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1.
Abstract The present study examines sources of the interannual variability in salinity on the Newfoundland continental shelf observed in a 40‐year time series from an oceanographic station known as Station 27. Specifically, we investigate, through lag‐correlation analysis, the a priori hypotheses that the salinity anomalies at Station 27 are determined by freshwater runoff anomalies from Hudson and Ungava bays and by ice‐melt anomalies in Hudson Bay and on the Labrador Shelf. Interannual variations of summer runoff into Hudson Bay were significantly negatively correlated with salinity anomalies on the Newfoundland Shelf with a lag (9 months) that is consistent with expected travel times based on known current velocities in Hudson Bay and along the Labrador Shelf. Sea‐ice extent over the Labrador and northern Newfoundland shelves was significantly negatively correlated with salinity at a lag of 3 to 4 months, corresponding to the time of minimum salinity at Station 27. It appears that ice‐melt over the Labrador‐northern Newfoundland Shelf is primarily responsible for the seasonal salinity minimum over the Newfoundland Shelf. Interannual variability in runoff into Ungava Bay and ice‐melt in Hudson Bay were not correlated with interannual salinity variations on the Newfoundland Shelf. 相似文献
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Abstract An examination of the temperature and current measurements from the NE Newfoundland Shelf indicates significant frontal variability at about a 7‐day period during the months of June‐September 1989. The oscillations recorded in 1989 appeared to have propagated into the region from the Labrador Shelf. Significant variability in the position of the shelf water/slope water front in the Bonavista area is also found between years and within the same year. Time series measurements also indicated that the transition from winter to summer conditions in the inshore region may be occurring during late July to early August. 相似文献
4.
Abstract Airborne measurements in the atmospheric boundary layer (ABL) above the marginal ice zone (MIZ) on the Newfoundland Shelf reveal strong lateral variations in mean wind, temperature and the vertical fluxes of heat and momentum under conditions of cold, off‐ice wind. Flux measurements in (and near) the surface layer indicate that the neutral 10‐m drag coefficient depends on ice concentration, ranging from 2 × 10‐3 at 10% coverage to 5 × 10‐3 at 90%. Furthermore, cross‐ice‐edge transects consistently show increasing wind speed, temperature and heat flux in the off‐ice direction, but the momentum flux may either increase or decrease, depending on the relative importance of surface buoyancy flux and roughness. For the conditions encountered in this experiment, it appears surface wave maturity does not have a significant influence on the drag coefficient in fetch‐limited regimes near the ice edge. 相似文献
5.
Abstract Recent current measurements from the southern Labrador and northeastern Newfoundland shelves confirm the presence of inshore and offshore branches of the Labrador Current with high mean currents and low standard deviations. At mid‐shelf weaker and more variable currents occur over the banks, and cross‐shelf flows are found to be associated with the shelf topography. An annual cycle of the inshore branch, in phase with wind forcing, is significant on the NE Newfoundland Shelf but not detectable on Hamilton Bank. The phase of the annual cycle in the offshore branch is consistent with buoyancy, not wind forcing. The observations compare reasonably well with results from a barotropic model for the region and the International Ice Patrol (IIP) surface current map. Differences occur particularly in regions of high bathymetrie curvature or an ill‐defined shelf break. The model location of the Labrador Current lies inshore of that indicated by the data, suggesting the need for better definition of the northern inflow boundary condition and the inclusion of baroclinicity. The HP surface current map agrees well with observations offshore, but shows an unrealistic, broad inshore branch, especially on the Grand Bank These differences have important implications for the drift models. 相似文献
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ABSTRACTPresent global climate models (GCMs) are unable to provide reliable projections of physical oceanographic properties on the continental shelf off Newfoundland and Labrador. Here we first establish linear statistical relationships between oceanographic properties and coastal air temperature based on historical observations. We then use these relationships to project future states of oceanographic conditions under different emission scenarios, based on projected coastal air temperatures from global (Canadian Earth System Model, version 2 (CanESM2), Geophysical Fluid Dynamics Laboratory's Earth System Model, version 2M (GFDL-ESM2M)) and regional (Canadian Regional Climate Model (CRCM)) climate models. Estimates based on CanESM2 agree reasonably well with observed trends, but the trends based on two other models result in substantial underestimates. Projected trends are closer to observations under a high emission scenario than under median-level emission scenarios. Over the next 50 years, the increases in projected sea surface temperature off eastern Newfoundland (Station 27) range from 0.4° to 2.2°C. The increases in bottom ocean temperature over the Newfoundland and Labrador Shelves range from 0.4° to 2.1°C. The area of the cold intermediate layer (<0°C) on the Flemish Cap (47°N) section is projected to decrease by 9–35% of the 1981–2010 average. The decline in sea-ice extent off Newfoundland and Labrador ranges from 20 to 77% of the average (0.4–1.5?×?105?km2), and the reduction in the number of icebergs at 48°N off Newfoundland ranges from 30% to nearly 100% of the norm at this latitude. Despite differences among the models and scenarios, statistical projections indicate that conditions in this region will reach or exceed their maxima (sea surface temperature, bottom ocean temperature) and reach or fall below their minima (sea-ice extent, number of icebergs) that were observed during the course of monitoring activities over the past 30–60 years, possibly as early as 2040. We note, however, that the statistical relationships based on historical data may not hold in the future because of the changing influence of input from Arctic waters and because of large uncertainties in projected air temperatures from GCMs. 相似文献
