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1.
R.A. Flather 《大气与海洋》2013,51(1):22-45
Abstract The development of a tidal model for the west coast of Canada is described. The model is intermediate in resolution between coarse‐gridded global models and fine‐gridded local models; it provides a good representation of the main shelf regions and also includes a substantial area of the neighbouring ocean. The physical processes relevant to tides in both deep and shallow water are included. Calculations have been carried out for the M2 and K1 constituents and the model results were compared with extensive tide‐gauge observations and empirically based charts. For M2, the agreement between model results and observations is generally excellent, but for K1, which contains more small‐scale variability, the model results are not quite so good. The variability in K1 is associated with tidally generated continental shelf waves. Examination of the computed currents and energy fluxes suggests that shelf‐wave components are present in the model solution but, for the Vancouver Island shelf, their propagation is not reproduced accurately. This may be due to deficiencies in the model and/or to the influences of stratification and mean currents, which are neglected here. The model predicts that shelf‐wave components should also occur in diurnal tides on the Alaskan shelf. The significance of the tide‐generating potential and advection are also examined and further work proposed. 相似文献
2.
A. G. Nidheesh Matthieu Lengaigne Jérôme Vialard A. S. Unnikrishnan H. Dayan 《Climate Dynamics》2013,41(2):381-402
In this study, we analysed decadal and long-term steric sea level variations over 1966–2007 period in the Indo-Pacific sector, using an ocean general circulation model forced by reanalysis winds. The simulated steric sea level compares favourably with sea level from satellite altimetry and tide gauges at interannual and decadal timescales. The amplitude of decadal sea level variability (up to ~5 cm standard deviation) is typically nearly half of the interannual variations (up to ~10 cm) and two to three times larger than long-term sea level variations (up to 2 cm). Zonal wind stress varies at decadal timescales in the western Pacific and in the southern Indian Ocean, with coherent signals in ERA-40 (from which the model forcing is derived), NCEP, twentieth century and WASWind products. Contrary to the variability at interannual timescale, for which there is a tendency of El Niño and Indian Ocean Dipole events to co-occur, decadal wind stress variations are relatively independent in the two basins. In the Pacific, those wind stress variations drive Ekman pumping on either side of the equator, and induce low frequency sea level variations in the western Pacific through planetary wave propagation. The equatorial signal from the western Pacific travels southward to the west Australian coast through equatorial and coastal wave guides. In the Indian Ocean, decadal zonal wind stress variations induce sea level fluctuations in the eastern equatorial Indian Ocean and the Bay of Bengal, through equatorial and coastal wave-guides. Wind stress curl in the southern Indian Ocean drives decadal variability in the south-western Indian Ocean through planetary waves. Decadal sea level variations in the south–western Indian Ocean, in the eastern equatorial Indian Ocean and in the Bay of Bengal are weakly correlated to variability in the Pacific Ocean. Even though the wind variability is coherent among various wind products at decadal timescales, they show a large contrast in long-term wind stress changes, suggesting that long-term sea level changes from forced ocean models need to be interpreted with caution. 相似文献
3.
《大气与海洋》2013,51(4):405-422
Abstract To develop an understanding of the complex internal tidal phenomena observed near and inside Dixon Entrance, an idealized numerical model was developed for the area, which explores the influence of various topographic features on the scattering of internal tides. The model uses a non‐linear, two‐layered, frictionless finite difference formulation of the shallow water equations and is forced by a barotropic wave over simplified topography. It was found that the main bathymetric features responsible for the generation of semi‐diurnal internal tides are the steep continental slope together with the orientation of Dixon Entrance. The prevalent baroclinic wave pattern, which is similar to the one found by Buchwald (1971), suggests that the western end of Dixon Entrance can be considered as an internal tide generation region for the open ocean. Use of the simple model allows easy identification of the generated waves. When the model is run with a non‐flat channel it reproduces features observed inside Dixon Entrance. 相似文献
4.
Abstract Current meters and a thermistor chain deployed in the proximity of a drill‐ship over the continental shelf off Baffin Island revealed the presence of large amplitude internal waves. This paper reviews the properties of the internal waves, observed to propagate away from the coast and to coincide with the local low water phase of the tide at the drill‐ship. The observations are considered in terms of internal solitary wave models. A detailed comparison is presented of wave properties with a long‐wave model incorporating continuous stratification and shear. 相似文献
5.
