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1.
Modelling the tides and their impacts on the vertical stratification over the Sofala Bank,Mozambique
The Sofala Bank, a wide shelf located along the central coast of Mozambique, hosts tides with high amplitudes. The Regional Ocean Modelling System (ROMS) was used to analyse the tidal currents on the bank and to investigate their effects on the stratification and generation of tidal fronts. During spring tides, barotropic tidal currents with maximum values ranging from 40 cm s–1 to 70 cm s–1 are found on the central bank. The major axis of the tidal ellipses for M2 and S2 follow a cross-shelf direction with mainly anticlockwise rotation. Similar to observations, three distinct regimes occur: (i) a warm well-mixed region on the inner shelf where the depths are <30 m; (ii) a wellmixed colder region above the shelf edge; and (iii) a stratified region offshore. The model shows that the tides lead to cooling where two criteria are satisfied: the Simpson and Hunter parameter log10(h/U3) <3.2 and the depth h >30 m. The shelf edge of the bank is important for internal tide generation. Two frontal structures result, one offshore between cooler mixed waters and warmer stratified waters and the other in shallow inshore waters, between cooler mixed waters and solar heated mixed waters. 相似文献
2.
2002年夏季广东陆架边缘上升流海域的内潮现象及其局地反馈初探 总被引：1，自引：0，他引：1
基于2002年夏季开展的"中国近海环流形成变异机理、数值预测方法及对环境的影响"观测项目获得的往复走航温盐流资料,结合同期的卫星观测(风、SST、海表动力高度)数据,初步探讨了粤东陆架边缘上升流区的内潮现象及其局地反馈特征.研究结果表明:粤东陆架边缘海域存在显著的、间歇性的相对低温海水的沿陆坡涌升现象,其中A航段的低温(18～23℃)海水涌升发生在约50～150m深度,B航段的低温(<18℃)海水涌升则主要位于150 m以深.由于观测期间海表风变化很小,而海洋涡旋在几周至几个月内相对稳定,并且研究海域涡旋对流场的影响似乎局限于75 m以浅的上层海洋,因而A、B航段的差异显然不能用海表风或海表动力高度变化来解释.进一步的分析表明粤东陆架边缘上升流区存在显著的内潮现象,尽管资料所限使得我们无法准确判定该内潮性质,往复走航海流剖面的确揭示了1阶和5阶内潮模的存在.内潮的不同模态极大地改变了上层海洋的热力和环流结构;低阶内潮模导致沿最大温度水平梯度处水温的剧烈垂向起伏(>30 m)以及跃层两侧的海流反向现象;高阶内潮模导致垂直陆坡方向水平流速的多次反向,强烈的流剪切可能与增强的混合联系在一起.导致低阶内潮模(A航段)向高阶内潮模(B航段)转变的原因可能是由于内潮特征线倾角与地形坡度比较接近而激发的"临界反射"效应.分析结果还表明,不同内潮模态导致的环流结构变异叠加在背景环流场之上,会显著影响粤东陆架边缘上升流的空间结构及强度. 相似文献
3.
The effects of scattering and resonance on the energy dissipation of an internal tide were investigated using a two-dimensional
model which is a reassembled version of the theoretical generation model devised by Rattray et al. (1969) for internal tide. The basic character of the scattering process at the step bottom was first investigated with a
wide shelf model. When the internal wave incited from a deep region (Region II) into the shallow shelf region (Region I),
a passing wave into the shallow region, a reflected wave into the deep region, and a beam-like wave, i.e. a scattered wave
(SW), emanated at the step bottom. The SW, which consists of the superposition of numerous internal modes, propagated upward/downward
into both regions. The general properties of the SW were well expressed around the shelf edge, even in the present model with
viscosity effect. The amplitude of the SW decreased dramatically when the depth of the velocity maximum of the incident internal
wave in Region II corresponded with the depth of the shelf edge. In the narrow shelf model, where the decay distance of the
internal wave in Region I is longer than the shelf width, the incident internal wave reflected at the coast to form a standing
wave. When the internal wave in Region I is enhanced by the resonance, the energy of the SW in Region II is also intensified.
