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1.
Laboratory experiments on the dynamics of a downwelling coastal current over a sloping bottom were conducted in a tank on a rotating platform. The current was generated by a source of stable water flow of the same density (barotropic case) or of lesser density (baroclinic case) compared with the surrounding water in the tank. It was found that even in the case of the baroclinic current, a less dense water downflow in the bottom Ekman layer was formed under certain conditions. At some moment, this downflow undergoes convective instability. Taking into account the results of the experiment, the parameters of the bottom Ekman layer on the continental shelf/slope of the Black Sea were preliminarily estimated and the possible sinking depth of less dense water was calculated. 相似文献
2.
《Ocean Modelling》2010,33(3-4):118-131
We investigate three of the most common hypotheses underpinning parameterizations of baroclinic eddy fluxes in the context of the differentially heated rotating annulus experiment. The investigation is carried out over a region of parameter space which embraces the onset of baroclinic instability, the regular wave regime and the onset of irregular flows, the latter of which is arguably most relevant to oceanic conditions. Through diagnostics from a 2D axisymmetric and a 3D eddy-resolving numerical model, it was found that the transport of heat by baroclinic eddies is not strictly an adiabatic process but that diffusive ‘ventilation’ of the flow in the thermal boundary layers is significant during the nonlinear development of the flow. Total heat transport, however, is conserved overall. Depending on the stages of flow evolution and on the region in parameter space under consideration, either heat, quasi-geostrophic potential vorticity (QGPV) or relative vorticity (QGRV) may become a suitable variable on which to parameterize baroclinic eddy fluxes in a down-gradient manner. These results raise issues for eddy parameterization schemes that rely on these assumptions in ocean and atmosphere models. 相似文献
3.
C. Hansen E. Kvaleberg A. Samuelsen 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(9):1079-1091
Altimetry and ocean color observations are used in combination with a coupled physical-primary production ocean model to investigate anticyclonic eddies at two locations in the Norwegian Sea. Of particular interest are the formation of the anticyclonic eddies, and their influence on primary production. The formation of these anticyclonic eddies are due to baroclinic instabilities set up by shifts in the wind in north/south direction, leading to simultaneously formation of eddies throughout the area. After a density stratification develops in the upper 100 m of the water column, the anticyclones become a subsurface lens of well mixed water with the characteristics of intra-thermocline eddies. The deep mixed layer inside anticyclonic eddies delay phytoplankton bloom by approximately two weeks compared to the surrounding areas. As the mixed layer within the anticyclones become smaller than the critical depth, the combination of this and sufficiently high nutrient levels support a phytoplankton bloom. From the satellite observations, there is an evidence of phytoplankton being advected toward the center of the eddies, but also of isolated phytoplankton blooms within the intra-thermocline eddies. The combined use of a numerical model and satellite observations provides three-dimensional information on the structure and properties of both eddies and primary production. The presented model is particularly useful in cloud-covered areas where ocean color images are frequently unavailable. 相似文献
4.
三维斜压陆架海模式的应用: 南海上混合层的季节变化 总被引：6，自引：0，他引：6
从一个三维斜压陆架海模式的数值模拟结果来揭示南海上混合层的季节变化规律,结果表明:(1)在南海北部上混合层的厚度(即混合层的下界深度)具有明显的季节性变化,与在南海南部上混合层的变化明显不同,前者的混合强度的变化幅度远比后者的要大得多.(2)在中南半岛中部东岸外海的西边界区域内,由于经常受冷涡控制,下层冷水涌升,上层水体层化显着,使得该海区垂直混合减弱.(3)在一些气旋(反气旋)涡的边缘,混合层厚度等值线分布密集,且水平梯度较大.(4)南海上混合层的厚度分布特征与上层环流的分布格局之间存在着较好的地转调整关系. 相似文献
5.
