共查询到20条相似文献，搜索用时 431 毫秒
1.
Using a two-dimensional blocking index, the cause and effect relationship between European blocking (EB) events and North Atlantic Oscillation (NAO) events is investigated. It is shown that the EB event frequency is enhanced over Northern (Southern) Europe for negative (positive) phases of the NAO. Enhanced EB events over Northern Europe precede the establishment of negative phase NAO (NAO-) events, while the enhanced frequency of EB events over Southern Europe lags positive phase NAO (NAO+) events. The physical explanation for why enhanced EB events over Northern (Southern) Europe lead (lag) NAO- (NAO+) events is also provided. It is found that the lead-lag relationship between EB events in different regions and the phase of NAO events can be explained in terms of the different latitudinal distribution of zonal wind associated with the different phases of NAO events. For NAO+ events, the self-maintained eastward displacement of intensified midlatitude positive height anomalies owing to the intensified zonal wind can enhance the frequency of EB events over Southern Europe, thus supporting a standpoint that EB events over Southern Europe lag NAO+ events. Over Northern Europe, EB events lead NAO- events because NAO- events arise from the self-maintained westward migration of intensified blocking anticyclones due to the weakened zonal wind in higher latitudes. 相似文献
2.
An Observed Connection Between Wintertime Temperature Anomalies over Northwest China and Weather Regime Transitions in North Atlantic 
下载免费PDF全文
下载免费PDF全文 In this study, the association between wintertime temperature anomalies over Northwest China and the weather regime transitions in North Atlantic on synoptic scale is analyzed by using observational surface air temperature(SAT) data and atmospheric reanalysis data. Daily SAT anomaly and duration time are used in order to define SAT anomaly cases. Differences with regard to the circulation anomalies over the Ural Mountains and the upstream North Atlantic area are evident. It is found that the colder than normal SAT is caused by the enhanced Ural high and associated southward flow over Northwest China. Time-lagged composites reveal possible connections between the SAT anomalies and the different development phases of the North Atlantic Oscillation(NAO). The Ural highs tend to be strengthened during the negative phase of NAO(NAO–) to Atlantic ridge transition, which are closely related to the downstream-propagating Rossby wave activity. The opposite circulation patterns are observed in the warm SAT cases. A cyclonic circulation anomaly is distinctly enhanced over the Urals during the positive phase of NAO(NAO+) to Scandinavian blocking transition, which would cause warmer SAT over Northwest China. Further analyses suggest that the intensified zonal wind over North Atlantic would favor the NAO– to Atlantic ridge transition, while the weakened zonal wind may be responsible for the transition between NAO+ and Scandinavian blocking. 相似文献
3.
In a weakly nonlinear model how an initial dipole mode develops to the North Atlantic Oscillation (NAO) in a localized shifting
jet under the prescribed eddy forcing is examined. It is found that the zonal structure of the eddy-driven NAO anomaly is
not only dominated by the longitudinal distribution of the preexisting Atlantic storm track, but also by the initial condition
of the NAO anomaly itself associated with the interaction between a localized shifting jet and a topographic standing wave
over the Atlantic basin. When both the initial NAO anomaly and the eddy vorticity forcing in the prior Atlantic storm track
are more zonally localized, the subsequent eddy-driven NAO anomaly can be more zonally isolated and asymmetric. But, it seems
that the shape of the initial NAO anomaly associated with the latitudinal shift of a prior Atlantic jet plays a more important
role in producing the zonal asymmetry of subsequent NAO patterns. The zonal asymmetry of the NAO anomaly can be enhanced as
the height of topography increases. In addition, it is further found that blocking events occur easily over the Europe continent
through the decaying of positive-phase NAO events. However, prior to the positive-phase NAO life cycle the variability in
each of three factors: the Atlantic jet, the eddy vorticity forcing in the Atlantic storm track and the initial NAO anomaly
can result in a variation in the blocking activity over the Europe sector in strength, duration, position and pattern. 相似文献
4.