6.
Abstract Winter‐time (1985–86) observations of sea‐level, surface waves, currents, bottom pressure, and water properties were made on the Scotian Shelf as part of the Canadian Atlantic Storms Program (CASP). The purpose of the field program and the locations, instrument systems, and sampling schemes are described. Statistics on the observed currents are presented, and monthly estimates of the longshore transport of the Nova Scotian Current are given for four months spanning the winter season (December to March). The 1985–86 transports are compared with previous estimates of the baroclinic transport made using the dynamic method. Cross‐shelf temperature and salinity distributions corresponding to the beginning and end of the field program are described and compared with the climatological means. The autospectra of the observed currents exhibit energy concentrations at frequencies of 0.2–0.5, 1.0, 1.4 and 2.0 cycles per day (cpd). Coastal‐trapped wave motions account for significant portions of the energy in the two lowest frequency bands, forced by wind stress and the diurnal tide, respectively. Inertial oscillations generated by wind stress events predominate at 1.4 cpd, and the semidiurnal tide, at 2 cpd. These motions are described separately, and references to more detailed discussions are given. 相似文献
7.
《大气与海洋》2013,51(4):239-266
Abstract The resonance of semi‐diurnal tidal elevations is investigated with a forward numerical forced damped global tide model and an analytical model of forced‐damped tides in a deep ocean basin coupled to a shelf. The analytical model contains the classical half‐wavelength and quarter‐wavelength resonances in the deep ocean and shelf, respectively, as well as a forcing‐scale dependence which depends on the ratio of the phase speed of open‐ocean gravity waves to that of the astronomical forcing. In the analytical model, when the deep ocean and shelf resonate separately at the same frequency, the resonance in the coupled system shifts to frequencies slightly higher and lower than the original frequency, such that a ‘double bump’ is seen in plots of elevation amplitude versus frequency. The addition of a shelf to a resonant open ocean tends to reduce open‐ocean tides, especially when the shelf is also near resonance. The magnitude of this ‘back‐effect’ is controlled by shelf friction. A weakly damped resonant shelf has a larger back‐effect on the open‐ocean tide than does a strongly damped shelf. Numerical simulations largely bear out the analytical model predictions, at least qualitatively. Idealized simulations show that continents enhance tides by enabling the half‐wavelength resonance. Simulations with realistic geometry and topography but varying longitudinal structure in the astronomical forcing display an influence of the forcing scale on tidal amplitudes somewhat similar to that seen in the analytical model. A frequency sweep in the semi‐diurnal band in experiments with realistic geometry and topography reveals weakly resonant peaks in the amplitudes of several shelf regions and in the globally averaged open‐ocean amplitudes. Finally, the back‐effect of the shelf upon the open ocean is seen in simulations in which locations of resonant coastal tides are blocked out and open‐ocean tidal elevations are significantly altered (increased, generally) as a result. 相似文献
8.
William W. Hsieh 《大气与海洋》2013,51(2):123-126
Abstract The First Nations (Da ‘naxda ‘xw) village of Kwalate, Knight Inlet, British Columbia was located along the shore of a funnel‐shaped bay. Archaeological investigations show that this was a major village that stretched 90 m along the shoreline and was home to possibly 100 or more inhabitants. Oral stories indicate that the village was completely swept away by a tsunami that formed when an 840‐m high rock avalanche descended into the water on the opposite side of the fjord. Shipboard geological mapping, combined with empirical tsunami modelling, indicate that the tsunami was likely 2 to 6 m high prior to run‐up into the village. Radiocarbon dates reveal that the village was occupied from the late 1300s CE until the late 1500s CE when it was destroyed by the tsunami. 相似文献
9.
The results of forecasting the Chilean tsunami in the Pacific Ocean on April 1,2014are presented. For the first time in Russia the forecast was prepared in the near real-time mode 9.5-10.5 hours before the tsunami attacked the Russian coast. A good agreement was obtained with the tsunami forms registered by DART stations along the US West Coast and the Aleutian and Kuril Islands. The information about the expected tsunami meets the requirements to the short-term tsunami forecast formulated by UNESCO Intergovernmental Oceanographic Commission. 相似文献
10.
