CLIMATIC FEATURES OF SEA TEMPERATURE OF WARM POOL AND RELATIONSHIP WITH SST OF ITS ADJACENT REGIONS*

In this paper,climatic features of sea temperature of western Pacific warm pool and the relationship with sea surface temperature (SST) of its adjacent regions are analyzed based on the observed sea temperature on vertical cross section along 137°E in western Pacific,the monthly mean SST of Xisha Station in South China Sea and the global monthly mean SST with resolution of 1°×1° (U.K./GISST2.2).The results indicate that (1) in a sense of correlation.SST of western Pacific warm pool can represent its sea subsurface temperature from surface to 200 m-depth level in winter,and it can only represent sea temperature from surface to 70 m depth in summer.The sea subsurface temperature anomaly of warm pool may be more suitable for representing thermal regime of western Pacific warm pool.The sea subsurface temperature of warm pool has a characteristic of quasi-biennial oscillation.(2)Warm pool and Kuroshio current are subject to different ocean current systems (3)Furthermore,the relationship between SST of Xisha Station and SST of warm pool has a characteristic of negative correlation in winter and positive correlation in summer,and a better lag negative correlation of SST of Xisha Station with sea subsurface temperature of warm pool exists.(4)Additionally,oscillation structure of sea temperature like "a seesaw" exists in between warm pool and Regions Nino3 and Nino4.January (June) maximum (minimum) sea subsurface temperature anomaly of warm pool may serve as a strong signal that indicates maturity phase (development phase) of La Nina (El Nino) event,it also acts as a strong signal which reveals variations of SST of Regions Nino3 and Nino4.     

On quasi–biennial oscillation in air–sea system

From the COADS (Comprehensive Ocean-Atmosphere Data Set) I and the COADS II, we got a monthly data set of sea surface temperature (SST). zonal and meridional wind components at sea level (U,V) and sea level pressure (SLP) with 4o × 4o grid system covering the period from Jan. 1950 to Dec. 1987 to study the evolutional features of the quasi-biennial oscillation (QBO) in the air-sea system. The analytic method of complex empirical orthogonal function (CEOF) is used to obtain the composite temporal sequences of amplitude (six phases for half a period) for the first and the second main components of SST, U, V and SLP. It is shown from the results that the main character-istics for different phases of the sea surface temperature anomaly’s (SSTA) QBO are warm water / cold water in the equator of the eastern Pacific (EEP). There are two warm or cold water centers of the SSTA in the EEP, which are lo-cated in the equator of the central Pacific (ECP) and the east part of the EEP. The features of the source propagation and the influence of these two centers on atmospheric circulation are discussed and it can be seen that in the forma-tion of these two centers, there are different features in oceanic and atmospheric circulations and air-sea coupled pro-cess.     

The propagation characteristics of interannual low-frequency oscillations in the tropical air-sea system

The time series of sea surface temperature (SST), sea level pressure (SLP), zonal wind (U) and total cloudiness (CA), for the period of 1950-1979, over a 8o×8o grid-point latitudinal belt between 32oS and 32oN are made from COADS (Comprehensive Ocean-Atmosphere Data Set). The time harmonic analysis and power spectra analysis show that there exist quasi-biennial oscillation (QBO), three and half years oscillation (SO), five and half years oscillation (FYO) and eleven years oscillation (EYO) in these time series. The main propagation characteristics of these interannual low-frequency oscillations are as follows:(1) The variance analysis of SST shows that there is an active region of QBO and SO (with maximum variance), coming from the southwestern part of the subtropical Pacific, stretching eastward up to the west coast of South America, and then northward to the eastern equatorial Pacific. The QBO and SO disturbances of SST follow the same route and cause the anomaly of SST (El Nino and period of cold water) in the eastern equatorial Pacific.(2) Either the QBO or SO of SST can cause El Nino events, although it is easier when they are situated in the same phase of warm water at the eastern equatorial Pacific. The FYO of SST seems to be a standing oscillation. It plays an important role on the formation of strong El Nino events or strong cold water events.(3) The QBO and SO of U propagate eastward along the equator. The origin of QBO and SO may at least be traced as far as the western Indian Ocean. While they propagate along the equator, it strengthens two times at 90oE and the western Pacific, respectively. Like SST, the FYO of U is somehow a standing oscillation.(4) The Oscillations of U have a good coupling relationship with those of SST, while they propagate. When the QBO and SO of SST move to the east side of the eastern equatorial Pacific, it is the time for the QBO and SO of U to enter into the east part of the western Pacific.It is clear that, when we do research work on the formation of El Nino events, our consideration would not be confined to the tropics, it should cover the subtropical region in the southern Pacific. The features of the circulation and other oceanic states in this area are very important to the El Nino events.     

