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1.
The secular trends for local tidal datums, tide ranges, and tidal harmonic constituents at 13 tidal gauge stations located along the coast of Japan were analyzed in this study. The general trends for mean higher high water (MHHW), mean high water (MHW), diurnal tide range (DTR), mean tide range (MTR), and relative mean sea level (RMSL) were positive, and for mean lower low water (MLLW) and mean low water (MLW) the trends were negative. The variation patterns were largest at Kushiro and Ofunato stations, both located in the open waters of the North Pacific Ocean. The tidal datums and tide ranges remained fairly stable at the Hakodate station, and an opposite trend was observed at the Maisaka station. The analysis of tidal harmonic constituents revealed a less pronounced pattern. The most distinct trend was observed for the M2 amplitude, which appears to be negative at a majority of the stations. The largest decrease in the M2 amplitude was observed at Kushimoto and Mera stations, also located in the open waters of the North Pacific Ocean. The negative trend is attributed to decreasing water depths at these stations, owing to small-scale local processes.  相似文献   

2.
A regional sea-ice?Cocean model was used to investigate the response of sea ice and oceanic heat storage in the Hudson Bay system to a climate-warming scenario. Projections of air temperature (for the years 2041?C2070; effective CO2 concentration of 707?C950?ppmv) obtained from the Canadian Regional Climate Model (CRCM 4.2.3), driven by the third-generation coupled global climate model (CGCM 3) for lateral atmospheric and land and ocean surface boundaries, were used to drive a single sensitivity experiment with the delta-change approach. The projected change in air temperature varies from 0.8°C (summer) to 10°C (winter), with a mean warming of 3.9°C. The hydrologic forcing in the warmer climate scenario was identical to the one used for the present climate simulation. Under this warmer climate scenario, the sea-ice season is reduced by 7?C9?weeks. The highest change in summer sea-surface temperature, up to 5°C, is found in southeastern Hudson Bay, along the Nunavik coast and in James Bay. In central Hudson Bay, sea-surface temperature increases by over 3°C. Analysis of the heat content stored in the water column revealed an accumulation of additional heat, exceeding 3?MJ?m?3, trapped along the eastern shore of James and Hudson bays during winter. Despite the stratification due to meltwater and river runoff during summer, the shallow coastal regions demonstrate a higher capacity of heat storage. The maximum volume of dense water produced at the end of winter was halved under the climate-warming perturbation. The maximum volume of sea ice is reduced by 31% (592?km3) while the difference in the maximum cover is only 2.6% (32,350?km2). Overall, the depletion of sea-ice thickness in Hudson Bay follows a southeast?Cnorthwest gradient. Sea-ice thickness in Hudson Strait and Ungava Bay is 50% thinner than in present climate conditions during wintertime. The model indicates that the greatest changes in both sea-ice climate and heat content would occur in southeastern Hudson Bay, James Bay, and Hudson Strait.  相似文献   

3.
The seasonal cycle of water masses and sea ice in the Hudson Bay marine system is examined using a three-dimensional coastal ice-ocean model, with 10 km horizontal resolution and realistic tidal, atmospheric, hydrologic and oceanic forcing. The model includes a level 2.5 turbulent kinetic energy equation, multi-category elastic-viscous-plastic sea-ice rheology, and two layer sea ice with a single snow layer. Results from a two-year long model simulation between August 1996 and July 1998 are analyzed and compared with various observations. The results demonstrate a consistent seasonal cycle in atmosphere-ocean exchanges and the formation and circulation of water masses and sea ice. The model reproduces the summer and winter surface mixed layers, the general cyclonic circulation including the strong coastal current in eastern Hudson Bay, and the inflow of oceanic waters into Hudson Bay. The maximum sea-ice growth rates are found in western Foxe Basin, and in a relatively large and persistent polynya in northwestern Hudson Bay. Sea-ice advection and ridging are more important than local thermodynamic growth in the regions of maximum sea-ice cover concentration and thickness that are found in eastern Foxe Basin and southern Hudson Bay. The estimate of freshwater transport to the Labrador Sea confirms a broad maximum during wintertime that is associated with the previous summers freshwater moving through Hudson Strait from southern Hudson Bay. Tidally driven mixing is shown to have a strong effect on the modeled ice-ocean circulation.  相似文献   

