1,262 research outputs found
Common Ownership in Canada with Particular Reference to Regulation of Acquisition of Motor Carriers
The Interface between Intellectual Property Law and Commpetition Law in Canada
intellectual property and competition law in North Americ
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The effect of a new drag-law parameterization on ice shelf water plume dynamics
A drag law accounting for Ekman rotation adjacent to a flat, horizontal bou
ndary is proposed for use in
a plume model that is written in terms of the depth-mean velocity. The drag l
aw contains a variable turning
angle between the mean velocity and the drag imposed by the turbulent bound
ary layer. The effect of the
variable turning angle in the drag law is studied for a plume of ice shelf wat
er (ISW) ascending and turning
beneath an Antarctic ice shelf with draft decreasing away from the groundi
ng line. As the ISW plume
ascends the sloping ice shelf–ocean boundary, it can melt the ice shelf, wh
ich alters the buoyancy forcing
driving the plume motion. Under these conditions, the typical turning ang
le is of order
10° over most of
the plume area for a range of drag coefficients (the minus sign arises for th
e Southern Hemisphere). The
rotation of the drag with respect to the mean velocity is found to be signifi
cant if the drag coefficient exceeds
0.003; in this case the plume body propagates farther along and across the b
ase of the ice shelf than a plume
with the standard quadratic drag law with no turning angle
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Sea ice and the ocean mixed layer over the Antarctic shelf seas
An ocean mixed-layer model has been incorporated into the Los Alamos sea ice
model CICE to investigate regional variations in the surface-driven formation
of Antarctic shelf waters. This model captures well the expected sea ice
thickness distribution, and produces deep (> 500 m) mixed layers in the
Weddell and Ross shelf seas each winter. This results in the complete
destratification of the water column in deep southern coastal regions leading
to high-salinity shelf water (HSSW) formation, and also in some shallower
regions (no HSSW formation) of these seas. Shallower mixed layers are
produced in the Amundsen and Bellingshausen seas. By deconstructing the
surface processes driving the mixed-layer depth evolution, we show that the
net salt flux from sea ice growth/melt dominates the evolution of the mixed
layer in all regions, with a smaller contribution from the surface heat flux
and a negligible input from wind stress. The Weddell and Ross shelf seas
receive an annual surplus of mixing energy at the surface; the Amundsen shelf
sea energy input in autumn/winter is balanced by energy extraction in
spring/summer; and the Bellingshausen shelf sea experiences an annual surface
energy deficit, through both a low energy input in autumn/winter and the
highest energy loss in spring/summer. An analysis of the sea ice mass balance
demonstrates the contrasting mean ice growth, melt and export in each region.
The Weddell and Ross shelf seas have the highest annual ice growth, with a
large fraction exported northwards each year, whereas the Bellingshausen
shelf sea experiences the highest annual ice melt, driven by the advection of
ice from the northeast. A linear regression analysis is performed to
determine the link between the autumn/winter mixed-layer deepening and
several atmospheric variables. The Weddell and Ross shelf seas show stronger
spatial correlations (temporal mean – intra-regional variability) between the
autumn/winter mixed-layer deepening and several atmospheric variables
compared to the Amundsen and Bellingshausen. In contrast, the Amundsen and
Bellingshausen shelf seas show stronger temporal correlations (shelf sea mean
– interannual variability) between the autumn/winter mixed-layer deepening
and several atmospheric variables
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Micromechanics of sea ice frictional slip from test basin scale experiments
