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1.
用1958～2000年NCEP/NCAR再分析资料、中国160站降水量及1958～1998年月平均海温资料分析了中国夏季相邻月份降水异常型的相关特征，及其与大气热源的关系和相关物理过程。结果表明，7月长江流域的降水异常与8月长江和黄河之间地区的降水异常有很好的同号性。7、8月长江流域及附近地区持续性偏旱（涝）与太平洋洋盆尺度的大气热源异常有关，并与前期5、6月热带中、东太平洋大范围的热源异常、青藏高原热源异常也有密切的联系，即当5、 6月赤道东太平洋的大气热源正异常，而赤道中太平洋北侧的热源负异常，则中国7月长江中下游偏涝，8月长江中上游与江淮流域和内蒙古东部偏涝，华南偏旱；反之亦然。前期热带中、东太平洋上空的热源异常中心和与之联系的异常垂直运动中心的西扩和西移，以及青藏高原东部的热源异常中心是影响我国7、8月持续偏旱（涝）的重要环流异常特征。另外，南海－西太平洋海温在前期也已经具有我国夏季长江流域发生旱涝对应的同期海温异常分布型的特征。 相似文献
2.
利用1981—2016年的中国160站降水资料、OISST海温资料和NCEP/NCAR大气环流资料,对比分析了中等强度El Nio和2015/2016超强El Nio对中国东南部、江淮流域和西南地区冬春季降水影响的异同。结果表明:在中等强度El Nio的冬季,偏暖的赤道中东太平洋海表面温度(Sea Surface Temperature,SST)所激发的西北太平洋和日本附近的异常反气旋环流,其异常的西南风会加强南海—西北太平洋的水汽向中国东部输送,造成中国东南部和江淮流域的降水一致偏多。2015/2016超强El Nio的冬季,赤道中东太平洋SST的强度异常偏强,中国东部异常偏冷的表面气温和对流层低层温度加强大陆冷高压,长江流域及其以北地区受异常强的北风控制,从而造成中国东南部降水增多、江淮流域降水减少。在2015/2016超强El Nio事件衰减位相的春季,中国东南部和西南部降水的增加主要归因于异常偏暖的西北印度洋和东南印度洋SST的作用。经CAM5模式试验证明,西北印度洋异常偏暖的SST引起了北印度洋的异常西南风,激发了孟加拉湾—西北太平洋的异常反气旋,加强了印度洋和南海—西北太平洋的水汽向中国西南和东南部输送。此外,东南印度洋异常偏暖的SST还会激发局地异常上升运动,通过经向垂直环流加强南海—西北太平洋异常下沉运动,诱使中国东南部的上升运动加强,导致降水增多。 相似文献
3.
ENSO及其组合模态对中国东部各季节降水的影响 总被引：7，自引：1，他引：6
近期的研究发现,热带太平洋低层大气存在两种主要模态,即经向对称ENSO模态和ENSO与海表温度(SST)年循环相互作用产生的经向反对称组合模态。主要探讨了这两种不同ENSO模态对中国东部各季节降水的影响。结果表明,厄尔尼诺年秋季,中国西南、长江及华南大部分区域呈现显著正降水异常;冬季,正降水异常范围扩大,覆盖华南、华东及华北东南部地区。这两个季节的异常降水都主要受ENSO模态的影响。与ENSO模态相关的正异常海温局地强迫导致120°E以西出现反气旋性环流,其西北侧增强的西南暖湿气流使得中国东部地区降水增多。次年春季,从中国华南延伸到东北出现正的异常降水,主要是ENSO组合模态的贡献。因为次年春季热带太平洋地区ENSO模态信号只局限于赤道地区,并没有对中国东部降水有显著的影响,而ENSO与海温年循环相互作用的组合模态使得与ENSO相关的赤道大气异常可以扩展到赤道以外地区。ENSO组合模态对中国降水异常有重要影响,在今后的研究和短期预测中需引起重视。 相似文献
4.
