共查询到20条相似文献，搜索用时 15 毫秒
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建立了一类非线性海气耦合波的模式,并用该模式作了解析研究,讨论了该类海气耦合波的存在条件,发现当海气耦合较强时分别存在以海洋为主导方面及以大气为主导方面的两支海气耦合波,而耦合较弱时则仅有前者存在。还求得了该模式中该类海气耦合波的椭圆余弦波解及孤立波解,并对以海洋为主导的海气耦合波的性质作了讨论,认为海气相互作用耦合也是产生大气季节内振荡的机制之一。 相似文献
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H. A. R. de Bruin 《Boundary-Layer Meteorology》1994,68(4):427-432
With the temperature fluctuation method, the sensible heat flux and friction velocity can be evaluated from standard deviation of the temperature and horizontal wind speed at one level. In principle, for unstable conditions the governing equations have to be solved by iteration. In this note, an approximate analytic solution is presented. Also, the solution for stable situations is discussed. 相似文献
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Keith W. Ayotte 《Boundary-Layer Meteorology》1997,83(2):285-309
This paper describes an adjoint method for data assimilation intoupstream boundary conditions of numerical modelsusing optimal control theory. Mathematical formalisms are given along with the numerical implementation of the schemein a column model of the atmospheric boundary layer. The optimized mean and turbulence profiles are used as an upstream solutionin a model of turbulent flow in complex terrain. To contrast thiswith other methods, two solutions for flow over an isolatedhill are calculated, one with an optimized upstream solution andone with a simple surface-layer formulation for the upstream solution.These two solutions are compared to observations and analytical theory. The adjoint optimization method is shown to producesolutions of flow in complex terrain that are substantively differentat the two solutions, with the optimized solution giving more accurate results. 相似文献
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对称不稳定的非线性问题和对称型重力惯性波的非线性周期解 总被引：4，自引：0，他引：4
本文利用密度的空间分布不均匀性引入非线性项，从准动量无辐散模式出发导出了一个自治的二阶非线性系统，应用这个系统讨论了非线性项对对称不稳定以及对称型重力惯性波非线性周期解的作用。从本系统的一次近似系统可得到类似Hoskins于1974年得到的结论，同样可导出对称不稳定的位涡判据。由于本系统是一有限次的非线性系统，故应用Poincare形式级数法可证明非线性周期解的存在性，并可求得周期解的一系列近似解。 相似文献
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Chang-Kou Tai 《Dynamics of Atmospheres and Oceans》1983,7(3):147-165
Stability problems involving parallel shear flow are considered in the context of wave-reflection problems. It is found that if an unstable solution exists and its growth rate is sufficiently small, the growth rate can be connected to the reflection coefficient through a formula as if the unstable growth were the direct result of repeated over-reflections. If the stability problem under consideration has time symmetry, then for every growing solution there exists a corresponding decaying solution. It is shown that a consistent formula can also be derived for the decaying solution, and the existence of at least one critical layer in the corresponding wave-reflection problem is needed in order to account for both the growing and decaying solutions. As an application of these concepts, the small-scale non-geostrophic instabilities found by Stone (1970) are identified to be associated with over-reflection of inertia-gravity waves. 相似文献
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本文提出了一个可以用于大气定常波数值模拟的非线性初始方程三维谱模式,模式的动力学框架与文献[1]中的线性模式是相互对应的。利用线性模式的定常解作为初值,通过Newton-Raphson迭代法求出了收敛的非线性定常解。文中给出了这一模式大气对于北半球大尺度地形和1979年1月平均非绝热加热场的响应作为计算实例,并与对应的线性响应以及观测事实进行了对比,证明在考虑了大气中波动之间的非线性相互作用之后数值模拟的结果确实比线性模式有显著的改进,尤其是对于低纬环流系统更是如此。这表明了非线性作用对于热带环流系统的极端重要性。 相似文献
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在ｕαｖ／αｘ＝０的条件下，求出了某一类低涡的孤立波解，然后将它同一般低涡的孤立波解进行比较，结果发现，由于采用了ｕαｖ／αｘ＝０的假定，使得模式方程组的非线性增强，垂直输送ｗαｖ／αｐ赖以保留，使温度平流，非绝热加热（Ｑ１和Ｑ２）的强迫效应能够通过温度局地变化、垂直运动两条渠道表现出来。 相似文献
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An analytical framework is proposed for studying variations in the diurnal wind structure in the planetary boundary layer (PBL) and the evolution of the low-level nocturnal jet. A time-dependent eddy-diffusivity coefficient corresponding to solar input is proposed, and an appropriate coordinate transformation ensures that mixing height varies continuously with ground heat-flux changes. The solution exhibits the receding character of the daytime PBL as evening approaches, thereby dividing the PBL into two regimes — the one just above the ground, representing the nocturnal boundary layer, and the region above it. It is assumed that inertial oscillations (IO) are triggered in the upper layer at about the time of sunset when the reversal in the direction of ground heat flux is felt in the upper layer. Two approaches are adopted to determine the characteristic features of IO and the evolution of the nocturnal low-level jet. The first one is based on the physical principle that release of horizontal momentum due to deviation from the geostrophic wind gives rise to the IO. The solution captures all the characteristic features of the IO, such as phase shift and decreasing amplitude of the IO with increasing height. According to this analysis the IO is triggered at a level as soon as the top of the receding boundary layer leaves that level. The solution is discontinuous with respect to the vertical coordinate. In the second approach we solve an initial-value problem to determine the solution in the upper layer, assuming that at about the time of sunset there is a rapid collapse of the daytime PBL to the steady, nocturnal boundary layer. The assumption is based on the mixing-height profiles prepared from climatological data collected at Delhi. The solution for the nocturnal boundary-layer regime is then obtained as a boundary-value problem. The solutions so obtained are continuous throughout the domain of interest and exhibit the characteristic features of an IO. The analysis leads to the conditions under which a low-level nocturnal jet is produced and provides quantitative estimates of the parameters, such as length of night, latitude, mixing height at sunset and nocturnal mixing height, that are conducive to the generation of a jet. The nocturnal wind profile produced by this approach compares well both with typical atmospheric data observed at Delhi and with output from a mesoscale numerical model. There is still some uncertainty related to the time of initiation of the IO as a function of latitude. 相似文献