Furthermore, the energy of the modes in Region II predominated when the velocity maximum is identical to that of the dominant
mode in Region I. These results suggest that the spatial scale of shelf region is a very important factor governing the energy
dissipation of the internal tide through reflection and scattering in a narrow shelf. 相似文献
4.
Role of mean circulation,tides, and waves in the transport of bottom sediment on the New Zealand continental shelf 总被引：1，自引：1，他引：0
Evaluation of velocity data on water movements over the New Zealand continental shelf has revealed that the mean circulation by itself is too slow to induce transport of bottom sediments. Tides generally have higher velocities, but are still not the main transporting agent except in the tide‐dominated Cook and Foveaux. Straits. Waves have the potential to stir sediments on the inner and middle shelf (less than about 70 m deep) during annual storms, and probably down to 130 m depth during the maximum 25‐y storm. For sediment transport to take place, energies of at least two of the major water movements would have to complement one another. Optimum conditions for transport probably occur during storm periods when wave‐suspended sediment is readily moved by tides and the mean circulation. The direction of transport is mainly along the continental shelf and is largely in response to prevailing weather patterns coincident with the direction of the mean circulation and strongly reinforced by the appropriate phase of the tide. 相似文献
5.
6.
Internal tidal currents and associated water-mass displacements were investigated during multiple cruises in the Kaoping Submarine Canyon off southwestern Taiwan. Observations from both moored and shipboard Acoustic Doppler Current Profilers and hydrographic casts were conducted along the canyon. The velocity data showed that in the lower layer the major axis of the tidal currents aligned with the orientation of the canyon, and currents moved up-canyon during flood and down-canyon during ebb. The vertical-phase shift and amplitude of the currents indicated that the semidiurnal internal tide dominated with intensity increasing with depth toward the canyon head. Tidal energy was channeled from the shelf landward with a beamlike internal wave, guided by bottom topography. The estimated phase velocity was 1.4–1.7 m s−1, based on normal mode analysis and the phase lag between sampling stations. Empirical orthogonal function analysis of hydrographic profiles confirmed that the first mode (M2 internal tide) explained 70% of the total variance. The strong convergence of internal tidal currents near the canyon head during flood may play an important role in the daily migration of cherry shrimps, which burrow along the canyon wall. 相似文献
7.
A. V. Zimin I. E. Kozlov O. A. Atadzhanova B. Chapron 《Izvestiya Atmospheric and Oceanic Physics》2016,52(9):951-960
Widespread short-period internal wave (SPIW) activity in the White Sea has been revealed for the first time based on long-term (2009–2013) monitoring performed using satellite and in situ observations, and the statistical characteristics of these waves have been obtained. Two main regions where short-period waves constantly exist have been identified: the shelf area near the frontal zone at the boundary between the Basin and the Gorlo Strait and the shallow shelf area where the depths are about 30–50 m near Solovetskie Islands. Intense internal waves (IIWs), which are substantially nonlinear and are related to specific phases of a barotropic tide, are regularly observed near frontal zones. The wave height can reach half the sea depth and the wave periods vary from 7 to 18 min. 相似文献
8.
The branching of the Tsushima Warm Current (TWC) along the Japanese coast is studied based upon intensive ADCP and CTD measurements
conducted off the Wakasa Bay in every early summer of 1995–1998, the analysis of the temperature distribution at 100 m depth
and the tracks of the surface drifters (Ishii and Michida, 1996; Lee et al., 1997). The first branch of TWC (FBTWC) exists throughout the year. It starts from the eastern channel of the Tsushima Straits,
flows along the isobath shallower than 200 m along the Japanese coast and flows out through the Tsugaru Strait. The current
flowing through the western channel of the Tsushima Straits feeds the second branch of TWC (SBTWC) which develops from spring
to fall. The development of SBTWC propagates from the Tsushima Straits to Noto Peninsula at a speed of about 7 cm sec−1 following the continental shelf break with a strong baroclinicity. However, SBTWC cannot be always found around the shelf
break because its path is influenced by the development of eddies. It is concluded that SBTWC is a topographically steered
current; a current steered by the continental shelf break. Salient features at intermediate depth are the southwestward subsurface
counter current (SWSCC) between 150 m and 300 m depths over the shelf region in 1995–1998 with the velocity exceeding about
5 cm sec−1, although discrepancies of the velocity and its location are observed between the ADCP data and the geostrophic currents.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
9.
