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1.
根据对卫星观测的海平面高度资料的分析，进一步证实了在北太平洋副热带两支向东的流（副热带逆流和夏威夷背风逆流）所在的区域内，海平面高度的70～210天周期振荡是主要的低频变化.发现在这两支向东的逆流区Rossby波的特性不同：副热带逆流区70～210天周期振荡对应的Rossby波西传过程中增幅，在台湾以东振幅达到最大；而在夏威夷背风逆流区，70～210天周期Rossby波在西传过程中不出现增幅现象.依据25层海洋模式得到的关于Rossby波振幅、频率与海洋层结之间的关系，揭示了周期为70～210天的Rossby波为不稳定波，这是由于副热带逆流海域模态水存在使得密度的垂直梯度变小的缘故；而在夏威夷背风逆流区位于表层逆流下的北赤道流西深东浅，70～210天周期Rossby长波在逆流的东部有可能不稳定，但其在逆流的西部是稳定的，因此不出现在西传过程中增幅现象；发现在北太平洋副热带两个向东流的海域，年周期Rossby波是稳定的，因此，在该海域海平面周期为70～210天的振荡的振幅要比年周期振荡的振幅大.  相似文献   

2.
北太平洋海表面高度的年际变化及其机制   总被引：4，自引：0，他引：4       下载免费PDF全文
利用15年（1993～2007年）月平均的海表面高度（SSH）异常资料,分析了北太平洋海表面高度的年际变化的时空结构,并研究了热通量和风应力两个因子对其的强迫作用.结果表明,北太平洋年际时间尺度SSH变化的大值区在黑潮延伸区和西太平洋暖池区.EOF分解第一模态的空间结构沿纬向呈带状分布,第二模态为沿经向呈带状分布.热通量强迫作用在中纬度的东北太平洋可以解释SSH年际变化40%以上.风应力对SSH的作用包括正压和斜压两个方面.正压Sverdrup平衡模型模拟的SSH年际变化较弱,仅能解释高纬度副极地环流西部的20%~40%.由大尺度风应力强迫的第一阶斜压Rossby波模型可以解释热带地区的20%~60%,中纬度中部的20%~40%,以及阿拉斯加环流东部和副极地环流西部的20%~60%.风应力强迫的一阶斜压Rossby波模型对SSH的强迫机理又可分为局地风应力强迫和西传Rossby波作用.其中,风应力的局地强迫作用（Ekman抽吸）在东北太平洋、白令海以及热带中部有显著的预报技巧,可以解释SSH年际变异的40%以上.Rossby波的传播作用在中纬度海域的副热带环流中西部和夏威夷岛以东起着重要作用,可解释20%~60%.  相似文献   

3.
Based on the merged satellite altimeter data and in-situ observations,as well as a diagnosis of linear baroclinic Rossby wave solutions,this study analyzed the rapidly rise of sea level/sea surface height(SSH)in the tropical Pacific and Indian Oceans during recent two decades.Results show that the sea level rise signals in the tropical west Pacific and the southeast Indian Ocean are closely linked to each other through the pathways of oceanic waveguide within the Indonesian Seas in the form of thermocline adjustment.The sea level changes in the southeast Indian Ocean are strongly influenced by the low-frequency westward-propagating waves originated in the tropical Pacific,whereas those in the southwest Indian Ocean respond mainly to the local wind forcing.Analyses of the lead-lag correlation further reveal the different origins of interannual and interdecadal variabilities in the tropical Pacific.The interannual wave signals are dominated by the wind variability along the equatorial Pacific,which is associated with the El Ni?o-Southern Oscillation;whereas the interdecadal signals are driven mainly by the wind curl off the equatorial Pacific,which is closely related to the Pacific Decadal Oscillation.  相似文献   

