Physical properties and isotopic characteristics of landfast sea ice around the North Water (NOW) Polynya region     

Toshiyuki Kawamura  Kunio Shirasawa  Kunio Kobinata 《大气与海洋》2013,51(3):173-182

Abstract

An ice core sampling program was conducted during the North Water (NOW) Polynya Project 1998 Experiment in northern Baffin Bay during April‐May 1998. The physical properties of snow and sea ice as well as the microstructure and stable isotopic composition of first‐year landfast sea ice near the polynya were investigated. The thickness of sea ice at the sampling sites ranged between 147 and 194 cm with thinner snow cover during the period between mid‐April and late May. The ice was characterized as typical first‐year landfast sea ice, being composed of a thin granular ice layer at the top and an underlying columnar ice layer towards the bottom of the ice. The samples obtained at a site closer to the ice edge of the polynya contained a thin granular ice layer originating from frazil ice near the ice bottom. Formation of frazil ice was considered to be caused by turbulent processes induced by winds, waves and currents forced from the polynya and also mixing with water masses produced at the polynya.  相似文献   

C‐band SAR backscatter characteristics of Arctic sea and land ice during winter     

Konrad Steffen  John Heinrichs 《大气与海洋》2013,51(3):289-299

Abstract

Synthetic Aperture Radar (SAR) data has become an important tool for studies of polar regions, due to high spatial resolution even during the polar night and under cloudy skies. We have studied the temporal variation of sea and land ice backscatter of twenty‐four SAR images from the European Remote Sensing satellite (ERS‐1) covering an area in Lady Ann Strait and Jones Sound, Nunavut, from January to March 1992. The presence of fast ice in Jones Sound and glaciers and ice caps on the surrounding islands provides an ideal setting for temporal backscatter studies of ice surfaces. Sample regions for eight different ice types were selected and the temporal backscatter variation was studied. The observed backscatter values for each ice type characterize the radar signatures of the ice surfaces. This time series of twenty‐four SAR images over a 3‐month period provides new insights into the degree of temporal variability of each surface. Ice caps exhibit the highest backscatter value of ‐3.9 dB with high temporal variability. Valley glacier ice backscatter values decrease with decreasing altitude, and are temporally the most stable, with standard deviations of 0.08–0.10 dB over the 90‐day period.

First‐year ice and lead ice show a negative trend in backscatter values in time and a positive correlation of up to 0.59 with air temperature over the 90‐day period. For first‐year ice and lead ice, episodes of large temperature fluctuations (±12°C) are associated with rapid changes in backscatter values (±2 dB). We attribute the backscatter increase to a temperature‐induced increase in brine volume at the base of the snow pack. Multi‐year ice, conglomerate ice and shore ice are relatively stable over the 3‐month period, with a backscatter variation of only a few dBs. An observed lag time of up to three days between backscatter increase/decrease and air temperature can be attributed to the insulation effect of the snow cover over sea ice. The net range of the backscatter values observed on the most temporally stable surface, valley glacier ice, of about 0.30 dB indicates that the ERS‐1 SAR instrument exceeds the 1 dB calibration accuracy specified for the Alaska SAR Facility processor for the three winter months.  相似文献   

Significance of nitrogen dioxide absorption in estimating aerosol optical depth and size distributions     

R. Schroeder  J.A. Davies 《大气与海洋》2013,51(2):107-114

Abstract

Changes to the Beaufort Sea shoreline occur due to the impact of storms and rising relative sea level. During the open‐water season (June to October), storm winds predominantly from the north‐west generate waves and storm surges which are effective in eroding thawing ice‐rich cliffs and causing overwash of gravel beaches. Climate change is expected to be enhanced in Arctic regions relative to the global mean and include accelerated sea‐level rise, more frequent extreme storm winds, more frequent and extreme storm surge flooding, decreased sea‐ice extent, more frequent and higher waves, and increased temperatures. We investigate historical records of wind speeds and directions, water levels, sea‐ice extent and temperature to identify variability in past forcing and use the Canadian Global Coupled Model ensembles 1 and 2 (CGCM1 and CGCM2) climate modelling results to develop a scenario forcing future change of Beaufort Sea shorelines. This scenario and future return periods of peak storm wind speeds and water levels likely indicate increased forcing of coastal change during the next century resulting in increased rates of cliff erosion and beach migration, and more extreme flooding.  相似文献   

Some measurements and observations of very old sea ice and brackish ice,Ward Hunt Ice Shelf,N.W.T.     

