冬季欧亚海平面气压场主要空间模态的年代际变化特征

运用非线性主成分分析法对欧亚地区1948-2007年冬季海平面气压距平场进行分析。结果表明：冬季欧亚地区海平面气压异常变率具有显著的非线性特征,当非线性主成分取不同的异常值时,对应的空间气压异常分布型具有显著的非对称性。同时,第一非线性模态（NLPC1）年际振荡强度和周期在20世纪70年代初存在明显的年代际变化,1970年以后,年际振荡强度显著增强。     

冬季欧亚海平面气压场主要空间模态的年代际变化特征

 运用非线性主成分分析法对欧亚地区1948-2007年冬季海平面气压距平场进行分析。结果表明：冬季欧亚地区海平面气压异常变率具有显著的非线性特征,当非线性主成分取不同的异常值时,对应的空间气压异常分布型具有显著的非对称性。同时,第一非线性模态（NLPC1）年际振荡强度和周期在20世纪70年代初存在明显的年代际变化,1970年以后,年际振荡强度显著增强。     

EOF/PCA诊断气象变量场问题的新探讨

进一步论证了经验正交函数/主分量分析(EOF/PCA)在气象变量场诊断中的物理内涵,证明基于EOF/PCA的R型和Q型展开,可描述为气象变量场主要振荡型分解和主要空间分布型分解两种方案.前者表明,气象变量场的准周期振荡可分解为各主分量的周期振荡,它们各自等价于不同网格点(或站点)以其载荷为权重的迭加周期振荡,因此,气象变量场准周期振荡可视为来自不同周期源(网格点或站点)的准周期振荡逐层叠加的结果;后者表明,气象变量场的水平空间分布可视为各种主要空间分布型的叠加,而Q型展开才是对各种主要空间分布型的正交分解.由此深化了EOF/PCA气象变量场诊断的物理内涵.     

北半球夏季500hPa候平均高度场的遥相关和环流特征

本文用10年(1980—1989)夏季北半球500hPa候平均高度场资料进行遥相关分析,得到东亚太平洋型(EAP)和西欧型(WE)两种遥相关型及西亚-太平洋-大西洋振荡,并对高度场进行主成分分析(PCA),讨论了环流的时空分布特征.     

云南盛夏大雨物理量因子的选取及效果检验

从物理量因子场与云南盛夏（7－8月）大雨作为预报量之间的相关系数计算入手，通过相关场分析来提取因子信息，经过不同组合试验，选出新的预报因子。检验表明，新的组合因子与预报量之间的相关性有明显提高。由此而建立的预报方程有较好的历史拟合率和较稳定的实际预报能力。     

云南盛夏大雨物理量因子的选取及效果检验

从物理量因子场与云南盛夏（７－８月）大雨作为预报量之间的相关系数计算入手，通过相关场分析来提取因子信息，经过不同组合试验，选出新的预报因子，检验表明，新的组合因子与预报量之间的相关性有明显提高。由此而建立的预报方程有较好的历史拟合率和较稳定的实际预报能力。     

气候场的主分量逐步回归预测模型及应用

提出一种气候场的主分量逐步回归预测模型,该模型将气候场的预测变成对该场主分量的预测。提取对气候场变化有重要影响的500 hPa高度、太平洋及印度洋海温和全球海平面气压等含不同区域不同季节的因子场的前若干个含高信息量的优质主分量因子。通过相关筛选和双重检验逐步回归,建立气候场的主分量的预测方程,由此就建立气候场与多个因子场之间的联系,但是模型却仍然保持着两个场相关的特点。根据气候场的特征向量的近似不变性,将其与主分量配合进行反算,从而得到气候场的预测。以广东汛期降水预测作为试验例子,计算了它的主分量,分析了它的时空分布特征及分类,对2003—2005年的分布作预测并与实测分布作比较及进行误差检测,发现预测效能显著。有关预测的年限、区域范围、要素和因子的物理背景等问题有待进一步研究。     

长江下游旱涝与夏半年欧亚环流30～60天振荡的年际变化

对 2 5a(1 971～ 1 995年 )逐候东半球热带外 50 0 h Pa高度距平场进行小波分析和旋转主成分分析 ,研究了 30～ 60 d低频振荡的时空变化及其与长江下游夏季旱涝和暴雨频数年际变化的关系。结果表明 :6～ 1 0月欧亚型 (EU)低频振荡强度与长江下游暴雨频数成显著负相关 ,同时 ,提出了能揭示变量间非线性关系的对比函数分析 (CFA)方法 ,发现当 5～ 8月西太平洋型 (WP)低频流型偏强时 ,长江下游暴雨频数增加 ,容易发生洪涝 ;反之 ,无明显影响。仅当前期 3～ 5月南亚大陆型偏强时长江下游降水量偏少 ,而 3～ 5月南亚大陆型偏弱时暴雨频数明显增加。因此 ,长江下游旱涝与低频流型异常之间同时存在线性和非线性相关。     

