共查询到20条相似文献，搜索用时 31 毫秒
1.
Steven L. Morey Mark A. Bourassa Dmitry S. Dukhovskoy James J. O’Brien 《Ocean Dynamics》2006,56(5-6):594-606
A coupled ocean and boundary layer flux numerical modeling system is used to study the upper ocean response to surface heat
and momentum fluxes associated with a major hurricane, namely, Hurricane Dennis (July 2005) in the Gulf of Mexico. A suite
of experiments is run using this modeling system, constructed by coupling a Navy Coastal Ocean Model simulation of the Gulf
of Mexico to an atmospheric flux model. The modeling system is forced by wind fields produced from satellite scatterometer
and atmospheric model wind data, and by numerical weather prediction air temperature data. The experiments are initialized
from a data assimilative hindcast model run and then forced by surface fluxes with no assimilation for the time during which
Hurricane Dennis impacted the region. Four experiments are run to aid in the analysis: one is forced by heat and momentum
fluxes, one by only momentum fluxes, one by only heat fluxes, and one with no surface forcing. An equation describing the
change in the upper ocean hurricane heat potential due to the storm is developed. Analysis of the model results show that
surface heat fluxes are primarily responsible for widespread reduction (0.5°–1.5°C) of sea surface temperature over the inner
West Florida Shelf 100–300 km away from the storm center. Momentum fluxes are responsible for stronger surface cooling (2°C)
near the center of the storm. The upper ocean heat loss near the storm center of more than 200 MJ/m2 is primarily due to the vertical flux of thermal energy between the surface layer and deep ocean. Heat loss to the atmosphere
during the storm’s passage is approximately 100–150 MJ/m2. The upper ocean cooling is enhanced where the preexisting mixed layer is shallow, e.g., within a cyclonic circulation feature,
although the heat flux to the atmosphere in these locations is markedly reduced. 相似文献
2.
A new circulation model of the western North Pacific Ocean based on the parallelized version of the Princeton Ocean Model and incorporating the Local Ensemble Transform Kalman Filter (LETKF) data assimilation scheme has been developed. The new model assimilates satellite data and is tested for the period January 1 to April 3, 2012 initialized from a 24-year simulation to estimate the ocean state focusing in the South China Sea (SCS). Model results are compared against estimates based on the optimum interpolation (OI) assimilation scheme and are validated against independent Argo float and transport data to assess model skills. LETKF provides improved estimates of the western North Pacific Ocean state including transports through various straits in the SCS. In the Luzon Strait, the model confirms, for the first time, the three-layer transport structure previously deduced in the literature from sparse observations: westward in the upper and lower layers and eastward in the middle layer. This structure is shown to be robust, and the related dynamics are analyzed using the results of a long-term (18 years) unassimilated North Pacific Ocean model. Potential vorticity and mass conservations suggest a basin-wide cyclonic circulation in the upper layer of the SCS (z?>??570 m), an anticyclonic circulation in the middle layer (?570 m?≥?z?>??2,000 m), and, in the abyssal basin (<?2,000 m), the circulation is cyclonic in the north and anticyclonic in the south. The cyclone–anticyclone abyssal circulation is confirmed and explained using a deep-layer reduced-gravity model as being caused by overflow over the deep sill of the Luzon Strait, coupled with intense, localized upwelling west of the strait. 相似文献
3.
Jacques Verron 《地球物理与天体物理流体动力学》2013,107(1-4):257-276
Abstract In this paper we examine the behaviour of oceanic unsteady flow impinging on isolated topography by means of numerical simulation. The ocean model is quasigeostrophic and forced by an oscillatory mean flow. The fluid domain is of the channel type and open-boundary numerical conditions are used to represent downstream and upstream flow. In certain cases, vortex shedding, either cyclonic or anticyclonic, is observed in the lee of obstacles. Such shedding can be explained as the consequence of both an enhanced process of vorticity dissipation over the topography which locally affects the balance of potential vorticity on the advective timescale, and a periodic dominance of advective effects which sweep the fluid particles trapped on the seamount. For refined resolution and smallest viscosity the model will predict flows in which the shed eddies are coherent structures with closed streamlines. The model suggests a mechanism by which topographically generated eddies may be swept away from a seamount in the ocean. 相似文献
4.
The Yellow Sea is a semi-enclosed shallow sea with a deep trough of about 80 m. On the hy-drographic condition in the Yellow Sea, Lie[1] pointed out that it is strongly associated with winter cooling and summer heating, fresh input from rivers into the co… 相似文献
5.