Daisuke Hirano Yujiro Kitade Hideki Nagashima Masaji Matsuyama 《Journal of Oceanography》2010,66(1):95-104
The strength of mixing due to turbulence in the Antarctic Slope Front (ASF) region was investigated using CTD (conductivity-temperature-depth profilers) observations and direct measurements of turbulence conducted off Adélie Land, East Antarctica along 140°E from the 12th–14th February, 2005. The strongest horizontal gradient of the ASF was located below 300 m depth near the 1000 m isobath. The turbulent measurements revealed that the energy dissipation rate frequently exceeded 10?8 Wkg?1 on the continental shelf and upper slope regions. Turbulent diffusivities near the shelf break were higher than 10?3 m2s?1. Near the ASF the average turbulent heat flux was 5.7 Wm?2 and 1.1 Wm?2 across the temperature minimum layer to 250 m and from 300 to 600 m, respectively. The distribution of the high dissipation rate was consistently explained by the characteristic curve of the M2 internal wave emanating from the shelf break and continental slope. The water mass observed in the ASF below 300 m in the continental slope comprised Modified Circumpolar Deep Water and low salinity Shelf Water originating from either the upper layer of the Adélie Depression or the Adélie Bank, and produced by boundary mixing near the shelf break. 相似文献
10.
Tidal observations on the West Coast,South Island,New Zealand 总被引：1，自引：1，他引：0
R. A. Heath 《新西兰海洋与淡水研究杂志》2013,47(2):251-261
Harmonic tidal constants, calculated from sea surface elevation observations at Jackson Bay on the West Coast of the South Island, are consistent with available semi‐diurnal and diurnal tidal phase distributions. Current observations taken over a 111 day period at mid‐depth in 1505 m of water on the southern flank of the Challenger Plateau and over a 240 day period in 1430 m of water on the South Island western coast continental slope, are subject to tidal analysis. At both sites there is a component of energy flux directed across the isobaths and only at the northern site for the M2 tide is the phase consistent with a dominant progressive barotropic tide. The successive 30 day harmonic constants at the southern continental slope site exhibit a trend in the M2 tidal ellipse speed and ellipticity suggesting the presence of a regular internal tide. Superposition of ‘internal tidal’ and barotropic tidal flows, as prescribed from progressive‐ and standing‐wave elevations, to fit the observations indicates that the ‘internal tide’ is probably associated with the first baroclinic mode. At the current‐meter depths the speeds of the ‘internal tide’ for the M2 tide are about the same as the barotropic speeds, whereas, the S2 ‘internal tide’ speeds are larger than those of the barotropic tide. The consistency of the trend in ellipse parameters lends support to the theoretical progressive trapped barotropic tidal flows being a good approximation to the actual barotropic tide. Some support for the hypothesis that the S2 tide on the West Coast of New Zealand has a substantial standing wave contribution is given by the northern observations, where the ratio of the S2: M2 internal tidal ellipse current amplitudes are substantially larger than the ratio of the elevations, the internal tide being generated by across‐isobath flows. 相似文献
11.