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This paper is adapted from a presentation at the session of the European Geophysical Society meeting in 2002 honouring Joost
Businger. It documents the interaction of the non-linear planetary boundary-layer (PBL) model (UW-PBL) and satellite remote
sensing of marine surface winds from verification and calibration studies for the sensor model function to the current state
of verification of the model by satellite data. It is also a personal history where Joost Businger had seminal input to this
research at several critical junctures. The first scatterometer in space was on SeaSat in 1978, while currently in orbit there
are the QuikSCAT and ERS-2 scatterometers and the WindSat radiometer. The volume and detail of data from the scatterometers
during the past decade are unprecedented, though the value of these data depends on a careful interpretation of the PBL dynamics.
The model functions (algorithms) that relate surface wind to sensor signal have evolved from straight empirical correlation
with simple surface-layer 10-m winds to satellite sensor model functions for surface pressure fields. A surface stress model
function is also available. The validation data for the satellite model functions depended crucially on the PBL solution.
The non-linear solution for the flow of fluid in the boundary layer of a rotating coordinate system was completed in 1969.
The implications for traditional ways of measuring and modelling the PBL were huge and continue to this day. Unfortunately,
this solution replaced an elegant one by Ekman with a stability/finite perturbation equilibrium solution. Consequently, there
has been great reluctance to accept this solution. The verification of model predictions has been obtained from the satellite
data. 相似文献
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The analytical solutions of the continuous accretion rate equation are compared regarding two different size distributions for cloud and rain water, two hail terminal velocities for different turbulent regimes and two solution types. The Khrgian-Mazin and Marshall-Palmer size distributions are assumed for rain water fraction, while the Khrgian-Mazin and monodisperse ones are applied to cloud water. In all cases the exponential-type size distribution for hail is used. In the calculation procedure for hail terminal velocity we take into consideration that the drag coefficient may be fixed or dependent on Reynolds number. Both approximate and exact solutions of the accretion rate under the same other conditions are also compared.Results show that the Khrgian-Mazin size distribution makes the approximate accretion rate between hail and rain considerably higher compared to its former parameterization for both hail terminal velocity assumptions. On the other side, the new treatment of hail terminal velocity with a variable drag coefficient produces lower accretion rates compared to the fixed drag coefficient case for all size distributions used. The approximate solution of the accretion rate equation is mainly lower than the exact one. Only in the case of raindrops-cloud droplets interaction it is much higher than the exact one with the Khrgian-Mazin size distribution used. 相似文献
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A simple moments model used in studying the large-scale thermally driven ocean circulation, in one hemisphere, is extended
with a set of evolution equations for the basin-averaged salinity gradients. Natural formulations of the boundary conditions
for the heat flux and the (virtual) salt flux are given, the latter based on the SST-evaporation feedback. Stommel’s box model
result, a coexisting thermal and saline solution, is retrieved in the limit of no rotation. Including rotation in a salt-dominated
setting, a steady circulation is found which bifurcates for higher Rayleigh numbers in a periodic solution which becomes chaotic
through a cascade of subharmonic bifurcations. Periodic motion results from two different mechanisms. First, the stable stationary
state bifurcates into a periodic solution where anomalously saline water is advected by the overturning circulation. Second,
this periodic solution bifurcates into a state which is dominated, during the larger part of the cycle, by diffusion and inertia,
characterized by a decreasing overturning rate, and, during the subsequent shorter part of the cycle, by rapid advection and
restratification of the entire basin. The basin-averaged vertical density field is stably stratified in the steady and the
periodic regimes and remains statically stable in the chaotic regime.