中国东部北方地区冬季降雪的时空特征及其与全球异常海温的联系

基于中国东部北方地区279个气象台站1961-2008年的观测资料,以及1°×1°的全球海表温度资料,运用主成分分析、小波分析、相关分析等方法探讨中国东部北方地区冬季降雪的时空特征及同期全球海温与其的相关性。研究发现：中国东部北方区域（以下简称研究区）冬季降雪量存在2-3a、7-8a的高频振荡周期,及一个准16a的年代际尺度的低频振荡周期。在1961-2008年间,研究区域冬季降雪量总体呈现上升趋势,特别是45°N以北的研究区北部区域冬季降雪量在48年问增加显著,而45°N以南的研究区南部区域冬季降雪量变化并不明显。分析发现,位于北大西洋上30°-50°N,10°-40°W海区的海温与研究区域降雪的第一、二特征向量均为显著的正相关,研究区北部冬季降雪量与海温关系密切,南部区域冬季降雪量与全球海温的相关性不明显,海温变暖可能是导致研究区北部降雪显著增加的重要因素。     

THE EFFECTS OF THE ARCTIC SEA ICE ON THE VARIATIONS OF ATMOSPHERIC GENERAL CIRCULATION AND CLIMATE

The SST anomaly of the central-eastern equatorial Pacific and the arctic sea ice anomalies of the four districts lo-cated respectively in 160°E—110°W,110°W—20°W,70°E—160°E and 20°W—70°E are taken as five separate factors.And the relationship between each factor and the atmospheric general circulation and the climate is investigated byobservational analysis and numerical experiments.It is shown that the effects of the arctic sea ice anomalies on the varia-tions of atmospheric circulation and climate are comparable to or even in some cases greater than that of EI Ninoevents.So one should pay much attention to the study of polar sea ice anomalies in climate research.     

A NUMERICAL STUDY OF SHORT-RANGE CLIMATIC OSCILLATION WITH VARIOUS TIME SCALES FORCED BY EL NINO DURING THE NORTHERN SUMMER

The normal mode method is adopted to decompose the differences between simulations with SST(seasurface temperature)anomahes over centra-eastern Pacific and normal SST by use of a nine-layer global spec-tral model in order to investigate short-range climatic oscillation with various time scales forced by ElNino during the northern summer.Investigation shows that El Nino may have the following influence onatmosphere on various space-time scales.Extra-long wave components of Rossby mode forced by convectiveanomaly over equatorial western Pacific resulting from El Nino produce climatic oscillation on monthly(sea-sonal)time scale in middle-high latitudes of Southern and Northern Hemispheres;extra-long wave componentsof Kelvin mode forced by SST anomalies propagate along the equator,resulting in 30—60 day oscillation oftropical and subtropical atmosphere;and its long waves move eastward with westerly,resulting in quasi-biweekoscillation.     

Multi-stage onset of the summer monsoon over the western North Pacific

 The climatological summer monsoon onset displays a distinct step wise northeastward movement over the South China Sea and the western North Pacific (WNP) (110°–160°E, 10°–20°N). Monsoon rain commences over the South China Sea-Philippines region in mid-May, extends abruptly to the southwestern Philippine Sea in early to mid-June, and finally penetrates to the northeastern part of the domain around mid-July. In association, three abrupt changes are identified in the atmospheric circulation. Specifically, the WNP subtropical high displays a sudden eastward retreat or quick northward displacement and the monsoon trough pushes abruptly eastward or northeastward at the onset of the three stages. The step wise movement of the onset results from the slow northeastward seasonal evolution of large-scale circulation and the phase-locked intraseasonal oscillation (ISO). The seasonal evolution establishes a large-scale background for the development of convection and the ISO triggers deep convection. The ISO over the WNP has a dominant period of about 20–30 days. This determines up the time interval between the consecutive stages of the monsoon onset. From the atmospheric perspective, the seasonal sea surface temperature (SST) change in the WNP plays a critical role in the northeastward advance of the onset. The seasonal northeastward march of the warmest SST tongue (SST exceeding 29.5 °C) favors the northeastward movement of the monsoon trough and the high convective instability region. The seasonal SST change, in turn, is affected by the monsoon through cloud-radiation and wind-evaporation feedbacks. Received: 19 October 1999 / Accepted: 5 June 2000     

