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1.
海洋内孤立波和中尺度涡是南海北部常见的中尺度动力过程。本文利用2010?2015年的Terra/Aqua-MODIS、ENVISAT ASAR和多源卫星高度计资料开展了南海海洋内孤立波和中尺度涡遥感探测研究,分析了中尺度涡对内孤立波传播方向的影响。结果表明,中尺度涡和内孤立波主要在南海东北部海域共存,当二者共存时,气旋（冷涡）促使内孤立波偏离原来的传播方向,向西偏南方向传播;反气旋（暖涡）促使内孤立波向西偏北方向传播,气旋与反气旋改变的内孤立波传播方向刚好相反。内孤立波和中尺度涡共存时间主要集中在3?9月,其中,3月受气旋和反气旋的共同作用,内孤立波传播方向几乎无变化;4月和5月,主要受气旋影响,内孤立波偏离原来传播方向向南传播;6?9月,主要受反气旋影响,内孤立波偏离原来的传播方向向北传播。本文利用遥感手段探索了海洋中尺度涡对内孤立波传播方向的影响,结果与现场观测结果一致。 相似文献
2.
Dynamical analysis of mesoscale eddy-induced ocean internal waves using linear theories 总被引：3，自引：1，他引：2
This study aims to explore generation mechanisms of the ocean internal wave using the dynamical analysis methods based on linear theories. Historical cruise measurements and recent synthetic aperture radar （SAR） observations of mesoscale eddies with diameter of several tens of kilometers to hundreds of kilometers show that the internal wave packets with wavelength of hundreds of meters to kilometer exist inside the mesoscale eddies. This coexistence phenomenon and inherent links between the two different scale processes are revealed in the solutions of governing equations and boundary conditions for the internal wave disturbance with a horizontally slowly variable amplitude in a cylindrical coordinate system. The theoretical solutions indicate that the instability of eddy current field provides the dynamical mechanism to internal wave generation. The derived dispersion relation indicates that the internal wave propagation is modified by the eddy current field structure. The energy equation of the internal waves clearly shows the internal wave energy increment comes from the eddy. The theoretical models are used to explain the observation of the mesoscale eddy-induced internal waves off the Norwegian coast. The two-dimensional waveform solution of the anticyclonic eddy-induced internal wave packet appears as ring-shaped curves, which contains the typical features of eddy stream lines. The comparison of theoretical solutions to the structure of the internal wave packets on SAR image shows a good agreement on the major features. 相似文献
3.
建立了一个描述中尺度涡的新的非线性方程,然后利用变分原理研究了孤立涡旋的Liapunov稳定性,指出反气旋和气旋涡都是稳定的。数值计算结果发现在β效应的作用下这些涡旋都向西移动而不存在向南的移动,然而在反气旋涡的上游存在一个孤立地形(例如海山)的话,孤立地形会使反气旋涡向南移动,而且移动的轨迹取决于孤立地形的位置。当两个反气旋涡同时存在并发生相互作用时,上游孤立地形使这两个反气旋涡产生弱合并并出现弱分离。而且孤立地形的位置对这两个涡的移动和旋转有重要影响。 相似文献
4.