Redistribution of sea level rise associated with enhanced greenhouse warming: a simple model study 总被引：1，自引：0，他引：1
Future sea level rise from thermal expansion of the World Ocean due to global warming has been explored in several recent studies using coupled ocean-atmosphere models. These coupled models show that the heat input by the model atmosphere to the ocean in such an event could be quite non-uniform in different areas of the ocean. One of the most significant effects predicted by some of the models is a weakening of the thermohaline circulation, which normally transports heat poleward. Since the greatest heat input from enhanced greenhouse warming is in the higher latitudes, a weakening of the poleward heat transport effectively redistributes the heat anomaly and the associated sea level rise to lower latitudes. In this study, the mechanism of ocean circulation spindown and heat redistribution was studied in the context of a much simpler, linearized shallow water model. Although the model is much simpler than the three-dimensional ocean circulation models used in the coupled model experiments, and neglects several important physical effects, it has a nearly 10-fold increase in horizontal resolution and clearer dynamical interpretations. The results indicated that advanced signals of sea level rise propagated rapidly through the action of Kelvin and Rossby waves, but the full adjustment toward a more uniform sea level rise took place much more slowly. Long time scales were required to redistribute mass through narrow currents trapped along coasts and the equatorial wave guide. For realistic greenhouse warming, the model showed why the sea level rise due to ocean heating could be far from uniform over the globe and hence difficult to estimate from coastal tide gauge stations. 相似文献
11.
Abstract In this paper, an overview of storm waves associated with intense weather systems affecting the east and west coasts of Canada is presented. The paper presents the wave climatology of the east and west coasts in terms of the 100‐year significant and maximum wave heights and further analyses the directional distribution of wave heights at selected locations in the Canadian east and west coasts offshore. The paper also analyses wave hazards associated with storm waves in the Beaufort Sea as well as the Canadian Great Lakes region. A section on ocean wave modelling provides a brief history of the development of ocean surface wave models and its present status. The paper further considers the impact of climate change scenarios on wave hazards and finally examines mitigation measures in terms of wave products available from operational wave models and related wave climatology. 相似文献
12.
S. Dutta 《Meteorology and Atmospheric Physics》2005,90(3-4):139-152
Summary In this paper, an attempt has been made to examine the effect of static stability on the pattern of three dimensional (3-D)
baroclinic lee wave across a meso-scale elliptical barrier. For this purpose first a 3-D meso scale lee wave model has been
developed. Then the model is applied to the Western Ghats (WG) using real time radio sonde data of Santacruz (19°7′N, 72°51′E)
(here after SCZ), a station on the windward side of WG, on the days when dynamic and thermodynamic conditions of the atmosphere
were favourable to generate lee waves.
It is found that the pattern of 3-D baroclinic lee wave is very much sensitive to the value of the static stability parameter
N2. It is found that during southwest monsoon season trapped lee waves are convergent type (contours of perturbation vertical
velocity w′ are crescent shaped convex down wind) and during winter they are divergent type (contours of w′ are crescent shaped concave down wind). The study shows that for a given profile of wind, the value of N2 must exceed certain threshold value to obtain divergent type lee wave, otherwise convergent type lee waves are found.
It is also found that in the southwest monsoon season, when atmosphere is neutrally stratified, a single divergent lee wave
corresponds to a single transverse lee wave, whereas in the winter season, when atmosphere is strongly stratified, a single
divergent lee wave corresponds to a number of transverse lee wave. Furthermore, in the former case long (or short) divergent
lee wave corresponds to short (or long) transverse lee wave, whereas in the later case long (or short) divergent lee wave,
in general, corresponds to long (or short) transverse lee wave.
This revised version was published online in November 2004 with corrected captions of Figs. 1 and 2. 相似文献
13.
Abstract Three arrays of current‐meter moorings were deployed under landfast sea ice in southeast Hudson Bay for eight weeks in spring 1986. Spectral analysis shows low‐frequency signals with periods of 3 to 11 days. These signals are interpreted as being due to coastal‐trapped waves propagating cyclonically in Hudson Bay; their theoretical dispersion relations and corresponding modal structures are presented for winter stratification and are compared with observations. At a period of 3 days both the modified external Kelvin wave and higher mode continental shelf waves may be important in describing the observed low‐frequency variability, whereas at a period of 10 days the Kelvin wave appears to be the dominant mode. The generation mechanisms for these coastal trapped waves are also investigated. Two sources have been studied: the longshore atmospheric pressure gradient and the average atmospheric pressure over the ice cover in Hudson Bay. Coherence and phase analyses performed with time series of longshore current and atmospheric forcing data reveal that both the average atmospheric pressure and the longshore atmospheric pressure gradient are important in explaining the observed low‐frequency variability, without indicating which one is the most important. 相似文献
14.
