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1.
In this paper,a tropical atmospheric model of relevance to shorts-term climate variations(Wang and Li 1993) is utilized for study of the development of Madden-Julian oscillation.The model contains an interactive process of boundary-layer Ekman convergence and precipitation heating.The model is solved by expanding dependent variables in terms of parabolic cylindrical functions in the meridional direction and truncating three meridional modes n=0,2,4 for equatorial symmetric solutions.The free wave solutions obtained under long-wave approximation are induced as a Kelvin wave and two Rossby waves.After considering the effect of boundary-layer dynamic process,the modified Kelvin wave becomes unstable in long-wave bands with a typical growth rate on an order of 10-6 s-1and an eastward phase speed of 10 m s-1;the most unstable mode is wavenumber one.These theoretical results are consistent with the observed Madden-Julian oscillation in equatorial area.For the two modified Rossby waves,one with a smaller meridional scale(n=4) decays except for extra long-waves;the other with a larger meridional scale(n=2) grows in short-wave bands.This may be relevant to explaining the westward propagation of super cloud clusters in the Madden-Julian oscillation.The theory suggests that the boundary-layer dynamic process is an important mechanism in the development of the Madden-Julian oscillation. 相似文献
2.
利用包括边界层爱克曼辐合－降水加热过程在内的短期气候变化模式［１］，研究了Ｍａｄｄｅｎ－Ｊｕｌｉａｎ振荡［１１，１２］形成的机制。当经圈方向用抛物圆柱函数展开，并对赤道偶对称解取ｎ＝０，２，４三个截断模时，在长波近似下的自由波解，一为向东的Ｋｅｌｖｉｎ波，另外两支为向西的Ｒｏｓｓｂｙ波。当考虑边界层动力影响后，修正后的Ｋｅｌｖｉｎ波，其向东传播的速度约为１０ｍｓ－１，且在长波波段是不稳定的，最不稳定的波出现在纬向一波附近，不稳定增长率的量级约为Ｏ（１０ｍ－６ｓ－１），理论结果和Ｍａｄｄｅｎ－Ｊｕｌｉａｎ振荡在赤道附近主体环流东传的观测事实接近。另外两支修正后的Ｒｏｓｓｂｙ波，其中经圈尺度较小的那支波，除波长极长的波外，波是阻尼的；但另一支经圈尺度较大的波，在短的波段是不稳定增长的，这似乎可以用来解释Ｍａｄｄｅｎ－Ｊｕｌｉａｎ振荡中大尺度超级云团的西传过程。这些结果表明边界层动力过程在Ｍａｄｄｅｎ－Ｊｕｌｉａｎ振荡的形成中是一种重要的机制。 相似文献
3.
在前文［１］的基础上，进一步研究当海表温度存在经圈方向不均匀分布或偏离气候状态（距平）时，改变水分收支平衡及边界层的湿度辐合这一物理过程对Ｍａｄｄｅｎ－Ｊｕｌｉａｎ振荡的可能影响。结果表明，它对修正的Ｋｅｌｖｉｎ波和Ｒｏｓｓｂｙ波的传播性质影响不大。但当海表温度为正距平时，修正后东传Ｋｅｌｖｉｎ波振幅不稳定增长到ｅ倍的时间约减小了１４．５％，其不稳定增长率随着热源特征宽度的增加而增加，当特征宽度为２倍Ｒｏｓｓｂｙ变形半径时，不稳定增长率达极大，但当特征宽度继续增大时，其不稳定增长率又将减小。当海表温度为负距平时，修正后东传Ｋｅｌｖｉｎ波振幅不稳定增长到ｅ倍的时间约增加２０％，其不稳定增长率随着冷源特征宽度的增加而减小，当特征宽度为２倍Ｒｏｓｓｂｙ变形半径时，其不稳定增长率达极小，此后；随着特征宽度的增加其不稳定增长率随之增加，但始终小于无海表温度异常的情形。经圈尺度较小的那支修正的Ｒｏｓｓｂｙ波除波长极长的波段外，波仍是阻尼的；而经圈尺度较大的那支修正的Ｒｏｓｓｂｙ波，在短的波段内仍是不稳定增长的。 相似文献
4.
