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1.
Internal Wave (IW) characteristics and the impact of IW on acoustic field have been studied utilizing the hourly time series of temperature and salinity data collected at a coastal site off Paradeep (north Bay of Bengal) during 24–25 October 2008. The IW characteristics, viz. period (t per ), velocity (C vel ), wavelength (L), and wave numbers (k), are found to be 2.133–34.72 h, 0.135 km h−1, 0.37–6.2 km and 2.70–0.16 cycles km−1, respectively. The semi-diurnal tidal forces are predominant than diurnal as well as at other frequencies and its contribution is about 64% towards the total potential energy (E 0 = 3.34 J m−2). Sound velocity perturbations with space and time in the presence of IW field are examined from Garrettt-Munk (GM) model. Transmission loss anomaly for optimized source-receiver configuration at the depth of 53 m and range of 9 km has been computed from acoustic modelling. The loss in the acoustic transmission is found to be 38.4 dB in the presence of low-frequency IW field.  相似文献   

2.
Elkhorn Slough is a shallow, tidally forced estuary that is directly connected to Monterey Bay. It is ebb-dominated and, due to continued erosion, the tidal prism has tripled over the past 40 years. Water level measurements at four locations are used to examine tidal and nontidal oscillations in Elkhorn Slough. The tidal response of Elkhorn Slough differs from that of Monterey Bay primarily due to the generation of a relatively large number of shallow-water tidal constituents that are due to tidal distortion caused by friction along the bottom and lateral boundaries, intertidal storage, and nonlinear advection. The shallow-water constituents range from 3 to almost 15 cycles per day (cpd) and include a rich variety of overtides and compound tides, whose amplitudes generally increase toward the head of the slough. The tidal harmonics are seasonally dependent, with lower amplitudes during the fall and winter and higher amplitudes in summer. The tidal constituents were examined using two types of spectral decomposition, the conventional power spectrum and the more recent Hilbert spectrum. Unlike the power spectrum, the Hilbert spectrum does not reveal any harmonic structure in the data. Energy associated with tidal distortion in this case appears to be broadly distributed across the spectral continuum. At least four nontidal oscillations occur in Elkhorn Slough with frequencies of 26.0, 39.7, 52.7, and 66.9 cpd. The Hilbert spectrum reveals maxima at 26, 39.7, and 66.9 cpd, but not at 52.7 cpd, suggesting that it is harmonically related to the oscillation at 26.0 cpd. The nontidal oscillations fall into the range of frequencies associated with the natural oscillations of Monterey Bay. However, evolutionary power spectra indicate that they appear to be permanent features of the system and thus are not necessarily consistent with seiche-like oscillations that are often transient and subject to damping. These oscillations could be caused by several factors including edge waves along the coast of Monterey Bay, long-period surface waves of atmospheric origin that enter the bay from offshore, or breaking internal waves in and around the Monterey Submarine Canyon. In conclusion, detailed hydrodynamic models are needed to provide a better understanding of how tidal harmonics are generated and preserved in Elkhorn Slough, and to determine the origin of the natural oscillations in Monterey Bay.  相似文献   

