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1.
利用风场、20℃等温线深度、海表温度以及Wheeler·和Hendon提出的逐日MJO指数资料,通过合成分析方法对比分析了EP型和CP型El Nio发生前各要素场的特征,以及近30年来两类El Nio事件发生前MJO活动的差异。结果表明,在赤道西太平洋,EP型El Nio的异常西风要早于CP型El Nio出现,其强度也远远强于CP型事件。EP型El Nio的异常西风在发生前2个月已东扩至东太平洋地区,而CP型El Nio的异常西风在El Nio事件发生前3个月东扩至日界线附近,此后也只维持在日界线以西。而在赤道东太平洋,不同于EP型El Nio,CP型El Nio事件在El Nio事件发生前始终有偏东风存在。EP型El Nio温跃层有明显的加深东移现象,温跃层的演变要超前于海表温度的变化。由MJO处于5~8位相的异常概率分布,可知EP型El Nio在中西太平洋的MJO活动要比CP型El Nio早发生,比较赤道纬向风平方的均方差,发现EP型El Nio发生前对应的MJO活动要明显地强于CP型El Nio事件。 相似文献
2.
利用1979—2012年Hadley中心海表温度、中国2 474个台站逐日降水和NCEP/NCAR全球再分析资料,分析了不同类型ENSO事件秋冬季和次年春季中国南方地区10~30 d降水低频变率的变化特征。结果表明,中国南方地区10~30 d降水低频变率对不同类型ENSO事件的响应存在显著的季节差异。EP型El Ni1o的冬季和次年春季,低频降水变率显著增强; CP型El Ni1o秋冬季低频降水强度呈现相反的异常,秋季低频降水偏弱,而冬季则偏强; La Ni1a事件期间中国南方低频降水变率的变化较小且不稳定。进一步分析发现,ENSO对南方地区10~30 d低频降水变率的影响与西北太平洋地区季节平均大气环流背景场对ENSO的响应密切相关。相比正常年份,EP型El Ni1o冬春季菲律宾反气旋性异常环流的强度较强且范围较大,其西侧的异常西南风向中国南方地区输送了大量水汽,从而有利于低频降水的增强; CP型El Ni1o年秋季西北太平洋表现为气旋性环流异常,抑制了热带水汽向东亚大陆的输送,而冬季却产生了与EP型El Ni1o年类似的异常反气旋环流,只是强度有所减弱,因此中国南方地区低频降水强度在秋冬季呈相反异常。La Ni1a年菲律宾附近虽然存在气旋性环流异常,但强度较弱,因而我国南方地区低频降水变率的响应也较弱。 相似文献
3.
利用1979-2016年ERA-Interim再分析资料,分析了ENSO对冬季北太平洋地区水汽输送特征的影响,包括整层水汽含量、整层水汽输送及其散度和大气河频率。结果表明,在El Ni1o年冬季,东北太平洋地区的气旋式环流异常增强了自副热带太平洋向北美西海岸的水汽输送,导致区域性的水汽辐合与辐散异常;La Ni1a年冬季的水汽输送特征与厄尔尼诺年大致相反。根据尺度分解的方法,对水汽输送及其散度的异常成因进行分析,得到结论如下:除El Ni1o年黑潮及其续流区外,ENSO年冬季北太平洋的水汽输送异常主要由环流异常导致;水汽输送散度异常则主要由环流异常的散度、气候态比湿的经向梯度和异常比湿的纬向梯度三部分决定。此外,El Ni1o年冬季北太平洋大气河频率分布的向极弯曲增强,分布更加集中;而La Ni1a年冬季大气河频率分布更加分散,纬向跨度减小,经向跨度增加。 相似文献
4.