长江梅雨的长期变率与海洋的关系及其可预报性研究

采用最新发布的梅雨国家标准资料,以长江区域梅雨为代表,在分析区域梅雨的多时间尺度变化特征的基础上,从海洋外强迫影响因子角度探讨了梅雨的可预报性来源,进一步综合海洋背景变率和预测模型回报试验讨论梅雨异常的可预报性。结果表明:（1）长江梅雨呈现周期为3-4、6-8、12-16、32、64 a的多时间尺度变化分量和长期减少趋势。其中,3-4 a准周期变化是梅雨异常变化的主要分量。梅雨的干湿位相转变受12-16 a的准周期变化调制,极端涝年易出现在12-16 a准周期变化湿位相和3-4 a变化分量峰值位相叠加的情况。（2）长江梅雨的各准周期变化分量有不同的海洋外强迫背景,是梅雨可预报性的重要来源。与时间尺度较短的年际变化分量相关联的海温关键区主要分布于热带,而与时间尺度较长的年代际或多年代际变化分量相联系的海温关键区则来自中高纬度。3-4 a准周期变化分量的海洋外强迫强信号随季节变化由前冬的ENSO（厄尔尼诺-南方涛动）转为春末夏初的印度洋偶极子（IOD）。6-8和12-16 a年准周期变化分量的海洋强迫关键区主要位于太平洋。准32和准64 a周期振荡则受北太平洋多年代际变化（PDO）和北大西洋多年代际变化（AMO）的共同影响。梅雨的长期变化趋势则与全球变暖背景及以PDO为代表的年代际海洋外强迫因子相联系。（3）尽管梅雨异常与ENSO的正相关关系呈现减弱趋势,但20世纪70年代以后的梅雨异常年际变化分量的可预报性有所增大。（4）将梅雨各变化分量作为预测对象分别建模,进一步构建梅雨异常预测统计模型。采用该模型对近5年梅雨预测进行独立样本检验,有较好的回报效果,验证了梅雨异常年际分量可预报性的稳定性以及基于多时间尺度分离建立梅雨预测模型的优越性。      

冬季北太平洋海温主模态在1990年前后调整及其成因初探?

太平洋年代际振荡(PDO)和北太平洋涡旋振荡(NPGO)是北太平洋(20°~60°N,120°E~120°W)海温(SST)的EOF前两个模态,本文通过比较1990年前后北太平洋冬季SST EOF前两个模态,揭示了PDO和NPGO在1990年前后特征,并从关键区海温变化、北太平洋涛动(NPO)、赤道太平洋中部变暖(CPW)和北极涛动(AO)的影响,揭示了北太平洋主模态在1990年之后调整的成因。我们发现,1990年之前,北太平洋SST场的EOF前两个模态与PDO和NPGO的空间结构类似,但是在1990年之后,SST的EOF第一模态的最大荷载中心向日界线移动,40°N以北的太平洋被正的SST异常控制,表现出与NPGO模态的负位相相似的空间分布特征,而EOF第二模态由偶极子演变成了三极子结构。北太平洋中部(28°~36°N,152°~178°W)和北太平洋北部(44°~49°N,151°~177°W)海温距平在1990年之后呈显著的负相关变化,是导致在1990年之后冬季NPGO成为主模态的内部原因,而NPO在1990年之后的显著增强则是重要的外部原因。分析显示,NPO在1980年开始表现出增强趋势,通过风生流机制,NPO可以增强北太平洋45°N附近的气压梯度和西风异常幅度,从而导致了1990年之后NPGO海温模态的加强。虽然CPW和AO对NPO的南支(夏威夷)和北支(阿拉斯加)的海平面气压异常中心加强有贡献,但是上述两个因子与NPGO之间的关系在1990年之前并不明显。因此,CPW和AO与NPGO之间并不存在稳定的物理联系。     

