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1.
In the Weddell Sea during the winters of 1974–1976 a significant opening in the sea-ice cover occurred in the vicinity of a large bathymetric feature — the Maud Rise seamount. The event is commonly referred to as the Weddell Polynya. Aside from such a large-scale, relatively persistent polynya in the Weddell Sea, transient, small-scale polynya can also appear in the sea-ice cover at various times throughout the winter and at various locations with respect to the Maud Rise. The underlying causes for the occurrence of such transient polynya have not been unambiguously identified. We hypothesize that variations in the mean ocean currents are one major contributor to such variability in the sea-ice cover. Analysis of the sea-ice equations with certain idealized patterns of ocean currents serving as forcing is shown to lead to Ekman transports of sea ice favorable to the initiation of transient polynya. Aside from the actual spatial pattern of the idealized ocean currents, many other factors need also be taken into account when looking at such transient polynya. Two other such factors discussed are variations in the sea-ice thickness field and the treatment of the sea-ice rheology. Simulations of a sea-ice model coupled to a dynamical ocean model show that the interaction of (dynamical) oceanic currents with large-scale topographic features, such as the Maud Rise, does lead to the formation of transient polynya, again through Ekman transport effects. This occurs because the seamount has a dynamic impact on the three-dimensional oceanic flow field all the way up through the water column, and hence on the near surface ocean currents that are in physical contact with the sea ice. Further simulations of a sea-ice model coupled to a dynamic ocean model and forced with atmospheric buoyancy fluxes show that transient polynya can be enhanced when atmospheric cooling provides a positive feedback mechanism allowing preferential open-ocean convection to occur. The convection, which takes hold at sites where transient polynya have been initiated by sea-ice–ocean stress interaction, has an enhancing effect arising from the convective access to warmer, deeper waters. To investigate all of these effects in a hierarchical manner we use a primitive equation coupled sea-ice–ocean numerical model configured in a periodic channel domain with specified atmospheric conditions. We show that oceanic flow variability can account for temporal variability in small-scale, transient polynya and thus point to a plausible mechanism for the initiation of large-scale, sustained polynya such as the Weddell Polynya event of the mid 1970s.  相似文献   

2.
Two numerical studies (Endoh, 1977;Harashima et al., 1978) have been proposed on a front formed by a coupling effect of cooling of the sea surface and inflow of the fresh water in a vertical two-dimensional plane without the rotation of the earth. It is, however, not easy to interpret their numerical results. A simple interpretation will be proposed by an analytical study in this paper.It is found that local convection due to the density inversion, which is expressed by the convective adjustment of the vertical diffusion coefficient in the actual numerical calculations, plays an important role on the front formation.The characteristics of the front is also clarified in the case of steady state. Namely, simple functional dependences are obtained of the position and the width of the front, the horizontal and the vertical velocities and the distribution of the buoyancy and the salinity in the neighborhood of the front on the horizontal coordinate, the cooling rate, the eddy coefficients of diffusion and viscosity, the water depth and the vertically averaged horizontal fluxes of buoyancy and salinity.  相似文献   

3.
The physical processes responsible for the formation in a large‐scale ice–ocean model of an offshore polynya near the Greenwich meridian in the Southern Ocean are analysed. In this area, the brine release during ice formation in autumn is sufficient to destabilise the water column and trigger convection. This incorporates relatively warm water into the surface layer which, in a first step, slows down ice formation. In a second step, it gives rise to ice melting until the total disappearance of the ice at the end of September. Two elements are crucial for the polynya opening. The first one is a strong ice‐transport divergence in fall induced by south‐easterly winds, which enhances the amount of local ice formation and thus of brine release. The second is an inflow of relatively warm water at depth originating from the Antarctic Circumpolar Current, that sustains the intense vertical heat flux in the ocean during convection. The simulated polynya occurs in a region where such features have been frequently observed. Nevertheless, the model polynya is too wide and persistent. In addition, it develops each year, contrary to observations. The use of a climatological forcing with no interannual variability is the major cause of these deficiencies, the simulated too low density in the deep Southern Ocean and the coarse resolution of the model playing also a role. A passive tracer released in the polynya area indicates that the water mass produced there contributes significantly to the renewal of deep water in the Weddell Gyre and that it is a major component of the Antarctic Bottom Water (AABW) inflow into the model Atlantic.  相似文献   