文中重点研究与热带季节内振荡－超级云团系统相关联的赤道波的识别。考虑到赤道波的本质为截获在赤道地区的一般的气候平衡场附近的线性动力过程的固有模态,首先从原理上阐明了ＰＯＰｓ分析技术对于分离各类赤道波动的有效性,以后利用这种分析方法对日本静止气象卫星所观测到的黑体红外辐射温度资料进行了ＰＯＰｓ分析。结果表明,在热带季节内振荡－超级云团系统中,对应于４０ｄ振荡的模态基本表现为Ｋｅｌｖｉｎ波的结构;对应于１０ｄ左右的模态,亦为Ｋｅｌｖｉｎ波,而在２ｄ尺度上,则分别存在经向模态序号ｎ＝１和ｎ＝２的西进和东进惯性重力波。分析中还发现了西进的混合Ｒｏｓｓｂｙ重力波的存在。 相似文献
5.
Scale analyses for long wave, zonal ultralong wave (with zonal scale of disturbance L1~104 km and meridional scale L2~103 km) and meridional ultralong wave (L1~103 km, L2~104 km) are carried out and a set of approximate equations suitable for the study of these waves in a dry tropical atmosphere is obtained. Under the condition of sheared basic current, frequency analyses for the equations are carried out. It is found that Rossby waves and gravity waves may be separated for n ≥ l where n is the meridional wave number, whereas for n = 0 and L1~1000 km, the mixed Rossby-gravity wave will appear. Hence it is confirmed that the above results of scale analyses are correct. The consistency be-tween frequency analysis and scale analysis is established.The effect of shear of basic current on the equatorial waves is to change their frequencies and phase velocities and hence their group velocities. It increases the velocity of westward travelling Rossby waves and inertia-gravity and mixed waves, but decelerates the eastward inertia-gravity waves and the Kelvin wave. The recently observed low-frequency equatorial ocean wave may be interpreted as an eastward Kelvin wave in a basic current with shear. 相似文献
6.
大气季节内振荡对印度洋—西太平洋地区热带低压/气旋生成的影响 总被引：24，自引：4，他引：24
文中利用EOF分析大气季节内振荡 (MJO)的时空变化的方法 ,研究了 1996年 9月～ 1997年 6月间的MJO活动对生成在印度洋—西太平洋海域的热带低压 /气旋的影响。结果发现 ,除西北太平洋之外 ,发生在其他区域的热带低压 /气旋有半数以上生成在向东移动的MJO的湿位相中。伴随MJO的向东传播 ,热带低压 /气旋平均生成位置也随之向东移动 ,而生成在西北太平洋的热带低压 /气旋分别受到向东和向西传播的MJO影响 相似文献
7.
A NUMERICAL STUDY OF SHORT-RANGE CLIMATIC OSCILLATION WITH VARIOUS TIME SCALES FORCED BY EL NINO DURING THE NORTHERN SUMMER 
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下载免费PDF全文 The normal mode method is adopted to decompose the differences between simulations with SST(seasurface temperature)anomahes over centra-eastern Pacific and normal SST by use of a nine-layer global spec-tral model in order to investigate short-range climatic oscillation with various time scales forced by ElNino during the northern summer.Investigation shows that El Nino may have the following influence onatmosphere on various space-time scales.Extra-long wave components of Rossby mode forced by convectiveanomaly over equatorial western Pacific resulting from El Nino produce climatic oscillation on monthly(sea-sonal)time scale in middle-high latitudes of Southern and Northern Hemispheres;extra-long wave componentsof Kelvin mode forced by SST anomalies propagate along the equator,resulting in 30—60 day oscillation oftropical and subtropical atmosphere;and its long waves move eastward with westerly,resulting in quasi-biweekoscillation. 相似文献
8.