Ramesh V. Godbole 《Pure and Applied Geophysics》1977,115(5-6):1373-1381
A diagnostie method of cumulus parameterization is suggested in which vertical transport of horizontal momentum by cumulus-scale is derived by making use of large-scale vorticity as well as divergence budget equations. Data for composite monsoon depression over India available from our earlier studies used to test the method. As a first approximation, the results are obtained using only the vorticity budget equation.The results show that in the southwest sector of the monsoon depression, which is characterized by maximum cloudiness and precipitation, there is an excess of cyclonic vorticity in the lower troposphere and anticyclonic vorticity in the upper troposphere associated with the large-scale motion. The distribution of eddy vertical transport of horizontal momentum is such that anticyclonic vorticity is generated in the lower troposphere and cyclonic vorticity aloft. Cumulus-scale eddies thus work against the large-scale system and tend to off-set the large-scale imbalance in vorticity. 相似文献
6.
The oceanic response to a typhoon, where mesoscale ocean circulations co-exist, was investigated by analyzing the independent
observations of profiling floats data at three different locations, satellite altimetry data near the eye of Typhoon Man-Yi
(2007) before and after its passage, and synthetic aperture radar data taken during the typhoon’s passage. In spite of the
nearly symmetric wind pattern around the eye, the distribution of mesoscale eddies had a major impact on the surface currents
and mixed layer (ML) depths. As a result, the entrainment of the water below the ML into the ML was affected by the mesoscale
circulation and became asymmetric, which accounted for most of the changes observed in the temperature profiles. Changes in
the isotherms were driven primarily by the westward propagation of the mesoscale pattern rather than by the typhoon-induced
shoaling. The typhoon-induced shoaling could have played a significant role in the generation of high-frequency (e.g., near-inertial)
oscillations and/or sub-mesoscale structures. Although a similar or even greater energy flux was observed at the surface,
the entrainment within the anticyclonic circulation was weaker than that within the cyclonic circulation and at the edge of
the anticyclonic circulation because of the thick pre-existing ML. A strong ocean response to Typhoon Man-Yi (2007) within
a cyclonic circulation or at the edge of an anticyclonic circulation, rather than within an anticyclonic eddy, has implications
for the role of mesoscale ocean circulations in better understanding and forecasting the typhoon intensity. 相似文献
7.
A. D. McEwan 《地球物理与天体物理流体动力学》2013,107(1):283-311
AbstractIt is successfully demonstrated that substantial redistribution of the angular momentum within a completely liquid-filled cylinder in uniform rotation can be brought about by the induction of turbulent mixing through the resonant excitation of standing inertial waves. This means of mixing is accomplished without significant net circulation in the meridional plane, or strong boundary restraint.Intense cyclonic vortices are created with an apparently high conversion of energy from the inertial wave excited. Visualizations and measurements of vortex strength and circulation distribution are presented and dimensional arguments are applied to interpret from the measurements the partition of the turbulence into relative velocity- and angular momentum-diffusing elements. This indicates tentatively the mechanism responsible; momentum advected by the inertial wave is irreversibly diffused by turbulence of smaller scale. Anisotropy with enhanced radial transport is an essential feature of the nett turbulence in such a mechanism. Similar combinations of large-scale waves and turbulence can be expected to occur in the geophysical situations to which the phenomenon of angular momentum mixing relates. The experiment does not, however, test the effectiveness of isotropic turbulence in the same rôle. 相似文献
8.
Ya. D. Afanasyev 《地球物理与天体物理流体动力学》2013,107(1):31-48
We present results from a new series of experiments on the geophysically important issue of the instability of anticyclonic columnar vortices in a rotating fluid in circumstances such that the Rossby number exceeds unity. The vortex pair consisting of a cyclonic and an anticyclonic vortex is induced by a rotating flap in a fluid which is itself initially in a state of solid-body rotation. The anticyclonic vortex is then subject to either centrifugal or elliptical instability, depending on whether its initial ellipticity is small or large, while the cyclone always remains stable. The experimental results demonstrate that the perturbations due to centrifugal instability have a typical form of toroidal vortices of alternating sign (rib vortices). The perturbations due to elliptical instability are of the form of sinuous deformation of the vortex filament in the plane of maximal stretching which corresponds to the plane of symmetry for the vortex pair. The initial perturbations in both cases are characterized by a definite wave number in the vertical direction. The characteristics of the unstable anticyclone are determined by the main nondimensional parameter of the flow - the Rossby number. The appearance of both centrifugal and elliptical instabilities are in accord with the predictions of theoretical criteria for these cases. 相似文献
9.