Global observations of nonlinear mesoscale eddies 总被引：51，自引：0，他引：51
Sixteen years of sea-surface height (SSH) fields constructed by merging the measurements from two simultaneously operating altimeters are analyzed to investigate mesoscale variability in the global ocean. The prevalence of coherent mesoscale features (referred to here as “eddies”) with radius scales of O(100 km) is readily apparent in these high-resolution SSH fields. An automated procedure for identifying and tracking mesoscale features based on their SSH signatures yields 35,891 eddies with lifetimes ?16 weeks. These long-lived eddies, comprising approximately 1.15 million individual eddy observations, have an average lifetime of 32 weeks and an average propagation distance of 550 km. Their mean amplitude and a speed-based radius scale as defined by the automated procedure are 8 cm and 90 km, respectively.The tracked eddies are found to originate nearly everywhere in the World Ocean, consistent with previous conclusions that virtually all of the World Ocean is baroclinically unstable. Overall, there is a slight preference for cyclonic eddies. However, there is a preference for the eddies with long lifetimes and large propagation distances to be anticyclonic. In the southern hemisphere, the distributions of the amplitudes and rotational speeds of eddies are more skewed toward large values for cyclonic eddies than for anticyclonic eddies. As a result, eddies with amplitudes >10 cm and rotational speeds >20 cm s−1 are preferentially cyclonic in the southern hemisphere. By contrast, there is a slight preference for anticyclonic eddies for nearly all amplitudes and rotational speeds in the northern hemisphere.On average, there is no evidence of anisotropy of these eddies. Their average shape is well represented as Gaussian within the central 2/3 of the eddy, but the implied radius of maximum rotational speed is 64% smaller than the observed radius of maximum speed. In part because of this mismatch between the radii of maximum axial speed in the observations and the Gaussian approximation, a case is made that a quadratic function that is a very close approximation of the mode profile of the eddy (i.e., the most frequently occurring value at each radius) is a better representation of the composite shape of the eddies. This would imply that the relative vorticity is nearly constant within the interiors of most eddies, i.e., the fluid motion consists approximately of solid-body rotation.Perhaps the most significant conclusion of this study is that essentially all of the observed mesoscale features outside of the tropical band 20°S-20°N are nonlinear by the metric U/c, where U is the maximum circum-average geostrophic speed within the eddy interior and c is the translation speed of the eddy. A value of U/c > 1 implies that there is trapped fluid within the eddy interior. Many of the extratropical eddies are highly nonlinear, with 48% having U/c > 5 and 21% having U/c > 10. Even in the tropics, approximately 90% of the observed mesoscale features are nonlinear by this measure.Two other nondimensional parameters also indicate strong degrees of nonlinearity in the tracked eddies. The distributions of all three measures of nonlinearity are more skewed toward large values for cyclonic eddies than for anticyclonic eddies in the southern hemisphere extratropics but the opposite is found in the northern hemisphere extratropics. There is thus a preference for highly nonlinear extratropical eddies to be cyclonic in the southern hemisphere but anticyclonic in the northern hemisphere.Further evidence in support of the interpretation of the observed features as nonlinear eddies is the fact that they propagate nearly due west with small opposing meridional deflections of cyclones and anticyclones (poleward and equatorward, respectively) and with propagation speeds that are nearly equal to the long baroclinic Rossby wave phase speed. These characteristics are consistent with theoretical expectations for large, nonlinear eddies. While there is no apparent dependence of propagation speed on eddy polarity, the eddy speeds relative to the local long Rossby wave phase speeds are found to be about 20% faster in the southern hemisphere than in the northern hemisphere. The distributions of the propagation directions of cyclones and anticyclones are essentially the same, except mirrored about a central azimuth angle of about 1.5° equatorward. This small, but we believe statistically significant, equatorward rotation of the central azimuth may be evidence of the effects of ambient currents (meridional advection or the effects of vertical shear on the potential vorticity gradient vector) on the propagation directions of the eddies.While the results presented here are persuasive evidence that most of the observed westward-propagating SSH variability consists of isolated nonlinear mesoscale eddies, it is shown that the eddy propagation speeds are about 25% slower than the westward propagation speeds of features in the SSH field that have scales larger than those of the tracked eddies. This scale dependence of the propagation speed may be evidence for the existence of dispersion and the presence of features that obey linear Rossby wave dynamics and have larger scales and faster propagation speeds than the nonlinear eddies. The amplitudes of these larger-scale signals are evidently smaller than those of the mesoscale eddy field since they are not easily isolated from the energetic nonlinear eddies. 相似文献
5.
内孤立波具有振幅尺度大、能量集中的特点,其引起流场和密度场的迅速变化可能对海洋工程结构物以及水下潜体造成严重威胁。因此研究不同造波条件下生成的内孤立波运动的流场特征具有重要的学术意义和实际应用价值。采用直接数值模拟方法和给定的初始密度场密度跃迁函数,对重力塌陷激发内孤立波的运动过程进行研究,探讨了不同造波条件下,激发产生的内孤立波波型、涡度、振幅和水平速度等流场特征。结果表明:(1)直接模拟数值方法能够模拟内孤立波传播过程中的密度界面波型反转现象;(2)从定性和定量的角度,证实了不稳定内孤立波传播过程中存在能量的向后传递;(3)对于相同的台阶深度(水闸两侧初始密度界面的高度差),初始涡流保持相同,但是随着上下层水深比的减小,其强度下降显著;(4)台阶深度对初始涡流的垂直结构的影响要大于上下层水深比,且台阶深度对内孤立波的振幅、水平速度的影响显著。 相似文献
6.
