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1.
将理想化的南中国海海盆在垂直方向上划分为Ekman层、惯性层和摩擦层. Ekman层中的运动由大气风应力驱动，其底部的扰动压力将作为其下惯性层中运动的上边界条件. 惯性层中的运动是由f 平面三维非线性方程在准地转近似下位势涡度守恒控制，由此得到控制惯性层中运动关于扰动压力的三维椭圆型方程. 在惯性层以下考虑到深层的海盆水平尺度很小，由此引进带有底部摩擦的线性控制方程，方程的边界条件为惯性层和摩擦层交界面上的扰动压力连续，沿海盆边界假定海水与相邻的固壁间无热量交换，由此设在海盆边界上扰动温度为零. 在此基础上分别利用惯性层和摩擦层中的椭圆型控制方程计算了相应层次上冬、夏季的扰动压力和准地转流. 结果表明冬季各层上以气旋式环流为主，且随深度的增加流速减小；夏季各层上以反气旋式环流为主，流速也随深度增加而减小. 这在一定程度上和观测事实相符. 相似文献
2.
The classical Ekman theory tells us that the ocean surface current turns to the right(left) side of wind direction with 45° in the north(south) hemisphere,but the observation and research results show that the surface current deflexion angle is smaller than 45° in the Arctic and high latitude areas while larger than 45° in the low latitude areas.In order to explain these phenomena,a series of idealized numerical experiments are designed to investigate the influence of vertical viscosity coefficients with different vertical distribution characteristics on the classical and steady Ekman spiral structure.Results show that when the vertical viscosity coefficient decreases with water depth,the surface current deflexion angle is larger than 45°,whereas the angle is smaller than 45° when the vertical viscosity coefficient increases with water depth.So the different observed surface current deflexion angles in low latitude sea areas and the Arctic regions should be attributed to the different vertical distribution characteristics of vertical viscosity coefficients in the upper ocean.The flatness of the Ekman spiral is not equal to one and does not show regular behaviors for the numerical experiments with different distribution of vertical viscosity.However,the magnitudes and directions of volume transport of Ekman spirals are almost the same as the results of classical Ekman theory,i.e.,vertical viscosity coefficient distributions have no effect on the magnitudes and directions of volume transport. 相似文献
3.
The main modes of interannal variabilities of thermocline and sea surface wind stress in the tropical Pacific and their interactions are investigated,which show the following results.(1) The thermocline anomalies in the tropical Pacific have a zonal dipole pattern with 160°W as its axis and a meridional seesaw pattern with 6-8°N as its transverse axis.The meridional oscillation has a phase lag of about 90° to the zonal oscillation,both oscillations get together to form the El Ni?o/La Ni?a cycle,which be-haves as a mixed layer water oscillates anticlockwise within the tropical Pacific basin between equator and 12°N.(2) There are two main patterns of wind stress anomalies in the tropical Pacific,of which the first component caused by trade wind anomaly is characterized by the zonal wind stress anomalies and its corresponding divergences field in the equatorial Pacific,and the abnormal cross-equatorial flow wind stress and its corresponding divergence field,which has a sign opposite to that of the equatorial region,in the off-equator of the tropical North Pacific,and the second component represents the wind stress anomalies and corresponding divergences caused by the ITCZ anomaly.(3) The trade winds anomaly plays a decisive role in the strength and phase transition of the ENSO cycle,which results in the sea level tilting,provides an initial potential energy to the mixed layer water oscillation,and causes the opposite thermocline displacement between the west side and east side of the equator and also between the equator and 12°N of the North Pacific basin,therefore determines the amplitude and route for ENSO cycle.The ITCZ anomaly has some effects on the phase transition.(4) The thermal anomaly of the tropical western Pacific causes the wind stress anomaly and extends eastward along the equator accompanied with the mixed layer water oscillation in the equatorial Pacific,which causes the trade winds anomaly and produces the anomalous wind stress and the corresponding divergence in favor to conduce the oscillation,which in turn intensifies the oscillation.The coupled system of ocean-atmo-sphere interactions and the inertia gravity of the mixed layer water oscillation provide together a phase-switching mechanism and interannual memory for the ENSO cycle.In conclusion,the ENSO cycle essentially is an inertial oscillation of the mixed layer water induced by both the trade winds anomaly and the coupled ocean-atmosphere interaction in the tropical Pacific basin between the equator and 12°N.When the force produced by the coupled ocean-atmosphere interaction is larger than or equal to the resistance caused by the mixed layer water oscillation,the oscillation will be stronger or maintain as it is,while when the force is less than the resistance,the oscillation will be weaker,even break. 相似文献
4.
