Measuring the sea ice floe size distribution
Measuring the sea ice floe size distribution
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DOI：
10.1029/jc089ic04p06477
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发表时间：
1984-07
影响因子：
--
通讯作者：
D. Rothrock;A. Thorndike
中科院分区：
文献类型：
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作者：
D. Rothrock;A. Thorndike
海冰破裂成浮冰，直径从几米到一百公里不等。这种破碎会影响冰盖在夏季对变形和浮冰侧壁融化的抵抗力。浮冰被波浪击碎，并在冰缘附近膨胀，并且在整个浮冰块中，由于均衡不平衡、热裂、风和洋流的作用，浮冰会膨胀。冬天，它们通过冷冻焊接在一起。絮体尺寸可以通过多种属性来测量，例如面积或平均卡尺直径。絮凝物尺寸分布的两个定义似乎很有用：F(p)，不小于 p 的絮凝物覆盖的面积分数； N(p)，单位面积上不小于p的絮凝物数量。 F(p) 可以通过面积以外的集合来测量，例如被不小于 p 的浮冰覆盖的线或点集的分数。如果对于小 ρ，N 的行为类似于 ρα，其中 ρ 是平均卡尺直径，则 α 必须大于 -2，以便小絮凝物占据有限的面积。如果−2<α<−1，则小浮冰的周长是无穷大。已经测量了几个夏季分布。在双对数图上，它们的斜率（α 的局部值）范围从 -1.7 到 -2.5。一种分布遵循幂律；其他的对于较大的浮冰有更陡的斜坡，对于较小的浮冰有更平缓的斜坡。另一种采样策略是测量浮冰上线段的长度。这些弦长的分布相当于絮凝物直径的分布。任何尺寸范围内的浮冰覆盖面积分数 g 的估计方差为 g(1 - g)K−1，其中 K 是独立样本的等效数量。 K 可以从所选尺寸范围的指示函数的自协方差中找到。对于小范围絮凝物直径的线性取样，K 是样品长度与絮凝物直径的比率。
Sea ice is broken into floes whose diameters range from meters to a hundred kilometers. This fragmentation affects the resistance of the ice cover to deformation and the melting at floe sidewalls in summer. Floes are broken by waves and swell near the ice edge and, throughout the pack, by isostatic imbalances, thermal cracking, winds, and currents. In winter, they are welded together by freezing. Floe size can be measured by several properties p, for instance, area or mean caliper diameter. Two definitions of floe size distribution seem useful: F(p), the fraction of area covered by floes no smaller than p; and N(p), the number of floes per unit area no smaller than p. F(p) can be measured by sets other than areas, such as the fraction of a line or of a point set covered by floes no smaller than p. If N behaves like ρα for small ρ, where ρ is mean caliper diameter, α must be greater than −2 so that the small floes occupy finite area. If −2<α<−1, the perimeter of small floes is infinite. Several summertime distributions have been measured. On a log-log graph their slopes (local values of α) range from −1.7 to −2.5. One distribution follows a power law; the others have steeper slopes for larger floes and more gradual slopes for smaller floes. Another sampling strategy is to measure the lengths of line segments on floes. The distribution of these chord lengths is equivalent to the distribution of floe diameters. The variance of an estimate of the fraction g of area covered by floes in any size range is g(1 - g)K−1, where K is the equivalent number of independent samples. K can be found from the autocovariance of the indicator function for the chosen size range. For line sampling of a narrow range of floe diameters, K is the ratio of the sample length to the floe diameter.