4.
Numerical ocean modelling is computationally very demanding. Traditionally, the hydrostatic approximation has been applied to reduce the computational burden. This approximation is valid in large scale studies with coarse grid resolution. With faster computers and gradually smaller grid sizes, we may expect that more studies will be performed with non-hydrostatic ocean models. In recent papers several methods for including non-hydrostatic pressure in σ-coordinate models have been suggested. In this paper the sensitivity of the non-hydrostatic pressure field, the velocity fields, and the density fields to changes in the method for computing non-hydrostatic pressure in σ-coordinate ocean models is addressed.The first test case used involves the propagation and breaking of an internal wave at an incline in a tank. The other test case concerns tidally driven flow over a sill in a stratified fjord. The results from our numerical exercises suggest that the velocity and density fields are very robust to the model choices investigated here. The differences between the model results are of the same order as the uncertainty due to the internal pressure gradient error, and they are smaller than an estimate of the uncertainty due to subgrid scale closure.  相似文献   

5.
The term cabbeling describes the convection that can occur when a mixture of two oceanic water masses is more dense than both of the parent water masses. When the two water masses are situated one above the other, the temperature and salinity distributions are in the correct senses for double-diffusive convection to occur and it is found that the prime effects of the nonlinearity of the equation of state are firstly to drive a greater level of double-diffusive convective activity in the lower layer than in the upper layer, and secondly, to make the lower edge of the interfacial region less gravitationally stable. Both of these effects cause the interface to migrate upwards as the lower layer grows at the expense of the upper layer. We introduce a nondimensional parameter δ (called the cabbeling parameter) which represents the importance of the nonlinearity of the equation of state:—δ is zero when the equation of state is linear and when cabbeling is normally thought to be possible, δ is greater than unity. Experiments set up in both the finger and diffuse sense show how the nondimensional measure of the upward interface migration (called the “entrainment” parameter E) varies with the density anomaly ration R? for various values of δ between zero and 2.0 and that no abrupt change in this behaviour occurs at δ = 1.0. It is impossible to explain these observation by neglecting double-diffusive convection and considering only the convection driven by the conventional cabbeling instability. The successful interpretation of the laboratory results relies on considering the effects of a non-linear equation of state on the double-diffusive convection process.  相似文献   

6.
Dissolved organic nitrogen (DON), dissolved organic carbon (DOC) and inorganic nutrient concentrations were determined in samples from an area encompassing the Northeast Water Polynya from June to August 1993. In June, still ice-covered polynya area surface waters (PySW) had significantly higher (p<0.05) DOC concentrations (110 μM, n=68) than surface water outside the polynya area (96 μM, n=6). Melting ice and ice algae are suggested as DOC sources. DOC concentrations found in this study are consistent with other studies showing higher DOC concentrations in the Arctic than in other ocean areas. As the productive season progressed, DOC concentrations in Polynya surface water (PySW) decreased (p<0.05) from 110 to 105 μM, while DON concentrations increased (p<0.05) from 5.6 to 6.1 μM, causing a significant decrease (p<0.05) in the C : N ratios of DOM from spring (C : N ratio 20) to summer (C : N ratio 17). We found a significant (p<0.05) decrease in the DOM C : N ratio in all water masses within the polynya area as the productive season progressed. DON was the largest fraction of total dissolved nitrogen (TDN) in PySW and surface waters outside the polynya area. TDN was calculated as the sum of DON, nitrate, nitrite and ammonium concentrations. DON increased (p<0.05) from 62% to 73% of TDN in PySW from spring to summer, a result of increasing DON concentrations and decreasing inorganic nitrogen concentrations over the productive season. The seasonal accumulation of DON and the corresponding decrease in nitrate concentrations in waters with primary production indicate that it is important to take the DON pool into account when estimating export production from nitrate concentration decreases in surface waters. PySW TDN concentrations decreased (p<0.05) from 9.1 (n=61) to 8.6 μM (n=60) from spring (May 25 through June 19) to summer (July 1 through July 27). The seasonal decrease in surface water TDN concentrations corresponded to increases in TDN concentrations in deeper water masses within the Polynya. Most of the TDN increase in deep water was in the form of DON. A possible explanation is that PON was dissolved (partially remineralized) in the water column at mid depths, causing increases in the DON concentration. Transfer of N from PySW (with a short residence time in the polynya area) to Polynya Intermediate Water and deep waters of the Norske and Westwind Trough with multi-year residence times keeps N from leaving the polynya area. In spring, nutrients from degradation of OM in PyIW could support primary production. The role of PyIW as an OM trap could be important in supporting primary production in the polynya area.  相似文献   