4.
Abstract

Trends in regional mean sea levels can be substantially different from the global mean trend. Here, we first use tide-gauge data and satellite altimetry measurements to examine trends in mean relative sea level (MRSL) for the coasts of Canada over approximately the past 50–100 years. We then combine model output and satellite observations to provide sea level projections for the twenty-first century. The MRSL trend based on historical tide-gauge data shows large regional variations, from 3?mm?y?1 (higher than the global mean MRSL rise rate of 1.7?mm?y?1 for 1900–2009) along the southeast Atlantic coast, close to or below the global mean along the Pacific and Arctic coasts, to –9?mm?y?1 in Hudson Bay, as indicated by the vertical land motion. The combination of altimeter-measured sea level change with Global Positioning System (GPS) data approximately accounts for tide-gauge measurements at most stations for the 1993–2011 period. The projected MRSL change between 1980 and 1999 and between 2090 and 2099 under a medium-high climate change emission scenario (A2) ranges from ?50?cm in northeastern Canada to 75?cm in southeastern Canada. Along the coast of the Beaufort Sea, the MRSL rise is as high as 70?cm. The MRSL change along the Pacific coast varies from ?15 to 50?cm. The ocean steric and dynamical effects contribute to the rise in MRSL along Canadian coasts and are dominant on the southeast coast. Land-ice (glaciers and ice sheets) melt contributes 10–20?cm to the rise in MRSL, except in northeastern Canada. The effect of the vertical land uplift is large and centred near Hudson Bay, significantly reducing the rise in MRSL. The land-ice melt also causes a decrease in MRSL in northeastern Canada. The projected MRSL change under a high emission scenario (Representative Concentration Pathway 8.5) has a spatial pattern similar to that under A2, with a slightly greater rise in MRSL of 7?cm, on average, and some notable differences at specific sites.  相似文献   

5.
Abstract

This study treats the energy balance during fast‐ice and floating‐ice conditions and examines overall seasonal patterns. The rate of ablation of the fast ice was controlled equally by net radiation and air temperature. The ratio of net/solar radiation increased 2.5 times during the ablation period owing to the decrease in ice albedo. Air temperature in the ablation zone was up to 8°C colder than that over the adjacent snow‐free terrestrial surface and remained near 0°Cfor the full ablation period. The sensible heat flux was small and downward (negative), whereas the evaporative heat flux was small and positive. Thus, the energy used in melting the ice was approximately equal to that provided by the net radiation. Above‐freezing air temperatures decreased the albedo through surface melting thus increasing net radiation. This combination of higher temperature and large net radiation was associated with offshore winds and resulted in large ablation relative to periods with colder onshore winds.

The floating‐ice period is one of great variability owing to changing ice conditions, variable current behaviour, tidal cycles and changing wind direction. The intertidal zone acts as a major heat sink, both early and late in the floating‐ice period. The turbulent heat fluxes were small and were either positive or negative. Nearly all of the energy from net radiation was used in melting ice and in warming tidal water during high tide and in warming the residual tidal ponds and in melting stranded ice rafts during low tide.

The overall study period, from May to September, included most of the season of positive radiation balance and above‐freezing temperatures. Winds were dominantly onshore in the first half of the period and equally onshore and offshore in the second half. Wind frequencies resembled longer term averages for other stations on James Bay and Hudson Bay. The ratio of net to solar radiation was at a maximum during the ice‐free period in August, whereas for adjacent terrestrial surfaces, it was largest at the summer solstice. Land‐sea breezes first developed in mid‐July and were influential in making offshore winds the dominant nocturnal regime. As a result, offshore winds were associated with small magnitudes of net radiation. Onshore winds were more than 5°C colder than those blowing offshore and their vapour pressure deficits were three times smaller. Convective heat fluxes were small for onshore winds and very small and usually negative for offshore winds. For all wind directions throughout the period, most of the available radiant energy was used to melt ice and to heat the sea water. This is a pattern similar to that of the ice‐covered or open sea and dissimilar to that of the adjacent terrestrial environment. It implies that the main energy‐balance transitions, during onshore airflow, occur at the high‐tide line.  相似文献   

6.
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   

7.
Observations and records maintained by the Hudson's Bay Company at York Factory and Churchill Factory on Hudson Bay between 1714 and 1825, serve as the source of information for a study of changes in the date of arrival of geese as a phonological indicator of climatic change. Changes in the migration pattern of geese are reflected in the changing date of arrival at the same location over a long period of time. Variations in this date are determined to be a function of southerly or tailwinds in the northward spring migration.  相似文献   