A premonitory sign of an anomalous SST over the eastern equatorial Pacific shows up in the North Pacific Subtropical Mode Water (STMW) 18 months earlier,and the air-sea relationship between the STMW and the anomalous SST over the eastern equatorial Pacific is shown.This premonitory connection involves an air-sea coupling between the longtime persistent mid-latitude sea surface temperature anomaly (SSTA) induced by the remote re-emergence of the STMW and the following spring subtropical atmospheric circulation anomalies.An examination of the air-sea interaction reveals that the following spring subtropical atmospheric circulation,which responds to the longtime persistent SSTA,is dominated by the anomalous negative (positive) geopotential height downstream of the negative (positive) SSTA in the strong (weak) STMW case.Thus,the tropics adjust to these anomalies through coupled dynamics,producing positive (negative) SST anomalies over the eastern equatorial Pacific.A cold water event that occurred over the eastern equatorial Pacific during winter 2008-09 was successfully forecasted by the weak summer STMW index in 2007.The evolution of this process for the air-sea interactions from the autumn of 2007 to December 2008 is presented. 相似文献
5.
利用1951-2011年中国160站降水资料及NCEP/NCAR再分析资料,分析了中国东南部冬季降水的年际变化及与之相关的环流和水汽输送特征。结果表明:中国东南部冬季降水年际差异较明显,当降水异常偏多(少)时,蒙古高压及中国广大南方地区海平面气压异常偏低(高),而亚洲附近的洋面上则异常偏高(低);500 hPa上,巴尔喀什湖附近的高压脊和东亚大槽均偏弱(强);高层东亚西风急流异常偏弱(强),中东地区急流异常偏强(弱);中国东部20~30°N出现显著异常上升(下沉)运动,低纬度地区出现异常下沉(上升)运动。影响中国东南部冬季降水的水汽输送主要有两支:来自西风带绕高原的南支气流,经过阿拉伯海和孟加拉湾向华南的输送水汽;来自低纬西太平洋,经南海向中国西南的水汽输送。此外,东亚冬季风与中国东南部冬季降水关系密切。 相似文献
6.
热带印度洋-西太平洋水汽输送异常对中国东部夏季降水的影响 总被引：1，自引：0，他引：1
利用1979~2015年NCEP/NCAR发布的月平均全球再分析资料,分析了热带印度洋-西太平洋水汽输送异常对中国东部夏季降水的影响及其形成机理。研究结果表明:热带印度洋-西太平洋地区（10°S~30°N,60°~140°E）夏季异常水汽输送主要包括两个模态,他们可以解释总的水汽输送异常34%的方差。其中,第一模态（EOF1）表现为异常水汽沿反气旋从热带西太平洋经过南海及孟加拉湾输送到中国东部上空,对应南海、孟加拉湾水汽路径输送均偏多,此时西太平洋副热带高压显著偏强,异常水汽在长江中下游地区辐合并伴随显著上升运动,有利于长江中下游降水偏多;第二模态（EOF2）表现为异常水汽从热带印度洋沿阿拉伯海、印度半岛、中南半岛等呈反气旋式输送,华南上空相应出现气旋式水汽输送异常,并对应异常水汽辐合和上升运动,有利于华南降水偏多。就可能的外部成因而言,EOF1与ENSO关系密切,表现为前冬热带中东太平洋显著偏暖,夏季同期热带北印度洋、南海上空显著偏暖,造成西太平洋副热带高压显著偏强,异常水汽主要来源于热带西太平洋和南海;EOF2与同期热带印度洋偶极子（TIOD）异常有关,TIOD为正位相时热带印度洋上空出现异常东风,华南上空出现异常气旋并伴随水汽异常辐合,异常水汽主要来源于热带南印度洋。 相似文献
7.
