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1.
G. K. Korotaev 《Physical Oceanography》2000,10(6):495-502
We consider the problem of geostrophic adjustment of nonlinear axially symmetric formations in a two-layer fluid with infinitely
deep lower layer and demonstrate the existence of a new integral of motion, which enables us to determine the final equilibrium
state of perturbations without analyzing the transient (wave) stage of the process. It is shown that the final motions caused
by initial perturbations of the opposite signs are not equivalent.
Translated by Peter V. Malyshev and Dmitry V. Malyshev 相似文献
2.
S. F. Dotsenko 《Physical Oceanography》2000,10(4):287-295
Within the framework of the general linear statement of the problem, we determine the conditions of generation of a geostrophic
current in a layer of uniform rotating fluid for small displacements of the bottom of a basin. We deduce an equation relating
the equilibrium shape of the surface of the fluid with residual deformations of the bottom and find its general solution.
It is shown that the geostrophic current is generated only in the presence of residual deformations. We present numerical
estimates of the intensity of the generated geostrophic formation for a model of motion of the bottom. The investigated mechanism
of generation of geostrophic vortex fields is especially efficient in the shelf zone of the ocean.
Translated by Peter V. Malyshev and Dmitry V. Malyshev 相似文献
3.
We analyze model simulations of a wind-forced upper ocean front to understand the generation of near-surface submesoscale, O(1 km), structures with intense vertical motion. The largest vertical velocities are in the downward direction; their maxima are situated at approximately 25 m depth and magnitudes exceed 1 mm/s or 100 m/day. They are correlated with high rates of lateral strain, large relative vorticity and the loss of geostrophic balance. We examine several mechanisms for the formation of submesoscale structure and vertical velocity in the upper ocean. These include: (i) frontogenesis, (ii) frictional effects at fronts, (iii) mixed layer instabilities, (iv) ageostrophic anticyclonic instability, and (v) nonlinear Ekman effects. We assess the role of these mechanisms in generating vertical motion within the nonlinear, three-dimensionally evolving flow field of the nonhydrostatic model. We find that the strong submesoscale down-welling in the model is explained by nonlinear Ekman pumping and is also consistent with the potential vorticity arguments that analogize down-front winds to buoyancy-forcing. Conditions also support the formation of ageostrophic anticyclonic instabilities, but the contribution of these is difficult to assess because the decomposition of the flow into balanced and unbalanced components via semigeostrophic analysis breaks down at O(1) Rossby numbers. Mixed layer instabilities do not dominate the structure, but shear and frontogenesis contribute to the relative vorticity and strain fields that generate ageostrophy. 相似文献
4.
-STD Data obtained from the Third Chinese National Antarctic Research Expedition from January to February 1987 in the region near the South Shetland Islands are used to investigate an oceanic front, continental water boundary (CWB), north of the South Shetland Islands. The characteristics of the CWB in surface and subsurface layers as well as deep layer are discussed respectively. The estimations of the geostrophic currents and the baroclinic deformed radius Rbc in this area show that the flow along the front is in the geostrophic equilibrium approximately, and the formation of the front is mainly due to the strong boundary current north of the South Shetland Islands. Its length along the front is estimated to be about 360 km and its width across the front is about 30 km. 相似文献
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The intensification of upwelling front and two-cell circulation is studied numerically in a two dimensional level model. Upwelling front is set initially with longshore geostrophic flow. The uniform wind stress forces the ocean which has an infinite north-south coast line. Two-cell circulation, downwelling just inshore-side of the front and upwelling offshore-side, is induced, and the front is intensified. It is found that the intensification is occurred in the inshore-side of the front, and the intensification is basically due to the deviation from the thermal-wind balance, as is shown bySuginohara (1977). It is found that the inshore-side cell intrudes under the pycnocline. It seems to reproduce the observed two-cell circulation. 相似文献
7.
V. N. Kudryavtsev 《Physical Oceanography》1996,7(2):99-125
This paper discusses a simplified model for the evolution of the atmospheric planetary boundary layer overlying a thermal
front in the sea. The model provides local values of the friction/heat transfer geostrophic coefficients and the direction
of surface wind stress, as well as the wind/temperature profiles at any point on the front. With the running over a warm front,
the baroclinicity of the internal boundary layer leads to the generation of a near-surface current of air directed down the
front. The model can be used to interpret radar imagery of the sea surface with the purpose of determining its mesoscale variability.
Translated by Vladimir A. Puchkin. 相似文献
8.
