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1.
在大洋环流模式中,铅直混合的参数化方法起着关键性的作用。将大洋细结构混合参数化方法首次应用于世界大洋环流模式中。使用中科院大气所(LASG)发展的20层世界大洋环流模式(OGCM)ML20,月平均风场作为强迫场,利用ML20模式在稳定初始状态下运行300a后的计算结果作为本实验进行数值模拟的初始场。该参数化方法对世界大洋环流模式的影响主要表现为：永久性温度跃层的厚度明显变薄;对深层水和底层水的模拟有改进;对南极中层水的模拟比较成功;但是对赤道海区的模拟结果欠佳。 相似文献
2.
For the Black-Sea region, we perform the dynamic reanalysis of the data on atmospheric circulation for the period 1958–2001
by using the HadRM3P model with a space resolution of 25 km. We estimate the mean climatic atmospheric fields of vorticity and divergence of the
wind velocity and study their space structure and seasonal variability. The climatic estimates of the annual course of vorticity
of the wind velocity over the sea are presented. The obtained large annual average values of vorticity of the velocity reveal
the predominant role played by the wind action in the generation not only of the seasonal variability but also of the mean
cyclonic circulation of waters in the Black Sea. 相似文献
3.
Based on a two-level nested model from the global ocean to the western Pacific and then to the South China Sea（SCS）, the high-resolution SCS deep circulation is numerically investigated. The SCS deep circulation shows a basin-scale cyclonic structure with a strong southward western boundary current in summer（July）, a northeastsouthwest through-flow pattern across the deep basin without a western boundary current in winter（January）,and a transitional pattern in spring and autumn. The sensitivity ... 相似文献
4.
Analysis of measurements from two long-term moored arrays in and near the Gulf Stream suggests a simple parameterization of eddy spatial covariance statistics: a parameterization that can be referred to as “quasi-homogeneous and isotropic”. Taking the normalized covariance function (i.e. the correlation function) for streamfunction to be homogeneous and isotropic and assuming motions to be horizontally nondivergent and hydrostatic permit the velocity and temperature covariances to be derived from the streamfunction covariance. Statistical tests indicate that deviations from these assumptions are indistinguishable from Gaussian random noise. The spatial correlation function used in Gaussian with a decay scale of about 140 km, which is only weakly depth dependent. A simple form is also suggested for the vertical lag dependence. This parameterization permits calculation of derived quantities such as the eddy vorticity flux divergence which is discussed in the context of the mean potential vorticity balances for the depth integrated circulation and for the subthermocline layer. The divergence of the relative vorticity flux is found capable of driving two counter-rotating gyres of strength 30–40 Sv on either side of the Stream, as are observed. The “thickness flux” dominates the lower layer eddy potential vorticity flux and is of the correct sign to make the recirculation more barotropic. The lower layer eddy forcing is weak and the gyres exist in a region of nearly uniform mean potential vorticity. 相似文献
5.
Comparison of gravity current mixing parameterizations and calibration using a high-resolution 3D nonhydrostatic spectral element model 总被引：1，自引：3，他引：1
Yeon S. Chang Xiaobiao Xu Tamay M.
zgkmen Eric P. Chassignet Hartmut Peters Paul F. Fischer 《Ocean Modelling》2005,10(3-4):342-368
In light of the pressing need for development and testing of reliable parameterizations of gravity current entrainment in ocean general circulation models, two existing entrainment parameterization schemes, K-profile parameterization (KPP) and one based on Turner’s work (TP), are compared using idealized experiments of dense water flow over a constant-slope wedge using the HYbrid Coordinate Ocean Model (HYCOM). It is found that the gravity current entrainment resulting from KPP and TP differ significantly from one another. Parameters of KPP and TP are then calibrated using results from the high-order nonhydrostatic spectral element model Nek5000. It is shown that a very good agreement can be reached between the HYCOM simulations with KPP and TP, even though these schemes are quite different from each other. 相似文献
6.
《Deep Sea Research Part I: Oceanographic Research Papers》2000,47(4):737-743
Recent works have shown that parameterizing eddy fluxes as a downgradient diffusion of potential vorticity (PV) generates circulation over topography. This result is examined in the context of a simple barotropic quasi-geostrophic model. It is shown that, unless a constraint on the eddy diffusivity is maintained, the PV mixing parameterization creates a fictitious torque which generates angular momentum. These considerations indicate that momentum conservation is not maintained in recent models that purport to show generation of net alongslope flow associated with PV mixing over topography. 相似文献
7.
