scholarly journals Measurements and Analyses of Velocity Profiles and Frazil Ice-Crystal Rise Velocities During Periods of Frazil-Ice Formation in Rivers

1983 ◽  
Vol 4 ◽  
pp. 79-84 ◽  
Author(s):  
J. P. Gosink ◽  
T. E. Osterkamp
Keyword(s):  
Time Scale ◽  
Velocity Profiles ◽  
Ice Crystals ◽  
Ice Formation ◽  
Rise Velocity ◽  
Mixed Flow ◽  
Frazil Ice ◽  
Time Required ◽  
Ice Water

The vertical concentration distribution of frazil-ice crystals in a stream during the formation and growth of frazil ice was discussed in a preliminary way by Gosink and Osterkamp (1981). This paper extends and completes the analysis of buoyant rise velocities of frazil-ice crystals and applies the results to an interpretation of measured velocity profiles in rivers during frazil-ice events. Additional experimental data are also presented. Two time scales are defined: the buoyant time scale TB, which represents the time required for a frazil crystal to rise, buoyantly, from the river bottom to the water surface, and the diffusive tine scale TD, which represents the time required for a frazil crystal to he transported by turbulence through the depth. It is shown that the ratio of the time scales TB/TD defines the nature of the layering processes; in particular, if TB/TD<1, then buoyant forces Till lift a frazil crystal faster than turbulent diffusion can redistribute it and the flow will be layered. Conversely, if TB./TD>1, turbulent mixing will proceed faster than buoyant lifting and the flow will be well-mixed. This ratio, for frazil particles of diameter 2 mm or more, corresponds to rule-of-thumb velocity criteria developed in Norway and Canada to distinguish layered frazil-ice/water flow from well-mixed flow.The development of this theory depends in large part upon the determination of TB, which depends upon the rise velocity of frazil-ice crystals. A force balance .nodel was developed for the rise velocity of a frazil crystal. Field observations during frazil -ice formation in Goldstream Creek and in the Chatanika River north of Fairbanks are reported, including a series of measurements of the rise velocities of frazil-ice crystals. Typical particle size of frazil ice was about 2 mm with a rise velocity of about 10.0 mm s -1. The agreement of measured rise velocities with the theoretical model is good considering uncertainties in the drag coefficient and in the determination of frazil crystal sizes under field conditions.Velocity profiles in the Chatanika River and in Goldstream Creek during frazil formation suggest that the time-scale ratio may serve as a transition criterion between layered frazil-ice/water flow and well-mixed flow. This ratio was calculated with the rise velocity of frazil-ice crystals arbitrarily chosen to be 0.01 m s−1.

scholarly journals Measurements and Analyses of Velocity Profiles and Frazil Ice-Crystal Rise Velocities During Periods of Frazil-Ice Formation in Rivers

1983 ◽  
Vol 4 ◽  
pp. 79-84 ◽  
Author(s):  
J. P. Gosink ◽  
T. E. Osterkamp
Keyword(s):  
Time Scale ◽  
Velocity Profiles ◽  
Ice Crystals ◽  
Ice Formation ◽  
Rise Velocity ◽  
Mixed Flow ◽  
Frazil Ice ◽  
Time Required ◽  
Ice Water

The vertical concentration distribution of frazil-ice crystals in a stream during the formation and growth of frazil ice was discussed in a preliminary way by Gosink and Osterkamp (1981). This paper extends and completes the analysis of buoyant rise velocities of frazil-ice crystals and applies the results to an interpretation of measured velocity profiles in rivers during frazil-ice events. Additional experimental data are also presented. Two time scales are defined: the buoyant time scale TB, which represents the time required for a frazil crystal to rise, buoyantly, from the river bottom to the water surface, and the diffusive tine scale TD, which represents the time required for a frazil crystal to he transported by turbulence through the depth. It is shown that the ratio of the time scales TB/TD defines the nature of the layering processes; in particular, if TB/TD&lt;1, then buoyant forces Till lift a frazil crystal faster than turbulent diffusion can redistribute it and the flow will be layered. Conversely, if TB./TD&gt;1, turbulent mixing will proceed faster than buoyant lifting and the flow will be well-mixed. This ratio, for frazil particles of diameter 2 mm or more, corresponds to rule-of-thumb velocity criteria developed in Norway and Canada to distinguish layered frazil-ice/water flow from well-mixed flow. The development of this theory depends in large part upon the determination of TB, which depends upon the rise velocity of frazil-ice crystals. A force balance .nodel was developed for the rise velocity of a frazil crystal. Field observations during frazil -ice formation in Goldstream Creek and in the Chatanika River north of Fairbanks are reported, including a series of measurements of the rise velocities of frazil-ice crystals. Typical particle size of frazil ice was about 2 mm with a rise velocity of about 10.0 mm s -1. The agreement of measured rise velocities with the theoretical model is good considering uncertainties in the drag coefficient and in the determination of frazil crystal sizes under field conditions. Velocity profiles in the Chatanika River and in Goldstream Creek during frazil formation suggest that the time-scale ratio may serve as a transition criterion between layered frazil-ice/water flow and well-mixed flow. This ratio was calculated with the rise velocity of frazil-ice crystals arbitrarily chosen to be 0.01 m s−1.