Abstract The dynamic behavior of baroclinic point vortices in two-layer quasi-geostrophic flow provides a compact model for studying the transport of heat in a variety of geophysical flows including recent heton models for open ocean convection as a response to spatially localized intense surface cooling. In such heton models, the exchange of heat with the region external to the compact cooling region reaches a statistical equilibrium through the propagation of tilted heton clusters. Such tilted heton clusters are aggregates of cyclonic vortices in the upper layer and anti-cyclonic vortices in the lower layer which collectively propagate almost as an elementary tilted heton pair even though the individual vortices undergo shifts in their relative locations. One main result in this paper is a mathematical theorem demonstrating the existence of large families of long-lived propagating heton clusters for the two-layer model in a fashion compatible to a remarkable degree with the earlier numerical simulations. Two-layer quasi-geostrophic flow is an idealization of coupled surface/interior quasi-geostrophic flow. The second family of results in this paper involves the systematic development of Hamiltonian point vortex dynamics for coupled surface/interior QG with an emphasis on propagating solutions that transport heat. These are novel vortex systems of mixed species where surface heat particles interact with quasi-geostrophic point vortices. The variety of elementary two-vortex exact solutions that transport heat include two surface heat particles of opposite strength, tilted pairs of a surface heat particle coupled to an interior vortex of opposite strength and two interior tilted vortices of opposite strength at different depths. The propagation speeds of the tilted elementary hetons in the coupled surface/interior QG model are compared and contrasted with those in the simpler two-layer heton models. Finally, mathematical theorems are presented for the existence of large families of propagating long-lived tilted heton clusters for point vortex solutions in coupled surface/interior QG flow. 相似文献
10.
H. Naeser 《地球物理与天体物理流体动力学》2013,107(1):335-345
Abstract In an ocean with a horizontal bottom where no wind is blowing it is shown that the spin (angular momentum) of the ocean is conserved. Thus, when energy is dissipated, at least one of three things will happen: i) Wave spectra may move towards lower frequencies. ii) The directional distribution may be changed towards long-crested waves. iii) Shear currents may be generated. By neglecting ii) and iii), the frequency shift of a spectrum is calculated due to molecular dissipation. When all energy transforming phenomena as e.g. wave breaking and turbulence generation are taken into account, the conservation of spin seems to be able to explain the frequency shift of wave spectra. In shallow water it is shown that there is energy transfer from the waves to shear currents. 相似文献
11.
L. L. Kichatinov 《地球物理与天体物理流体动力学》2013,107(3-4):145-160
Abstract Fluxes of angular momentum produced by turbulence in rotating fluids are derived with the effects of a magnetic field included. It is assumed that the rotation is slow but that the magnetic field is of arbitrary strength. A mean magnetic field is shown to produce qualitative changes of the sources of the differential rotation rather than the quenching of differential rotation usually expected. A new equatorward flux of angular momentum arises through the influence of the toroidal magnetic field. The possibility of interpreting the torsional oscillations of the Sun as a consequence of the magnetic perturbations of the turbulent angular momentum fluxes is discussed. 相似文献
12.
Phillip Hignett 《地球物理与天体物理流体动力学》2013,107(3-4):293-299
Abstract Some new measurements are presented of the axisymmetric heat transport in a differentially heated rotating fluid annulus. Both rigid and free upper surface cases are studied, for Prandtl numbers of 7 and 45, from low to high rotation rates. The rigid lid case is extended to high rotation rates by suppressing the baroclinic waves, that would normally develop at some intermediate rotation rate, with the use of sloping endwalls. A parameter P is defined as the square of the ratio of the (non-rotating) thermal sidewall layer thickness to the Ekman layer thickness. For small P the heat transport remains unaffected by the rotation, but as P increases to order unity the Ekman layer becomes thin enough to inhibit the radial mass transport, and hence the heat flux. No explicit Prandtl number dependence is observed. Also this scaling allows the identification of the region in which the azimuthal velocity reaches its maximum. Direct comparisons are drawn with previous experimental and numerical results, which show what can be interpreted as an inhibiting effect of increasing curvature on the heat transport. 相似文献
13.
