共查询到18条相似文献，搜索用时 906 毫秒
1.
本文应用守恒型非弹性模式研究了三维非静力平衡大气中平行切变流上重力内波的不稳定，推广了Miles定理和半圆定理，得到了有限深度气层的半椭圆定理。该定理指出不稳定波的复波速被限制在相速复平面上一个内接于霍华德（Howard）半圆的半椭圆内。该半椭圆长轴重合于半圆的直径，而短轴则取决于最小Ri数、波长、波宽等因素。 相似文献
2.
进一步了球面上正压准地转运动中不稳定波的Ｈｏｗａｒｄ半圆定理，发现在某些特定的基本流分布下，该定理可以发展成圆弧定理，由此得到不稳定扰动增长率的更为精确的估计式。 相似文献
3.
4.
斜压切变基流中横波型扰动的特征波动 Ⅱ:谱函数 总被引：3，自引：0，他引：3
“斜压切变基流中横波型扰动的特征波动Ⅰ谱点分布”一文中分析了斜压切变基流中横波型扰动的谱点分布，这里又对其谱函数进行了分析讨论。结果表明当基流在垂直方向存在切变时，重力惯性波与涡旋波的谱函数在垂直方向上均可出现临界层，临界层的高度随频率σ而变化，即重力惯性波与涡旋波都存在连续谱，但涡旋波与重力惯性波连续谱的结构却不同；对天气尺度扰动，两支重力惯性波和1支涡旋波的连续谱不重叠，此时每支波动仅有1个临界层；而对次天气尺度的扰动，重力惯性波与涡旋波的连续谱区会发生重叠，在连续谱的重叠区，重力惯性波仍只有1个临界层，但涡旋波则可以有2个或3个临界层。无论是涡旋波还是重力惯性波其连续谱的波包随时间都是衰减的，但涡旋波波包比重力惯性波波包衰减得慢。 相似文献
5.
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
6.
本对斜交型扰动不稳定谱点的分布做了理论分析，得到了该谱点分布的半圆定理一该谱点分布在复一面上以原点为圆心以R0为半径的上半平面上，同时还对该不稳定增长率的上界作了估计。发现水平永度越小，模式顶越高则该估计值越大；垂直风切变的增大和纬度的增高对该增长率的增大有正贡献；当层结稳定度减小时，最大增长率随相对最大增长率得增大而减小。 相似文献
7.
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
8.
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
9.
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
10.
圆形涡旋中的惯性重力内波不稳定和对称不稳定 总被引：10，自引：2，他引：10
用Boussinesq近似下的轴对称径向二维柱坐标系中的线性扰动方程组，讨论了圆形大气涡旋系统中扰动的惯性重力不稳定和对称不稳定。在环境为正压情形时，惯性重力内波不稳定的条件为#A(μj/R0)2N2+n2F2<0；当环境为斜压时，具有平行型扰动特征的惯性重力波发展的条件为Ri＊<1-[(3/2)+m]2，此时表现为对称不稳定。可见，惯性重力内波不稳定和对称不稳定都可作为台风、气旋一类圆形涡旋中扰动形成和发展的机制。 相似文献
11.
Robert E. Hall 《Dynamics of Atmospheres and Oceans》1980,5(2):113-121
A new semicircle theorem is derived for unstable barotropic disturbances to a class of rectilinear barotropic currents u(y) in systems with an ambient potential vorticity gradient (f/h)y which satisfies (u—us)(f/h)y ? 0 throughout the y domain, where us is some value of u. In the conventional semicircle theorem for this flow, the radius of the semicircle is a function of both the range of u and the maximum speed of the stable Rossby waves that can exist in the system when u = 0. In the new semicircle theorem, the radius is only a function of the former when it is small compared to the latter. Currents which do not satisfy the above condition, as well as stable modes and baroclinic systems, are also discussed. 相似文献
12.