Development and propagation of equatorial waves are investigated with the model which includes convection -wave convergence feedback and convection-frictional convergence feedback. Two experiments with an initial Kelvin wave (Exp. K) and with an initial Rossby wave (Exp. R) are carried out. The equatorial waves in Exp. R grow much faster than those in Exp. K. The equatorial waves in both experiments follow zonal (eastward / westward) and meridional (poleward) propagation. The equatorial waves can be partitioned into two meridional modes using Parabolic Cylinder Function. An equa?tor mode denotes a wave component with a positive precipitation center at the equator and an off-equator mode rep?resents a wave component with positive precipitation centers off the equator. The equator mode dominates in Exp. K whereeas the off-equator mode dominates in Exp. R. The rapid wave growth in Exp. R is interpreted by analyzing the eddy available potential energy (EAPE) generation. Stronger off-equator mode in Exp. R obtains more EAPE through convection-frictional convergence feedback which results in more rapid wave growth. The relative vorticity tendency is determined by interactions between Earth’s vorticity and lower-troposphere convergence (divergence effect) and between the meridional gradient and lower-troposphere circulation (beta effect). The eastward and poleward propagation of equatorial waves is a result of the divergence effect, and the westward movement is caused by the beta effect. 相似文献
9.
应用含有非绝热因子的正压模式方程组,着重分析了对流凝结加热、蒸发－风反馈和ＣＩＳＫ机制等非绝热因子对低纬Ｒｏｓｓｂｙ波和Ｋｅｌｖｉｎ波的影响。既获得了圆频率的表达式,又分析了波的周期与稳定性。结果表明：非绝热因子的存在不但扩大了绝热波的周期,而且改变了波的稳定性。因此,可以认为：所谓季节内振荡（３０—６０天的周期振荡）等低频振荡实际上是一类非绝热波,这类非绝热波是引起中长期天气变化及短期气候演变的重要因素。 相似文献
10.
The equations of barotropic model are used to discuss the effects of diabatic factors such as heat-ing of convective condensation, evaporation-wind feedback and CISK on the Rossby wave and the Kelvin wave. In low latitudes we have obtained the angular frequency and analyzed the period and stability of waves. The result shows the existence of the diabatic factors not only enlarges the period of adiabatic waves but also changes the stability of waves. Thus we think that the so-called intraseasonal oscillation and some other low-frequency oscillations are a kind of diabatic waves which are important factors producing the long-term weather changes and short-term climatic evolution. 相似文献
11.
12.
An Assessment of MJO and Tropical Waves Simulated by Different Versions of the GAMIL Model 下载免费PDF全文
下载免费PDF全文 Simulated outgoing longwave radiation (OLR) outputs by two versions of the grid-point atmospheric general circulation model (GAMIL) were analyzed to assess the influences of improvements in cloud microphysics and convective parameterization schemes on the simulation of the Madden-Julian oscillation (MJO) and other tropical waves. The wavenumber-frequency spectral analysis was applied to isolate dominant modes of convectively coupled equatorial waves, including the MJO, Kelvin, equatorial Rossby (ER), mixed Rossby-gravity (MRG), and inertio-gravity (IG) waves. The performances of different versions of the GAMIL model (version 1.0 (GAMIL1.0) and version 2.0 (GAMIL2.0)) were evaluated by comparing the power spectrum distributions of these waves among GAMIL1.0, GAMIL2.0, and observational data. GAMIL1.0 shows a weak MJO signal, with the maximum variability occurring separately at wavenumbers 1 and 4 rather than being concentrated on wavenumbers 1–3, suggesting that GAMIL1.0 could not effectively capture the intraseasonal variability. However, GAMIL2.0 is able to effectively reproduce both the symmetric and anti-symmetric waves, and the significant spectra of the MJO, Kelvin, and MRG waves are in agreement with observational data, indicating that the ability of GAMIL2.0 to simulate the MJO and other tropical waves is enhanced by improving the cloud microphysics and convective parameterization schemes and implying that such improvements are crucial to further improving this model’s performance. 相似文献
13.
