ENSO对印度洋偶极子非对称性的影响及机制研究北大核心

利用海表温度再分析资料、NCEP/NCAR大气环流再分析资料以及MPI-ESM1-2-LR气候模式PI-Control试验输出数据等,通过对不同强度的厄尔尼诺-南方涛动(El Nino-Southern Oscillation, ENSO)事件所对应的印度洋偶极子(Indian Ocean Dipole, IOD)事件的分析,探讨了ENSO对IOD偏度的调制作用。结果表明,伴随着赤道中东太平洋明显的正海温偏度,秋季印度洋海表温度存在西正东负的偏度。IOD与ENSO之间呈现出较强的非线性关系,且大部分强的正IOD事件对应着强El Nino事件。强El Nino位相下,IOD事件相关的海温与风场表现出很强的响应,强于La Nina事件产生的响应,表现为强的非对称性;相比较而言,弱El Nino事件与La Nina事件下引起的印度洋海温和风场的强度相当,并没有显著的非对称性。因此,ENSO可通过激发非对称的大气遥相关对IOD强度非对称性产生调制作用,印度洋海表温度偏度很大程度上是由强El Nino事件导致的强正IOD事件所贡献。     

卫星双通道反演的赤道纬向环流的气候特征及与ENS0关系的研究

利用1979－1995年共17年美国NOAA卫星观测的OLR，HIRS－Tb12与NCEP再分析的同期资料进行对比分析，证明了用卫星观测的红外，水汽双通道（OLR反演上升运动，HIRS－Tb12反演下沉运动）去反演纬向垂直环流是一个很好的途径，定义了卫星双通道反演的纬向垂直环流指数，利用该定义用卫星资料计算并反演了气候平均的全年及四季的纬向垂直环流，详细地讨论了它的气候学特征，同时又利用上述定义研究了3次典型ENSO过程的演变特征，指出太平洋的东上升支，在ENSO盛期都越过日界线，这是ENSO过程的一个共同特征，太平洋上的正Walker环流上升在ENSO盛期的强度与ENSO过程的一个共同特征，太平洋上的正Walker环流上升支在ENSO盛期的强度与ENSO过程的强弱有关。     

利用MSU序列研究高空大气温度变化的进展

美国NOAA卫星上搭载的微波大气探测仪MSU以及后续继承改进仪器AMSU,自1978年投入运行以来,已经积累了超过30年的全球大气温度的观测资料。近年来,国外学者通过仪器定标误差订正、卫星轨道衰减订正、观测时间差异导致的温度日变化订正、仪器间的相互定标处理等技术,发现并剔除了一些影响较大的非气候因素,提高了该序列资料的质量,并用于全球气候变化研究,特别是对流层和平流层近30年的温度变化研究,研究结果是对常规地面和探空资料分析结果的重要补充。本文对目前国际上3种常用的MSU序列资料集的定标误差、偏差订正和不同卫星上仪器观测序列的一致化处理方法进行了综合介绍,并比较分析了3种资料用于30年高空大气温度变化趋势分析的异同。     

两类ENSO事件非对称性特征分析北大核心CSCD

利用1961—2010年多种海、气观测资料,分析了东部型(EP)和中部型(CP)ENSO事件海温异常的非对称性及可能原因,并讨论了两类ENSO事件的非对称性对大气环流的可能影响。结果表明,海温异常非对称性包括空间分布非对称、强度非对称以及持续性非对称。从动力学角度来看,虽然不同事件发展衰减阶段主导的动力作用不尽相同,但就两类事件强度非对称性而言,海洋垂直对流项起关键性的作用。此外,研究发现,无论是通过海温强迫直接影响的赤道地区或是通过遥相关影响的赤道外地区,大气非对称响应都表现出与海温异常非对称较强的一致性,其中东部型ENSO的非对称性分布与事件暖位相分布相似,而中部型ENSO的非对称性分布与事件冷位相分布相似,且东部型ENSO非对称性差异大于中部型ENSO。     