The flow patterns of Euro-Atlantic blocking events in winter are investigated by dividing the sector into three sub- regions： 60°-30°W （Greenland region）; 20°W-30°E [eastern Atlantic-Europe （EAE） region]; and 50°-90°E （Ural region）. It is shown that blocking events in winter are extremely frequent in the three sub-regions. Composite 500-mb geopotential height fields for intense and long-lived blocking events demonstrate that the blocking fields over Greenland and Ural regions exhibit southwest-northeast （SW-NE） and southeast-northwest （SE-NW） oriented dipole-type patterns, respectively, while the composite field over the EAE region exhibits an Ω-type pattern. The type of composite blocking pattern seems to be related to the position of the blocking region relative to the positive center of the climatological stationary wave （CSW） anomaly existing near 10°W.
The physical cause of why there are different composite blocking types in the three sub-regions is identified using a nonlinear multiscale interaction model. It is found that when the blocking event is in almost the same position as the positive CSW anomaly, the planetary-scale field can exhibit an Ω-type pattern due to the enhanced positive CSW anomaly. Neverthe- less, a SW-NE （SE-NW） oriented dipole-type block can occur due to the reduced positive CSW anomaly as it is farther in the west （east） of the positive CSW anomaly. The total fields of blocking in the three regions may exhibit a meandering flow comprised of several isolated anticyclonic and cyclonic vortices, which resembles the Berggren-Bolin-Rossby meandering jet type. 相似文献
The physical cause of why there are different composite blocking types in the three sub-regions is identified using a nonlinear multiscale interaction model. It is found that when the blocking event is in almost the same position as the positive CSW anomaly, the planetary-scale field can exhibit an Ω-type pattern due to the enhanced positive CSW anomaly. Neverthe- less, a SW-NE （SE-NW） oriented dipole-type block can occur due to the reduced positive CSW anomaly as it is farther in the west （east） of the positive CSW anomaly. The total fields of blocking in the three regions may exhibit a meandering flow comprised of several isolated anticyclonic and cyclonic vortices, which resembles the Berggren-Bolin-Rossby meandering jet type. 相似文献
5.
欧洲地区夏季热浪的特征及其与阻塞环流的联系 总被引：2，自引：1，他引：1
选取了一个热浪指数,利用地面2 m气温场和500 h Pa位势高度场的美国环境预报中心和国家大气研究中心(NCEP/NCAR)再分析资料,通过聚类分析发现欧洲大陆容易产生6类热浪:西欧型(WE)、俄罗斯型(RU)、东欧型(EE)、斯堪的纳维亚半岛型(SC)、北海型(NS)、伊比利亚半岛型(IB);这些热浪事件都与欧洲大陆阻塞的位置有关。同时我们发现这6类热浪发生的频率出现明显的年代际变化,特别在20世纪80年代以后欧洲大陆热浪发生频率明显的增多趋势可能与欧洲大陆增暖背景有关,而欧洲大陆热浪发生频率的年代际变化可能是夏季北大西洋涛动(NAO)的年代际变化的结果。夏季NAO偶极子通过欧洲地区的阻塞异常对欧洲大陆气温有重要的调制作用。当夏季NAO指数处于正位相阶段时,欧洲大陆容易产生高纬度热浪,反之则容易产生低纬度热浪,并且欧洲大陆增暖趋势并不影响NAO对欧洲气温的调制作用。同时还发现:大西洋夏季NAO事件可以是欧洲热浪发生的前期条件,欧洲大陆阻塞异常落后于NAO事件1~5 d,其中IB型和WE型与NAO同期相关,其余4类型热浪对应阻塞落后于NAO 4~5 d。另外,也发现大西洋—欧洲大陆定常波列正距平的位置通过对欧洲阻塞的影响,而影响欧洲热浪发生的频率和位置。 相似文献
6.
The impact on temperature and precipitation anomalies over the European continent of the different action centers of blocking events in the Euro-Atlantic sector was investigated. It was found that the position of the blocking action center in the Euro-Atlantic region seems to dominate European climates. When the center of the blocking action is in the Greenland region, there is a strong negative temperature anomaly over Central and Northern Europe, as well as a strong positive precipitation anomaly over southern Europe. However, there tends to be a strong negative temperature anomaly in the west （east） part of Europe when the center of the blocking action is shifted to the Eastern Atlantic and west Europe （east Europe）. In particular, when the blocking action center is closer to the European continent, the fall in temperature becomes more evident over Central and south Europe than over other regions. Moreover, it was found that when the region where the blocking action center exists changes from the Eastern Atlantic and west Europe region to the east Europe region, the existing region of dominant positive precipitation anomalies varies from southwest Europe to southeast Europe and the Middle East. 相似文献
7.