Richard D. Ray 《大气与海洋》2016,54(2):108-116
Since the late 1990s the semi-diurnal tide at Churchill, on the western shore of Hudson Bay, has been decreasing in amplitude, with M2 amplitudes falling from approximately 154?cm in 1998 to 146?cm in 2012 and 142?cm in 2014. There has been a corresponding small increase in phase lag. Mean low water, decreasing throughout most of the twentieth century, has levelled off. Although the tidal changes could reflect merely a malfunctioning tide gauge, the fact that there are no other measurements in the region and the possibility that the tide is revealing important environmental changes calls for serious investigation. Satellite altimeter measurements of the tide in Hudson Bay are complicated by the seasonal ice cover; at most locations less than 40% of satellite passes return valid ocean heights and even those can be impacted by errors from sea ice. Because the combined TOPEX/Poseidon, Jason-1, and Jason-2 time series is more than 23 years long, it is now possible to obtain sufficient data at crossover locations near Churchill to search for tidal changes. The satellites sense no changes in M2 that are comparable to the changes seen at the Churchill gauge. The changes appear to be localized to the harbour, or to the Churchill River, or to the gauge itself. 相似文献
15.
Abstract The design of a spar buoy, employed as one component of a current monitoring system deployed during 1980 in Davis Strait, and some of its response characteristics to ocean waves are presented. The buoy was 36.5 ft (11.13 m) in length with upper and lower masts 0.5ft (15.2 cm) in diameter and buoyancy hulls, centrally located, 2 ft (61.0 cm) in diameter. Power for the system was supplied from lead‐acid batteries in a ballast tank on the lower end. Telemetry electronics were located in a 1‐ft (30.5‐cm) diameter case on the upper end, below the antenna. The buoy weighed about 1,635 lb (746kg) and could be man‐handled at sea with relatively light lifting equipment. It had a damped period of 16s and a significant heave response of about 62% of the significant wave height of the forcing spectrum. Scale model tests indicated that the buoy would be operational in heavy sea swell up to about 20ft in height with pitching angles of less than 10° off vertical. Observations at sea have shown that the buoy followed swell waves better than the 62% heave response figure would imply and had negligible pitching motions except during severe storms. The design was judged to be successful in providing a stable base for VHF transmission and is recommended for use in other applications. 相似文献
16.
Abstract A powerful storm passed over the coastal waters of eastern Canada on the 21 and 22 January 2000 causing significant damage to coastal infrastructure. The storm generated a large (>1.4 m) storm surge in the southern Gulf of St. Lawrence that unfortunately coincided with a high spring tide. This resulted in record high water levels in the southern Gulf of St. Lawrence (e.g., the highest level at Charlottetown since records began in 1911) and severe flooding around Prince Edward Island and along the eastern shore of New Brunswick. During January 2000, a recently developed storm surge forecast system was running in pre‐operational mode at Dalhousie University. The core of the forecast system is a depth‐averaged, non‐linear, barotropic ocean model driven by forecast winds and air pressures produced by the Canadian Meteorological Centre's regional atmospheric forecast model. In this study we assess the forecast skill of the surge model for the 21 January storm by comparing its 24‐hour forecasts with two independent hourly dataseis: (i) sea levels recorded by 12 tide gauges located in eastern Canada and the north‐eastern United States, and (ii) depth‐mean currents recorded by an acoustic Doppler current profiler deployed on the outer Scotian Shelf. Overall, the forecasts of coastal sea level and depth‐mean currents are reasonable and have forecast errors below about 0.1 m and 0.1 m s?1 respectively. 相似文献
17.