Mesoscale eddies, which are mainly caused by baroclinic effects in the ocean, are common oceanic phenomena in the Northwest Pacific Ocean and play very important roles in ocean circulation, ocean dynamics and material energy transport. The temperature structure of mesoscale eddies will lead to variations in oceanic baroclinity, which can be reflected in the sea level anomaly (SLA). Deep learning can automatically extract different features of data at multiple levels without human intervention, and find the hidden relations of data. Therefore, combining satellite SLA data with deep learning is a good way to invert the temperature structure inside eddies. This paper proposes a deep learning algorithm, eddy convolution neural network (ECN), which can train the relationship between mesoscale eddy temperature anomalies and sea level anomalies (SLAs), relying on the powerful feature extraction and learning abilities of convolutional neural networks. After obtaining the temperature structure model through ECN, according to climatic temperature data, the temperature structure of mesoscale eddies in the Northwest Pacific is retrieved with a spatial resolution of 0.25° at depths of 0–1 000 m. The overall accuracy of the ECN temperature structure is verified using Argo profiles at the locations of cyclonic and anticyclonic eddies during 2015–2016. Taking 10% error as the acceptable threshold of accuracy, 89.64% and 87.25% of the cyclonic and anticyclonic eddy temperature structures obtained by ECN met the threshold, respectively. 相似文献
7.
为获取南海北部陆坡海区第一模态内孤立波的动力结构及时间变化特征,本文利用该海区1套内孤立波浮标观测数据,对陆坡海区的内孤立波现场观测数据分析,识别判定了2021年5月5日至6月3日共30 d的179次第1模态内孤立波过程,并进行了内孤立波的特征分析。南海北部陆坡海区第1模态内孤立波剖面流场为双层结构,上层主要为西偏北向流动,下层流向与之相背,流速转向发生在100～150 m深度处。内孤立波期间,最大流速多发生于上层,流速为60～120 cm/s,底层流增强,上层流与下层流流向相反。受内潮影响,研究区域内孤立波存在半日和全日2个周期,主要以20～30 min间隔的波列形式向西偏北方向传播。本文关于南海北部陆坡海区第一模态内孤立波的分析研究有助于提升对该海区内孤立波时空变化特征的认识,为工程水下施工提供参考和依据。 相似文献
8.
Path Transition of the Kuroshio Due to Mesoscale Eddies: A Two-Layer, Wind-Driven Experiment 总被引：1，自引：0，他引：1
We have executed numerical experiments using a two-layer, wind-driven ocean model with simplified coastal geometry and bottom
topography to investigate the possibility of the Kuroshio path transition due to mesoscale eddies. A straight path easily
changes into a meandering path due to the eddy action. For this transition, an anticyclonic eddy is preferable to a cyclonic
one when imposed in the beginning region of the Kuroshio (east of Taiwan). When imposed southeast of Kyushu, on the other
hand, a cyclonic eddy is more effective than an anticyclonic one. The reverse transition, from a meandering to a straight
path, did not occur at all in this experiment.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
9.
Wenjin Sun Jingsong Yang Wei Tan Yu Liu Baojun Zhao Yijun He Changming Dong 《海洋学报(英文版)》2021,40(10):1-2
The spatial distribution of eddy diffusivity, basic characteristics of coherent mesoscale eddies and their relationship are analyzed from numerical model outputs in the Southern Ocean. Mesoscale fluctuation information is obtained by a temporal-spatial filtering method, and the eddy diffusivity is calculated using a linear regression analysis between isoneutral thickness flux and large-scale isoneutral thickness gradient. The eddy diffusivity is on the order of O (103 m2/s) with a significant spatial variation, and it is larger in the area with strong coherent mesoscale eddy activity. The mesoscale eddies are mainly located in the upper ocean layer, with the average intensity no larger than 0.2. The mean radius of the coherent mesoscale cyclonic (anticyclonic) eddy gradually decays from (121.2±10.4) km ((117.8±9.6) km) at 30°S to (43.9±5.3) km ((44.7±4.9) km) at 65°S. Their vertical penetration depths (lifespans) are deeper (longer) between the northern side of the Subpolar Antarctic Front and 48°S. The normalized eddy diffusivity and coherent mesoscale eddy activity show a significant positive correlation, indicating that coherent mesoscale eddy plays an important role in eddy diffusivity. 相似文献
10.