The representation of the wintertime North Atlantic Oscillation (NAO) and its relationship with atmospheric blocking and the Atlantic jet stream is investigated in a set of CMIP5 models. It is shown that some state-of-the-art climate models are unable to correctly simulate the physical processes connected to the NAO. This is especially true for models with a strongly underestimated frequency of high-latitude blocking over Greenland. In these models the first empirical orthogonal function (EOF1) of the Euro-Atlantic sector can represent at least three different categories of dominant modes of variability associated with different prevalent regions of blocking occurrence and jet stream displacements. It is therefore possible to show that such “biased NAOs” are connected with different dynamical processes with respect to the canonical NAO seen in observations. Since the NAO is a widely used concept in scientific community, the consequent “dynamical misinterpretation” of the NAO that can result when climate models are analyzed may have important implications for the NAO-related studies. This may be especially relevant for the ones involving climate scenarios, since these modeled NAOs may react differently to greenhouse gas forcing. 相似文献
8.
北大西洋涛动指数变化与北半球冬季阻塞活动 总被引：2，自引：0，他引：2
线性回归分析表明北大西洋涛动(NAO)主要与大西洋、欧洲及乌拉尔山地区阻塞的频率和强度的变化存在显著相关关系.在NAO负位相时期阻塞活动在大西洋地区较为频繁且强度较强,正位相时期大西洋地区阻塞活动减少,强度减弱,而欧洲阻塞加强,频率增加,同时乌拉尔山地区的阻塞活动也显著减少.NAO正指数的增强和减弱对应于大西洋和欧洲阻... 相似文献
9.
In the Northern hemisphere, regions characterized by an enhanced frequency of atmospheric blocking overlap significantly with
those associated with the major extra-tropical patterns of large-scale climate variability—namely the North Atlantic Oscillation
(NAO) and the Pacific North American (PNA) pattern. There is likewise an overlap in the temporal band-width of blocks and
these climate patterns. Here the nature of the linkage between blocks and the climate patterns is explored by using the ERA-40
re-analysis data set to examine (1) their temporal and spatial correlation and (2) the interrelationship between blocks and
the NAO/PNA. It is shown that a strong anti-correlation exists between blocking occurrence and the phase of the NAO (PNA)
in the North Atlantic (western North Pacific), and that there are distinctive inter-basin differences with a clear geographical
(over North Atlantic) and quantitative (over North Pacific) separation of typical blocking genesis/lysis regions during the
opposing phases of the climate patterns. An Empirical Orthogonal Function (EOF) analysis points to a significant influence
of blocking upon the NAO pattern (identifiable as the leading EOF in the Euro-Atlantic), and a temporal analysis indicates
that long-lasting blocks are associated with the development of negative NAO/PNA index values throughout their life-time.
In addition an indication of a cause-and effect relationship is set-out for the North Atlantic linkage. 相似文献
10.
Temporal Structures of the North Atlantic Oscillation and Its Impact on the Regional Climate Variability 总被引：3，自引：0，他引：3
In this study, the temporal structure of the variation of North Atlantic Oscillation （NAO） and its impact on regional climate variability are analyzed using various datasets. The results show that blocking formations in the Atlantic region are sensitive to the phase of the NAO. Sixty-seven percent more winter blocking days are observed during the negative phase compared to the positive phase of the NAO. The average length of blocking during the negative phase is about 11 days, which is nearly twice as long as the 6-day length observed during the positive phase of the NAO. The NAO-related differences in blocking frequency and persistence are associated with changes in the distribution of the surface air temperature anomaly, which, to a large extent, is determined by the phase of the NAO. The distribution of regional cloud amount is also sensitive to the phase of the NAO. For the negative phase, the cloud amounts are significant, positive anomalies in the convective zone in the Tropics and much less cloudiness in the mid latitudes. But for the positive phase of the NAO, the cloud amount is much higher in the mid-latitude storm track region. In the whole Atlantic region, the cloud amount shows a decrease with the increase of surface air temperature. These results suggest that there may be a negative feedback between the cloud amount and the surface air t.emperature in the Atlantic region. 相似文献
11.
