共查询到20条相似文献，搜索用时 30 毫秒
1.
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
2.
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
3.
Abstract The Barents Sea is divided into a northern and a southern part by the Polar Front (at about 75–76° N) where Atlantic waters descend under Arctic waters. Near to and north of the Polar Front, the spring bloom of phytoplankton is triggered by the stability induced in the upper 20 m by the melting of ice. The pycnocline is too strong to be eroded by wind. Primary productivity after the bloom is therefore small and largely regenerative. Underneath the pycnocline there is a 3–5 m thick layer characterized by dense, slow‐growing algal populations. New productivity north of the Polar Front is no more than 40 g C m?2 a?1. In permanently open waters south of the Polar Front, the spring bloom starts in early May. Rhythmic wind‐induced mixing related to the atmospheric low‐pressure belt reaches an average 40–60 m depth in the growth season, and secondary phytoplankton maxima may arise. As a result, new annual productivity is more than doubled, i.e. 90 g C m?2 a?1, relative to the same system without wind. Although productivity is highest south of the Polar Front, it is more concentrated north of it, in the sense that high new production is mainly related to a 20–50 km wide belt that sweeps the area following the ice edge northwards while the ice melts through the summer. 相似文献
4.
Abstract We present an analysis of current‐meter, sea‐level and hydrographic data collected in the Strait of Belle Isle and the northeastern Gulf of St Lawrence. From an array of moorings in the Strait from July to October 1980, we calculate a net transport into the Gulf of 0.13 × 106 m3 s?1 and show that the mean and eddy fluxes of heat through the Strait represented a net loss of heat to the northeastern Gulf. The estimated rate of loss of heat is less than the long‐term mean computed by Bugden (1981) but becomes comparable if adjusted for interannual changes of transport and water temperature. Moreover, the 1980 data permit the permanent tide‐gauge stations in the Strait at West Ste Modeste and Savage Cove to be levelled relative to one another, thus allowing surface currents to be calculated from sea‐level alone. Hence the long‐term wintertime transport into the Gulf can be calculated after fractional effects on the vertical structure of the flow are considered. During an average winter it appears that advection through the Strait can account for about 35% of the Gulf Intermediate Layer. A multiple regression involving average Intermediate Layer temperatures over 9 years suggests that winter air temperature in the Gulf, representative of atmospheric cooling, and sea‐level difference across the Strait, representative of advection, are equally important variables and together account for 50% of the Layer's temperature variability. Analysis of current‐meter, sea‐level and hydrographic data collected in 1975 supports earlier hypotheses that the strongest inflow of water with ? < 0° C and salinity between 32 and 3 3 should occur in winter. It appears that during the 1975 field program the inflow was about 0.6 × 106 m3 s?1, which is about twice the long‐term average for January to May. 相似文献
5.
Donald O. Hodgins 《大气与海洋》2013,51(3):285-298
Abstract Compliant fairing made of plastic ribbons or flexible rubber filaments can be attached to the cables of taut‐line moorings to reduce the drag force of the currents. The efficiency of such fairing depends upon its orientation in the flow and the Reynolds number of the cable. Results of using filament fairing manufactured by ENDECO Inc. on a 337‐m long mooring in the mouth of Hudson Strait are discussed. The fairing was found to be detrimental in this application because of twisting of the wire rope, producing a “bottle‐brush” configuration, and because the normal drag coefficient Cd ? 2.5 ± 0.45 was found to exceed that of a bare cable by 65 per cent on average. The Reynolds number range for this drag coefficient was 2.6 × 103 to 4.2 × 103 and was determined by force measurements in a flume. It is concluded that the problems of correctly orienting the fairing in the flow, and the true drag coefficient for Reynolds numbers less than about 5 × 104 must be carefully addressed in the design of conventional taut‐line moorings. Drag coefficients found in this study imply that compliant fairings would not be warranted for Reynolds numbers below about 5 × 104 unless strumming was expected for bare cables. 相似文献
6.
