Characterising the Ice Shelf/Ocean Boundary Layer

描述冰架/海洋边界层的特征

基本信息

批准号：
NE/N010027/1
负责人：
Paul Holland
金额：
$ 36.6万
依托单位：
British Antarctic Survey
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2016
资助国家：
英国
起止时间：
2016 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FN010027%2F1
关键词：
Characterising Ice Shelf Ocean Boundary

项目摘要

Global average sea level is rising by approximately 3 millimetres per year. Given the huge economic and societal impacts of this change, accurate forecasts of sea level are urgently needed to inform policymakers considering mitigation and adaptation strategies. Melting of the ice sheets of Antarctica and Greenland currently contributes about one third of sea level rise. The future of this melting is highly uncertain, and the worst-case scenario involves a substantial ice-sheet contribution to dangerous sea-level rise. The largest contribution to sea level rise from ice sheets occurs when the ocean melts the base of ice shelves (floating extensions of the grounded ice sheet). The melt rate of ice in seawater is determined by the transfer of heat and salt from the ocean towards the ice. Observations reveal a turbulent boundary layer in the ocean beneath ice shelves, where vigorous mixing is driven by the flow of rising meltwater, large-scale circulation in the ocean, and tides. Mixing of heat and salt in the boundary layer influences the ice melt rate, but the physical processes involved are poorly understood and will not be resolved in climate models for the foreseeable future. The proposed project will improve our understanding of the ice shelf/ocean boundary layer and develop improved representations of ice-shelf melting for use in climate models.To achieve these aims we will use a suite of numerical models and the latest observations. We will start with direct numerical simulations (DNS) to model a small box of ocean next to an ice shelf (~1 cubic metre) at ultra-high resolution (~1 millimetre). This will provide insight into the turbulence near the ice and its interaction with melting. We will then use large-eddy simulations (LES) to study a larger volume (~1 square kilometre in area by 100 metres height) at high resolution (~10 centimetres - 1 metre). This will resolve the largest turbulent motions in the whole boundary layer. Both models will be validated using recent observations obtained from mooring sites at the George VI and Larsen C ice shelves (Nicholls, NE/H009205/1). The model results will in turn help interpret and understand the observations.We will use these numerical models to devise and calibrate parameterisations for ice melting and vertical mixing for use in ocean climate models. We will add candidate parameterisations to a one-dimensional (vertical) model that incorporates many popular ocean mixing schemes, and test them directly against the DNS and LES results. We will begin with existing parameterisations and modify them as needed to match the high resolution models. The successful parameterisations will be implemented in the UK ocean model (NEMO) and shared with climate modelling groups (including the Met Office) to improve predictions of sea-level rise.

全球平均海平面每年上升约3毫米。鉴于这一变化所产生的巨大经济和社会影响，迫切需要准确的海平面预测，以便为决策者考虑缓解和适应战略提供信息。目前，约三分之一的海平面上升是由南极洲和格陵兰岛冰盖融化造成的。这种融化的未来是高度不确定的，最坏的情况是冰盖对危险的海平面上升造成巨大影响。当海洋融化冰架底部（接地冰盖的浮动延伸部分）时，冰盖对海平面上升的最大贡献发生。海水中冰的融化速度取决于热量和盐从海洋向冰的传递。观测结果显示，冰架下方的海洋存在湍流边界层，上升的融水流、海洋中的大规模环流和潮汐推动了剧烈的混合。边界层中热量和盐的混合会影响冰的融化速率，但人们对所涉及的物理过程知之甚少，并且在可预见的将来不会在气候模型中得到解决。拟议的项目将增进我们对冰架/海洋边界层的了解，并开发改进的冰架融化表示方法，用于气候模型。为了实现这些目标，我们将使用一套数值模型和最新的观测结果。我们将从直接数值模拟 (DNS) 开始，以超高分辨率（~1 毫米）对冰架（~1 立方米）旁边的一小片海洋进行建模。这将有助于深入了解冰附近的湍流及其与融化的相互作用。然后，我们将使用大涡模拟 (LES) 以高分辨率（约 10 厘米 - 1 米）研究更大的体积（面积约 1 平方公里、高度 100 米）。这将解决整个边界层中最大的湍流运动。这两个模型都将使用从乔治六世和拉森 C 冰架停泊点获得的最新观测结果进行验证（Nicholls，NE/H009205/1）。模型结果反过来将有助于解释和理解观测结果。我们将使用这些数值模型来设计和校准用于海洋气候模型的冰融化和垂直混合的参数化。我们将向一维（垂直）模型添加候选参数化，该模型包含许多流行的海洋混合方案，并直接根据 DNS 和 LES 结果对其进行测试。我们将从现有的参数开始，并根据需要修改它们以匹配高分辨率模型。成功的参数化将在英国海洋模型（NEMO）中实施，并与气候建模小组（包括英国气象局）共享，以改进对海平面上升的预测。