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灾害性长期天气的转折期是短期气候变化中引人关注的重要问题 .众所周知 ,异常的大气环流会导致异常短期灾害性 (旱涝 )气候 ,因此根据前期月、季尺度的环流物理因子 ,可进行预测 .但灾害性短期气候的转折期 ,如梅雨的暴发、四川盆地夏旱的结束 ,往往发生在较月更短的时间尺度里 .为了反映环流月内时间尺度的变化特征 ,我们从 50 0 h Pa月平均高度场中选取欧亚地区与四川夏旱有关的环流区 ,分析其候际变化的特点 ,用切比雪夫多项系数将其主要演变特征定量化 ,用最优子集回归、逐步回归模式来分别研制夏旱结束期的预报 ,并将历史预报效果及… 相似文献
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平流层大气动力学及其与对流层大气相互作用的研究:进展与问题 总被引：2，自引：2，他引：0
本文综述了近年来关于平流层大气动力学及其与对流层大气相互作用动力过程的研究进展,特别是回顾了近年来关于平流层大气环流和行星波动力学、热带平流层大气波动及其与基本气流相互作用、平流层大气环流变异对对流层环流和气候变异的影响及其动力过程、平流层大气数值模拟以及在全球变暖背景下平流层大气的长期演变趋势预估等的研究进展。最近的研究揭示了大气准定常行星波传播波导的振荡现象、重力波在热带平流层准两年振荡和全球物质输送中的作用、平流层长期的变冷趋势变化、平流层在对流层天气和气候变化中的作用等现象,表明了平流层大气动力学研究的重要性。平流层大气动力学的深入研究,以及对数值模式中平流层模拟性能的提高,最终都会推动整个大气科学和气候变化研究的进一步发展。 相似文献
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中国气候年代际变化的大气环流形势对比分析 总被引：25，自引：3，他引：22
该文通过５０年代和８０年代大气环流形势异常的对比,分析了中国气候年代际变化的特征．其主要结果是：中国气候变化存在明显的年代际变化特征;在中国气候年代际变化的不同气候阶段,北半球大气环流也有明显的不同异常形势,尤其是西北太平洋和中国大陆一带地区的环流异常非常不一样;同时,与空间分布的明显差异相类似,子波分析表明对于不同的气候阶段,也有不同的时间变化型与之相对应． 相似文献
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冬季积雪的异常分布型及其与冬、夏大气环流的耦合关系 总被引：4，自引：0，他引：4
采用 ECMWF1 979～ 1 993年 2 .5°× 2 .5°的网格点积雪深度资料 ,研究了较为细致的积雪异常的空间分布特征 ,揭示了欧亚大陆冬季积雪的异常空间分布型 ;并采用 SVD方法研究了冬季积雪的异常分布型与冬、夏大气环流的耦合关系。结果表明 :欧亚大陆冬季积雪深度存在典型的异常空间分布型 ;积雪的异常分布型与冬、夏大气环流之间均存在一定的耦合关系。冬季积雪的异常分布型与大气 EU遥相关型存在明显的同时性相互作用 ,大气 EU遥相关型有利于冬季积雪异常分布型的出现和维持 ,而积雪异常分布型对大气 EU遥相关型的发生起一定的作用 ,进而对冬季风活动产生影响。冬季积雪的这种异常分布型与夏季大气环流 ,尤其是东亚地区的夏季大气环流 ,也存在一定的联系。积雪异常分布型可以通过影响副热带高压的南北进退 ,对东亚季风及中国夏季雨带产生影响。 相似文献
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文章简要综述了次网格尺度海非均匀性大对大气环流模式性能的影响，南极冰在全球环流和短期气候变化中的作用，以及模式中不同的海冰反照率参数化对地表温度和辐射的影响等研究结果，说明海冰对极地海洋和大气的能量收支及短期气候变化有重要作用，不同的海洋参数化方案对气候模拟结果有重要影响。 相似文献
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海冰在大气环流模式中的重要作用 总被引：1，自引：0，他引：1
文章简要综述了次网格尺度海冰非均匀性对大气环流模式性能的影响；南极冰在全球环流和短期气候变化中的作用；以及模式中不同的海冰反照率参数化对地表温度和辐射的影响等研究结果．说明海冰对极地海洋和大气的能量收支及短期气候变化有重要作用，不同的海冰参数化方案对气候模拟结果有重要影响． 相似文献
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东亚低纬地区局地Hadley环流特征及其与大气臭氧的关系 总被引：2，自引：1，他引：1
利用1975—2008年NCEP/NCAR的逐月平均风场资料及1975—2001年ECMWF的逐月多层臭氧质量混合比资料,用大气环流三维分解方法研究了东亚低纬度地区之局地Hadley环流的结构及年代际演变特征,分析了该区域局地Hadley环流异常时对应大气臭氧的空间距平分布。研究结果表明:(1)东亚低纬度地区局地Hadley环流既与纬圈平均Hadley环流具有明显的季节变化,但又具有明显区别于纬圈平均Hadley环流的自身结构特征:除冬季存在明显向南、向北输送的两闭合环流圈外,局地Hadley环流在其余季节均以向南输送为主;(2)该局地Hadley环流具有不同于纬圈平均Hadley环流的年代际演变特征,在整个研究时段上以振荡变化为主,并没有表现出象纬圈平均值那样明显的增强趋势;(3)区域赤道上空平流层20～50 hPa大气臭氧的正负距平异常中包含有局地Hadley环流的异常信息:当局地Hadley环流异常强时,区域赤道上空20～50 hPa大气臭氧有一显著负距平异常中心,反之亦然。 相似文献
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《大气与海洋》2013,51(3):217-231
Abstract An intermediate coupled model of the tropical Pacific ocean‐atmosphere system was reduced by projecting the non‐linear model onto a truncated basis set of its own empirical orthogonal functions (EOFs). For moderate coupling strengths, the simulated El Niño/Southern Oscillation (ENSO) variability consists of a dominant quasi‐quadrennial mode with a period of approximately four years and a smaller quasi‐biennial mode at a period of approximately two years. In the absence of a seasonal cycle, the leading two EOFs capture the dynamics of the leading interannual mode, with a further two EOFs being required to capture the secondary oscillation. The presence of seasonal forcing increases the EOF requirement by two, the leading pair of EOFs being dominated by the annual cycle. Normal mode analysis of the reduced models indicates that the quasi‐biennial mode manifests itself, even though it is linearly stable, by non‐linear coupling to the quasi‐quadrennial mode. The nonlinearity does not produce the quasi‐biennial signal unless the spatial degrees of freedom associated with the linear quasi‐biennial mode are present. Other linearly stable modes also couple non‐linearly to the leading interannual mode and to the seasonal cycle, but the quasi‐biennial mode is favoured over other, less‐damped linear modes because of its proximity to a multiple of the quasi‐quadrennial frequency. 相似文献