4.
The linear theory predicts that Rossby waves are the large scale mechanism of adjustment to perturbations of the geophysical fluid. Satellite measurements of sea level anomaly (SLA) provided sturdy evidence of the existence of these waves. Recent studies suggest that the variability in the altimeter records is mostly due to mesoscale nonlinear eddies and challenges the original interpretation of westward propagating features as Rossby waves. The objective of this work is to test whether a classic linear dynamic model is a reasonable explanation for the observed SLA. A linear-reduced gravity non-dispersive Rossby wave model is used to estimate the SLA forced by direct and remote wind stress. Correlations between model results and observations are up to 0.88. The best agreement is in the tropical region of all ocean basins. These correlations decrease towards insignificance in mid-latitudes. The relative contributions of eastern boundary (remote) forcing and local wind forcing in the generation of Rossby waves are also estimated and suggest that the main wave forming mechanism is the remote forcing. Results suggest that linear long baroclinic Rossby wave dynamics explain a significant part of the SLA annual variability at least in the tropical oceans.  相似文献   

5.
The tropical Indian Ocean circulation system includes the equatorial and near-equatorial circulations, the marginal sea circulation, and eddies. The dynamic processes of these circulation systems show significant multi-scale variability associated with the Indian Monsoon and the Indian Ocean dipole. This paper summarizes the research progress over recent years on the tropical Indian Ocean circulation system based on the large-scale hydrological observations and numerical simulations by the South China Sea Institute of Oceanology(SCSIO), Chinese Academy of Sciences. Results show that:(1) the wind-driven Kelvin and Rossby waves and eastern boundary-reflected Rossby waves regulate the formation and evolution of the Equatorial Undercurrent and the Equatorial Intermediate Current;(2) the equatorial wind-driven dynamics are the main factor controlling the inter-annual variability of the thermocline in the eastern Indian Ocean upwelling;(3) the equatorial waves transport large amounts of energy into the Bay of Bengal in forms of coastal Kelvin and reflected free Rossby waves. Several unresolved issues within the tropical Indian Ocean are discussed:(i) the potential effects of the momentum balance and the basin resonance on the variability of the equatorial circulation system, and(ii) the potential contribution of wind-driven dynamics to the life cycle of the eastern Indian Ocean upwelling. This paper also briefly introduces the international Indian Ocean investigation project of the SCSIO, which will advance the study of the multi-scale variability of the tropical Indian Ocean circulation system, and provide a theoretical and data basis to support marine environmental security for the countries around the Maritime Silk Road.  相似文献   

6.
The mechanism of the effects of the upwelling mean on the ENSO event mature phase locking is ex-amined by using a mixed-mode model. The results show that the positive feedback process of the ef-fects of the seasonal variation of the upwelling mean on the Kelvin wave is the mechanism of the locking of the event mature phase to the end of the calendar year. The memory of the Rossby waves for the sign-shifting of the sea surface temperature anomaly from positive to negative 6 months before the cold peak time is the other mechanism of the locking of the La Nia event mature phase to the end of the calendar year. The results here are different from previous ones which suggest that the balance between cold and warm trends of sea surface temperature anomaly is the mechanism involved. The cold trend is caused by the upwelling Kelvin wave from upwelling Rossby wave reflected at the western boundary, excited by the westerly anomaly stress over the central Pacific and amplified by the seasonal variation of the coupled strength in its way propagating westward. The warm trend is caused by the Kelvin wave forced by the western wind stress over the middle and eastern equatorial Pacific. The cause of the differences is due to the opposite phase of the seasonal variation of the upwelling mean to that in the observation and an improper parameterization scheme for the effects of the seasonal varia-tion of the upwelling mean on the ENSO cycle in previous studies.  相似文献   

