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中高纬度大气低频模态研究进展 总被引：1，自引：0，他引：1
大气低频模态是导致中高纬地区季节及气候变化的主要因素,加强低频模态动力机制的认识对于提高短期气候预测水平具有十分重要的科研意义和应用价值。由于中高纬大气低频环流本身的复杂性,关于其动力机制的研究仍然是大气动力学中重点难点问题。本文简单回顾了激发维持低频模态的前两种机制,即:外源强迫、气流的纬向非均匀性对大气低频模态的影响。从观测事实和模式结果出发,着重介绍了瞬变波与基本气流相互作用激发维持低频模态的第三种机制,且详细阐述了线性假设条件下,瞬变波与基本气流相互作用的动力机制。本文最后针对瞬变波与基本气流相互作用研究中一些尚未解决的问题进行了讨论。 相似文献
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大气对外强迫低频遥响应的数值模拟 II:对欧亚中高纬“寒潮”异常的响应 总被引：6，自引：2，他引：4
本文通过用IAP GCM所作的数值模拟研究了欧亚大陆中高纬度地区的外强迫在全球大气中激发的响应.结果清楚表明,同赤道地区的热源强迫一样,中高纬度地区的外强迫也可以在全球大气中产生低频遥响应;通过低频波列EAP,欧亚大陆中高纬度地区的寒潮异常可以对赤道中西太平洋地区的大气运动及全球大气环流有重要影响.对30—60天振荡的强迫激发来讲,地球大气的气候基本态是极为重要的,热带大气对于全球大气的低频振荡活动具有尤为突出的作用. 相似文献
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最近的一系列研究工作指出,大气环流基本气流纬向非对称结构是产生大气低频变化的重要因子之一[1-4]。在低频时间尺度上,大气运动必然要受到外强迫因子的影响。但外因必须通过大气环流运动中的内因才能产生低频环流变化。 相似文献
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本文建立了一个二维定常大气中尺度数值模式，并用该模式讨论了由下垫面粗糙分布非均匀（局地动力强迫）和温度分布非均匀（局地热力强迫）而产生的局地大气环流与大气边界层湍流的相互作用。结果指出：下垫面存在温度分布非均匀时运动方程中的湍流交换项与水平气压梯项一样可促使局地热力环境的形成，由粗糙度分布非均匀强迫产生的局地环流与由下垫面温度分布非均匀强迫产和的局地热力环流间的非线笥相互作用是通过湍流交换实现的。 相似文献
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1大气低频振荡的一般概念一些气象因子具有10～90天的准周期变化规律，这种振荡常在30～60天具有较大的振幅，通常将大气中一些气象因子具有的10～20天和30～60天准周期性变化称为大气低频振荡。现在发现具有低频振荡特性的气象因子主要有：纬向风速。气压。云量、降水、南亚季风槽位置、地气系统的射出（外逸）长波辐射等。2大气低频振荡的研究动态七十年代初Madden－J；11tan发现热带岛屿上的风场和地面气压场存在40～50天的准周期性变化，最早提出热带大气低频振荡的现象。此后由于EINino现象和海一气相互作用的深入研究，大气低频振荡… 相似文献
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运用ＬＡＰＧＣＭ模式证实了大气对南极冰异常的强迫遥响应是激发全球大气季节内振荡的重要机制,进而着重考察候平均偏差结果的时间序列,并且通过带通以处理,特别分析了响应场中３０－６０天低频振荡的重要特征,发现：大报对南极冰减退的响应是一种具有３０－６０天周期的低频遥响应。强迫场中的重要成分是３０－６０天季节内振荡,并且具有同实际大气中的低频振荡相类的垂直结构以及传播和分布特征。 相似文献
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运用ＩＡＰＡＧＣＭ模式证实了大气对南极冰异常的强迫遥响应是激发产生全球大气季节内振荡的重要机制,进而着重考察了候平均偏差结果的时间序列,并且通过带通滤波处理,特别分析了响应场中３０～６０ｄ低频振荡的特征及其活动。通过分析发现：大气对南极冰减退的响应是一种具有３０～６０ｄ周期的低频遥响应,并呈现出清楚的二维Ｒｏｓｓｂｙ波列特征;强迫场中的３０～６０ｄ季节内振荡具有着同实际大气中的低频振荡相类似的垂直结构和传播特征。大气响应场中３０～６０ｄ振荡能量在垂直方向上随高度的增加而增加,在纬向上表现出明显的区域性特征,即季节内振荡的最大动能区（由于ＣＩＳＫ机制）分布在大洋内;ＥＵＰ,ＰＮＡ,ＡＳＡ和ＲＳＡ波列可能是全球大气低频扰动传播的主要路径,３０～６０ｄ低频扰动在波列路径上的传播具有很大的一致性和系统性,从而使中高纬和热带地区、以及南北半球的３０～６０ｄ大气振荡相互联系起来,而且可以认为,赤道中太平洋和赤道中大西洋地区是南北半球３０～６０ｄ低频振荡间相互作用和相互联系的重要通道。 相似文献
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利用“绿洲系统能量与水分循环过程观测与数值研究”的观测资料和酒泉站的地面和探空气象资料,计算了酒泉绿洲夏季大气边界层的加热（冷却）率,分析了酒泉绿洲近地面层和行星边界层的大气加热（冷却）率逐日变化,研究了不同典型天气下大气加热（冷却）率的变化特征。结果表明,酒泉绿洲近地面层和行星边界层内,大气加热（冷却）率具有明显的逐日变化特征;近地面层和行星边界层及整个大气层白天的大气加热率和夜晚的大气冷却率基本相当,大气能量基本守恒;日照时数、云量和特殊天气过程（如冷空气活动、沙尘天气和降水等）对大气加热（冷却）率有很大影响。 相似文献
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在合适的实验参数下(热力Rossby数R_(OT)=0.1,Taylor数T_a=2.2 ×10~7),在旋转斜压流中,大尺度地形强迫造成低频振荡以及大气环流中的“阻塞”流型。这是由于地形强迫造成的准静止波与行进波的相互作用及共振引起的。地形把波数单一的流动变成多波数的流动。地形强迫使波数减少。 相似文献
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本文使用一个简单的全球二层大气环流模式作了强迫响应数值试验。模式中引入了代表热带低频偶极型对流的异常强迫.结果表明这一强迫不仅能激发显著的局地大气响应,也能引起北半球中纬显著的低频异常波列,中纬波列的发展与热带强迫变化之间存在四分之一位相差关系.这些结果与观测研究的结果一致.进一步的分析表明,大气响应的位相滞后与强迫产生的能量从内模向外模的非线性转换过程有关.最后提出了季节内尺度热带-中纬相互作用的可能机制. 相似文献
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Dynamic and numerical methods are used to discuss the atmospheric response to SST thermal
forcing. The results show that for planetary scale systems, the standing SST thermal forcing can quickly excite a
stable atmospheric equilibrium state response, which is characterized by obvious large-scale teleconnection
oscillation in east-west and south-north directions. For synoptic scale systems, the SST thermal forcing mainly