利用1979—2019年Hadley中心的海表温度资料、GPCP的降水资料以及NCEP-DOE的再分析资料等,分析了北半球春季热带南大西洋海表温度异常与北半球夏季亚澳季风区降水异常的联系。研究表明,北半球春季热带南大西洋海表温度异常与随后夏季热带西太平洋到南海（澳大利亚东侧海域到热带东印度洋）地区的降水异常为显著负相关（正相关）关系。北半球春季热带南大西洋的海表温度正异常可以引起热带大西洋和热带太平洋间的异常垂直环流,其中异常上升支（下沉支）位于热带大西洋（热带中太平洋）。热带中太平洋的异常下沉气流和低层辐散气流引起热带中西太平洋低层的异常东风,后者有利于热带中东太平洋海表温度出现负异常。通过Bjerknes正反馈机制,热带中东太平洋海表温度异常从北半球春季到夏季得到发展。热带中东太平洋海表温度负异常激发的Rossby波使得北半球夏季热带西太平洋低层出现一对异常反气旋。此时,850 hPa上热带西太平洋到海洋性大陆地区为显著的异常东风,有利于热带西太平洋到南海（澳大利亚东侧海域到热带东印度洋）地区出现异常的水汽辐散（辐合）,导致该地区降水减少（增加）。 相似文献
8.
Interdecadal changes in the relationship between Southern China winter-spring precipitation and ENSO 总被引：3，自引：0，他引：3
Jiepeng Chen Zhiping Wen Renguang Wu Zesheng Chen Ping Zhao 《Climate Dynamics》2014,43(5-6):1327-1338
Winter-spring precipitation in southern China tends to be higher (lower) than normal in El Niño (La Niña) years during 1953–1973. The relationship between the southern China winter-spring precipitation and El Niño-Southern Oscillation (ENSO) is weakened during 1974–1994. During 1953–1973, above-normal southern China rainfall corresponds to warmer sea surface temperature (SST) in the equatorial central Pacific. There are two anomalous vertical circulations with ascent over the equatorial central Pacific and ascent over southern China and a common branch of descent over the western North Pacific that is accompanied by an anomalous lower-level anticyclone. During 1974–1994, above-normal southern China rainfall corresponds to warmer SST in eastern South Indian Ocean and cooler SST in western South Indian Ocean. Two anomalous vertical circulations act to link southern China rainfall and eastern South Indian Ocean SST anomalies, with ascent over eastern South Indian Ocean and southern China and a common branch of descent over the western North Pacific. Present analysis shows that South Indian Ocean SST anomalies can contribute to southern China winter-spring precipitation variability independently. The observed change in the relationship between southern China winter-spring rainfall and ENSO is likely related to the increased SST variability in eastern South Indian Ocean and the modulation of the Pacific decadal oscillation. 相似文献
9.
本文利用观测和再分析资料,通过奇异值分解(Singular Value Decomposition, SVD)分析,发现北极涛动(Arctic Oscillation, AO)是显著影响中国夏季降水年际异常的前冬中高纬大气环流变异的主模态。AO在冬季发展成熟,在春季衰亡,在夏季发生位相反转。AO会导致华北、东北、长江中下游和华南夏季降水异常呈现三极型分布。伴随正位相的AO,在黄海至日本海上空的异常低压伴随的东北风异常引起华北和东北水汽通量异常辐散及降水减少,而西北太平洋的异常高压不仅增强其北侧的西南风水汽输送,和北部异常低压共同作用导致长江中下游水汽通量异常辐合及降水增加,而且使得华南水汽通量异常辐散,降水减少。因此,本文发现的前冬AO模态与我国夏季三极型异常降水分布的关系可为我国夏季旱涝预测提供一个重要的中高纬前期因子。 相似文献
10.
This paper investigates the contrasts between strong and weak Madden-Julian
Oscillation (MJO) activity over the equatorial western Pacific during winter using the NCEP
reanalysis data. It is shown that the MJO over the equatorial western Pacific in winter shows
significant interannual and interdecadal variabilities. During the winters with strong MJO
activity, an anomalous cyclonic circulation lies east of the Philippines, strong anomalous
easterlies control the equatorial eastern Pacific, and anomalous westerlies extend from the
Indian Ocean to the western Pacific in the lower troposphere, which strengthens the
convergence and convection over the equatorial western Pacific. The moisture convergence in
the lower troposphere is also enhanced over the western Pacific, which is favorable to the
activity of MJO. Eastward propagation is a significant feature of the MJO, though there is
some westward propagation. The space-time spectral power and center period of the MJO are
higher during strong MJO activity winters. The anomalous activity of MJO is closely related to
the sea surface temperature (SST) and East Asian winter monsoon (EAWM). During strong MJO
activity winters, there are positive/negative anomalies at high/low latitudes in both sea
level pressure and 500 hPa geopotential height, and the temperature is lower over the central
part of the Chinese mainland, which indicates a strong EAWM. China experiences more rainfall
between the Yellow and Yangtze Rivers, but less rainfall south of the Yangtze River. The SSTA
is negative near the Taiwan Island due to the impact of strong EAWM and shows a La Ni?a
pattern anomaly over the eastern Pacific. During the weak MJO activity winters, the situation
is reversed. 相似文献
11.