3.
The first sandstone unit of the Esdolomada Member of the Roda Formation (hereafter referred to as ‘Esdolomada 1’) was formed by a laterally‐migrating, shelf tidal bar. This interpretation is based on detailed mapping of the bedding surfaces on the digital terrain model of the outcrop built from light detection and ranging data and outcrop photomosaics combined with vertical measured sections. The Esdolomada 1 sandbody migrated laterally (i.e. transverse to the tidal currents) towards the south‐west along slightly inclined (1.6° to 4.6°) master bedding surfaces. The locally dominant tidal current flowed to the north‐west. This current direction is indicated by the presence of stacked sets of high‐angle (average 21°) cross‐stratification formed by dunes that migrated in this direction, apparently in an approximately coast‐parallel direction. The tidal bar contains sets and cosets of medium‐grained cross‐stratified sandstone that stack to reach a thickness of about 5·5 m. Individual cross‐bed sets average about 50 cm thick (with a range of 10 to 70 cm) and have lengths of ca 130 to 250 m in a direction perpendicular to the palaeocurrent. Set thickness decreases in the direction of migration, towards the south‐west, and the degree of bioturbation increases, so that the cross‐bedded sandstones gradually change into highly bioturbated finer‐grained and thinner‐bedded sandstones lacking any cross‐stratification. The rate of thinning of individual dune sets as they are traced down any obliquely‐accreting master surface is some 40 cm per 100 m (0·004) for the older, thicker sandstones, whereas the younger, thinner beds thin at a rate of 15 cm over 100 m (0·0015). The tidal bar has a sharp base and top and is encased in finer‐grained bioturbated, marine sandstones. The Esdolomada bar crest was oriented north‐west to south‐east, parallel to the tidal palaeocurrents and to the nearby palaeoshoreline, but built by lateral accretion towards the south‐west. Lateral outbuilding generated a flat‐topped bar with a measured width of about 1700 m, and a preserved height of 5·5 m. The bar, disconnected from a genetically related south‐westward prograding delta some 2 km to the north‐east, developed during the transgressive phase of a sedimentary cycle. The tidal bar was most probably initiated as a delta‐attached bar at the toesets of the delta front and during transgression evolved into a detached tidal bar.  相似文献   

4.
Mohanty  Sachiko  Rao  A. D.  Pradhan  Himansu 《Natural Hazards》2017,87(2):1109-1124

The influence of seasonal and cyclonic winds is studied on the characteristics of internal waves (IWs) over the western Bay of Bengal (BoB) by using MITgcm model. As the BoB experiences reversal of seasonal winds and also tropical cyclones during pre-monsoon and post-monsoon months, its effect is seen through the computation of spectral estimates of the IWs. It is seen that the peak estimate is associated with the semidiurnal frequency at all the depths and is found higher in May compared to November. This is attributed to the presence of shallow mixed layer depth and deep thermocline due to the upwelling favorable winds. The computation of isopycnal displacement infers that the internal tides are present from 40 to 120 m depth in case of upwelling favorable winds of May, whereas, the presence of internal tides is restricted between 90 and 120 m for the downwelling favorable winds of November. During May, the available potential energy is also seen in a narrow coastal stretch, whilst it is absent in November. During the Hudhud cyclone period of October 7–14, 2014, it is noticed from the spectral estimates that the IWs of tidal frequency are replaced by inertial frequency with a periodicity of about 2 days as a consequence of strong cyclonic winds. The progressive vector diagram shows the mean current is initially westward up to October 17, 2014 and then northeastward with well-defined clockwise circulation. The maximum radius of inertial oscillation of 15 km is observed. After the cyclone ceases, the estimate associated with inertial frequency slowly diminishes and enhances the estimates related to internal tides. The simulations also suggest that the internal tides are absent for about 6 weeks as a response of the cyclonic winds.

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5.
Evolution and mechanics of a Miocene tidal sandwave   总被引：3，自引：0，他引：3  
A remarkable exposure of Miocene marine molasse in western Switzerland records the evolution of a tidal sandwave over a period of approximately 2 1/2 months. The sandwave is composed of tidal ‘bundles’ in which a sandwave reactivation stage and full vortex stage can be recognized for the dominant flow (ebb tide) and a rippled flood apron overlain by high water drape for the reversed flow. Bundle thicknesses vary systematically through neap–spring cycles, with a periodicity of 27 demonstrating the semi-diurnal lunar control of sedimentation. Waves were an additional component, especially when superimposed on flood tides, producing near-symmetrical combined-flow ripple marks in the flood apron. Tidal current velocities are estimated using critical shear velocities for entrainment, the ripple-dune transition and the dune-plane bed transition. Using appropriate estimates of roughness lengths and a logarithmic velocity law, maximum tidal speeds at 1 m above the bed were approximately 0·6 m sec?1 for ebbs and up to 0·5 m sec?1 for floods. The enhancement by waves of bed shear stress (τwc/τ of approximately 2 for 1 m high waves) under flood currents implies flood tidal velocities closer to 0·2–0·3 m sec?1. Peak instantaneous bedload sediment transport rates using a modified Bagnold equation are nearly 5 times greater under ebb tides than floods. The average net sediment transport rate at springs (0·04 kg m?1 sec?1) is over 10 times greater than at neaps (0·002 kg m?1 sec?1). Comparison with transport rates in modern tidal environments suggests that the marine molasse of Switzerland was deposited under spatially confined and relatively swift tidal flows not dissimilar to those of the present Dutch tidal estuaries.  相似文献   