7.
We explore the efficacy of “super parameterization” (SP) in ocean modeling in which local 2-d non-hydrostatic plume-resolving fine-grained (FG) models are embedded at each vertical column of a coarse-grained (CG) hydrostatic model. A general multi-scale algorithm is described in which tendencies from the FG models are projected onto the CG model which in turn constrains the average state of the FG models, coupling the two models together. The approach is tested in the context of models of open ocean deep convection and compared with a pure hydrostatic, coarse resolution model using convective adjustment (HYD) and a full 3-d non-hydrostatic plume-resolving simulation (NH). The SP model is found to be greatly superior to HYD at much less computational cost than the fully non-hydrostatic calculation.  相似文献   

8.
A two-dimensional non-hydrostatic ocean model and a hydrostatic version of the same model are used to simulate convective adjustment, without the use of an instantaneous adjustment parameterization. The model geometry is a domain on the vertical plane of width 40 km and depth 500 m. Model results for four cases are examined: hydrostatic and non-hydrostatic, at 0.1 and 1 km spatial resolution. The convectively adjusted stable state obtained in all four cases are qualitatively similar; thus the hydrostatic approximation does not eliminate convective adjustment. The details of the simulated convective plumes depend on resolution and whether the hydrostatic approximation is made. The adjusted state has significant stratification which cannot be captured by the conventional instantaneous adjustment or diffusion-based parameterizations. We also compare the results to the case when an instantaneous adjustment parameterization is used.  相似文献   

9.
This study addresses sources and diagenetic state of early-season dissolved organic matter (DOM) in the Northeast Water Polynya (NEWP) area northeast of Greenland from distributions of humic substance fluorescence (HSfl), dissolved organic carbon (DOC), and dissolved organic nitrogen (DON) in the water column inside and outside the NEWP area. The water masses of the polynya area had acquired their spring/summer temperature–salinity characteristics at the time of sampling, and also had individual, different DOM signatures. DOC concentrations were variable within and among water masses in the polynya area, indicating patchy local sources and sinks of DOC. PySW and polynya intermediate water (PyIW) had higher average DON concentrations and average lower C:N ratios than polynya bottom water (PyBW), indicating a larger fraction of fresh DOM in PySW and PyIW than in PyBW. Ice-covered, polynya area surface waters (PySW) had higher DOC concentrations (113±14 μM, n=68) than surface water (SW) outside the polynya area (96±18 μM, n=6). The DOM C:N ratios in a low-salinity, ice-melt subgroup of PySW samples indicate labile material, and these low-salinity surface waters appeared to have a local DOC and DON source. In contrast, HSfl was significantly lower inside than outside the NEWP area. Despite the lower HSfl values within the NEWP area, the PySW values were high when compared to open-ocean water. There were no local terrestrial sources for HSfl to the NEWP area and the East Greenland Current is therefore proposed as a likely source of allochtonous HSfl. When HSfl was used as a conservative tracer, up to 70% of the water in PySW and PyIW was found to be derived from SW, which contains a high fraction of water from the East Greenland Current. Similarly, a mixing model based on HSfl indicated that 80% of early-season DOC and 90–100% of early-season DON in PySW and PyIW were derived from SW, indicating a potentially high fraction of terrestrially-derived, relatively refractory DOM in the early-season NEWP area.  相似文献   

