The sensitivity of flowline models of tidewater glaciers to parameter uncertainty
The sensitivity of flowline models of tidewater glaciers to parameter uncertainty
复制标题
潮水冰川流线模型对参数不确定性的敏感性
DOI：
10.5194/tc-7-1579-2013
复制
发表时间：
2013
期刊：
影响因子：
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通讯作者：
T. Bartholomaus
中科院分区：
文献类型：
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作者：
E. Enderlin;T. Bartholomaus
摘要。深度积分（1-D）流线模型被广泛用于模拟快速流动的潮汐冰川和预测变化，因为连续的接地线跟踪、高水平分辨率和基于物理的产犊准则是潮汐冰川真实建模所必需的，可以很容易地纳入模型，同时保持较高的计算效率。与所有模型一样，描述冰流变和基础摩擦的参数值必须根据观测进行假设和/或调整。对于预测研究，这些参数通常进行调整，使冰川在初始状态下与观测到的厚度和速度相匹配，并对其施加扰动。众所周知，冰流模型对这些参数非常敏感，但潮汐冰川模型的敏感性尚未得到系统的研究。本文研究了这种出口冰川动力学流线模型对影响冰川阻力应力分量的三个关键参数的不确定性的敏感性。我们发现，在典型的观测不确定性范围内，相似的初始（即稳态）冰川构型可以通过参数值的完全不同的组合产生，从而导致施加扰动后不同的瞬态响应。在冰川最初是在靠近浮力的地方搁浅的情况下，就像在快速变化的冰川中通常观察到的那样，由于浮力标准规定的稳定性阈值，这些差异可能是巨大的。模拟的瞬态响应对冰流变的参数化特别敏感：~ 2°C的冰温差异可以决定冰川是否变薄，不稳定地漂浮和后退，还是继续搁浅在海洋浅滩上。由于潮汐冰川对模式参数的高度非线性依赖，我们建议在预测时进行考虑参数不确定性的敏感性测试。
Abstract. Depth-integrated (1-D) flowline models have been widely used to simulate fast-flowing tidewater glaciers and predict change because the continuous grounding line tracking, high horizontal resolution, and physically based calving criterion that are essential to realistic modeling of tidewater glaciers can easily be incorporated into the models while maintaining high computational efficiency. As with all models, the values for parameters describing ice rheology and basal friction must be assumed and/or tuned based on observations. For prognostic studies, these parameters are typically tuned so that the glacier matches observed thickness and speeds at an initial state, to which a perturbation is applied. While it is well know that ice flow models are sensitive to these parameters, the sensitivity of tidewater glacier models has not been systematically investigated. Here we investigate the sensitivity of such flowline models of outlet glacier dynamics to uncertainty in three key parameters that influence a glacier's resistive stress components. We find that, within typical observational uncertainty, similar initial (i.e., steady-state) glacier configurations can be produced with substantially different combinations of parameter values, leading to differing transient responses after a perturbation is applied. In cases where the glacier is initially grounded near flotation across a basal over-deepening, as typically observed for rapidly changing glaciers, these differences can be dramatic owing to the threshold of stability imposed by the flotation criterion. The simulated transient response is particularly sensitive to the parameterization of ice rheology: differences in ice temperature of ~ 2 °C can determine whether the glaciers thin to flotation and retreat unstably or remain grounded on a marine shoal. Due to the highly non-linear dependence of tidewater glaciers on model parameters, we recommend that their predictions are accompanied by sensitivity tests that take parameter uncertainty into account.