四川主汛期降水与西风环流指数的典型相关分析

在气候变化研究中,存在着大量两个变量场之间的相关问题,本文利用场相关理论分析了四川6～8月降水场与16个环流指数的相关关系得到一些有意义的结果1)1～5月的环流因子中,亚洲经向环流指数、西太平洋副高脊线、北半球极涡中心强度是影响四川汛期降水的最显著因子2)1～5月环流指数对四川夏季降水空间分布的影响主要是东西振荡分布3)四川主汛期降水变化的敏感点在康定、雅安和广元、内江4)4月西太平洋副热带高压脊线西伸明显,汛期川西北产生多雨, 5月西太平洋副热带高压脊线偏北西伸,则汛期川南多雨6)亚洲经向环流对四川降水的影响主要是一致性分布,而且在相关性上主要是正相关7)前期(1～5月)环流指数与夏季降水场的相关关系中,4月和5月的典型变量时间序列存在11年的周期,其余都无周期.     

北半球冬季环流异常与ENSO的非线性关系

运用非线性典型相关分析（nonlinear canonical correlation analysis,简称NLCCA）方法,对热带太平洋海表温度异常（SSTA）场与北半球冬季海平面气压异常场（SLPA）进行非线性分析,以反映ENSO与北半球冬季环流异常之间的非线性关系。NLCCA的结果表明：从极冷到极暖期,北半球冬季SLPA场对ENSO的投影在各主成分所分别构成的平面或空间中分别形成一条直线和一条抛物线,说明北半球冬季环流异常与ENSO的相关包含线性和具有二次特征的非线性两部分。无论ENSO的冷、暖事件都能导致冰岛低压减弱,且西伯利亚高压、北美高压和北太平洋高压随SSTA的变化不对称,进一步证明了ENSO对北半球冬季环流异常的非线性影响,其中冰岛低压对于ENSO响应的非线性特征最强,而阿留中低压与ENSO则主要是线性相关。     

Predictability of Indian Ocean sea surface temperature using canonical correlation analysis

There is strong evidence that Indian Ocean sea surface temperatures (SSTs) influence the climate variability of Southern Asia and Africa; hence, accurate prediction of these SSTs is a high priority. In this study, we use canonical correlation analysis (CCA) to design empirical models to assess the predictability of tropical Indian Ocean SST from sea level pressure (SLP) and SST themselves with lead-times up to one year. One model uses the first twelve empirical orthogonal functions (EOFs) of SLP over the Indian Ocean using different lead-times to predict SST. A CCA model with EOFs of SST as the predictor at the same lead-times is compared to SLP as a predictor and shows the auto-correlation of the system. A CCA using the first five extended empirical orthogonal functions (EEOFs) of sea level pressure over the Indian Ocean basin for an interval of two years combined with SST EOFs as predictors is found to produce the greatest correlation between forecast and observed SSTs. This model obtains higher skill by explicitly considering the development in time of SLP anomalies in the region. The skill of this model, assessed from retroactive forecasts of an 18 year period, shows improvement relative to other empirical forecasts particularly for the central and eastern Indian Ocean and boreal autumn months preceding the Southern Hemisphere summer rainfall season. This is likely due to the limited domain of this model identifying modes of variability that are more pronounced in these areas during this season. Finally, a nonlinear canonical correlation analysis (NLCCA) derived from a neural network is used to analyze the leading nonlinear modes. These nonlinear modes differ from the linear CCA modes with distinct cold and warm SST phases suggesting a nonlinear relationship between SST and SLP over the tropical Indian Ocean.     

On the separability of the North Atlantic oscillation and Arctic oscillation

We address the issue of whether the Arctic (AO), and North Atlantic oscillations (NAO) are inseparable, forming an annular mode in the Northern Hemisphere atmospheric circulation. This annular mode is the leading empirical orthogonal function of hemispheric sea level pressure (SLP) data, explaining the largest amount of its variability. We examine whether the NAO and AO are inseparable spatial modes of the atmospheric circulation using rotated principal component analysis (RPCA), a methodology that identifies simple and unique patterns of spatial dataset variability. RPCA of the spring, summer, and autumn SLP fields from 1946-1998 reveal NAO and AO-like patterns, occurring as separate regional teleconnections forming the first and second principal components respectively. The RPCA-based NAO dipole pattern is like that observed in many prior studies, while the AO-like pattern exhibits high SLP variability over the Kara and Laptev seas. During winter however, and in annual analyses, a distinct AO-like pattern is not obtained and the two patterns may be inseparable using commonly accepted RPCA methods. The RPCA-based AO-like mode is significantly linked to north-central Siberian seasonal air temperatures and to the prevailing direction of motion of the underlying Arctic Ocean in summer, suggesting that the non-winter AO-like pattern, as a stand alone teleconnection separate from the NAO, contributes significantly to high-latitude climate and ocean variability. The winter NAO/AO inseparability is discussed as a possible effect of a shared winter storm track between the northeastern Atlantic and the Arctic.     