借助于六套海洋模式资料,本文初步分析了热带西太平洋深层环流的基本特征。与气候态数据集WOA13相比,水深3000m层除HYCOM以正温度偏差为主外,其余模式均为负温度偏差,且随着深度增加偏差幅度变大。盐度偏差方面,HYCOM和OFES以正偏差为主,其余模式以负偏差为主。温盐偏差在各个深海海盆中的时间变化趋势不尽相同,且与实际观测结果存在较大差异。水深1000—3000m以纬向东西向交替变化的射流为主。3000—5000m的纬向流速减小,形成海盆内环流,不同海盆之间可通过深水通道进行海水交换。3000m以深的关键深海通道的输运通量存在明显的季节变化,甚至不同季节流向也不一致,而海盆内的环流形态受制于位涡收支积分约束方程,进而也表征出季节变化的特征,即不同季节海盆内的环流主要旋转形态不同。在分析了初始温盐场、潮汐及其他要素对深海环流的影响后,本文为日后构建适合热带西太平洋深海环流研究的模式提供了建议。 相似文献
8.
基于卫星数据改进计算白冠覆盖率的模型 总被引：2，自引：1，他引：1
本文基于白冠覆盖率的历史研究,总结了计算白冠覆盖率的参数化方案和海浪破碎统计模型,并分析比较其优缺点。通过结合基于卫星数据的参数化公式,利用最优拟合的方法,得到不同限制条件下模型中的系数Cen和n。通过分析考虑海浪破碎条件,确定了适用于一般海浪状况的系数值。通过比较白冠覆盖率的卫星数据和原始模型的模拟结果,可知改进后模型的结果更合理,同时与历史研究结论相符。文中还分析了从1998年到2008年十年平均的全球白冠覆盖率的季节性分布特征。在中高纬度海域,全年白冠覆盖率的值最大,而在低纬度和赤道海域,白冠覆盖率小于0.5%,全球白冠覆盖率的平均值大约为1% ~3%。北半球中高纬度海域的白冠覆盖率的季节性变化显著大于南半球。 相似文献
9.
10.
Modern methods for predicting thunderstorms and lightnings with the use of high-resolution numerical models are considered. An analysis of the Lightning Potential Index (LPI) is performed for various microphysics parameterizations with the use of the Weather Research and Forecasting (WRF) model. The maximum index values are shown to depend significantly on the type of parameterization. This makes it impossible to specify a single threshold LPI for various parameterizations as a criterion for the occurrence of lightning flashes. The topographic LPI maps underestimate the sizes of regions of likely thunderstorm-hazard events. Calculating the electric field under the assumption that ice and graupel are the main charge carriers is considered a new algorithm of lightning prediction. The model shows that the potential difference (between the ground and cloud layer at a given altitude) sufficient to generate a discharge is retained in a larger region than is predicted by the LPI. The main features of the spatial distribution of the electric field and potential agree with observed data. 相似文献
11.
《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
12.
《Ocean Modelling》2004,6(1):83-100
A series of vertical mixing schemes implemented in a circumpolar coupled ice–ocean model of the BRIOS family is validated against observations of hydrography and sea ice coverage in the Weddell Sea. Assessed parameterizations include the Richardson number-dependent Pacanowski–Philander scheme, the Mellor–Yamada turbulent closure scheme, the K-profile parameterization, a bulk mixed layer model and the ocean penetrative plume scheme (OPPS). Combinations of the Pacanowski–Philander parameterization or the OPPS with a simple diagnostic model depending on the Monin–Obukhov length yield particularly good results. In contrast, experiments using a constant diffusivity and the traditional convective adjustment cannot reproduce the observations. An underestimation of wind-driven mixing in summer leads to an accumulation of salt in the winter water layer, inducing deep convection in the central Weddell Sea and a homogenization of the water column. Large upward heat fluxes in these simulations lead to the formation of unrealistic, large polynyas in the central Weddell Sea after only a few years of integration. Furthermore, spurious open-ocean convection affects the basin-scale circulation and leads to a significant overestimation of meridional overturning rates. We conclude that an adequate parameterization of both wind-induced mixing and buoyancy-driven convection is crucial for realistic simulations of processes in seasonally ice-covered seas. 相似文献
13.
The seasonal variation of water circulation in the Seto Inland Sea is investigated using a high resolution, three-dimensional
numerical ocean model. The model results are assessed by comparison with long-term mean surface current and hydrographic data.