6.
Response of the coastal regions of eastern Arabian Sea (AS) and Kavaratti Island lagoon in the AS to the tropical cyclonic storm `Phyan??, which developed in winter in the south-eastern AS and swept northward along the eastern AS during 9?C12 November 2009 until its landfall at the northwest coast of India, is examined based on in situ and satellite-derived measurements. Wind was predominantly south/south-westerly and the maximum wind speed (U10) of ~16 m/s occurred at Kavaratti Island region followed by ~8 m/s at Dwarka (Gujarat) and ~7 m/s at Diu (located south of Dwarka) as well as two southwest Indian coastal locations (Mangalore and Malpe). All other west Indian coastal sites recorded maximum wind speed of ~5?C6 m/s. Gust factor (i.e., gust-to-speed ratio) during peak storm event was highly variable with respect to topography, with steep hilly stations (Karwar and Ratnagiri) and proximate thick and tall vegetation-rich site (Kochi) exhibiting large values (~6), whereas Island station (Kavaratti) exhibiting ~1 (indicating consistently steady wind). Rainfall in association with Phyan was temporally scattered, with the highest 24-h accumulated precipitation (~60 mm) at Karwar and ~45 mm at several other west Indian coastal sites. Impact of Phyan on the west Indian coastal regions was manifested in terms of intensified significant waves (~2.2 m at Karwar and Panaji), sea surface cooling (~5°C at Calicut), and moderate surge (~50 cm at Verem, Goa). The surface waves were south-westerly and the peak wave period (T p) shortened from ~10?C17 s to ~5?C10 s during Phyan, indicating their transition from the long-period `swell?? to the short-period `sea??. Reduction in the spread of the mean wave period (T z) from ~5?C10 s to a steady period of ~6 s was another manifestation of the influence of the cyclone on the surface wave field. Several factors such as (1) water piling-up at the coast supported by south/south-westerly wind and seaward flow of the excess water in the rivers due to heavy rains, (2) reduction of piling-up at the coast, supported by the upstream penetration of seawater into the rivers, and (3) possible interaction of upstream flow with river run-off, together resulted in the observed moderate surge at the west Indian coast. Despite the intense wind forcing, Kavaratti Island lagoon experienced insignificantly weak surge (~7 cm) because of lack of river influx and absence of a sufficiently large land boundary required for the generation and sustenance of wave/wind-driven water mass piling-up at the land?Csea interface.  相似文献   

7.
Current understanding of bedform dynamics is largely based on field and laboratory observations of bedforms in steady flow environments. There are relatively few investigations of bedforms in flows dominated by unsteadiness associated with rapidly changing flows or tides. As a consequence, the ability to predict bedform response to variable flow is rudimentary. Using high‐resolution multibeam bathymetric data, this study explores the dynamics of a dune field developed by tidally modulated, fluvially dominated flow in the Fraser River Estuary, British Columbia, Canada. The dunes were dominantly low lee angle features characteristic of large, deep river channels. Data were collected over a field ca 1·0 km long and 0·5 km wide through a complete diurnal tidal cycle during the rising limb of the hydrograph immediately prior to peak freshet, yielding the most comprehensive characterization of low‐angle dunes ever reported. The data show that bedform height and lee angle slope respond to variable flow by declining as the tide ebbs, then increasing as the tide rises and the flow velocities decrease. Bedform lengths do not appear to respond to the changes in velocity caused by the tides. Changes in the bedform height and lee angle have a counterclockwise hysteresis with mean flow velocity, indicating that changes in the bedform geometry lag changes in the flow. The data reveal that lee angle slope responds directly to suspended sediment concentration, supporting previous speculation that low‐angle dune morphology is maintained by erosion of the dune stoss and crest at high flow, and deposition of that material in the dune trough.  相似文献   