Abstract A laser Doppler velocimeter (LDV) has been successfully mounted on a high quality rotating turntable. The capability of this LDV is demonstrated by some detailed measurements of the relative flow during the spin-up of a homogeneous fluid in a cylinder. Local measurements in water of the zonal flow component of magnitude 0.1 cm/sec have been made with an error of about 0.003 cm/sec. The spatial resolution was about 0.1 cm and the temporal resolution about 0.5 Hz. Effects on the flow due to absorption of the low power laser beam (5 milliwatts) and to the low concentration (3 parts/million) of 0.5 micron diameter scattering particles were negligible. The results are compared with analytical theory and the agreement is good. For a Rossby number of 0.1, the weak inertial modes excited by the Ekman layer formation can be clearly seen and identified. The LDV offers great promise for checking numerical and analytical solutions against experiments. This is particularly true for contained flows where conventional probes often significantly disturb the flow. 相似文献
5.
The drift trajectory of a floe near the North Pole (87° N, 175° W) was observed during 8–19 August, 2010 based on the fourth Chinese National Arctic Research Expedition. The trajectory of the floe showed circular motions superimposed on straight drift. Each cycle had a period of about 12?h. The circular motion is inertial oscillation. The largest amplitude of inertial oscillation speed can reach 20?cm/s. After removing the inertial oscillation, the floe drift direction is about 40° on average to the right of the observed 10-m wind which is much larger than previous reports on the angle between sea-ice velocity and the geostrophic wind, and floe drift moves with a speed of about 1.4?% of the observed 10-m wind speed throughout the whole observation period. A simple dynamic sea ice-ocean coupled model and a three-dimensional sea ice-ocean coupled model are employed to simulate the floe drift. Both numerical models are with the widely used quadratic water-drag formulation, i.e., the stress is proportional to the square of the ice velocity relative to the ocean surface current. The inertial oscillation of the floe is successfully simulated by the simple passive drag model, while the floe drift amplitudes simulated from the three-dimensional model are relatively small. 相似文献
6.
Hezi Gildor 《地球物理与天体物理流体动力学》2013,107(6):593-599
The solution for the bottom Ekman layer has a somewhat counter intuitive character, which seems to violate the maximum principle: at a certain level the velocity within the Ekman layer is higher than the velocity in the geostrophic layer above. I explain this character by looking at an analogous problem in an inertial frame of reference and show that it is the result of observing the flow from a rotating frame of reference (i.e. within a system that is not in steady state). The flow in the bottom Ekman layer is a superposition of the flow that results from the force exerted on the fluid by the rotating Earth and of the flow that results from the pressure-gradient term. Therefore, at a certain level the speed is higher than the speed of the geostrophic layer above which results from the pressure gradient alone. 相似文献
7.
Prof. Dr. Wolfgang Krauss 《Ocean Dynamics》1972,25(6):241-250
Summary The ocean is subdivided into a homogeneous upper layer (Ekman layer) and a continuously stratified lower layer. Horizontal velocities which in analogy to Fredholm's solution contain inertial oscillations, are generated in the upper layer by the tangential stress of the wind field varying both in space and time. The spatial structure of the wave field corresponds to that o the stress field. If the surface remains at rest (=0), vertical motions result from the horizontal oscillations. At the bottom of the Ekman layer the spatial structure of these vertical motions is proportional to divergence and rotation of the wind stress. Internal waves of the lower layer which primarily have periods approaching the inertial-period are generated by the vertical velocity field at the bottom of the Ekman layer (Ekman suction). Their structure is essentially more complicated than near the surface. Beats are a common phenomenon due to the superposition of internal modes.