7.
The interannual variability of the tropical Indian Ocean is studied using Simple Ocean Data Assimilation (SODA) sea surface height anomalies (SSHA) and Hadley Centre Ice Sea Surface Temperature anomalies. Biannual Rossby waves (BRW) were observed along the 1.5° S and 10.5° S latitudes during the Indian Ocean Dipole (IOD) years. The SODA SSHA and its BRW components were comparable with those of Topex/Poseidon. The phase speed of BRW along 1.5° S is −28 cm/s, which is comparable with the theoretical speed of first mode baroclinic (equatorially trapped) Rossby waves. This is the first study to show that no such propagation is seen along 1.5° S during El Nino years in the absence of IOD. Thus the westward propagating downwelling BRW in the equatorial Indian Ocean is hypothesized as a potential predictor for IOD. These waves transport heat from the eastern equatorial Indian Ocean to west, long before the dipole formation. Along 10.5° S, the BRW formation mechanisms during the El Nino and IOD years were found to be different. The eastern boundary variations along 10.5° S, being localized, do not influence the ocean interior considerably. Major portion of the interannual variability of the thermocline, is caused by the Ekman pumping integrated along the characteristic lines of Rossby waves. The study provides evidence of internal dynamics in the IOD formation. The positive trend in the downwelling BRW (both in SODA and Topex/Poseidon) is of great concern, as it contributes to the Indian Ocean warming.  相似文献   

8.
Abstract

The mutual interaction of fields induced by spatially separated potential vorticity sources in a quasi-geostrophic barotropic flow is investigated using the weakly nonlinear approach. It is found that a powerful nonlinear response can be triggered by Rossby lee waves. This resonance phenomenon which dominates all other nonlinear corrections depends on certain global resonance conditions and on the change in the phase of the Rossby lee wave across the distance separating the sources. The response is particularly strong for topographic forcing possessing δ-function characterisitics.  相似文献   

9.
A wave–tide–circulation coupled model based on Princeton Ocean Model is established to study the seasonal circulation in the Malay Peninsula Eastern Continental Shelf region. The model successfully reconstructs the observed seasonal variation of the circulation in the region, as well as the main currents. The simulated tidal harmonic constants, sea surface temperature, and sea surface height anomaly agree with the observations well. The model results show that the upper-layer circulation in the region is mainly controlled by the monsoon winds, while there are two transitions in spring and fall. An anti-cyclonic eddy is present off the Peninsular Malaysia’s east coast in summer, centered at 5°N and 105.5°E, both in the TOPEX/Poseidon data and in the model. Numerical experiments show that the wind stress curl and bathymetry steering are responsible for its formation.  相似文献   

10.
Observational studies on the semiannual oscillation in the tropical stratosphere and mesosphere are reviewed. Results of many statistics based on rocket and satellite observations reveal that the long-term behavior of the mean zonal wind exhibits two semiannual cycles which have their maximum amplitudes centered at the stratopause level and the mesopause level, each one being associated with the semiannual temperature variations predominating at levels about 10 km lower.Observational evidence obtained from recent studies of the dynamical properties of upper stratospheric waves strongly supports the theoretical consideration that the stratospheric semiannual oscillation is the manifestation of the wave-zonal flow interaction with alternating accelerations of the westerly flow by Kelvin waves and the easterly flow by planetary Rossby waves.Regarding the semiannual variation in the upper mesosphere, however, very little is known about the possible momentum source. Therefore, emphasis is placed on the need for further observations of the structure and behavior of the tropical middle atmosphere.  相似文献   