为研究内孤立波的地形和背景流共振机制,用地形和背景流共振机制计算了3个潜标观测的内孤立波(不同模态、不同波长)的流速和传播速度,并与观测到的内孤立波进行比较。潜标观测的第一模态内孤立波(波长分别为6.4和3.3km)都是下凹型内孤立波,2个内孤立波的传播速度约为1.4m/s、最大振幅约为48m,水平流向结构都是上层西北向、下层东南向,波长3.3km 的内孤立波波峰前后有更明显的下降流和上升流。用共振机制计算出的第一模态和第二模态纬向流速的垂向结构与观测相同,最大纬向流速出现的深度与观测一致,分别相差5和12m。用共振机制计算出的内孤立波传播速度与用 KdV 方程计算的传播速度相当,共振机制计算波速为0.66~1.21m/s,KdV 方程计算波速为0.79~1.40m/s。 相似文献
11.
Eddy activity in the lee of the Hawaiian Islands 总被引：2，自引：0，他引：2
Paulo H.R. Calil Kelvin J. Richards Yanli Jia Robert R. Bidigare 《Deep Sea Research Part II: Topical Studies in Oceanography》2008,55(10-13):1179
Persistent northeasterly trade winds have a substantial impact on the oceanic circulation around the Hawaiian Islands. A regional ocean model is applied to understand the effect of different temporal and spatial resolutions of surface momentum forcing on the formation of strong mesoscale vortices and on the simulation of realistic levels of eddy kinetic energy. The higher spatial and temporal resolutions of wind forcing is shown to substantially affect the vorticity and deformation field in the immediate lee of the Hawaiian Islands and produce patterns of eddy kinetic energy similar to observations. This suggests that the surface eddy field in the region is mostly dominated by the local surface momentum forcing. Mesoscale cyclones and anticyclones formed in the lee of the Island of Hawaii are shown to have different propagation patterns. Mesoscale cyclones are more confined to the lee and are hence subject to interactions with the strong wind forcing and deformation field as well as smaller vortices formed in the wake of the other islands. Mesoscale anticyclones show not only a tendency to propagate further westward, but also to persist as coherent features as they propagate, even at relatively lower values of relative vorticity. The large strain rates that affect the propagation of the cyclones cause them to break down into filaments of positive vorticity. Rossby numbers of O(1) within vortices and filaments indicate that nonlinear interactions between the wind stress and the vertical component of the relative vorticity field is potentially important in producing large vertical velocities. Modeled cyclonic eddies show a good resemblance to observations both in terms of vertical structure and propagation patterns. 相似文献
12.
孟加拉湾内和湾口附近有丰富的中尺度现象,本文利用2.0版可分辨低纬地区中尺度涡的Chelton数据集,通过溯源的方法得到中尺度涡的源地分布。苏门答腊岛西北海域(以5°N,94°E为核心的区域)是中尺度涡重要源区之一。通过拉格朗日方法的涡旋追踪表明,1993—2017年该海域(3°N—6°N、92°E—95°E),分别有57个气旋式和40个反气旋式中尺度涡。频谱分析显示海表面高度异常存在180 d和360 d两个显著周期。地形和风场的共同作用是该海域产生中尺度涡的动力机制：沿5°N西传的罗斯贝波在海岭地形的作用下触发了中尺度涡的生成;赤道风场是源区重要的能量来源,局地风场能诱发中尺度涡的极性。本研究也揭示了以往文献虽刻画了苏门答腊岛西北部海域为高涡动能区,却没有识别出较多中尺度涡的原因。 相似文献
13.