利用再分析数据,以在北半球冬季与北大西洋涛动(North Atlantic Oscillation,NAO)相关的向下游传播的准定常波列在欧洲地区是否发生反射为标准,将1957/1958年至2001/2002年这45个冬季分为高纬型和低纬型两类冬季,分别简称为在H型和L型冬季。在H(L)型冬季,和NAO相联系的向下游传播的Rossby波列主要沿高纬度(低纬度)路径传播。对比了在两种类型冬季NAO与同期大气环流、近地面温度(Surface Air Temperature,SAT)、海表面温度(Sea Surface Tempertaure,SST)和降水的关系。结果表明:大气环流方面,在H型冬季,300 hPa位势高度异常在西-西伯利亚和中-西伯利亚西部与NAO呈现正相关,而在L型冬季300 hPa位势高度异常在亚洲东海岸(约40°N)和北太平洋呈现正相关,在H型冬季与NAO相关的经向风异常在中纬度形成波列,而在L型冬季与NAO相关的经向风异常在副热带形成波列;SAT方面,在H型冬季SAT异常在欧亚大陆腹地高纬度地区与NAO呈现正相关,而在L型冬季与NAO相关的SAT异常在欧亚大陆腹地的高纬度地区相对较弱,但NAO造成的SAT异常可以扩展到亚洲东北部;降水方面,H型冬季与L型冬季主要区别在中国南方,在H型冬季降水异常与NAO的关系相对较弱,而在L型冬季降水异常与NAO呈现正相关关系;SST方面,同期SST异常在北大西洋中纬度海域与NAO呈现正相关,而在L型冬季与NAO相关的SST异常在北大西洋中纬度地区相对较弱,在北大西洋北部和南部较强。总体而言,在H型和L型冬季,NAO具有不同下游影响。 相似文献
12.
13.
Sea surface temperature anomaly in the tropical North Atlantic during El Nino decaying years 下载免费PDF全文
下载免费PDF全文 基于1979年到2016年多种再分析资料,本文分析了El Ni?o衰减年热带北大西洋的海温异常.结果表明,热带北大西洋海温在此期间呈显著变暖趋势.10次El Ni?o事件的合成结果表明热带北大西洋海温异常在El Ni?o事件峰值之后的春季达到最大值,并持续到夏季.一般而言,这种异常与三个因子有关,即El Nino,北大西洋涛动和长期趋势,能分别导致局地海温上升0.4℃,0.3℃和0.35℃.1983年和2005年的对比分析表明,尽管El Ni?o强度对春季北大西洋海温起到决定性作用,与长期趋势密切相关的前冬海温也很重要.此外,超前-滞后相关结果表明北大西洋涛动超前海温约2-3个月.比较两个冬季相反位相北大西洋涛动的年份(即1992年和2010年),表明北大西洋涛动也能调制北大西洋海温异常.冬季负位相北大西洋涛动能显著增强El Ni?o的强迫影响,反之亦然.换言之,如果北大西洋涛动与El Ni?o位相相合,衰减年北大西洋海温异常才更为显著.因此,为全面理解热带北大西洋海温变化,除长期趋势外,还必须考虑El Ni?o和北大西洋涛动的综合影响. 相似文献
14.