11.
Chen  Huan-Huan  Qi  Yiquan  Wang  Yuntao  Chai  Fei 《Ocean Dynamics》2019,69(11):1387-1399

Fourteen years (September 2002 to August 2016) of high-resolution satellite observations of sea surface temperature (SST) data are used to describe the frontal pattern and frontogenesis on the southeastern continental shelf of Brazil. The daily SST fronts are obtained using an edge-detection algorithm, and the monthly frontal probability (FP) is subsequently calculated. High SST FPs are mainly distributed along the coast and decrease with distance from the coastline. The results from empirical orthogonal function (EOF) decompositions reveal strong seasonal variability of the coastal SST FP with maximum (minimum) in the astral summer (winter). Wind plays an important role in driving the frontal activities, and high FPs are accompanied by strong alongshore wind stress and wind stress curl. This is particularly true during the summer, when the total transport induced by the alongshore component of upwelling-favorable winds and the wind stress curl reaches the annual maximum. The fronts are influenced by multiple factors other than wind forcing, such as the orientation of the coastline, the seafloor topography, and the meandering of the Brazil Current. As a result, there is a slight difference between the seasonality of the SST fronts and the wind, and their relationship was varying with spatial locations. The impact of the air-sea interaction is further investigated in the frontal zone, and large coupling coefficients are found between the crosswind (downwind) SST gradients and the wind stress curl (divergence). The analysis of the SST fronts and wind leads to a better understanding of the dynamics and frontogenesis off the southeastern continental shelf of Brazil, and the results can be used to further understand the air-sea coupling process at regional level.

  相似文献   

12.
The sensitivity of the bifurcation of the North Equatorial Current in the Pacific to different wind products is investigated. Variations of the bifurcation latitude with season is simulated in a purely wind-driven model and is found to be in agreement with recent observations. The seasonal cycle is nearly independent of the wind climatology, but the annual average latitude depends on the wind stress curl. It is also shown that in the upper ocean, the poleward shift in bifurcation latitude with depth is realistic in our simple model. This implies that given a stratification close to the observed, it is primarily the wind forcing that determines the location of the bifurcation and its seasonal variation.  相似文献   

13.
The characteristics and forcing mechanisms of high-frequency flow variations (periods of minutes to days) were investigated near Gladden Spit, a reef promontory off the coast of Belize. Direct field observations and a high-resolution (50-m grid size) numerical ocean model are used to describe the flow variations that impact the initial dispersion of eggs and larvae from this site, which serves as a spawning aggregation site for many species of reef fishes. Idealized sensitivity model experiments isolate the role of various processes, such as internal waves, wind, tides, and large-scale flow variations. The acute horizontal curvature and steep topography of the reef intensify the flow, create small-scale convergence and divergence zones, and excite high-frequency oscillations and internal waves. Although the tides in this area are relatively small (∼10-cm amplitude), the model simulations show that tides can excite significant high-frequency flow variations near the reef, which suggests that the preference of fish to aggregate and spawn in the days following the time of full moon may not be coincidental. Even small variations in remote flows (2–5 cm s−1) due to say, meso-scale eddies, are enough to excite near-reef oscillations. Model simulations and the observations further suggest that the spawning site at the tip of the reef provides initial strong dispersion for eggs, but then the combined influence of the along-isobath flow and the westward wind will transport the eggs and larvae downstream of Gladden Spit toward less turbulent region, which may contribute to enhanced larval survival.  相似文献   

14.
The aim of this study is to intervalidate observations and numerical simulation results for the turbulent dissipation rate under strong wind conditions in the Northern North Sea during one week in October 1998. The observations were obtained by spatially and temporally averaging measurements of small-scale shear with a free-falling shear probe. The 1D numerical model used for this study is based on a state-of-the-art two-equation k− turbulence model with an algebraic second-moment closure scheme. It is discussed by means of annual and seasonal model simulations how the influence of heat and salt advection and internal waves can be accounted for. After these precautions, the agreement between observations and simulations of the turbulent dissipation rate are fairly good. Remaining differences cannot only be explained by problems such as undersampling and noise level, but also by idealising model assumptions.  相似文献   

