北极熊想去海峡对面看看怎么办？大自然建冰桥来帮忙！新的理论成果预测了海冰阻塞狭窄海峡从而形成自然桥梁的条件。
撰文 Ana Lopes
翻译 许雅澜
审校 王腾
图片来源：NASA Worldview
加拿大北极群岛的海峡及水道几乎每年冬天都会被大量的海冰堵塞，形成结冰的“桥梁”。这些自然形成的通道可以帮助北极熊及其他动物“探索新世界”——到达之前无法进入的区域。此外，冰桥也可以通过阻碍海冰漂入温暖的海域而影响当地与全球气候。然而我们对冰桥的形成所知甚少。来自普林斯顿大学的 Bhargav Rallabandi、Howard Stone 及其同事建立了一个理论模型，详细描述了“冰桥”形成的某些必要条件。他们还指出，该模型可能同样适用于密集颗粒流在受限环境中发生阻塞的情况。
研究团队对一层海冰沿着一条狭窄海峡（类似白令海峡，长度远大于宽度）的运动进行了模拟。该层海冰在作用于其顶面上的外部风力驱动下运动，但也受到水对其底面的阻力和内部应力的阻碍。研究人员假设，由海峡的宽度、冰区厚度和密实度共同决定的内部应力主导了海冰受到的水流阻力。在这种情况下，他们的理论模型预测：对于给定的风压与海峡宽度范围，冰桥只会在冰层的厚度和密实度超出临界值时形成。在如今这个冰层变薄、风速下降、全球变暖的时代，这些临界阈值可能有助于预测冰桥的形成与解体。
文章来源 http://physics.aps.org/synopsis-for/10.1103/PhysRevLett.118.128701
论文信息
【题目】Formation of wind-driven ice bridges in narrow straits
【作者】 B Rallabandi，Z Zheng，M Winton，H A. Stone
【刊期】Phys. Rev. Lett. 118, 128701 (2017)
【日期】Published March 21, 2017
【DOI】10.1103/PhysRevLett.118.128701
【摘要】Ice bridges are static structures composed of tightly packed sea ice that can form during the course of its flow through a narrow strait. Despite their important role in local ecology and climate, the formation and breakup of ice bridges is not well understood and has proved difficult to predict. Using long-wave approximations and a continuum description of sea ice dynamics, we develop a one-dimensional theory for the wind-driven formation of ice bridges in narrow straits, which is verified against direct numerical simulations. We show that for a given wind stress and minimum and maximum channel widths, a steady-state ice bridge can only form beyond a critical value of the thickness and the compactness of the ice field. The theory also makes quantitative predictions for ice fluxes, which are particularly useful to estimate the ice export associated with the breakup of ice bridges. We note that similar ideas are applicable to dense granular flows in confined geometries.
【链接】 https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.118.128701
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