共查询到19条相似文献，搜索用时 135 毫秒
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利用斜压两层模式研究了赤道平面近似下的低纬热带大气适应过程。指出低纬斜压大气适应过程主要受重力惯性内波控制。通过重力惯性内波对初始非地转能量的频散,使纬向运动达到地转平衡,而经向维持非地转运动,正压模式下称为半地转平衡,斜压模式下称为半热成风平衡。通过对垂直运动方程的求解,可知,垂直运动只与重力惯性内波相联系,其产生与初始斜压位涡度无关,而只与初始时刻的垂直运动和垂直运动倾向有关,半地转适应使运动趋向水平运动。讨论了半热成风平衡的建立及其物理机制,指出由于重力惯性内波激发出垂直运动,与垂直运动相联系的水平辐合辐散调整流场和温度场之间的关系,使温压场最终达到半热成风平衡。通过对适应过程终态的分析,指出平均温度场和切变流场之间的适应方向决定于初始非半地转扰动的尺度与斜压Ｒｏｓｓｂｙ变形半径有关的特征尺度的比值,当比值大于１时,切变流场向平均温度场适应;当比值小于１时,平均温度场向切变流场适应 相似文献
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热带地转适应运动的动力学基础 总被引：3，自引：1，他引：2
文中讨论了热带斜压大气地转适应过程中的若干动力学约束关系 ,在不考虑行星位势涡度梯度的前提下给出了三维重力惯性波的频散方程、位势涡度时间不变式。在这基础上指出由于 Taylor- Proudman定理成立 ,运动将趋于水平化。同时指出 ,在热带纬圈半地转平衡更易出现。地转适应后的运动 ,一般是水平无辐散的 ,虽然垂直运动趋于零 ,但物理场随高度仍然有变化 ,即是层结的。 相似文献
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本文采用多时间尺度方法分析热带大气的大尺度运动,得到了三个阶段的运动性质。结果表明,热带大尺度大气运动与中纬度大尺度大气运动一样,具有双适应现象,即第一阶段由于重力波频散,产生了地转适应;第二阶段由于长波频散,产生了位涡适应。 同时指出,运动的三个阶段的演变过程,可以统一为位势涡度适应过程,这是一种非线性过程,而地转适应是位涡适应的初级阶段。 相似文献
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基于WRF模式对2011年6月16—19日一次东移西南涡过程的模拟,开展了西南涡激发平流层重力波的特征研究。东移西南涡可以分为发展、强盛和减弱3个阶段,每个阶段均伴随着强降雨天气,但由于降水位置和强度的不同,平流层重力波的分布和强度也不同。西南涡发展阶段,平流层重力波主要位于低涡的东侧,并向东北传播;西南涡强盛阶段,伴随对流降水的强度和范围明显增大,平流层重力波的振幅和范围也显著增大,且围绕西南涡的东侧和南侧呈现出半环状的重力波分布特征可分为两支,东侧波动波列表现为东北西南向分布,南侧的波列表现为东—西向分布;西南涡减弱阶段,重力波的振幅和范围均减小。波谱分析表明,重力波的纬向波数频率谱关于零频率呈非对称分布,且随着西南涡的增强,波谱在小尺度范围显著增大,即强对流更容易激发出小尺度的高频波;经向波数频率谱在波数较小谱段关于零频率基本呈对称分布,但在波数较大谱段,也呈非对称分布,这说明受平流层东风气流的影响,重力波主要向东传播。 相似文献
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在半地转近似［１］下，利用层结大气中的涡度方程、散度方程、连续方程和绝热方程结合行波解的方法得到了关于垂直速度的单一变量方程。这是与ＫｄＶ方程相应的非线性常微分方程，可得到椭圆余弦波或弧立波。此波动的频率有两种，表明层结大气中存在着两种性质不同的非线性波动。其一是东传的惯性重力椭圆余弦波，另一是混合Ｒｏｓｓｂｙ－重力椭圆余弦波，其性质介于Ｒｏｓｓｂｙ椭圆余弦波与西传的惯性重力椭圆余弦波之间。这两种非线性波的相速不但与波数和振幅有关，而且与β因子和静力稳定度有关，即纬度越低，则传播越慢；大气越稳定，则传播越快。 相似文献
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本文利用多重尺度方法研究了大气中重力内波的非线性问题,指出,当大气中的Bruntvaisala频率随高度变化时,我们可以得到一个非线性Schrodinger方程,同时还指出,当N~2按N~2=N_0~2+vcosnz(v>o)和N~2=N_0~2+vsinnz(v>0)分布时,可得到如下结论:当大气中的重力内波的波数满足3n~2-k~2<0时,大气中的重力内波可能会出现Benjammin-Feir不稳定,也就是说,大气中垂直方向的波长较长、水平方向的波长较短的重力内波容易出现Bebhanub-Feir不稳 相似文献
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切变基流对赤道大气波动稳定性的作用 总被引：3，自引：2，他引：3
在赤道β平面近似条件下，使用纬向切变基流下线性化Boussinesq方程组，分析了在纬向切变基流下几种赤道大气波动的稳定性特征。研究结果表明，基本气流的水平切变对赤道大气波动起到不稳定的作用，但是对赤道大气Kelvin波的频率、稳定性以及传播的相速度并不起作用。基本气流的水平切变使得相对于基本气流向东传播的重力惯性内波相速度减慢，而使得相对于基本气流向西传播的重力惯性内波的相速度加快，却造成相对于基本气流向西传播的Rossby波相速度减慢。基本气流的水平切变对于对赤道混合Rossby-重力惯性内波的影响主要取决于纬向波数k值的范围大小。当纬向波数k值较小时，基流的水平切变使得相对于基本气流向西传播的混合Rossby-重力惯性内波相速度加快；而当纬向波数k值较大时，则使得相对于基本气流向西传播的混合Rossby-重力惯性内波相速度减慢。在半地转近似下，风速水平切变的存在，会使得波长较大（纬向波数k→0）的赤道Rossby波相对于基本气流向西传播的相速度减慢；而风速垂直切变的存在，必然会引起这种波长较大（k→0）的Rossby波出现不稳定增长，同样也会造成赤道Rossby波相对于基本气流向西传播的相速度减慢。最后通过扰动发展能量方程，说明了基本气流的水平切变和垂直切变可以为扰动的发展提供能量来源。 相似文献