相似文献
Windbedingte interne Wellen und Trägheitswellen
Zusammenfassung Das Meer wird in eine homogene Deckschicht (Ekmansche Reibungsschicht) und eine kontinuierlich geschichtete innere Region unterteilt. Die raum-zeitlich variable tangentiale Schubspannung erzeugt in der Deckschicht Horizontalgeschwindigkeiten, denen analog der Fredholmschen Lösung Trägheitswellen aufgeprägt sind. Ihre räumliche Struktur ist mit der des Schubspannungsfeldes identisch. Wenn keine Stauerscheinungen auftreten (=0), werden durch diese Horizontalbewegungen Vertikalbewegungen bedingt. An der Untergrenze der Ekman-Schicht ist deren räumliche Struktur der Divergenz und Rotation des Schubspannungsfeldes proportional. Das Vertikalgeschwindigkeitsfeld an der Untergrenze der Deckschicht erregt interne Wellen in der unteren Region, die vorwiegend Perioden in der Nähe der Trägheitsperiode aufweisen. Ihre Struktur ist wesentlich komplizierter als in der Deckschicht. Insbesondere zeigen sich Schwebungen.
Ondulations internes dues au vent et mouvements dont la période dépend de l'inertie
Résumé L'Océan se divise en une couche supérieure homogène (couche d'Ekman) et une couche inférieure stratifiée d'une façon continue. Les vélocités horizontales, affectées, par analogie avec la solution de Fredholm, d'oscillations dues à l'inertie, prennent naissance dans la couche supérieure par suite de l'effort tangentiel du champ du vent, variable à la fois dans l'espace et dans le temps. La structure du champ du vent, dans l'espace, correspond à celle du champ de l'effort. Si la surface reste calme (-0) les mouvements verticaux sont dus aux oscillations horizontales. Au fond de la couche d'Ekman, la structure dans l'espace de ces mouvements verticaux est en rapport avec la divergence et la rotation de l'effort du vent. Les ondulations internes de la couche inférieure qui ont, à l'origine, des périodes proches de celle due à l'inertie, sont engendrées par le champ de la vitesse verticale au fond de la couche d'Ekman (succion d'Ekman). Leur structure est beaucoup plus compliquée que près de la surface. Les battements sont un phénomène commun du à la superposition de modes internes.
相似文献
8.
We investigate, through both asymptotic analysis and direct numerical simulation, precessionally driven flow of a homogeneous fluid confined in a fluid-filled circular cylinder that rotates rapidly about its symmetry axis and precesses about a different axis that is fixed in space. A particular emphasis is placed on a spherical-like cylinder whose diameter is nearly the same as its length. At this special aspect ratio, the strongest direct resonance occurs between the spatially simplest inertial mode and the precessional Poincaré forcing. An asymptotic analytical solution in closed form describing weakly precessing flow is derived in the mantle frame of reference for asymptotically small Ekman numbers. We also construct a nonlinear three-dimensional finite element model – which is validated against both the asymptotic solution and a constructed exact solution – for elucidating the nonlinear transition leading to disordered flow in the precessing spherical-like cylinder. Properties of both weakly and strongly precessing flows are investigated with the aid of a complete inertial-mode decomposition of the fully nonlinear solution. Despite a large effort being made, the well-known triadic resonance is not found in the precessing spherical-like cylinder. The energy contained in the precessionally forced inertial mode is primarily transferred, through nonlinear effects in the viscous boundary layers, to the geostrophic flow that becomes predominant when the precessional Poincaré force is sufficiently large. It is found that the nonlinear flow evolutes gradually and progressively from the laminar to disordered as the precessional force increases. 相似文献
9.
Inertial waves as oscillatory motions in rotating fluids generate internal shear layers at critical latitudes. We investigated
the nonlinear interaction of inertial waves for global flows (3D flows) in dependence on the Ekman number. When the value
of the Ekman number decreases, the influence of the Ekman layers to the flow pattern increases. Critical latitudes, the attractor
flow pattern and certainly internal shear layers are observable mainly at greater values of the Ekman number. Although, with
decreasing the Ekman number smaller flow structures become visible, nonlinear interactions in shear layers drive an axisymmetric
flow whose amplitude diverges at the limit of the vanishing Ekman number. We show that this conclusion is valid not only for
zonal wind driven by inertial modes but also for similarly driven global flows. 相似文献
10.