The simulated model results are consistent with observations, showing a distinct summer and winter circulation patterns. In
summer the sea water is highly stratified in basin regions, while it is well mixed near the straits due to strong tidal mixing
there. During this period, a cold dome is formed in several basins, setting up stable cyclonic eddies. The cyclonic circulation
associated with the cold dome develops from May and disappears in autumn when the surface cooling starts. The experiment without
freshwater input shows that a basin-scale estuarine circulation coexists with cyclonic eddy in summer. The former becomes
dominant in autumn circulation after the cold dome disappears. In winter the water is vertically well mixed, and the winter
winds play a significant role in the circulation. The northwesterly winds induce upwind (downwind) currents over the deep
(shallow) water, forming a “double-gyre pattern” in the Suo-Nada, two cyclonic eddies in Hiuchi-Nada, and anticyclonic circulation
in Harima-Nada in vertically averaged current fields. 相似文献
14.
A model is presented that simulates the formation of marine aggregates from particles of different origin inside a model of pelagic biological processes. Experiments are carried out with parameterizations appropriate for different types of aggregates, using different kinds of physical forcing, and compared to observations of dissolved inorganic nitrogen (DIN), particulate organic nitrogen (PON), marine snow concentration, and sedimentation.The occurrence of large, macroscopically visible aggregates (marine snow) can best be simulated with parameterizations that have been derived from in situ observations of marine snow, but not with a parameterization sufficient for dense particles. The parameterization strongly determines the amount and timing of deep export, as well as the post-bloom development of the food web in the upper layers.Detritus in aggregates plays a role mainly during times when zooplankton are abundant, as e.g. in the western Arabian Sea during Southwest Monsoon. Then the large aggregates as fast sinking vehicles may remove detritus quickly from shallow and mid-water depth, preventing the accumulation of nutrients that are produced via detritus decomposition. In this region, detritus contributes strongly to deep sedimentation. The nitrogen budget at this location with regard to the observations cannot be closed: depending on model type, either the model simulates too high sedimentation, or too high DIN. Possible causes for this mismatch include undercollection by sediment traps, inaccurate representation of physical processes in the model and the neglect of biological processes, such as production of dissolved organic matter or denitrification. 相似文献
15.
The surface heat budget of the Arctic Ocean （SHEBA） project has shown that the study of the surface heat budget characteristics is crucial to understanding the interface process and environmental change in the polar region. An arctic single - column model （ARCSCM） of Colorado University is used to simulate the arctic surface radiation and energy budget during the summertime. The simulation results are analyzed and compared with the SHEBA measurements. Sensitivity analyses are performed to test microphysical and radiative parameterizations in this model. The results show that the ARCSCM model is able to simulate the surface radiation and energy budget in the arctic during the summertime, and the different parameterizations have a significant influence on the results. The combination of cloud microphysics and RRTM parameterizations can fairly derive the surface solar shortwave radiation and downwelling longwave radiation flux. But this cloud microphysics parameterization scheme deviates notably from the simulation of surface sensible and latent heat flux. Further improvement for the parameterization scheme applied to the Arctic Regions is necessary. 相似文献
16.
Yutaka Yoshikawa 《Journal of Oceanography》2012,68(6):971-983
Numerical experiments were performed to investigate the effects of eddies generated in deep water formation processes on an abyssal circulation in a closed bowl-shaped basin. Two sets of experiments were performed. One set was eddy-restricted experiments in which only a volume-driven (upwelling-driven) circulation was simulated and the other set was eddy-permitted experiments in which both a volume-driven circulation and an eddy-driven circulation were simulated. In the two layer experiment where the lower layer water is formed, a mean along-slope current is formed in the lower layer for both the eddy-restricted and eddy-permitted experiments. The direction of the current was not unique in the eddy-restricted experiment, but it was cyclonic in the eddy-permitted experiment. In the three layer experiments where water of the intermediate layer is formed, the mean along-slope current in the lowest layer is negligibly small in the eddy-restricted experiment, while it is large and cyclonic in the eddy-permitted experiment. The driving forcings of the eddy-driven circulation are quantified in terms of eddy fluxes of relative vorticity (Reynolds stress) and layer thickness (bolus velocity). These terms increase as the volume of the newly formed water increases, but they do not change greatly with the slope height. The magnitude of these terms changes with the slope width, but the sum of these terms does not vary greatly. As a result, the intensity of the eddy-driven circulation depends primarily on the volume of newly formed water. These dependences of eddy fluxes were interpreted using downgradient diffusion of potential vorticity. 相似文献
17.