Pauline Maury François Lott Lionel Guez Jean-Philippe Duvel 《Climate Dynamics》2013,40(9-10):2331-2344
The atmospheric variability in the equatorial regions is analysed in the Earth System Model pre-industrial simulation done at IPSL in the framework of CMIP5. We find that the model has an interannual variability of about the right amplitude and temporal scale, when compared to the El-Niño Southern Oscillation (ENSO), but that is too confined to the western Pacific. At the intra-seasonal periods, the model variability lacks of large-scale organisation, and only produces one characteristic Madden-Julian Oscillation every 10 winters typically. At shorter time-scales and in the troposphere, the model has Rossby and Kelvin Convectively Coupled Equatorial Waves (CCEWs), but underestimates the Kelvin CCEWs signal on OLR. In the model stratosphere, a composite analysis shows that the Temperature and velocities fluctuations due to the Kelvin waves are quite realistic. In the model nevertheless, the stratospheric waves are less related to the convection than in the observations, suggesting that their forcing by the midlatitudes plays a larger role. Still in the model, the Kelvin waves are not predominantly occurring during the life cycle of the tropospheric Kelvin CCEWs, a behaviour that we find to be dominant in the observations. The composite analysis is also used to illustrate how the waves modify the zonal mean-flow, and to show that the model Kelvin waves are too weak in this respect. This illustrates how a model can have a reasonable Kelvin waves signal on the velocities and temperature, but can at the same time underestimate their amplitude to modify the mean flow. We also use this very long simulation to establish that in the model, the stratospheric equatorial waves are significantly affected by ENSO, hence supporting the idea that the ENSO can have an influence on the Quasi-Biennial Oscillation. 相似文献
14.
本文分析了当大气和海洋中未经耦合前的自由波分别为Kelvin波和Rossby波,经相互作用后所产生的耦合波的性质。结果表明,不管大气的自由波为Kelvin波或Rossby波,而海洋的自由波为Rossby波或Kelvin波,经相互作用后的耦合波可以分成两类。一类耦合波的色散关系接近自由的Kelvin波;另一类则由不同经圈模的Rossby波经相互作用后的耦合波。这两类波都具有不稳定性。文中讨论了耦合波的传播和不稳定的物理机制,并指出这类不稳定的热带耦合波,对研究ENSO事件中的某些现象有一定的参考意义。 相似文献
15.
为了分析 ＥＩ Ｎｉｏ事件发生和消亡中热带太平洋纬向风应力的动力作用，建立一个类似于Ｚｅｂｉａｋ的简单热带海洋数值模式，在观测到的风应力异常的强迫下，模拟赤道太平洋地区 １９７１年１月至 １９９８年８月海表温度异常的变化。结果表明，模式对观测的Ｎｉｏ３区海表温度异常（ＳＳＴＡ）有很好的模拟能力。模拟和观测Ｎｉ区ＳＳＴＡ之间的相关系数可达 ０．９０。模式对 Ｅｌ Ｎｉｏ事件期间赤道太平洋海表温度异常随时间变化也有较好的模拟能力。为了分析Ｅｌ Ｎｉｏ期间ＳＳＴＡ的空间分布及其随时间变化的动力学机制，还对１９８６～１９８９年 ＥＮＳＯ循环期间赤道太平洋地区观测的 ＳＳＴＡ的传播特征及其形成机制进行了分析。模式较好地模拟出了观测到的赤道太平洋地区ＳＳＴＡ的传播特征，即从１９８６年底至１９８７年 ４月， ＳＳＴＡ具有向东传播的特征，从 １９８７年 ６月至 １９８８年 ２月具有向西传播的特征。动力学分析的结果表明，赤道中西太平洋地区的缔向风应力异常对 Ｅｌ Ｎｉｏ事件的发生和消亡具有重要作用。赤道中西太平洋地区的西风异常可强迫出东传的Ｋｅｌｖｉｎ波，这个东传的 Ｋｅｌｖｉｎ波对正 ＳＳＴＡ的东传起主要作用，当这个东传的 Ｋｅｌｖ 相似文献
16.
为了分析热带海气耦合系统中不稳定扰动究竟由哪种自由波占主导地位，根据本文第I部分提出的热带海气耦合模式，讨论了取耦合系统中不同的径向模时耦合波的性质，即分别讨论了大气长Rossby波和海洋长Rossby波、大气Kelvin波和海洋长Rossby波、大气长Rossby波和海洋Kelvin波的耦合波以及考虑了大气和海洋中所有这些波动时耦合波的性质。结果指出，这些耦合波对海气耦合模式中参数的取值很敏感，不同的参数可以产生性质不同的耦合波。本文的结果也说明了海气耦合系统的性质与热带大气的性质和结构有很大关系。 相似文献
17.