Data on East Australian Current (EAC) warm-core eddies were obtained over the period 1976–1978 by the Department of Defence and the Commonwealth Scientific and Industrial Research Organization (CSIRO). In that time we have learned that warm eddies form by pinch-off of poleward EAC meanders, can coalesce with the EAC and appear generally similar to Gulf Stream, Kuroshio and other current system eddies. Two eddies were tracked over 1977–1978 with satellite buoys and one (eddy B) was repeatedly studied over eleven months. A deep winter core formed by winter convective cooling and the following summer a new surface mixed layer formed on top of the core. The seasonal changes have been analysed for heat content and changes in dynamic relief. The eddy decayed with a time constant of 650 ± 150 days, due to upwelling below the seasonal thermocline. Surface cooling had little effect on eddy lifetime. The eddy contracted horizontally, possibly after some interaction with the EAC, giving rise to eddy spin-up with increasing age. Surface currents increased after eleven months to 2.0 m s?1. The dynamic relief during summer was also apparently boosted by contact with the EAC. Eddy B was observed to coalesce with a new meander of the EAC rather than drift away to the south. It is proposed that the formation of these eddies is governed by the westward propagation of the baroclinic Rossby wave known as the Tasman Front. Pinch-off of eddies adjacent to the coast and the variable flow of the EAC may be caused by the baroclinic wave ‘breaking’ on the coast. The eddy formation rate is about two per year and most eddies coalesce with the EAC and do not escape to the south. Eddies coalesce and re-separate, creating many subsurface isothermal layers from old cores south of 34°S. 相似文献
6.
Seasonal Variation of Submesoscale Flow Features in a Mesoscale Eddy-dominant Region in the East Sea
Seasonal changes in the distribution of submesoscale (SM) flow features were examined using a fine-resolution numerical simulation. The SM flows are expected to be strong where mesoscale (MS) eddies actively develop and also when the mixed layer depth (MLD) is deep due to enhanced baroclinic instability. In the East Sea (ES), MS eddies more actively develop in summer while the MLD is deeper in winter, which provided the motivation to conduct this study to test the effects of MLD and MS eddies on the SM activity in this region. Finite-scale Liapunov exponents and the vertical velocity components were employed to analyze the SM activities. It was found that the SM intensity was marked by seasonality: it is stronger in winter when the mixed layer is deep but weaker in summer - despite the greater eddy kinetic energy. This is because in summer the mixed layer is so thin that there is not enough available potential energy. When the SM activity was quantified based on parameterization, (MLD × density gradient), it was determined that the seasonal variation of MLD plays a more important role than the lateral density gradient variation on SM flow motion in the ES. 相似文献
7.
Mesoscale features in the eastward extension of the Kuroshio were investigated using assimilation of TOPEX/POSEIDON (T/P)
data into a three-layer quasi-geostrophic model. The T/P data exhibited an elongated state of the southern recirculation gyre
in 1993–95 and 1997, between whose two periods the gyre had a contracted state in 1995–96. A few stationary eddies were located
in the southern gyre during the contracted state. The baroclinic instability, which was indicated by the phase shift from
the uppermost-to the lowest-layer anomalies toward the downstream side, was evident near the Kuroshio Extension (KE) path.
Since the instability never appeared in the artificial model without bottom topography, the topographic barrier for the eastward
flow in the lowest layer was a necessary condition for the instability. The instability synchronized with the transition in
the western region of the KE axis from the elongated to the contracted states. This evolution was interpreted as if the baroclinic
instability played some part in the KE states and was a trigger for the transition from the elongated to the contracted states. 相似文献
8.
Various important features could be found on the open ocean deep convection and the subsequent deep water formation from large
eddy simulation (LES), and the results were applied to the East Sea (Japan Sea). It was found that under a strong cold wind
outburst with the heat flux of 1000 Wm−2 for 5 days generates a deep convection which can penetrate to the depth 1500 m, but under the continuous cooling with the
heat flux of 250 Wm−2 the growth of a mixed layer is suppressed at 700 m. The effects of the spatial and temporal variations of the surface forcing
were investigated with regard to the penetrative depth of convection, the generation of baroclinic eddies, the volume of the
water mass formation, and the intensity of the rim current. The deep water formations in the intermediate and deep layer of
the East Sea were explained in terms of the simulation results, and the intensity of the consequent circulation and the volume
of water mass formation were compared with the observation data.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
9.
10.
采用海洋再分析结果,研究了海洋涡旋和锋面波动对台湾以东黑潮锋的影响,结果表明,Rossby波第一斜压模态形成的冷涡(暖涡),减弱(增强)台湾以东黑潮温度锋强度,减小(加大)锋的宽度.在再分析结果中,捕获到1991年1-2月台湾以东的一次黑潮锋面波动.锋面波动的波槽(波脊)到达时,该温度锋强度减弱(增强),宽度和厚度减小... 相似文献
11.