两个典型ENSO季节演变模态及其与我国东部降水的联系 总被引：2，自引：0，他引：2
本文根据1950~2014年月平均海温和大气环流资料以及中国160站降水等资料,利用扩展经验正交函数（EEOF）分析、相关分析以及合成分析等方法,分析了太平洋海温季节演变的主导模态,并探讨了各模态与中国东部降水和东亚环流季节变异的关系及其联系的物理过程。结果表明,ENSO（El Ni?o/Southern Oscillation）季节演变存在2个主导模态,包含4种类型:El Ni?o持续型、La Ni?a持续型、La Ni?a转El Ni?o型和El Ni?o转La Ni?a型。发现不同模态和类型的ENSO季节变化过程我国东部降水距平的分布和强度都有明显差异。El Ni?o持续型和El Ni?o转La Ni?a型,冬春季和初夏均处在El Ni?o背景下,降水异常分布存在一定共性,但盛夏和秋季分别受El Ni?o和La Ni?a影响,降水异常分布差异十分明显,前者雨带北跳慢、位置偏南而后者雨带北跳快、位置偏北。La Ni?a持续型和La Ni?a转El Ni?o型也是如此,冬春季和初夏降水异常分布大致相似,但盛夏和秋季分别受La Ni?a和El Ni?o影响,前者雨带北跳快、位置偏北而后者雨带北跳慢、位置偏南。因此,利用ENSO做我国降水的气候预测时,不能只着眼于前期冬季El Ni?o或La Ni?a事件,还应考虑其未来演变所属的可能模态和类型。对他们之间联系的物理过程分析表明,不同ENSO季节演变模态和类型主要通过影响西太平洋副热带高压以及西风带经向型/纬向型环流调整及伴随的低纬暖湿水汽输送以及中高纬冷空气活动变化来影响我国东部降水。其中,西太平洋菲律宾群岛附近异常反气旋（或气旋）、赤道Walker环流和北半球Hadley环流分别是联系ENSO与西太平洋副热带高压活动和东亚西风带经向型/纬向型环流的重要环节。 相似文献
5.
大气水汽稳定同位素是现代水循环的重要示踪剂,可以有效地追踪水汽来源及其输送过程。在中低纬度季风区,局地“降水量效应”是大气水汽稳定同位素的主要特征,但是近期研究表明,水汽来源及其输送过程等非局地因素也有重要影响。因此,本文基于拉格朗日粒子扩散模式和卫星遥感观测的大气水汽稳定氘同位素数据（数值表示为千分差,δD）,针对前人研究较少的中国东部石笋氧同位素区域,进行水汽源地追踪,并在季节和年际尺度上分析水汽δD的主要影响因素。结果表明,在季节尺度上,水汽δD在夏末秋初较低,冬春季较高,这种特征与局地气象因子、水汽源地贡献的关系较弱,水汽输送路径上的累积降水是影响水汽δD季节变化的主要因素,两者为显著的负相关关系。在年际尺度上,厄尔尼诺（El Ni?o）年夏季中国东部水汽δD较高,拉尼娜（La Ni?a）年夏季水汽δD较低。水汽源地贡献在ENSO（厄尔尼诺—南方涛动）不同位相的变化较小,而水汽输送路径上的累积降水在La Ni?a年较之El Ni?o年偏多,表明La Ni?a年热带对流活动和水汽输送过程的贫化作用更强,导致目标区域的水汽δD更低。因此,代表热带对流活动的累积降水是水汽δD季节和年... 相似文献
6.