To assess the extent to which atmospheric low-frequency variability can be ascribed to internal dynamical causes, two extended
runs (1200 winter seasons) of a three level quasi-geostrophic model have been carried out. In the first experiment the model
was forced by an average forcing field computed from nine winter seasons; in the second experiment we used a periodically
variable forcing in order to simulate a seasonal cycle. The analysis has been focused on the leading Northern Hemisphere teleconnection
patterns, namely the Pacific North American (PNA) and the North Atlantic Oscillation (NAO) patterns, and on blocking, both
in the Euro-Atlantic and Pacific sectors. The NAO and PNA patterns are realistically simulated by the model; the main difference
with observations is a westward shift of the centres of action of the NAO. Related to this, the region of maximum frequency
of Atlantic blocking is shifted from the eastern boundary of the North Atlantic to its central part. Apart from this shift,
the statistics of blocking frequency and duration compare favourably with their observed counterparts. In particular, the
model exhibits a level of interannual and interdecadal variability in blocking frequency which is (at least) as large as the
observed one, despite the absence of any variability in the atmospheric energy sources and boundary conditions on such time
scales.
Received: 30 January 1997 / Accepted: 17 June 1997 相似文献
15.
Interannual Variations of the Blocking High over the Ural Mountains and Its Association with the AO/NAO in Boreal Winter 总被引：1，自引：0，他引：1 下载免费PDF全文
下载免费PDF全文 This paper analyzes interannual variations of the blocking high over the Ural Mountains in the boreal winter and their association with the Arctic Oscillation/North Atlantic Oscillation (AO/NAO).In Jan... 相似文献
16.
Variations of winter precipitation over southeastern China in association with the North Atlantic Oscillation 下载免费PDF全文
下载免费PDF全文 The synoptic-scale winter precipitation variations over southeastern China (22°–32°N, 105°–125°E) and their association with the North Atlantic Oscillation (NAO) during 1951–2007 are investigated in this paper. The variability of wintertime precipitation is characterized by meridional displacement of its maximum center. Two precipitation regimes, with maximum centers located over the Yangtze and Pearl River basins, are identified via cluster analysis. Time-lagged analyses suggest that the two precipitation regimes are connected with the decaying phases of positive NAO (NAO+) events of different amplitudes. A strong (medium) NAO+ event is defined as one when the maximum amplitude of the NAO index exceeds 1.0 (in the range of 0.7–1.0) for at least 4 consecutive days and drops to less than 0.3 within 7 days following the peak index. After the peak of a strong NAO+, southerly winds expand northward to the Yangtze River (about 30°N), a northeast–southwest-tilted trough migrates to east of Lake Baikal, and cold air intrudes into central eastern China; thus, precipitation is strengthened over the Yangtze River basin where warm and cold air masses converge. In comparison, during the decaying phase of medium NAO+ events, the southerly winds are relatively weak, and precipitation tends to be enhanced at lower latitudes (around 25°N). Further analysis indicates that downstream Rossby-wave propagation may account for the latitudinal expansion of the southerly wind anomalies over the eastern coastal area of China during the decaying phase of NAO+ events of different strengths. 相似文献
17.
The relation between sudden stratospheric warmings (SSWs) and blocking events is analyzed in a multi-centennial pre-industrial simulation of the Institut Pierre Simon Laplace coupled model (IPSL-CM5A), prepared for the fifth phase of the coupled model intercomparison project. The IPSL model captures a fairly realistic distribution of both SSWs and tropospheric blocking events, albeit with a tendency to overestimate the frequency of blocking in the western Pacific and underestimate it in the Euro-Atlantic sector. The 1000-year long simulation reveals statistically significant differences in blocking frequency and duration over the 40-day periods preceding and following the onset of SSWs. More specifically, there is an enhanced blocking frequency over Eurasia before SSWs, followed by an westward displacement of blocking anomalies over the Atlantic region as SSWs evolve and then decline. The frequency of blocking is reduced over the western Pacific sector during the life-cycle of SSWs, while the model simulates no significant relationship with eastern Pacific blocks. Finally, these changes in blocking frequency tend to be associated with a shift in the distribution of blocking lifetime toward longer-lasting blocking events before the onset of SSWs and shorter-lived blocks after the warmings. This study systematically verifies that the results are consistent with the two pictures that (1) blockings produce planetary scale anomalies that can force vertically propagating Rossby waves and then SSWs when the waves break and (2) SSWs affect blockings in return, for instance via the effect they have on the North Atlantic Oscillation. 相似文献
18.