8.
Indices of summer sea ice severity in the eighteenth and nineteenth centuries have been reconstructed from sailing ships' log-books. The ice record for Hudson Strait extends from 1751 to 1889. Ice records are available for two parts of Hudson Bay and these extend from 1751 to 1870. The three records were derived from the same sources but the method of derivation applied in the bay was different to that applied in the strait. The years having the five largest ice indices in each of these records were identified. Also identified were the years in which major volcanic eruptions occurred between 1751 and 1889. The number of concurrences between the years with severe ice in Hudson Strait and the years with major eruptions was significant at the 99.5% level. In the western part of Hudson Bay this significance level was 95%. The years with severe ice in eastern Hudson Bay did not concur with major eruptions.  相似文献   

9.
As a result of affiliation between the Hudson's Bay Company and the Royal Society a relatively large number of instrumental temperature records are available from York Factory and Churchill Factory on the southwest of Hudson Bay beginning in 1768. The nature of these records, details of the instruments and information about the observers are presented. The major difficulty with the records is that the number of observations and the time of observation varied considerably. Adjustment factors were calculated for all of the combinations using a modern record maintained at the Churchill airport. By combining the Hudson's Bay Company record with data recorded by members of the Royal Canadian Mounted Police after 1852, and up to 1910, a long and relatively continuous record of daily and monthly average temperatures has been created for Central Canada.  相似文献   

10.
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11.
Abstract

The spatial and temporal relationships between subarctic Canadian sea‐ice cover and atmospheric forcing are investigated by analysing sea‐ice concentration, sea‐level pressure and surface air temperature data from 1953 to 1988. The sea‐ice anomalies in Hudson Bay, Baffin Bay and the Labrador Sea are found to be related to the North Atlantic Oscillation (NAO) and the Southern Oscillation (SO). Through a spatial Student's i‐test and a Monte Carlo simulation, it is found that sea‐ice cover in both Hudson Bay and the Baffin Bay‐Labrador Sea region responds to a Low/Wet episode of the SO (defined as the period when the SO index becomes negative) mainly in summer. In this case, the sea‐ice cover has a large positive anomaly that starts in summer and continues through to autumn. The ice anomaly is attributed to the negative anomalies in the regional surface air temperature record during the summer and autumn when the Low/Wet episode is developing. During strong winter westerly wind events of the NAO, the Baffin Bay‐Labrador Sea ice cover in winter and spring has a positive anomaly due to the associated negative anomaly in surface air temperature. During the years in which strong westerly NAO and Low/Wet SO events occur simultaneously (as in 1972/73 and 1982/83), the sea ice is found to have large positive anomalies in the study region; in particular, such anomalies occurred for a major portion of one of the two years. A spectral analysis shows that sea‐ice fluctuations in the Baffin Bay‐Labrador Sea region respond to the SO and surface air temperature at about 1.7‐, 5‐ and 10‐year periods. In addition, a noticeable sea‐ice change was found (i.e. more polynyas occurred) around the time of the so‐called “climate jump” during the early 1960s. Data on ice thickness and on ice‐melt dates from Hudson Bay are also used to verify some of the above findings.  相似文献   

12.
Previous work has found Hudson Bay seasonal sea ice particularly sensitive to climate change with a strong signal of earlier breakup dates. This work extends the previous analysis by including eight additional years of recent sea ice data. The expanded sea ice record, 1971 to 2011, revealed stronger and more statistically significant trends than the earlier work, most strikingly for the later freeze up. The average magnitude of the temporal trend for all 36 locations studied is 0.50 days/year for earlier breakup, 0.46 days/year for the later freeze-up, and 0.91 days/year for longer ice-free period. Of the 36 points, 12 points for the breakup period, 30 points for the freeze-up period, and 22 points for the ice-free season have accelerating temporal trends during the past decade.  相似文献   