Cross-season relation of the South China Sea precipitation variability between winter and summer 总被引：3，自引：1，他引：2
The present study reveals cross-season connections of rainfall variability in the South China Sea (SCS) region between winter and summer. Rainfall anomalies over northern South China Sea in boreal summer tend to be preceded by the same sign rainfall anomalies over southern South China Sea in boreal winter (denoted as in-phase relation) and succeeded by opposite sign rainfall anomalies over southern South China Sea in the following winter (denoted as out-of-phase relation). Analysis shows that the in-phase relation from winter to summer occurs more often in El Niño/La Niña decaying years and the out-of-phase relation from summer to winter appears more frequently in El Niño/La Niña developing years. In the summer during the El Niño/La Niña decaying years, cold/warm and warm/cold sea surface temperature (SST) anomalies develop in tropical central North Pacific and the North Indian Ocean, respectively, forming an east–west contrast pattern. The in-phase relation is associated with the influence of anomalous heating/cooling over the equatorial central Pacific during the mature phase of El Niño/La Niña events that suppresses/enhances precipitation over southern South China Sea and the impact of the above east–west SST anomaly pattern that reduces/increases precipitation over northern South China Sea during the following summer. The impact of the east–west contrast SST anomaly pattern is confirmed by numerical experiments with specified SST anomalies. In the El Niño/La Niña developing years, regional air-sea interactions induce cold/warm SST anomalies in the equatorial western North Pacific. The out-of-phase relation is associated with a Rossby wave type response to anomalous heating/cooling over the equatorial central Pacific during summer and the combined effect of warm/cold SST anomalies in the equatorial central Pacific and cold/warm SST anomalies in the western North Pacific during the mature phase of El Niño/La Niña events. 相似文献
12.
中国东部夏季暴雨的年代际跃变及其大尺度环流背景 总被引：4，自引：0，他引：4
本文利用1960~2011年中国东部地面测站的逐日降水资料和JRA-55再分析资料探讨了夏季暴雨分布的年代际跃变及其相关联的大尺度环流异常特征。基于暴雨频数和占比(夏季暴雨占比是指5~8月暴雨降水量对总降水量的贡献百分比)的分析结果表明:中国东部夏季暴雨分布在20世纪70年代末和90年代初经历两次反相的经向"三极子"跃变。中国东部夏季暴雨的年代际演变过程可分为三个时段:1960~1979年为华南和华北暴雨偏多、江淮流域暴雨偏少的经向"三极子"分布;1980~1991年为南方和华北暴雨偏少、江淮流域暴雨偏多的经向三极子"分布;1992~2011年为南方暴雨显著偏多、华北暴雨持续偏少,逐渐形成经向"偶极子"分布,并导致近十多年我国夏季"南涝北旱"的整体格局。1970年代末(1990年代初)跃变相关联的大尺度环流异常配置:东亚夏季风的减弱(增强),西太平洋副高的增强西伸但南撤(北抬),南亚高压的减弱南缩(增强东扩),以及蒙古高原中低层的气旋式(反气旋式)环流异常。与此同时,低层局地环流也发生调整:华北和黄淮地区以及华南和江南地区均为反气旋式(气旋式)环流异常,而江淮流域和四川盆地受控于风场切变式辐合(辐散)异常;涡度场发生相应变化,南北方大部分地区的负(正)涡度异常不(有)利于低涡的发展,而江淮流域和四川盆地的正(负)涡度异常有(不)利于低涡的发展,进而引发江南和华南暴雨减少(增加)、江淮流域和四川盆地暴雨增加(减少)、黄淮和华北暴雨减少(增加)的经向"三极子"跃变。 相似文献
13.
