The Effect Of Rheology On Seasonal Sea-Ice Simulations
The Effect Of Rheology On Seasonal Sea-Ice Simulations
复制标题
流变学对季节性海冰模拟的影响
作者：
B. Ip;W. Hibler;G. Flato
在与气候数值研究相关的季节时间尺度上，大尺度海冰模式中使用的流变学显著影响冰厚积累和冰速度场。具有正常流动规则的塑性流变学迄今已被用于季节性动态热力学模拟。这些流变学已被证明是有用的，在模拟海岸附近的不连续滑动，同时仍然提供相对强大的速度场在北极盆地中部。然而，有限的数值敏感性研究表明，不同类型的椭圆屈服曲线，剪切强度的量显着影响冰的积累，并可能会导致通过弗拉姆海峡的冰流出的停止。除剪切强度问题外，还存在非正常流动规则流变性的可能性，例如土壤力学中使用的Mohr Coulomb破坏准则，可能会导致不同类型的流动模式，特别是在弗拉姆海峡地区。然而，迄今为止，还没有进行这种非正常流动规则流变的季节性模拟。为了研究不同流变性对北极海盆大尺度流态的作用，本文发展了一个比Hibler（1979）更一般的数值方案，它允许模拟具有各种不同非线性流变性的海冰的动态热力学行为。使用这个数值方案，进行比较模拟的季节性平衡与几种变化的莫尔库仑流变学和比较标准的椭圆屈服曲线的结果。特别是，主要控制Mohr Coulomb情况是上限流变学，其中剪切强度与压应力成正比。在这种情况下，只有剪切流是允许的，直到达到最大允许压应力。该冰帽强度被参数化为冰厚度和密实度的函数。为了进行比较，还进行了具有非常大的帽强度的模拟，以及具有类似的压缩帽但剪切强度低得多的实验。总的来说，对结果进行分析，以确定结冰对流动规则和剪切强度大小的敏感性。此外，特别注意通过弗拉姆海峡的流量和阻塞（如有）的特性。
On the seasonal time scales relevant to numerical investigations of climate, the rheology used in large-scale sea ice models significantly affects the ice thickness build-up and ice velocity fields. Plastic rheologies with a normal flow rule have been used to-date in seasonal dynamic thermodynamic simulations. These rheologies have proved useful in simulating discontinuous slip near the coast while still supplying relatively robust velocity fields in the central Arctic Basin. However, as indicated by limited numerical sensitivity studies with different types of elliptical yield curves, the amount of shear strength significantly affects the ice build-up and can possibly cause a stoppage of the ice outflow through Fram Strait. In addition to the shear strength issue, there is also the possibility that non-normal flow rule rheologies, such as the Mohr Coulomb failure criterion used in soil mechanics, may cause somewhat different types of flow patterns, especially in the Fram Strait region. However, to date no seasonal simulations with such non-normal flow rule rheologies have been carried out. In order to investigate the role of different rheologies on the large-scale flow patterns in the Arctic Basin, a more general numerical scheme than that of Hibler (1979) is developed, which allows the simulation of the dynamic thermodynamic behavior of sea ice with a wide variety of different non linear rheologies. Using this numerical scheme, comparative simulations are carried out to seasonal equilibrium with several variations of the Mohr Coulomb rheology and compared to the more standard Elliptical yield curve results. In particular, the main control Mohr Coulomb case is a capped rheology in which the shear strength is taken to be proportional to the compressive stress. In this capped case only shear flow is allowed until a maximum allowable compressive stress is reached. This cap strength is parameterized to be a function of the ice thickness and compactness. For comparison, a simulation with a very large cap strength is also carried out, and an experiment with a similar compressive cap but much lower shear strength. Overall the results are analyzed to determine the sensitivity of the ice build-up to flow rule and shear strength magnitude. In addition special attention is given to the character of the flow and stoppage (if any) through Fram Strait.