Recent realistic high resolution modeling studies show a net increase of submesoscale activity in fall and winter when the mixed layer depth is at its maximum. This submesoscale activity increase is associated with a reduced deepening of the mixed layer. Both phenomena can be related to the development of mixed layer instabilities, which convert available potential energy into submesoscale eddy kinetic energy and contribute to a fast restratification by slumping the horizontal density gradient in the mixed layer. In the present work, the mixed layer formation and restratification were studied by uniformly cooling a fully turbulent zonal jet in a periodic channel at different resolutions, from eddy resolving (10 km) to submesoscale permitting (2 km). The effect of the submesoscale activity, highlighted by these different horizontal resolutions, was quantified in terms of mixed layer depth, restratification rate and buoyancy fluxes. Contrary to many idealized studies focusing on the restratification phase only, this study addresses a continuous event of mixed layer formation followed by its complete restratification. The robustness of the present results was established by ensemble simulations. The results show that, at higher resolution, when submesoscale starts to be resolved, the mixed layer formed during the surface cooling is significantly shallower and the total restratification is almost three times faster. Such differences between coarse and fine resolution models are consistent with the submesoscale upward buoyancy flux, which balances the convection during the formation phase and accelerates the restratification once the surface cooling is stopped. This submesoscale buoyancy flux is active even below the mixed layer. Our simulations show that mesoscale dynamics also cause restratification, but on longer time scales. Finally, the spatial distribution of the mixed layer depth is highly heterogeneous in the presence of submesoscale activity, prompting the question of whether it is possible to parameterize submesoscale effects and their effects on the marine biology as a function of a spatially-averaged mixed layer depth. 相似文献
12.
《Ocean Modelling》2002,4(2):121-135
Numerical studies of surface ocean fronts forced by inhomogeneous buoyancy loss show nonhydrostatic convective plumes coexisting with baroclinic eddies. The character of the vertical overturning depends sensitively on the treatment of the vertical momentum equation in the model. It is less well known how the frontal evolution over scales of O(10 km) is affected by these dynamics. Here, we compare highly resolved numerical experiments using nonhydrostatic and hydrostatic models and the convective-adjustment parametrization. The impact of nonhydrostatic processes on average cross-frontal transfer is weak compared to the effect of the O(1 km) scale baroclinic motions. For water-mass distribution and formation rate nonhydrostatic dynamics have similar influence to the baroclinic eddies although adequate resolution of the gradients in forcing fluxes is more important. The overall implication is that including nonhydrostatic surface frontal dynamics in ocean general circulation models will have only a minor effect on scales of O(1 km) and greater. 相似文献
13.
We document the accuracy and convergence of solutions for a z-coordinate primitive-equation model of internal tide generation and propagation. The model, which is based on MOM3 numerics, is linearized around a state of rest to facilitate comparison with analytic estimates of baroclinic generation at finite-amplitude topography in a channel forced by barotropic tidal flow at its boundaries. Unlike the analytical model, the numerical model includes mixing of both buoyancy and momentum, and several definitions of “baroclinic conversion” are possible. These are clarified by writing out the energetics of the linearized equations in terms of barotropic kinetic energy, baroclinic kinetic energy, and available potential energy. The tidal conversion computed from the model, defined as the rate of conversion of barotropic kinetic energy into available potential energy, agrees well with analytical predictions. A comparison of different treatments of bottom topography (full-cells, partial-cells, and ghost-cells) indicates that the partial-cell treatment is the most accurate in this application. Convergence studies of flow over a smooth supercritical ridge show that the dissipation along tidal characteristics is, apparently, an integrable singularity. When the ocean bottom is not smooth, the accuracy and convergence of the model depend on the power spectrum of the topography. A numerical experiment suggests that the power spectrum of the resolved topography must roll off faster than k−2 to obtain convergent results from a linear numerical model of this type. 相似文献
14.
Baroclinic eddies south of Cheju Island in the East China Sea 总被引：3，自引：0，他引：3
The detailed structures of baroclinic eddies, that is, an anticlockwise circulation in the upper layer and a clockwise one in the lower layer south of Cheju Island in the East China Sea have been revealed by intensive field observation. Such baroclinic eddies are accompanied by the southward spreading of the Yellow Sea Bottom Cold Water. 相似文献
15.
Huang Weigen 《海洋学报(英文版)》2000,19(3):33-43
I~IOXSatellite infrared measurements are now accepted as an effeCtive way of mapping sea surfacetemperature (SST) distributions on global and regional scales. While regional SST maps are widely uest as background data for oceanographic experiments, they tend to be considered by oceanographers as at best qualitative tools. There is SCOPe for developing the use of satellite SST imagesac extensively for the study of mesoscale d~ical processes, as this paper seeks to demonstrate. As Part O… 相似文献
16.