scholarly journals Melting of Ice and Sea Ice into Seawater and Frazil Ice Formation

2014 ◽  
Vol 44 (7) ◽  
pp. 1751-1775 ◽  
Author(s):  
Trevor J. McDougall ◽  
Paul M. Barker ◽  
Rainer Feistel ◽  
Ben K. Galton-Fenzi
Keyword(s):  
Sea Ice ◽  
Vertical Velocity ◽  
Computer Software ◽  
Ice Crystals ◽  
Ice Formation ◽  
Thermodynamic Equation ◽  
Frazil Ice ◽  
Salinity Changes ◽  
Thermodynamic Relationships

Abstract The thermodynamic consequences of the melting of ice and sea ice into seawater are considered. The International Thermodynamic Equation Of Seawater—2010 (TEOS-10) is used to derive the changes in the Conservative Temperature and Absolute Salinity of seawater that occurs as a consequence of the melting of ice and sea ice into seawater. Also, a study of the thermodynamic relationships involved in the formation of frazil ice enables the calculation of the magnitudes of the Conservative Temperature and Absolute Salinity changes with pressure when frazil ice is present in a seawater parcel, assuming that the frazil ice crystals are sufficiently small that their relative vertical velocity can be ignored. The main results of this paper are the equations that describe the changes to these quantities when ice and seawater interact, and these equations can be evaluated using computer software that the authors have developed and is publicly available in the Gibbs SeaWater (GSW) Oceanographic Toolbox of TEOS-10.

scholarly journals Study of the Impact of Ice Formation in Leads upon the Sea Ice Pack Mass Balance Using a New Frazil and Grease Ice Parameterization

2015 ◽  
Vol 45 (8) ◽  
pp. 2025-2047 ◽  
Author(s):  
Alexander V. Wilchinsky ◽  
Harold D. B. S. Heorton ◽  
Daniel L. Feltham ◽  
Paul R. Holland
Keyword(s):  
Sea Ice ◽  
Mass Balance ◽  
Ice Crystals ◽  
The Arctic ◽  
Ice Formation ◽  
Frazil Ice ◽  
Marginal Seas ◽  
Ice Production ◽  
The Impact ◽  
Ice Pack

AbstractLeads are cracks in sea ice that often form because of deformation. During winter months, leads expose the ocean to the cold atmosphere, resulting in supercooling and the formation of frazil ice crystals within the mixed layer. Here the authors investigate the role of frazil ice formation in leads on the mass balance of the sea ice pack through the incorporation of a new module into the Los Alamos sea ice model (CICE). The frazil ice module considers an initial cooling of leads followed by a steady-state formation of uniformly distributed single size frazil ice crystals that precipitate to the ocean surface as grease ice. The grease ice is pushed against one of the lead edges by wind and water drag that the authors represent through a variable collection thickness for new sea ice. Simulations of the sea ice cover in the Arctic and Antarctic are performed and compared to a model that treats leads the same as the open ocean. The processes of ice formation in the new module slow down the refreezing of leads, resulting in a longer period of frazil ice production. The fraction of frazil-derived sea ice increases from 10% to 50%, corresponding better to observations. The new module has higher ice formation rates in areas of high ice concentration and thus has a greater impact within multiyear ice than it does in the marginal seas. The thickness of sea ice in the central Arctic increases by over 0.5 m, whereas within the Antarctic it remains unchanged.