One of the main challenges of the Copernicus Marine Service is the implementation of coupled ocean/waves systems that accurately estimate the momentum and energy fluxes provided by the atmosphere to the ocean. This study aims to investigate the impact of forcing the Nucleus for European Modelling of the Ocean (NEMO) ocean model with forecasts from the wave model of Météo-France (MFWAM) to improve classical air-sea flux parametrizations, these latter being mostly driven by the 10-m wind. Three wave-related processes, namely, wave-state-dependent stress, Stokes drift-related effects (Stokes-Coriolis force, Stokes drift advection on tracers and on mass), and wave-state-dependent surface turbulence, are examined at a global scale with a horizontal resolution of 0.25°. Three years of sensitivity simulations (2014–2016) show positive feedback on sea surface temperature (SST) and currents when the wave model is used. A significant reduction in SST bias is observed in the tropical Atlantic Ocean. This is mainly due to the more realistic momentum flux provided by the wave model. In mid-latitudes, the most interesting impact occurs during the summer stratification, when the wind is low and the wave model produces a reduction in the turbulence linked with wave breaking. Magnitudes of the large-scale currents in the equatorial region are also improved by 10% compared to observations. In general, it is shown that using the wave model reduces on average the momentum and energy fluxes to the ocean in tropical regions, but increases them in mid-latitudes. These differences are in the order of 10 to 20% compared with the classical parametrizations found in stand-alone ocean models. 相似文献
14.
J. A. Van De Konijnenberg V. Naulin J. Juul Rasmussen B. Stenum G. J. F. Van Heijst 《地球物理与天体物理流体动力学》2013,107(1-2):85-114
Abstract spin-up and spin-down in a circular tank with a uniformly sloping bottom are studied experimentally and numerically for small values of the relative change in the angular velocity of the tank. Generally, the initial single-cell flow evolves into a number of smaller vortices. The evolution is compared with an analytical model based on an expansion of the flow field in linear Rossby waves (Pedlosky and Greenspan, 1967). Although it is possible to tune the experimental parameters in such a way that agreement with the theory is found, in most cases the experiments show shedding of vortices in the initial stage of the spin-up or spin-down, a phenomenon not described by the analytical model. Nonetheless, in such cases the analytical model still accounts for other observations: the alternating generation of cyclonic and anticyclonic vortices in the eastern part of the tank and their subsequent westward motion. 相似文献
15.
Estimating vertical velocity in the oceanic upper layers is a key issue for understanding ocean dynamics and the transport
of biogeochemical elements. This paper aims to identify the physical sources of vertical velocity associated with sub-mesoscale
dynamics (fronts, eddies) and mixed-layer depth (MLD) structures, using (a) an ocean adaptation of the generalized Q-vector form of the ω-equation deduced from a primitive equation system which takes into account the turbulent buoyancy and momentum fluxes and
(b) an application of this diagnostic method for an ocean simulation of the Programme Océan Multidisciplinaire Méso Echelle
(POMME) field experiment in the North-Eastern Atlantic. The approach indicates that w-sources can play a significant role in the ocean dynamics and strongly depend on the dynamical structure (anticyclonic eddy,
front, MLD, etc.). Our results stress the important contribution of the ageostrophic forcing, even under quasi-geostrophic
conditions. The turbulent w-forcing was split into two components associated with the spatial variability of (a) the buoyancy and momentum (Ekman pumping)
surface fluxes and (b) the MLD. Process (b) represents the trapping of the buoyancy and momentum surface energy into the MLD
structure and is identified as an atmosphere/oceanic mixed-layer coupling. The momentum-trapping process is 10 to 100 times
stronger than the Ekman pumping and is at least 1,000 times stronger than the buoyancy w-sources. When this decomposition is applied to a filamentary mixed-layer structure simulated during the POMME experiment,
we find that the associated vertical velocity is created by trapping the surface wind-stress energy into this structure and
not by Ekman pumping. 相似文献
16.
The effect of the atmosphere on the Earth's rotation can be computed by twodifferent but fundamentally equivalent approaches. The more commonly used is the so-called angular momentum approach, and the second is the torque approach. Their physicalmeanings are recalled, and numerical results from the two are intercompared, concentrating on the lowest periods of a few days or shorter. The indirect effect of the atmosphereon the Earth rotation due to atmospheric forcing on the ocean is also described based on both static and dynamic oceanic models.Results are discussed for the equatorial components and for the highest frequencies. 相似文献
17.
