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|Title:||Growth, structure, and strength of sea ice|
Weeks, W. F.
|Publisher:||Cold Regions Research and Engineering Laboratory (U.S.)|
Engineer Research and Development Center (U.S.)
|Series/Report no.:||Research report (Cold Regions Research and Engineering Laboratory (U.S.)) ; 135.|
Summary: The freezing interface primarily determines the basic characteristics of sea ice. As the platelets composing the individual crystals of salt ice grow, impurities such as salt are rejected by the ice crystals and diffuse away from the platelets. The freezing point is lowered within the diffusion cloud preventing other platelets from growing in the vicinity. As a result, the plate width decreases with increasing growth rate. The physical constants involved are the diffusion coefficient of salt in water and the roughness of the freezing interface. In an earlier paper the authors showed that plate width varied with the 6th root of the distance beneath the upper surface of the ice sheet. This corresponds to an ice growth equation with the power 3/4 in time. Past empirical equations as well as laboratory tests confirm the applicability of this power for moderately thick ice (~10 to ~40 cm). Considering that heat transfer from the ice surface is the primary factor governing growth while the ice is thin, it is shown that the power in time is 1 for thin ice and gradually changes to 1/2 for thick ice. One may also start with the exact growth equation which considers surface heat transfer and develop an expression for the plate width as a function of ice thickness. The plate width affects the strength of sea ice profoundly because it determines how the liquid brine, which weakens the ice, is distributed. Several possible solutions to the problem of developing a general relation for sea-ice strength using only physical parameters are considered. The strength of sea ice (σ) is shown to depend on the past weather history. The relations allow the determination of σ in terms of easily measurable or known parameters, including air temperature and snow thickness. They also allow one to explain observed discrepancies between properties of sea ice in various geographical areas. A simplified operational relation is suggested which expresses σ in terms of the initial sea water salinity, the age and thickness of the ice, the thickness of the snow cover, and the recent air temperature.
|Rights:||Approved for public release; distribution is unlimited.|
|Appears in Collections:||Research Report|
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