Regularized Coulomb Friction Laws for Ice Sheet Sliding: Application to Pine Island Glacier, Antarctica
Regularized Coulomb Friction Laws for Ice Sheet Sliding: Application to Pine Island Glacier, Antarctica
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DOI：
10.1029/2019gl082526
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发表时间：
2019-05-16
影响因子：
5.2
通讯作者：
Schoof, Christian G.
中科院分区：
文献类型：
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作者：
Joughin, Ian;Smith, Benjamin E.;Schoof, Christian G.
选择在冰盖模型中使用的最佳基本摩擦定律仍然是海平面预测中的一个不确定性来源。通常使用的摩擦定律中的参数可以产生很大范围的行为，并且约束很差。在这里，我们使用海拔和速度的时间序列数据来检验南极洲松岛冰川在其接地线后退时对失去基本牵引力的模拟瞬时响应。我们评估了各种摩擦定律，这些定律产生了不同的反应，以确定哪种摩擦定律最能再现观测到的速度比，当与观测到的稀释力一起强迫时。与较少使用的正则化库仑摩擦相比，常用的幂定律摩擦的形式提供了更大的模型数据不一致。在规则库仑摩擦中，空化效应产生了基础摩擦的上限。因此，采用这种摩擦定律可以大大提高大规模模拟的保真度，以确定未来的海平面。简单语言摘要尽管人们在改进用于海平面预测的冰盖行为的数值模拟方面做了很多努力，但控制冰层滑动到海床上的摩擦定律的最佳选择仍然鲜为人知。因此，冰盖模型界使用了广泛的摩擦定律。在这里，我们利用几个遥感数据集来模拟南极洲松岛冰川近20年来的速度变化，使用各种现有的摩擦定律。我们发现，当使用“正则库仑”摩擦定律时，相对于观测值，该冰川的行为被模拟得更加真实。这种摩擦定律解释了当冰在其床上快速滑动时产生的加压基础水囊(空化)的形成，这以一种可能放大冰盖不稳定性的方式限制了摩擦。相比之下，在更传统的幂定律摩擦参数中，低阶指数会随着速度的增加产生无界的基础摩擦，对不稳定的冰盖行为起到更大的抑制作用。因此，这些结果为采用有界正则化库仑摩擦定律代替更常用的无界摩擦定律提供了有力的理由。
The choice of the best basal friction law to use in ice-sheet models remains a source of uncertainty in projections of sea level. The parameters in commonly used friction laws can produce a broad range of behavior and are poorly constrained. Here we use a time series of elevation and speed data to examine the simulated transient response of Pine Island Glacier, Antarctica, to a loss of basal traction as its grounding line retreats. We evaluate a variety of friction laws, which produces a diversity of responses, to determine which best reproduces the observed speedup when forced with the observed thinning. Forms of the commonly used power law friction provide much larger model-data disagreement than less commonly used regularized Coulomb friction in which cavitation effects yield an upper bound on basal friction. Thus, adoption of such friction laws could substantially improve the fidelity of large-scale simulations to determine future sea level.Plain Language Summary Although much effort has gone into improving numerical simulations of ice-sheet behavior for sea-level projection, the best choice for the friction law that governs the sliding of ice over its bed remains poorly known. As a consequence, a wide range of friction laws is used by the ice-sheet modeling community. Here we take advantage of several remotely sensed data sets to model the changes in speed of Pine Island Glacier, Antarctica, over nearly two decades, using a variety of existing friction laws. We find that the behavior of this glacier is simulated far more faithfully relative to observations when a "regularized Coulomb" friction law is used. This type of friction law accounts for the formation of pressurized basal water pockets (cavitation) that occur when ice slides rapidly over its bed, which limits friction in a way that may amplify ice-sheet instability. By contrast, low-order exponents in more traditional power law friction parameterizations yield unbounded basal friction as speed increases, placing a much stronger brake on unstable ice-sheet behavior. Thus, these results make a strong case for adopting bounded regularized Coulomb friction laws in place of the more commonly used unbounded friction laws.