Drag at the bed and along the lateral margins are the primary forces resisting flow in outlet glaciers. Simultaneously inferring these parameters is challenging since basal drag and ice viscosity are coupled in the momentum balance, which governs ice flow. We test the ability of adjoint-based inverse methods to infer the slipperiness coefficient in a power-law sliding law and the flow-rate parameter in the constitutive relation for ice using a regularization scheme that includes coefficients weighted by surface strain rates. Using synthetic data with spatial variations in basal drag and ice rheology comparable to those in West Antarctic Ice Streams, we show that this approach allows for more accurate inferences. We apply this method to Bindschadler and MacAyeal Ice Streams in West Antarctica. Our results show relatively soft ice in the shear margins and spatially varying basal drag, with an increase in drag with distance upstream of the grounding line punctuated by localized areas of relatively high drag. We interpret soft ice to reflect a combination of heating through viscous dissipation and changes in the crystalline structure. These results suggest that adjoint-based inverse methods can provide inferences of basal drag and ice rheology when regularization is informed by strain rates.

中文翻译：

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一种推断冰流中基础阻力和冰流变性的新方法，并应用于南极西部冰流

河床和沿横向边缘的阻力是出口冰川中抵抗流动的主要力量。同时推断这些参数具有挑战性，因为基础阻力和冰粘度在控制冰流动的动量平衡中耦合。我们使用包括由表面应变率加权的系数的正则化方案测试基于伴随的逆方法推断幂律滑动定律中的滑度系数和冰的本构关系中的流速参数的能力。使用具有与南极西部冰流相当的基础阻力和冰流变学空间变化的合成数据，我们表明这种方法可以进行更准确的推断。我们将此方法应用于南极洲西部的 Bindschadler 和 MacAyeal 冰流。我们的结果表明，剪切边缘的冰相对较软，基础阻力在空间上有所变化，阻力随着接地线上游距离的增加而增加，局部区域的阻力相对较高。我们将软冰解释为通过粘性耗散和晶体结构变化来反映加热的组合。这些结果表明，当通过应变率进行正则化时，基于伴随的逆向方法可以提供基础阻力和冰流变学的推断。