Swadhin Behera Jayanthi V. Ratnam Yukio Masumoto Toshio Yamagata 《Climate Dynamics》2013,41(3-4):663-676
Extreme summers of Europe are usually affected by blocking highs that shift between Western and Eastern Europe to cause regional variations in the surface temperature anomalies. Generally, the blocking high induces a regional temperature dipole with poles of warm and cold anomalies on two sides of Europe. The extreme summers of Western Europe, when the Eastern Europe is colder than normal, are usually associated with the teleconnections arising from positive Indian Ocean Dipole (IOD) events. In contrast, analogous warm events in Eastern Europe are usually associated with La Niña. The western Pacific conditions that prevail during the turnaround phase of El Niño to La Niña are found to be responsible for developing the extreme Eastern Europe events. The role of North Atlantic Oscillation (NAO) is not blatant for the Eastern Europe summers though it has a weaker influence on Western Europe summers for which IOD plays a dominant role: The seasonal July–August correlation for Western Europe temperature with IOD index is higher than that with the NAO index. The teleconnections for both types of extremes are associated with a Rossby wavetrain that travel around the globe to reach the Europe. This circumglobal teleconnection is largely determined by the location of the tropospheric heat source. For Western Europe warm events, major contributions come from the atmospheric convections/diabatic heating over northwest India and southern Pakistan. For the Eastern Europe events, the convections over northwest Pacific, south of Japan, are found to project the signals on to the mid-latitude wave-guide. These patterns of teleconnection are so robust that those can be seen on daily to seasonal time-scales of atmospheric anomalies. The wavetrains are found to set-in a couple of weeks prior to the development of blocking highs and extreme hot conditions over Europe. 相似文献
19.
The nonlinear association between ENSO and the Euro-Atlantic winter sea level pressure 总被引：1，自引：0，他引：1
A nonlinear projection of the tropical Pacific sea surface temperature anomalies (SSTA) onto the Northern Hemisphere winter sea level pressure (SLP) anomalies by neural networks (NN) was performed to investigate the nonlinear association between El Niño-Southern Oscillation (ENSO) and the Euro-Atlantic winter climate. While the linear impact of ENSO on the Euro-Atlantic winter SLP is weak, the NN projection reveals statistically significant SLP anomalies over the Euro-Atlantic sector during both extreme cold and warm ENSO episodes, suggesting that the Euro-Atlantic climate mainly responds to ENSO nonlinearly. The nonlinear response, mainly a quadratic response to the SSTA, reveals that regardless of the sign of the SSTA, positive SLP anomalies are found over the North Atlantic, stretching from eastern Canada to Europe (with anomaly center located just northwestward of Portugal), and negative anomalies centered over Scandinavia and Norwegian Sea, consistent with the excitation of the positive North Atlantic Oscillation pattern. 相似文献
20.
Paolo Davini Chiara Cagnazzo Pier Giuseppe Fogli Elisa Manzini Silvio Gualdi Antonio Navarra 《Climate Dynamics》2014,43(1-2):71-85
The relationship between atmospheric blocking over Europe and the Atlantic eddy-driven jet stream is investigated in the NCEP/NCAR Reanalysis and in a climate model. This is carried out using a bidimensional blocking index based on geopotential height and a diagnostic providing daily latitudinal position and strength of the jet stream. It is shown that European Blocking (EB) is not decoupled from the jet stream but it is mainly associated with its poleward displacements. Moreover, the whole blocking area placed on the equatorward side of the jet stream, broadly ranging from Azores up to Scandinavia, emerges as associated with poleward jet displacements. The diagnostics are hence applied to two different climate model simulations in order to evaluate the biases in the jet stream and in the blocking representation. This analysis highlights large underestimation of EB, typical feature of general circulation models. Interestingly, observed blocking and jet biases over the Euro-Atlantic area are consistent with the blocking-jet relationship observed in the NCEP/NCAR Reanalysis. Finally, the importance of sea surface temperatures (SSTs) is investigated showing that realistic SSTs can reduce the bias in the jet stream variability but not in the frequency of EB. We conclude highlighting that blocking-related diagnostics can provide more information about the Euro-Atlantic variability than diagnostics simply based on the Atlantic jet stream. 相似文献