Investigations of the vertical exchange coefficientK
z
, considering turbulent and advective transport, are summarized. The values ofK
z
are determined from the climaticT, S characteristics, heat and salinity fluxes, and the rate of the low-Bosporus water transformation over the entire Black Sea water column; namely, in the upper mixed layer, the active layer, the cold intermediate layer, the halocline, and in the deep and near-bottom waters. A characteristic for annual fluctuations ofK
z
in the active layer is given; it is noted that the coefficient tends to grow in transit from the centre of the cyclonic gyre toward its periphery.Translated by V. Puchkin. 相似文献
17.
The role of meso-scale eddies in mixed layer deepening and mode water formation in the western North Pacific 总被引：3，自引：1，他引：2
Shinya Kouketsu Hiroyuki Tomita Eitarou Oka Shigeki Hosoda Taiyo Kobayashi Kanako Sato 《Journal of Oceanography》2012,68(1):63-77
Distributions of mixed layer depths around the centers of anti-cyclonic and cyclonic eddies in the North Pacific Ocean were
composited by using satellite-derived sea surface height anomaly data and Argo profiling float data. The composite distributions
showed that in late winter, deeper mixed layers were more (less) frequently observed inside the cores of the anti-cyclonic
(cyclonic) eddies than outside. This relationship was the clearest in the region of 140°E–160°W and 35°N–40°N, where the temperature
and salinity of the deep mixed layers were similar to those of the lighter variety of central mode water (L-CMW). A simple
one-dimensional bulk mixed layer model showed that both strong sea-surface heat and momentum fluxes and weak preexisting stratification
contributed to formation of the deep mixed layer. These conditions were associated with the anti-cyclonic eddies, suggesting
that these eddies are important in the formation of mode waters, particularly L-CMW. 相似文献
18.
Intercomparison of three South China Sea circulation models 总被引：2，自引：1，他引：1
1IntroductionTheSouthChinaSeaisthelargesttropicalmarginaldeepsealocatingbetweenthewesternPacificOceanandtheeasternIndianOcean.AsapartofAsia-Australiamaritimecontinent,monsoonisaprimaryfactorforcingtheSouthChinaSeaCurrent(SCSC)variation.Drivenbynortheasterlymonsooninwinterandsouth-westerlymonsooninsummer,respectively,theSCSCbehavesacyclonicgyreandananticy-clonicgyre,correspondingly(Wyrtki,1961;Xuetal.,1982).Owingtotheshortageandexpen-sivenessofdirectobservationsintheSCS,fur-therunder… 相似文献
19.
Realistic representation of sea ice in ocean models involves the use of a non-linear free-surface, a real freshwater flux and observance of requisite conservation laws. We show here that these properties can be achieved in practice through use of a rescaled vertical coordinate “z*” in z-coordinate models that allows one to follow undulations in the free-surface under sea ice loading. In particular, the adoption of “z*” avoids the difficult issue of vanishing levels under thick ice.Details of the implementation within MITgcm are provided. A high resolution global ocean sea ice simulation illustrates the robustness of the z* formulation and reveals a source of oceanic variability associated with sea ice dynamics and ice-loading effects. The use of the z* coordinate allows one to achieve perfect conservation of fresh water, heat and salt, as shown in extended integration of coupled ocean sea ice atmospheric model. 相似文献
20.
《Deep Sea Research Part I: Oceanographic Research Papers》1999,46(7):1137-1160
In the northwestern Mediterranean Sea, Coastal Zone Color Scanner images suggest that the eddies that participate in the restratification following deep convection interact with the spring phytoplankton bloom. The mechanisms for this interaction are studied using a biogeochemical model embedded in an eddy-resolving primitive equation ocean model. The model is initialized with a patch of dense water surrounded by a stratified ocean, which is characteristic of the winter situation. The atmospheric forcing is artificially held constant, in order to focus solely on the mesoscale variability. After a few days, meanders develop at the periphery of the patch, inducing its sinking and spreading. Mesoscale upward motions are responsible for the shoaling of the mixing layer in the trough of the meanders. As sunlight is the main factor regulating primary production at this time of year, this shoaling increases the mean exposure time of the phytoplankton cells and thus enhances productivity. Consequently, the majority of phytoplankton production is obtained at the edge of the patch, in agreement with in situ data. Through advection, phytoplankton is then subducted from these sources towards the crest of the meanders. Our results suggest that this mesoscale transport is responsible for a decorrelation between phytoplankton biomass and primary production. 相似文献