8.
Due to a lack of modern analogues, debate surrounds the importance of tides in ancient epi-continental seas. However, numerical modelling can provide a quantitative means of investigating palaeo-tidality without recourse to analogues. Finite element modelling of the European Upper Carboniferous epi-continental seaway predicts an exceedingly low Lunar tidal range (ca 5 cm in the open water regions of the UK and Southern North Sea). The Imperial College Ocean Model (ICOM) uses finite element methods and an unstructured tetrahedral mesh that is computationally very efficient. The accuracy and sensitivity of ICOM tidal range predictions were tested using bathymetric data from the present-day Mediterranean Sea. The Mediterranean Sea is micro-tidal and varies in depth up to 5·4 km with an average depth of 1–2 km. ICOM accurately predicts the tidal range given both a realistic, but smoothed, bathymetry and a straight sided basin with a uniform depth of 1 km. Variation in uniform depth from 100 to 3000 m with and without islands consistently predicts micro-tidality, demonstrating that the model is robust and the effect of bathymetric uncertainty on model output is relatively small. The extremely low tidal range predicted for the European Upper Carboniferous is thus deemed robust. Putative Upper Carboniferous tidal deposits have been described in the UK and southern North Sea, but are represented by cyclic rhythmites and are limited to palaeo-estuaries. Calculations based on an embayed coast model show that the tidal range could have been amplified to ca 1 m in estuaries and that this is sufficient to form cyclic rhythmites. Without tidal mixing, the tropical equatorial heat and salinity enhancement would promote stratification in the open water body. The introduction of organic matter probably caused anoxia, biotic mortality and carbon accumulation, as evidenced by numerous black ‘marine-band’ shales.  相似文献   

9.
The paper presents comprehensive statistical analyses of winds and water levels in Mobile Bay, Alabama, based on long-term meteorological and tidal observations at several locations. A procedure has been developed to select the most probable parent distribution function from a list of candidate distributions. The theoretical functions that fit the data best enable us to predict the extreme values of winds and water levels at different return periods. We have demonstrated the importance of dividing the winds into hurricane and nonhurricane seasons and separating astronomical tides from weather-driven water level changes. The statistical analysis suggests that the wind speed averaged over 8 min at Dauphin Island, Alabama, at the 100-year return period would be 48.9 m/s, which is equivalent to a sustained 1-min wind of 205 km/h, a very strong category 3 hurricane on the Saffir-Simpson scale. The probability distribution models predict that the 100-year maximum water level would be 3.23 m above the mean lower low water (MLLW) level at the bay entrance and 3.41 m above the MLLW level near the head of the bay, respectively. Extremely low water levels important to navigation are also found. Application of the predicted extreme winds and surges is illustrated through the development of a storm wave atlas in the estuary. It is expected that the methodology and results presented in this paper will benefit the management and preservation of the ecosystems and habitats in Mobile Bay.  相似文献   