Distinct Modes of Winter Arctic Sea Ice Motion and Their Associations with Surface Wind Variability

Using monthly mean sea ice velocity data obtained from the International Arctic Buoy Programme (IABP) for the period of 1979–1998 and the monthly mean NCEP/NCAR re-analysis dataset (1960–2002), we investigated the spatiotemporal evolution of the leading sea ice motion mode (based on a complex correlation matrix constructed of normalized sea ice motion velocity) and their association with sea level pressure (SLP) and the predominant modes of surface wind field variability. The results indicate that the leadi...     

Mediterranean wave climate variability and its links with NAO and Indian Monsoon

This study examines the variability of the monthly average significant wave height (SWH) field in the Mediterranean Sea, in the period 1958–2001. The analysed data are provided by simulations carried out using the WAM model (WAMDI group, 1988) forced by the wind fields of the ERA-40 (ECMWF Re-Analysis). Comparison with buoy observations, satellite data, and simulations forced by higher resolution wind fields shows that, though results underestimate the actual SWH, they provide a reliable representation of its real space and time variability. Principal component analysis (PCA) shows that the annual cycle is characterised by two main empirical orthogonal functions (EOF) patterns. Most inter-monthly variability is associated with the first EOF, whose positive/negative phase is due to the action of Mistral/Etesian wind regimes. The second EOF is related to the action of southerly winds (Libeccio and Sirocco). The annual cycle presents two main seasons, winter and summer characterised, the first, by the prevalence of eastwards and southeastwards propagating waves all over the basin, and the second, by high southwards propagating waves in the Aegean Sea and Levantin Basin. Spring and fall are transitional seasons, characterised by northwards and northeastwards propagating waves, associated to an intense meridional atmospheric circulation, and by attenuation and amplification, respectively, of the action of Mistral. These wave field variability patterns are associated with consistent sea level pressure (SLP) and surface wind field structures. The intensity of the SWH field shows large inter-annual and inter-decadal variability and a statistically significant decreasing trend of mean winter values. The winter average SWH is anti-correlated with the winter NAO (North Atlantic Oscillation) index, which shows a correspondingly increasing trend. During summer, a minor component of the wave field inter-annual variability (associated to the second EOF) presents a statistically significant correlation with the Indian Monsoon reflecting its influence on the meridional Mediterranean circulation. However, the SLP patterns associated with the SWH inter-annual variability reveal structures different from NAO and Monsoon circulation. In fact, wave field variability is conditioned by regional storminess in combination with the effect of fetch. The latter is likely to be the most important. Therefore, the inter-annual variability of the mean SWH is associated to SLP patterns, which present their most intense features above or close to Mediterranean region, where they are most effective for wave generation.

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Large-scale variability modes of freshwater flux and precipitation over the Atlantic

 Precipitation (P) and freshwater (E-P) fluxes at the air-sea interface are investigated in the Atlantic Ocean sector using the reanalyses of the European Centre for Medium Range Weather Forecasts (ERA) and of the National Centers for Environmental Prediction (NCEP). A canonical correlation analysis method between these fields and sea level pressure (SLP) is used to identify patterns. We also test whether precipitation and freshwater fluxes can be reconstructed from SLP data. In the winter months, patterns associated with both the North Atlantic Oscillation (NAO) and the East Atlantic (EA) mode are identified. The signals are strong enough to be reconstructed from the reanalysis fields, and they correspond to a significant part of the variability. The NAO signal is more robust than the EA one. The NAO-related variability mode is also present when the monthly precipitation rate is averaged for the winter season and even for annual averages. However, in the later case, other variability of natural origin (for instance, ENSO variability) or noise from the model and assimilation system prevents the reconstruction of E-P associated with NAO from SLP variability. Difficulties are identified in the tropical Atlantic with a different behaviour of NCEP and ERA precipitation variability, especially near the Inter Tropical Convergence Zone (ITCZ). The ERA patterns suggest a NAO signature in the tropical Atlantic which has clear monthly patterns and indicates a link between the phase of NAO and changes in the position and intensity of ITCZ. However, the analysis of winter rainfall based on satellite and in situ data does not support the monthly tropical pattern of ERA precipitation although it suggests a relation between convection near 15°S and NAO during northern winter. Received: 10 February 2000 / Accepted: 7 May 2001     