Significant fluctuations of the currents of the tidal frequencies have been detected in the Kuroshio Current northeast of Taiwan and in the Tokara Strait, with total amplitudes comparable to the mean surface current (about 4050 cm s−1). At the continental shelf the tidal signal varies considerably with distance from the axis of the Kuroshio. Tidal ellipses on the continental shelf consistently have major axes in the northwest-southeast direction. Because tidal signals in the Kuroshio regions have very small spatial scales, they may not be caused by the barotropic tide but the baroclinic tide. It is inferred that the Kuroshio interacts with the baroclinic tides over the continental slope. 相似文献
12.
Box cores were collected close to river mouths along the eastern Brazilian shelf at water depths of 10–30 m. One core was
taken from more than 1000 m depth at the shelf slope. 210Pb and 226Ra activities were measured to establish sediment accumulation rates. Seven of the 10 cores exhibited an exponential decrease
with depth of excess 210Pb activities. The sediments from the sheltered Sudeste Channel off Caravelas revealed the highest sediment accumulation rate
of 0.81 cm yr−1. The sediments at the shelf slope seaward of the Rio Doce revealed the lowest accumulation rate of 0.13 cm yr−1. Sediment accumulation rates increased towards the Caravelas Bank. Current patterns and the morphology of the seabed favor
sediment deposition in this area. 相似文献
13.
Turbulent mixing in the upper ocean(30-200 m) of the northwestern Weddell Sea is investigated based on profiles of temperature,salinity and microstructure data obtained during February 2014.Vertical thermohaline structures are distinct due to geographic features and sea ice distribution,resulting in that turbulent dissipation rates(ε) and turbulent diffusivity(K) are vertically and spatially non-uniform.On the shelf north of Antarctic Peninsula and Philip Ridge,with a relatively homogeneous vertical structure of temperature and salinity through the entire water column in the upper 200 m,both ε and K show significantly enhanced values in the order of O(10~(-7))-O(10~(-6)) W/kg and O(10~(-3))-O(10~(-2)) m~2/s respectively,about two or three orders of magnitude higher than those in the open ocean.Mixing intensities tend to be mild due to strong stratification in the Powell Basin and South Orkney Plateau,where s decreases with depth from O(10~(-8)) to O(10~(-9)) W/kg,while K changes vertically in an inverse direction relative to s from O(10~(-6)) to O(10~(-5)) m~2/s.In the marginal ice zone,K is vertically stable with the order of10~(-4) m~2/s although both intense dissipation and strong stratification occur at depth of 50-100 m below a cold freshened mixed layer.Though previous studies indentify wind work and tides as the primary energy sources for turbulent mixing in coastal regions,our results indicate weak relationship between K and wind stress or tidal kinetic energy.Instead,intensified mixing occurs with large bottom roughness,demonstrating that only when internal waves generated by wind and tide impinge on steep topography can the energy dissipate to support mixing.In addition,geostrophic current flowing out of the Weddell Sea through the gap west of Philip Passage is another energy source contributing to the local intense mixing. 相似文献
14.
Current meter data collected over the last 20 years are presented and used to describe the residual currents on the Celtic and Armorican slope and shelf regions. On the slopes, a poleward current of about 6cm s−1 exists at the 500m depth contour. At mid depths, these currents are directed onslope, whereas near the bottom the flow in markedly downslope, reaching mean speeds of about 15cm s−1 near 6°40′W. The downslope currents are thought to be largely tidally induced and balanced by Stokes transports. The total slope transport near 48°N is about 4Sv. On the upper slopes (<1000m depth) the transport increases poleward. On the outer Celtic shelf, a weak (2 cm s−1) counter-current flowing southeastwards was observed. On the Armorican shelf, the residual flow is again nothwestwards and this coastal flow appears to continue northwards across the mouth of the English Chanel and past the Isles of Scilly with typical mean upper layer speeds of about 2cm s−1. Southwest of Ireland the flow is again northwesterly. Numerical model simulations show that the eastern slope boundary current of the NE Atlantic can be driven by realistic distributions of seawater density. The simulations also show only a small wind driven barotropic response on the Celtic and Armorican shelf region and that a component of the residual shelf flows, like the slope current, may be driven by pressure distributions arising from regional differences in the distribution of seawater density, or from non local wind stress. 相似文献
15.