东亚冬季风对ENSO事件的响应特征 总被引：23，自引：5，他引：18
基于美国NOAA在ENSO诊断分析中使用的海洋Ni?o指数 （Oceanic Ni?o Index, 简称ONI）,将1950～2005年冬季分成强El Ni?o、强La Ni?a、弱El Ni?o、弱La Ni?a和没有发生ENSO事件5类,用分类合成方法研究了冬季东亚大气环流对ENSO事件的响应。结果表明,在低纬度,大气环流对ENSO事件的响应具有较明显的准线性特征,即大气对海洋暖事件与冷事件的响应大致是反位相的,对弱ENSO事件的响应与强ENSO事件相似但强度较弱。中高纬度大气环流与ENSO事件也有一定的联系,但同等强度暖事件与冷事件下大气环流距平场上的系统分布没有呈现明显的反位相,表明大气对海温异常的响应是复杂的。强El Ni?o事件时大气的响应信号显著,主要表现在东亚中高纬西风气流增强, 亚洲北部地区气温偏高,距平风场上的切变线从长江中下游向东伸展,菲律宾海距平反气旋西北侧的偏南气流和南支槽前西南气流加强,其共同作用使南海和中国东南沿海出现显著的偏南风距平;强La Nia事件时,长江中下游向东伸展的脊线不明显,中国南方至南海处于偏北风距平区,但通过统计检验的范围减小;弱El Ni?o事件时,菲律宾海距平反气旋西北侧的西南气流偏东,与南支槽前西南气流分开,使得华南和南海的偏南风距平没有强El Ni?o时显著; 弱La Ni?a事件时,西风带纬向气流减弱,亚洲北部地区气温偏低。对ONI指数与亚洲北部温度指数（NTI）的散点图的分析显示,9个强El Ni?o冬季中有8年亚洲北部温度距平偏高,7个弱El Ni?o冬季中只有1年温度偏高;8个强La Ni?a冬季有4年温度偏低,12个弱La Ni?a冬季中有11年温度偏低;亚洲强暖冬和强冷冬的发生与ENSO事件的联系不紧密。 相似文献
7.
ENSO对中国冬半年降水影响的不对称性及机制分析 总被引：2，自引：4，他引：2
利用1979—2010年观测和再分析资料,诊断分析ENSO对中国华南冬半年降水的影响及其机制。结果表明,在El Ni?o冬半年期间,东亚沿岸上空对流层低层南风的增强导致了水汽输送明显偏多,水汽在华南辐合,使得大气可降水量和比湿增加,降水显著偏多。而在La Ni?a冬半年期间,这些大气要素并没有呈现显著的相反变化,负异常的量值很弱并在统计上不显著。通过进一步分析El Ni?o和La Ni?a冬半年期间季节内振荡的特点,给出一种华南冬半年降水对ENSO信号不对称响应的物理解释。El Ni?o期间,热带西太平洋到南海地区的季节内振荡不活跃,与El Ni?o相联系的西北太平洋反气旋性环流异常造成的水汽输送以及水汽辐合在华南能够稳定维持,致使华南降水明显偏多。但在La Ni?a冬半年期间,季节内振荡很活跃,与La Ni?a相联系的西北太平洋气旋性环流异常受到季节内时间尺度的扰动影响,ENSO的年际变化信号被季节内振荡破坏,使得西北太平洋和华南的年际异常信号不能得到稳定维持,导致与ENSO信号相联系的年际变化在统计上不显著。因此,热带西太平洋到南海地区的季节内振荡强度在El Ni?o和La Ni?a冬半年期间的差异,是华南冬半年降水对ENSO信号不对称响应的一个主要原因。 相似文献
8.
根据1951-2010年川西高原区7个气象站降水资料和气温资料以及60 a间发生的厄尔尼诺(El Ni?o)/拉尼娜(La Ni?a)事件,分析降水量、气温与El Ni?o /La Ni?a事件之间的关系,研究El Ni?o/La Ni?a事件对川西高原区气候的影响。结果表明：1951年以来川西高原区年降水量变化不大,呈现微弱的增加趋势,El Ni?o/La Ni?a 事件的发生对川西高原区年平均降水量有影响,El Ni?o事件影响下的年平均降水量减少,La Ni?a事件影响下的年平均降水量增加;El Ni?o年降水量低于正常年降水量39.14 mm,拉尼娜年降水量高于正常年降水量22.56 mm。1951年以来川西高原区年平均气温呈现微弱的波动上升趋势,川西高原区年平均气温与ENSO事件等级之间的相关性不显著。 相似文献
9.
