ENSO对东亚夏季风强度的影响

夏季风的形成和强弱变化是季风问题中的一个重要方面。本文使用１９５１￣１９９２年的海平面气压（ＳＬＰ）和太平洋海表温度（ＳＳＴ）资料,地东亚夏季负强度指数进行研究,试探讨其与ＥＮＳＯ间的联系。结果表明,厄尔尼诺当年,东亚季风偏弱,次年夏季风偏强;反厄尔尼诺年反之。     

Modeling the tropical Pacific Ocean using a regional coupled climate model

A high-resolution tropical Pacific general circulation model (GCM) coupled to a global atmospheric GCM is described in this paper. The atmosphere component is the 5°×4°global general circulation model of the Institute of Atmospheric Physics (IAP) with 9 levels in the vertical direction. The ocean component with a horizontal resolution of 0.5°, is based on a low-resolution model (2°×1°in longitude-latitude).Simulations of the ocean component are first compared with its previous version. Results show that the enhanced ocean horizontal resolution allows an improved ocean state to be simulated; this involves (1) an apparent decrease in errors in the tropical Pacific cold tongue region, which exists in many ocean models,(2) more realistic large-scale flows, and (3) an improved ability to simulate the interannual variability and a reduced root mean square error (RMSE) in a long time integration. In coupling these component models, a monthly "linear-regression" method is employed to correct the model's exchanged flux between the sea and the atmosphere. A 100-year integration conducted with the coupled GCM (CGCM) shows the effectiveness of such a method in reducing climate drift. Results from years 70 to 100 are described.The model produces a reasonably realistic annual cycle of equatorial SST. The large SSTA is confined to the eastern equatorial Pacific with little propagation. Irregular warm and cold events alternate with a broad spectrum of periods between 24 and 50 months, which is very realistic. But the simulated variability is weaker than the observed and is also asymmetric in the sense of the amplitude of the warm and cold events.     

Interannual variations of the boreal summer intraseasonal variability predicted by ten atmosphere–ocean coupled models

The reproducibility of boreal summer intraseasonal variability (ISV) and its interannual variation by dynamical models are assessed through diagnosing 21-year retrospective forecasts from ten state-of-the-art ocean–atmosphere coupled prediction models. To facilitate the assessment, we have defined the strength of ISV activity by the standard deviation of 20–90 days filtered precipitation during the boreal summer of each year. The observed climatological ISV activity exhibits its largest values over the western North Pacific and Indian monsoon regions. The notable interannual variation of ISV activity is found primarily over the western North Pacific in observation while most models have the largest variability over the central tropical Pacific and exhibit a wide range of variability in spatial patterns that are different from observation. Although the models have large systematic biases in spatial pattern of dominant variability, the leading EOF modes of the ISV activity in the models are closely linked to the models’ El Nino-Southern Oscillation (ENSO), which is a feature that resembles the observed ISV and ENSO relationship. The ENSO-induced easterly vertical shear anomalies in the western and central tropical Pacific, where the summer mean vertical wind shear is weak, result in ENSO-related changes of ISV activity in both observation and models. It is found that the principal components of the predicted dominant modes of ISV activity fluctuate in a very similar way with observed ones. The model biases in the dominant modes are systematic and related to the external SST forcing. Thus the statistical correction method of this study based on singular value decomposition is capable of removing a large portion of the systematic errors in the predicted spatial patterns. The 21-year-averaged pattern correlation skill increases from 0.25 to 0.65 over the entire Asian monsoon region after applying the bias correction method to the multi-model ensemble mean prediction.     

Different Impacts of Typical and Atypical ENSO on the Indian Summer Rainfall: ENSO-Developing Phase

The El Niño–Southern Oscillation (ENSO) is a main driving force of the northern hemisphere summer monsoon rainfall, including the Indian Summer Rainfall (ISR). The impacts of typical ENSO and atypical ENSO events on the ISR remain unclear during their developing summers. This study examines the different linkages between a typical ENSO and the ISR and between an a typical ENSO and the ISR. During the developing summer of a typical El Niño, negative rainfall anomalies are seen over the northeastern Indian subcontinent, while the anomalous rainfall pattern is almost the opposite for a typical La Niña; as for an atypical ENSO, the approximate “linear opposite” phenomenon vanishes. Furthermore, an anomalous global zonal wave train is found at mid-latitudes, with a local tripole circulation pattern over central–eastern Eurasia during the developing summer of a typical ENSO, which might explain the corresponding rainfall response over the Indian Peninsula. By contrast, such features are not obvious during the developing summer of an atypical ENSO. Among 106-year historical runs (1900–2005) of nine state-of-the-art models from the Coupled Model Intercomparison Project, Phase 5 (CMIP5), HadGEM2-ES exhibits promising skill in simulating the anomalous circulation pattern over mid-latitudes and central–eastern Eurasia. Probably, it is the model’s ability to capture the linkage between a typical ENSO and the ISR and the characteristics of a typical ENSO that makes the difference.     

Revisiting Asymmetry for the Decaying Phases of El Nino and La Nina

This study investigated the relationship be- tween the asymmetry in the duration of El Nifio and La Nina and the length of their decaying phases. The results suggested that the duration asymmetry comes from the long decaying ENSO cases rather than the short decaying ones. The evolutions of short decaying El Nino and La Nina are approximately a mirror image with a rapid decline in the following summer for the warm and cold events. However, a robust asymmetry was found in long decaying cases, with a prolonged and re-intensified La Nina in the following winter. The asymmetry for long decaying cases starts from the westward extension of the zonal wind anomalies in a mature winter, and is further contributed to by the air-sea interaction over the tropical Pacific in the following seasons.     

