与不同El Nino相伴的IOD事件的季节演变特征对比

基于1951—2012年逐月海洋和大气多种要素的再分析资料,分析了与两类El Nino相伴的IOD(Indian Ocean Dipole,印度洋偶极子)事件盛期的海洋和大气异常特征,并进一步对比了与不同类型El Nino相伴的IOD事件的季节演变及对应的海气耦合过程。结果表明:两类IOD事件盛期时,暖海温强度和位置有显著差异。发生在东部型El Nino期间的IOD事件(简称EP-IOD)盛期,正(负)SSTA中心出现在热带西北(赤道东南)印度洋,强度相当,对应的热带印度洋—海洋大陆异常Walker环流强度较强、范围较大;与中部型CP El Nino相伴的IOD事件(简称CP-IOD)的正SSTA相对较弱,且偏于南印度洋,异常Walker环流较弱、较窄。在季节演变中,两类IOD事件期间的局地海气过程差异显著,伴随着西印度洋西南季风减弱和东印度洋异常东风加强,EP-IOD事件的发展以西正东负的偶极型异常海温的出现及加强为主要特征;而CP-IOD事件的发生发展则与西北印度洋异常冷海温的生消及南印度洋暖水的堆积相伴,表现为"-+-"三极型SSTA的出现并转为西正东负偶极型的过程,夏季时出现在东印度洋的异常东风以及赤道中印度洋低层负涡度异常水平环流对其发展具有重要作用。     

Summer monsoon circulation and precipitation over the tropical Indian Ocean during ENSO in the NCEP climate forecast system

This study investigates the El Niño Southern Oscillation (ENSO) teleconnections to tropical Indian Ocean (TIO) and their relationship with the Indian summer monsoon in the coupled general circulation model climate forecast system (CFS). The model shows good skill in simulating the impact of El Niño over the Indian Oceanic rim during its decay phase (the summer following peak phase of El Niño). Summer surface circulation patterns during the developing phase of El Niño are more influenced by local Sea Surface Temperature (SST) anomalies in the model unlike in observations. Eastern TIO cooling similar to that of Indian Ocean Dipole (IOD) is a dominant model feature in summer. This anomalous SST pattern therefore is attributed to the tendency of the model to simulate more frequent IOD events. On the other hand, in the model baroclinic response to the diabatic heating anomalies induced by the El Niño related warm SSTs is weak, resulting in reduced zonal extension of the Rossby wave response. This is mostly due to weak eastern Pacific summer time SST anomalies in the model during the developing phase of El Niño as compared to observations. Both eastern TIO cooling and weak SST warming in El Niño region combined together undermine the ENSO teleconnections to the TIO and south Asia regions. The model is able to capture the spatial patterns of SST, circulation and precipitation well during the decay phase of El Niño over the Indo-western Pacific including the typical spring asymmetric mode and summer basin-wide warming in TIO. The model simulated El Niño decay one or two seasons later, resulting long persistent warm SST and circulation anomalies mainly over the southwest TIO. In response to the late decay of El Niño, Ekman pumping shows two maxima over the southern TIO. In conjunction with this unrealistic Ekman pumping, westward propagating Rossby waves display two peaks, which play key role in the long-persistence of the TIO warming in the model (for more than a season after summer). This study strongly supports the need of simulating the correct onset and decay phases of El Niño/La Niña for capturing the realistic ENSO teleconnections. These results have strong implications for the forecasting of Indian summer monsoon as this model is currently being adopted as an operational model in India.     

Seasonality in the relationship between El Nino and Indian Ocean dipole

The seasonal change in the relationship between El Nino and Indian Ocean dipole (IOD) is examined using the European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40), and the twentieth century simulations (20c3m) from the Geophysical Fluid Dynamics Laboratory Coupled Model, version 2.1. It is found that, both in ERA-40 and the model simulations, the correlation between El Nino (Nino3 index) and the eastern part of the IOD (90?C110°E; 10°S-equator) is predominantly positive from January to June, and then changes to negative from July to December. Correlation maps of atmospheric and oceanic variables with respect to the Nino3 index are constructed for each season in order to examine the spatial structure of their seasonal response to El Nino. The occurrence of El Nino conditions during January to March induces low-level anti-cyclonic circulation anomalies over the southeastern Indian Ocean, which counteracts the climatological cyclonic circulation in that region. As a result, evaporation decreases and the southeastern Indian Ocean warms up as the El Nino proceeds, and weaken the development of a positive phase of an IOD. This warming of the southeastern Indian Ocean associated with the El Nino does not exist past June because the climatological winds there develop into the monsoon-type flow, enhancing the anomalous circulation over the region. Furthermore, the development of El Nino from July to September induces upwelling in the southeastern Indian Ocean, thereby contributing to further cooling of the region during the summer season. This results in the enhancement of a positive phase of an IOD. Once the climatological circulation shifts from the boreal summer to winter mode, the negative correlation between El Nino and SST of the southeastern Indian Ocean changes back to a positive one.     

