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1.
This paper contains estimations of the spatial variability of the kinetic energy density in semidiurnal tidal waves of the lowest baroclinic mode in the North Equatorial Countercurrent region. We have noted an essential reduction in the energetic density of semi-diurnal waves at the north boundary of the North Equatorial Countercurrent and a build-up of energy in short-period internal waves. The hydrodynamic instability of baroclinic tidal waves may be regarded as the mechanism responsible for the frequency energy redistribution.Translated by Vladimir A. Puchkin.  相似文献   

2.
Mesoscale eddies and tropical instability waves in the eastern tropical Pacific, first revealed by satellite infrared imagery, play an important role in the dynamics and biology of the region, and in the transfer of mass, energy, heat, and biological constituents from the shelf to the deep ocean and across the equatorial currents.From boreal late autumn to early spring, four to 18 cyclonic or anticyclonic eddies are formed off the coastal region between southern Mexico and Panama. The anticyclonic gyres, which tend to be larger and last longer than the cyclonic ones, are the best studied: they typically are 180–500 km in diameter, depress the pycnocline from 60 to 145 m at the eddy center, have swirl speeds in excess of 1 m s−1, migrate west at velocities ranging from 11 to 19 cm s−1 (with a slight southward component), and maintain a height signature of up to 30 cm. The primary generating agents for these eddies are the strong, intermittent wind jets that blow across the isthmus of Tehuantepec in Mexico, the lake district in Nicaragua and Costa Rica, and the Panama canal. Other proposed eddy-generating mechanisms are the conservation of vorticity as the North Equatorial Counter Current (NECC) turns north on reaching America, and the instability of coastally trapped waves/currents.Tropical Instability Waves (TIWs) are perturbations in the SST fronts on either side of the equatorial cold tongue. They produce SST variations on the order of 1–2 °C, have periods of 20–40 days, wavelengths of 1000–2000 km, phase speeds of around 0.5 m s−1 and propagate westward both north and south of the Equator. The Tropical Instability Vortices (TIVs) are a train of westward-propagating anticyclonic eddies associated with the TIWs. They exhibit eddy currents exceeding 1.3 m s−1, a westward phase propagation speed between 30 and 40 km d−1, a signature above the pycnocline, and eastward energy propagation. Like the TIWs, they result from the latitudinal barotropically unstable shear between the South Equatorial Current (SEC) and the NECC with a potential secondary source of energy from baroclinic instability of the vertical shear with the Equatorial Undercurrent (EUC).This review of mesoscale processes is part of a comprehensive review of the oceanography of the eastern tropical Pacific Ocean.  相似文献   

3.
An anticyclonic eddy with a horizontal dimension of 20 km travelling north-westwards at a speed of 10 cm/s has been found during an experiment carried out off the Black Sea coast. Dynamic instability owing to horizontal velocity shear could be the reason for its origin. The eddy's passage favours the development of shear instability and the generation of short-period internal waves.Translated by Mikhail M. Trufanov.  相似文献   

4.
Phase velocity of semi-diurnal internal waves is determined from differences between phases at three stations which were situated to form a triangle in the vicinity of sta. T (29N, 135E). The wave phases are estimated from temporal variations in depths of isotherms obtained from serial measurements of vertical temperature profiles at these stations. The measurements were carried out in cooperative operation of two vessels, the R. V.Tansei-maru and theNojima, during the period from 30 July to 1 August 1965. Wave propagation with the speed of about 2 m/s in the direction from east to west is obtained as an average over several isotherms of temperature from 19C to 23C. The area of measurement is to the west of Izu-Mariana ridge and the distance from the ridge to the station is about 500 km, which would be about 5 times as large as the wave length of the internal waves under consideration, and so it is possible to suppose that the internal waves observed generated at the ridge and propagated to the area without being subjected to serious refraction, scattering, reflection and decay.  相似文献   