excites the atmospheric low-frequency oscillation. Some basic relation and dynamic processes between SST
thermal forcing and atmospheric response pattern are revealed and some new viewpoints are presented. 相似文献
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Analysis is done of five-year low-pass filtered data by a Five-layer low-order global spectral model, indicating that although any non-seasonal external forcing is not considered in the model atmosphere, monthly-scale anomaly takes place which is of remarkable seasonality and interannual variability.Analysis also shows that for the same seasonal external forcing the model atmosphere can exhibit two climatic states, similar in the departure pattern but opposite in sign, indicating that the anomaly is but the manifestation of the adverse states, which supports the theory of multi-equilibria proposed by Charney and Devore (l979) once again.Finally, the source for the low-frequency oscillation of the global atmosphere is found to be the convective heat source / sink inside the tropical atmosphere as discussed before in our study.Therefore, the key approach to the exploration of atmospheric steady low-frequency oscillation and the associ-ated climatic effect lies in the examination of the distribution of convective heat sources / sinks and the variation in the tropical atmosphere. 相似文献
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Simon Grainger Carsten S. Frederiksen Xiaogu Zheng David Fereday Chris K. Folland Emilia K. Jin James L. Kinter Jeff R. Knight Siegfried Schubert Jozef Syktus 《Climate Dynamics》2011,36(3-4):473-490
The seasonal mean variability of the atmospheric circulation is affected by processes with time scales from less than seasonal to interannual or longer. Using monthly mean data from an ensemble of Atmospheric General Circulation Model (AGCM) realisations, the interannual variability of the seasonal mean is separated into intraseasonal, and slowly varying components. For the first time, using a recently developed method, the slowly varying component in multiple AGCM ensembles is further separated into internal and externally forced components. This is done for Southern Hemisphere 500?hPa geopotential height from five AGCMs in the CLIVAR International Climate of the Twentieth Century project for the summer and winter seasons. In both seasons, the intraseasonal and slow modes of variability are qualitatively well reproduced by the models when compared with reanalysis data, with a relative metric finding little overall difference between the models. The Southern Annular Mode (SAM) is by far the dominant mode of slowly varying internal atmospheric variability. Two slow-external modes of variability are related to El Ni?o-Southern Oscillation (ENSO) variability, and a third is the atmospheric response to trends in external forcing. An ENSO-SAM relationship is found in the model slow modes of variability, similar to that found by earlier studies using reanalysis data. There is a greater spread in the representation of model slow-external modes in winter than summer, particularly in the atmospheric response to external forcing trends. This may be attributable to weaker external forcing constraints on SH atmospheric circulation in winter. 相似文献