Martin O. Jeffries  William M. Sackinger 《大气与海洋》2013,51(3):553-564

Abstract

Using ¹⁸O/¹⁶O ratio measurements, sea ice and brackish ice have been identified in a 10‐m ice core from Ward Hunt Ice Shelf. Brackish ice constitutes 62% of the core, and sea ice the remainder. The sea ice and brackish ice occur in alternating layers of 2–4 m thickness. The mean salinity of brackish ice (0.22) is an order of magnitude lower than that of the sea ice (1.26). The discrete sea and brackish ice layers and their individual salinity populations have been maintained apparently while the ice has aged and been raised about 40–50 m from the bottom of the ice shelf to its surface, a process taking roughly 400–500 years. Thin sections of the brackish ice reveal variable textures and an almost complete absence of cellular substructure that is associated with brine inclusion and retention in modern sea ice. Thin sections of the old sea ice show evidence of the former cellular substructure that appears to have been altered from the original. The discrete salinity populations and variable textures are briefly discussed.  相似文献   

Coupled ice‐ocean variability in the Greenland Sea     

A.T. Roach  K. Aagaard  F. Carsey 《大气与海洋》2013,51(3):319-337

Abstract

A major surface feature of the Greenland Sea during winter is the frequent eastward extension of sea ice south of 75°N and an associated embayment to the north. These features are nominally connected with the East Greenland Current, and both the promontory and the embayment are readily apparent on climatic ice charts. However, there are significant changes in these features on time‐scales as short as a few days. Using a combination of satellite microwave images (SSM/I) of ice cover, meteorological data and in situ velocity, temperature and salinity records, we relate the ice distribution and its changes to the developing structure and circulation of the upper ocean during winter 1988–1989. Our measurements illustrate the preconditioning that leads to convective overturn, which in turn brings warmer water to the surface and results in the rapid disappearance of ice. In particular, the surface was cooled to the freezing point by early December and the salinity then increased through ice formation (about 0.016 m d^‐1) and brine rejection. Once the vertical density gradient was sufficiently eroded, a period of high heat flux (>300 W m^‐2) in late January provided enough buoyancy loss to convectively mix the upper water column to at least 200 m. We estimate vertical velocities at about 3 cm s^‐1 downward during the initial sinking. The deepening of the thermocline raised surface temperatures by over 1°C resulting in nearly 1.5 × 10⁵ km² of ice‐melt within two days. Average rates of ice retreat are about 11 km d^‐1 southwestward, generally consistent with a wind‐driven flow. Comparison of hydrographic surveys from before and after the overturning indicate the fresh water was advected out of the area, possibly to the south and east of our moorings.  相似文献   

Pre-Melt Energy Budget of an Arctic Snowpack on Landfast First-Year Sea Ice     

R. L. Raddatz  D. G. Barber 《大气与海洋》2016,54(4):353-363

The pre-melt energy budget of a snowpack on landfast first-year sea ice at a remote site in the Canadian Arctic Archipelago was analyzed. Over a 19-day period, the total heat conducted into the snowpack at the snow–sea-ice interface was the largest single energy transfer to the snowpack, while each of the turbulent heat fluxes removed comparable amounts of energy. The total energy transferred from the snowpack (∑Q?≈??7027?kJ?m^?2) should have reduced its temperature; however, the opposite occurred. The snowpack’s temperature at both the 7 and 13?cm depths increased over the pre-melt period. The total change in internal energy and latent heat of the snowpack (ΔU_snowpack)_, derived from 15-minute changes in the snowpack’s temperature over the pre-melt period, was approximately 672?kJ?m^?2. Closure of the energy budget was not achieved for either the daily or the total pre-melt period. The terms of the energy budget were determined independently; thus, the failure to close the energy budget was the result of the accumulation of errors associated with all the terms. However, for snow on first-year sea ice, the parameterization of the salinity and temperature dependence of the “specific heat” of the basal layer of the snowpack was likely the primary source of error. The snowpack plays a central role in the transfer of energy across the ocean–sea-ice–atmosphere interface, but an adequate method for modelling the evolution of snow on Arctic sea ice including the energy budget, which determines the warming rate and subsequent melt rate of the snow, has yet to be developed.  相似文献   