Shinya Minato 《Journal of Oceanography》1982,38(4):225-235
Geostrophic adjustment of a two-layer fluid near a straight coast is investigated for an initial pressure disturbance which has no closed geostrophic contours by using a reduced gravity (divergent barotropic) model. Propagation of a volume of water along the coast due to the internal Kelvin wave allows a non-zero solution for the final geostrophic state. Energy partitions among geostrophic motion, the internal Kelvin wave and internal Poincaré waves are obtained and compared with the result of the classical problem of geostrophic adjustment without the coast. It is found that energy partition to the geostrophic motion (EPG) with the coast is always smaller than that without the coast (EPG
), while the scale of the initial disturbance is the same. The difference betweenEPG andEPG
is smaller than the energy partition to the internal Kelvin waves (EPK) and approachesEPK as the scale of the initial disturbance increases. 相似文献
9.
水下滑翔机其通过集成生物、化学、物理传感器可以测量如温度、盐度、溶解氧等多种海洋基础水文要素,其利用卫星定位系统获得实际出水速度和理论出水模型获得理论出水速度之差可以计算深度平均流,。本文利用海翼水下滑翔机获得温盐场及卫星定位数据评估深度平均流,结果显示利用温盐场获得深度平均地转流与水下滑翔机获得深度平均流相关系数0.95,表明其流场的一致性,同时根据船载观测ADCP误差分析法估算深度平均流误差约为0.036 m/s。借助深度平均流可以估算绝对地转流,包括正压地转流和斜压地转流。在零动力面的假设下,我们选取了海翼号水下滑翔机在南海的一组实验对流量误差进行了评估。该实验为2019年1月3日-2月16日海翼号水下滑翔机自南向北穿越西沙群岛附近一个中尺度涡观测。观测结果表明,该中尺度涡为冷涡流核,在涡心以南,绝对地转流为东向流,最大流速约为0.48 m/s;涡心以北,绝对地转流为西向流,最大流速约为0.47 m/s,稍弱于南侧。受不均匀时空观测计划影响,本文未对流量做出估计。 相似文献
10.
V. V. Knysh G. K. Korotaev A. I. Mizyuk A. S. Sarkisyan 《Izvestiya Atmospheric and Oceanic Physics》2012,48(1):57-73
This paper considers the main steps in improving the methods for calculating the ocean (sea) dynamics on the basis of observational
data on sea-water temperature and salinity. The results of diagnostic and adaptation calculations for the near-equatorial
area of the West Atlantic in the area of the Lomonosov countercurrent formation are presented. We consider the problem of
the complex use of measurements of temperature, salinity, and current velocity in the POLYMODE polygons with their assimilation
into the model using a Kalman filter. The results of calculations of the coordinated fields with the mechanism of geostrophic
adaptation and using asynchronous measurements obtained by the Razrezy program are given. We discuss further modifications
of the assimilation algorithms for hydrological observation data in models of sea dynamics and the principles of adaptation
of hydrophysical fields that made it possible to reconstruct the climate fields of the Black Sea and to reproduce the basin
dynamics for 23 years. 相似文献
11.
Some numerical experiments by the barotropic nonlinear two dimensional models are performed to study the water circulations in Lake Biwa, especially to study the large anticlockwise gyre in the north basin. The wind fields used in the experiments have no rotational component. This gyre is induced by the southerly wind and is approximately on the geostrophic balance. The vorticity of this gyre is contributed from the vertical stretching of the vortex tube by the variable bottom topography and the inertia term. But the latter term does not become effective if the bottom profile of the basin is flat. Therefore the horizontal circulation in the barotropic closed basin is the “topographic gyres”. The bottom stress has a little contribution to the vorticity balance of the gyre. 相似文献
12.
徐肇廷 《中国海洋大学学报(自然科学版)》1989,(3)
本文从流体力学基本方程组出发,在非地转条件下导得了分层海洋的内孤立波方程—Kbv和mKdv方程,证实了在非地转条件下,一类海洋非线性波动是可以严格满足内孤立波方程的。在地转条件下采用f平面近似导出了KdV方程的演化形式一有源KdV方程,地转的影响含于源项中。由初步的分析得出,f对KdV方程的影响是微弱的。由已得的KdV和mKdV方程的解可知,内孤立波与线性波有着本质差别。 相似文献
13.
The instability of long-wave disturbances of a geostrophic current with linear velocity shear is studied with allowance for the diffusion of buoyancy. A detailed derivation of the model problem in dimensionless variables is presented, which is used for analyzing the dynamics of disturbances in a vertically bounded layer and for describing the formation of large-scale intrusions in the Arctic basin. The problem is solved numerically based on a high-precision method developed for solving fourth-order differential equations. It is established that there is an eigenvalue in the spectrum of eigenvalues that corresponds to unstable (growing with time) disturbances, which are characterized by a phase velocity exceeding the maximum velocity of the geostrophic flow. A discussion is presented to explain some features of the instability. 相似文献
14.