1986—1987厄尔尼诺事件的数值模拟

用高分辨率自由表面热带太平洋环流模式，在观测到的风应力和热量、水汽通量驱动下，对１９８６—１９８７厄尔尼诺（Ｅ１Ｎｉｎｏ）事件进行了数值模拟。各种变量场的时空结构及其演变表明，模式成功地模拟出１９８６—１９８７厄尔尼诺现象。始于１９８６年年中，赤道西太平洋的西风异常所推动的向东表层洋流不断向中、东太平洋输送暖水，至１１月份，大量暖水在日界线附近堆积，造成海面上升（达３２ｃｍ）和斜温层（用２０℃等温线深度表示）加深。１９８６年年底的强西风异常激发出赤道Ｋｅｌｖｉｎ波，并向赤道东太平洋和南美沿岸传播，使那里的斜温层加深和海面上升，且具有双峰结构；Ｋｅｌｖｉｎ波所伴随的垂直冷平流的减弱造成赤道中、东太平洋海表温度上升；１９８７年春季在中、东太平洋和南美沿岸地区存在强的正海表温度异常，并伴随着整个赤道太平洋斜温层东西方向变平、赤道潜流弱而中心位置变浅。厄尔尼诺相伴随的热带太平洋环流异常首先于１９８７年年中从东太平洋开始消失，而中、西太平洋则一直维持到１９８８年初。     

初夏孟加拉湾东部降水异常对印度洋海温偶极子的触发作用

基于1982—2013年逐月NCEP资料及GODAS资料,采用回归分析、合成分析以及2.5层简化海洋模式数值模拟等方法,研究了热带东印度洋的大气和海洋过程对印度洋海温偶极子(IOD,Indian Ocean Dipole)东极(IODE,IOD East pole)海温异常的影响。结果表明,IODE海温异常的演变超前IOD西极(IODW,IOD West pole)海温异常的演变,并对IOD事件的生成和发展起到关键作用。初夏,来自阿拉伯海、中南半岛地区以及孟加拉湾西南部的水汽输送,导致孟加拉湾东部出现强降水。降水释放的潜热在热带东印度形成了一个跨越赤道的经向环流,有利于加强赤道东印度洋的过赤道气流,并在苏门答腊沿岸形成偏南风异常。该异常偏南风通过影响混合层垂向夹卷混合过程和纬向平流过程,导致IODE海温迅速下降。随后赤道东南印度洋异常东南风迅速增强以及赤道中印度洋东风异常的出现,增强了自东南印度洋向西印度洋的水汽输送,削弱了向孟加拉湾的水汽输送,使西南印度洋的降水增强,孟加拉湾东部的降水减弱。因此,IOD达到盛期前孟加拉湾东部的降水通过局地经向环流在苏门答腊沿岸形成偏南风异常,导致苏门答腊沿岸迅速的降温,并最终导致IOD事件的发生。     

The Positive Indian Ocean Dipole–like Response in the Tropical Indian Ocean to Global Warming

Climate models project a positive Indian Ocean Dipole(p IOD)–like SST response in the tropical Indian Ocean to global warming. By employing the Community Earth System Model and applying an overriding technique to its ocean component(version 2 of the Parallel Ocean Program), this study investigates the similarities and differences of the formation mechanisms for the changes in the tropical Indian Ocean during the p IOD versus global warming. Results show that their formation processes and related seasonality are quite similar; in particular, wind–thermocline–SST feedback is the leading mechanism in producing the anomalous cooling over the eastern tropics in both cases. Some differences are also found, including the fact that the cooling effect of the vertical advection over the eastern tropical Indian Ocean is dominated by the anomalous vertical velocity during the p IOD but by the anomalous upper-ocean stratification under global warming. These findings are further examined through an analysis of the mixed layer heat budget.     