The effects of precipitation and river runoff in a coupled ice-ocean model of the Arctic   总被引：1，自引：0，他引：1  

J. W. Weatherly  J. E. Walsh 《Climate Dynamics》1996,12(11):785-798

A coupled ice-ocean model of the Arctic is developed in order to study the effects of precipitation and river runoff on sea ice. A dynamic-thermodynamic sea ice model is coupled to an ocean general circulation model which includes a turbulent closure scheme for vertical mixing. The model is forced by interannually varying atmospheric temperature and pressure data from 1980–1989, and spatially varying mean monthly precipitation and river runoffs. Salinity and fresh water fluxes to the ocean from ice growth, snow melt, rain, and runoffs are computed, with no artificial constraints on the ocean salinity. The modeled ice thickness is similar to the observed pattern, with the thickest ice remaining against the Canadian Archipelago throughout the year. The modeled ice drift reproduces the Beaufort gyre and Transpolar drift exiting through Fram Strait. The stable arctic halocline produced by the vertical mixing scheme isolates the surface from the Atlantic layer and reduces the vertical fluxes of heat and salinity. A sensitivity experiment with zero precipitation results in rapidly decreasing ice thickness, in response to greater ocean heat flux from a weakening of the halocline, while an experiment with doubled precipitation results in a smaller increase in ice thickness. A zero-runoff experiment results in a slower decrease in ice thickness than the zero-precipitation case, due to the decadal time scale of the transport of runoff in the model. The results suggest that decadal trends in both arctic precipitation and river runoffs, caused either by anthropogenic or natural climatic change, have the potential to exert broad-scale impacts on the arctic sea ice regime. Received: 6 February 1996 / Accepted: 4 April 1996  相似文献   

Energy balance of the intertidal zone of Western Hudson bay II: Ice‐dominated periods and seasonal patterns     

Wayne R. Rouse 《大气与海洋》2013,51(2):346-366

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   

On vertical interpolation and truncation in connexion with use of sigma system models     

Hilding Sundqvist 《大气与海洋》2013,51(1):37-52

Abstract

The Mackenzie Shelf in the Canadian Beaufort Sea receives large amounts of freshwater runoff in winter and, yet, it also produces ventilating water masses by brine rejection from growing ice. We examine physical and chemical data to see how these contradictory processes can occur juxtaposed on the shelf. Measurements of salinity and δ¹⁸O both from ice cores and the water column are used to infer the separation into two convective regimes due to the under‐ice topography of the system of large pressure ridges that forms at the boundary between landfast ice and pack ice. Outside this ridge system the ice cover is subject to frequent openings due to offshore ice motion. The inner regime is thus dominated by the impoundment of Mackenzie River water, whereas the outer regime is subject to brine enhancement. This paper compares freezing processes and system evolution for these two regimes in winter.  相似文献   

Comparison of weather station snowfall with winter snow accumulation in high arctic basins     

Ming‐ko Woo  Richard Heron  Philip Marsh  Peter Steer 《大气与海洋》2013,51(3):312-325

Abstract

Most water balance studies in the High Arctic indicate that the weather stations underestimate annual precipitation, but the magnitude of such error is unknown. Based on up to seven years of field measurements, this study provides a comparison of snowfall at weather stations with the winter snow accumulation in their nearby drainage basins.

Snowfall is the major form of precipitation in the polar region for nine months every year. Without vegetation, snowdrift is controlled by the local terrain. By establishing the snow characteristics for different terrain types, total basin snow storage can be obtained by areally weighting the snow cover for various terrain units in the basin. Such a method was successfully employed to compute total winter snowfall in the drainage basins near Resolute, Eureka and Mould Bay. Results show that the basins had 130 to 300per cent more snow than the weather stations recorded. Using revised snowfall values that are reinforced by Koerner's snow core measurements from ice‐caps, it is hoped that a more realistic precipitation map can be provided for the High Arctic.  相似文献   

The international polar year (IPY) circumpolar flaw lead (CFL) system study: The importance of brine processes for α‐ and γ‐hexachlorocyclohexane (HCH) accumulation or rejection in sea ice     