Denis Aelbrecht Gabriel Chabert d'Hires Dominique Renouard 《Continental Shelf Research》1999,19(15-16)
In homogeneous rotating fluid, when there is an oscillating forcing in the interior fluid with a period long enough for an Ekman layer to develop, there is an interaction between the oscillatory Ekman layer and the vertical wall, since the latter imposes an alternating adjustment flow confined near the wall. As a result, this coastal rectification process leads to a Lagrangian transport along the coast. The Ekman number, the Rossby number and the temporal Rossby number of the forcing flow are the governing parameters of that mechanism which can be described by a simplified analytical model taking into account both the vertical time-dependent structure of the current and the presence of the wall. The model shows that the residual (rectified) current flowing with the coast to its right results from the strong nonlinear interaction between along- and cross-shore tidal currents leading to asymmetrical momentum exchanges between the Ekman bottom layer and the coastal boundary layer. The model provides simple scaling laws for the maximum intensity and width of the residual current. The latter is significantly larger than the friction (Stokes) lateral boundary layer of the forcing flow. A comprehensive set of experiments is performed in the 13 m diameter rotating tank by oscillating an 8 m×2 m horizontal plate and vertical wall in a homogeneous fluid at rest in solid-body rotation and measuring the two horizontal components of the current at several locations and depths above the central part of the plate. The predicted and experimentally measured maximum intensity and width of the residual current are in very good agreement, within the range of validity of the model, i.e. when the Ekman number is sufficiently small. However experiments also show that the residual current still occurs when the Ekman layer thickness is of the same order as the fluid depth, but it is then confined to a narrower band along the vertical wall. The flow structure found experimentally is also correctly described by a numerical model developed by Zhang et al. (1994). Current measurements in the Eastern part of the English Channel near the French coast reveal a significant coastal residual current flowing Northward and the coastal rectification process described here may account for part of it. 相似文献
11.
Nonlinear mechanisms of long-term variations in the Caspian Sea level are described. It is shown that with account taken of the dependence of the evaporation depth from the Volga basin surface on soil moisture content and the dependence of the evaporation depth from the sea surface on its level, we obtain a fundamentally new (chaotic) oscillation mechanism with several attraction levels. The stochastic differential equations describing the water budget of the sea basin and the sea proper and the respective solutions of the Fokker–Planck–Kolmogorov equation are shown to have stationary bimodal density of the level probability. The random process, characterizing the sea level variations at a nonlinear dependence between the evaporation rate and the level is found to be non-Gaussian. Noise-induced transitions, caused by nonlinear evaporation processes are described. A new nonlinear stochastic theory describing the Caspian Sea level variations and based on predicted physical effects is suggested. 相似文献
12.
O. Goepfert 《地球物理与天体物理流体动力学》2019,113(1-2):222-234
ABSTRACTIt is shown that flows in precessing cubes develop at certain parameters large axisymmetric components in the velocity field which are large enough to either generate magnetic fields by themselves, or to contribute to the dynamo effect if inertial modes are already excited and acting as a dynamo. This effect disappears at small Ekman numbers. The critical magnetic Reynolds number also increases at low Ekman numbers because of turbulence and small-scale structures. 相似文献
13.
Andrew F. Bennett 《地球物理与天体物理流体动力学》2013,107(1):113-142
AbstractThe flow in a mechanically driven thin barotropic rotating fluid system is analysed. The linear theory of Baker and Robinson (1969) is modified and extended into the non-linear regime.An internal parameter, the “local Rossby number”, is indicative of the onset of nonlinear effects. If this parameter is 0(1) then inertial effects are as important as Coriolis accelerations in the interior of the transport-turning western boundary layer and both of its Ekman layers. The inertial effects in the Ekman layers, ignored in previous explorations of non-linear wind driven oceanic circulation, are retained here and calculated using an approximation of the Oseen type. The circulation problem is reduced to a system of scalar equations in only two independent variables; the system is valid for non-small local Rossby number provided only that the approximate total vorticity is positive.To complete the solution for small Rossby number a boundary condition for the inertially induced transport is needed. It is found by examining the dynamics controlling this additional transport from the western boundary layer as the transport recirculates through the rest of the ocean basin. The strong constraint of total recirculation within the western boundary layer (zero net inertial transport) is derived.The calculated primary inertial effects are in agreement with the observations of the laboratory model of Baker and Robinson (1969).The analysis indicates the extent to which three-dimensional non-linear circulation can be reduced to a two dimensional problem. 相似文献
14.