Received: 16 July 1996 / Accepted: 29 December 1997 相似文献
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Dr. Lev Kh. Ingel 《Meteorology and Atmospheric Physics》1996,58(1-4):13-19
Summary The problem of the thermal circulation over the underlying surface, has been studied analytically for the case when the temperature of the underlying surface depends linearly on one of the horizontal coordinates. A horizontal pressure gradient is specified at the upper boundary of the medium horizontal layer (that has been rotating around the vertical axis) being under consideration, and this fact provides the existence of the background horizontal flow. The problem is essentially nonlinear, since, first, the heat advection, second, the square friction and the heat exchange at the underlying surface are taken into account. The solution depends on three non-dimensional parameters that are determined by the absolute values of the specified horizontal temperature and pressure gradients and by the angle between these vectors. In dependence on the values of the above mentioned parameters the solution properties may be very different. When the horizontal temperature gradient is absent, the solution is a generalization of the Ekman boundary layer classical theory for a case of the nonlinear friction against the underlying surface. The temperature and pressure fields essentially depend on the existence or absence of the background motion velocity component in the direction of the temperature horizontal gradient.With 2 Figures 相似文献
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把地球一大气系统,近似地看作是具有随机干扰的对太阳辐射线性响应的系统,求得了一个随机解。证明了大气运动的长期状态是许多时刻无数随机因素影响的迭加。 相似文献
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生态环境的好坏是人类赖以生存发展的重要风素,人类的活动和生态环境息息相关,而气候是影响生态环境变化的主要原因之一。通过近20a额济纳旗的生态环境恶化引起的气候变化的事实．讨论提出额济纳旗生态维持的解决方案。 相似文献
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James C. McWilliams William R. Holland Julianna H.S. Chow 《Dynamics of Atmospheres and Oceans》1978,2(3):213-291
A sequence of numerical calculations has been made for the equilibrium balances of eddies and mean currents in open and partially blocked, periodic channels. The physical model employed is a two-layer, quasigeostrophic, wind-driven one, with important bottom friction and weak lateral friction. The resolved eddies provide the interior fluxes of momentum and potential vorticity which allow the mean state to be a balanced one. The set of calculations does not provide a parameter study as such, but does provide examples of the influences of alternative physical processes and geometrical constraints. These alternatives include the presence or absence of a partial barrier across the channel, the length of the channel, the addition of a transient component to the wind-driving, and the addition of a topographic sill across the channel gap. Particular attention is focused upon the steadily driven general circulation of a β-plane channel, because of the structural simplicity of the solution. The results may be broadly summarized as follows. The eddies are generated by a baroclinic instability of the mean flow. They act to intensity the upper layer mean jet and mean cross-jet potential vorticity gradient (through eddy horizontal Reynolds stress and relative vorticity flux divergence, respectively) and to transfer downwards mean zonal momentum, energy, and potential vorticity gradient (through eddy interfacial pressure drag, vertical pressure work, and vortex stretching flux divergence, respectively). In the case of a zonally uniform channel, the meridional heat flux is found not to conform closely to previously proposed parameterizations. The presence of a partial meridional barrier and a topographic obstacle are found to strongly influence the equilibrium solution, while neither a change in the basin length nor the presence of a transient wind component appear to importantly alter the solution. 相似文献
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应用经验模态分析方法(经验模态分解(EMD)和Hilbert谱),对夏季副热带大气系统在周期态和振荡态下的流函数数值解序列进行本征模态函数(IMF)及其Hilbert谱的分析。结果表明:(1)周期态下的流函数分量时间序列一般由1个IMF构成,而且其周期就是该流函数的周期。对周期性的IMF分量使用Hilbert变换得到的瞬时频率和振幅都不随时间变化。(2)振荡态下的流函数分量时间序列一般由2个以上的IMF构成,其中有的IMF分量具有显著的周期性,相应的瞬时频率和振幅都不随时间变化;有的IMF分量则没有显著的周期性,相应的瞬时频率和振幅有变化,而且随着振荡态复杂程度的增大,瞬时频率和振幅的变化也趋于复杂。(3)瞬时振幅有明确的物理意义,表示IMF振荡的能量;振幅的局部相对大值对应着原序列(IMF)的强振荡,小值则对应着弱的变化。瞬时频率的显著增大,表示原序列有大的变化。 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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Dynamics of nonlinear baroclinic Ekman boundary layer 总被引：2，自引：0，他引：2
By the geostrophic momentum approximation, the wind structure and vertical motion within the non-linear baroclinic Ekman layer matching with the surface layer are determined. A comparison of the Ekman solution with the classical one is made. It is demonstrated that the contributions of baroclinity, stratification and nonlinear effects to the wind profile within the layer are all of definite importance. 相似文献