Response of the tropical Indian Ocean SST to decay phase of La Niña and associated processes

Delayed impact of El Niño on Tropical Indian Ocean (TIO) Sea Surface Temperature (SST) variations and associated physical mechanisms are well documented by several studies. However, TIO SST evolution during the decay phase of La Niña and related processes are not adequately addressed before. Strong cooling associated with La Niña decay over the TIO could influence climate over the Indian Oceanic rim including Indian summer monsoon circulation and remotely northwest Pacific circulation. Thus understanding the TIO basin-wide cooling and related physical mechanisms during decaying La Niña years is important. Composite analyses revealed that negative SST anomalies allied to La Niña gradually dissipate from its mature phase (winter) till subsequent summer in central and eastern Pacific. In contrast, magnitude of negative SST anomalies in TIO, induced by La Niña, starts increasing from winter and attains their peak values in early summer. It is found that variations in heat flux play an important role in SST cooling over the central and eastern equatorial Indian Ocean, Bay of Bengal and part of Arabian Sea from late winter to early summer during the decay phase of La Niña. Ocean dynamical processes are mainly responsible for the evolution of southern TIO SST cooling. Strong signals of westward propagating upwelling Rossby waves between 10°S to 20°S are noted throughout (the decaying phase of La Niña) spring and summer. Anomalous cyclonic wind stress curl to the south of the equator is responsible for triggering upwelling Rossby waves over the southeastern TIO. Further, upwelling Rossby waves are also apparent in the Arabian Sea from spring to summer and partly contributing to the SST cooling. Heat budget analysis reveals that negative SST/MLT (mixed layer temperature) anomalies over the Arabian Sea are mostly controlled by heat flux from winter to spring and vertical advection plays an important role during early summer. Vertical and horizontal advection terms primarily contribute to the SST cooling anomalies over southern TIO and the Bay of Bengal cooling is primarily dominated by heat flux. Further we have discussed influence of TIO cooling on local rainfall variations.     

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.     

On the Mechanism of the Locking of the El Nino Event Onset Phase to Boreal Spring

The mechanism of the locking of the E1 Nino event onset phase to boreal spring （from April to June） in an intermediate coupled ocean-atmosphere model is investigated. The results show that the seasonal variation of the zonal wind anomaly over the equatorial Pacific associated with the seasonal variation of the ITCZ is the mechanism of the locking in the model. From January to March of the E1 Nino year, the western wind anomaly over the western equatorial Pacific can excite the downwelling Kelvin wave that propagates eastward to the eastern and middle Pacific by April to June. From April to December of the year before the E1 Nifio year, the eastern wind anomaly over the equatorial Pacific forces the downwelling Rossby waves that modulate the ENSO cycle. The modulation and the reflection at the western boundary modulate the time of the transition from the cool to the warm phase to September of the year before the E1 Nifio year and cause the strongest downwelling Kelvin wave from the reflected Rossby waves at the western boundary to arrive in the middle and eastern equatorial Pacific by April to June of the E1 Nino year. The superposition of these two kinds of downwelling Kelvin waves causes the El Nino event to tend to occur from April to June.     

On the Mechanism of the Locking of the El Nio Event Onset Phase to Boreal Spring

1. Introduction The observed facts show that the ENSO cycle has obvious phase-locking and oscillates irregularly (An and Wang, 2001; Kaplan et al., 1998). Based on Zibiak and Cane's (1987) model (hereafter, the Z-C model) and simple, coupled ocean-atmosph…     

Tidal mixing in the Indonesian Seas and its effect on the tropical climate system

The sensitivity of the tropical climate to tidal mixing in the Indonesian Archipelago (IA) is investigated using a coupled general circulation model. It is shown that the introduction of tidal mixing considerably improves water masses properties in the IA, generating fresh and cold anomalies in the thermocline and salty and cold anomalies at the surface. The subsurface fresh anomalies are advected in the Indian Ocean thermocline and ultimately surface to freshen the western part of the basin whereas surface salty anomalies are advected in the Leuwin current to salt waters along the Australian coast. The ~0.5°C surface cooling in the IA reduces by 20% the overlying deep convection. This improves both the amount and structure of the rainfall and weakens the wind convergence over the IA, relaxes the equatorial Pacific trade winds and strengthens the winds along Java coast. These wind changes causes the thermocline to be deeper in the eastern equatorial Pacific and shallower in the eastern Indian Ocean. The El Nino Southern Oscillation (ENSO) amplitude is therefore slightly reduced while the Indian Ocean Dipole/Zonal Mode (IODZM) variability increases. IODZM precursors, related to ENSO events the preceding winter in this model, are also shown to be more efficient in promoting an IODZM thanks to an enhanced wind/thermocline coupling. Changes in the coupled system in response tidal mixing are as large as those found when closing the Indonesian Throughflow, emphasizing the key role of IA on the Indo-Pacific climate.     