13.
Abstract

The vertical structures of the mean and tidal flows in Hudson Strait are described from moored current‐meter data collected during an 8‐week period in August to October of 1982. The residual flow in the strongly stratified waters off Quebec is directed along the Strait to the southeast, is highly baroclinic and is concentrated near shore (within an offshore length scale of approximately an internal Rossby radius). Maximum mean speeds of 0.3 m s?1 were observed near‐surface (30 m). In the weakly stratified waters on the northern side of the Strait along Baffin Island the mean flow is northwestward. The maximum speeds are 0.1 m s?1 near‐surface (30 m) and the current amplitudes decrease to 0.05 m s?1 at 100 m. The mean southeastward transport is estimated to be 0.93 ±0.23 × 106 m3 s?1 with a northwestward transport of 0.82 ± 0.24 × 106 m3 s?1. Over most of the Strait the across‐channel residual currents are directed towards the Quebec shore with velocities ranging from 0.02 to 0.1 ms?1. Current variability is dominated by the tides, the M2 being the major tidal constituent. In the vicinity of the mooring the M2 tide is primarily barotropic, progressive in nature, and has along‐channel current amplitudes varying across the Strait from 0.20 to 0.45 m s?1. Observed differences in tidal sea‐level elevations across the Strait can be accounted for by the cross‐channel variations characteristic of Kelvin waves.  相似文献   

14.
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   

15.
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   

16.
Abstract

Three sites were instrumented to measure all components of the energy balance. The sites were located in the Churchill, Manitoba region and comprised a Sea Site on a sand spit 1 km seaward from the mainland, a Nearcoast Site 2 km inland from the coast and an Inland Site 65 km inland. Measurements were made continuously over a 90‐day period from 19 May to 16 August 1984. This period encompassed the bulk of the growing season.

The measurements were stratified into onshore and offshore wind directions and were compared for 10‐day periods. The comparisons show very significant differences attributable to the cold summer conditions promoted by the sea ice in Hudson Bay. The ground heat flux and latent heat flux were much greater during offshore winds but the sensible heat flux was greatest for onshore winds. Air temperatures averaged 7°C warmer for offshore than for onshore winds. The reasons for these differences are detailed and the climatic modifications that would probably result from earlier sea‐ice melt are discussed. Some implications of climatic modification are also noted.  相似文献   

17.
将8个主要平衡分潮加入到耦合模式中,对比研究潮汐对北大西洋模拟影响。由于潮汐的引入,模式模拟SST在北大西洋中纬度区域偏差显著减小,高纬度区域SST降温明显。SST模拟的改变使潮汐试验的海表净热通量模拟误差下降了约30%,但高纬度海冰显著增加。模式中引入潮汐对北大西洋上层环流,尤其是西边界流的路径模拟改进显著,这是SST及海表净热通量模拟改变的主要原因。同时,北大西洋上层和深层西边界流在潮汐的作用下,都表现出环流减弱的特点,这也使得大西洋经向翻转环流在26.5°N处上层2 km的输送减弱,与观测数据更为接近。较弱的大西洋经向翻转环流导致海洋热量在中低纬度聚集而无法输送到高纬度区域,这是造成潮汐试验模拟的海温在中低纬度偏高、高纬度偏低的原因,较弱的热输送也同时导致了潮汐试验中北半球海冰面积增加。  相似文献   

18.
Abstract

Total alkalinity and total carbonate determinations together with salinity and temperature are used to characterize water masses in Foxe Basin, Hudson Bay and Hudson Strait. From these measurements, we are able to infer the amounts of fresh water from river runoff and from sea‐ice meltwater. The average ice cover is estimated to be 1.9 m, and the residence time of river runoff in Hudson Bay is 3—4 years. Estimates of biological productivity were made by “correcting” total carbonate measurements for effects of biological processes, giving a value of 24 gC m a for new production.  相似文献   

19.
Abstract

Using satellite pictures of Baffin Bay and Davis Strait, ice‐floes were tracked in order to give weekly surface velocities for 1978–1979. The approximate location of the edge of the ice sheet was also determined.

In winter the direction of travel was mainly southward in Davis Strait then, as the summer approached, the edge of the ice sheet retreated northward and floe motion became less clearly defined — even going north on occasion in Baffin Bay.

Near shore speeds along Baffin Island exceeded 50 cm s‐1 in Davis Strait during November and February. Typical values in the winter/spring period were 10–15 cm s‐1 between Davis Strait and Hudson Strait. Wind records at nearby shore stations showed directions to be mainly from the northwest, roughly parallel to the Baffin Island coastline.

The study confirms the usefulness of satellite pictures as a data source for modelling surface ice movement and for selecting navigation routes in these northern waters.  相似文献   

20.
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