两类ENSO事件非对称性特征分析

利用1961—2010年多种海、气观测资料,分析了东部型(EP)和中部型(CP)ENSO事件海温异常的非对称性及可能原因,并讨论了两类ENSO事件的非对称性对大气环流的可能影响。结果表明,海温异常非对称性包括空间分布非对称、强度非对称以及持续性非对称。从动力学角度来看,虽然不同事件发展衰减阶段主导的动力作用不尽相同,但就两类事件强度非对称性而言,海洋垂直对流项起关键性的作用。此外,研究发现,无论是通过海温强迫直接影响的赤道地区或是通过遥相关影响的赤道外地区,大气非对称响应都表现出与海温异常非对称较强的一致性,其中东部型ENSO的非对称性分布与事件暖位相分布相似,而中部型ENSO的非对称性分布与事件冷位相分布相似,且东部型ENSO非对称性差异大于中部型ENSO。     

ENSO与北半球冬季大气环流异常的年代际关系

利用NCEP/NCAR再分析资料和CPC(气候预测中心)Nino3-4区海表温度序列,研究了1950/1951-2002/2003年冬季ENSO事件与北半球大气环流的相互关系及其年代际变化.结果表明:北半球大气环流对ENSO事件的响应在1978/1979年有一个明显的跃变.跃变后,低纬中高层大气环流对ENSO事件的响应明显减弱,其中东南亚的减弱最为明显,而低层大气环流对ENSO事件的响应则有所增强;东半球中高纬大气环流异常与ENSO事件关系明显减弱;西半球中高纬大气环流与ENSO事件的关系加强.     

ENSO事件对云南及临近地区春末初夏降水的影响

本文采用合成及相关分析的方法,应用55年中国降水资料、美国NOAA海表温度资料以及NCEP/NCAR再分析资料,研究了ENSO事件对我国云南及其邻近地区春末初夏降水的影响及物理机理.研究结果表明:(1)在El Ni(n)o (La Ni(n)a)年,云南大部分地区4～5月降水偏少(多),东部地区相关信号尤其明显;(2)...     

NCEP/NCAR逐时分析与中国实测地表温度和地面气温对比分析

美国国家环境预报中心(NCEP) 和国家大气中心(NCAR) 的全球分析资料,不仅应用于气候模拟和预测研究中而且也可作为卫星遥感云检测的初始场资料.通过对2005年NCEP逐6小时全球最终分析资料(FNL)与中国753个台站实测资料的地表温度和地面1.5m高气温进行Cressman插值, 从时次变化和空间变化等方面系统地分析和比较了这一年间NCEP分析值与中国区域内观测值之间的差异, 得到结果: NCEP分析地表温度较观测值普遍偏低, 而地面气温NCEP分析值的空间分布大致表现为在北部地区大于观测值、而南部地区小于观测值;就2005年季节变化而言,NCEP分析值在夏季比冬季符合得好,而在我国东南部比东北、西北符合得好;从时次上看,地温和气温都呈现出随着时次推进(从2时到20时),正值区(NCEP分析值-实测值＞0)减弱、负值区(NCEP分析值-实测值＜0)加强的趋势;而通过标准化均方根误差的分析,可以知道气温的NCEP分析资料在我国可行性比地温要好.     

ENSO背景下印度洋偶极子海温异常对中国冬季降水的影响

利用1950—2009年Hadley环流中心全球月平均海表温度资料、1960—2009年NCEP/NCAR再分析资料以及中国气象局整编的160站降水资料,研究分析了印度洋偶极子(IOD)和太平洋异常海温(ENSO)对中国冬季降水的协同影响和不同作用,通过对比分析,揭示了IOD独立发生、ENSO独立发生以及IOD与ENSO联合发生时中国冬季降水的差异。研究结果表明: IOD异常海温和ENSO异常海温的出现虽然具有较高的协同性,但二者对我国冬季降水的影响效应不尽相同,IOD与ENSO的同时发生并不是两者单独发生时各自作用的叠加,而是具有协同或抵消作用。仅有IOD发生时,其正位相年使得中国西南(云南西部除外)、华南以及华北、东北地区的冬季降水出现正异常,在江淮流域出现负异常,反之亦然。但是IOD正位相比负位相对中国冬季降水的影响更显著。当IOD与ENSO同时出现时,IOD的作用使得ENSO对我国西南(云南西部除外)、内蒙、东北地区冬季降水的影响作用更为显著。此外还初步分析了IOD与中国冬季降水关系影响的环流成因。      

太阳活动11年周期对ENSO事件海温异常演变和东亚降水的影响

本文利用美国NCEP/NCAR再分析资料、海温、降水和反映太阳活动强弱的太阳10.7 cm射电流量资料,研究了1952～2010年太阳活动11年周期对ENSO年海温异常演变以及与之相联系的东亚降水的影响,在此基础上着重分析了ENSO发展期秋季东亚地区降水异常对太阳射电流量高(HS)/低(LS)的不同响应以及相关的物理过...     