10.
The mechanism of the formation of horizontal temperature/density gradients above underwater coastal slopes of natural basins due to heating/cooling from the surface is considered. It is shown that the time required for formation of the gradients is rather small (tens of minutes for a thermocline depth of tens of meters), but the development of the corresponding flows may not be accomplished even in a day long cycle. The time dependence of the horizontal water exchange between the shallow and deep areas is analytically treated. The spatial scale of the problem is the main parameter that defines the resulting quasi-stationary value of the flow rate. The joint analysis of the published field, laboratory, and numerical data of many authors in the range of the above-slope depths of 10−2 m < d < 3 × 102 m (d ≤ D, where D is the thickness of the upper thermally active layer of a basin) indicates that the relation between the value of the horizontal quasi-stationary volumetric flow rate and the local depth looks like Q = 0.00l3 × d 1.37 (R 2 = 0.96). The horizontal convective water exchange is shown to be generally two-layered, ageostrophic, and exhibits its maximum flow rate at the end of the slope. The inferences agree well with the field data and conclusions of other authors.  相似文献   

11.
Cold seep communities discovered at three previously unknown sites between 600 and 1000 m in Monterey Bay, California, are dominated by chemoautotrophic bacteria (Beggiatoa sp.) and vesicomyid clams (5 sp.). Other seep-associated fauna included galatheid crabs (Munidopsis sp.), vestimentiferan worms (Lamellibrachia barhami?), solemyid clams (Solemya sp.), columbellid snails (Mitrella permodesta, Amphissa sp.), and pyropeltid limpets (Pyropelta sp.). More than 50 species of regional (i.e. non-seep) benthic fauna were also observed at seeps. Ratios of stable carbon isotopes (δ13C) in clam tissues near 36‰ indicate sulfur-oxidizing chemosynthetic production, rather than non-seep food sources, as their principal trophic pathway. The “Mt Crushmore” cold seep site is located in a vertically faulted and fractured region of the Pliocene Purisima Formation along the walls of Monterey Canyon ( 635 m), where seepage appears to derive from sulfide-rich fluids within the Purisima Formation. The “Clam Field” cold seep site, also in Monterey Canyon ( 900 m) is located near outcrops in the hydrocarbon-bearing Monterey Formation. Chemosynthetic communities were also found at an accretionary-like prism on the continental slope near 1000 m depth (Clam Flat site). Fluid flow at the “Clam Flat” site is thought to represent dewatering of accretionary sediments by tectonic compression, or hydrocarbon formation at depth, or both. Sulfide levels in pore waters were low at Mt Crushmore (ca 0.2 mM), and high at the two deeper sites (ca 7.011.0 mM). Methane was not detected at the Mt Crushmore site, but ranged from 0.06 to 2.0 mM at the other sites.  相似文献   

12.
厚壳贻贝是我国东部沿海重要的经济贝类之一,自然环境中栖息范围不甚明确。本文于2014年7月间利用水下摄像的手段,调查和分析了渔山列岛不同断面上厚壳贻贝的自然分布特征。结果表明:渔山列岛潮下带5条断面的生态类型差异显著,不同断面栖息的优势种也不相同;断面间厚壳贻贝的栖息密度均值为37.04~185.80 ind/m2,其中断面A的栖息密度最低,断面E的栖息密度最高,断面C和断面D的栖息密度相差不大,但是不同调查样方内厚壳贻贝的栖息密度从0~388.89 ind/m2不等;厚壳贻贝主要分布在水深3~9 m的水层中,其中以水深5~8 m的水层中最为密集,约占总栖息密度的90%以上;在水深8 m的区带上,厚壳贻贝的栖息密度为160.19 ind/m2,当水深小于1 m和大于11 m时,厚壳贻贝分布极少;经双因素方差分析表明,厚壳贻贝栖息密度在不同断面(F=57.011,P<0.01)和不同水层(F=66.495,P<0.01)中的差异均极显著,断面和水层的交互作用(F=10.483,P<0.01)对厚壳贻贝的自然分布也有极显著差异;经检验,厚壳贻贝栖息密度(A)的自然分布与水深(D)呈正态分布,可以用高斯方程拟合,R2的取值范围为0.8753~0.9997;利用聚类分析发现,调查样方被明显的分为3组,体现了水深在厚壳贻贝自然分布中的显著作用。  相似文献   