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On the basis of the 1950–2001 NCEP reanalysis data, space-time variability of the surface pressure (SP), surface air temperature (SAT), and precipitation fields in Eurasia is studied in connection with the 1976–1977 climate shift. The effect of the shift manifests itself in the change in the space-time structure of empirical orthogonal functions (EOFs) in all these fields from September to April. For SP and SAT, during this period, only two first EOFs are stable with respect to the climate shift. Also, for SAT and SP, the second EOFs are stable from November to April and from September to December, respectively. For the precipitation field, even the first EOFs are unstable during the whole period, with the exception of January and February. Instability with respect to the climate shift appears first in change in the EOF spatial pattern of the fields. Stability of the first modes of the Eurasian meteorological fields to the 1976–1977 climate shift is caused by a relative stability of the North Atlantic Oscillation, which explains up to 70 and 30% of variance of the first and second EOFs, respectively, of the hydrometeorological fields in the region. 相似文献
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Large scale aspects of India-China summer monsoon rainfall 总被引：1，自引：0，他引：1
This study investigates the dominant modes of variability in monthly and seasonal rainfall over the India-China region mainly through Empirical Orthogonal Function (EOF) analysis. The EOFs have shown that whereas the rain-fall over India varies as one coherent zone, that over China varies in east-west oriented bands. The influence of this banded structure extends well into India.Relationship of rainfall with large scale parameters such as the subtropical ridge over the Indian and the western Pacific regions, Southern Oscillation, the Northern Hemispheric surface air temperature and stratospheric winds have also been investigated. These results show that the rainfall over the area around 40oN, 110oE over China is highly related with rainfall over India. The subtropical ridge over the Indian region is an important predictor over India as well as over the northern China legion. 相似文献
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Evaluating EOF modes against a stochastic null hypothesis 总被引：1，自引：2，他引：1
Dietmar Dommenget 《Climate Dynamics》2007,28(5):517-531
In this paper it is suggested that a stochastic isotropic diffusive process, representing a spatial first order auto regressive
process (AR(1)-process), can be used as a null hypothesis for the spatial structure of climate variability. By comparing the
leading empirical orthogonal functions (EOFs) of a fitted null hypothesis with EOF modes of an observed data set, inferences
about the nature of the observed modes can be made. The concept and procedure of fitting the null hypothesis to the observed
EOFs is in analogy to time analysis, where an AR(1)-process is fitted to the statistics of the time series in order to evaluate
the nature of the time scale behavior of the time series. The formulation of a stochastic null hypothesis allows one to define
teleconnection patterns as those modes that are most distinguished from the stochastic null hypothesis. The method is applied
to several artificial and real data sets including the sea surface temperature of the tropical Pacific and Indian Ocean and
the Northern Hemisphere wintertime and tropical sea level pressure. 相似文献