The seasonal footprinting mechanism in CFSv2: simulation and impact on ENSO prediction

The seasonal footprinting mechanism (SFM) is thought to be a pre-cursor to the El Nino Southern Oscillation (ENSO). Fluctuations in the North Pacific Oscillation (NPO) impact the ocean via surface heat fluxes during winter, leaving a sea-surface temperature (SST) “footprint” in the subtropics. This footprint persists through the spring, impacting the tropical Pacific atmosphere–ocean circulation throughout the following year. The simulation of the SFM in the National Centers for Environmental Prediction (NCEP)/Climate Forecast System, version 2 (CFSv2) is likely to have an impact on operational predictions of ENSO and potentially seasonal predictions in the United States associated with ENSO teleconnection patterns. The ability of the CFSv2 to simulate the SFM and the relationship between the SFM and ENSO prediction skill in the NCEP/CFSv2 are investigated. Results indicate that the CFSv2 is able to simulate the basic characteristics of the SFM and its relationship with ENSO, including extratropical sea level pressure anomalies associated with the NPO in the winter, corresponding wind and SST anomalies that impact the tropics, and the development of ENSO-related SST anomalies the following winter. Although the model is able to predict the correct sign of ENSO associated with the SFM in a composite sense, probabilistic predictions of ENSO following a positive or negative NPO event are generally less reliable than when the NPO is not active.     

关于ENSO本质的进一步研究

基于ENSO是热带太平洋海气相互作用产物的科学观点,一系列的分析研究表明:赤道太平洋次表层海温异常(SOTA)有明显的年际变化(循环),并且与ENSO发生密切相关;ENSO的真正源区在赤道西太平洋暖池,赤道西太平洋暖池正(负)SOTA沿赤道温跃层东传到东太平洋,导致El Nino(La Nina)的爆发;在暖池正(负)SOTA沿赤道温跃层东传的同时,将有负(正)SOTA沿10°N和10°S两个纬度带向西传播,从而构成SOTA的循环;热带太平洋SOTA年际循环的驱动者主要是由异常东亚季风所引起的赤道西太平洋纬向风的异常.进而,可以提出关于ENSO本质的一种新理论,即ENSO实质上主要是由异常东亚季风引起的赤道西太平洋异常纬向风所驱动的热带太平洋次表层海温距平的年际循环.       

热带太平洋海表能量收支平衡特征及其与两类ENSO事件的联系

利用月平均的HadISST海表温度、NCEP再分析资料、OAFlux海表面热通量及相关物理量资料、NCAR/NOAA云量场资料,分析了热带太平洋海表热通量的年际特征,并且进一步分析了传统El Ni?o和El Ni?o Modoki事件中湍流热通量的异常演变特征以及影响因子。在热带太平洋上,净热通量的年际变化最大振幅出现在赤道太平洋上,且主要取决于潜热通量和短波辐射通量的变化。本文还利用两类ENSO事件旺盛期海温指数对不同时期海面热通量场的偏回归分析,考察了热带太平洋海表面热通量与两类ENSO事件中海温的联系。两类海温指数对各时期热带太平洋净热通量的回归均表现为赤道太平洋上存在显著的负异常,在Ni?o3指数偏回归下的负异常范围和强度都较El Ni?o Modoki指数回归的要大,且更偏于赤道东太平洋,而旺盛期海温对同期赤道东太平洋上湍流热通量的影响最大。     