《大气与海洋》2013,51(4):244-262

Abstract

We present evidence that both geophysical and thermodynamic conditions in sea ice are important in understanding pathways of accumulation or rejection of hexachlorocyclohexanes (HCHs). α‐ and γ‐HCH concentrations and α‐HCH enantiomer fractions have been measured in various ice classes and ages from the Canadian High Arctic. Mean α‐HCH concentrations reached 0.642 ± 0.046 ng L–1 in new and young ice (<30 cm), 0.261 ±0.015 ng L–1 in the first‐year ice (30–200 cm) and 0.208 ±0.045 in the old ice (>200 cm). Mean γ‐HCH concentrations were 0.066 ± 0.006 ng L–1 in new and young ice, 0.040 ±0.002 ng L–1 in the first‐year ice and 0.040 ±0.007 ng L–1 in the old ice. In general, α‐HCH concentrations and vertical distributions were highly dependent on the initial entrapment of brine and the subsequent desalination process. γ‐HCH levels and distribution in sea ice were not as clearly related to ice formation processes. During the year, first‐year ice progressed from freezing (accumulation) to melting (ablation). Relations between the geophysical state of the sea ice and the vertical distribution of HCHs are described as ice passes through these thermodynamic states. In melting ice, which corresponded to the algal bloom period, the influence of biological processes within the bottom part of the ice on HCH concentrations and α‐HCH enantiomer fraction is discussed using both univariate and multivariate approaches.  相似文献   

Using δ<Superscript>18</Superscript>O as a Tracer of the Formation of Water Masses in the Laptev Sea. Part 1. Quantification of Ice Formation and Melting     

I. A. Semeryuk  A. A. Namyatov 《Russian Meteorology and Hydrology》2018,43(9):591-598

Data on salinity and δ¹⁸O from the NASA open-source database are used to estimate the Laptev Sea water mass transformation during ice formation and melting. The indicator of these processes is salinity variation. The estimates for the Laptev Sea show that the amount of meltwater can reach 40% for the sea water with salinity below 7 psu. In this case, sea water salinity reduction due to the meltwater inflow alone can be equal to 0.2-0.7 psu. In the sea water with salinity above 7 psu, ice formation prevails over ice melting. This process is the most strongly pronounced in the range of sea water salinity from 15 to 25 psu. In this salinity range, the average water removal for the ice formation makes up 9% (the maximum is 24%), and the average salinity growth is 0.5 psu (the maximum is 1.7 psu). The most transformed sea water masses during ice formation are located in the bottom layer of the shallow southern and southeastern parts of the Laptev Sea, where the sea depth is not more than 50 m.  相似文献   

A note on brine layer spacing of first‐year sea ice     

M. Nakawo  N.K. Sinha 《大气与海洋》2013,51(2):193-206

Abstract

Brine layer spacing has been measured in a core sample taken 19 January 1978 from Eclipse Sound, Baffin Island, Canada. Observations on snow and ice conditions and a record of air temperatures for the entire growth season allowed correlation of the brine layer spacing with the growth rate of the sea ice. Growth rate is related to climatology, and the vertical brine layer spacing profile in the ice provides a record of previous weather conditions. It is suggested that the spacing is inversely proportional to the growth rate, and could also be dependent on crystallographic orientation. The spacing decreased rapidly with depth near the bottom of the core sample, and this is not compatible with a general relation between spacing and growth rate. Before a definitive statement can be made, cores from a variety of locations, grown in a range of meteorological conditions, will have to be studied.  相似文献   

Comparison of airborne electromagnetic ice thickness data with NOAA/AVHRR and ERS‐1/SAR images     

S.J. Prinsenberg  I.K. Peterson  Scott Holladay 《大气与海洋》2013,51(1):185-205

Abstract

Snow‐plus‐ice thickness and surface‐ice roughness data collected by a helicopter‐towed sensor package was used to identify surface‐ice properties in March 1992 AVHRR and SAR images for the land‐fast and mobile pack ice off the northern coast of Newfoundland. The sensor package consisted of an electromagnetic induction sensor and laser profilometer. Observed snow depths and ice thicknesses verified that snow‐plus‐ice thickness over undeformed ice can be obtained to an accuracy of ±10 cm. Snow‐plus‐ice thickness and surface roughness data for flight sections covering several hundred kilometres indicated the change in pack ice properties seen in images from thin, smooth coastal ice and open water conditions to thick, rough consolidated offshore pack ice. Ice charts covering the same area showed similar variations in ice conditions based on AVHRR and fixed‐wing reconnaissance data. In the ERS‐1 SAR image, low backscattering coefficients were associated with large, smooth coastal floes interspersed with areas of high backscatter indicating the presence of waves in open water areas. Backscattering coefficients were higher in the rubble areas near the inshore edge of the pack ice than in the interior of the pack ice itself. Distinguishing ice types on the basis of tone alone in SAR imagery was found to be problematic; however in combination with other remotely sensed data such as AVHRR data, SAR data will become more useful in distinguishing ice types.  相似文献   