南海东北部亚中尺度过程时空分布特征 总被引：6，自引：3，他引：3
基于高分辨率模型2009-2012年的模拟结果，本文对南海东北部亚中尺度过程的时空分布特征进行了研究。模拟结果表明，南海东北部上层广泛存在着相对涡度接近于局地行星涡度的亚中尺度过程。统计结果发现，亚中尺度过程的相对涡度的分布具有着明显的非对称性，即正涡度明显强于负涡度。这意味着相比于负涡度，具有正涡度的亚中尺度过程要更为活跃，而这主要是由离心不稳定导致。同时，亚中尺度过程在时间分布上表现出明显的冬强夏弱的季节变化特征。通过对该海区亚中尺度过程可能生成机制的分析发现，该季节变化与流场拉伸和混合层的厚度有着密切关系，冬季更强的流场拉伸和更深的混合层有利于通过锋生过程和混合层不稳定为亚中尺度过程生成提供更多的能量。 相似文献
18.
验证基于GM(Garret-Munk)大洋内波普适谱的细尺度参数化方案在不同海域的适用性,对于湍流混合研究来说非常重要。包含背景GM内波场的高分辨率数值模式被用于评估细尺度参数化方案在背风波生成源地处的适用性。细尺度参数化方案主要包括基于剪切的G89 (Gregg 1989)方案、基于应变的W93 (Wijesekera 1993)方案、基于剪切和应变的GHP (Gregg-Henyey-Polzin)方案以及对GHP方案中的频率矫正项作出变换的IH (Ijichi-Hibiya)方案。计算结果显示,背风波的生成伴随着海底上方近惯性内波的增强,使得内波场的动能与势能的比值相较于GM内波场偏大。在这种情况下,基于剪切的G89方案会因为高估内波场的总能量而高估耗散率。反之,基于应变的W93方案会因为低估内波场的总能量而低估耗散率。计算结果还显示,已经考虑了内波谱变形的GHP方案仍然会高估耗散率,但IH方案能比较准确地估算耗散率。 相似文献
19.
On the general ocean circulation forced by the asymmetric wind stress curl, the role of the eddies which are detached from the western boundary current is studied using an eddy-resolving two-layered quasi-geostrophic numerical model with free-slip boundary condition. An ideal sinusoidal function is used as the wind stress curl, and amplitude is assumed to be larger over the southern basin than over the northern one. In contrast with the antisymmetric wind forcing, in the asymmetric wind stress case, the subtropical western boundary current overshoots to the north from the zero wind stress curl line. As the asymmetricity of the wind forcing becomes larger, the separation point of the time mean field is located further north. The eddies generated in the region of the subtropical recirculation are advected northward by the western boundary current and they are detached from subtropical gyre. The release of these eddies to the north basin leads to weaken the subtropical recirculation system. From the analysis of the potential vorticity budgets, in the asymmetric case, it is shown that detached eddies play an important role in transporting the negative vorticity which is excessively inputted into the southern basin, to the northern basin, in addition to the terms which transport vorticity in the antisymmetric case, i.e., the vorticity transport by the meander of the jet. Under the free-slip boundary, more than a quarter of that excess vorticity is transported by those detached eddies in some cases. 相似文献
20.
《Ocean Modelling》2011,36(4):277-303
We investigate the influence of bottom topography on the formation and trapping of long upwelling filaments using a 2-layer shallow water model on the f-plane. A wind forced along-shore current, associated with coastal upwelling along a vertical wall, encounters a promontory of finite width and length, perpendicular to the coast.In the lower layer, topographic eddies form, which are shown to drive the formation of a filament on the front. Indeed, as the upwelling current and front develop along the coast, the along shore flow crosses the promontory, re-arranging the potential vorticity structure and generating intense vortical structures: water columns with high potential vorticity initially localized upon the promontory are advected into the deep ocean, forming cyclonic eddies, while water columns from the deep ocean with low potential vorticity climb on the topography forming a trapped anticyclonic circulation. These topographic eddies interact with the upper layer upwelling front and form an elongated, trapped and narrow filament.Sensitivity tests are then carried out and it is shown that:
- •baroclinic instability of the front does not play a major role on the formation of long trapped filaments;
- •increasing the duration of the wind forcing increases the upwelling current and limits the offshore growth of the filament;
- •modifying the promontory characteristics (width, length, height and slopes) has strong impact on the filament evolution, sometimes leading to a multipolarisation of the potential vorticity anomaly structure which results in much more complicated patterns in the upper layer (numerous shorter and less coherent filaments). This shows that only specific promontory shapes can lead to the formation of well defined filaments;
- •adding bottom friction introduces a slight generation of potential vorticity in the bottom layer over the promontory, but does not significantly alter significantly the formation of the filament along the outcropped front in the present configuration;
- •modifying the stratification characteristics, in particular the density jump between the layers, has only a weak influence on the dynamics of topographic eddies and on filament formation;
- •the influence of capes is also modest in our simulations, showing that topography plays the major role in the formation of long and trapped upwelling filaments.