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Forward and adjoint coupled ocean-ice sheet modelling

正向和伴随耦合海洋冰盖建模

基本信息

批准号：
2285049
负责人：
金额：
--
依托单位：
Imperial College London
依托单位国家：
英国
项目类别：
Studentship
财政年份：
2019
资助国家：
英国
起止时间：
2019 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=studentship-2285049
关键词：
Forward adjoint coupled ocean ice

项目摘要

The Antarctic Ice Sheet is a giant slab of glacial ice that is the size of Europe and a few kilometres thick. It rests on bedrock that is below sea level, so around the margins where the ice is thinner it floats free of the seabed to form floating ice shelves (Fig. 1). Over the last few decades it has become clear that the seawater circulating in the cavities beneath ice shelves is melting the Antarctic Ice Sheet at an increasing rate. This impacts on the speed with which glaciers flow towards the ocean and thus is a critical factor in predictions of sea-level rise. West Antarctica represents the largest source of uncertainty in projections of sea level over the 21st Century, with Thwaites Glacier (TG) having greater potential to influence sea level than any other. The importance of this overall topic and this geographical location in particular led to a recent £20M joint NERC-NSF programme on Thwaites Glacier (https://nerc.ukri.org/press/releases/2018/14-glacier/). A team at Imperial College London, led by Prof. Piggott, is contributing to one of these projects (https://www.bas.ac.uk/project/melting-at-thwaites-grounding-zone-and-its-control-on-sea-level/ led by BAS) through detailed numerical modelling of the critical grounding line region. Over the past few years there has been progress in the use of flexible mesh methods to simulate the ocean in complex ice shelf cavities (Jordan et al., 2014; Yeager 2018), as well as the use of flexible mesh methods along with the use of adjoint sensitivity techniques in ice sheet modelling (Kyrke-Smith et al., 2017; https://github.com/gahansen/Albany/wiki/PAALS-Tutorial-2016), and fully coupled ocean-ice sheet modelling is now possible (Asay-Davis et al., 2016).In recent years the ability for automatic code generation to provide easy access to adjoints has been taken up in the development of several ice sheet models (Kyrke-Smith et al., 2017; https://icepack.github.io/index.html). The underlying technology which has facilitated this development (https://www.firedrakeproject.org/) originates from Imperial College London and we have recently used it to generate an adjoint enabled ocean model (https://thetisproject.org/). There is therefore an opportunity here at Imperial to combine these cutting-edge research topics within a single modelling framework: flexible mesh modelling of the coupled ocean and ice sheet, and the use of adjoints for sensitivity analyses and data assimilation. The ultimate goal is a fully coupled model with an adjoint capability that allows for sensitivities to be propagated between the ocean and ice sheet. This capability can be used for data assimilation, uncertainty quantification, and model calibration and initialisation. In particular, this model will be the first capable of solving the crucial problem of initialisation shock. When ocean and ice models are coupled together, the ice spends centuries adjusting to the ocean model state, and this artificial signal over-rides any real sea-level change. This shock can be avoided by using the coupled adjoint to initialise the ice/ocean model perfectly, thus isolating the real ice sheet change driven by changes in ocean melting.This work would contribute to the wider activities of the Imperial-BAS team, and in particular would be able to take advantage of the data and modelling activities planned under the above-mentioned NERC-NSF Thwaites glacier project. It is highly likely that the student will get the chance to experience Antarctic fieldwork first-hand, as part of an oceanographic cruse during the project.

南极冰盖是一块巨大的冰川板，面积相当于欧洲，厚度为几公里。它坐落在低于海平面的基岩上，因此在冰较薄的边缘周围，它漂浮在海床上，形成漂浮的冰架（图1）。在过去的几十年里，人们已经清楚地看到，在冰架下面的洞穴中循环的海水正在以越来越快的速度融化南极冰盖。这影响到冰川流向海洋的速度，因此是预测海平面上升的关键因素。南极洲西部是21世纪海平面预测的最大不确定性来源，其中思韦茨冰川（TG）比其他冰川更有可能影响海平面。这一整体主题的重要性，特别是这一地理位置，导致了最近2000万英镑的NERC-NSF联合Thwaites冰川计划（https：//nerc.ukri.org/press/releases/2018/14-glacier/）。由Piggott教授领导的伦敦帝国理工学院的一个团队正在通过对关键接地线区域进行详细的数值建模，为其中一个项目（BAS领导的https：//www.example.com）做出贡献。www.bas.ac.uk/project/melting-at-thwaites-grounding-zone-and-its-control-on-sea-level/在过去的几年里，在使用柔性网格方法模拟复杂冰架空腔中的海洋方面取得了进展（Jordan等人，二〇一四年Yeager 2018），以及在冰盖建模中使用柔性网格方法沿着伴随灵敏度技术（Kyrke-Smith等人，2017年; https：//github.com/gahansen/Albany/wiki/PAALS-Tutorial-2016），现在可以进行完全耦合的海洋冰盖建模（Asay-Davis et al.，近年来，自动代码生成以提供对伴随点的容易访问的能力已经在几个冰盖模型的开发中被采用（Kyrke-Smith等人，2017; https：//icepack.github.io/index.html）。促进这一发展的基础技术（https：//www.firedrakeproject.org/）源自伦敦帝国理工学院伦敦，我们最近用它来生成一个伴随启用海洋模型（https：//thetisproject.org/）。因此，帝国理工有机会在一个单一的建模框架内结合联合收割机这些前沿的研究课题：耦合海洋和冰盖的灵活网格建模，以及使用伴随的敏感性分析和数据同化。最终的目标是一个完全耦合的模式，伴随能力，允许敏感性之间传播的海洋和冰盖。这种能力可用于数据同化、不确定性量化以及模型校准和初始化。特别是，这个模型将是第一个能够解决初始化冲击的关键问题。当海洋和冰的模型结合在一起时，冰会花几个世纪的时间来适应海洋模型的状态，这种人工信号会覆盖任何真实的海平面变化。这种冲击可以通过使用耦合伴随来完美地初始化冰/海洋模型来避免，从而隔离由海洋融化变化驱动的真实的冰盖变化。这项工作将有助于帝国-BAS团队更广泛的活动，特别是能够利用上述NERC-NSF Thwaites冰川项目下计划的数据和建模活动。学生很有可能有机会亲身体验南极实地考察，作为项目期间海洋学课程的一部分。