Mean Profiles of Moisture Fluxes in Snow-Filled Boundary Layers   总被引：1，自引：0，他引：1  

David A. R. Kristovich  Roscoe R. Braham Jr 《Boundary-Layer Meteorology》1998,87(2):195-215

Profiles of moisture fluxes have been examined for convective boundary layers containing clouds and snow, using data derived from aircraft measurements taken on four dates during the 1983/1984 University of Chicago lake-effect snow project. Flux profiles were derived from vertical stacks of aircraft cross-wind flight legs taken at various heights over Lake Michigan near the downwind shore. It was found that, if ice processes are taken into account, profiles of potential temperature and water content were very similar to those presented in past studies of convective boundary layers strongly heated from below. Profiles of total water content and equivalent potential temperature adjusted for ice were nearly invariant with height, except very near the top of the boundary layer, suggesting that internal boundary-layer mixing processes were rapid relative to the rates at which heat and vapour were transported into the boundary layer through entrainment and surface fluxes. Ice was found to play a significant, measurable role in boundary-layer moisture fluxes. It was estimated that 40 to 57% of the upward vapour flux was returned to the surface in the form of snow, converting about 45 to 64% of the surface latent heat flux into sensible heat in the snow-producing process. Assuming advective fluxes are relatively small (thought to be appropriate after the first few tens of km over the lake as suggested by past studies), the boundary layer was found to warm at a rate faster than could be explained by surface heat fluxes and latent heat releases alone, the remainder of the heating presumably coming from radiational processes and entrainment. Discussions of moisture phase change processes throughout the boundary layer and estimates of errors of these flux measurements are presented.  相似文献   

Sea‐ice interaction and the stability of the thermohaline circulation     

Jiayan Yang  J. David Neelin 《大气与海洋》2013,51(4):433-469

Abstract

The role of sea‐ice in affecting the stability and long‐term variability of the oceanic thermohaline circulation (THC) is studied in this paper. The emphasis is placed on studying how sea‐ice might affect the stability and the long‐term variability of the THC through modulations of the surface heat and freshwater fluxes. A simple box model is analyzed to elucidate qualitatively the distinct physical meanings of these two processes. The analytical solution of this simple model indicates that, for the long timescales considered here, the thermal insulation stabilizes the THC while the freshwater feedback increases the effective inertia of the coupled ice‐ocean system. Sea‐ice insulation lessens the negative feedback between heat flux and the SST, and therefore, allows the SST to play a greater role in counteracting changes of the THC and high latitude salinity field. The freshwater feedback effectively links the surface heat flux to a freshwater reservoir, and thus, increases the effective inertia of the coupled ocean‐ice system. A two‐dimensional ocean model coupled with a thermodynamic sea‐ice model is used to estimate quantitatively the magnitudes of these two feedbacks. The numerical experiments involve the model's responses both to initial anomalies and to changes of forcing fields. For the free response cases (model responses to initial anomalies without changing the forcing fields), the model shows that the decay rate of an initial anomaly is greater when sea‐ice is included. For small perturbations the thermal insulation effect dominates over the freshwater feedback. The latter becomes increasingly more important for larger perturbations. In response to a change of external forcing, the presence of sea‐ice reduces the magnitude and the pace of the model's response. The numerical results are qualitatively consistent with the analytical solution of the box model.  相似文献   

Sea‐ice dynamics and CO2 sensitivity in a global climate model     

David Pollard  Starley L. Thompson 《大气与海洋》2013,51(2):449-467

Abstract

Present‐day results and CO₂ sensitivity are described for two versions of a global climate model (genesis) with and without sea‐ice dynamics. Sea‐ice dynamics is modelled using the cavitating‐fluid method of Flato and Hibler (1990, 1992). The atmospheric general circulation model originated from the NCAR Community Climate Model version 1, but is heavily modified to include new treatments of clouds, penetrative convection, planetary boundary‐layer mixing, solar radiation, the diurnal cycle and the semi‐Lagrangian transport of water vapour. The surface models include an explicit model of vegetation (similar to BATS and SiB), multilayer models of soil, snow and sea ice, and a slab ocean mixed layer.