Ren Shuzhan 《大气科学进展》1994,11(1):74-78
The general property of zonally symmetric stability of quasi-homogeneous and incompressible rotating ocean can be determined by a nondimensional parameter Rs which is similar to the Richardson number in Howard’s paper. The results indicate that the rotating effect leads to stabilize the basic flows and the horizontal shear effect leads to destabilize the basic flows. In addition, the most unstable growth rate is obtained and the semicircle and semiellipse theorem about the distributions of the unstable phase velocity are given in this paper. 相似文献
13.
L. Kristensen D. H. Lenschow P. Kirkegaard M. Courtney 《Boundary-Layer Meteorology》1989,47(1-4):149-193
We have postulated a simple model for the spectral tensor
ij
(k) of an anisotropic, but homogeneous turbulent velocity field. It is a simple generalization of the spectral tensor
inf
ij
piso(k) for isotropic turbulence and we show how in the limit of isotropy,
ij
(k) becomes equal to
inf
ij
piso(k). Whereas
inf
ij
piso(k) is determined entirely by one scalar function of k = ¦k¦, namely the energy spectrum, we need three independent scalar functions of k to specify
ij
(k). We show how it is possible by means of the three stream-wise velocity component spectra to determine the three scalar functions in
ij
(k) by solving two uncoupled, ordinary linear differential equations of first and second order. The analytic form of the component spectra each has a set of three parameters: the variance and the integral length scale of the velocity component and a dimensionless parameter, which governs the curvature of the spectrum in the transition domain from the inertial subrange towards lower wave numbers. When the three sets of parameters are the same, the three spectra correspond to isotropic turbulence and they are all interrelated and related to the energy spectrum. We show how it is possible to obtain these spectral forms in the neutral surface layer and in the convective boundary layer from data reported in the literature. The spectral tensor is used to predict the lateral coherences for all three velocity components and these predictions are compared with coherences obtained in two experiments, one using three masts at a horizontally homogeneous site in Denmark and one employing two aircraft flying in formation over eastern Colorado. Comparison shows reasonable agreement although with considerable experimental scatter.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
14.
The influence of an idealized moving wavy surface on the overlying airflow is investigated using direct numerical simulations (DNS). In the present simulations, the bulk Reynolds number is Re = 8000 (; where U0 is the forcing velocity of the flow, h the height of the domain and v the kinematic viscosity) and the phase speed of the imposed waves relative to the friction velocity, i.e., the wave age varies from very slow to fast waves. The wave signal is clearly present in the airflow up to at least 0.15λ (where λ is the wave length) and is present up to higher levels for faster waves. In the kinetic energy budgets, pressure transport is mainly of importance for slow waves. For fast waves, viscous transport and turbulent transport dominate near the surface. Kinetic energy budgets for the wave and turbulent perturbations show a non-negligible transport of turbulent kinetic energy directed from turbulence to the wave perturbation in the airflow. The wave-turbulent energy transport depends on the size, tilt, and phase of the wave-induced part of the turbulent Reynolds stresses.According to the DNS data, slow waves are more efficient in generating isotropic turbulence than fast waves.Despite the differences in wave-shape as well as in Reynolds number between the idealized direct numerical simulations and the atmosphere, there are intriguing similarities in the turbulence structure. Important information about the turbulence above waves in the atmosphere can be obtained from DNS—the data must, however, be interpreted with care. 相似文献
15.
A number of authors have reported the problem of unrealistic velocities (“rogue trajectories”) when computing the paths of
particles in a turbulent flow using modern Lagrangian stochastic (LS) models, and have resorted to ad hoc interventions. We
suggest that this problem stems from two causes: (1) unstable modes that are intrinsic to the dynamical system constituted
by the generalized Langevin equations, and whose actual triggering (expression) is conditional on the fields of the mean velocity
and Reynolds stress tensor and is liable to occur in complex, disturbed flows (which, if computational, will also be imperfect
and discontinuous); and, (2) the “stiffness” of the generalized Langevin equations, which implies that the simple stochastic
generalization of the Euler scheme usually used to integrate these equations is not sufficient to keep round-off errors under
control. These two causes are connected, with the first cause (dynamical instability) exacerbating the second (numerical instability);
removing the first cause does not necessarily correct the second, and vice versa. To overcome this problem, we introduce a
fractional-step integration scheme that splits the velocity increment into contributions that are linear (U
i
) and nonlinear (U
i
U
j
) in the Lagrangian velocity fluctuation vector U, the nonlinear contribution being further split into its diagonal and off-diagonal parts. The linear contribution and the
diagonal part of the nonlinear contribution to the solution are computed exactly (analytically) over a finite timestep Δt, allowing any dynamical instabilities in the system to be diagnosed and removed, and circumventing the numerical instability
that can potentially result in integrating stiff equations using the commonly applied explicit Euler scheme. We contrast results
using this and the primitive Euler integration scheme for computed trajectories in a drastically inhomogeneous urban canopy
flow. 相似文献
16.