10.
Two large (200 to 300 km), near‐continuous outcrop transects and extensive well‐log data (ca 2800 wells) allow analysis of sedimentological characteristics and stratigraphic architecture across a large area (ca 60 000 km2) of the latest Santonian to middle Campanian shelf along the western margin of the Western Interior Seaway in eastern Utah and western Colorado, USA. Genetically linked depositional systems are mapped at high chronostratigraphic resolution (ca 0·1 to 0·5 Ma) within their sequence stratigraphic context. In the lower part of the studied interval, sediment was dispersed via wave‐dominated deltaic systems with a ‘compound clinoform’ geomorphology in which an inner, wave‐dominated shoreface clinoform was separated by a muddy subaqueous topset from an outer clinoform containing sand‐poor, gravity‐flow deposits. These strata are characterized by relatively steep, net‐regressive shoreline trajectories (>0·1°) with concave‐landward geometries, narrow nearshore belts of storm‐reworked sandstones (2 to 22 km), wide offshore mudstone belts (>250 km) and relatively high sediment accumulation rates (ca 0·27 mm year?1). The middle and upper parts of the studied interval also contain wave‐dominated shorefaces, but coeval offshore mudstones enclose abundant ‘isolated’ tide‐influenced sandstones that were transported sub‐parallel to the regional palaeoshoreline by basinal hydrodynamic (tidal?) circulation. These strata are characterized by relatively shallow, net‐regressive shoreline trajectories (<0·1°) with straight to concave‐seaward geometries, wide nearshore belts of storm‐reworked sandstones (19 to 70 km), offshore mudstone belts of variable width (130 to >190 km) and relatively low sediment accumulation rates (ca ≤0·11 mm year?1). The change in shelfal sediment dispersal and stratigraphic architecture, from: (i) ‘compound clinoform’ deltas characterized by across‐shelf sediment transport; to (ii) wave‐dominated shorelines with ‘isolated’ tide‐influenced sandbodies characterized by along‐shelf sediment transport, is interpreted as reflecting increased interaction with the hydrodynamic regime in the seaway as successive shelfal depositional systems advanced out of a sheltered embayment (‘Utah Bight’). This advance was driven by a decreasing tectonic subsidence rate, which also suppressed autogenic controls on stratigraphic architecture.  相似文献   

11.
Bertioga Channel is a partially mixed (type 2) tidal estuary on the coastal plain of São Paulo, Brazil. Hourly current and salinity measurements during neap and spring tides in July 1991 yielded information about the physical structure of the system. Peak along-channel velocities varied from 40 cm s?1 to 60 cm s?1 during flood tides and from 70 cm s?1 to 100 cm s?1 during ebb tides. Net vertical velocity profiles indicate that the net current reverses directions at a depth of 2.5–3.0 m in the halocline. Due to appreciable fortnightly tidal modulation, the estuary alternates from being highly stratified (type 2b) during neap tides, with advection and diffusion contributing equally to the net upstream salt flux, to being moderately stratified (type 2a) during spring tides, when 90% of the net upstream salt transport is the result of effective tidal diffusion. Decomposition of the salt flux indicates that the relative contribution to the upstream salt transport by gravitational circulation shear is greater than the oscillatory tidal flux by a factor of 2.6 during neap tides. The oscillatory tidal flux is generated by the correlation of the tidal components of the u-velocity and salinity and is responsible for approximately the same amount of upstream salt transport, during neap and spring tides. However, during spring tides, this oscillatory term is greater than the other salt flux terms by a factor of 1.4. The total salt transport, through a unit width of the section perpendicular to the flow, was within 2% of the sum of the seven major decomposed, advective and dispersive terms. On the assumption that the Bertioga Channel is laterally homogeneous, the results also indicate that the estuary is not in steady state with respect to salt flux.  相似文献   

12.
Data from a moderate energy, meso-tidal beach on the east side of Delaware Bay, New Jersey, USA, revealed the significance of both beach width as a source for aeolian transport and the effect of tidal rise on source width. Wind speeds averaged over 17·1 min, recorded 6 m above the crest of a 0·5 m high dune, ranged from 11·6 to 12·7 m s?1 during the experiment. The highest observed rate of transport on the beach was 0·0085 kg m?1 s?1, monitored at rising low tide when the average wind speed was 11·6 m s?1 across 0·35 mm diameter surface sediments. The wind direction was oblique to the shoreline, creating a source width of 34 m. The reduction in the width of the beach as a source for aeolian transport during rising tide was approximately arithmetic, whereas the reduction in volume of sediment trapped was exponential. Aeolian transport effectively ceased when source width was less than 8 m. Wind conditions, moisture content of the surface sediments and presence of binding salts did not appear to vary dramatically, and no coarse grained lag deposit formed on the surface of the beach. The decrease in rate of sediment trapped through time in the tidal cycle is attributed to differences in source width. Sediment deposited in the litter behind the active beach by strong winds during the rising tide was eroded during the high water period by the high waves and storm surge generated by these winds, and net losses of sediment were observed despite initial aeolian accretion.  相似文献   

