Dynamics versus Thermodynamics: The Sea Ice Thickness Distribution
Dynamics versus Thermodynamics: The Sea Ice Thickness Distribution
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DOI：
10.1002/9780470757161.ch3
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发表时间：
2010-01
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影响因子：
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通讯作者：
C. Haas
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作者：
C. Haas
Eicken第2章)描述了海冰最初是如何从开阔的水域形成并随后生长成冰盖的，或者换句话说，海冰是如何从热力学角度生长的。其中一个基本概念是，由于在冰中建立了更大的温度梯度和更高的冻结率，空气越冷，冰就越厚。反之亦然，由于气候变暖，极地海冰覆盖将变得更薄。然而，另一个过程有助于海冰的厚度分布：由于其相对薄（±1到几米），漂浮在深水上的海冰受到风和洋流的影响，这些风和洋流会稳定地移动海冰，即冰盖漂移。结果，它分裂成浮冰，由开放的水道点缀。随着漂移方向和速度的改变，浮冰会被推到一起并相互碰撞。如果冰的作用力变得太大，它最终会破裂。由此产生的冰碎片和冰块将被推到浮冰的边缘上或下面，形成所谓的压力脊（图3.1）。显然，这种动态形成的脊要比邻近的、热力学生长的、未变形的水平冰厚得多。就统计方法而言，这一讨论表明，考虑不同的冰厚（从薄冰到厚冰）是很重要的，并且可以通过许多不同的薄冰和厚冰的排列来获得一定的平均冰厚。因此，很难将冰厚数据解释为气候变暖或变冷的迹象。这将在本章后面的章节中加以说明。评估全球海冰覆盖萎缩或增长的最终变量是冰体积，即面积冰覆盖和冰厚度的数学乘积。与冰的厚度相比，利用卫星从太空可以很好地监测海冰覆盖（参见第4章）。然而，从上面的讨论可以得出，只要冰厚未知，观测到的近期变化
Eicken Chapter 2) has described how sea ice initially forms from open water and subsequently grows into an ice cover, or in other terms, how sea ice grows thermodynamically. One of the basic concepts is that the ice grows thicker the colder the air is due to the establishment of greater temperature gradients in the ice, and higher freezing rates. Vice versa, it would follow that as a consequence of climate warming, polar sea ice cover would become thinner. However, another process contributes to the sea ice thickness distribution: Due to its relative thinness±one to a few metres±sea ice floating over deep water is subject to winds and currents which steadily move the ice around, ie the ice cover drifts. As a result, it breaks up into floes interspersed by open water leads. With changing drift directions and speeds, the ice floes will be pushed together and collide with each other. If the resulting forces in the ice become too large, it will finally break. The resulting ice fragments and blocks will be pushed onto, and below, the edges of the floes forming so-called pressure ridges Fig. 3.1).Obviously, such dynamically formed ridges are much thicker than the adjacent, thermodynamically grown undeformed level ice. In terms of a statistical approach, this discussion shows that it is important to take into account different ice thickness classes from thin to thick ice), and that a certain mean ice thickness can be attained by many different arrangements of thin and thick ice. As a consequence, it is quite difficult to interpret ice thickness data for indications of climate warming or cooling. This will be illustrated in later sections of this chapter. The ultimate variable to assess the shrinking or growing of the global sea ice cover is ice volume, ie the mathematical product of areal ice coverage and ice thickness. In contrast to ice thickness, sea ice coverage can be monitored reasonably well from space using satellites Comiso, Chapter 4). However, from the discussion above it follows that as long as the ice thickness is unknown, the observed recent changes of