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利用2019年1月1—7日AIRS观测的(80°—100°W,30°—45°N)范围内0—45 km高度的大气温度剖面数据,根据重力波的线性理论,分别采用垂直滑动窗口法、双滤波器法、单滤波器法对温度廓线数据进行处理,从中得到初始扰动剖面,再使用分离出来的对流层到平流层低层的背景温度和重力波扰动剖面计算重力波势能,最后根据提取结果比较三种方法的差异。结果表明:1) 采用垂直滑动窗口法提取的重力波势能对波长较小的波动有很好的反映,在对流层顶区域重力波势能异常偏大。2) 采用双滤波器法提取的重力波势能很好地反映各个波长的波动,更符合真实情况。3) 采用单滤波器法能够提取波长较大的重力波扰动,且扰动在对流层贡献更大;而采用双滤波器提取的重力波扰动分别在对流层顶和平流层贡献更大。 相似文献
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An ensemble of random-phase internal gravity waves is considered in the dynamical framework of the Euler–Boussinesq equations. For flows with zero mean potential vorticity, a kinetic equation for the mean spectral energy density of the waves is obtained under hypothesis of Gaussian statistics with zero correlation length. Stationary scaling solutions of this equation are found for almost vertically propagating waves. The resulting spectra are anisotropic in vertical and horizontal wave numbers. For flows with small but non-zero mean potential vorticity, under the same statistical hypothesis applied to the wave part of the flow, it is shown that the vortex part and the wave part decouple. The vortex part obeys a limiting slow dynamics equation exhibiting vertical collapse and layering which may contaminate the wave-part spectra. Relation of these results to the in situ atmospheric measurements and previous work on oceanic gravity waves is discussed. 相似文献
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Energy- and Flux-Budget Turbulence Closure Model for Stably Stratified Flows. Part II: The Role of Internal Gravity Waves 总被引：1，自引：1，他引：0
S. S. Zilitinkevich T. Elperin N. Kleeorin V. L’vov I. Rogachevskii 《Boundary-Layer Meteorology》2009,133(2):139-164
We advance our prior energy- and flux-budget (EFB) turbulence closure model for stably stratified atmospheric flow and extend it to account for an additional vertical flux of momentum and additional productions of turbulent kinetic energy (TKE), turbulent potential energy (TPE) and turbulent flux of potential temperature due to large-scale internal gravity waves (IGW). For the stationary, homogeneous regime, the first version of the EFB model disregarding large-scale IGW yielded universal dependencies of the flux Richardson number, turbulent Prandtl number, energy ratios, and normalised vertical fluxes of momentum and heat on the gradient Richardson number, Ri. Due to the large-scale IGW, these dependencies lose their universality. The maximal value of the flux Richardson number (universal constant ≈0.2–0.25 in the no-IGW regime) becomes strongly variable. In the vertically homogeneous stratification, it increases with increasing wave energy and can even exceed 1. For heterogeneous stratification, when internal gravity waves propagate towards stronger stratification, the maximal flux