海洋是多尺度强迫-耗散系统,机械能主要在大尺度输入,在小尺度耗散。在大、中尺度运动的能量向小尺度湍流传递过程中,内波扮演着重要角色。内波的生成和破碎可打破海洋动力平衡,而在陆架区,内波（主要是内孤立波）的浅化演变与耗散则是驱动湍流混合的关键过程。通过长期的理论、观测与数值模拟研究,目前已认识到内波浅化过程中主要发生如下演变：波形调制、极性转变、裂变、破碎与耗散。相较于直接发生破碎,浅化演变过程中的裂变及其引发的剪切不稳定和对流不稳定是内孤立波在陆架区的主要耗散机制,显著调制陆架区的跃层混合。从能量串级的角度讲,内孤立波浅化裂变为动力不稳定的高频内波是潮能串级的重要通道。本文简要回顾南海北部陆架区内波的研究历史,并着重总结内波在陆架区演变与耗散机制的研究进展。 相似文献
14.
Numerical study on the interactions between a mesoscale eddy and a western boundary current 总被引：4，自引：3，他引：1
A reduced-gravity primitive equation eddy resolving model has been used to study the decay of a mesoscale eddy as it migrates
toward a western boundary current (WBC) region. The model results indicated that the gradient of the relative vorticity to
the east of the WBC is an important factor in the interaction between an eddy and a WBC. A circular eddy is deformed into
an elliptical form during the eddy–WBC interaction with the major axis of a cyclonic/anticyclonic eddy aligning in the NW/NNE
direction, respectively. Because of the difference in the major axes orientations for the cyclonic and anticyclonic eddies,
the kinetic energy transfer between a WBC and a particular eddy has very different behavior. A cyclonic eddy loses its energy
to the mean field, whereas an anticyclonic eddy can obtain energy from the mean flow during the WBC–eddy interaction. An anticyclonic
eddy, however, still decayed from losing its water and friction dissipation during the interaction period. 相似文献
15.
On the basis of the time series observations from a temperature chain and an acoustic Doppler current profiler on the continental shelf of the northern South China Sea, a sequence of internal solitary waves （ISWs） and background waves （BWs, including internal tides and near-inertial waves） on the continental shelf were captured simultaneously after the transit of Typhoon Neast in October 2011. These measurementsprovided a unique opportunity to explore the influence of BWs on the ISWs. The BWs appeared a conversion on the current strength and vertical mode structure during the observational period. The BWs were dominated by weak and mode-one waves before October 2 and then turned to strong and high-mode waves after that time. Meanwhile, the ISWs displayed different wave structures before and after October 2, which was closely related to BWs＇ changes. According to the current profiles of BWs, the high-mode wave structure with strong current could significantly strengthen the vertical shear of ISWs in the near-surface layer and promote the breaking of ISWs, and thus it may play an important role in affecting the background current condition. 相似文献
16.
Using AVISO satellite altimeter observations during 1993–2015 and a manual eddy detection method, a total of 276 anticyclonic rings and 242 cyclonic rings shed from the Kuroshio Extension(KE) were identified, and their three-dimensional(3D) anomaly structures were further reconstructd based on the Argo float data and the Japan Agency for Marine-Earth Science and Technology(JAMSTEC) cruise and buoy data through an interpolation method. It is found that the cyclonic(anticyclonic) rings presented consistent negative(positive) anomalies of potential temperature;meanwhile the relevant maximum anomaly center became increasingly shallow for the cyclonic rings whereas it went deeper for the anticyclonic rings as the potential temperature anomaly decreased from the west to the east. The above deepening or shoaling trend is associated with the zonal change of the depth of the main thermocline. Moreover, the composite cold ring between 140° and 150°E was found to exhibit a double-core vertical structure due to the existence of mode water with low potential vorticity. Specifically, a relatively large negative(positive) salinity anomaly and a small positive(negative) one appeared for the composite cyclonic(anticyclonic) ring at the depth above and below 600 m, respectively. The underlying driving force for the temperature and salinity anomaly of the composite rings was also attempted, which varies depending on the intensity of the background current and the temperature and salinity fields in different areas of the KE region, and the rings’ influences on the temperature and salinity could reach deeper than 1 000 m on average. 相似文献
17.
