Impact of sea ice floe size distribution on seasonal fragmentation and melt of Arctic sea ice
Impact of sea ice floe size distribution on seasonal fragmentation and melt of Arctic sea ice
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DOI：
10.5194/tc-14-403-2020
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发表时间：
2020-02-04
期刊：
影响因子：
5.2
通讯作者：
Aksenov, Yevgeny
中科院分区：
文献类型：
--
作者：
Bateson, Adam W.;Feltham, Daniel L.;Aksenov, Yevgeny
近年来，夏季北极海冰面积迅速减少。为了了解这一趋势并预测夏季北极海冰的未来演变，需要更好地了解驱动海冰季节性损失的物理过程。边缘冰带，这里定义为海冰覆盖率在15%到80%之间的区域，是将浮冰与公海分开的区域。这一地区的精确模拟对于理解季节性海冰损失的主要机制非常重要。边缘冰带的演变是由大气、海冰、海洋和海面波浪之间复杂的相互作用决定的。因此，该区域提出了一个重大的建模挑战。海冰的大小不一，但气候模型中的海冰模型假定它们的大小是恒定的。浮冰的大小影响海冰的侧向融化速率以及大气、海冰和海洋之间的动量传递，这些都是边缘冰带内的重要过程。在本研究中，用幂律来表示粒径分布，幂律由上粒径截止点、下粒径截止点和幂律指数定义。这种分布也由一种新的示踪剂来定义，该示踪剂根据侧向融化、波浪引起的破裂、冻结条件和平流的变化而变化。这种分布是在与预测海洋混合层模型耦合的海冰模型中实现的。我们提出的结果表明，使用幂律浮冰大小分布对海冰具有时空依赖性的影响，特别是增加了边缘冰带在季节性海冰损失中的作用。这一特征对于纠正海冰模型中存在的偏差非常重要。此外，我们还发现，与用于计算横向熔体的其他参数相比，模型对粒径分布参数的敏感性要强得多，这证明了在模型开发中关注粒径分布是合理的。我们还发现，在海冰覆盖下传播的波浪的衰减速率调节了波浪破碎对浮冰大小分布的影响。最后得出结论，本文提出的模型方法是一种灵活的工具，可以评估浮冰大小分布在海冰演变中的重要性，是浮冰大小模型未来发展的一个有用的垫脚石。
Recent years have seen a rapid reduction in the summer Arctic sea ice extent. To both understand this trend and project the future evolution of the summer Arctic sea ice, a better understanding of the physical processes that drive the seasonal loss of sea ice is required. The marginal ice zone, here defined as regions with between 15 % and 80 % sea ice cover, is the region separating pack ice from the open ocean. Accurate modelling of this region is important to understand the dominant mechanisms involved in seasonal sea ice loss. Evolution of the marginal ice zone is determined by complex interactions between the atmosphere, sea ice, ocean, and ocean surface waves. Therefore, this region presents a significant modelling challenge. Sea ice floes span a range of sizes but sea ice models within climate models assume they adopt a constant size. Floe size influences the lateral melt rate of sea ice and momentum transfer between atmosphere, sea ice, and ocean, all important processes within the marginal ice zone. In this study, the floe size distribution is represented as a power law defined by an upper floe size cut-off, lower floe size cut-off, and power-law exponent. This distribution is also defined by a new tracer that varies in response to lateral melting, wave-induced break-up, freezing conditions, and advection. This distribution is implemented within a sea ice model coupled to a prognostic ocean mixed-layer model. We present results to show that the use of a power-law floe size distribution has a spatially and temporally dependent impact on the sea ice, in particular increasing the role of the marginal ice zone in seasonal sea ice loss. This feature is important in correcting existing biases within sea ice models. In addition, we show a much stronger model sensitivity to floe size distribution parameters than other parameters used to calculate lateral melt, justifying the focus on floe size distribution in model development. We also find that the attenuation rate of waves propagating under the sea ice cover modulates the impact of wave break-up on the floe size distribution. It is finally concluded that the model approach presented here is a flexible tool for assessing the importance of a floe size distribution in the evolution of sea ice and is a useful stepping stone for future development of floe size modelling.