when the sinking branch of the WPHC moves poleward. Based on the temperature diagnostic analysis, negative surface temperature tendency anomalies over central China are mostly attributable to the cold zonal temperature advection and ascent-induced adiabatic cooling, while the negative anomalies over South China are largely due to the cold meridional temperature advection. These findings could improve our knowledge of the WPHCE variability and enrich the knowledge of forcing factors for East Asian winter climate.

     

ENSO和北极涛动对东亚冬季气候异常的综合影响

基于1901-2000年多种海-气资料,分析了厄尔尼诺成熟年冬季-初夏西北太平洋异常反气旋（WNPAC）的年际变化特征及其对东亚气候的影响。结果表明,无论是厄尔尼诺事件成熟期的冬季还是次年的春季和初夏,WNPAC的年际变化主要存在两个空间变化型,即反映其强度变化的经验正交函数分解第1模态和反映其位置变化的第2模态。厄尔尼诺成熟年冬季WNPAC强度不仅与赤道中东太平洋海温异常有关,而且与太平洋西部（WP）型遥相关的强度有关,而其位置的变化则主要与西北太平洋局地海温异常以及北极涛动（AO）有关;次年春季,WNPAC的强度除了与赤道中东太平洋海温异常和太平洋西部型遥相关存在显著相关外,还与赤道大西洋海温异常有关,而其位置的变化则主要与西北太平洋局地海温异常和太平洋西部型遥相关有关;次年初夏,WNPAC强度主要与西北印度洋和西南印度洋的海温异常以及东亚-太平洋（EAP）型遥相关的强度有关。进一步分析表明,成熟年冬季-初夏WNPAC的强度和位置的变化均可对东亚地区降水异常分布产生影响,这对预测厄尔尼诺事件发生后冬季及后期春、夏季节东亚地区降水异常分布具有一定的指示意义。此外,次年初夏,WNPAC强度变化与西北太平洋台风发生频数存在显著负相关,即WNPAC越强,台风发生的频数越少,反之亦然。     

Rotational atmospheric circulation during North Atlantic-European winter: the influence of ENSO

The dominant variability modes of the North Atlantic-European rotational flow are examined by applying a principal component analysis (PCA/EOF) to the 200?hPa streamfunction mid-winter anomalies (Jan?CFeb monthly means). The results reveal that, when this norm is used, the leading mode (EOF1) does not correspond to the traditional North Atlantic Oscillation (NAO, which appears in our analysis as the second leading mode, EOF2) but is the local manifestation of the leading hemispheric streamfunction EOF. The regression of this regional mode onto the global SST field exhibits a clear El Ni?o signature, with no signal over the Atlantic, while the associated upper height anomalies resemble the Tropical/Northern Hemisphere (TNH) pattern. East of North America, this TNH-like wavetrain produces a meridional dipole-like pattern at lower levels. Although in some ways this pattern resembles the NAO (EOF2), the dynamics of these two modes are very different in that only EOF2 is associated with a latitudinal shift of the North Atlantic stormtrack. Thus, the choice of the streamfunction norm in the EOF analysis allows the separation of two different phenomena that can produce similar dipolar surface pressure anomalies over the North Atlantic but that have different impact on European climate. These two modes also differ on their contribution to variability at lower levels: while NAO-EOF2 is mostly confined to the North Atlantic, TNH-EOF1 has a more annular, global character. At upper levels NAO-EOF2 also produces a global pattern but with no annular structure, reminiscent of the ??circumglobal?? teleconnection.     

Simulated impacts of historical land cover changes on global climate in northern winter

This ten-year general circulation model experiment compared a simulation where land surface boundary conditions were represented by observed, present day land cover to a simulation where the surface was represented by natural, potential land cover conditions. As a result of these estimated changes in historical land cover, significant temperature and hydrology changes affected tropical land surfaces, where some of the largest historical disruptions in total vegetation biomass have occurred. Also of considerable interest because of their broad scope and magnitude were changes in high-latitude Northern Hemisphere winter climate which resulted from changes in tropical convection, upper-level tropical outflow, and the generation of low-frequency tropical waves which propagated to the extratropics. These effects combined to move the Northern Hemisphere zonally averaged westerly jet to higher latitudes, broaden it, and reduce its maximum intensity. Low-level easterlies were also reduced over much of the tropical Pacific basin while positive anomalies in convective precipitation occurred in the central Pacific. Globally averaged changes were small. Comparisons of recent, observed trends in tropical and Northern Hemisphere, mid-latitude climate with these simulations suggests an interaction between the climatic effects of historical land cover changes and other modes of climate variability. Received: 8 September 1998 / Accepted: 31 July 1999     

The impacts of climate change on the winter hardiness zones of woody plants in Europe

The potential impacts of climate change on potatoes cropping in the Peruvian highlands (Altiplano) is assessed using climate projections for 2071–2100, obtained from the HadRM3P regional atmospheric model of the Hadley Centre. The atmospheric model is run under two different special report on emission scenarios: high CO₂ concentration (A2) and moderate CO₂ concentration (B2) for four locations situated in the surroundings of Lake Titicaca. The two main varieties of potato cultivated in the area are studied: the Andean potato (Solanum tuberosum) and the bitter potato (Solanum juzepczukii). A simple process-oriented model is used to quantify the climatic impacts on crops cycles and yields by combining the effects of temperature on phenology, of radiation and CO₂ on maximum yield and of water balance on yield deficit. In future climates, air temperature systematically increases, precipitation tends to increase at the beginning of the rainy season and slightly decreases during the rest of the season. The direct effects of these climatic changes are earlier planting dates, less planting failures and shorter crop cycles in all the four locations and for both scenarios. Consequently, the harvesting dates occur systematically earlier: roughly in January for the Andean potato instead of March in the current situation and in February for the bitter potato instead of April. Overall, yield deficits will be higher under climate change than in the current climate. There will be a strong negative impact on yields for S. tuberosum (stronger under A2 scenario than under B2); the impact on S. juzepczukii yields, however, appears to be relatively mixed and not so negative.     