近65年ENSO事件强度变化及时频特征研究 总被引：6，自引：2，他引：6
利用海洋尼诺指数(ONI)、南方涛动指数(SOI)和多变量ENSO指数(MEI)等ENSO特征值分析了1951年1月—2016年5月近65年ENSO事件的强度与时频特征,并将其强度划分为5个等级。结果表明:近65年共发生22次暖事件（El Ni?o）和13次冷事件（La Ni?a）;对ENSO特征值进行频次分析发现,强El Ni?o月份所占比例比强La Ni?a多;使用连续小波、交叉小波和小波相干分析得出,ENSO循环主要具有2~7 a的周期,还具有10~16 a的年代际变化。 相似文献
10.
利用1961—2015年Hadley中心逐月海表温度资料、海冰密集度资料以及NCEP/NCAR再分析资料,探讨了秋季北极海冰对于EP型ENSO事件的异常响应,并进一步研究了这种异常响应的可能原因。结果表明,秋季北极海冰对EP型ENSO的响应具有非线性,特别是喀拉海海域(60°～90°E,70°～80°N)海冰无论在EP型El Ni?o或是La Ni?a位相,均表现为显著的负异常。进一步研究发现,不同ENSO位相造成该区域海冰异常偏少的机制有明显不同。EP型El Ni?o年秋季菲律宾附近海域对流活动被抑制,所激发的经向波列在高纬地区形成异常反气旋环流,其南风分量向喀拉海输送暖平流,造成海冰异常偏少。而EP型La Ni?a年喀拉海海域则主要受到来自大西洋开放性海域西风异常的影响,合成结果和个例年均显示EP型La Ni?a年秋季北大西洋上空存在一个显著的西风急流中心,有利于北大西洋开放性海域较暖海水向下游输送,进而影响喀拉海海冰。这些结果表明,热带外地区大气环流场对EP型ENSO的非线性响应导致了喀拉海海冰对EP型ENSO事件的响应也表现出明显的非线性。 相似文献
11.
ENSO regulation of MJO teleconnection 总被引：1，自引：0，他引：1
The extratropical teleconnections associated with Madden?CJulian Oscillation (MJO) are shown to have an action center in the North Pacific where the pressure anomalies have opposite polarities between the Phase 3 (convective Indian Ocean) and Phase 7 (convective western Pacific) of the MJO. The teleconnection in the same phase of MJO may induce opposite anomalies over East Asia and North America between El Ni?o and La Ni?a years. During MJO Phase 3, a gigantic North Pacific anticyclonic anomaly occurs during La Ni?a, making coastal northeast Asia warmer/wetter than normal, but the west US colder/drier; whereas during El Ni?o the anticyclonic anomaly is confined to the central North Pacific, hence the northwest US experiences warmer than normal weather under influence of a downstream cyclonic anomaly. During Phase 7, an extratropical cyclonic anomaly forms over the northwest Pacific during La Ni?a due to convective enhancement over the Philippine Sea, causing bitter winter monsoon over Japan; whereas during El Ni?o, the corresponding cyclonic anomaly shifts to the northeast Pacific due to enhanced convection over the equatorial central Pacific, which causes warm and wet conditions along the west coast of US and Canada. Further, the presence of ENSO-induced seasonal anomalies can significantly modify MJO teleconnection, but the aforementioned MJO teleconnection can still be well identified. During Phase 3, the MJO teleconnection pattern over North Pacific will be counterbalanced (enhanced) by El Ni?o (La Ni?a)-induced seasonal mean anomalies. During Phase 7, on the other hand, the MJO teleconnection anomalies in the northeastern Pacific will be enhanced during El Ni?o but reduced during La Ni?a; thereby the impacts of MJO teleconnection on the North America is expected to be stronger during El Ni?o than during La Ni?a. 相似文献
12.