FEATURES AND COMPARISONS OF THE QUASI-BIENNIAL VARIATIONS IN THE ASIA-PACIFIC MONSOON SUBSYSTEMS

The National Centers for Environmental Prediction (NCEP) reanalysis data, Climate Diagnostics Center Merged Analysis of Precipitation (CMAP) results, and NOAA Extended Reconstructed Sea Surface Temperature (SST), have been utilized in this paper to study the quasi-biennial variations in Asia-Pacific monsoon subsystems and associated SST anomalies (SSTA) and wind anomalies. Four monsoon indices are computed from NCEP/ National Center for Atmospheric Research (NCAR) reanalysis to represent the South Asian monsoon (SAM), South China Sea summer monsoon (SCSSM), Western North Pacific monsoon (WNPM) and East Asian monsoon (EAM), respectively. The quasi-biennial periods are very significant in Asia-Pacific monsoons (as discovered by power spectrum analysis), and for SAM and EAM---with moderate effects by El Ni?o-Southern Oscillation (ENSO)---the quasi-biennial periods are the most important factor. For SCSSM and WNPM (once again due to the effects of ENSO), the quasi-biennial periods are of secondary durations. There are obvious interdecadal variations in the quasi-biennial modes of the Asia-Pacific monsoon, so in the negative phase the biennial modes will not be significant or outstanding. The wind anomalies and SSTA associated with the biennial modes are very different in the SAM, WNPM and EAM regions. Since the WNPM and SCSSM are very similar in the biennial modes, they can be combined into one subsystem, called SCS/WNPM.     

我国华南3月份降水异常的可能影响因子分析

利用1951～2005年华南地区3月份的降水资料、NOAA海温资料、Ni?o3.4指数和NCEP再分析资料,分析了华南3月份降水异常与同期环流场、全球海温场的关系,从环流和海温的角度揭示了华南3月份降水异常的可能原因。结果表明,当华南3月份降水偏多(少)时,在对流层中低层,北太平洋海区存在气旋(反气旋)性环流异常,西太平洋及南海海面上存在反气旋(气旋)性环流异常,这样的环流异常有利(不利)于东南暖湿气流与北方东部异常冷空气在华南地区形成水汽辐合,导致降水显著增多(减少)。进一步的分析表明,ENSO和北印度洋及南海附近海温是影响华南3月份降水异常的重要外强迫因子,ENSO对华南3月降水异常的影响是通过影响春季西太平洋副热带高压和低层风场异常实现的,而北印度洋及南海附近海温对华南3月降水异常的影响则是通过垂直环流场异常和低层风场以及西太平洋副热带高压异常来实现的。     

热带印度洋春季海表温度异常与南海夏季风强度变化的关系

利用50年的Reynolds月平均海表温度资料和NCEP/NCAR全球大气再分析资料,分析了热带印度洋春季海温异常对南海夏季风强度变化的影响。结果表明:1)热带印度洋春季海表温度距平(SSTA)的模态主要是全区一致型(USBM)和热带南印度洋偶极型(SIODM),USBM模态既有年际时间尺度的变化特征,又有年际以上时间尺度的变化特征,既包含有对冬季ENSO信号响应的变化特征,又有独立于ENSO的变化特征;SIODM模态主要表现为独立于ENSO的年际时间尺度变化。2)USBM模态与南海夏季风强度变化呈显著负相关关系,且二者都是对冬季ENSO信号的响应,USBM模态的年际变化不能独立于ENSO信号影响南海夏季风的强度变化。3)经(1~8年)带通滤波及去除ENSO信号的热带印度洋春季SSTA的SIODM型分布是影响南海夏季风强度变化的主要模态,表现为热带东南印度洋为负(正)、其他海区为正(负)时,南海夏季风强度增强(减弱),大气环流对热带东南印度洋SSTA热力作用的响应是造成这一关系的直接原因,SIODM型的SSTA分布与南海夏季风年际异常关系在热带印度洋长期变化趋势的暖位相期显著,在长期变化趋势的冷位相期不显著。     

NUMERICAL MODELING STUDY OF EFFECTS OF EASTERN PACIFIC WARM POOL ON ENSO

In this study, sensitivity experiments were conducted with the Zebiak-Cane ocean-atmosphere coupled model forced by the wind stress anomaly from the U.S. National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data to study the impacts of eastern Pacific warm pool on the formation and development of ENSO events. The effects of climatological mean sea surface temperature of the warm pool on forecast skill during the ENSO events of 1982–1999 are more considerable that those of climatological mean meridional winds and ocean currents. The forecast skill for the 1997/1998 El Ni?o event is characterized by sensitivity to climatological mean sea surface temperature and anomalies of northerly winds and currents. The forecast skill is found insensitive to climatological mean northerly meridional winds and currents.     

