Price Stephen F, Hoffman Matthew J, Bonin Jennifer A, Howat Ian M, Neumann Thomas, Saba Jack, Tezaur Irina, Guerber Jeffrey, Chambers Don P, Evans Katherine J, Kennedy Joseph H, Lenaerts Jan, Lipscomb William H, Perego Mauro, Salinger Andrew G, Tuminaro Raymond S, van den Broeke Michiel R, Nowicki Sophie M J
Los Alamos National Laboratory, MS B216, Los Alamos, NM 87545, USA.
University of South Florida, St. Petersburg, FL 33701, USA.
Geosci Model Dev. 2017;10(1):255-270. doi: 10.5194/gmd-10-255-2017. Epub 2017 Jan 17.
We propose a new ice sheet model validation framework - the Cryospheric Model Comparison Tool (CmCt) - that takes advantage of ice sheet altimetry and gravimetry observations collected over the past several decades and is applied here to modeling of the Greenland ice sheet. We use realistic simulations performed with the Community Ice Sheet Model (CISM) along with two idealized, non-dynamic models to demonstrate the framework and its use. Dynamic simulations with CISM are forced from 1991 to 2013 using combinations of reanalysis-based surface mass balance and observations of outlet glacier flux change. We propose and demonstrate qualitative and quantitative metrics for use in evaluating the different model simulations against the observations. We find that the altimetry observations used here are largely ambiguous in terms of their ability to distinguish one simulation from another. Based on basin- and whole-ice-sheet scale metrics, we find that simulations using both idealized conceptual models and dynamic, numerical models provide an equally reasonable representation of the ice sheet surface (mean elevation differences of <1 m). This is likely due to their short period of record, biases inherent to digital elevation models used for model initial conditions, and biases resulting from firn dynamics, which are not explicitly accounted for in the models or observations. On the other hand, we find that the gravimetry observations used here are able to unambiguously distinguish between simulations of varying complexity, and along with the CmCt, can provide a quantitative score for assessing a particular model and/or simulation. The new framework demonstrates that our proposed metrics can distinguish relatively better from relatively worse simulations and that dynamic ice sheet models, when appropriately initialized and forced with the right boundary conditions, demonstrate predictive skill with respect to observed dynamic changes occurring on Greenland over the past few decades. An extensible design will allow for continued use of the CmCt as future altimetry, gravimetry, and other remotely sensed data become available for use in ice sheet model validation.
我们提出了一种新的冰盖模型验证框架——冰冻圈模型比较工具（CmCt），该框架利用了过去几十年收集的冰盖测高和重力观测数据，并在此应用于格陵兰冰盖建模。我们使用社区冰盖模型（CISM）进行的实际模拟以及两个理想化的非动态模型来演示该框架及其用途。使用基于再分析的表面质量平衡和出口冰川通量变化观测的组合，对CISM进行1991年至2013年的动态模拟。我们提出并演示了用于根据观测评估不同模型模拟的定性和定量指标。我们发现，这里使用的测高观测在区分不同模拟的能力方面很大程度上不明确。基于流域和整个冰盖尺度的指标，我们发现使用理想化概念模型和动态数值模型的模拟对冰盖表面提供了同样合理的表示（平均海拔差异<1米）。这可能是由于它们的记录期较短、用于模型初始条件的数字高程模型固有的偏差以及雪层动力学产生的偏差，而这些偏差在模型或观测中没有明确考虑。另一方面，我们发现这里使用的重力观测能够明确区分不同复杂程度的模拟，并且与CmCt一起，可以为评估特定模型和/或模拟提供定量分数。新框架表明，我们提出的指标能够相对较好地区分相对较差的模拟，并且当动态冰盖模型适当地初始化并受到正确的边界条件强迫时，能够对过去几十年格陵兰岛上发生的观测到的动态变化表现出预测能力。可扩展的设计将允许在未来有更多的测高、重力和其他遥感数据可用于冰盖模型验证时继续使用CmCt。