黑潮SSTA与赤道太平洋风场及ENSO关系初探

利用NCEP/NCAR的1950—1998年海表温度场和1958—1997年海表风场再分析资料,采用相关、合成等分析方法,研究了黑潮区域SSTA(sea surface temperature anomaly)与太平洋风场的关系。结果表明:从SSTA滞后风场3月起,与其关系密切的经向风关键区位于赤道西太平洋(140~160°E,5°S~5°N),纬向风关键区位于赤道中太平洋(160°E~150°W,5°S~5°N),两者对SSTA的影响均可持续6月左右;纬向风关键区的强度和范围均大于经向风。进一步研究表明,黑潮SS-TA与ENSO事件有着密切的联系:E l N ino(La N ina)事件当年11月—次年12月期间黑潮海温多为正(负)异常。     

东南亚地区年际降水变化及其与ENSO的关系

用Chen等最新创建的全球陆地和海洋的月降水资料（PREC／L和PREC／O），采用加权平均的降水距平指数和旱涝面积指数分别划分1948-2002年东南亚地区年、季的旱涝年，并对划分的旱、涝年进行了旱涝年差异的Monte Carlo检验。研究了东南亚地区降水与ENSO的关系，指出东南亚地区年、秋季和冬季的降水与ENSO事件的关系比较密切，春季降水与其关系稍差一些，夏季与ENSO事件没有明显的联系。研究了东南亚地区旱涝年的分布规律和特征，指出1948-1959年期间除了夏季旱年比涝年多以外，年和春、秋、冬季都是涝年明显多于旱年，60年代年、四季的旱涝相差不多，年和夏季在70年代涝多于旱，春、秋、冬季旱涝相同；1980-1989年是旱年的多发期；1990-2002年期间旱涝年频繁爆发，旱年多于涝年。通过计算东南亚地区年、季的降水趋势系数，得出东南亚地区年、季的降水量大都存在下降趋势，其中年和秋季的下降趋势很明显，春夏两季存在弱的下降趋势，而冬季则有较弱的上升趋势。     

Interannual heat content variability in the South China Sea and its response to ENSO

The interannual variability of upper ocean heat content (OHC) in the South China Sea (SCS) for the period of 1987–2006 and its response to ENSO events are investigated. It is found that the variability has a good correspondence with ENSO events, but with opposite phase. Negative OHC anomalies appear during ENSO warm phases, while positive OHC anomalies occur during ENSO cool phases. In addition, negative (positive) OHC anomalies propagate westward obviously during ENSO warm (cool) phases in the northern SCS. In contrast, OHC anomalies in the southern SCS do not exhibit distinct westward propagation during ENSO events. To explore why the OHC anomalies cannot propagate westward in the southern SCS, the interannual variability of oceanic and atmospheric anomaly fields including wind stress curl (WSC), horizontal wind stress, latent heat flux (LHF) and sea level pressure (SLP) is investigated. The results show that after a mature phase of ENSO warm (cool) event, negative (positive) OHC anomalies first appear in the northern SCS, which comes from the western Pacific through Luzon Strait. Then cyclonic (anticyclonic) wind stress anomalies occur in the northern SCS, which leads to positive (negative) WSC anomalies. Meanwhile, positive (negative) LHF anomalies which correspond to oceanic heat loss (gain) occur in this region. The effects of WSC and LHF, combined with the westward propagating negative (positive) OHC anomalies from the western Pacific, may contribute to rapid growth and propagation of the OHC anomalies in the northern SCS. On the contrary, the negative (positive) WSC and LHF anomalies associated with positive (negative) SLP in the southern SCS seem to be the important processes responsible for the weakening and non-propagation of the OHC anomalies in the southern SCS after a mature phase of ENSO warm (cool) event.     

LAP ENSO预测系统预报技巧的时间依赖性及对1999年La Nia事件的预测

利用LAPENSO预测系统对 1981年 11月至 1997年 12月系统性回报实验的结果 ,分析了预报技巧的时间依赖性。结果表明 :该预测系统对 80年代的ENSO具有较强的预报能力 ,在Nino 3区接近 0 8预报相关技巧 (预报与观测的相关系数 )可达到 1年半左右 ,而对 90年代的ENSO现象 ,预报技巧则较低 ,超前半年以上的预报仅在 0 4左右 ;预报技巧具有季节依赖性 ,从春季到秋初开始的预报较好 ,高于 0 5的技巧均可维持 15个月以上 ,其中从 7月到 9月开始的预报 ,其高于 0 6的相关技巧可达 16个月 ;而从秋末和冬季开始的预报 ,其技巧衰减较快 ,预报 5个月后降到 0 5以下。对 1999年LaNi na事件的实时预测总体上是成功的 ,即此次LaNI na事件将维持到 2 0 0 0年 ;但未能预测出其在 1999年春季以后再次加强的过程。对其未来变化趋势的预测显示 ,此次LaNi na事件有可能于今年夏秋季结束     

热带太平洋与印度洋相互作用的年代际变化

利用全球海表海温资料（GISST）和NCEP／NCAR再分析资料,研究了热带太平洋与印度洋之间的相互作用及其在不同年代二者作用关系的变化。结果表明：热带印度洋偶板子指数超前热带太平洋Nin03指数2月时相关最大,印度洋单板子指数滞后Nin03指数3～4月时相关最大。印度洋偶板子在一定程度上影响E1 Nino事件的发生,而E1 Nino事件的发生、发展会影响印度洋单板子事件的发生。热带印度洋偶板子事件与热带太平洋ENSO事件的相互作用在1961年发生了明显跃变,其原因可能是1961年之前热带印度洋偶板子对热带太平洋上空的纬向风影响很小,而1961年以后其影响明显加强。热带印度洋单板子事件与热带太平洋ENSO事件的相关一直显著,没有明显跃变。