1979~2013年西北太平洋地区海平面气压场季节转换时间的变化分析

采用1979~2013年NCEP/NCAR再分析资料,借助线性趋势、距平、累积距平、Mann-Kendall突变检验及Morlet小波等方法分析了西北太平洋地区海平面气压场季节转换时间的长期趋势和多尺度周期变化特征。结果表明:海平面气压场一年中存在两次季节转变,20°N~50°N海平面气压场冬夏季节转变的时间在第20候左右,而夏冬季节转变发生在第51候。并且海平面气压场的季节转换时间存在纬度差异与经度差异。通过趋势分析,发现海平面气压场由冬季型转变到夏季型的时间存在显著的趋势变化,并且在近35年内是趋于提前,其气候倾向率为-0.33候/10 a;夏季型转换为冬季型的时间趋于延后,气候倾向率为0.25候/10 a。季节转换时间的Mann-Kendall突变检测结果表明,海平面气压场由冬向夏的转换时间在1997~1998年间发生了突变;夏季型转换为冬季型的时间尚未发现显著突变。最后通过对季节转换时间的小波分析与小波功率谱的显著性检验得出,冬夏季节转换的时间具有显著的15 a周期变化;夏冬季节转换时间8 a周期振荡最为剧烈。     

ENSO dynamics and seasonal cycle in the tropical Pacific as simulated by the ECHAM4/OPYC3 coupled general circulation model

 The new version of the atmospheric general circulation model (AGCM), ECHAM4, at the Max Planck Institute for Meteorology, Hamburg, has been coupled to the OPYC3 isopycnic global ocean general circulation and sea ice model in a multi-century present-day climate simulation. Non-seasonal constant flux adjustment for heat and freshwater was employed to ensure a long-term annual mean state close to present-day climatology. This study examines the simulated upper ocean seasonal cycle and interannual variability in the tropical Pacific for the first 100 years. The coupled model’s seasonal cycle of tropical Pacific SSTs is satisfactory with respect to both the warm pool variation and the Central and Eastern Pacific, with significant errors only in the cold tongue around April. The cold phase cold tongue extent and strength is as observed, and for this the heat flux adjustment does not play a decisive role. A well-established South Pacific convergence zone is characteristic for the new AGCM version. Apart from extending the southeast trades seasonal maximum to midbasin, wind stress pattern and strength are captured. Overall the subsurface structure is consistent with the observed, with a pronounced thermocline at about 150 m depth in the west and rising to the surface from 160 °W to 100 °W. The current system is better resolved than in some previous global models and, on the whole, has the expected shape. The equatorial undercurrent is correctly positioned but the core is only half as strong as observed. The north equatorial current and counter-current also have reduced maximum speeds but the April minimum is captured. As with the companion publication from Roeckner et al. this study finds pronounced tropical Eastern and Central Pacific interannual variability. Simulated and observed NINO3 sea surface temperature (SST) variability is represented by a single, rather broadband, maximum of power spectral density, centered on about 28 months for the simulation and four years for the observations. For simulation and observations, SST, windstress, and upper ocean heat content each exhibit a single dominant large-scale amplitude and phase pattern, suggesting that the model captures the essential dynamics. The amplitude of the essentially standing oscillation in SST in the NINO3 region attains the observed strength, but is weaker at the eastern boundary. Anomalies of upper ocean heat content show off-equatorial westward and equatorial eastward propagation, the latter’s arrival in the east of the basin coinciding with the SST anomalies. Equatorial wind stress anomalies near the date line provide the appropriate forcing and clearly form a response to the anomalous SST. Received: 14 June 1996 / Accepted: 11 November 1997     