《Deep Sea Research Part II: Topical Studies in Oceanography》1999,46(10):2003-2027
Spatial and temporal characteristics of the water masses and the dispersion of the suspended particulate matter were investigated using current meter, hydrographic and nephelometric observations, gathered during the ECOFER experiment (1989–1991) in the Cap-Ferret Canyon on the Aquitanian margin of the Bay of Biscay. While characteristics of the deep water masses were stable from one year to another, large hydrographic change in the upper 500 m related to winter renewal induced by poleward advection of warm and saline water along the continental slope. The slope circulation and seasonal eddy activity appear as important dynamical mechanisms that control the entrainment and the dispersion of the suspended particulate matter from the neritic domain to the deep ocean. A predominantly northward along-slope current with occasional reversal characterizes this circulation. The nephelometric structures also showed seasonal changes in the overall suspended particulate matter content, but recurrent features, such as the presence of intermediate nepheloid layers at the shelf-break depth and various depths along the slope (∼500, 1000 and 2000 m), were observed. These nepheloid layers extended off the slope to about 10–30 km, but especially laterally along the slope. Their presence indicated that suspended particulate matter exchanges between the shelf and the slope occurred mainly in the head of the canyon and along the southern open slope. The intermediate nepheloid layers around 500 m depth detached from the slope particularly in regions where the bottom slope is close to critical for the M2 internal tide. 相似文献
16.
《Ocean Modelling》2002,4(3-4):221-248
Three-dimensional numerical simulations of the generation and propagation of the semidiurnal internal tide in a submarine canyon with dimensions similar to those of the Monterey Canyon are carried out using a primitive equation model. Forcing with just sea level at the offshore boundary in an initially horizontally homogeneous ocean with realistic vertical stratification, internal tides are generated at the canyon foot and rim, and along portions of the canyon floor. The results compare favorably with observations, both indicating enhancement of energy along the canyon floor propagating at an angle consistent with linear internal wave theory. Due to the earth's rotation, internal tide energy is distributed asymmetrically in the cross-canyon direction, favoring the southern side. The effect of canyon floor slope is explored, with the finding that small changes in the slope result in large changes in the amount and distribution of the internal tide energy. Canyons whose floors are subcritical with respect to the semidiurnal frequency along their entire length have very little baroclinic energy, whereas canyons that are near-critical along much of their length, such as the Monterey Canyon, develop strong internal tides that propagate shoreward. Canyons that are near-critical at their mouths but supercritical further inshore generate the most internal tidal energy overall, although little of it makes it onto the continental shelf shoreward of the canyon head. The effects of internal tides within the canyons can be seen outside the canyons as well. Water is transported from depth onto the adjacent continental shelf along the canyon rims. This tidal pumping can be responsible for alongshore internal tide propagation and tidal-period surface currents with relatively small horizontal scales of variability. 相似文献
17.
This study is devoted to oceanographic features of the semi-enclosed Gulf of Aqaba, Red Sea. The data were recorded in winter—spring
1999 on the R/V Meteor cruise leg 44/2. Temperature and salinity profiles were measured at six positions (I—VI). The shipboard
NarrowBand Acoustic Doppler Current Profiler (NB ADCP) 150 kHz continuously recorded current profiles down to 350 m en route.
The research revealed that the current near the Strait of Tiran front (position VI) represents a semidiurnal signal of an
internal tide wave (∼12 h period; 0.2 ms−1 amplitude) that might be generated by the barotropic tide at the sill of the Strait. A sequence of cyclonic and anticyclonic
eddy pairs is found along the axis of the Gulf of Aqaba during winter-spring seasons. These sub-mesoscale signals are dominant
above the main thermocline and might be caused by wind forcing and the narrowness of the Gulf; it might remain in other seasons
with different dimensions in relation to the depth of thermocline. The total diameter of each pair was twice the baroclinic
Rossby radius (R ≈ 10 km). A single anti-cyclonic eddy was observed in the upper 300 m in the northern tip of the Gulf with a diameter of
about 5–8 km. 相似文献
18.