Many previous studies have demonstrated that the boreal winters of super El Nino events are usually accompanied by severely suppressed Madden-Julian oscillation(MJO) activity over the western Pacific due to strong descending motion associated with a weakened Walker Circulation. However, the boreal winter of the 2015/16 super El Nino event is concurrent with enhanced MJO activity over the western Pacific despite its sea surface temperature anomaly(SSTA)magnitude over the Nino 3.4 region being comparable to the SSTA magnitudes of the two former super El Nino events(i.e.,1982/83 and 1997/98). This study suggests that the MJO enhanced over western Pacific during the 2015/16 super El Nino event is mainly related to its distinctive SSTA structure and associated background thermodynamic conditions. In comparison with the previous super El Nino events, the warming SSTA center of the 2015/16 super El Nino is located further westward, and a strong cold SSTA is not detected in the western Pacific. Accordingly, the low-level moisture and air temperature(as well as the moist static energy, MSE) tend to increase in the central-western Pacific. In contrast, the low-level moisture and MSE show negative anomalies over the western Pacific during the previous super El Nino events.As the MJO-related horizontal wind anomalies contribute to the further westward warm SST-induced positive moisture and MSE anomalies over the western tropical Pacific in the boreal winter of 2015/16, stronger moisture convergence and MSE advection are generated over the western Pacific and lead to the enhancement of MJO convection. 相似文献
13.
利用1979~2013年实时多要素MJO（Madden-Julian Oscillation）监测（RMM）指数,美国NOAA逐日长波辐射资料和NCEP/NCAR再分析资料等,分析了全球变化背景下北半球冬季MJO传播的年代际变化特征。从全球平均气温快速增暖期（1985~1997）到变暖趋缓期（2000~2012）,MJO 2~4位相频次减少,5~7位相频次增多,即MJO对流活跃区在热带印度洋地区停留时间缩短、传播速度加快,而在热带西太平洋停留时间加长、传播明显减缓。进一步分析发现,以上MJO的年代际变化特征与全球变化年代际波动有关。当太平洋年代际涛动（PDO）处于负位相时,全球变暖趋缓,热带东印度洋—西太平洋海温异常偏暖,使其上空对流加强,垂直上升运动加强,对流层低层辐合,大气中的水汽含量增多,该区域的湿静力能（MSE）为正异常。当MJO对流活跃区位于热带印度洋地区时,MJO异常环流对季节平均MSE的输送在强对流中心东侧为正、西侧为负,有利于东侧MSE扰动增加,使得MJO对流扰动东移加快;而当MJO对流活跃区在热带西太平洋地区,MJO异常环流对平均MSE的输送形成东负西正的形势,东侧MSE扰动减小,不利于MJO快速东传。因此,全球变化背景下PDO引起的大气中水汽含量及MSE的变化可能是MJO传播年代际变化的重要原因。 相似文献
14.
The atmospheric and oceanic conditions before the onset of EP El Ni?o and CP El Ni?o in nearly 30 years are compared and analyzed by using 850 hPa wind, 20℃ isotherm depth, sea surface temperature and the Wheeler and Hendon index. The results are as follows: In the western equatorial Pacific, the occurrence of the anomalously strong westerly winds of the EP El Ni?o is earlier than that of the CP El Ni?o. Its intensity is far stronger than that of the CP El Ni?o. Two months before the El Ni?o, the anomaly westerly winds of the EP El Ni?o have extended to the eastern Pacific region, while the westerly wind anomaly of the CP El Ni?o can only extend to the west of the dateline three months before the El Ni?o and later stay there. Unlike the EP El Ni?o, the CP El Ni?o is always associated with easterly wind anomaly in the eastern equatorial Pacific before its onset. The thermocline depth anomaly of the EP El Ni?o can significantly move eastward and deepen. In addition, we also find that the evolution of thermocline is ahead of the development of the sea surface temperature for the EP El Ni?o. The strong MJO activity of the EP El Ni?o in the western and central Pacific is earlier than that of the CP El Ni?o. Measured by the standard deviation of the zonal wind square, the intensity of MJO activity of the EP El Ni?o is significantly greater than that of the CP El Ni?o before the onset of El Ni?o. 相似文献
15.
