[论文解读] Towards the inclusion of wave-ice interactions in large-scale models for the Marginal Ice Zone

Timothy Williams, Luke G. Bennetts+3 more|arXiv (Cornell University)|Mar 13, 2012

Arctic and Antarctic ice dynamics被引用 6

一句话总结

本文提出了一种用于边缘浮冰区（MIZ）的波-冰相互作用模型，该模型将海冰引起的波能衰减与波致冰体破裂相耦合，使其能够整合进大尺度业务化海洋-海冰模型。结果表明，MIZ宽度的预测对波能衰减模型、数值格式以及海冰属性高度敏感，准确实现这些参数对避免过度衰减和低估MIZ范围至关重要。

ABSTRACT

A wave-ice interaction model for the marginal ice zone (MIZ) is reported, which involves both the attenuation of ocean surface waves by sea ice and the concomitant breaking of the ice by waves. It is specifically designed to embed wave-ice interactions in an operational ice/ocean model for the first time. We investigate different methods of including the wave forcing, and different criteria for determining if they cause floes to break. We also investigate and discuss the effects of using various attenuation models, finding that predicted MIZ widths are quite sensitive to the choice of model. Additional sensitivity tests are performed on: (i) different parameterizations of the floe size distribution (FSD), including the initial FSD used; (ii) the properties of the wave field; and (iii) the sea ice properties such as concentration, thickness and breaking strain. Results are relatively insensitive to FSD parameterization but vary noticeably and systematically with its initial configuration, as they do with properties (ii-iii). An additional, somewhat surprising sensitivity, is the degree of influence of the numerical scheme that performs wave attenuation and advection. This is because a naive implementation of spatial and temporal discretizations can cause the waves to be over-attenuated, leading to a reduction of the predicted MIZ width by a substantial factor. Example simulations intended to represent conditions in the Fram Strait in 2007, which exploit reanalyzed wave and ice model data, are shown to conclude the results section. These compare favorably to estimates of MIZ width using concentrations obtained from remotely-sensed passive microwave images.

研究动机与目标

• 开发一种波-冰相互作用的参数化方案，以纳入业务化的大尺度海洋-海冰模型中。
• 研究不同波强迫表示方式和冰体破裂判据对MIZ动力学的影响。
• 评估MIZ宽度预测对波能衰减模型、初始冰体尺寸分布（FSD）和海冰属性选择的敏感性。
• 评估数值格式对波能衰减和传播的影响，特别是避免过度衰减。
• 利用2007年弗朗斯海峡的实际模拟结果，通过遥感数据对模型进行验证。

提出的方法

• 采用集成谱方法（ISM）以涵盖整个频率谱的波能，从而能够体现干涉效应。
• 应用Squire等（2009）提出的衰减系数，以模拟因冰体相互作用导致的波能损失。
• 采用基于波致应力的应变驱动冰体破裂判据，基于Fox和Squire（1994）的弹性板模型。
• 对冰体尺寸分布（FSD）采用分段幂律分布，参数通过观测数据进行标定。
• 使用有限差分数值格式集成波能衰减与传播，并对网格分辨率和时间步长进行敏感性测试。
• 利用被动微波遥感数据（AMSR-E，不伦瑞克大学）对MIZ宽度估计结果进行模型验证。

实验结果

研究问题

• RQ1 波能衰减模型的选择如何影响预测的MIZ宽度？
• RQ2 波传播与衰减的数值格式差异对模型精度和过度衰减有何影响？
• RQ3 MIZ宽度预测对初始FSD参数化及其演化过程的敏感性如何？
• RQ4 波场特性、冰浓度、厚度及破裂应变的变化如何影响MIZ动力学？
• RQ5 该模型在使用再分析波和海冰数据时，能在多大程度上再现弗朗斯海峡的实际MIZ宽度？

主要发现

• 预测的MIZ宽度对波能衰减模型的选择极为敏感，预测范围差异可达两倍之多。
• 波传播与衰减的简单数值实现可能导致严重的过度衰减，使预测的MIZ宽度显著减小。
• 初始FSD配置对模型结果有显著影响，尽管FSD参数化本身对结果的敏感性低于其初始状态。
• 随着冰浓度、厚度和破裂应变的变化，MIZ宽度系统性变化，表明其强烈依赖于海冰力学属性。
• 2007年弗朗斯海峡的模拟结果与基于被动微波遥感（AMSR-E）估算的MIZ宽度高度一致，验证了模型的预测能力。
• 该模型首次成功地将波-冰耦合机制嵌入大尺度海洋-海冰框架中，实现了MIZ动力学的业务化预报。