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There is strong evidence that Indian Ocean sea surface temperatures (SSTs) influence the climate variability of Southern Asia and Africa; hence, accurate prediction of these SSTs is a high priority. In this study, we use canonical correlation analysis (CCA) to design empirical models to assess the predictability of tropical Indian Ocean SST from sea level pressure (SLP) and SST themselves with lead-times up to one year. One model uses the first twelve empirical orthogonal functions (EOFs) of SLP over the Indian Ocean using different lead-times to predict SST. A CCA model with EOFs of SST as the predictor at the same lead-times is compared to SLP as a predictor and shows the auto-correlation of the system. A CCA using the first five extended empirical orthogonal functions (EEOFs) of sea level pressure over the Indian Ocean basin for an interval of two years combined with SST EOFs as predictors is found to produce the greatest correlation between forecast and observed SSTs. This model obtains higher skill by explicitly considering the development in time of SLP anomalies in the region. The skill of this model, assessed from retroactive forecasts of an 18 year period, shows improvement relative to other empirical forecasts particularly for the central and eastern Indian Ocean and boreal autumn months preceding the Southern Hemisphere summer rainfall season. This is likely due to the limited domain of this model identifying modes of variability that are more pronounced in these areas during this season. Finally, a nonlinear canonical correlation analysis (NLCCA) derived from a neural network is used to analyze the leading nonlinear modes. These nonlinear modes differ from the linear CCA modes with distinct cold and warm SST phases suggesting a nonlinear relationship between SST and SLP over the tropical Indian Ocean. 相似文献
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Monthly mean sea surface temperature (SST), free air temperature from satellite microwave sounding units (MSU) and oceanic surface energy fluxes are subjected to empirical orthogonal function (EOF) analysis for a common decade to investigate the physical relationships involved. The first seasonal modes of surface solar energy flux and SST show similar inter-hemispheric patterns with an annual cycle. Solar flux appears to control this pattern of SST. The first seasonal mode of MSU is similar with, additionally, land-sea differences; MSU is apparently partly controlled by absorption of solar near-infrared radiation and partly by sensible heat from the land surface. The second and third seasonal eigenvector of SST and solar flux exhibit semi-annual oscillations associated with a pattern of cloudiness in the subtropics accompanying the translation of the Hadley cell rising motion between the hemispheres. The second seasonal mode of MSU is dominated by an El Niño signal. The first nonseasonal EOFs of SST and solar flux exhibit El Niño characteristics with the solar pattern being governed by west-to-east translation of a Walker cell type pattern. The first non-seasonal EOF of MSU shows a tropical strip pattern for the El Niño mode, which is well correlated with the latent heat fluxes in the tropical east Pacific but not in the tropical west Pacific. Two possible explanations are: an increase in subsidence throughout the tropical strip driven by extra evaporation in the tropical east Pacific and consequent additional latent heat liberation; a decrease of meridional heat flux out of the tropics. 相似文献
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S. K. Deb H. C. Upadhyaya O. P. Sharma A. Chakraborty 《Meteorology and Atmospheric Physics》2006,94(1-4):43-64
Summary Hindcasts for the Indian summer monsoons (ISMs) of 2002 and 2003 have been produced from an ensemble of numerical simulations
performed with a global model by changing SST. Two sets of ensemble simulations have been produced without vegetation: (i)
by prescribing the weekly observed SST from ECMWF (European Centre for Medium Range Weather Forecasting) analyses, and (ii)
by adding weekly SST anomalies (SSTA) of April to the climatological SST during the simulation period from May to August.