Comparison of Wintertime North American Climate Impacts Associated with Multiple ENSO Indices

This analysis compares the climate impacts over North America during winter associated with various El Niño–Southern Oscillation (ENSO) indices, including the Niño 3.4 index, the leading tropical Pacific outgoing longwave radiation and sea surface temperature (OLR-SST) covariability, and the eastern Pacific (EP) and central Pacific (CP) types of ENSO identified from both partial-regression–empirical orthogonal function (EOF) and regression–EOF approaches. The traditional Niño 3.4 SST index is found to be optimal for monitoring the tropical Pacific OLR-SST covariability and for the tropical SST impact on North America. The circulation anomalies associated with the Niño 3.4 index project on both the Pacific/North American (PNA) and Tropical/Northern Hemisphere (TNH) patterns. The ENSO associated with the PNA tends to come from both the EP and CP ENSOs, whereas that associated with the TNH comes more from the EP ENSO. The variability of ENSO significantly affects North American temperature and precipitation, as well as temperature and precipitation extremes. For either the EP or CP types of ENSO, qualitatively similar patterns of climate and climate extreme anomalies are apparent associated with the indices identified by the two EOF approaches, with differences mainly in the anomalous amplitude. The anomalous patterns are generally field significant over North America for the EP ENSO but not field significant for the CP ENSO.

The circulation anomalies associated with ENSO are reinforced and maintained by synoptic vorticity fluxes in the upper troposphere. The anomalous surface temperature is mainly determined by the anomalies in surface radiative heating in the face of upward surface longwave radiative damping. The precipitation anomalies are supported by the vertically integrated moisture transport. The differences in atmospheric circulation, surface temperature, and precipitation among the various ENSO indices, including the intensity and spatial structure of the fields, can be attributed to the corresponding differences in synoptic eddy vorticity forcing, surface radiative heating, and vertically integrated moisture transport.     

Equatorial pacific SSTA-related decadal variations of potential predictability of ENSO and interannual climate

Summary Based on analysis of NCEP reanalysis data and SST indices of the recent 50 years, decadal changes of the potential predictability of ENSO and interannual climate anomalies were investigated. Autocorrelation of Nino3 SST anomalies (SSTA) and correlation between atmospheric anomalies fields and Nino3 SSTA exhibit obvious variation in different decades, which indicates that Nino3 SSTA-related potential predictability of ENSO and interannual climate anomalies has significant decadal changes. Time around 1977 is not only a shift point of climate on the interdecadal time scale but also a catastrophe point of potential predictability of ENSO and interannual climate. As a whole, ENSO and the PNA pattern in boreal winter are more predictable in 1980s than in 1960s and 1970s, while the Nino3 SSTA-related potential predictability of the Indian monsoon and the East Asian Monsoon is lower in 1980s than in 1960s and 1970s. Received October 19, 1999 Revised December 30, 1999     

EFFECTS OF INDIAN OCEAN SSTA WITH ENSO ON WINTER RAINFALL IN CHINA

Based on Hadley Center monthly global SST, 1960-2009 NCEP/NCAR reanalysis data and observation rainfall data over 160 stations across China, the combined effect of Indian Ocean Dipole （IOD） and Pacific SSTA （ENSO） on winter rainfall in China and their different roles are investigated in the work. The study focuses on the differences among the winter precipitation pattern during the years with Indian Ocean Dipole （IOD） only, ENSO only, and IOD and ENSO concurrence. It is shown that although the occurrences of the sea surface temperature anomalies of IOD and ENSO are of a high degree of synergy, their impacts on the winter precipitation are not the same. In the year with positive phase of IOD, the winter rainfall will be more than normal in Southwest China （except western Yunnan）, North China and Northeast China while it will be less in Yangtze River and Huaihe River Basins. The result is contrary during the year with negative phase of IOD. However, the impact of IOD positive phase on winter precipitation is more significant than that of the negative phase. When the IOD appears along with ENSO, the ENSO signal will enhance the influence of IOD on winter precipitation of Southwest China （except western Yunnan）, Inner Mongolia and Northeast China. In addition, this paper makes a preliminary analysis of the circulation causes of the relationship between IOD and the winter rainfall in China.