15.
A three-dimensional baroclinic nonlinear numerical model is employed to investigate the summer upwelling in the northern continental shelf of the South China Sea (NCSCS) and the mechanisms of the local winds inducing the coastal upwelling, associated with the QuikSCAT wind data. First, the persistent signals of the summer upwelling are illustrated by the climatological the Advanced Very High-Resolution Radiometer (AVHRR) Sea Surface Temperature (SST) image over 1985–2006 and field observations in 2006 summer. Then, after the successful simulation of the summer upwelling in the NCSCS, four numerical experiments are conducted to explore the different effects of local winds, including the wind stress and wind stress curl, on the coastal upwelling in two typical strong summer upwelling regions of the NCSCS. The modeled results indicate that the summer upwelling is a seasonal common phenomenon during June–September in the NCSCS with the spatial extent of a basin-scale. Typical continental shelf upwelling characteristics are clearly shown in the coastal surface and subsurface water, such as low temperature, high salinity and high potential density in the east of the Hainan Island, the east of the Leizhou Peninsula and the southeast of the Zhanjiang Bay (noted as the Qiongdong-QD), and the inshore areas from the Shantou Coast to the Nanri Islands of the Fujian Coast (noted as the Yuedong-YD). The analysis of the QuikSCAT wind data and modeled upwelling index suggests that the local winds play significant roles in causing the coastal upwelling, but the alongshore wind stress and wind stress curl have different contributions to the upwelling in the Qiongdong (QDU) and the coastal upwelling in the Yuedong (YDU), respectively. Furthermore, model results from the numerical experiments show that in the YD the stable alongshore wind stress is a very important dynamic factor to induce the coastal upwelling but the wind stress curl has little contribution and even unfavorable to the YDU. However, in the QD the coastal upwelling is strongly linked to the local wind stress curl. It is also found that not only the offshore Ekman transport driven by the alongshore wind stress, the wind stress curl-induced Ekman pumping also plays a crucial effect on the QDU. Generally, the wind stress curl even has more contributions to the QDU than the alongshore wind stress.  相似文献   

16.
Numerical model experiments have been performed to analyze the low-latitude baroclinic continental shelf response to a tropical cyclone. The theory of coastally trapped waves suggests that, provided appropriate slope, latitude, stratification and wind stress, bottom-intensified topographic Rossby waves can be generated by the storm. Based on a scale analysis, the Nicaragua Shelf is chosen to study propagating topographic waves excited by a storm, and a model domain is configured with simplified but similar geometry. The model is forced with wind stress representative of a hurricane translating slowly over the region at 6 km h−1. Scale analysis leads to the assumption that baroclinic Kelvin wave modes have minimal effect on the low-frequency wave motions along the slope, and coastal-trapped waves are restricted to topographic Rossby waves. Analysis of the simulated motions suggests that the shallow part of the continental slope is under the influence of barotropic topographic wave motions and at the deeper part of the slope baroclinic topographic Rossby waves dominate the low-frequency motions. Numerical solutions are in a good agreement with theoretical scale analysis. Characteristics of the simulated baroclinic waves are calculated based on linear theory of bottom-intensified topographic Rossby waves. Simulated waves have periods ranging from 153 to 203 h. The length scale of the waves is from 59 to 87 km. Analysis of energy fluxes for a fixed volume on the slope reveals predominantly along-isobath energy propagation in the direction of the group velocity of a topographic Rossby wave. Another model experiment forced with a faster translating hurricane demonstrates that fast moving tropical cyclones do not excite energetic baroclinic topographic Rossby waves. Instead, robust inertial oscillations are identified over the slope.  相似文献   

17.
Tal Ezer 《Ocean Dynamics》2017,67(5):651-664
Two aspects of the interactions between the Gulf Stream (GS) and the bottom topography are investigated: 1. the spatial variations associated with the north-south tilt of mean sea level along the US East Coast and 2. the high-frequency temporal variations of coastal sea level (CSL) that are related to Gulf Stream dynamics. A regional ocean circulation model is used to assess the role of topography; this is done by conducting numerical simulations of the GS with two different topographies–one case with a realistic topography and another case with an idealized smooth topography that neglects the details of the coastline and the very deep ocean. High-frequency oscillations (with a 5-day period) in the zonal wind and in the GS transport are imposed on the model; the source of the GS variability is either the Florida Current (FC) in the south or the Slope Current (SC) in the north. The results demonstrate that the abrupt change of topography at Cape Hatteras, near the point where the GS separates from the coast, amplifies the northward downward mean sea level tilt along the coast there. The results suggest that idealized or coarse resolution models that do not resolve the details of the coastline may underestimate the difference between the higher mean sea level in the South Atlantic Bight (SAB) and the lower mean sea level in the Mid-Atlantic Bight (MAB). Imposed variations in the model’s GS transport can generate coherent sea level variability along the coast, similar to the observations. However, when the bottom topography in the model is modified (or not well resolved), the shape of the coastline and the continental shelf influence the propagation of coastal-trapped waves and impact the CSL variability. The results can explain the different characteristics of sea level variability in the SAB and in the MAB and help understand unexpected water level anomalies and flooding related to remote influence of the GS.  相似文献   