scholarly journals On Supercooling and Ice Formation in Turbulent Sea-water

1985 ◽  
Vol 31 (109) ◽  
pp. 263-271 ◽  
Author(s):  
Anders Omstedt
Keyword(s):  
Boundary Layer ◽  
Sea Water ◽  
Laboratory Data ◽  
Turbulent Channel Flow ◽  
Ice Crystals ◽  
Ice Formation ◽  
Layer Model ◽  
Frazil Ice ◽  
M 10 ◽  
Experimental Findings

AbstractLaboratory data on supercooling and frazil-ice formation in sea-water are analysed using a boundary-layer model. The model is based on a turbulent channel-flow boundary-layer theory, in which buoyancy effects become important because of vertical gradients in temperature, salinity, and suspended frazil-ice crystals. The frazil-ice crystals are treated as thin uniform plates. By assuming a mean face diameter, a mean thickness, and a mean Nusselt number of 10−3 m, 10−4 m, and 4, respectively, the general experimental findings are well reproduced by the model.

scholarly journals Incorporation of particulates into accreted ice above subglacial Vostok lake, Antarctica

2005 ◽  
Vol 40 ◽  
pp. 145-150 ◽  
Author(s):  
George Royston-Bishop ◽  
John C. Priscu ◽  
Martyn Tranter ◽  
Brent Christner ◽  
Martin J. Siegert ◽  
...  
Keyword(s):  
Ice Core ◽  
Major Axis ◽  
Ice Crystals ◽  
Shape Factors ◽  
Frazil Ice ◽  
Surface Areas ◽  
Single Process ◽  
Polycarbonate Membranes ◽  
Ice Water ◽  
Electron Microscope Image

AbstractThe nature of microscopic particulates in meteoric and accreted ice from the Vostok (Antarctica) ice core is assessed in conjunction with existing ice-core data to investigate the mechanism by which particulates are incorporated into refrozen lake water. Melted ice samples from a range of ice-core depths were filtered through 0.2 μm polycarbonate membranes, and secondary electron images were collected at ×500 magnification using a scanning electron microscope. Image analysis software was used to characterize the size and shape of particulates. Similar distributions of major-axis lengths, surface areas and shape factors (aspect ratio and compactness) for particulates in all accreted ice samples suggest that a single process may be responsible for incorporating the vast majority of particulates for all depths. Calculation of Stokes settling velocities for particulates of various sizes implies that 98% of particulates observed could ‘float’ to the ice–water interface with upward water velocities of 0.0003 ms–1 where they could be incorporated by growing ice crystals, or by rising frazil ice crystals. The presence of particulates that are expected to sink in the water column (2%) and the uneven distribution of particulates in the ice core further implies that periodic perturbations to the lake’s circulation, involving increased velocities, may have occurred in the past.

scholarly journals On Supercooling and Ice Formation in Turbulent Sea-water

1985 ◽  
Vol 31 (109) ◽  
pp. 263-271 ◽  
Author(s):  
Anders Omstedt
Keyword(s):  
Boundary Layer ◽  
Sea Water ◽  
Laboratory Data ◽  
Turbulent Channel Flow ◽  
Ice Crystals ◽  
Ice Formation ◽  
Layer Model ◽  
Frazil Ice ◽  
M 10 ◽  
Experimental Findings

AbstractLaboratory data on supercooling and frazil-ice formation in sea-water are analysed using a boundary-layer model. The model is based on a turbulent channel-flow boundary-layer theory, in which buoyancy effects become important because of vertical gradients in temperature, salinity, and suspended frazil-ice crystals. The frazil-ice crystals are treated as thin uniform plates. By assuming a mean face diameter, a mean thickness, and a mean Nusselt number of 10−3m, 10−4m, and 4, respectively, the general experimental findings are well reproduced by the model.

scholarly journals A conceptual model for pancake-ice formation in a wave field

2001 ◽  
Vol 33 ◽  
pp. 361-367 ◽  
Author(s):  
Hayley H. Shen ◽  
Stephen F. Ackley ◽  
Mark A. Hopkins
Keyword(s):  
Wave Field ◽  
Ice Cover ◽  
Ice Crystals ◽  
Ice Formation ◽  
Governing Equations ◽  
Time Rate ◽  
Wave Condition ◽  
Frazil Ice ◽  
Marginal Ice Zone ◽  
Theoretical Paper