Abstract The European Space Agency ERS‐1 C‐band V‐V polarization synthetic aperture radar (SAR) and the Russian Almaz S‐band H‐H polarization SAR are compared for their wavenumber response to ocean wave fields existing on 23 November 1991 at the Grand Banks site of the North American ERS‐1 SAR Wave Spectra Validation Experiment. Two‐dimensional wave spectra from two Wavec heave, pitch and roll buoys and a Canadian CV‐580 aircraft C‐band V‐V polarization SAR are used to condition a linear modulation transfer model of wave imaging with SAR. A model of hydrodynamic modulation is included with the velocity bunching and tilt imaging mechanisms to better understand wind and wave interactions. Krogstad's quasi‐linear formulation of Hasselmann's ocean‐SAR integral transform is applied to model SAR velocity bunching and azimuth smearing. Narrow and broad bandwidth components of azimuth wavenumber response for the aircraft SAR are associated with, respectively, non‐linear and incoherent velocity smearing during Doppler resolution of the radar scene. The stationary resolutions of the SAR systems are compared for homogeneous scenes of wind‐roughened, but fetch‐limited, sea surfaces. This comparison is conducted in the Chesapeake Bay of Maryland using ERS‐1 and Almaz satellite imagery collected on 9 May 1992 and 14 May 1991, respectively. The results confirm that SAR imaging of ocean waves can be improved by flying platforms with low R/V (range/velocity) ratios to alleviate the azimuth velocity smear, and near‐nadir incidence angles to increase the effect of tilt modulation. 相似文献
18.
Abstract The propagation of baroclinic Kelvin and Rossby waves in a fairly coarse‐resolution numerical reduced‐gravity ocean model is investigated using simple geostrophic adjustment experiments in a box‐like domain. Numerical experiments using three different horizontal resolutions (4° × 5°,2° × 2.5° and l° × 1.25°) with properly scaled eddy viscosity coefficients show that the phase speed of the model Kelvin waves is almost exactly proportional to the grid resolution, but is virtually independent of the model viscosity. These results are consistent with the findings of Hsieh et al. (1983) and Wajsowicz and Gill (1986). It is also shown that the two relevant parameters that govern the propagation and decay of these waves, namely the grid‐resolution parameter Δ = Δx/a (where Δx is the grid size and a is the baroclinic Rossby radius, viz. a = C/f, with C being the phase speed of inviscid internal gravity waves in a continuum) and the viscosity parameterΔ = Amλ/2πfa3 (where Am is the eddy viscosity coefficient and λ is the alongshore wavelength) can be replaced with Δ only. This is because in Munk (1950)‐type models, the viscosity parameter Δ scales with Δ3. For Δ3 >1, the Kelvin wave phase speed is cK ΔC/Δ and the alongshore decay length scale is of the order of the perimeter of the basin, viz., 0(104) km. In contrast to the case for Kelvin waves, the phase speed of the model Rossby waves is not that much different from its value in a continuum and depends only weakly on the model resolution. This is in good agreement with the theoretical results of Wajsowicz (1986). On the other hand, the model Rossby waves are severely damped, within a distance of the order of a wavelength, by the large eddy viscosity of the model. We therefore extrapolate that for a proper simulanon of Kelvin and Rossby waves in this type of numerical ocean model, we need a grid size smaller than 1° × 1°, and a higher‐order turbulent closure scheme that will reduce the eddy viscosity coefficient. 相似文献
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High temperature accompanied with high humidity may result in unbearable and oppressive weather. In this study, future changes of extreme high temperature and heat stress in mainland China are examined based on daily maximum temperature (Tx) and daily maximum wet-bulb globe temperature (Tw). Tw has integrated the effects of both temperature and humidity. Future climate projections are derived from the bias-corrected climate data of five general circulation models under the Representative Concentration Pathways (RCPs) 2.6 and 8.5 scenarios. Changes of hot days and heat waves in July and August in the future (particularly for 2020–50 and 2070–99), relative to the baseline period (1981–2010), are estimated and analyzed. The results show that the future Tx and Tw of entire China will increase by 1.5–5°C on average around 2085 under different RCPs. Future increases in Tx and Tw exhibit high spatial heterogeneity, ranging from 1.2 to 6°C across different regions and RCPs. By around 2085, the mean duration of heat waves will increase by 5 days per annum under RCP8.5. According to Tx, heat waves will mostly occur in Northwest and Southeast China, whereas based on Tw estimates, heat waves will mostly occur over Southeast China and the mean heat wave duration will be much longer than those from Tx. The total extreme hot days (Tx or Tw > 35°C) will increase by 10–30 days. Southeast China will experience the severest heat stress in the near future as extreme high temperature and heat waves will occur more often in this region, which is particularly true when heat waves are assessed based on Tw. In comparison to those purely temperature-based indices, the index Tw provides a new perspective for heat stress assessment in China. 相似文献