This study evaluates the convectively coupled equatorial waves in ten coupled general circulation models (GCMs) in the twentieth century experiment from the Coupled Model Intercomparison Project phase 3 of the World Climate Research Programme. The antisymmetric bands in all GCMs are weaker than in observations, and the mixed Rossby-gravity (MRG) wave seems to be a mixture of the equatorial Rossby (ER) and tropical depression-type (TD-type) waves rather than a mixture of the ER and inertiogravity waves found in observations. The simulated TD-type wave is more organized than in observations with a quasilinear wavenumber–frequency relationship. In most GCMs, the two observed activity centers of the MRG and TD-type waves over the southern Indian Ocean and the southwestern Pacific cannot be separated; only one wave activity center is found over the Maritime Continent. The observed northwestward propagation of the TD-type wave over the western North Pacific is also not well simulated in the GCMs. The simulated active season of the MRG and TD-type waves over the northern hemisphere during the boreal summer and fall is much shorter than in observations. The models from CCSR utilizing the Pan and Randall scheme with the convection suppression simulate the realistic Kelvin wave activity with the maximum activity near the equator, while the wave activities filtered for the Kelvin wave in the other GCMs are similar to the extratropical Rossby wave with the maximum activity at higher latitudes. Likewise, only these two models produce a realistic seasonal cycle of the Kelvin wave activity. 相似文献
18.
Timothy J. Dunkerton 《大气与海洋》2013,51(1):55-68
Abstract It is shown that oscillating mean flow solutions exist in the one‐dimensional Holton‐Lindzen (1972) model in the presence of a single Kelvin wave, mean flow diffusion, and an easterly zonal force per unit mass that is constant in height and time except at those points in the time‐height cross‐section where the latitudinally‐integrated mean flow is less than some prescribed easterly value. The latter forcing is intended to crudely represent the absorption of quasi‐stationary planetary Rossby waves at the tropical zero‐wind line. Our results suggest an alternative, and somewhat simpler, possible interpretation of the quasi‐biennial mean zonal wind oscillation in the equatorial lower stratosphere. 相似文献
19.
1. Introduction The observed facts show that the ENSO cycle has obvious phase-locking and oscillates irregularly (An and Wang, 2001; Kaplan et al., 1998). Based on Zibiak and Cane's (1987) model (hereafter, the Z-C model) and simple, coupled ocean-atmosph… 相似文献
20.
为了分析ElNio事件发生和消亡中热带太平洋纬向风应力的动力作用，建立一个类似于Zebiak的简单热带海洋数值模式，在观测到的风应力异常的强迫下，模拟赤道太平洋地区1971年1月至1998年8月海表温度异常的变化。结果表明，模式对观测的Nio3区海表温度异常(SSTA)有很好的模拟能力。模拟和观测Nio3区SSTA之间的相关系数可达0.90。模式对ElNio事件期间赤道太平洋海表温度异常随时间变化也有较好的模拟能力。为了分析ElNio期间SSTA的空间分布及其随时间变化的动力学机制，还对19861989年ENSO循环期间赤道太平洋地区观测的SSTA的传播特征及其形成机制进行了分析。模式较好地模拟出了观测到的赤道太平洋地区SSTA的传播特征，即从1986年底至1987年4月，SSTA具有向东传播的特征，从1987年6月至1988年2月具有向西传播的特征。动力学分析的结果表明，赤道中西太平洋地区的纬向风应力异常对ElNio事件的发生和消亡具有重要作用。赤道中西太平洋地区的西风异常可强迫出东传的Kelvin波，这个东传的Kelvin波对正SSTA的东传起主要作用，当这个东传的Kelvin波到达东边界，由于东边界的反射作用，在东边界产生西传的Rossby波，这个西传的Rossby波对赤道中东太平洋地区正SSTA的西传起主要作用。东传Kelvin波和反射的Rossby波对ElNio期间赤道东太平洋正SSTA二次峰值的形成具有重要作用。 相似文献