Abstract Radar reflectivity measurements and sounding data were analyzed to investigate snowfall production in a long‐lasting snowband that formed in advance of a warm surface front moving across Alberta. The sounding data indicated that the band could have been forced by slantwise overturning during the release of moist symmetric instability combined with frontogenesis. The stability analysis presented here is novel in that it includes ice phase thermodynamics, neglected in previous studies of slantwise convection. Radar reflectivity fields were analyzed to determine the total snow content and the mass outflow rate as factors of time. The peak value of total snow content was 17 kilotons per km of snowband, and the peak mass outflow rate was 10 tons s‐1 km‐1. The snowfall rate averaged across the cloud base was about 0.8 cm h‐1, and the average snow content remained close to 0.2 g m‐1. The characteristic time (defined as the ratio of total snow content over mass outflow rate) was about 30 minutes, which is approximately the time needed for the growth of snowflakes by aggregation in the observed temperature range. The precipitation efficiency of the snowband, defined as the ratio of snow mass outflow to water vapour inflow was estimated to be 14%. The precipitation production values observed in the Alberta snowband are compared with previous estimates reported for frontal rainbands and Alberta thunderstorms. 相似文献
7.
《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
8.
Springtime fetch in the Cape Bathurst Polynya System may present opportunities for winds to generate waves capable of propagating into the thick pack ice formed over the winter. A waves-in-ice event at a study site located on the Canadian Shelf in the southern Beaufort Sea that occurred 22–23 May 2011 is presented and analyzed for wave energy attenuation and dissipation characteristics. The event was monitored near the ice edge and, therefore, presents information on attenuation of waves from the ice edge into the pack. Waves of T?=?5?s, λ?=?37.5?m were observed up to approximately 143?m and approximately 77?m away from the ice edge during two separate observation periods of ice edge wave propagation. We estimated reflection coefficients of 53% and 52% and wave attenuation coefficients of α?=?2.4?×?10?2?m?1 and α?=?5.4?×?10?2?m?1, respectively, for the two periods. Estimated attenuation rates are an order of magnitude greater than in comparable studies and are inconsistent with previous findings of a “rollover” effect in attenuation rates for short-period waves. 相似文献
9.
Abstract Past theoretical investigations have reported that observed peaks in the diffusional growth of ice crystals in the vicinity of ‐5 and ‐15°C could be qualitatively modelled assuming certain specific crystal properties. This study re‐examines the ice crystal diffusional growth model using more recently available observations of pertinent crystal parameters. The results, indicative of the growth of average crystals, imply a much weaker dependence of the diffusional mass growth rate on temperature in the range of ‐5 to ‐15°C. Extension of the model to include growth by accretion, also suggests that the mass of heavily rimed crystals is not very sensitive to the original crystal habit. The results of the calculations are compared with observed crystal sizes in cumulus clouds following seeding on three different days. The observations indicate that small crystals were continuously being produced as long as 15 min after seeding. In two cases, crystals much larger than those predicted by the model for any reasonable set of parameters suggest that crystal aggregation may have been occurring at a significant rate. 相似文献
10.
K.F. Drinkwater 《大气与海洋》2013,51(2):252-266
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
11.
S. M. Vakulovskii M. A. Novitskii N. F. Mazurin E. G. Tertyshnik L. M. Khachaturova 《Russian Meteorology and Hydrology》2007,32(8):508-513
Experimental field and laboratory studies on washout of radionuclides from the snow cover during snow melting were carried out in the winter of 2005/06. In the field studies, a specially equipped runoff site was used. In the laboratory conditions, the experiments were conducted using prepared soil monoliths. In the winter of 2006, 25 g/m2 of water-free cesium chloride (CsCl) and 25 g/m3 of strontium chloride (SrCl2) were put onto the snow cover surface of the runoff site. The snow surface of the soil monolith was coated with a 137Cs-bearing solution, then with SrCl2. Under experimental conditions, practically no surface runoff from the runoff site was recorded. The experiments with the soil monoliths demonstrated that the coefficient of the liquid washout of 137Cs normalized to the runoff layer was within 0.9 × 10?6–1.2 × 10?4 mm?1, and that of 90Sr normalized to the runoff layer was within 2 × 10?–1.6 × 10?4 mm?1. 相似文献
12.