5.
By using the data of observations over the spatial variability of the temperature field in the northwest part of the Tropical Atlantic carried out in a test range 400 × 400 miles in size with a horizontal resolution Δx ≈ 2 km and a vertical resolution Δz ≈ 0.5 m, we recorded quasiperiodic fluctuations of temperature with semidiurnal period in the subsurface layer. The internal baroclinic waves with the same period generated, most likely, on the northeast shelf of South America and propagating to the northeast are detected in the seasonal thermocline. The vertical fine structure of the temperature field has different intensities in the test range. The maximum levels of dispersions of temperature fluctuations are recorded on the boundary of the North Equatorial Countercurrent and the North Equatorial Current. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 6, pp. 44–52, November–December, 2006.  相似文献   

6.
This paper describes the geotectonics of the Caspian Sea basin and the seismicity of its central part. The seismicity analysis enables us to identify the most probable zones of tsunami generation. We also present a brief review of the historical records of tsunamis in the Caspian Sea. In order to estimate the tsunami risk, we used the method of numerical hydrodynamic simulation while taking into account the real topography of the Caspian Sea. The computation of the wave field for the possible tsunamis occurring in the central part of the Caspian Sea allowed us to estimate the maximum expected heights of the waves along the coast of the CIS countries (Russia, Azerbaijan, Kazakhstan, and Turkmenistan). On the basis of the earthquake statistics in the region and the results of numerical experiments, we show that the extreme wave heights can reach 10 m at certain parts of the coast. Such extreme events correspond to extended (up to 200 km) seismic sources with M S ～ 8 and a recurrence period of T ≈ 1600 years. The tsunami wave heights are expected to be as high as 3 m for sources of lesser extent (<50 km) with earthquake magnitudes of M S ～ 7 and a recurrence period of 200 years.  相似文献   

7.
Unusual large-scale phytoplankton blooms in the equatorial Pacific   总被引：1，自引：0，他引：1  
Unusual large-scale accumulations of phytoplankton occurred across 10,000 km of the equatorial Pacific during the 1998 transition from El Niño to La Niña. The forcing and dynamics of these phytoplankton blooms were studied using satellite-based observations of sea surface height, temperature and chlorophyll, and mooring-based observations of winds, hydrography and ocean currents. During the bloom period, the thermocline (nutricline) was anomalously shallow across the equatorial Pacific. The relative importance of processes that enhanced nutrient flux into the euphotic zone differed between the western and eastern regions of the blooms. In the western bloom region, the important vertical processes were turbulent vertical mixing and wind-driven upwelling. In contrast, the important processes in the eastern bloom region were wave-forced shoaling of nutrient source waters directly into the euphotic zone, along-isopycnal upwelling, and wind-driven upwelling. Advection by the Equatorial Undercurrent spread the largest bloom 4500 km east of where it began, and advection by meridional currents of tropical instability waves transported the bloom hundreds of kilometers north and south of the equator. Many processes influenced the intricate development of these massive biological events. Diverse observations and novel analysis methods of this work advance the conceptual framework for understanding the complex dynamics and ecology of the equatorial Pacific.  相似文献   

8.
Behavior of warm water flowing into a model ocean with flat bottom filled with cold water is investigated numerically with a three-dimensional level model in a rotating system.The warm water which flows through the southern opening into the ocean is found to progress in two directions. The east front of the warm water progresses along the east coast and reaches the northern opening. And an eastern boundary current associated with this density structure is formed. The west front progresses along the west coast with the speed much less than that of the eastside front. However, the progression of the west front slows down remarkably half way between the southern and northern boundaries due to-effect, and a baroclinic western boundary current system is formed. Unstable waves whose scales are 200–400 km are found in the region of the eastern boundary current and propagate toward the west. These waves seem to be caused by the baroclinic instability.The boundary currents obtained in the present model are considered to represent some characteristics of the Tsushima Current system in the Japan Sea.  相似文献   