Martin Claussen 《Boundary-Layer Meteorology》1985,33(2):151-172
The spectral equations of turbulent kinetic energy and temperature variance have been solved by using Onsager's energy cascade model and by extending Onsager's model to closure of terms that embody the interaction of turbulent and mean flow.The spectral model yields the following results: In a stably stratified shear flow, the peak wave numbers of the spectra of energy and temperature variance shift toward larger wave numbers as stability increases. In an unstably stratified flow, the peak wave numbers of energy spectra move toward smaller wave numbers as instability increases, whereas the opposite trend is observed for the peak wave numbers of temperature variance spectra. Hence, the peak wave numbers of temperature spectra show a discontinuity at the transition from stable to unstable stratification. At near neutral stratification, both spectra reveal a bimodal structure.The universal functions of the Monin-Obukhov similarity theory are predicted to behave as
m
~
H
~ (- Z/L)-1/3 in an extremely unstable stratification and as
m
~
H
~ z/L in an extremely stable stratification. For a stably stratified flow, a constant turbulent Prandtl number is expected. 相似文献
17.
《Dynamics of Atmospheres and Oceans》2005,38(3-4):173-193
A three-dimensional spectral analysis of Topex altimeter data reveals a large meridional component ky of the wavevector k for baroclinic Rossby waves of all timescales. Its existence necessitates some refinements in our estimates of certain basic properties of the Rossby wave field. In particular, by taking into account an actual off-zonal direction of k (often exceeding 70°), one finds that the wavelength, phase speed, and group velocity of mid-latitude Rossby waves (with periods less than 2 years) are much smaller than they appear to be on the assumption of a purely zonal wavenumber vector. Because of a shorter wavelength (yielding kL as high as 0.6, where L is the Rossby radius of deformation), these waves are essentially dispersive. Their group velocity vector may depart from zonal by more than 30°. An important intrinsic feature of the wave spectrum confirmed by our analysis is a broad-band distribution with respect to ky. Some of the dynamical implications of the large ky/kx ratio are discussed. 相似文献
18.
P. K. Pasricha R. Singh S. K. Sarkar H. N. Dutta B. M. Reddy P. K. Das 《Boundary-Layer Meteorology》1991,57(3):207-217
This paper presents meteorological measurements made during the antarctic summer period, on two 9 m and 3 m towers, on the rocky and ice shelf terrains of the Indian antarctic stations Maitri and Dakshin Gangotri, respectively. The measurements of fluctuations in temperature and wind speed made with relatively lesser precision instrumentation pertain to smaller wave numbers ~10-2 m-1 appropriate to outer scale L
0 of the atmospheric turbulence spectrum. Autocorrelation analysis of the fluctuations in temperature and wind speed has been performed. A new autoregressive scheme has been developed to represent the computed autocorrelation functions by a Yule statistical model, and to estimate the correlation period T
0 of the turbulent medium. Height profiles of outer scale L
0 of turbulence may be given in terms of T
0 and mean wind speed u. Further, the similarity theory of Monin-Obukhov has been used to compute height profiles of temperature structure parameter C
T
2. At Maitri, values of L
0 and C
T
2 are higher between 03–22 h local time than between 22–03 h. Values of L
0 and C
T
2 are smaller over the ice shelf terrain of the Dakshin Gangotri station, compared to those over the rocky terrain of the Maitri station. 相似文献