For each ensemble, 10 simulations have been realized with different initial conditions that are prepared from ECMWF data with
five each from April and May analyses of both the years. The predicted June–July monsoon rainfall over the Indian region shows
good agreement with the GPCP (observed) pentad rainfall distribution when 5 member ensemble is taken from May initial conditions.
The All-India June–July simulated rainfall time series matches favourably with the observed time series in both the years
for the five member ensemble from May initial condition but drifts away from observation with April initial conditions. This
underscores the role of initial conditions in the seasonal forecasting. But the model has failed to capture the strong intra-seasonal
oscillation in July 2002. Heating over equatorial Indian Ocean for June 2002 in a particular experiment using 29th May 12
GMT as initial conditions shows some intra-seasonal oscillation in July 2002 rainfall, as in observation. Further evaluation
of the seasonal simulations from this model is done by calculating the empirical orthogonal functions (EOFs) of the GPCP rainfall
over India. The first four EOFs explain more than 80% of the total variance of the observed rainfall. The time series of expansion
coefficients (principal components), obtained by projecting on the observed EOFs, provide a better framework for inter-comparing
model simulations and their evaluation with observed data. The main finding of this study is that the All-India rainfall from
various experiments with prescribed SST is better predicted on seasonal scale as compares to prescribed SST anomalies. This
is indicative of a possible useful seasonal forecasts from a GCM at least for the case when monsoon is going to be good. The
model responses do not differ much for 2002 and 2003 since the evolution of SST during these years was very similar, hence
July rainfall seems to be largely modulated by the other feedbacks on the overall circulation. 相似文献
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M. Pontaud J.-P. Céron M. Kimoto F. Pluviaud L. Terray A. Vintzileos 《Climate Dynamics》2000,16(12):917-933
The interannual variability over the tropical Pacific and a possible link with the mean state or the seasonal cycle is examined
in four coupled ocean-atmosphere general circulation models (GCM). Each model is composed of a high-resolution ocean GCM of
either the tropical Pacific or near-global oceans coupled to a moderate-resolution atmospheric GCM, without using flux correction.
The oceanic subsurface is considered to describe the mean state or the seasonal cycle through the analytical formulations
of some potential coupled processes. These coupled processes characterise the zonal gradient of sea surface temperature (hereafter
SST), the oceanic vertical gradient of temperature and the equatorial upwelling. The simulated SST patterns of the mean state
and the interannual signals are generally too narrow. The grid of the oceanic model could control the structure of the SST
interannual signals while the behaviour of the atmospheric model could be important in the link between the oceanic surface
and the subsurface. The first SST EOFs are different between the coupled models, however, the second SST EOFs are quite similar
and could correspond to the return to the normal state while that of the observations (COADS) could favour the initial anomaly.
All the models seem to simulate a similar equatorial wave-like dynamics to return to the normal state. The more the basic
state is unstable from the coupled processes point of view, the more the interannual signal are high. It seems that the basic
state could control the intensity of the interannual variability. Two models, which have a significant seasonal variation
of the interannual variance, also have a significant seasonal variation of the instability with a few months lag. The potential
seasonal phase locking of the interannual fluctuations need to be examined in more models to confirm its existence in current
tropical GCMs.
Received: 30 July 1999 / Accepted: 25 April 2000 相似文献
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Robust GEFA Assessment of Climate Feedback to SST EOF Modes 总被引：2，自引：0，他引：2
Atmospheric response to SST variability was estimated using generalized equilibrium feedback analysis (GEFA) in the SST EOF space with synthesis data from an idealized climate model. Results show that the GEFA atmospheric response to the leading SST EOF modes is much more accurate and robust than the GEFA feedback matrix in physical space. Therefore, GEFA provides a practical method for assessing atmospheric response to large-scale SST anomalies in terms of the leading EOFs. 相似文献
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非均匀站网EOFs展开的失真性及其修正 总被引：11，自引：0，他引：11
从理论上证明，非均匀站网ＥＯＦｓ展开有不同程度的失真。在同等条件下，均匀站网与非均匀站网ＥＯＦｓ展开结果有明显差异．提出了一种附加面积权重的修正方案用以弥补非均匀站网ＥＯＦｓ展开的失真现象。实例计算表明，中国气温场（１６０站）经修正ＥＯＦｓ展开后，其气温变化主分量趋势与特征能更加客观地揭示中国地区增暖效应的局地差异。 相似文献