9.
热带非稳定波（ＴＩＷｓ）关于赤道的径向不对称是其突出特征之一。本文利用二层半线性海洋模式研究各种不对称背景条件对非稳定波不对称性的影响。结果表明，在大西洋和太平洋上热带非稳定波（ＴＩＷｓ）的不对称性似是由于南赤道流的两个分支和海面温度锋面对于赤道的不对称性，而不是由于北赤道逆流的出现。  相似文献   

10.
This paper describes GLORIA sidescan sonar data from a single swath along the Cocos-Nazca Spreading Centre between the 95.5° W propagating rift and the Pacific-Cocos-Nazca triple junction. Almost the whole of the plate boundary was imaged. Five medium sized offsets of the spreading centre, ranging from 10 to 25 km, were seen. Of these, at least one (at 99° W) is a previously unknown propagating rift, propagating westwards away from the Galapagos hotspot at about 40 mm a-1. Two other offsets have some, but not all, of the characteristics of propagating rifts, and may be poorly developed (possibly duelling) propagating rifts or migrating overlapping spreading centres. In each case the apparent propagation rate is between one and two times the half spreading rate. The average length of ridge segments in this region is 70 km, but lengths range from 12 to 135 km. The longest segments are those immediately behind actively propagating ridge offsets. The overall plan shape of the ridge axis is roughly sinusoidal, with a wavelength of 400–500 km and an amplitude of ±20 km. This nonlinear shape has arisen since the spreading centre was created, and may reflect an instability in the mantle plumes that control ridge segmentation.  相似文献   

11.
This paper reports the results of a numerical study on the hydrodynamic instability parameters of a long-shore wave current in a surf zone with convex and concave bottom profiles. The limits of the change of the relative length of a long-shore meander have been derived in the form of 2/66, and structural and dynamic peculiarities of perturbations in a surf zone with various bottom profiles have been demonstrated.Translated by Vladimir A. Puchkin.  相似文献   

12.
Finite-differential schemes (continous in time) are studied for the shallow water equations on the equatorial -plane on the grids B and C. The B-grid spectrum is shown to be symmetrical about fourgrid interval waves. It results in the wrong sign of the group velocity in the ddomain of wavelengths less than four intervals of the grid. An analytical solution is given for the differential analogues of Kelving and Yanai waves on grid C. A conclusion is drawn on the advantage of grid, C and the necessary filtration of the high-frequency band of the spectrum for grid B, if the grid intervals are 100 km or less.Translated by Mikhail M. Trufanov  相似文献   

13.
Sources of very low frequency (0.01 to 1.0 Hz) ambient seismic noise in the shallow (<100 m) water continental margin sediments are investigated using Ocean Bottom Seismometers (OBS). The predominant seismic motions are found to be due to surface gravity (water) waves and water-sediment interface waves. Actual experimental measurements of seabed acceleration and hydrodynamic pressure are given, including side by side comparisons between buried and plate-mounted OBS units. OBS-sediment resonant effects are found to be negligible at the low frequencies under investigation. Wherever there exists relative motion between the seabed and the water, however, an exposed OBS is subject to added mass forces that cause it to move with the water rather than the sediments. Calculations based on measured seabed motions show that a neutral density, buried seismometer has superior sediment coupling charactersitics to any exposed OBS design.  相似文献   

14.
In this paper, the main results of field research into the seawater dynamics on the shelf of the Crimea in the summer of 1991 are reported. It is shown that in the weather frequency band, the oscillations with periods of 11–12 days have the greatest amplitude. These represent coastal-trapped waves with a spatial scale of the order of the length of the Black Sea coastline. These waves are generated by distant winds and significantly disturb the response of the Crimea shelf waters to local wind forcing. A transient upwelling-downwelling circulation having a period of 5–7 days is induced by local winds and is not accompanied by the generation of trapped waves at the frequency of forcing. Since the average circulation on the shelf of the Crimea is of cyclonic character, downwelling events are found more frequently and have longer time periods than the upwelling events. The wind-generated trapped waves on the shelves of the Crimea and Kerch Peninsula have an average period of 27 h. The inertial oscillations were well expressed during an experiment resembling long-wave motions.Translated by Mikhail M. Trufanov.  相似文献   