ENSO 年冬季北半球平流层大气环流异常特征分析

利用1957-2002年欧洲中心的再分析资料和Hadley气候预测和研究中心的全球海表温度资料,对ENSO年冬季的平流层环流进行了合成分析,分别从暖事件和冷事件年的温度场、高度场和风场,分析研究了平流层大气环流的异常特征.分析结果表明,对应El Ni(n)o年冬季,在赤道东太平洋的温度场、高度场和纬向风场都有由大气低层的正距平转变为平流层负距平的特征;与之相反,在El Ni(n)a年冬季,赤道东太平洋大气低层的负距平到了高层变为正距平.同时,在纬向平均垂直剖面图中, El Ni(n)o年冬季北半球高纬地区从对流层顶到平流层温度场和高度场为正距平,而La Ni(n)na年出现相反的情况.在热带平流层,El Ni(n)o年冬季高空纬向风场在50 hPa到15 hPa左右为负距平,从15 hPa到1 hPa为正距平;而El Ni(n)a年则相反.在El Ni(n)o年冬季100 hPa以上的北半球高纬度地区存在一个类偶极子结构的异常高度场和风场,El Ni(n)o年在极区主要为正距平,El Ni(n)a年在极区主要为负距平.     

伴随IOD型和独立型ENSO对山东气候年际变化的影响

使用1951年以来66 a的观测和再分析资料,通过合成分析的方法对比分析了厄尔尼诺/拉尼娜（El Niño /La Niña）伴随正/负印度洋偶极子（positive/negative Indian Ocean Dipole,pIOD/nIOD）发生年或独立发生年山东夏、秋季气温和降水的年际变化特征,结果表明,伴随IOD型和独立型El Niño/La Niña对山东夏、秋季气温和降水的影响在强度、范围、正负位相、空间型态上存在很大的差异。在气温方面,El Niño在pIOD的调制作用下对山东南部地区夏季气温年际变化的影响加强;El Niño与pIOD伴随发生时,山东秋季气温较常年偏高,而独立发生时气温则偏低,呈反位相变化;La Niña与nIOD伴随发生年夏季鲁西北气温较常年偏低,La Niña独立发生年夏季半岛东部气温较常年偏高,气温异常呈反位相变化;nIOD对La Niña的调制促进作用有利于山东秋季气温较常年异常偏高;850 hPa气温异常与山东表面气温异常有很强的正相关关系。在降水方面,El Niño在pIOD的调制作用下容易引起山东北部地区夏季降水偏少,但会削弱其对山东中部地区秋季降水负异常的影响;La Niña在nIOD的调制作用下山东境内降水都较常年偏多,但降水异常地域分布非常不均,鲁西北降水较常年显著偏多;独立型La Niña更易引起鲁西北西部、鲁中、鲁南大部分地区夏季降水偏少。850 hPa环流异常配合温度场异常对山东夏、秋季降水异常分布有一定的影响。     

A diagnostic analysis of winter atmospheric circulation during the 1982–1983 ENSO event

In this paper, the winter atmospheric circulation, the convection along the equator and their variations of 1982 und 1983 are investigated. It is suggested that there was a well organized three dimensional structure of anomalies of the atmospheric circulations during 1982 winter which may be related to the variations of the convection in the equa-torial region.     

The influence of the Madden-Julian oscillation on high-latitude surface air temperature during boreal winter

By analyzing NCEP-NCAR reanalysis daily data for 1979–2016, the modulation by Madden-Julian Oscillation (MJO) of the wintertime surface air temperature (SAT) over high latitude is examined. The real-time multivariate MJO (RMM) index, which divides the MJO into eight phases, is used. It is found that a significantly negative SAT anomaly over the northern high latitude region of (180°–60 °W, 60°–90 °N) lags the MJO convection for 1∼2 weeks in phase 3, in which the enhanced convective activity exists over the Indian Ocean. While a significantly positive SAT anomaly appears over the same region following the MJO phase 7, as the tropical heating shows an opposite sign. Analysis of the anomalous circulation indicates that the observed SAT signal is probably a result of the northeastward propagating Rossby wave train triggered by MJO-related tropical forcing through Rossby wave energy dispersion. By using an anomalous atmospheric general circulation model (AGCM), the significant effect of tropical forcing on organizing the extratropical circulation anomaly is confirmed. Analysis of a temperature tendency equation further reveals that the intraseasonal SAT anomaly is primarily attributed to the advection of the mean temperature by the wind anomaly associated with the anomalous circulation of the MJO-related variability.     

Origins and interrelationship of Intraseasonal rainfall variations around the Maritime Continent during boreal winter

Theoretical and Applied Climatology - Large intraseasonal rainfall variations are identified over the southern South China Sea (SSCS), tropical southeastern Indian Ocean (SEIO), and east coast of...