13.
The fractions of river runoff and sea-ice melted water in the Canada Basin in summer 2003 were determined by the salinity-18O system. The fraction of river runoff(fR) was high in the upper 50 m of the water column and decreased with depth and latitude. The signals of the river runoff were confined to water depths above 200 m. The total amount of river runoff in the Canada Basin was higher than that in other arctic seas, indicating that the Canada Basin is a main storage region for river runoff. The penetration depth of the sea-ice melted water was less than 50 m to the south of 78°N, while it was about 150 m to the north of 78°N. The total amount of sea-ice melted water was much higher to the north of 78°N than to the south of 78°N, indicating the sea-ice melted waters accumulated on the ice edge. The abundant sea-ice melted water on the ice edge was attributed to the earlier melted water in the southern Canada Basin and transported by the Beaufort Gyre or the reinforced melting of sea ice by solar radiation in the polynya.  相似文献   

14.
The results of several recent isolated investigations in planing theory are consolidated in this paper, together with new insights generated by a recent numerical solution of the vertically impacting wedge problem by Zhao and Faltinsen [(1992), Water entry of two-dimensional bodies. J. Fluid Mech. 246, 593–612]. As a result, in contrast to some earlier studies, it is found that the “wetted width” associated with the added mass is not that of the intersection of the wedge with the undisturbed water surface, but the wetted width of the splashed-up water, as originally proposed by Wagner [(1932), Uber Stoss-und Gleitvorgange an der Oberflache von Flussig-Keiten, Zeitschrift für Angewandte Mathematik und Mechanik, Band 12, Heft 4 (August)]. However, the splash-up ratio is not the value of (π/2–1) which he proposed, but a value which decreases with increasing deadrise, originally proposed in the late-1940s by Pierson (“Pierson's hypothesis” in the paper). For 30° deadrise, for example, Pierson's splash-up ratio is two-thirds that of Wagner's.The new equations are employed to determine the increase in the “added mass” of prismatic hull sections due to chine immersion, using experimental data. If mo′ is the added amss of the hull section whose chines are just wetted, Payne [(1988), Design of High-speed Boats. Volume 1: Planing. Fishergate, Inc., Annapolis, Maryland, U.S.A.] postulated that the increase in added mass due to a chine submergence (zc) would be
where b is the chine beam and k is a constant which Payne [(1988), Design of High-speed Boats. Volume 1: Planing. Fishergate, Inc., Annapolis, Maryland, U.S.A.] gave as .The present analysis includes the “one-sided flow” correction introduced in Payne [(1990), Planing and impacting forces at large trim angels. Ocean Engng 17, 201–234]. Partly for that reason and partly because of the more precise analysis of the experimental data, the present paper revises the value to k = 2 for wetted length to beam ratios normally employed. For deadrise angles in excess of 40° and wetted keel to beam ratios in excess of 2.0, there is some evidence that k < 2.0.The revised theoretical formulation is compared with eight different sets of experimental data for flat plate and prismatic hull forms and is found to be in excellent agreement when the speed is high enough for “dynamic suction” (a loss of buoyancy at low speeds and low wetted lenghts) to be unimportant. This is true for “chines-dry” operation with deadrise angles up to 50° and chines-wet operation at length to beam ratios far in excess of the most extreme conventional practice.The research involved in performing this analysis led to the realization that different towing tanks measure different wetted chine lengths for the same hulls and test conditions. Some consistently measure more splash-up than “theory” (based on Pierson's splash-up hypothesis) predicts and others measure somewhat less than the theory. Some examples are given in Appendix B. The reason for this is not understood.  相似文献   