13.
The continental shelf on the west coast of India is widest off Bombay and leads into a strongly converging channel, the Gulf of Khambhat. Tides in the Gulf are among the largest on the coast. We use data on amplitude and phase of major semi-diurnal and diurnal constituents at forty-two ports in the Gulf and surrounding areas to define characteristics of the tides. We then use a barotropic numerical model based on shallow water wave equations to simulate the sea level and circulation in the region. The model is forced by prescribing the tide along the open boundaries of the model domain. Observed sea level at Bombay and currents from the Bombay High region at the centre of the model domain and from a shallow station off the port of Dahanu compare favourably with the fields simulated by the model. The simulated amplitudes and phases of the four most prominent tidal constituents also compare favourably with those observed along the coast, except at a few locations where the model spatial resolution (6.37 km × 6.37 km) appears to be inadequate to resolve the local geometry. Though this encourages us to conclude that the circulation in the region is dominated by barotropic tides, a concern is that the observational database on hydrography and directly measured currents in the region is weak.  相似文献   

14.
《Sedimentology》2018,65(3):721-744
Storm surges generated by tropical cyclones have been considered a primary process for building coarse‐sand beach ridges along the north‐eastern Queensland coast, Australia. This interpretation has led to the development of palaeotempestology based on the beach ridges. To better identify the sedimentary processes responsible for these ridges, a high‐resolution chronostratigraphic analysis of a series of ridges was carried out at Cowley Beach, Queensland, a meso‐tidal beach system with a >3 m tide range. Optically stimulated luminescence ages indicate that 10 ridges accreted seaward over the last 2500 to 2700 years. The ridge crests sit +3·5 to 5·1 m above Australian Height Datum (ca mean sea‐level). A ground‐penetrating radar profile shows two distinct radar facies, both of which are dissected by truncation surfaces. Hummocky structures in the upper facies indicate that the nucleus of the beach ridge forms as a berm at +2·5 m Australian Height Datum, equivalent to the fair‐weather swash limit during high tide. The lower facies comprises a sequence of seaward‐dipping reflections. Beach progradation thus occurs via fair‐weather‐wave accretion of sand, with erosion by storm waves resulting in a sporadic sedimentary record. The ridge deposits above the fair‐weather swash limit are primarily composed of coarse and medium sands with pumice gravels and are largely emplaced during surge events. Inundation of the ridges is more likely to occur in relation to a cyclone passing during high tide. The ridges may also include an aeolian component as cyclonic winds can transport beach sand inland, especially during low tide, and some layers above +2·5 m Australian Height Datum are finer than aeolian ripples found on the backshore. Coarse‐sand ridges at Cowley Beach are thus products of fair‐weather swash and cyclone inundation modulated by tides. Knowledge of this composite depositional process can better inform the development of robust palaeoenvironmental reconstructions from the ridges.  相似文献   

15.
Impact of sea breeze on wind-seas off Goa, west coast of India   总被引：1，自引：0，他引：1  
After withdrawal of the Indian Summer Monsoon and until onset of the next monsoon, i.e., roughly during November–May, winds in the coastal regions of India are dominated by sea breeze. It has an impact on the daily cycle of the sea state near the coast. The impact is quite significant when large scale winds are weak. During one such event, 1–15 April 1997, a Datawell directional waverider buoy was deployed in 23 m water depth off Goa, west coast of India. Twenty-minute averaged spectra, collected once every three hours, show that the spectrum of sea-breeze-related ‘wind-seas’ peaked at 0.23 ±0.05 Hz. These wind-seas were well separated from swells of frequencies less than 0.15 Hz. The TMA spectrum (Bouwset al 1985) matched the observed seas spectra very well when the sea-breeze was active and the fetch corresponding to equilibrium spectrum was found to be 77±43 km during such occasions. We emphasize on the diurnal cycle of sea-breeze-related sea off the coast of Goa and write an equation for the energy of the seas as a function of the local wind  相似文献   