华南热带气旋相关物理量场的线性及非线性统计分析研究

选取西太平洋海平面温度场、海平面气压场、500 hPa位势高度场作为物理因子场,并普查计算1949—2013年影响我国华南地区的热带气旋的年均频数、年均最低气压、年均最大风速作为相关物理量场。对因子场分别应用主成分分析 (PCA) 与核主成分分析 (KPCA) 算法进行主成分提取,在此基础上,对因子场的前六主成分进行功率谱估计与凝聚谱分析。最后,利用典型相关分析 (CCA) 与核典型相关分析 (KCCA) 算法对因子场与物理量场进行典型相关分析。结果表明,基于非线性的KPCA算法提取出西太平洋物理因子场前六成分的解释方差贡献率,均高于PCA算法;海温场、海压场、高度场的第一成分各自存在大概18年的周期性振荡变化,同时,在周期为2~3年的范围内,这三者的振荡频率的互相关性最强;而因子场与物理量场的非线性典型相关系数,明显高于线性典型相关系数。      

全球变暖背景下亚非典型干旱区降水变化及其与水汽输送的关系研究

分析比较了中蒙(35°N~50°N,75°E~105°E)、中亚(28°N~50°N,50°E~67°E)和北非(15°N~32°N,17°W~32°E)三个典型干旱区水汽输送特征的异同,及其1961~2010年间的降水时空变化,分析了水汽来源和输送变化及其可能原因。结果显示,由于受不同的气候系统影响,中蒙、北非和中亚干旱区的降水在年内变化上有着显著不同。中蒙和北非干旱区降水呈现夏季风降水的特征;而中亚干旱区降水则为更多受到冬季风的影响。1961~2010年,随着全球气温上升,中蒙干旱区冬季纬向水汽输送增加而经向输送减少,总水汽输送增加;中亚干旱区冬季纬向输送减少而经向增加,总水汽输送减少;北非干旱区冬季纬向输送增加而经向输送减少,总水汽输送增加。夏季中蒙和北非干旱区经向、纬向输送均减小,中亚干旱区夏季纬向输送减少而经向减少,总输送增加。相应的,中蒙干旱区年、冬季和夏季降水分别以4.2、1.3和1.0 mm/10 a的趋势增加;而中亚干旱区冬季(1.2 mm/10 a)和夏季(0.1 mm/10 a)降水增加,年降水则呈减少趋势(-0.8 mm/10 a);北非干旱区年降水和夏季降水分别以0.5 mm/10 a和0.1 mm/10 a的速率增加。冬季中蒙干旱区主要水汽来源是水汽经向输送,而中亚干旱区水汽主要为纬向输送,经纬向水汽均为净输出是北非干旱区降水极少的主要原因,平均总水汽输送量约为-9.48×104 kg/s。冬季低纬度和高纬度环流通过定常波影响干旱区冬季降水。中蒙和中亚干旱区冬季降水主要受西太平洋到印度洋由南向北的波列影响,北非干旱区冬季降水主要和北大西洋上空由北到南的波列相联系。各干旱区的降水对海温变化有着不同的响应:中蒙干旱区冬季降水与冬季太平洋西海岸和印度洋海温呈显著正相关,夏季与海温相关不显著;中亚干旱区与地中海和阿拉伯海温相关,且与阿拉伯海温为正相关。     

Influence of the South China Sea Biweekly Sea Surface Temperature on the South China Sea Summer Monsoon Especially during the Indian Ocean Dipole

The influence of the biweekly sea surface temperature (SST) in the South China Sea (SCS) on the SCS summer monsoon, especially during the Indian Ocean Dipole (IOD) is presented using the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) SST and rainfall data for April to June from 1999 to 2013. During positive IOD (PIOD) years the biweekly SST anomalies over the SCS lead the rain anomalies by three days, with a significant correlation (r?=?0.8, at the 99% confidence level), whereas during negative IOD (NIOD) years, the correlation is only 0.2. The biweekly SST is observed to influence the westward and northward propagating rainfall anomalies over the SCS and, hence, affect the SCS summer monsoon, especially during PIOD years. No such propagation was seen during NIOD years. The biweekly intraseasonal oscillation of SST in the SCS results in enhanced sea level pressure and surface shortwave radiation, especially during PIOD years. The potential findings here indicate that the biweekly SST in the SCS is strongly (weakly) influenced during PIOD (NIOD) years. Further, it is observed that SST in the SCS has a strong (weak) effect on the SCS summer monsoon by westward and northward propagation of rainfall, especially during PIOD (NIOD) years. When a PIOD or NIOD exists over the tropical Indian Ocean, the SCS SST will be strongly (r?=?0.6, at the 99% confidence level) or weakly correlated with the residual index, respectively.     