超强与普通厄尔尼诺海-气特征差异及对西太平洋副热带高压的不同影响

利用NCEP/NCAR再分析资料、GODAS海洋资料、哈得来中心海表温度（SST）以及中国国家气候中心（NCC）环流指数数据,依据美国气候预测中心的厄尔尼诺事件标准筛选出1980-2016年的超强与普通厄尔尼诺事件,对比了两类事件的不同生命阶段内海表及次表层温度特征的差异,并探讨了其对西太平洋副热带高压（西太副高）的不同影响。结果表明,对超强厄尔尼诺事件而言,海表温度正距平发展早且迅速,其大值中心偏东,纬向梯度强,但对普通厄尔尼诺事件而言,海表温度正距平中心偏西,纬向梯度小。厄尔尼诺事件的发展源于次表层海温距平（SOTA）随开尔文波东传并沿温跃层上升到达海表,其波动前部区域异常垂直海流对次表层海温距平的变化起重要作用;当海气激烈耦合时,可在温跃层激发出更强的海洋波动,使得次表层变暖更明显,激发出强的厄尔尼诺事件。海温异常强迫出的大气异常环流的强度与强迫源的强度关系密切。两类厄尔尼诺均能通过异常的沃克环流引起大气Gill型响应,使得西太副高偏强、西伸,且当超强厄尔尼诺发生时,异常沃克环流更强,海洋性大陆区域上空的异常强辐散导致Gill型响应而产生的反气旋更强,对西太副高的影响更甚。印度洋海表温度对厄尔尼诺的滞后变暖所带来的影响在上述亚太大气环流的持续异常中起重要作用。这些结果有利于加深对不同类型厄尔尼诺事件及影响西太副高机理的认识。      

Epochal changes in the seasonal evolution of tropical Indian Ocean warming associated with El Niño

The epochal changes in the seasonal evolution of El Niño induced tropical Indian Ocean (TIO) warming in the context of mid-1970s regime shift is investigated in this study. El Niño induced warming is delayed by one season in the northern TIO during epoch-2 (post mid-1970) and southern TIO during epoch-1 (pre mid-1970). Significant spatiotemporal changes in TIO (especially in the north) warming are apparent during the developing phase of El Niño. The ocean dynamics is the major driver in the basin wide warming during epoch-2 whereas heat fluxes are the dominant processes during epoch-1. Strong coupling between thermocline and sea surface temperature (SST) in epoch-2 indicates that El Niño induced oceanic changes are very significant in the seasonal evolution of basin-wide warming. The thermocline-SST coupling is strengthened by the upward propagating subsurface warming in epoch-2. The westward propagating barrier layer over southern TIO supports persistence of warm SST (over southwest TIO in epoch-2), which in turn induce spring asymmetric mode in winds and precipitation. The asymmetric wind pattern and persistent subsidence over maritime continent are primarily responsible for stronger spring warming in epoch-2. The strong east equatorial Indian Ocean cooling in epoch-2 is mainly driven by coastal upwelling over Java–Sumatra coast, whereas in epoch-1 the weak cooling is controlled by the latent heat flux. The spatiotemporal changes in TIO SST warming and their evolution have strong impact on atmospheric circulation and rainfall distribution over the Indian Oceanic rim through local air–sea interaction.     