C. Estournel V. Zervakis P. Marsaleix A. Papadopoulos F. Auclair L. Perivoliotis E. Tragou 《Continental Shelf Research》2005,25(19-20):2366
Observations of dense water formation on the shelf of the Gulf of Thermaikos (North Aegean) are presented, based mainly on continuous monitoring of temperature and currents, during the winter of 2001–2002, at an instrumented mooring and a CTD survey carried out in early February 2002. A 2.5-month realistic simulation, corresponding to the period of observation, was performed to investigate the processes of dense water formation and cascading. The simulation is first compared to the main characteristics of the dense water, time variation of bottom temperature and spatial distribution of the dense water on the shelf. Subsequently, the simulation is used (a) to show that the formation of dense water takes place within the semi-enclosed Thessaloniki Bay and (b) to explain the intermittence of cascading out of the bay in relation to wind variations. The pathways of the dense water through the shelf are investigated with an emphasis on the role of the bottom slope and friction in the Ekman layer. The export of dense water towards the open sea occurs primarily along the slope bounding the western coast. 相似文献
15.
Impact of Sea-Level Rise on Sea Water Intrusion in Coastal Aquifers 总被引：17，自引：0，他引：17
Despite its purported importance, previous studies of the influence of sea-level rise on coastal aquifers have focused on specific sites, and a generalized systematic analysis of the general case of the sea water intrusion response to sea-level rise has not been reported. In this study, a simple conceptual framework is used to provide a first-order assessment of sea water intrusion changes in coastal unconfined aquifers in response to sea-level rise. Two conceptual models are tested: (1) flux-controlled systems, in which ground water discharge to the sea is persistent despite changes in sea level, and (2) head-controlled systems, whereby ground water abstractions or surface features maintain the head condition in the aquifer despite sea-level changes. The conceptualization assumes steady-state conditions, a sharp interface sea water-fresh water transition zone, homogeneous and isotropic aquifer properties, and constant recharge. In the case of constant flux conditions, the upper limit for sea water intrusion due to sea-level rise (up to 1.5 m is tested) is no greater than 50 m for typical values of recharge, hydraulic conductivity, and aquifer depth. This is in striking contrast to the constant head cases, in which the magnitude of salt water toe migration is on the order of hundreds of meters to several kilometers for the same sea-level rise. This study has highlighted the importance of inland boundary conditions on the sea-level rise impact. It identifies combinations of hydrogeologic parameters that control whether large or small salt water toe migration will occur for any given change in a hydrogeologic variable. 相似文献
16.
H.J. Niebauer 《Continental Shelf Research》1982,1(1):49-98
A seasonal ice edge zone is a unique frontal system with an air-ice-sea interface. This paper is a report on the numerical results from a quasi-three dimensional, time dependent, non-linear numerical model of circulation at a continental shelf-seasonal ice edge zone. The purpose of the experiments is to model the hydrography and circulation, including upwelling, baroclinic geostrophic flow, and inertial oscillations, at the ice edge with emphasis on examining the driving forces of wind and melting ice. It is suggested that the non-linear acceleration terms and vertical density diffusion terms are negligible and that the horizontal density diffusion terms are of secondary importance within the time and space scales of the experiments. The vertical eddy viscosity terms are important in a spin-up time scale and for Ekman transport and a bottom Ekman layer. The effects of the horizontal eddy viscosity terms are observable (a long-ice jet is diffused away from the ice edge) by the end (72 h) of the model runs.Model results are compared with available oceanographic and meteorological data for verification. The observed and modeled features of melt water induced water column stability, frontal structure, and ice edge upwelling are briefly discussed relative to observed ice edge primary production. Because the model is relatively general in nature, it is readily applicable to other seasonal or marginal ice edge zones in either hemisphere. 相似文献
17.