When sea‐ice dynamics is turned off, the CO₂‐induced warming increases drastically around ～60–80°S in winter and spring. This is due to the much greater (and unrealistic) compactness of the Antarctic ice cover without dynamics, which is reduced considerably when CO₂ is doubled and exposes more open ocean to the atmosphere. With dynamics, the winter ice is already quite dispersed for 1 × CO₂ so that its compactness does not decrease as much when CO₂ is doubled.  相似文献   

The formation and maintenance of the North Water Polynya     

《大气与海洋》2013,51(3):187-201

Abstract

This paper investigates the formation and maintenance of the North Water Polynya, Baffin Bay in winter using a multi‐category sea‐ice model coupled with the Princeton ocean model. Monthly climatological atmospheric data from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis provides the forcing. An objectively‐analysed climatology provides the initial ocean temperature and salinity. Wind stress drives the ice in a cyclonic gyre around northern Baffin Bay. Localized regions of thin ice form where wind drives ice away from coastlines or fast ice. The regions of thin ice are characterized by enhanced ice growth, exceeding 1.2 m mo^?1. In the regions of thin ice, surface ocean heat flux is also enhanced and is between 30–60 W m^?2. Surface heat flux is, in part, attributable to convective mixing and entrainment driven by ice growth. The surface heat flux reflects advection of the warm West Greenland Current. Heat and salt balances show that horizontal advective exchange counterbalances surface fluxes of heat and salt.  相似文献   

Variations in momentum,mass and heat fluxes due to changes in the sea surface temperature of Hudson Bay     

S.J. Prinsenberg  Maurice Danard 《大气与海洋》2013,51(3):228-237

Abstract

The atmospheric model of Danard et al. (1983) is used to investigate the changes in heat, mass and momentum fluxes at the air‐sea interface in Hudson Bay when the seasonal sea surface temperature is varied. Comparisons of model predictions with data from a meteorological buoy located 400 km offshore showed that the model predicted the variations in wind speed and air temperature fairly well but underestimated their magnitudes. In addition it provided offshore heat and mass fluxes for which no direct observations were available.

The most important parameter determining air‐sea fluxes is the temperature difference between air and water. This determines the stability and the degree of vertical convection of the air. In the spring the colder water stabilizes the air, which depresses vertical convection. This reduces wind stress and evaporation while increasing the heat flux into the water. During the fall, the opposite occurs. The sea surface temperature is thus buffered against man‐made changes. When the temperature is decreased, for example, as the result of hydroelectric development in surrounding watersheds, the heat flux into the water increases while the wind stress decreases. Both effects increase the sea surface temperature, opposing the initial decrease. A one‐degree depression of sea surface temperature in summer is slowly offset by increased heating and no noticeable change in temperature remains at the end of the fall.  相似文献   

Sea‐level rise or coastal subsidence?     

Robert W. Stewart 《大气与海洋》2013,51(3):461-477

Abstract

Relative sea‐level rise along the Atlantic coast of North America is observed to be about 30 cm/century. No more than half of this rise can be explained by eustatic changes. It is improbable that the remainder is explicable by steric changes. It is therefore almost certainly produced by a systematic subsidence of that coast. The required rate of at least 15 cm/ century is very large by long‐term geologic standards. However, it is comparable with rates measured in relevelling programs, and we must recognize that we live in extraordinary times geologically in that ice‐ages are unusual, and we are in a very warm portion of the present ice‐age. If at least half of the observed relative sea‐level rise is caused by subsidence, it seems reasonable to suppose that nearly all, except for the effects of the observed melting of small glaciers, is so caused. Sea‐level rise is so variable in other parts of the world that there also it is better explained by crustal movements than by eustatic sea‐level rise.

The doubt that these considerations place on the usual interpretation of past sea‐level rise extends to consideration of a possible future rise brought ori by climate change. It is uncertainty that has clearly increased, not eustatic sea‐level.  相似文献