Richardson number decreases with increasing wave energy, reaches zero and then becomes negative. In other words, the vertical flux of potential temperature becomes counter-gradient. Internal gravity waves also reduce the anisotropy of turbulence: in contrast to the mean wind shear, which generates only horizontal TKE, internal gravity waves generate both horizontal and vertical TKE. Internal gravity waves also increase the share of TPE in the turbulent total energy (TTE = TKE + TPE). A well-known effect of internal gravity waves is their direct contribution to the vertical transport of momentum. Depending on the direction (downward or upward), internal gravity waves either strengthen or weaken the total vertical flux of momentum. Predictions from the proposed model are consistent with available data from atmospheric and laboratory experiments, direct numerical simulations and large-eddy simulations. 相似文献
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Yeli Yuan Lei Han Fangli Qiao Yongzeng Yang Ming Lu 《Dynamics of Atmospheres and Oceans》2011,51(1-2):55-74
A linearized instability analysis model with five unknowns was proposed to describe disturbance motions under general oceanic background conditions, including large-scale current shear, density stratification, frontal zone, and arbitrary topography. A unified linear theory of wavelike perturbations for surface gravity waves, internal gravity waves and inertial gravity waves was derived for the adiabatic case, and the solution was then found using Fourier integrals. In this theory, we discarded the assumptions widely accepted in the literature concerning derivations of wave motions such as the irrotationality assumption for surface gravity waves, the rigid-lid approximation for internal gravity waves, and the long-wave approximation for inertial gravity waves. Analytical solutions based on this theory indicate that the complex dispersion relationships between frequency and wave-number describing the propagation and development of the three types of wavelike perturbation motions include three components: complex dispersion relationships at the sea surface; vertical invariance of the complex frequency; and expressions of the vertical wave-number (phase). Classical results of both surface waves and internal waves were reproduced from the unified theory under idealized conditions. The unified wave theory can be applied in the dynamical explanation of the generation and propagation properties of internal waves that are visible in the satellite SAR images in the southern part of the China Seas. It can also serve as the theoretical basis for both a numerical internal-wave model and analytical estimation of the ocean fluxes transported by wavelike perturbations. 相似文献