利用1979-2015年NCEP/NCAR月平均再分析资料、美国国家海洋和大气管理局（NOAA）的月平均降水资料（CMAP）以及英国哈得来中心海表温度月平均资料,采用2009年Kao等定义的中部型ENSO指数,给出了夏季中部型海表温度（SST）异常指数,并分析了中部型ENSO和海洋性大陆（MC）区域气候的联系。结果表明,当夏季中部型海表温度正异常事件发生时,海洋性大陆核心区域（中太平洋）出现显著降水和气温负（正）异常,此时海洋性大陆核心区域有明显的负（正）热源异常,大气受冷却（加热）而下沉（上升）,同时潜热释放之外的非绝热加热表现为负（正）异常,易于导致降水负（正）异常。海洋性大陆区域与中太平洋间主要通过水平环流和垂直环流建立联系。（1）中部型ENSO指数显著正异常时,在对流层低（高）层,海洋性大陆区域和中太平洋间存在由关于赤道的对称气旋性（反气旋性）环流对而形成的直接联系,并使得海洋性大陆区域东部辐散（辐合）偏弱,而海洋性大陆区域西部辐散（辐合）偏强。（2）在垂直剖面上,赤道中太平洋海表温度的正异常和海洋性大陆核心区域的大气异常冷却有利于促使该地区低层赤道西风异常增强并进而利于中部型海表温度正异常的维持,并由此通过反沃克环流圈促进海洋性大陆区域下沉运动增强。此为海洋性大陆与中太平洋间的直接联系,可由皮叶克尼斯机制进行解释。而位于中太平洋与秘鲁地区的异常垂直环流亦可用这一机制进行解释。海洋性大陆与中太平洋的间接联系主要表现在由赤道外低纬和中纬度地区均存在的沿弧形路径上的垂直环流而建立的海洋性大陆与中太平洋地区的联系上。这些弧形垂直剖面上的垂直环流不仅与局地哈得来环流有关,还与热带和中纬度的罗斯贝波动有关。这些结果有利于深刻认识中部型ENSO对海洋性大陆区域气候的影响机理以及与热带外环流异常的联系。 相似文献
14.
In the summers of 2003 and 2007, eastern China suffered similar climate disasters with
severe flooding in the Huaihe River valley and heat waves in the southern Yangtze River delta and
South China. Using SST data and outgoing longwave radiation (OLR) data from NOAA along with
reanalysis data from NCEP/NCAR, the 2002/03 and 2006/07 El Nino episodes in the central Pacific
and their delayed impacts on the following early summertime climate anomalies of eastern China
were analyzed. The possible physical progresses behaved as follows: Both of the moderate El Nino
episodes matured in the central equatorial Pacific during the early winter. The zonal wind anomalies
near the sea surface of the west-central equatorial Pacific excited equatorial Kelvin waves
propagating eastward and affected the evolution of the El Ni\~no episodes. From spring to early
summer, the concurring anomalous easterly winds in the central equatorial Pacific and the end
of upwelling Kelvin waves propagating eastward in the western equatorial Pacific, favored the
equatorial warm water both of the SST and the subsurface temperature in the western Pacific.
These conditions favored the warm state of the western equatorial Pacific in the early summer
for both cases of 2003 and 2007. Due to the active convection in the western equatorial Pacific
in the early summer and the weak warm SST anomalies in the tropical western Pacific from spring
to early summer, the convective activities in the western Pacific warm pool showed the pattern
in which the anomalous strong convection only appeared over the southern regions of the tropical
western Pacific warm pool, which effects the meridional shift of the western Pacific subtropical
high in the summer. The physical progress of the delayed impacts of the El Ni\~no episodes in the
central equatorial Pacific and their decaying evolution on the climate anomalies in eastern China
were interpreted through the key role of special pattern for the heat convection in the tropical
western Pacific warm pool and the response of the western North Pacific anomalous anticyclone. 相似文献
15.