18.
从低纬的海气耦合的浅水模式方程组出发 ,运用正交模和特殊函数的方法进一步讨论地球自转速率变化对海气耦合系统的影响 .研究表明 :地球自转速率的变化通过海气耦合一方面使大气和海洋的Kelvin波和Rossby波的移动及稳定性发生变化 ,另一方面使纬向风、洋流和海表温度发生变化 .特别是在地球自转减慢时 ,通过海气耦合 ,出现纬向风和洋流异常和大洋东部海表温度增加 ,从而导致引起全球气候异常的ElNi no现象  相似文献   

19.
The generation and further dynamics of the planetary magnetized Rossby waves and inertial waves in a dissipative ionosphere in the presence of a smooth inhomogeneous zonal wind (shear flow) have been studied. The magnetized Rossby waves are caused by the interaction with the spatially inhomogeneous geomagnetic field and represent the ionospheric manifestations of usual tropospheric Rossby waves. The effective linear mechanism of amplification and mutual transformation of the Rossby and inertial waves has been revealed. For shear flows, the operators of linear problems are not self-adjoint, and the corresponding eigenfunctions are non-orthogonal; therefore, a canonical modal approach is of little use in studying such motions. It becomes necessary to apply the so-called nonmodal mathematical analysis, which has actively been developed for the last years. The nonmodal approach makes it possible to reveal that the transformation of wave-like disturbances in shear flows is caused by the nonorthogonality of eigenfunctions in the problem of linear dynamics. Thus, there appear a new degree of the system freedom and a new way of disturbance evolution in the medium.  相似文献   

20.
Halifax Harbour is located on the Atlantic coast of Nova Scotia, Canada. It is one of the world’s largest, ice-free natural harbours and of great economic importance to the region. A good understanding of the physical processes controlling tides, flooding, transport and dispersion, and hydrographic variability is required for pollution control and sustainable development of the Harbour. For the first time, a multi-nested, finite difference coastal ocean circulation model is used to reconstruct the three-dimensional circulation and hydrography of the Harbour and its variability on timescales of hours to months for 2006. The model is driven by tides, wind and sea level pressure, air-sea fluxes of heat, and terrestrial buoyancy fluxes associated with river and sewage discharge. The predictive skill of the model is assessed by comparing the model simulations with independent observations of sea level from coastal tide gauges and currents from moored instruments. The simulated hydrography is also compared against a new monthly climatology created from all available temperature and salinity observations made in the Harbour over the last century. It is shown that the model can reproduce accurately the main features of the observed tides and storm surge, seasonal mean circulation and hydrography, and wind driven variations. The model is next used to examine the main physical processes controlling the circulation and hydrography of the Harbour. It is shown that non-linear interaction between tidal currents and complex topography occurs over the Narrows. The overall circulation can be characterized as a two-layer estuarine circulation with seaward flow in the thin upper layer and landward flow in the broad lower layer. An important component of this estuarine circulation is a relatively strong, vertically sheared jet situated over a narrow sill connecting the inner Harbour to the deep and relatively quiescent Bedford Basin. Local wind driven variability is strongest in winter as expected but it is also shown that a significant part of the temperature and salinity variability is driven by physical processes occurring on the adjacent inner continental shelf, especially during storm and coastal upwelling events.  相似文献   

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