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为了研究垂直变量配置对静力适应过程的影响,本文从描写静力适应过程的方程组出发,分别在将所有变量置于整层上的非跳点N网格;将垂直速度和温度放置在整层,水平速度、气压和密度等变量放置在半层的Charney Phillips跳点网格(CP网格);将水平速度、气压和温度放置在整层,将垂直速度和密度放置在半层的Lorenz跳点网格(L网格);将密度变量放置在整层的Charney Phillips跳点网格(CP_N网格);将密度放置在整层的Lorenz跳点网格(L_N网格)上进行离散,垂直格距分1 km、0.5 km、0.2 km和0.01 km,研究了在这5种网格上产生的频率和垂直群速的相对误差。结果表明:(1)L_N网格和CP网格是完全等效的两种网格。(2)不论垂直格距为多少,CP网格和L网格的误差都是最小,N网格次之,CP_N网格的误差最大。(3)随着垂直格距的减少,在这几种网格上产生的误差都在减小。对于CP网格、L网格和N网格,在水平长波和垂直短波处产生的误差较大。而CP_N网格对水平波长变化不敏感,垂直波长越短,误差越大。(4)当垂直格距为0.01 km时,这几种网格都对水平波长的变化不敏感了,仅对垂直波长敏感。(5)CP网格、L_N网格和L网格在描写静力适应过程和斜压地转适应过程都是误差最小的垂直变量配置方案,因此在非静力完全可压缩深层大气数值预报模式中应优先选择这3种方案。 相似文献
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本文针对2008年上海8月25日暴雨过程,利用WRF中尺度数值模式对其较好模拟的结果,应用EOF分析方法对其做了动能偏差场的统计动力诊断。探讨了该暴雨过程中各种尺度天气系统,特别是β中尺度雨 团,其有效位能向动能的转化机制。所得主要结论有:对该暴雨过程,动能偏差场EOF分析的第一、二、三模态可分别称为暴雨背景模态、暴雨系统模态和暴雨雨团模态。在该暴雨落区附近,低层各模态动能偏差场水平梯度的绝对值均较大,系统演变也较剧烈,且尤以暴雨雨团模态为甚;这表明低层暴雨雨团模态该处风场具有强烈的非地转性,有着强辐合,运动是非平衡的,其性质为重力惯性波(含涡旋—重力惯性混合波)。在某等压面上,有效位能的时间变化与位势偏差的时间变化相同,而前者的水平梯度则与后者的空间梯度大致相同,这样讨论某层前者的变化就归结于讨论该层后者的变化。暴雨来临前在该暴雨落区附近,前三个模态都有有效位能向动能的 转化,其表现为动能的增长和有效位能的下降,且以暴雨雨团模态表现更突出。暴雨雨团模态的尺度为β中尺 度,这表明该尺度的系统在有效位能向动能转换中起着关键作用,且扮演着有效位能与涡旋场动能之间转换的中介角色。 相似文献
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非静力模式中几种垂直网格计算特性的对比研究 总被引：8，自引：0，他引：8
从非静力滞弹性方程组出发，将惯性重力波的水平波长分几百公里、几十公里和几公里三种情况，从频率、群速和各速的垂直尺度范围等方面对现有的几种垂直网格进行比较讨论。结果表明：在非静力模式中，CP网格和LZ网格适合于各种不同水平尺度惯性重力波的模拟；L网格和LY网格适合于水平尺度为几十公里以上的惯性重力波的模拟；LTS网格和CPTS网格比较适合于水平尺度的几十公里以下的惯性重力波的模拟。 相似文献
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The generation of internal gravity waves by barotropic tidal flow passing over a two-dimensional topography is investigated. Rather than calculating the conversion of tidal energy, this study focuses on delineating the geometric characteristics of the spatial structure of the resulting internal wave fields (i.e., the configurations of the internal beams and their horizontal projections) which have usually been ignored. It is found that the various possible wave types can be demarcated by three characteristic frequencies: the tidal frequency, ω0; the buoyancy frequency, N; and the vertical component of the Coriolis vector or earth's rotation, f. When different possibilities arising from the sequence of these frequencies are considered, there occur 12 kinds of wave structures in the full 3D space in contrast to the 5 kinds identified by the 2D theory. The constant wave phase lines may form as ellipses or hyperbolic lines on the horizontal plane, provided the buoyancy frequency is greater or less than the tidal frequency. The effect that stems from the consideration of the basic flow is also found, which not only serves as the reason for the occurrence of higher harmonics but also increases the wave strength in the direction of basic flow. 相似文献