The Oscillation between Tropical Indian Ocean and North Pacific:Evidence and Possible Impact on Winter Climate in China 
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下载免费PDF全文 This paper provides evidence that the variation of boreal winter sea level pressure (SLP) over the North Pacific is out-of-phase with SLP fluctuation over the tropical Indian Ocean on both the interdecadal and interannual time scales.Subsequently,a SLP between tropical Indian Ocean and North Pacific (TIO-NP) oscillation index is defined to indicate the variation of such out-of-phase fluctuation.Moreover,the simultaneous surface air temperature and precipitation anomalies in China are closely related to TIO-NP oscillations.Below-normal surface air temperature anomalies in the northern and the eastern part of China,and less rainfall in southern China,correspond to positive TIO-NP oscillation phase with negative SLP anomalies in tropical Indian Ocean and positive anomalies in North Pacific.The TIO-NP oscillation affects China’s winter climate anomalies,possibly through modulating the northeast East Asia winter monsoon. 相似文献
16.
In the summers of 2003 and 2007, eastern China suffered similar climate disasters with severe flooding in the Huaihe River valley and heat waves in the southern Yangtze River delta and South China. Using SST data and outgoing longwave radiation (OLR) data from NOAA along with reanalysis data from NCEP/NCAR, the 2002/03 and 2006/07 El Ni(n)o episodes in the central Pacific and their delayed impacts on the following early summertime climate anomalies of eastern China were analyzed. The possible physical progresses behaved as follows: Both of the moderate E1 Ni(n)o episodes matured in the central equatorial Pacific during the early winter. The zonal wind anomalies near the sea surface of the west-central equatorial Pacific excited equatorial Kelvin waves propagating eastward and affected the evolution of the E1 Ni(n)o episodes. From spring to early summer, the concurring anomalous easterly winds in the central equatorial Pacific and the end of upwelling Kelvin waves propagating eastward in the western equatorial Pacific, favored the equatorial warm water both of the SST and the subsurface temperature in the western Pacific. These conditions favored the warm state of the western equatorial Pacific in the early summer for both cases of 2003 and 2007. Due to the active convection in the western equatorial Pacific in the early summer and the weak warm SST anomalies in the tropical western Pacific from spring to early summer, the convective activities in the western Pacific warm pool showed the pattern in which the anomalous strong convection only appeared over the southern regions of the tropical western Pacific warm pool, which effects the meridional shift of the western Pacific subtropical high in the summer. The physical progress of the delayed impacts of the E1 Nifio episodes in the central equatorial Pacific and their decaying evolution on the climate anomalies in eastern China were interpreted through the key role of special pattern for the heat convection in the tropical western Pacific warm pool and the response of the western North Pacific anomalous anticyclone. 相似文献
17.
POSSIBLE INFLUENCES OF THE TROPICAL INDIAN OCEAN DIPOLE ON THE EASTWARD PROPAGATION OF MJO 总被引：1，自引：0，他引：1
Based on multiple datasets, correlation and composite analyses, and case studies, this paper investigated possible influences of the Indian Ocean dipole （IOD） mode on the eastward propagation of intraseasonal oscillation in the tropical atmosphere. The results showed that （1） the 30-60 day outgoing longwave radiation anomalies in the southeastern Indian Ocean and the 30-60 day 850-hPa zonal wind anomalies over the equatorial central Indian Ocean were significantly correlated with the IOD index; （2） during positive IOD years, the anomalously cold water in the southeastern Indian Ocean and the 850-hPa anomalous easterlies over the equatorial central Indian Ocean might act as barriers to the continuously eastward propagation of the intraseasonal convection, which interrupts the Madden-Julian oscillation （MJO） propagation in the eastern equatorial Indian Ocean and western Pacific; and （3） during negative IOD years, the anomalously warm water in the southeastern Indian Ocean and the low-level westerly anomalies over the equatorial central Indian Ocean favor the eastward movement of MJO. 相似文献
18.