THE WARMING MECHANISM IN THE SOUTHERN ARABIAN SEA DURING THE DEVELOPMENT OF INDIAN OCEAN DIPOLE EVENTS

This study aims to explore the relative role of oceanic dynamics and surface heat fluxes in the warming of southern Arabian Sea and southwest Indian Ocean during the development of Indian Ocean Dipole (IOD) events by using National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) daily reanalysis data and Global Ocean Data Assimilation System (GODAS) monthly mean ocean reanalysis data from 1982 to 2013, based on regression analysis, Empirical Orthogonal Function (EOF) analysis and combined with a 2? layer dynamic upper-ocean model. The results show that during the initial stage of IOD events, warm downwelling Rossby waves excited by an anomalous anticyclone over the west Indian Peninsula, southwest Indian Ocean and southeast Indian Ocean lead to the warming of the mixed layer by reducing entrainment cooling. An anomalous anticyclone over the west Indian Peninsula weakens the wind over the Arabian Sea and Somali coast, which helps decrease the sea surface heat loss and shallow the surface mixed layer, and also contributes to the sea surface temperature (SST) warming in the southern Arabian Sea by inhibiting entrainment. The weakened winds increase the SST along the Somali coast by inhibiting upwelling and zonal advection. The wind and net sea surface heat flux anomalies are not significant over the southwest Indian Ocean. During the antecedent stage of IOD events, the warming of the southern Arabian Sea is closely connected with the reduction of entrainment cooling caused by the Rossby waves and the weakened wind. With the appearance of an equatorial easterly wind anomaly, the warming of the southwest Indian Ocean is not only driven by weaker entrainment cooling caused by the Rossby waves, but also by the meridional heat transport carried by Ekman flow. The anomalous sea surface heat flux plays a key role to damp the warming of the west pole of the IOD.     

热带海面温度对亚马逊旱季降水年际变率的影响及机制

用偏最小二乘(Partial Least Square,PLS)回归方法分析了 1979～2018年影响亚马逊旱季(6～8月)降水年际变率的热带海面温度模态.第一海面温度模态解释了总方差的64％,主要表现为前期亚马逊雨季(12月至次年2月)至旱季(6～8月)热带东太平洋La Ni?a型海面温度异常演变.12月至次年2月...     

西北太平洋低空环流与海温异常关系的季节性差异

通过资料分析与数值模拟研究了西北太平洋低空环流特征及其与海面温度（SST）异常关系的季节性差异,得到如下结论：1）西北太平洋低空环流的空间尺度和位置在春季和夏季存在明显差异,从春季到夏季,异常环流范围缩小且中心位置向西北偏移;2）西北太平洋低空环流与西北太平洋局地海温的相互作用存在季节差异,春季西北太平洋冷海温与上空反气旋异常之间存在相互作用,而夏季则以大气影响海洋为主,异常的反气旋/气旋可以加热/冷却其下垫面的海温,大气超前3～4 d影响海洋;3）夏季异常反气旋环流（WNPAC）的维持主要来自非局地海温异常（北印度洋暖海温与中太平洋冷海温异常）的强迫,这两个海区对WNPAC的影响也存在季节性差异,北印度洋的影响主要体现在晚春至盛夏,而中太平洋则主要在晚夏发挥作用。     

厄尼诺现象对热带大气环流影响的研究

应用NMC 17年热带格点风及OLR资料，对比分析了厄尼诺年与反厄尼诺年热带环流的差异，发现厄尼诺现象使多年平均位于西太平洋上的最强盛的对流加热区东移到中太平洋，太平洋热带地区东西向对流加热梯度减弱，造成中东太平洋上的Walker环流及西太平洋与印度洋上的反Walker环流场比常年减弱；同时，厄尼诺现象也使中东太平洋地区经向反Hadley环流及美洲大陆上空的Hadley环流减弱。     