含水量对冰晶增长影响的风洞实验研究 总被引：1，自引：0，他引：1
用小型垂直过冷云风洞及其测试系统,使冰晶在自由悬浮的情况下生长。在实验温度为-5℃—15℃、含水量为0.5—2.0g/m~3的范围内,结果表明:在水面饱和条件下,冰晶的形状决定于所处的环境温度,含水量的大小对冰晶的基本形状没有影响,只是当含水量加大时,冰晶上会出现更加明显的碰冻增长的痕迹;冰晶的质量和速度增长的峰值和谷值温度分布与含水量的大小无关;随着含水量的增加,冰晶的质量和下落速度的增长会加快,但没有发现含水量的增加有加快冰晶2a轴增长的明显效果。 相似文献
13.
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
14.
O3,CO2浓度及太阳光谱变化对作物光合作用影响的数值模拟研究 总被引：4，自引：2，他引：4
对光合作用 蒸腾作用 气孔调节进行耦合 ,从生物化学尺度扩展至冠层尺度 ,发展了一个冬小麦冠层光合作用生态动力模式 ,模式考虑了O3,CO2 和光谱变化对作物光合的综合影响。利用美国光合作用实测资料对模式进行验证 ,叶片模式通过了相关显著性检验并具有较高的准确度。数值分析表明 :当O3 浓度由 0× 10 -9V/V上升至2 0 0× 10 -9V/V时 ,冠层光合速率下降 2 9%左右 ;当CO2 浓度由 330× 10 -6V/V上升至 6 6 0× 10 -6V/V时 ,冠层光合速率增加大约 37% ;当光谱比例系数由目前的 0 .5下降至 0 .4时 ,冠层光合速率将下降 2 7%左右。对于污染严重、易发生光化学烟雾的城郊附近 ,在阳光强烈的典型晴天 ,中午O3 浓度达到 2 0 0× 10 -9V/V时 ,即使气候条件不发生改变 ,CO2 浓度对作物光合作用的正效应也不足以弥补O3 浓度升高所造成的负效应 ,冠层光合速率将比目前干洁地区略有下降 ,如果进一步考虑光合作用有效辐射光谱成分下降至 0 .4左右 ,冠层光合作用将比目前的BASE值下降 35 %左右。 相似文献
15.
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
16.
