Atmosphere to ocean momentum transfer by sea ice

由于全球变暖，北极和南极的冰盖正在发生变化，北极海冰的夏季范围显著减少。北极海冰的减少比气候模式预测的更为迅速和极端，这表明这些模式不能充分代表控制这种减少的过程。夏季北极海冰覆盖的减少和冬季海冰覆盖的变化影响了空气和海洋之间的力学和热力学耦合。事实上，观测表明，在过去的15年中，海冰覆盖的流动性变得更大，海冰下的平均海洋环流有所增加。由于在同一时期，没有观测到风强度的增加，这表明海冰覆盖本身的变化是冰运动增强和风应力向海冰下海洋转移的原因。我们的项目假设是：北极海冰覆盖的变化导致了空气和海洋之间更有效的动量转移，导致海冰和北冰洋的旋转。我们将结合新数据、理论和数值模拟来检验这一假设。我们将研究冰盖粗糙度的变化，例如，通过更稀释的冰盖，更多的浮冰边缘暴露出来，如何改变空气对冰和冰对海洋施加的阻力。我们将研究冰盖的减少如何降低冰盖对风的阻力，使其更容易移动。我们特别提出了这样一个问题：北极海冰环流的加速在多大程度上是冰力减少与阻力增加的结果？我们将使用包含新物理学的气候模型，这些模型由新观测校准并推导而来，以检验以下预测：海冰覆盖的变化将继续导致空气和海洋之间的动量转移增强，从而使冰盖更具流动性和响应性，并增强北冰洋的流动和混合。虽然我们的分析重点是北冰洋，那里的海冰变化更为剧烈，但我们也将研究南大洋的气-冰-海动量交换。该提案汇集了海冰动力学、遥感、海洋和气候建模方面的主要研究人员，并以极地观测和建模中心在卫星观测、理论和海冰建模方面的现有专业知识为基础。除了科学成果之外，拟议的工作还将导致新的海冰阻力物理学被纳入海冰气候模型，并提交给气候模拟小组。这将直接帮助科学家调查和预测北极和南大洋海冰覆盖的未来变化，也有助于科学家试图了解和预测全球气候系统的变化。

In response to global warming, the ice covers of the Arctic and Antarctic are changing, with a significant reduction in the summer extent of Arctic sea ice. The reduction of Arctic sea ice is more rapid and extreme than climate models predict, suggesting that these models do not adequately represent the processes controlling this reduction. The reduced summer Arctic sea ice cover, and changes to the winter sea ice cover, affect the mechanical and thermodynamic coupling between the air and ocean. In fact, observations show that the sea ice cover has become more mobile in the last 15 years and that there has been an increase in the mean ocean circulation beneath the sea ice. Since, over the same period, there has not been an observed increase in wind strength, this suggests that changes to the sea ice cover itself are responsible for an enhanced ice motion and transfer of wind stress to the ocean beneath sea ice. Our project hypothesis is: Changes in the Arctic sea ice cover have resulted in a more efficient transfer of momentum between the air and ocean, resulting in spin up of sea ice and the Arctic Ocean. We will test this hypothesis with a combination of new data, theory and numerical modelling. We will investigate how changes in the roughness of the ice cover, e.g. through a more dilute ice cover having more floe edges exposed, change the drag forces exerted by the air on the ice and the ice on the ocean. We will investigate how a reduction in the ice cover may reduce the resistance of the ice cover to the wind, allowing it to move more easily. In particular we address the question: to what extent is acceleration of the Arctic sea ice gyre the result of decreased ice forces versus increased drag? We will use climate models containing new physics calibrated with, and derived from, new observations, to examine the prediction that: Changes in the sea ice cover will continue to lead to enhanced momentum transfer between the air and ocean, resulting in a more mobile and responsive ice cover and enhanced flow and mixing in the Arctic Ocean. Although we focus our analysis on the Arctic Ocean, where sea ice changes have been more dramatic, we will also examine air-ice-ocean momentum exchanges in the Southern Ocean. This proposal brings together leading researchers in sea ice dynamics, remote sensing, ocean and climate modelling, and builds upon existing expertise in satellite observation, theory, and modelling of sea ice in the Centre for Polar Observation and Modelling. In addition to the scientific outcomes, the proposed work will result in new sea ice drag physics being incorporated into a sea ice climate model and delivered to climate modelling groups. This will directly help scientists investigating and predicting future changes to the sea ice cover in the Arctic and Southern Oceans and also help scientists trying to understand and predict changes in the global climate system.