福建春雨多时空尺度变化特征

利用主成分分析和相关分析表明,近40 a来福建春雨量场的主要信息集中在前2个主分量上,可解释方差的83.8%,同时第1、第2主成分与福州、厦门春雨的相关显著性水平都超过0.01,因此,可用近百年福州、厦门3—4月降水量构造新序列代表福建春雨的前2个主分量,使分析资料延长至百年。采用连续小波分析和正交小波分析方法以及功率谱方法,研究福建春雨空间分布型的多时间尺度特征,研究结果表明：第1主分量表示的全省一致性旱涝具有显著的准4 a和24～26a的周期振荡;第2主分量表示的春雨分布南北差异主要表现为准两年和准11 a的周期振荡;春旱年南部的降水少于北部;从年代际角度看,20世纪50—60年代显著偏少,80年代显著偏多。福建目前处于春雨正常—偏少期,且南部的春旱比北部严重。     

近40年来东亚冬季风的年代际时空变化趋势

利用经验正交函数－奇异值分解（EOF－SVD）综合分析方法和1961～2000年NCEP/NCAR月平均再分析资料对近40年来东亚冬季风和冬季表面气温的年代际变化特征及其相关关系进行了分析。研究结果表明, EOF得到的冬季海平面气压场主成分空间结构（第一特征向量）及其时间系数可以较好地反映出东亚冬季风的变化, 而且可以同时得到东亚冬季风强度和南扩程度的变化, 具有一定的优越性。通过对冬季海平面气压和表面气温年代际分量的EOF－SVD综合分析, 发现了东亚冬季风强度减弱、南扩加强的年代际变化趋势, 冬季表面气温则表现出中高纬地区海陆热力差异减弱、低纬地区海陆热力差异加强的年代际变化特征, 两者之间存在很好的对应关系。另外, 大陆冬季表面气温与海平面气压的年代际对应关系比海洋的更加显著, 表明对温室效应的区域气候响应与东亚冬季风的年代际变化之间可能存在较为密切的联系。     

基于PC-CCA方法的气象场资料插补试验

引入主成分典型相关分析（ＰＣ－ＣＣＡ）方法建立缺测气象要素场序列的插补模式,对区域性气象场序列（以长江流域月气温距平场为例）各种时空缺测分布型态作插补试验。结果表明,当插补场站网分布型取包含子场在内的混合站网时,建模样本量达２５年就可有最优插补精度,且性能稳定,效果优良。尤其当距平符号单一且大尺度分量占优势时,插补精度随缺测场变化很小     

冬季北太平洋风暴轴的年际型态及其与大气环流的关系

利用NCEP/NCAR再分析资料,运用31点带通数字滤波、线性相关和合成分析方法,研究了1961/1962—2010/2011年冬季北太平洋风暴轴西部、东部区域强度指数的年际演变特征,划分了风暴轴的典型型态,并进一步探讨了与同期北半球500 hPa位势高度场和SLP的关系。结果表明:风暴轴气候态的极大值区域位于中纬度北太平洋中西部,最大值点的频数集中区域和均方差分布的异常中心都有两个。风暴轴西部和东部区域强度指数(WI和EI)的年际演变具有独立性,典型型态可分为单、双中心型两类。WI(EI)指数与北半球500 hPa位势高度场的相关分布类似于WP(PNA)遥相关型;单中心型风暴轴偏强时,极涡南扩,平均槽加深;呈双中心型时,极涡明显偏西。WI(EI)指数与SLP的相关分布类似于NPO(NAO)遥相关型;单中心型风暴轴偏强(弱)时,SLP距平场呈AO遥相关型的正(负)异常位相。     

The natural oscillation of two types of ENSO events based on analyses of CMIP5 model control runs

The eastern-and central-Pacific El Ni（n）o-Southem Oscillation （EP-and CP-ENSO） have been found to be dominant in the tropical Pacific Ocean,and are characterized by interannual and decadal oscillation,respectively.In the present study,we defined the EP-and CP-ENSO modes by singular value decomposition （SVD） between SST and sea level pressure （SLP） anomalous fields.We evaluated the natural features of these two types of ENSO modes as simulated by the pre-industrial control runs of 20 models involved in phase five of the Coupled Model Intercomparison Project （CMIP5）.The results suggested that all the models show good skill in simulating the SST and SLP anomaly dipolar structures for the EP-ENSO mode,but only 12 exhibit good performance in simulating the tripolar CP-ENSO modes.Wavelet analysis suggested that the ensemble principal components in these 12 models exhibit an interannual and multi-decadal oscillation related to the EP-and CP-ENSO,respectively.Since there are no changes in external forcing in the pre-industrial control runs,such a result implies that the decadal oscillation of CP-ENSO is possibly a result of natural climate variability rather than external forcing.