We have conducted a series of high-resolution friction experiments on large floating saline ice floes in an environmental test basin. In these experiments, a central ice floe was pushed between two other floes, sliding along two interfacial faults. The frictional motion was predominantly stick–slip. Shear stresses, normal stresses, local strains and slip displacement were measured along the sliding faults, and acoustic emissions were monitored. High-resolution measurements during a single stick–slip cycle at several positions along the fault allowed us to identify two phases of frictional slip: a nucleation phase, where a nucleation zone begins to slip before the rest of the fault, and a propagation phase when the entire fault is slipping. This is slip-weakening behaviour. We have therefore characterized what we consider to be a key deformation mechanism in Arctic Ocean dynamics. In order to understand the micromechanics of sea ice friction, we have employed a theoretical constitutive relation (i.e. an equation for shear stress in terms of temperature, normal load, acceleration, velocity and slip displacement) derived from the physics of asperity–asperity contact and sliding (Hatton et al. 2009 Phil. Mag. 89, 2771–2799 (doi:10.1080/14786430903113769)). We find that our experimental data conform reasonably with this frictional law once slip weakening is introduced. We find that the constitutive relation follows Archard's law rather than Amontons' law, with Embedded Image (where τ is the shear stress and σn is the normal stress) and n = 26/27, with a fractal asperity distribution, where the frictional shear stress, τ = ffractal Tmlws, where ffractal is the fractal asperity height distribution, Tml is the shear strength for frictional melting and lubrication and ws is the slip weakening. We can therefore deduce that the interfacial faults failed in shear for these experimental conditions through processes of brittle failure of asperities in shear, and, at higher velocities, through frictional heating, localized surface melting and hydrodynamic lubrication
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Sea ice–ocean feedbacks in the Antarctic shelf seas
Observed changes in Antarctic sea ice are poorly understood, in part due to the complexity of its interactions with the atmosphere and ocean. A highly simplified, coupled sea ice–ocean mixed layer model has been developed to investigate the importance of sea ice–ocean feedbacks on the evolution of sea ice and the ocean mixed layer in two contrasting regions of the Antarctic continental shelf ocean: the Amundsen Sea, which has warm shelf waters, and the Weddell Sea, which has cold and saline shelf waters. Modeling studies where we deny the feedback response to surface air temperature perturbations show the importance of feedbacks on the mixed layer and ice cover in the Weddell Sea to be smaller than the sensitivity to surface atmospheric conditions. In the Amundsen Sea the effect of surface air temperature perturbations on the sea ice are opposed by changes in the entrainment of warm deep waters into the mixed layer. The net impact depends on the relative balance between changes in sea ice growth driven by surface perturbations and basal-driven melting. The changes in the entrainment of warm water in the Amundsen Sea were found to have a much larger impact on the ice volume than perturbations in the surface energy budget. This creates a net negative ice albedo feedback in the Amundsen Sea, reversing the sign of this typically positive feedback mechanism
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Continuum sea ice rheology determined from subcontinuum mechanics
[1] A method is presented to calculate the continuum-scale sea ice stress as an imposed, continuum-scale strain-rate is varied. The continuum-scale stress is calculated as the area-average of the stresses within the floes and leads in a region (the continuum element). The continuum-scale stress depends upon: the imposed strain rate; the subcontinuum scale, material rheology of sea ice; the chosen configuration of sea ice floes and leads; and a prescribed rule for determining the motion of the floes in response to the continuum-scale strain-rate. We calculated plastic yield curves and flow rules associated with subcontinuum scale, material sea ice rheologies with elliptic, linear and modified Coulombic elliptic plastic yield curves, and with square, diamond and irregular, convex polygon-shaped floes. For the case of a tiling of square floes, only for particular orientations of the leads have the principal axes of strain rate and calculated continuum-scale sea ice stress aligned, and these have been investigated analytically. The ensemble average of calculated sea ice stress for square floes with uniform orientation with respect to the principal axes of strain rate yielded alignment of average stress and strain-rate principal axes and an isotropic, continuum-scale sea ice rheology. We present a lemon-shaped yield curve with normal flow rule, derived from ensemble averages of sea ice stress, suitable for direct inclusion into the current generation of sea ice models. This continuum-scale sea ice rheology directly relates the size (strength) of the continuum-scale yield curve to the material compressive strength
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