Meiofaunal standing stock and nematode community structure were investigated in the western continental shelf of India by collecting samples from every degree square of the shelf during two cruises of the FORV (Fishery and Oceanographic Research Vessel) Sagar Sampada, conducted in 1998 and 2001. Samples were collected from 30, 50, 100 and 200 m depths using a Smith Mc Intyre grab. Meiofaunal density ranged from 8 Ind. 10 cm−2 to 1208 Ind. 10 cm−2 and biomass from 0.07 mg 10 cm−2 to 6.11 mg 10 cm−2. Nematodes were the dominant meiofaunal group, contributing 88% of the density and 44% of the biomass. Harpacticoid copepods were the second important taxa, contributing 8% of both biomass and density. Altogether, 154 species of nematodes belonging to 28 families were recorded from the study area. Numerically, Desmodora spp., Dorylaimopsis sp., Tricoma spp., Theristus spp. and Halalaimus spp. were the dominant species. In general, there was a decrease in biomass and density of meiofauna and species diversity of nematodes with increase in depth. There was a 67% drop in species number from 51 to 100 m (106 species) to the shelf edge (35 species). Species richness and diversity indices showed consistent decrease with depth. The species dominance index was higher below 150 m depth. ANOSIM (from PRIMER) showed a significant difference between the nematodes of the near shore and shelf edge. Latitudinal variation was observed only in the number of nematode species. Biomass and abundance of nematodes were found to increase from coarse to fine sediment, while copepods showed an opposite trend. Multivariate analyses of nematode communities did not reveal any latitudinal or substratum differences. Variables such as depth, latitude, organic matter (OM) and amount of clay were the most relevant parameters influencing the biomass and density of meiofauna, while depth and temperature were the important parameters explaining the distribution of the nematode communities along the western Indian shelf. 相似文献
19.
An analytical model with three sub-regions for m2 tide in the yellow sea and the East China Sea 总被引：1，自引：0，他引：1
In this study an analytical tide model of uniform width with three sub-regions is presented. The three-subregions model takes
into account step-like variations in depths in the direction of the channel as a way to examine the M2 tide of the East China Sea (ECS) as well as the Yellow Sea (YS). A modified Proudman radiation condition has been applied
at the northern open head, while the sea surface elevation is specified at the southern open boundary. It is seen that, due
to the presence of an abrupt change in depth, co-amplitude lines of the M2 tide are splitted to the east and west near the end of the ECS shelf region. Variations in depths, bottom friction and the
open head boundary conditions all contribute to the determination of formation of amphidromes as well as overall patterns
of M2 tidal distribution. It is seen that increasing water depth and bottom friction in the ECS shelf results in the westward shift
of the southern amphidrome. There is however no hint at all of the well-known degenerated tidal pattern being formed. It is
inferred that a lateral variation of water depth has to be somehow incorporated to represent the tidal patterns in ECS in
a realistic manner. Regarding the radiation factor introduced by Fang et al. (1991), use of a value larger than one, possibly
with a phase shift, appears to be a proper way of incorporating the reflected waves from the northern Yellow Sea (NYS). Key
words - analytical model, M2 tide, Kelvin wave, Yellow Sea, East China Sea 相似文献
20.
Within the framework of the linear theory of long waves, we study internal waves generated by a barotropic tide in a two-layer
ocean of variable depth taking into account the influence of the Coriolis force. Barotropic waves run over an extended unevenness
of the bottom at an arbitrary angle. This unevenness is regarded as a model of the continental slope and shelf. We establish
the dependences of the amplitudes of generated internal waves on the angle of incidence of the barotropic tide, topography
of the bottom, and stratification.
Translated by Peter V. Malyshev and Dmitry V. Malyshev 相似文献