利用1948—2011年NCEP/NCAR月平均再分析资料和1951—2010年我国160站降水量资料,研究了冬季亚洲—太平洋区域的大气遥相关及其与东亚冬季风和降水的关系。结果表明:冬季在亚洲—西太平洋与中、东太平洋中低纬度对流层上层扰动温度之间存在类似于夏季的亚洲—太平洋涛动 (APO) 现象,即当东亚中低纬度对流层中、上层偏暖时,中东太平洋中低纬度对流层中上层温度偏冷,反之亦然。冬季APO可以反映冬季亚洲—太平洋东西向热力差异强度变化,与夏季相比,冬季APO遥相关在亚洲的中心位置略偏南、偏东,且冬季APO与大气环流关系与夏季也有所不同;当冬季APO指数偏高时,对流层上层东亚大槽位置偏西,而东亚热带地区的高压向北伸展,导致我国南方对流层为深厚的异常反气旋系统所控制,此时南方地区对流层低层盛行异常的偏东北气流,并伴随水汽辐散和异常下沉运动,南方降水偏少;冬季APO指数与ENSO有紧密联系。 相似文献
19.
1991～1994年El Niño的异常特征的诊断研究 总被引：3，自引：1，他引：2
1991～1994年热带中东太平洋海温持续4a多出现正距平。Niño3指数一直为正值。在此正距平背景下,产生了两次振荡和3次ElNiño暖期。在此期间赤道东太平洋海温在±5°纬度范围内发生了两次负距平的变化,形成了一个狭窄的温度梯度很大的“冷核”,而赤道外的中纬度海洋则持续维持两个正海温距平。这一时期海表温度资料EOF分析的结果进一步表明,第一特征向量的空间分布实际上反映了上述冷核特征。1991～1994年的ENSO事件主要是低频分量发生了较大异常,赤道低层纬向风和高层西风在前期减弱(1991-01-1992-05),后期加强(1992-06-1994-011).无论是海温还是风场的低频分量都表现出一次ENSO循环的特征。因此作者认为,虽然Niño3指数等在这4a多期间均为正值,但是大气和海洋耦合系统的低频变化部分只发生了一次完整的ENSO循环过程。1991年至1992年上半年对应于ElNiño暖位相,1992年下半年至1994年底对应于LaNina冷位相。但是这个冷位相没有能够得到充分发展,只出现两次极狭窄的冷核。冷位相的明显“夭折”,而代之以出现两次较弱的增暖,可能与季节内尺度的大气强迫与低频变化部分的相互作用有关。 相似文献
20.
R. H. Kripalani J.-H. Oh J.-H. Kang S. S. Sabade A. Kulkarni 《Theoretical and Applied Climatology》2005,82(1-2):81-94
Summary The influence of the Indian Ocean Zonal Mode on the extreme summer monsoon rainfall over East Asia (China, Korea, Japan) has been investigated applying simple statistical techniques of correlation and composite analysis. While the observed rainfall data are used as a measure of rainfall activity, the NCEP-NCAR Reanalysis data are used to examine the circulation features associated with the extreme monsoon phases and the dynamics of the zonal mode – monsoon variability connections. The data used covers the period 1960 to 2000.The equatorial Indian Ocean is dominated by westerly winds blowing towards Indonesia. However, during the positive phase of the zonal mode, an anomalous, intensified easterly flow prevails, consistent with the positive (negative) sea surface temperature anomalies over the western (southeastern) equatorial Indian Ocean. This positive phase of the zonal mode enhances summer monsoon activity over China, but suppresses the monsoon activity over the Korea-Japan sector, 3 to 4 seasons later. The relationship is more consistent and stronger over the Korea-Japan region than over China.The Indian Ocean influences the monsoon variability over East Asia via the northern hemisphere mid-latitudes or via the eastern Indian Ocean/west Pacific route. The monsoon-desert mechanism induces strong subsidence northwest of India due to the anomalous convection over the Indian Ocean region associated with the positive phase of the zonal mode. This induces a zonal wave pattern over the mid-latitudes of Asia propagating eastwards and displacing the north Pacific subtropical high over East Asia. The warming over the eastern Indian Ocean/west Pacific inhibits the westward extension of the north Pacific sub-tropical high. The location and shape of this high plays a dominant role in the monsoon variability over East Asia. The memory for delayed impact, three to four seasons later, could be carried by the surface boundary conditions of Eurasian snow cover via the northern channel or the equatorial SSTs near the Indonesian Through Flow via the southern channel. 相似文献