Abstract We analyse the trajectories of 24 deep‐drogued, satellite‐tracked drifters launched between 50 and 52°N in the northeast Pacific during June and October 1987. Three aspects of the observed motions at the drogue depths of 100 to 120 m are studied: (i) the spatial structure of the mean and variance velocity fields; (ii) the dispersion and eddy diffusion characteristics of the fluctuating motions; and (iii) the properties of selected mesoscale eddies. The mean Lagrangian velocity field is consistent with the mean flow pattern derived from the historical dynamic height topography. Fluctuating motions within the region are dominated by mesoscale eddies and meanders. Several instances of persistent O(100 days) westward flowing countercurrents were also observed. Based on the Lagrangian integral time‐ and length scales, drifter motions become decorrelated within a period of 10 days and a separation of 100 km. The mean zonal and meridional integral time‐scales of 4.5 and 3.6 days, respectively, are nearly identical with those obtained by Krauss and Böning (1987) from deep‐drogued drifter tracks in the North Atlantic. Because of the relatively small (<100 cm2 s?2) kinetic energy values in the northeast Pacific, the corresponding mean Lagrangian length scales of 29.4 and 29.9 km are roughly half those for the Atlantic. The observed drifter dispersion is generally consistent with Taylor's (1921) theory for single‐particle dispersion in homogeneous isotropic turbulence. Estimates obtained using 476 pseudo‐drifter tracks generated from the original records indicate that the dispersion increases linearly with time, t, within the first 3 to 5 days of launch and subsequently increases as t1/2 (the random‐walk regime) within 10 days of launch. The respective peak zonal and meridional eddy diffusion coefficients of 4.1 × and 3.8 × 107 cm2 s?1 are reached within 30 days of deployment. Similar estimates for the peak eddy diffusivities are obtained using dispersion curves for sets of 4 drifters launched at the same location during the June and October deployments. The dispersion of these clusters followed an exponential rather than a t1/2 dependence over the first 70 days after release. Eddies are predominantly clockwise rotary and are characterized by radii of 26 ± 16 km, periods of rotation of 16.0 ± 5.2 days, and azimuthal current speeds of 12.7 ± 8.6 cm s?1. One eddy was tracked for over 10 months. Oceanographic data collected during the October deployment period showed the eddies have vertical extents of 500 to 700 m and are linked to isotherm depressions of over 100 m in the main pycnocline. All eddies in the bifurcation zone propagate to the west at roughly 1.5 ± 0.4 cm s?1 counter to the prevailing mean flow and winds. These speeds are consistent with the westward phase speeds of first mode baroclinic planetary (Rossby) waves. 相似文献
17.
Ned P. Smith 《大气与海洋》2013,51(4):307-319
Abstract Meteorological and hydrographic data from the Indian River lagoon on the Atlantic coast of South Florida are used to describe the magnitude and relative importance of local heat flux processes in a bar‐built estuary for summer conditions. Over a 72‐day period in 1979, the energy gain by absorbed net insolation, averaging 316 W m‐2 is very nearly balanced by the energy loss due to net long‐wave radiation (‐61 W m‐2), sensible heat loss (‐54 W m‐2) and evaporation (‐194 W m‐2). Day‐to‐day imbalances, however, result in cycles of heating and cooling over time scales on the order of 4–6 days. Water temperatures fluctuate only ±0.5–1.0°C about the seasonal normal, reflecting relatively stable meteorological conditions. Heat energy stored in these estuarine waters in summer months is most highly correlated with the absorption of net insolation. 相似文献
18.
Abstract Observations in both the ice and slush layers suggest that sea water intrudes into the snow layer following a snow storm. Ice temperature values recorded at 1 cm below the snow‐ice interface show that the upward flux of sea water is of short duration. This is followed by a period of intense brine drainage characterized by the migration of a salty brine layer, with salinities up to 42 psu. These results suggest that a snow storm induces a complete (upward) flushing of the brine channel network and major modifications of snow and ice characteristics. Melt rates and downward brine fluxes were calculated using salinity measured in a 40 cm deep box placed on the ice‐water interface, which isolated a 50 × 50 cm area of sea ice from ocean mixing processes. In this semi‐isolated environment, observed salinity changes allowed us to determine melt water fluxes and brine drainage or flushing even though ice thickness measurements did not show any significant change. Melt rates up to 21 cm/month and equivalent growth rates up to 32 cm/month were measured. 相似文献
19.
ＯｎＭｅｃｈａｎｉｓｍｓｏｆＮｕｃｌｅａｔｉｏｎｏｆＩｃｅＣｒｙｓｔａｌｓｂｙＡｅｒｏｄｙｎａｍｉｃＣｏｏｌｉｎｇＨｕａｎｇＳｈｉｈｏｎｇ（黄世鸿）；ＱｉａｎＣｈａｎｇｇｕｏ（钱昌国）；ＷａｎｇＷｅｉｍｉｎ（王伟民）；ＬｉＲｕｘｉａｎｇ（李如祥）（Ｄ... 相似文献
20.
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