15.
Jiankang Wu  Bo Chen 《Ocean Engineering》2003,30(15):1899-1913
Based on Green–Naghdi equation this work studies unsteady ship waves in shallow water of varying depth. A moving ship is regarded as a moving pressure disturbance on free surface. The moving pressure is incorporated into the Green–Naghdi equation to formulate forcing of ship waves in shallow water. The frequency dispersion term of the Green–Naghdi equation accounts for the effects of finite water depth on ship waves. A wave equation model and the finite element method (WE/FEM) are adopted to solve the Green–Naghdi equation. The numerical examples of a Series 60 (CB=0.6) ship moving in shallow water are presented. Three-dimensional ship wave profiles and wave resistance are given when the ship moves in shallow water with a bed bump (or a trench). The numerical results indicate that the wave resistance increases first, then decreases, and finally returns to normal value as the ship passes a bed bump. A comparison between the numerical results predicted by the Green–Naghdi equation and the shallow water equations is made. It is found that the wave resistance predicted by the Green–Naghdi equation is larger than that predicted by the shallow water equations in subcritical flow , and the Green–Naghdi equation and the shallow water equations predict almost the same wave resistance when , the frequency dispersion can be neglected in supercritical flows.  相似文献   

16.
The representation of baroclinic instability in numerical models depends strongly upon the model physics and significant differences may be found depending on the vertical discretization of the governing dynamical equations. This dependency is explored in the context of the restratification of an idealized convective basin with no external forcing. A comparison is made between an isopycnic model including a mixed layer (the Miami Isopycnic Coordinate Ocean Model, MICOM), its adiabatic version (MICOM-ADIAB) in which the mixed layer physics are removed and the convective layer is described by a deep adiabatic layer outcropping at the surface instead of a thick dense mixed layer, and a z-coordinate model (OPA model).In the absence of a buoyancy source at the surface, the mixed layer geometry in MICOM prevents almost any retreat of this layer. As a result, lateral heat exchanges in the upper layers are limited while mass transfers across the outer boundary of the deep convective mixed layer result in an unrealistic outward spreading of this layer. Such a widespread deep mixed layer maintains a low level of baroclinic instability, and therefore limits lateral heat exchanges in the upper layers over most of the model domain. The behavior of the adiabatic isopycnic model and z-coordinate model is by far more satisfactory although contrasted features can be observed between the two simulations. In MICOM-ADIAB, the more baroclinic dynamics introduce a stronger contrast between the surface and the dense waters in the eddy kinetic energy and heat flux distributions. Better preservation of the density contrasts around the dense water patch maintains more persistent baroclinic instability, essentially associated with the process of dense water spreading. The OPA simulation shows a faster growth of the eddy kinetic energy in the early stages of the restratification which is attributed to more efficient baroclinic instability and leads to the most rapid buoyancy restoring in the convective area among the three simulations. Dense water spreading and warm surface capping occur on fairly similar time scales in MICOM-ADIAB although the former is more persistent that the latter. In this model, heat is mainly transported by anticyclonic eddies in the dense layer while both cyclonic and anticyclonic eddies are involved in the upper layers. In OPA, heat is mainly brought into the convective zone through the export of cold water trapped in cyclonic eddies with a strong barotropic structure. Probably the most interesting difference between the z-coordinate and the adiabatic isopycnic model is found in the temperature distribution ultimately produced by the restratification process. OPA generates a spurious volume of intermediate water which is not seen in MICOM-ADIAB where the volume of the dense water is preserved.  相似文献   

