Influence of sea ice lead-width distribution on turbulent heat transfer between the ocean and the atmosphere
Influence of sea ice lead-width distribution on turbulent heat transfer between the ocean and the atmosphere
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DOI：
10.5194/tc-6-143-2012
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发表时间：
2011-10
期刊：
影响因子：
--
通讯作者：
S. Marcq;J. Weiss
中科院分区：
文献类型：
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作者：
S. Marcq;J. Weiss
导火线是海冰覆盖层内开放水域的线状结构，由于发散或剪切而破裂。通过导线，空气和水接触，并通过它们之间巨大的温度和湿度差异驱动的对流过程直接交换潜热和显热。在北极中部，铅在冬季只覆盖1%至2%的海洋，但占向上热通量的70%以上。此外，窄导线（几米）在传递湍流热量方面的效率是大导线（几百米）的两倍多。我们发现，引线宽度是幂律分布，P（X）~ X −a，a >1，下降到非常小的空间尺度（20米或以下）。这意味着，开放水域部分是由非常小的铅到目前为止占主导地位。使用两个经典的公式，这提供了一阶湍流封闭的热通量的fetch依赖，我们发现，平均热通量，当考虑到从SPOT冰盖卫星图像获得的铅宽分布时，相比之下，开放水域部分构成一个独特的大铅和其他地区被冰覆盖的情况，因为它通常被认为是在气候模型的网格规模。如果我们假设引线宽度的幂律缩放扩展到更小（~1 m）的尺度，则这种差异可能更大。这样的估计可能是迈向亚网格尺度参数化的开放水域的空间分布的热通量计算在海洋/海冰耦合模式的第一步。
Leads are linear-like structures of open water within the sea ice cover that develop as the result of fracturing due to divergence or shear. Through leads, air and water come into contact and directly exchange latent and sensible heat through convective processes driven by the large temperature and moisture differences between them. In the central Arctic, leads only cover 1 to 2% of the ocean during winter, but account for more than 70% of the upward heat fluxes. Furthermore, narrow leads (several meters) are more than twice as efficient at transmitting turbulent heat than larger ones (several hundreds of meters). We show that lead widths are power law distributed, P(X) ~ X −a with a >1, down to very small spatial scales (20 m or below). This implies that the open water fraction is by far dominated by very small leads. Using two classical formulations, which provide first order turbulence closure for the fetch-dependence of heat fluxes, we find that the mean heat fluxes (sensible and latent) over open water are up to 55% larger when considering the lead-width distribution obtained from a SPOT satellite image of the ice cover, compared to the situation where the open water fraction constitutes one unique large lead and the rest of the area is covered by ice, as it is usually considered in climate models at the grid scale. This difference may be even larger if we assume that the power law scaling of lead widths extends down to smaller (~1 m) scales. Such estimations may be a first step towards a subgrid scale parameterization of the spatial distribution of open water for heat fluxes calculations in ocean/sea ice coupled models.