Summary Although variability is a fundamental aspect of the climate system, the interaction of different time scales of variability
remains difficult to assess and verbalize. Two well-documented examples of tropical variability on different time scales are
the El Ni?o/Southern Oscillation (ENSO) and the Madden-Julian Oscillation (MJO). Using the fifteen-year ECMWF Re-analysis
(ERA) data archive and outgoing longwave radiation (OLR) data, some of the ENSO modulations of the intraseasonal MJO are examined.
During El Ni˜o years, the MJO convection is able to propagate farther eastward into the central Pacific than it typically
does during normal years. The corresponding intraseasonal circulation anomalies are similarly translated farther east. However,
not all changes are this straight forward; for example, MJO convection is found to occur within westerly wind bursts during
the Normal years, but somewhat ahead of the winds during El Ni˜o.
ENSO-induced changes to the large-scale upper-tropospheric state provide different environments for outflow from MJO convection
across the North Pacific. During the El Ni?o years, the eastward shift of the local Hadley circulation means that MJO convection
must propagate farther east to reach an environment in which its meridional outflow can produce an appropriate Rossby wave
source for the extension of the east Asian jet and subsequent midlatitude height falls.
Received December 1, 1998 相似文献
16.
The mechanism for asymmetric atmospheric responses to the central Pacific(CP) El Ni?o and La Ni?a over the western North Pacific(WNP) is studied in this paper. The negative anomalies of rainfall over the key region of WNP are explained by diagnosing the column-integrated equations of moisture and moist static energy(MSE). It is revealed that the nonlinear advection of moist enthalpy is critical to introduce negative rainfall anomalies over the region. The anomalous easterly(westerly) in La Ni?a(CP El Ni?o) causes negative advection of anomalous moist enthalpy, inducing negative heating anomaly and an anticyclone anomaly in the WNP, which weakens(strengthens) the cyclone(anticyclone) in La Ni?a(CP El Ni?o). The MSE budget analysis shows a larger nonlinear term in CP El Ni?o than in eastern Pacific(EP) El Ni?o, inconsistent with the amplitudes of sea surface temperature anomalies. The reason is that the nonlinear term transforms to positive above 700 h Pa in EP El Ni?o, offsetting the negative advection below 700 h Pa and thus making the nonlinear term smaller. The nonlinear term is negative at low levels in CP El Ni?o, resulting in a larger nonlinear term. The stronger precipitation anomalies in the WNP during EP El Ni?o can be attributed to the linear moist enthalpy advection. The mean easterly wind at mid levels causes a larger(smaller) positive moist enthalpy advection in CP(EP) El Ni?o, due to a larger(smaller) moist enthalpy gradient, resulting in a positive(negative) linear moist enthalpy advection, which weakens(strengthens) the negative precipitation anomalies in the key region. 相似文献
17.
一种新的El Niño海气耦合指数 总被引：6，自引：1，他引：5
利用1980～2010 年月平均Hadley中心海表温度、美国全球海洋资料同化系统(GODAS)海洋温度和NCEP/NCAR 大气环流再分析资料,通过对2 个海洋要素(海表温度SST、上层热含量HC)和5 个大气要素(海平面气压SLP、850 hPa 风场、200 hPa 速度势和对外长波辐射OLR)的多变量经验正交函数展开(multivariate EOF,简称MV-EOF)探讨了热带太平洋的主要海气耦合特征。结果表明,MV-EOF 分析的前两个耦合模态分别很好地对应了传统型El Ni?o 和El Ni?o Modoki 的海气耦合特征:传统型El Ni?o 期间,伴随着赤道中东太平洋SST 的异常增温,HC、SLP、200 hPa 速度势等要素总体呈东西反相的“跷跷板”变化,低层850 hPa 赤道中太平洋出现较强西风距平,西北太平洋上空为反气旋性异常环流;El Ni?o Modoki 期间,SST 持续增温和HC 正异常中心均显著西移至中太平洋,低层SLP 和高空200 hPa 速度势均呈现纬向三极型异常分布,低层异常强西风向西移至暖池东部,西北太平洋上空呈现气旋性异常环流。两类El Ni?o 的海气耦合特征存在显著差异,较优的El Ni?o 指数应不仅可以客观描述和区分El Ni?o 现象本身,更要紧密联系两类事件所产生的大气响应。以往定量表征El Ni?o 年际变化的指标大多立足于SST 或SLP,本文选取HC 作为研究指标,定义了一组新的El Ni?o 指数HCEI 和HCEMI。较以往基于SST 的El Ni?o 指数,HCEI 和HCEMI 不仅能更清楚地表征和区分两类El Ni?o(如1993 年的传统型El Ni?o 和2006 年的El Ni?o Modoki),而且能更好地反映和区分两类El Ni?o 与大气间的海气耦合特征,为El Ni?o的监测和短期气候预测工作提供了一个新工具。 相似文献
18.