M. V. Kalashnik 《Izvestiya Atmospheric and Oceanic Physics》2011,47(4):439-444
Cyclone-anticyclone asymmetry in a rotating fluid results in vortices with cyclonic rotation being attenuated more rapidly than vortices with anticyclonic rotation due to the Ekman bottom friction. To explain this effect, some authors invoked rather complex integral (averaged along the vertical) models with the parametrization of nonlinear friction. A simple analytical model, free of the procedure of formal averaging and based on a separate consideration of the equations for external flow in the nonviscous region and internal flow in the boundary layer, is investigated in this work. The corresponding equations are written in the so-called geostrophic momentum approximation, which makes it possible to take into account the nonlinear advective mass transport in the boundary layer at small Rossby numbers. The nonlinear equation of the hyperbolic type for the tangential velocity, which describes the process of attenuation of an axisymmetric vortex, is obtained from the condition of total mass conservation. Based on the solutions to this equation, it was shown that distinctions in the character of vortex attenuation are caused by deviations from the geostrophic regime in the nonviscous region. It was established that the concentration (compression) of anticyclonic vortices and the extension of cyclonic ones take place in the process of attenuation. 相似文献
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16.
V. O. Kakhiani K. I. Patarashvili S. D. Tsakadze M. V. Kalashnik L. Kh. Ingel 《Izvestiya Atmospheric and Oceanic Physics》2009,45(4):403-410
The results of laboratory modeling of geostrophic adjustment in a shallow-water layer in rotating paraboloid are presented.
According to the Rossby-Obukhov theory, this process excites nonstationary wave and stationary vortex (geostrophic) components
of motion in a rotating fluid. In our experiments, the wave and vortex components were excited by extracting a preliminarily
imbedded hemisphere (which made the initial distribution of the depth of the fluid inhomogeneous) from the central area of
a rotating vessel with a parabolic base. Under this excitation technique, a prominent cyclonic eddy is formed in the central
portion; the structure of this eddy is satisfactorily described within the linear theory of adjustment. Along with the shallow-water
experiments, the published experimental data on modeling geostrophic adjustment in a two-layer medium are analyzed. A simple
analytic solution to the corresponding problem of the adjustment theory is obtained, and this solution agrees with the experiment. 相似文献
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《Deep Sea Research Part II: Topical Studies in Oceanography》1999,46(11-12):2941-2967
We report rate estimates for the horizontal transport of realized and potential “new” production across and along the Vancouver Island continental margin. Measurements consisted of three summer-season surveys (1993–1995) of water properties, chlorophyll and dissolved nutrient concentrations, zooplankton biomass and community composition. Sampling was done along paired 350-km station lines extending parallel to and approximately 25 km seaward of the shelf break. Horizontal transport of nutrients and plankton biomass was estimated from cross-products of concentration fields with cross-shore and alongshore geostrophic velocity fields and with space- and time-averaged estimates of Ekman volume transport. Because concentrations of nutrients and phytoplankton were low in the upper 30–50 m, their horizontal flux within the Ekman layer was relatively small (order 10% of geostrophic transport). Geostrophic transport was strongly localized and was correlated vertically with concentration gradients, and horizontally with eddies and meanders of the alongshore geostrophic currents. Net geostrophic transport was a small difference between larger localized seaward and shoreward components. Upper layer (0–50 m) transports of nutrients and phytoplankton biomass were of roughly similar magnitude. Both were much larger than transport of zooplankton biomass. Total cross-shore flux was a small fraction (<10%) of the estimated total productivity shoreward of the sampling lines. Direction and magnitude varied among survey periods, but for all 1990s surveys appear to have been weaker than in the mid-1980s, when summer-season averaged upwelling-favorable winds were stronger and the shelf-break current was faster. 相似文献
20.
A nonlinear problem of geostrophic adjustment in an ideal rotating two-component fluid in the field of gravity is studied analytically. The stratification of the fluid’s density is composed of its temperature stratification and stratification of the concentration of an admixture (in particular, these are salt seawater and moist air). Stationary states, which are reached after the adjustment process is terminated, are found with the use of Lagrange conservation laws. If the amplitudes of smooth initial disturbances are sufficiently large, discontinuity surfaces can appear in the course of evolution. Allowance for a two-component character of the medium makes qualitative properties of such surfaces especially varied. For example, a jump may be strongly marked in the field of one substance alone. It is shown that, if the initial ageostrophic property is related to temperature and/or admixture-concentration disturbances, the evolution of the fields of these substances can differ qualitatively from classical solutions to adjustment problems. For example, in the course of adjustment, the initial heat pulse can lead to the formation of a stationary temperature disturbance with a larger amplitude and/or the opposite sign. During the evolution of a smoothed temperature “step,” nonmonotonic distributions of temperature whose amplitudes are much greater than the amplitude of the initial step may appear. Some of such effects can manifest themselves even in a linear approximation. 相似文献