15.
The relationship between the scale of the spectral minimum of the first differences in temperature fluctuationsL and the local value of the Väisälä-Brunt frequencyN has been analysed using the results of more than 600 soundings made in various regions of the world's oceans. Allowing for the series of theoretical and experimental indications of the fact that the vertical scaleL at the boundary between the fine structure and microstructure in the ocean exists under the effect of processes of breaking of internal waves and hydrodynamic instability with the formation of turbulent patches, and using the energy relationships, the relationship for a solitary patch has been derived through the determining parameters. Based on two expressions forL, derived experimentally and using the energy estimations, the relationships for the averaged rate of absorption of the wave field energy by patches and the coefficient of the density vertical diffusion are derived, which do not contradict a series of independent estimations fromin situ measurements.Translated by Mikhail M. Trufanov.  相似文献   

16.
Circulations associated with the Indonesian Throughflow (IT), particularly concerning subsurface currents in the Pacific Ocean, are studied using three types of models: a linear, continuously stratified (LCS) model and a nonlinear, -layer model (LOM), both confined to the Indo-Pacific basin; and a global, ocean general circulation model (COCO). Solutions are wind forced, and obtained with both open and closed Indonesian passages. Layers 1-4 of LOM correspond to near-surface, thermocline, subthermocline (thermostad), and upper-intermediate (AAIW) water, respectively, and analogous layers are defined for COCO.The three models share a common dynamics. When the Indonesian passages are abruptly opened, barotropic and baroclinic waves radiate into the interiors of both oceans. The steady-state, barotropic flow field from the difference (open − closed) solution is an anticlockwise circulation around the perimeter of the southern Indian Ocean, with its meridional branches confined to the western boundaries of both oceans. In contrast, steady-state, baroclinic flows extend into the interiors of both basins, a consequence of damping of baroclinic waves by diapycnal processes (internal diffusion, upwelling and subduction, and convective overturning). Deep IT-associated currents are the subsurface parts of these baroclinic flows. In the Pacific, they tend to be directed eastward and poleward, extend throughout the basin, and are closed by upwelling in the eastern ocean and Subpolar Gyre. Smaller-scale aspects of their structure vary significantly among the models, depending on the nature of their diapycnal mixing.At the exit to the Indonesian Seas, the IT is highly surface trapped in all the models, with a prominent, deep core in the LCS model and in LOM. The separation into two cores is due to near-equatorial, eastward-flowing, subsurface currents in the Pacific Ocean, which drain layer 2 and layer 3 waters from the western ocean to supply water for the upwelling regions in the eastern ocean; indeed, depending on the strength and parameterization of vertical diffusion in the Pacific interior, the draining can be strong enough that layer 3 water flows from the Indian to Pacific Ocean. The IT in COCO lacks a significant deep core, likely because the model’s coarse bottom topography has no throughflow passage below 1000 m. Consistent with observations, water in the near-surface (deep) core comes mostly from the northern (southern) hemisphere, a consequence of the wind-driven circulation in the tropical North Pacific being mostly confined to the upper ocean; as a result, it causes the near-surface current along the New Guinea coast to retroflect eastward, but has little impact on the deeper New Guinea undercurrent.In the South Pacific, the IT-associated flow into the basin is spread roughly uniformly throughout all four layers, a consequence of downwelling processes in the Indian Ocean. The inflow first circulates around the Subtropical Gyre, and then bends northward at the Australian coast to flow to the equator within the western boundary currents. To allow for this additional, northward transport, the bifurcation latitude of the South Equatorial Current shifts southward when the Indonesian passages are open. The shift is greater at depth (layers 3 and 4), changing from about 14°S when the passages are closed to 19°S when they are open and, hence, accounting for the northward-flowing Great Barrier Reef Undercurrent in that latitude range.After flowing along the New Guinea coast, most waters in layers 1-3 bend offshore to join the North Equatorial Countercurrent, Equatorial Undercurrent, and southern Tsuchiya Jet, respectively, thereby ensuring that northern hemisphere waters contribute significantly to the IT. In contrast, much of the layer 4 water directly exits the basin via the IT, but some also flows into the subpolar North Pacific. Except for the direct layer 4 outflow, all other IT-associated waters circulate about the North Pacific before they finally enter the Indonesian Seas via the Mindanao Current.  相似文献   