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1. IntroductionInvestigations about atmospheric LFW have been a focus of research since Madden andJulian/s outstanding analysis works (1971, 1972). Many dynamical and thermal mechanisms(Chao et al., 1996; Fu et al., 1998; Hendon et al., 1998; Krishnamurti et al., 1988; Lau andChan, 1988) have been advised to explain LFW. Among them are oceanic effects, such as SSTeffect, thermal forcing and others. Usually atmosphere and ocean are taken as a coupled system, which is used to explain ENS… 相似文献
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A barotropic channel model in β-plane is used to study the effect of topographic forcing on the formation and maintenance of blocking. The approximate analytical solution of potential vorticity equation can show the main property of the whole process of blocking. It is indicated that the topographic forcing is one of the main factors caus-ing the blocking process. The results suggest that the nonlinear interaction plays a very important role in the stable “Ω” situation of blocking. The atmospheric circulation with periodic and low-frequency oscillation, perhaps, is partly caused by topographic forcing. 相似文献
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The simulated low-frequency variability patterns of the atmospheric circulation, ranging from interannual to interdecadal timescales, are studied in an area encompassing southern South America. The experiment is a transient simulation performed with the IPSL CCM2 coupled global model, in which the greenhouse forcing is continuously increasing. The main modes of low-frequency variability are found to remain stationary throughout the simulation, suggesting they depend more on the internal dynamics of the atmospheric flow than on its external forcing. Inspection of the circulation regimes that represent the more recurrent patterns at interannual and interdecadal timescales showed that climate change manifests itself as a change in regime population, suggesting that the negative phase of the Antarctic Oscillation-like pattern becomes more frequented in a climate change scenario. Changes of regime occurrence are superimposed to a positive trend whose spatial pattern is reminiscent of the structure of the Antarctic Oscillation-mode of variability. Moreover, it resembles the spatial patterns of those regimes that show a significant change in population. The change in regime frequencies of the circulation patterns of low-frequency variability are in opposite phase with respect to the trend, thus, the behaviour of these patterns of variability, superimposed to a changing mean state, modulates the climate change signal. The analysis of the high frequencies, in terms of recurrent patterns representing intraseasonal and synoptic-scale of variability, shows no significant changes in regime characteristics, concerning both spatial and temporal behaviour. 相似文献
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热带低层大气30～60天低频动能的年际变化与ENSO循环 总被引：17，自引：7，他引：10
利用NCEP再分析资料,通过统计相关及合成分析研究了热带大气季节内振荡(ISO)的年际变化与ENSO循环之间的关系.结果表明,热带大气季节内振荡(也称30～60天低频振荡)的年际变化在热带中西太平洋地区最强.在ElNino成熟之前的春夏季,热带西太平洋的30～60天振荡异常活跃,其动能明显增加且逐渐东移;在E1Nino成熟以后,热带西太平洋大气30～60天低频振荡迅速减弱.与这种加强的30～60天振荡相伴随,在赤道北侧为异常的气旋式环流,赤道地区出现偏西风异常.相反,在LaNina成熟之前的春夏季,热带西太平洋大气30～60天振荡偏弱.进一步的分析还发现,东亚冬季风的年际变化是引起热带大气30～60天振荡的年际变化的主要机制:强东亚冬季风导致热带西太平洋积云对流加强,从而引起热带西太平洋大气30～60天振荡加强;相反,对应于弱的东亚冬季风,热带西太平洋地区积云对流偏弱,大气30～60天振荡偏弱.作者的资料分析还证实,热带大气30～60天低频振荡的年际变化,作为一种外强迫,对ElNino的形成起着十分重要的作用. 相似文献