16.
The Patos Lagoon is a choked, microtidal coastal laggon situated in southern Brazil between 30°S and 32°S. The response of the lagoon to tidal oscillations is studied through data analysis and numerical modeling experiments. Two types of high frequency oscillations are observed in the tidal frequency band: mixed tides, predominantly diurnal; and forced oscillations having a period of 24 h occurring in the inner lagoon. In the southern portion of the lagoon, tides are selectively filtered by the entrance channel. The main diurnal constituent O1 is linearly attenuated as it progresses landwards. In the inner parts of the lagoon, 24-h oscillations are mainly forced by the combined effect of diurnal tides and sea breeze action. They are tied with a natural period of oscillation of 24 h. Results also indicate that these are not inertial frequency oscillations, despite the lagoon being placed in a critical 30°S area. The interaction between astronomical tides and meteorological effects produces a complicated picture for tidal forecasting derived from data collected inside the lagoon.  相似文献   

17.
Current meter records from two depths, approximately 1000 and 3000 m, at three moorings in the deep mid-Arabian Sea were used to study tidal components. Tidal ellipses for the semi-diurnal (M2, S2 and K2) and the diurnal (K1, and P1) tidal constituents have been determined using the currents recorded at hourly intervals during May 1986–May 1987. The clockwise rotating M2 tidal currents were the strongest. The maximum horizontal velocities due to M2,2 and K1 tides were 2.2 cm/s, l.0cm/s and 0.89 cm/s respectively. The amplitudes of the other two constituents (P1, and K2) were much smaller. The barotropic M2 ellipses have been estimated by averaging the M2 tidal currents at the upper and lower levels. Although the amplitudes of computed ellipses are lower than those that have been predicted using numerical models of global tidal model, their orientations are the same.  相似文献   

18.
The gradients of amplitude and phase of diurnal and semidiurnal components of zonal and meridional winds in the height intervals of 80–90 km and 90–100 km are studied using the meteor wind radar data collected at Atlanta (34°N, 84°W) during the period August 1974–March 1978. The results are compared with those at Adelaide (35°S, 139°E). It is found that the gradients vary in an opposite manner between the two height intervals.  相似文献   

19.
通过收集和实测到的研究区水位、潮位、潮流验证、沉积物类型和粒度参数、水深地形、风、径流值等边界条件,运用泥沙运动控制方程、泥沙再悬浮及再沉积方程,进行了工区泥沙运移相关参数的计算和模拟分析,并预测了工程实施后,工区内、外动力作用的程度和泥沙的蚀淤趋势发展。结果表明：开采区海采项目结束后,其淤积速度自NE 2～5 cm/...  相似文献   

20.
Sedimentation on the open-coast tidal flats of south-western Korea is controlled by seasonal variation in the intensity of onshore-directed winds and waves. As a result, an environmental oscillation takes place between tide-dominated conditions in summer and wave-dominated conditions in winter. In summer, thick muddy deposits, including sporadic storm deposits, accumulate in response to low wave energy, weak currents, and intense solar insolation that promotes consolidation of the mud at low tide. Bioturbation is minimal because of rapid sedimentation and soft substrate. During the autumn, the summer mud deposits experience erosion due to increasingly strong onshore winds and waves, until only small mud patches and mud pebbles remain. The concentration of ebb runoff between the mud patches produces small, ephemeral tidal creeks. In winter, storm waves occur frequently (ca 10 days a month) and dominate sedimentation in the intertidal zone, producing extensive wave-generated parallel lamination and short-wavelength (0·3–2 m) hummocky cross-stratification. The prevalence of strong onshore winds decreases in spring, allowing longer and more frequent intervals of calm weather, during which time muddy sediments are deposited by tidal processes. Over the long term, winter storm waves dominate sedimentation and the preserved deposits consist of amalgamated storm beds that resemble those generally associated with shorefaces. This raises the question of how many ancient ‘shorefaces’ are, in fact, open-coast tidal flats.  相似文献   

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