17.
通过对TOGA-COARE期间的一组锚系仪器阵列资料的分析得出:在赤道西太平洋1°45′S,156°E.海域存在显著的半日潮频内波,它的水平波数(波长)、垂向波数、水平传播速度和垂向传播速度分别约为:3.3×10-2 km-1 (210 km),-1.6×10-3 m-1,2.0 m/s,-3.8 cm/s.波形向斜下方传播,亦即波能向斜上方传输.它在观测点西南方生成后,向东北方向传播,到达观测海区.流速矢量旋转谱水平随深度的变化呈马鞍形,低谷及深处的峰所在深度分别与南赤道流及赤道潜流的南边界所在深度大体一致.旋转椭圆主轴方位角随深度变化,在浅层(40 m处)为北偏东30°,到深处(324 m)转为东偏南14°.总体上呈东北方向,表明波来自西南方向.  相似文献   

18.
The tsunami warning system in the Russian Far East employs the medium-period magnitude MS (BB) by Vaniek–Soloviev. However, its use may lead to inadequacies and underestimates for the tsunamigenic potential of an earthquake. Specifically, this can happen in the case of a so-called tsunami–earthquake. This kind of earthquakes with a nonstandard spectrum was revealed by H. Kanamori in 1972. This problem can be overcome by using a magnitude scale that deals with longer period seismic waves. This study develops a technique for determining the magnitudes at regional distances (from 70 to 4500 km) using the amplitudes of surface seismic waves of periods of 40 and 80 s. At distances of 70–250 km, the amplitude of the joint group of shear and surface waves is used. For the new magnitudes designated M S(40) and M S(80), experimental calibration curves are constructed using more than 1250 three-component records at 12 stations of the region. The magnitudes are calibrated so as to produce an unbiased estimate of the moment magnitude M w in the critical range 7.5–8.8. The rms error of the single-station estimate M w is around 0.27. At distances below 250 km and M w ≥ 8.3, the estimate of M w obtained by the proposed technique becomes saturated at the level of M w ~ 8.3, which is acceptable for operative analysis because no missed alarms arise. The technique can be used in operational tsunami warning based on seismological data. This can markedly decrease the number of false alarms.  相似文献   

19.
By synthesizing data of the turbulent structure beneath wind waves in laboratory tanks, with some re-analyses, we propose the existence of a particular turbulent boundary layer which is directly coupled with wind waves, a downward-bursting boundary layer (DBBL) in water beneath wind waves. The data set indicates that the depth of this layer is from 3 to 7, or about 5 times the significant wave height of wind waves. The data observed in laboratory tanks agree with data of acoustic observations of bubble clouds under breaking wind waves in the sea made by Thorpe (1986, 1992). It is inferred that DBBL is formed in equilibrium with the local wind waves, as a common feature from initially generated wind waves, young laboratory wind waves to mature wind waves in the sea.  相似文献   

20.
Within the framework of the linear theory of long waves, we study the process of incidence of a baroclinic tide on an unevenness of the sea bottom simulating an oceanic ridge. The liquid is assumed to be stratified and the action of the Coriolis force is taken into account. We determine the characteristics of wave disturbances in the region of the ridge induced by the incident baroclinic waves depending on the parameters of the bottom topography and tidal period. Thus, in particular, over the ridge, we reveal the existence of both the regions, where the amplitudes of internal waves are much higher than the amplitude of the incident baroclinic tide, and shaded regions, where the opposite phenomenon is observed.__________Translated from Morskoi Gidrofizicheskii Zhurnal, No. 6, pp. 3–9, November–December, 2004.  相似文献   

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