Decadal time scale variability recorded in the Quelccaya summit ice core δ18O isotopic ratio series and its relation with the sea surface temperature

 The spectral characteristics of the δ¹⁸O isotopic ratio time series of the Quelccaya ice cap summit core are investigated with the multi taper method (MTM), the singular spectrum analysis (SSA) and the wavelet transform (WT) techniques for the 500 y long 1485–1984 period. The most significant (at the 99.8% level) cycle according to the MTM F-test has a period centered at 14.4 y while the largest variance explaining oscillation according to the SSA technique has a period centered at 12.9 y. The stability over time of these periods is investigated by performing evolutive MTM and SSA on the 500 y long δ¹⁸O series with a 100 y wide moving window. It is shown that the cycles with largest amplitude and that the oscillations with largest extracting variance have corresponding periods aggregated around 13.5 y that are very stable over the period between 1485 and 1984. The WT of the same isotopic time series reveals the existence of a main oscillation around 12 y which are also very stable in time. The relation between the isotopic data at Quelccaya and the annual sea surface temperature (SST) field anomalies is then evaluated for the overlapping 1919–1984 period. Significant global correlation and significant coherency at 12.1 y are found between the isotopic series and the annual global sea surface temperature (GSST) series. Moreover, the correlation between the low (over 8 y) frequency component of the isotopic time series and the annual SST field point out significant values in the tropical North Atlantic. This region is characterized by a main SST variability at 12.8 y. The Quelccaya δ¹⁸O isotopic ratio series may therefore be considered as a good recorder of the tropical North Atlantic SSTs. This may be explained by the following mechanism: the water vapor amount evaporated by the tropical North Atlantic is function of the SST. So is the water vapor δ¹⁸O isotopic ratio. This water vapor is advected during the rainy season by northeast winds and precipitates at the Quelccaya summit with its tropical North Atlantic isotopic signature. It is also suggested from this described stability of the decadal time scale variability observed in the Quelccaya isotopic series, that the decadal time scale GSST variability was also stable during the last five centuries. Received: 12 February 1997 / Accepted: 9 September 1997     

太平洋海气相互作用的时空变化

本文根据1957—1976年赤道太平洋海温和北太平洋海平面气压的月平均资料,计算了它们之间全年(1—12月)逐月的时滞相关,分析了北太平洋副热带反气旋影响赤道海温和赤道海温对副高反馈的季节变化。发现它们之间的联系不同季节、不同地区有明显差异:副热带反气旋对赤道海温的影响(负相关)以春季最大,秋季最小;赤道海温的反馈,对副高的不同部分作用不同,对副高主体的作用(正相关)以冬半年最大、夏半年较小(尤其是盛夏),对西部副高脊的作用(负相关)相反,以夏半年最大,冬半年较小。其过渡期为5月和11月。同时对其季节变化的可能原因也提出了一些初步看法。其中特别强调了大型环流背景的基本状态(包括平均垂直环流)对海气相互作用过程的重要性。     

中国东部高空颠簸时空分布特征及其与热带中东太平洋海温的关系

本文利用1979～2014年NCEP-DOE日平均再分析资料和中国区域2375份航空器空中颠簸报告资料,研究中国东部区域高空颠簸的时空分布特征及其与热带中东太平洋海温异常（简称“海温异常”;空间范围:5°S～5°N,120°～170°W）的关系以及产生这种关系的可能原因。结果表明:中国东部地区高空颠簸与东亚副热带西风急流之间存在显著时空相关关系,其原因是高空纬向风引起的垂直风切变是构成高空颠簸时空分布的主导因素。中国东部夏季高空颠簸与海温异常存在正相关关系;冬季呈现南北两个正负相关区:以30°N为界,北部区域存在显著的负相关,南部区存在显著的正相关,在30°N急流轴附近区域无显著相关关系。海温异常影响中国高空颠簸时空分布的可能原因是海温变化引起对流层高层温度出现异常,进而影响温度的经向梯度,导致东亚副热带西风急流强度和位置出现异常（夏季,急流轴南侧出现西风异常;冬季,急流轴北侧出现东风异常,南侧出现西风异常）。高空纬向风的变化导致纬向风的垂直梯度和经向梯度出现异常,最终影响高空颠簸的时空分布特征。对流层高层温度的异常变化可能是由与热带海温异常相关的平流层水汽变化所引起。     