Generation and termination of Indian Ocean dipole events in 2003, 2006 and 2007

Evolution of Indian Ocean Dipole (IOD) events in 2003, 2006 and 2007 is investigated using observational and re-analysis data products. Efforts are made to understand various processes involved in three phases of IOD events; activation, maturation and termination. Three different triggers are found to activate the IOD events. In preceding months leading to the IOD evolution, the thermocline in southeastern Indian Ocean shoals by reflection of near equatorial upwelling Rossby waves at the East African coast into anomalous upwelling equatorial Kelvin waves. Strengthening (weakening) of northern (southern) portion of ITCZ in March/April and May/June of IOD years, leads to strengthening of alongshore winds along Sumatra/Java coasts. With the combined shallow thermocline and increased latent heat flux due to enhanced wind speeds, the SST in the southeastern Indian Ocean cools in following months. On intraseasonal time scales convection-suppressing phase of Madden-Julian oscillation (MJO) propagates from west to east in May/June of IOD year, and easterlies associated with this phase of MJO causes further shoaling of thermocline in southeastern Indian Ocean, through anomalous upwelling Kelvin wave. All these three mechanisms appear to be involved in initiating IOD event in 2006. On the other hand, except the strengthening/weakening of ITCZ, all other mechanisms are involved in activation of 2003 IOD event. Activation of 2007 IOD event was due to propagation of convection-suppressing MJO in May/June and strengthening of mean winds along Sumatra/Java coast from March to June through changes in convection. The IOD events matured into full-fledged events in the following months after activation, by surface heat fluxes, vertical and horizontal advection of cool waters supported by local along-shore upwelling favorable winds and remote equatorial easterly wind anomalies through excitation of upwelling Kelvin waves. Propagating MJO signals in the tropical Indian Ocean brings significant changes in evolution of IOD events on MJO time scales. Termination of 2003 and 2007 IOD events is achieved by strong convection-enhancing MJOs propagating from west to east in the tropical Indian Ocean which deepen the thermocline in the southeastern equatorial Indian Ocean. IOD event in 2006 was terminated by seasonal reversal of monsoon winds along Sumatra/Java coasts which stops the local coastal upwelling.     

印度洋对ENSO事件的响应:观测与模拟

观测事实显示,在El Ni(n～)o期间,伴随着赤道中东太平洋表层海温(SST)的升高,热带印度洋SST出现正距平.作者利用海气耦合模式模拟了印度洋对ENSO事件的上述响应,并进而讨论了其物理机制.所用模式为法国国家科研中心Pierre-Simon-Laplace 全球环境科学联合实验室(IPSL)发展的全球海气耦合模式.该模式成功地控制了气候漂移,能够合理再现印度洋的基本气候态.观测中与ENSO相关的热带印度洋SST变化,表现为全海盆一致的正距平,并且这种变化要滞后赤道中东太平洋SST变化大约一个季度,意味着它主要是对东太平洋SST强迫的一种遥响应,模式结果也支持这一机制,尽管模式中的南方涛动现象被夸大了,使得模拟的与ENSO相关联的SST正距平的位置南移,阿拉伯海和孟加拉湾被负距平(而不是正距平)所控制.研究表明,东太平洋主要通过大气桥影响潜热释放来影响印度洋SST变化.赤道东太平洋El Ni(n～)o事件的发展,导致印度洋上空风场异常自东而西传播;伴随着风场的变化,潜热发生相应变化,并最终导致SST异常的发生.非洲东海岸受索马里急流控制的海域,其SST的变化不能简单地利用热通量的变化来解释.证据显示,印度洋的增暖是ENSO事件发生的结果而不是其前期信号.     

Factors that affect the amplitude of El Nino in global coupled climate models

Historically, El Nino-like events simulated in global coupled climate models have had reduced amplitude compared to observations. Here, El Nino-like phenomena are compared in ten sensitivity experiments using two recent global coupled models. These models have various combinations of horizontal and vertical ocean resolution, ocean physics, and atmospheric model resolution. It is demonstrated that the lower the value of the ocean background vertical diffusivity, the greater the amplitude of El Nino variability which is related primarily to a sharper equatorial thermocline. Among models with low background vertical diffusivity, stronger equatorial zonal wind stress is associated with relatively higher amplitude El Nino variability along with more realistic east–west sea surface temperature (SST) gradient along the equator. The SST seasonal cycle in the eastern tropical Pacific has too much of a semiannual component with a double intertropical convergence zone (ITCZ) in all experiments, and thus does not affect, nor is it affected by, the amplitude of El Nino variability. Systematic errors affecting the spatial variability of El Nino in the experiments are characterized by the eastern equatorial Pacific cold tongue regime extending too far westward into the warm pool. The time scales of interannual variability (as represented by time series of Nino3 SSTs) show significant power in the 3–4 year ENSO band and 2–2.5 year tropospheric biennial oscillation (TBO) band in the model experiments. The TBO periods in the models agree well with the observations, while the ENSO periods are near the short end of the range of 3–6 years observed during the period 1950–94. The close association between interannual variability of equatorial eastern Pacific SSTs and large-scale SST patterns is represented by significant correlations between Nino3 time series and the PC time series of the first EOFs of near-global SSTs in the models and observations. Received: 17 April 2000 / Accepted: 17 August 2000