《Continental Shelf Research》1999,19(15-16):1851-1867
To investigate the instabilities of steady and oscillating Ekman layers, an 8 m×2 m horizontal plate was moved at controlled speed in homogeneous water at rest in solid body rotation in the “Coriolis” 13 m diameter rotating tank. For a steady Ekman layer two distinct wave types were found, in agreement with previous experimental or numerical studies. Type I was stationary, was oriented positively with respect to the flow direction and had a wavelength of about 10 times the Ekman layer thickness. Type II was oriented negatively with respect to the flow direction and had a wavelength which was more than 20 times the Ekman layer thickness and a phase-speed between 0.3 and 0.5 the forcing interior velocity. The growth rates of both type I and type II waves for various Reynolds numbers Re (computed with the Ekman layer thickness) were estimated and their Re-variations qualitatively agree with previous numerical results. For an oscillating Ekman layer, experimental results depended strongly on Rot, the temporal Rossby number: only when Rot<1 was it possible to observe either type I or type II instabilities. Moreover, for all Rot and average to high Re, there was a noticeable upward turbulent transport occurring during each cycle between the flow maximum and the flow reversal. Such an upward turbulent transport is consistent with observations in the English Channel where maximum upward benthic movements and maximum turbidity were recorded at the flow reversal, hence Ekman layer instabilities and transition to turbulence are likely to occur in shallow tidal seas where they may be relevant for sediment resuspension and transport as well as for some biological processes. 相似文献
18.
The role of inertial waves in the dynamies of the Earth's fluid core has been investigated through laboratory experiments on a spheroidal shell of rotating fluid. In these experiments inertial waves of azimuthal wavenumber 1, Ekman number 0(10?5), Rossby number 0(10?1) were excited by precession of an inner spheroidal body. Proximity to resonance was achieved by adjusting the ratio of the frequency of precession of the inner body to the rotational speed of the container to be near the eigenfrequency of the inertial wave mode being studied. Once the system was near resonance the perturbation was stopped and ringdown records were obtained. Amplitude, eigenfrequency and decay rate were recovered simultaneously for the principal and neighbouring modes excited using an iterative linearized least squares procedure.The recovery of complex eigenfrequencies for non-axisymmetric inertial waves in this shell geometry has given experimental verification of their existence. For those waves of azimuthal wavenumber one, a significant nonlinear interaction among modes is inferred from the simultaneous recovery of neighbouring modes. Other non linear effects include a mean azimuthal flow which appears to be stable for the low spatial order modes studied. These results contrast with highly unstable mean flow found experimentally in similar experiments carried out in cylindrical geometry. 相似文献
19.
V. N. Zyryanov 《Water Resources》2011,38(3):261-273
A closed, ice-covered water body containing water with homogeneous density distribution is considered. No-slip conditions
are specified for flow velocity at the lower ice boundary and on the bed. Two variants of boundary conditions are considered
on the side boundary: the boundary is either a solid vertical wall with a finite liquid depth or the liquid wedges out to
zero depth values. Ice either is attached fast to the shore or is separated from it by an open-water zone. A basic fourth
order equation is derived for the amplitude of ice oscillations. The introduction of friction results in the appearance of
reduced depth. Eigenvalue problem is considered for evaluating seiche periods. For the case when the liquid wedges out at
the shore, the basic equation becomes singular at water body boundaries. A lake with a longitudinal depth profile, which can
be approximated by a parabola, is considered. The solution is found by the method of matched asymptotic expansions. In the
inner domain, beyond the boundary layers, the equation is reduced to Legendre equation, which yields a new relationship for
the spectrum of seiche oscillations both in the presence of ice and in an open lake with varying depth. Boundary layers appear
at the margins of the lake, where the liquid wedges out; a solution is found for these layers. 相似文献
20.
— A series of mathematical and computer models describing alternative methods for the disposal of flue gases emitted from coal and gas fired power plants is discussed. Brunei Darussalam has three gas-fired power plants using approximately 3.106 m3/day gas and emitting substantial flue gases into the atmosphere. After desulphurisation with sea water, carbon-dioxide, the gas primarily associated with global warming and the main constituent of flue gas, can be dissolved under pressure in seawater and injected into the sea at suitable depth. The injected solution constitutes a negatively buoyant plume in the sea, carried by currents to deeper regions. It has been noted that the solution mixes and reacts with other oceanic components and converts to carbonates and sulphates that can remain near the bottom for several hundreds of years. Until a better alternative is developed, this may be an immediate solution to the problem of dealing with flue gases. The feasibility and economics of this alternative have been discussed in the literature. For optimal design criteria for such disposal, numerous parameters (such as location, pipe diameter, type of diffuser, angles of discharge, etc.) are involved in the mathematical analysis. Many alternative sets of these parameters must be used as input parameters to arrive at final design parameters for optimal results. 相似文献