AbstractIt is well known that waves jostle frazil-ice crystals together, providing opportunities for them to compact into floes. The shape of these consolidated floes is nearly circular, hence the name: pancakes. From field and laboratory observations, the size of these pancakes seems to depend on the wavelength. Further aggregation of these individual pancakes produces the seasonal ice cover. Pancake-ice covers prevail in the marginal ice zone of the Southern Ocean and along the edges of many polar and subpolar seas. This theoretical paper describes conceptually the formation process of a pancake-ice cover in a wave field. The mechanisms that affect the evolution of the entire ice cover are discussed. Governing equations for the time-rate change of the floe diameter, its thickness and the thickness of the ice-cover are derived based on these mechanisms. Two criteria are proposed to determine the maximum floe size under a given wave condition, one based on bending and the other on stretching. Field and laboratory observations to date are discussed in view of this theory.

Large-scale Motion of Solar Filaments

2000 ◽  
Vol 179 ◽  
pp. 205-208
Author(s):  
Pavel Ambrož ◽  
Alfred Schroll
Keyword(s):  
Magnetic Flux ◽  
Proper Motion ◽  
Time Scale ◽  
Large Scale ◽  
Accuracy Of Measurements ◽  
Solar Filaments ◽  
General Movement ◽  
Scale Motion ◽  
Velocity Scatter

AbstractPrecise measurements of heliographic position of solar filaments were used for determination of the proper motion of solar filaments on the time-scale of days. The filaments have a tendency to make a shaking or waving of the external structure and to make a general movement of whole filament body, coinciding with the transport of the magnetic flux in the photosphere. The velocity scatter of individual measured points is about one order higher than the accuracy of measurements.

Seasonal variations in the properties and structural composition of sea ice and snow cover in the Bellingshausen and Amundsen Seas, Antarctica

1997 ◽  
Vol 43 (143) ◽  
pp. 138-151 ◽  
Author(s):  
M. O. Jeffries ◽  
K. Morris ◽  
W.F. Weeks ◽  
A. P. Worby
Keyword(s):  
Sea Ice ◽  
Isotopic Composition ◽  
Snow Cover ◽  
Sea Water ◽  
Ice Cores ◽  
Ice Cover ◽  
Snow Accumulation ◽  
Ice Formation ◽  
Frazil Ice ◽  
Core Sets

AbstractSixty-three ice cores were collected in the Bellingshausen and Amundsen Seas in August and September 1993 during a cruise of the R.V. Nathaniel B. Palmer. The structure and stable-isotopic composition (18O/16O) of the cores were investigated in order to understand the growth conditions and to identify the key growth processes, particularly the contribution of snow to sea-ice formation. The structure and isotopic composition of a set of 12 cores that was collected for the same purpose in the Bellingshausen Sea in March 1992 are reassessed. Frazil ice and congelation ice contribute 44% and 26%, respectively, to the composition of both the winter and summer ice-core sets, evidence that the relatively calm conditions that favour congelation-ice formation are neither as common nor as prolonged as the more turbulent conditions that favour frazil-ice growth and pancake-ice formation. Both frazil- and congelation-ice layers have an av erage thickness of 0.12 m in winter, evidence that congelation ice and pancake ice thicken primarily by dynamic processes. The thermodynamic development of the ice cover relies heavily on the formation of snow ice at the surface of floes after sea water has flooded the snow cover. Snow-ice layers have a mean thickness of 0.20 and 0.28 m in the winter and summer cores, respectively, and the contribution of snow ice to the winter (24%) and summer (16%) core sets exceeds most quantities that have been reported previously in other Antarctic pack-ice zones. The thickness and quantity of snow ice may be due to a combination of high snow-accumulation rates and snow loads, environmental conditions that favour a warm ice cover in which brine convection between the bottom and top of the ice introduces sea water to the snow/ice interface, and bottom melting losses being compensated by snow-ice formation. Layers of superimposed ice at the top of each of the summer cores make up 4.6% of the ice that was examined and they increase by a factor of 3 the quantity of snow entrained in the ice. The accumulation of superimposed ice is evidence that melting in the snow cover on Antarctic sea-ice floes ran reach an advanced stage and contribute a significant amount of snow to the total ice mass.

Frazil Ice Formation,

1984 ◽  
Author(s):  
R. Ettema ◽  
M. F. Karim ◽  
J. F. Kennedy
Keyword(s):  
Ice Formation ◽  
Frazil Ice
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