Oceanic Odyssey of a satellite-tracked drifter: North Pacific variability delineated by a single drifter trajectory 总被引：2，自引：0，他引：2
Richard E. Thomson Paul H. LeBlond Alexander B. Rabinovich 《Journal of Oceanography》1997,53(1):81-87
A near-surface satellite-tracked drifter launched off the east coast of the Kuril Islands on September 4,1993 began a 2.5-year
Odyssey across the North Pacific Ocean. During its travels, the drifter encountered numerous energetic oceanographic regimes
as it moved from the region of the Kuril-Kamchatka Trench to the continental margin of the Kuril Islands, through Friza Strait
into the Sea of Okhotsk, seaward again through Bussol’ Strait, and then eastward across the North Pacific. Oceanic features
detected along the basin-wide trajectory include a quasi-permanent anticyclonic eddy over the Kuril-Kamchatka Trench, open-ocean
wind-driven inertial oscillations, coastal-trapped diurnal shelf waves, semidiurnal tidal currents, transient cyclonic and
anticyclonic eddies, through-strait flows, and wave-like mesoscale meanders. The single drifter track delineates the dynamically-rich
variability of upper ocean currents, emphasizes the marked difference in flow dynamics between boundary and open ocean regions,
and provides a time-scale for the movement of surface waters across the entire North Pacific. 相似文献
18.
Shenn-Yu Chao Ping-Tung Shaw Ming-Kuang Hsu Ying-Jang Yang 《Journal of Oceanography》2006,62(6):811-823
We have investigated the reflection and diffraction of first-mode and second-mode solitary waves by an island, using a three-dimensional
nonhydrostatic numerical model. The model domain consists of a circular island 15 km in diameter in an ocean 300 m deep. We
use prescribed density anomalies in an initially motionless ocean to produce highly energetic internal solitary waves; their
subsequent propagation is subject to island perturbations with and without the effect of earth’s rotation. In addition to
reflected waves, two wave branches pass around the island and reconnect behind it. Island perturbations to the first-mode
and second-mode waves are qualitatively similar, but the latter is more profound because of the longer contact time and, in
the presence of earth’s rotation, the scale compatibility between Rossby radius of the second baroclinic mode and the island
diameter. Without earth’s rotation, reflected and diffracted waves are symmetrical relative to the longitudinal axis passing
through the island center. With earth’s rotation, the current following the wave front veers to the right due to Coriolis
deflection. For a westward propagating incoming wave, the deflection favors northward wave propagation in the region between
the crossover point and the island, shifting the wave reconnection point behind the island northward. It also displaces the
most visible part of the reflected waves to the southeast. In the presence of earth’s rotation, a second-mode incoming wave
produces island-trapped internal Kelvin waves, which are visible after the passage of the wave front. 相似文献
19.
The propagation,shoaling and breaking of solitary waves on mild slopes are simulated byboundary element method.In this paper,the criterion of breaking solitary waves on mild slopes is discussed.The criterion is that the ratio of horizontal velocity of water particles on the wave crest to wave celerity equalsone.However,the case that the ratio of horizontal velocity of water particles on the wave crest to wave ce-lerity is below one but the front face of wave profile becomes vertical is also considered as a breaking criteri-on.According to the above criteria,the breaking index for slopes 1:10 to 1:25 is studied.The result is com-pared to other researchers'.The deformation of solitary waves on slopes is discussed and the distribution offluid velocities at breaking is shown. 相似文献
20.
Inertial oscillations as deep ocean response to hurricanes 总被引：1，自引：0，他引：1
We discuss the deep ocean response to passing hurricanes (aka typhoons), which are considered as generators of near-inertial, internal waves. The analysis of data collected in the northwestern
parts of the Pacific and Atlantic oceans in the hurricane season permit us to assess the deep ocean response to such a strong
atmospheric forcing. A large number of moorings (more than 100) in the northwestern Pacific have allowed us to characterize
the spatial features of the oceanic response to typhoons and the variable downward velocity of near-inertial wave propagation.
The velocity of their downward propagation varies in the range 1–10 m/hour. It is higher in the regions of low stratification
and high anticyclonic vorticity. The inertial oscillations generated by a hurricane last for 10–12 days. The mean anticyclonic
vorticity in the region increases the effective frequency of inertial oscillations by 0.001–0.004 cyc/hour. 相似文献