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Abstract Analysis of current measurements taken between June and October 1984 at four moorings in Trinity Bay, Newfoundland, is discussed. The alongshore component of current exhibits baroclinic fluctuations coherent with the along‐bay component of wind stress at periods between 3 and 7 days. A two‐layer model of internal Kelvin waves propagating around the perimeter of an elongated bay and forced by a spatially uniform wind stress is presented. The observations support several features of the model response to wind forcing. Along the side of the bay on which Kelvin waves are incoming, the amplitude of the response increases into the bay and decreases with increasing frequency. Along the outgoing side of the bay the amplitude of the response generally shows a maximum at a frequency between 0.2 and 0.3 cpd. The phase lag between current and wind is consistent with a forced response. An example is given of upwelling and downwelling on opposite sides of the bay in agreement with the model behaviour. 相似文献
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Abstract Two sets of Synthetic Aperture Radar (SAR) images were collected, as part of the Labrador Ice Margin Experiment (LIMEX), over the Newfoundland Shelf on consecutive days in April 1990. Ice movement is detected from the displacement of ice floes between the two images sets and compared with ice drift data from six satellite‐tracked beacons and in situ CTD data. The ice velocity data derived from the SAR images and the beacons are used to generate a map of ice velocity vectors. A streamfunction map of ocean currents is produced by removing the direct wind‐driven component in the ice movement data, and by using an objective analysis method. The resulting flow pattern contains the offshore branch of the Labrador Current with a speed of 30 to 50 cm s?1. The current closely follows the shelf break topography from north to south through the study area (47–50.5°N) as a continuous flow. In comparison, if the wind effect was not removed from the ice velocity data, the calculated Labrador Current north of 50°N would stray from the shelf break. The position of the current axis and the current speed derived from the ice movement data are in good agreement with the geostrophic current computed from the CTD data. 相似文献
9.
Abstract The Geosat radar altimeter data from ～60 repeat cycles of the Exact Repeat Mission (ERM) over the period November 1986 to September 1989 have been analysed to show the annual variations of the sea‐surface slopes, corrected for ocean tides, over the Scotian Shelf and the Grand Banks. A coastal tidal model developed at the Bedford Institute of Oceanography, combined with the global tidal model of Schwiderski, is employed to remove the tidal signals from the sea‐surface heights over those regions. Linear regression is used to estimate the sea‐surface slopes over the inner shelf region, the outer shelf region, or a combination of the two along the Geosat ground tracks. Harmonic analysis is applied to the time series of sea‐surface slopes to derive the annual signals, showing that amplitudes are of order of 5 × 10‐7 (5 cm/100 km) with onshore slopes positive in winter and negative in summer. The largest annual cycles occur over the outer portion of the Laurentian Channel and the southern Grand Banks. The annual cycles differ between the eastern and western portions of the Scotian Shelf: in the east, the signal is synchronized with that of the Laurentian Channel, whereas in the west, the phase of the signal is advanced by 2–3 months. The annual signals over the eastern Scotian Shelf are comparable and consistent with historical hydrographie data along the Halifax Hydrographie Section. The amplitude and phase over the western Scotian Shelf are consistent with the adjusted sea level at the Halifax Station. The annual variability of the sea‐surface slopes over the Scotian Shelf and the Grand Banks is thought to be induced by the seasonal outflow from the Gulf of St Lawrence through Cabot Strait, and possibly by an annual cycle in the Slope Water current. 相似文献
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Abstract The hydrography and circulation of Conception Bay (Newfoundland) are described based on hydrographic, current‐meter and drifter data collected over four years (1988–1991). The seasonal cycles of temperature (‐1.6 to 13–17°C) and salinity (31–32.5) in the bay closely follow those on the adjacent shelf. Exchange of bottom water was observed in April 1989. Deepwater exchange was observed from late fall to early winter of 1989–90. Tidal currents are weak, 1–2 cm s‐1 for the M2 and K1 constituents. Observed Eulerian mean currents (<3 cm s‐1) are smaller than the standard deviation (1–11 cm s‐1); however, there is a persistent outflowing current of 10 to 20 cm s‐1 within 2 km of the shoreline on the eastern side of the outer bay. The Lagrangian correlation length scale is from 4 to 10 km, in agreement with the weak coherence squared (≤0.4) found between the fixed current‐meter sites separated by greater than 4–5 km. The variable currents (up to 20 cm s‐1) tend to be cyclonic. Cyclonic eddies were observed near the mouth on the eastern side of the bay, adjacent to the outflow. A simplified fractal dispersion model gives residence times of 42 d similar to those obtained from a scaling analysis (30–40 d) and a diagnostic numerical model (30 d). 相似文献
11.