17.
The salinity minimum frequently occurring in the Mixed Water Region between the Oyashio and Kuroshio Fronts seems to originate from the salinity minimum at the density of 26.8σθ called the North Pacific Intermediate Water. We examined water exchange of this region with the Oyashio and the Kuroshio Extension using mixing ratio RK defined as (θ - θOY)/(θK - θOY) × 100, where θOY, θK, and θ represent potential temperature of the Oyashio and Kuroshio Waters and their mixture on the isopycnal surfaces, respectively. CTD data were obtained by repeated observation from January 1990 to May 1991. RK increases southward from the Oyashio Front to the Kuroshio Front with the range of −20 to 120%. The gradient of RK on the isopycnal surfaces is large around the Oyashio Front above the 26.8σθ surface, while it is large around the Kuroshio Front below it. This agrees with the average RK in the Mixed Water Region decreasing greatly with the increase of density at densities less dense than 26.8σθ. We calculated thickness and volume transport of the Oyashio between the isopycnal surfaces near the coast of Hokkaido. They increase largely with density at densities less dense than 26.8σθ. It is supposed that the salinity minimum in the Mixed Water Region is the upper limit of the water largely influenced by the Oyashio Water. Its density could depend only on the density structure of the Oyashio.  相似文献   

18.
Most of the existing relevant materials have been obtained from experiments, in which evaluating the added mass at the resonant frequency corresponding to the peak of a frequency-response curve obtained from the “forced” vibration analysis is the most popular technique. In this paper, a simple experimental method was presented where the “free” vibration responses instead of the “forced” ones were used to determine the values of mah and Iap. The main part of the experimental system is composed of a floating body (model) and a spring–shaft shaker. The “free” vibration of this main part was induced by imposing on it an initial displacement (and/or an initial velocity), and from the time histories of displacements information such as the “damped” natural frequencies, damping ratios, sectional added mass coefficients (CV and CP) were obtained. Since the displacements of the spring–shaft shaker are “translational” and those of the floating body due to pitch motions are “angular”, a technique for the transformation between the associated parameters of the two components of the main part was presented.  相似文献   

19.
In a series of numerical experiments, we simulate the process of generation of coastal upwelling induced by the winds of various directions in the central part of the Pacific Coast of Mexico (18–24°N, 103– 107°W). The numerical nonlinear multilevel model [see E. N. Mikhailova, I. M. Semenyuk, and N. B. Shapiro, “ Modeling of the variability of hydrophysical fields in the Tropical Atlantic,” Izv. Akad. Nauk SSSR, Fiz. Atmosf. Okean., 27, No. 10, 1139–1148 (1991)] is adapted to the region of investigations with 9-km space resolution by specifying the conditions of flow through the open lateral boundaries. The results of numerical experiments demonstrate that the NW, N, NE, and E winds are especially favorable for the generation of intense upwelling.__________Translated from Morskoi Gidrofizicheskii Zhurnal, No. 1, pp. 32–41, January–February, 2005.  相似文献   

20.
A nonlinear theory for the generation of the Ulleung Warm Eddy (UWE) is proposed. Using the nonlinear reduced gravity (shallow water) equations, it is shown analytically that the eddy is established in order to balance the northward momentum flux (i.e., the flow force) exerted by the separating western boundary current (WBC). In this scenario, the presence of β produces a southward (eddy) force balancing the northward momentum flux imparted by the separating East Korean Warm Current (EKWC).It is found that, for a high Rossby number EKWC (i.e., highly nonlinear current), the eddy radius is roughly 2Rd/ε1/6 (here ε≡βRd/f0, where Rd is the Rossby radius), implying that the UWE has a scale larger than that of most eddies (Rd). This solution suggests that, in contrast to the familiar idea attributing the formation of eddies to instabilities (i.e., the breakdown of a known steady solution), the UWE is an integral part of the steady stable solution. The solution also suggests that a weak WBC does not produce an eddy (due to the absence of nonlinearity).A reduced gravity numerical model is used to further analyze the relationship between β, nonlinearity and the eddy formation. First, we show that a high Rossby number WBC which is forced to separate from the wall on an f plane does not produce an eddy near the separation. To balance the northward momentum force imparted by the nonlinear boundary current, the f plane system moves constantly offshore, producing a southward Coriolis force. We then show that, as β is introduced to the problem, an anticyclonic eddy is formed. The numerical balance of forces shows that, as suggested by the analytical reasoning, the southward force produced by the eddy balances the northward flow force imparted by the boundary current. We also found that the observed eddy scale in the Japan/East Sea agrees with the analytical estimate for a nonlinear current.  相似文献   

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