基于中国气象局提供的气象站点月值资料,NOAA、CMAP降水格点月值资料,NDVI卫星资料及再分析资料,利用统计方法分析了1961-2014年青藏高原感热与中国东部季风雨带关键区夏季降水的年代际变化,并根据热动力平衡方程结合CESM模式试验解释了21世纪初高原感热异常对关键区夏季降水的影响机理.结果表明:21世纪初,黄淮、江淮地区降水增加,而长江以南地区降水减少.同时,高原感热也发生年代际增强,当春季感热增强后,大气热能上传导致夏季高原近地面产生气旋性环流异常,大气辐合;高层产生反气旋性环流异常,大气辐散.黄淮、江淮地区在对流层中低层受异常偏南风控制,高层受高原上空的大尺度反气旋环流影响产生异常偏北风.此外,高原感热增强通过影响黄淮、江淮地区产生暖平流输送和非绝热加热正异常,该区域产生异常的上升运动,降水量增加.长江以南地区在对流层中低层存在一个异常的反气性环流,有来自海洋的冷平流输送,同时大气非绝热加热在该地区为负异常,产生异常的下沉运动,降水量减少.模式敏感性试验的结果证实了当高原感热发生年代际增强,黄淮、江淮地区水平温度平流及非绝热加热为正异常,而在华南地区为负异常,从而导致黄淮、江淮地区大气上升运动增强,降水增加;而华南地区下沉运动增强,降水减少. 相似文献
18.
观测资料的分析极为清楚地表明,江淮流域的夏季降水有着极为明显的低频变化,周期为30-60d和近20d的振荡是其最基本的特征,尤其是在多雨的年份.对应江淮夏季多雨(涝)年和少雨(旱)年,大气环流的分析表明其大气季节内振荡(IS0)的形势有着显著的差异.例如在多雨(少雨)年,在长江以南的850hPa上为一个低频(IS0)反气旋(气旋)性环流控制,而中国北部和日本一带为气旋(反气旋)性环流,从而在江淮流域形成较强的低频辐合(辐散)气流;在200hPa的青藏高原上却为一个低频气旋(反气旋)性环流所控制.分析还表明,对应多雨年,在江淮流域有明显的由中高讳度向南传播和由低玮度向北传播的大气低频振荡的汇合情况;而对应于少雨年,由中高纬度向南传播的低频系统较不明显,在江淮流域低频系统的汇合也较为不清楚. 相似文献
19.
热带气旋是发生在热带洋面上的强烈气旋性涡旋.由于地转涡度梯度的存在,热带气旋在移动过程中不断发生Rossby波能量频散,并在热带气旋运动方向的后部激发出反气旋和气旋交替排列的Rossby波能量频散波列.多热带气旋共存和热带气旋的异常运动是当前国际热带气旋研究领域的热点问题,热带气旋Rossby能量频散被证实与多个热带气旋连续生成和异常运动密切相关.本文从热带气旋能量频散及波列特征、主要影响因子、反馈作用等方面,回顾总结了国内外关于热带气旋Rossby波能量频散的相关研究进展,并提出当前亟待解决的一些科学问题.目的是为深入研究热带气旋Rossby波能量频散及其影响提供基础和参考,以期使更多的研究学者关注热带气旋能量频散问题,从而进一步揭示热带气旋生成、发展和异常运动的动力学机理. 相似文献
20.
Daisuke Takahashi Kazuo Kido Yoshinori Nishida Naoto Kobayashi Naoyuki Higaki Hideo Miyake 《Continental Shelf Research》2007
We conducted hydrographic observations in 2002 to investigate the anticyclonic eddy that emerges every summer in Funka Bay, Hokkaido, Japan, and elucidate dynamical structure and wind-driven upwelling within the eddy. The anticyclonic eddy has a vertical scale of 32 m and is characterized by a strong baroclinic flow and a sharp pycnocline with a concave isopycnal structure. The sharp pycnocline occurs below a warm and relatively low-salinity water termed summer Funka Bay water (FS), which is formed by heating from solar radiation and dilution from river discharge in summertime Funka Bay. Flow of the anticyclonic eddy rotates as a rigid body at each layer, and the horizontal scale and rotation period of the eddy in the surface layer are about 15 km and 2.2 days, respectively. The dynamical balance of the anticyclonic eddy is well explained by the gradient flow balance. The contribution of centrifugal force to the gradient flow balance is about 27%. Therefore, the effect of the nonlinear term associated with centrifugal force cannot be neglected in considering the dynamics of the anticyclonic eddy in summertime Funka Bay. In addition, upwelling of subsurface water was observed in the surface layer of the central part of the eddy. The formation mechanism of this upwelling is consistent with interaction between horizontal uniform wind and the eddy. This upwelling is driven by upward Ekman pumping velocity related to the horizontal divergence of Ekman transport. In summertime Funka Bay, there are two wind effects that affect the anticyclonic eddy: a decay effect of the upwelling of subsurface water resulting from horizontal uniform wind (mainly northwesterly wind), and a maintenance or spin-up effect of horizontal non-uniform wind (mainly southerly–southeasterly seasonal wind) with negative wind stress curl. 相似文献