[论文解读] Buoy measurements of strong waves in ice amplitude modulation: a signature of complex physics governing waves in ice attenuation

Jean Rabault, Trygve Halsne+26 more|arXiv (Cornell University)|Jan 15, 2024

Arctic and Antarctic ice dynamicsEarth and Planetary Sciences被引用 3

一句话总结

本研究通过现场观测，揭示了海冰中12小时调制波幅的变化，表明波浪衰减存在周期性变化，可能由潮汐引起的海冰汇聚与离散驱动。该调制现象无法仅用开阔海域波浪变化或潮汐解释，表明在边缘浮冰区存在动态的、周期性切换的衰减机制。

ABSTRACT

The Marginal Ice Zone (MIZ) forms a critical transition region between the ocean and sea ice cover as it protects the close ice further in from the effect of the steepest and most energetic open ocean waves. As waves propagate through the MIZ, they get exponentially attenuated. Unfortunately, the associated attenuation coefficient is difficult to accurately estimate and model, and there are still large uncertainties around which attenuation mechanisms dominate depending on the conditions. This makes it challenging to predict waves in ice attenuation, as well as sea ice breakup and dynamics. Here, we report in-situ observations of strongly modulated waves-in-ice amplitude, with a modulation period of around 12 hours. We show that simple explanations, such as changes in the incoming open water waves, or the effect of tides and currents and bathymetry, cannot explain for the observed modulation. Therefore, the significant wave height modulation observed in the ice most likely comes from a modulation of the waves-in-ice attenuation coefficient. To explain this, we conjecture that one or several waves-in-ice attenuation mechanisms are periodically modulated and switched on and off in the area of interest. We gather evidence that sea ice convergence and divergence is likely the factor driving this change in the waves in ice attenuation mechanisms and attenuation coefficient, for example by modulating the intensity of floe-floe interaction mechanisms.

研究动机与目标

• 研究在边缘浮冰区（MIZ）海冰中传播的波浪出现强烈12小时波幅调制的原因。
• 确定观测到的波浪调制是否源于开阔海域波浪变化、潮汐、海流或水深变化。
• 识别导致海冰中波浪衰减变化的物理机制，特别是那些可能周期性开启或关闭的机制。
• 评估海冰动力学——尤其是汇聚与离散——对调制波浪衰减系数的作用。
• 为未来现场观测活动提供基础，以更详细地测量冰 floe-floe 相互作用及衰减动力学。

提出的方法

• 在斯瓦尔巴群岛附近边缘浮冰区部署具有高时间分辨率的海洋学浮标（OMBs），记录波高与海冰运动。
• 分析现场波幅时间序列，检测到以12小时为主导周期的周期性调制。
• 通过对比分析，排除了潮汐海流、水深及开阔海域波浪变化等外部驱动因素的影响。
• 利用卫星SAR数据和波浪模型输出（MFWAM）验证浮标观测结果，并评估空间波浪分布特征。
• 应用射线追踪与谱波分析方法，重建波浪传播与衰减行为。
• 通过与潮汐强迫及海冰运动数据的相关性分析，评估海冰动力学在调制机制中的作用。

Figure 1 : Overview of the buoy deployment during the modulated significant wave height event. A total of 9 buoys are clustered in the same area at the South East of Svalbard around 2021-03-01. The overview map subfigure (left) presents the sea ice concentration (SIC, data source: internal product a

实验结果

研究问题

• RQ1 海冰中观测到的12小时周期性波幅调制由何原因引起？
• RQ2 该调制是否可由开阔海域波浪变化、潮汐或水深变化解释？
• RQ3 边缘浮冰区的波浪衰减系数是否受到周期性调制？若是，其背后的物理过程是什么？
• RQ4 海冰汇聚与离散事件在多大程度上调制了波浪衰减机制？
• RQ5 未来测量活动如何能更有效地捕捉冰 floe-floe 相互作用及其对波能耗散的影响？

主要发现

• 在海冰中观测到显著的12小时波幅调制，波高在周期内变化幅度高达50%。
• 通过多源数据分析确认，该调制并非由开阔海域波浪变化、潮汐、海流或水深变化引起。
• 该观测结果最可能由海冰覆盖区域波浪衰减系数的周期性变化所解释。
• 潮汐强迫可能通过调制海冰汇聚与离散，进而周期性地开启或关闭控制波能耗散的 floe-floe 相互作用机制。
• 东南斯瓦尔巴地区因具备可靠的海冰动力学与有利的部署条件，被确定为未来长期研究的优选区域。
• 本研究呼吁未来现场观测活动应增强浮标仪器配置，以记录冰 floe 的碰撞统计与响应幅值算子。

Figure 2 : 1-dimensional wave spectrum for the 3 instruments furthest in the MIZ that are equipped with wave measurement capability (referred to as the Buoys Of Interest (BOIs) with IDs 19648, 200905, 13319), obtained during the time of the modulated SWH wave event. The instrument ID 19648 is a v202