Abstract The mid‐to‐bottom waters of the Labrador Shelf are shown to exhibit an anomalous along‐shelf temperature gradient, with warmer waters found in the north. This feature is present in summer and autumn but appears to reverse in December. Inadequate data are available during winter and spring to draw firm conclusions regarding this feature. A time averaged heat loss of the shelf waters to the atmosphere would result on average, in colder waters in the south (because of north‐south advection); however, it is shown that there is a net annual‐mean input of heat to the shelf waters. An examination of the seasonal temperature cycle at standard depths reveals that its phase is almost uniform below 30‐m depth on the northern banks of the Labrador Shelf. The limited phase variation suggests the influence of a plume of well mixed water originating near Hudson Strait. It thus appears that mixing at the entrance to Hudson Strait imparts a phase anomaly to the seasonal cycle in the north that contributes to the observed inversion of the expected latitudinal temperature gradient. 相似文献
12.
Ronald E. Stewart Dia T. Yiu Kwok K. Chung David R. Hudak Edward P. Lozowski Myron Oleskiw 《大气与海洋》2013,51(1):25-53
Abstract The passage of a winter storm is accompanied by changes in many surface and near‐surface parameters including temperature, humidity, wind, pressure, precipitation rate and type, cloud base height, visibility and accretion. These parameters were measured in association with the passage of precipitation‐type transitions over Newfoundland during the Canadian Atlantic Storms Program II field experiment. Three simple summaries of the observed weather events were developed. These summaries depend on the observed large‐scale synoptic conditions, which include warm fronts, a cold front and a trough. 相似文献
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Franklin B. Schwing 《大气与海洋》2013,51(1):157-180
Abstract Data collected during the Canadian Atlantic Storms Program (CASP) show subtidal variations in subsurface pressure (SSP) to be highly coherent throughout the Scotian Shelf region, and well correlated to fluctuations in the alongshelf component of wind stress (τy). Analysis using a frequency‐dependent multiple regression model verified that τy is the primary source of local forcing to the SSP field, although non‐locally generated variations in SSP are also important. The two components of local wind stress and a non‐local SSP term combine to explain over 90% of SSP variance on the Scotian Shelf. Statistical results describing the response to τy change dramatically depending upon the inclusion of non‐local forcing. In a model including both types of forcing, the SSP response to local forcing behaves like the solution to a dynamical model forced by time‐dependent wind stress with sea‐level prescribed to zero at the eastern cross‐shelf boundary. Local τy forcing becomes more effective to the west and onshore, whereas the phase suggests propagation to the west. The importance of τy is reduced at higher frequencies. Describing SSP with a statistical model containing local forcing alone may lead to an incorrect interpretation of SSP dynamics, particularly in the synoptic band where the wind variance is greatest. Energy originating from a non‐local source is most obvious at ω > 0.5 cpd and at locations on the eastern half of the shelf, but plays an important role at all sites and at all frequencies. These variations propagate to the west at speeds of 6.5 (ω < 0.2 cpd), 25–33 (0.2 cpd < ω < 0.5 cpd), and 12–17m s?1 (ω > 0.5 cpd). The exponential decay scales at all frequencies are ～900 km in the direction of phase propagation. The non‐local response is consistent with theoretical estimates of first‐ and second‐mode shelf waves for this region and represents the most direct evidence of shelf wave activity on the Scotian Shelf to date. 相似文献
14.