RECONSTRUCTION OF EL NINO EVENT CHRONOLOGY FOR THE LAST 600 YEAR PERIOD

The El Nino events for 1870—1989 were identified according to the sea surface temperature(SST)over the easternequatorial Pacific(0—10°S,90—180°W)and Southern Oscillation Index.The chronicle of the El Nino events in histori-cal time(14708—1879)was reconstructed by using of a series of proxy data such as Australian droughts,Nile floods,Peruvian floods,numbers of landing typhoon in China,cool summers in East Asia,SOI calculated from tree ring data,and El Nino events identified mainly from meteorological and oceanographical conditions along the Ecuador and Perucoast.Finally,114 El Nino events were found for the period 1470—1989.The mean return interval was 4.5 years.The fre-quency of the events seems to have a cyclical variation of 70 years.No close relationship was found between the globalwarming and the frequency of El Nino events.     

前期印度洋海温异常对夏季高原“湿池”水汽含量的影响及其可能原因

利用Hadley中心提供的逐月海温资料、ERA-Interim再分析资料以及NOAA（National Oceanic and Atmospheric Administration）的逐月向外长波辐射（OLR）资料探讨了1979~2011年夏季青藏高原“湿池”的水汽含量与前期印度洋海温异常的关系,并对可能的原因进行了分析。结果表明,夏季青藏高原水汽（去趋势）EOF第二模态与前期印度洋海温存在密切的正相关,前期3~4月关键区（5°S~20°N,45°E~75°E）的海温异常可以作为夏季高原水汽的预测信号。在暖水年,赤道附近显著的东风异常对夏季高原水汽输送起到了至关重要的作用。500 hPa上副热带高压显著增强并西移,600 hPa上赤道附近为显著的异常东风,将水汽从西太平洋、南海、孟加拉湾向西输送到印度半岛,并在异常反气旋环流西侧的南风作用下,将水汽带向青藏高原。高层风场上,西太平洋地区辐合,青藏高原上空辐散。以上环流形势表明暖水年夏季青藏高原水汽偏多;冷水年则相反。就影响机制而言,前期春季印度洋海温显著偏暖,引起其上空异常的对流上升运动,驱动异常沃克环流从春到夏显著维持,副热带高压的季节性北跳和异常增强西移,有利于赤道东风异常的增强和西移,并经过水汽输送通道将水汽带向青藏高原上空。     

NUMERICAL EXPERIMENTS ON THE FORMATION OF THE EASTERN PACIFIC SUMMER MONSOON

In this paper,we use a two-dimensional primary equation model which contains (1) heating ofradiation,(2) heating of condensation,and (3) transfers of sensible and latent heat between air andthe underlying surface.To investigate the causes for the formation of the eastern North Pacific sum-mer monsoon,the data at 110°W are obtained and winds at underlying surface and at 200 hPa aremodified under the conditions (1) removing topography and (2) changing meridional sea surface tem-perature (SST) gradient.In the numerical modification,we find that by removing the topography,the center's location ofthe eastern North Pacific summer monsoon does not change,but the intensity of the summer monsoonis weakened.Also the onset of the summer monsoon is delayed to the end of May.The tropical east-erly jet is weakened obviously,even changes to westerly wind.On the other hand,we find that theSST gradient along 110°W influences the eastern North Pacific summer monsoon distinctly.If theSST gradient is decreased,the center of the southwest wind near 12°N does not exist any more.theintensity of the whole summer monsoon becomes very weak and the circulation pattern of the summermonsoon also changes a lot.Finally,we indicate that both topography and meridional SST gradient play important roles inthe occurrence of the eastern North Pacific summer monsoon.The meridional SST gradient is themost important factor that triggers the summer monsoon and the topography along 110°W influencesthe intensity and the onset time of the summer monsoon there mostly.