Numerical Modelling Of Rutford Ice Stream, Antarctica
Numerical Modelling Of Rutford Ice Stream, Antarctica
复制标题
南极洲拉特福德冰流的数值模拟
DOI：
10.1017/s0260305500008971
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发表时间：
1990
影响因子：
2.9
通讯作者：
D. Macayeal
中科院分区：
文献类型：
--
作者：
R. Frolich;D. Macayeal
一个二维有限元模型已被应用到拉特福德冰流，南极洲，和部分的伦讷冰架的冰流流入。该模型是一个扩展的描述冰架流，并依赖于在冰流的垂直剪切是小的，在一些数学定义的意义。这等同于要求垂直剪切被限制到基底层或可变形基底。虽然没有直接的观测证据，这样一个层下面的拉特福德冰流，广泛的表面调查和估计的强度覆盖冰显示，一些动态等效的机制必须发生。如果根据线性粘性基底的厚度和粘度对基底剪切应力进行参数化，就像南极洲冰流B下面的情况一样，那么从接地线向上游前进，该层的厚度必须减小，粘度必须增加（以保持上游极限处的实际厚度），以便重现观测到的表面速度。这一物理上合理的图景目前被采纳为一个工作假设。冰流主体的垂直切变在接地线以上约70公里处似乎可以忽略不计。敏感性试验表明，冰架背应力是该断面的重要约束因素。背应力减少10%，接地线磁通立即增加15%。然而，在上游，较高的表面坡度和略低的表面流速表明，忽略垂直剪切可能不太合适。冰架回流减少的影响在这一地区并没有立即被感觉到，因为重力驱动力几乎被当地的基底剪切牵引力所平衡。一个复杂的表面形态已经揭示了卫星图像以下的接地线的拉特福德冰流。在此基础上，这可能是时间依赖性行为的证据，有限元模型被用来调查的图案的起源。冰架背应力、基底融化、支流冰川的质量通量和基底性质都可以以物理上现实的方式变化，以试图从质量上再现所观察到的表面形态。
A two-dimensional finite element model has been applied to Rutford Ice Stream, Antarctica, and part of Ronne Ice Shelf into which the ice stream flows. The model is an extension of one describing ice-shelf flow, and relies on vertical shear in the ice stream being small in some mathematically defined sense. This is equivalent to requiring the vertical shear to be confined to a basal layer or a deformable substrate. Although there is no direct observational evidence for such a layer beneath Rutford Ice Stream, extensive surface surveys and estimates of the strength of the overlying ice show that some dynamically equivalent mechanism must occur. If basal shear stress is parameterised in terms of the thickness and viscosity of a linearly viscous substrate, as may be the case beneath Ice Stream Β in Antarctica, then going upstream from the grounding line, the thickness of this layer must decrease, and the viscosity increase (to retain a realistic thickness at the upstream limit), in order to reproduce the observed surface velocities. This physically reasonable picture is currently adopted as a working hypothesis. Vertical shear in the body of the ice stream appears to be negligible for approximately 70 km above the grounding line. Sensitivity tests show that, in this lower section, ice-shelf back stress is an important restraining influence. A 10% reduction in back stress would produce an immediate 15% increase in grounding line flux. Further upstream, however, higher surface slopes and slightly lower surface velocities suggest that the neglect of vertical shear may be less appropriate. The effect of a reduction in ice-shelf back stream is not felt in this region immediately, as the gravitational driving force is almost balanced by local basal shear traction. A complex surface morphology has been revealed by satellite imagery below the grounding line of Rutford Ice Stream. On the basis that this may be evidence of time dependent behaviour, the finite element model is being used to investigate the origin of the pattern. Ice-shelf back stress, basal melting, mass flux from tributary glaciers and substrate properties can all be varied in physically realistic ways to try to reproduce, qualitatively, the observed surface morphology.