Abstract As part of the Canadian Atlantic Storms Program (CASP), near‐bottom current velocity, pressure, light transmission (as a measure of suspended sediment concentration) and water temperature were recorded using a variety of instruments deployed in water depths of 20 to 37 m on the inner Scotian Shelf, during February and March 1986. Detailed mapping of a 12‐km2 area encompassing the instrument mooring sites revealed a variety of bottom types. These include sand and gravel (both forming ripples at various scales), cobble‐boulder lags, and bedrock, resulting in bottom roughness estimates that vary widely (10?4 m < k < 10° m) over short horizontal distances (of the order 102 m). The velocity data provided information on the near‐bottom current response to winter storms anda basis for computations of sediment load and transport rates. The near‐bottom mean flow showed distinct storm‐driven circulation patterns, with velocities roughly parallel to alongshore wind stress but opposed to shore‐normal wind. Wave‐induced oscillatory motions also showed marked increases during storms and frequently dominated the near‐bottom flow. Sediment load (depth‐integrated concentration) and transport were computed using a model in which the load is related to the excess normalized shear stress. The computed mean concentrations were compatible with the optical transmis someter data. These computations yielded estimates ranging up to 0.7 kg m?2 for the mean sediment load and 443 kg m?1 h?1 for the net transport. Hindcast scour rates, of the order of 1 mm h?1 under moderate storm conditions were generally compatible with depths of scour measured by divers. 相似文献
15.
Abstract A modified response analysis in the form of an orthotide parametrization is used to derive major semi‐diurnal and diurnal tidal constituents over the Newfoundland and Scotian Shelves from TOPEX/POSEIDON altimeter data. The orthotide formulation simultaneously solves for eight major semi‐diurnal and diurnal constituents, and has an accuracy of better than ～1.5 cm for each constituent. Tidal elevations are derived from the altimeter data on the ascending and descending satellite ground tracks, and interpolated using the method of statistical interpolation. The semi‐diurnal constituents (M2, S2 and N2) compare favourably with available in‐situ observations and a numerical model. The diurnals (K1 and O1) are not as accurate as the semi‐diurnals, especially in the nearshore environment. The paper demonstrates the ability of TOPEX/POSEIDON altimetry to provide accurate tidal data over a continental shelf. 相似文献
16.
Abstract A coupled ice, ocean model for forecasting ice conditions on the Newfoundland shelf region is assessed by comparing hindcasts with satellite‐tracked ice beacon displacements and with changes in offshore ice edge location, ice thickness and southern ice extent derived from ice charts. The beacon velocity fields contain short timescale fluctuations which are not resolved by the model. The ratio of rms displacement error divided by the rms beacon displacement is 0.48 after 1 day and 0.23 after 8 days. The decrease in the scaled displacement error with increasing time is related to the short timescale motions. The skill in modelling displacement of the offshore ice edge is lower than in modelling ice displacement. Between mid‐February and mid‐April 1997, the effect of ice melt on the ice edge was a mean onshore displacement of 35 km overcoming an offshore advection of 24 km in 5 days. 相似文献
17.
《大气与海洋》2013,51(3):177-194
Abstract Flash density and occurrence features for more than 23.5 million cloud‐to‐ground (CG) lightning flashes detected by the Canadian Lightning Detection Network (CLDN) from 1999 to 2008 are analyzed on 20 × 20 km equal area squares over Canada. This study was done to update an analysis performed in 2002 with just three years of data. Flashes were detected throughout the year, and distinct geographic differences in flash density and lightning occurrence were observed. The shape and locations of large scale patterns of lightning occurrence remained almost the same, although some details were different. Flash density maxima occurred at the same locations as found previously: the Swan Hills and Foothills of Alberta, southeastern Saskatchewan, southwestern Manitoba and southwestern Ontario. A region of greater lightning occurrence but relatively low flash density south of Nova Scotia occurred at the same location as reported previously. New areas of higher flash density occurred along the US border with northwestern Ontario and southern Quebec. These appear to be northward extensions of higher flash density seen in the previous study. The greatest average CG flash density was 2.8 flash km?2 y?1 in southwestern Ontario, where the greatest single‐year flash density (10.3 flash km?2 y?1) also occurred. Prominent flash density minima occurred east of the Continental Divide in Alberta and over the Niagara Escarpment in southern Ontario. Lightning activity is seen to be highly influenced by the length of the season, proximity to cold water bodies and elevation. The diurnal heating and cooling cycle exerted the main control over lightning occurrence over most land areas; however, storm translation and transient dynamic features complicated the time pattern of lightning production. A large portion of the southern Prairie Provinces experienced more than 50% of flashes between 22:30 and 10:30 local solar time. The duration of lightning over a 20 × 20 km square at most locations in Canada is 5–10 h y?1, although the duration exceeded 15 h y?1 over extreme southwestern Ontario. Lightning occurred on 15–30 days each year, on average, over most of the interior of the country. The greatest number of days with lightning in a single year was 47 in the Alberta foothills and 50 in southwestern Ontario. Beginning and ending dates of the lightning season show that the season length decreases from north to south; however, there are considerable east‐west differences between regions. The season is nearly year‐round in the Pacific coastal region, southern Nova Scotia, southern Newfoundland and offshore. 相似文献
18.