The features of the MJO during two types of El Ni no events are investigated in this paper using the daily NCEP-2reanalysis data, OLR data from NOAA, and Real-time Multivariate MJO index for the period 1979–2012. The results indicate that the MJO exhibits distinct features during eastern Pacific(EP) El Ni no events, as compared to central Pacific(CP) El Ni no events. First, the intensity of the MJO is weakened during EP El Ni no winters from the tropical eastern Indian Ocean to the western Pacific, but enhanced during CP El Ni no winters. Second, the range of the MJO eastward propagation is different during the two types of El Ni no events. During EP El Ni no winters, the MJO propagates eastwards to 120?W, but only to 180?during CP El Ni no winters. Finally, the frequency in eight phases of the MJO may be affected by the two types of El Ni no. Phases 2 and 3 display a stronger MJO frequency during EP El Ni no winters, but phases 4 and 5 during CP El Ni no winters. 相似文献
19.
ENSO多样性研究进展 总被引：2，自引：0，他引：2
El Ni?o是热带中东太平洋异常偏暖的现象,发展过程具有显著的季节锁相特征。近年来,新形态事件更频繁发生引起了科学界广泛关注。学者们根据空间分布形态或爆发时间将ENSO事件分为两类,虽然选取标准不同,分类结果却有诸多相似点:中太平洋(Dateline、Modoki、CP、WP及SU型)El Ni?o事件发展至成熟时,正SSTA中心位于赤道太平洋中部;东太平洋(传统、EP、CT及SP型)El Ni?o发展至成熟时,正SSTA中心位于赤道东太平洋,低层西风异常更强,向东传输的距离也更远。研究结果显示,东太平洋El Ni?o比中太平洋El Ni?o持续时间更长,强度也更强;两类事件对全球气候的影响模态有很大的差异。近几十年,中太平洋El Ni?o出现频率有所增加,但其原因尚未清楚。关于两类事件生成发展和位相转换的动力原因,目前科学界普遍认为东太平洋El Ni?o是一个海盆尺度的海气耦合过程,其生消过程与温跃层的变化有紧密联系,但对中太平洋El Ni?o的动力机制尚未有统一的认识。 相似文献
20.
In this study, two possible persistent anomalies of the Madden-Julian Oscillation mode (MJO) are found in the summer season (persistently Pacific active and Indian Ocean active), and an index is set to define the intensity of the two modes. They are proved to have high statistical correlations to the later ENSO events in the autumn and winter seasons: When persistent anomaly of MJO happens in the Pacific Ocean in summer, El Ni?o events are often induced during the autumn and winter seasons of that year. However, during the other MJO mode when the summer persistent anomaly of MJO occurs in the Indian Ocean, La Ni?a events often follow instead. The analysis of the atmospheric circulation field indicates that persistent anomaly of MJO can probably affect the entire Equatorial Pacific circulation, and results in wind stress anomalies. The wind stress anomalies could excite warm or cold water masses which propagate eastwards at the subsurface ocean. The accumulation of warm or cold subsurface water in the Equatorial Eastern Pacific Ocean may eventually lead to the formation of an ENSO. 相似文献