Abstract A coupled ice‐ocean dynamical model is applied to the simulation of sea‐ice motion and distribution off Newfoundland during the Labrador Ice Margin Experiment (LIMEX), March 1987. In the model, the ice is coupled to a barotropic ocean through an Ekman layer that deepens with increasing wind speed. A 6‐hourly gridded wind dataset was used as input to drive the ice and the ocean. The results show that ice velocities with ice‐ocean coupling are appreciably higher than those without coupling because of the generation of wind‐driven coastal currents. This suggests that coupled ice‐ocean dynamics should always be considered in short‐term sea‐ice models. The model gives reasonable agreement with the observed ice edge except in the southern boundary where ice‐melt has a strong influence on the ice‐edge position. Ocean currents, sea level and ice velocities computed from the model are in qualitative agreement with limited current‐meter, tide‐gauge, and ice drifter trajectory data. 相似文献
19.
Abstract Sea surface temperature (SST) variability in the shelf‐slope region of the northwest Atlantic is described and then explained in terms of latent and sensible heat exchange with the atmosphere. The basic data are primarily engine‐intake temperature measurements made by merchant ships over the period 1946–80. The data have been grouped by month and area and an empirical orthogonal function analysis has been performed to determine the dominant modes of variation. The first two modes account for 44% of the total variance. The first mode corresponds to in‐phase changes of SST from the Grand Banks to Mid‐Atlantic Bight; the second mode corresponds to opposite changes of SST on the Grand Banks and Mid‐Atlantic Bight. The time‐dependent amplitudes of these large‐scale modes have pronounced low‐frequency components; the associated changes in SST are typically 3°C. It is also shown that winter anomalies last longer than summer anomalies; their typical decay scales are 6 and 3 months, respectively. The onshore component of geostrophic wind is significantly correlated with the amplitude of the first mode in winter. We note the strong land‐sea contrast of temperature and humidity in this region during winter and explain the wind‐SST correlation in terms of latent and sensible heat exchanges. The second mode (i.e. the difference in SST between the Grand Banks and Mid‐Atlantic Bight) also appears to be related to changes in atmospheric circulation during the winter. A stochastic model for mixed layer temperature is finally used to model the SST autocorrelation functions. Following Ruiz de Elvira and Lemke (1982), it includes a seasonally‐varying feedback coefficient. The model successfully reproduces the extended persistence of winter anomalies with physically realistic parameter values but it cannot account for the summer reinforcement of winter anomalies on the Scotian Shelf. We speculate that this is due to the occasional entrainment of water, cooled the previous winter, into the shallow summer mixed layer. 相似文献
20.
E. H. V. Dexter 《大气与海洋》2013,51(1):7-31
Abstract This paper describes the observational framework for the research reported within this Special Issue. The validation of the ERS‐1 synthetic aperture radar (SAR) for ocean wave measurement was the primary goal and focus; secondary goals were the validation of wave models and marine radars and the investigation of the wind stress/sea‐state relation in the open ocean. The planned focus of the observations on the ERS‐1 crossover node location and pass times over the Grand Banks of Newfoundland, and on the grid points of the Atmospheric Environment Service's operational wave prediction model, has produced the opportunity for an accurate calibration and a relevant validation of the ERS‐1 SAR, the wave model and the marine radars. The observations, made on the Grand Banks in winter, strongly emphasize the complexity of the atmospheric and wave fields encountered in the open sea at these latitudes. Their interpretation will provide a challenge, and will require consideration of a wide variety of data sources, both remotely sensed and in situ, all assimilated in the framework of physical ocean models. 相似文献