Compensating Biases and a Noteworthy Success in the CMIP5 Representation of Antarctic Sea Ice Processes
Compensating Biases and a Noteworthy Success in the CMIP5 Representation of Antarctic Sea Ice Processes
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DOI：
10.1029/2018gl081796
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发表时间：
2019-04-28
影响因子：
5.2
通讯作者：
Bracegirdle, T. J.
中科院分区：
文献类型：
--
作者：
Holmes, C. R.;Holland, P. R.;Bracegirdle, T. J.
耦合模式相互比较项目第5阶段（CMIP 5）气候模式模拟了历史上广泛的海冰区域。即使模型的面积接近观测值，也可能含有补偿误差，影响其预测的可靠性。这项研究的重点是海冰的季节性循环，包括模式浓度预算的分析。许多模型没有足够的秋季冰增长，导致大的冬季偏差。模型的一个子集准确地反映了海冰全年的演变。然而，将它们的冬季冰浓度预算与观测结果进行比较，揭示了一系列行为。至少有一个模型有一个准确的冰预算，这是唯一可能的，由于现实的冰漂移。因此，CMIP 5生成的模型物理和分辨率在结构上能够准确地表示南极海冰的过程。这意味着，通过对现有气候模式进行适当的子集设置，可以大大改进对南极密集海水形成和冰盖融化的预测。因此，试图使用这些模型来了解南极海冰以及南极气候，海平面上升和海洋环流在未来将如何变化的尝试受到了严重的影响。这项研究超越了海冰的标准测量，例如被冰覆盖的海洋面积。相反，我们计算一年中海冰的变化有多少是由局部融化和冻结以及冰输送（例如风和洋流）引起的。在已经为数不多的确实显示出真实海冰数量的模型中，我们发现有些模型是出于错误的原因。但是，有一个模型使用已建立的模型组件，显示了真实的行为。该模型能够与海冰漂移观测相匹配。这表明，现有的气候模型能够代表南极海冰，而无需进一步提高复杂性。把重点放在气候预测的这类模型上，可能会提高未来预测的可靠性。
Coupled Model Intercomparison Project phase 5 (CMIP5) climate models simulate a wide range of historical sea ice areas. Even models with areas close to observed values may contain compensating errors, affecting reliability of their projections. This study focuses on the seasonal cycle of sea ice, including analysis of model concentration budgets. Many models have insufficient autumn ice growth, leading to large winter biases. A subset of models accurately represent sea ice evolution year-round. However, comparing their winter ice concentration budget to observations reveals a range of behaviors. At least one model has an accurate ice budget, which is only possible due to realistic ice drifts. The CMIP5 generation of model physics and resolution is therefore structurally capable of accurately representing processes in Antarctic sea ice. This implies that substantially improved projections of Antarctic dense ocean water formation and ice sheet melting are possible with appropriate subsetting of existing climate models.Plain Language Summary Antarctic sea ice simulated by numerical climate models generally exhibits large differences compared to satellite-based estimates. Therefore, attempts to use these models to understand how Antarctic sea ice-and as a result Antarctic climate, sea level rise, and ocean circulation-will change in the future are severely compromised. This study looks beyond standard measures of sea ice such as the area of ocean covered by ice. Instead, we calculate how much of the change in sea ice over the course of a year is caused by local melting and freezing on the one hand and ice transport (for example by winds and ocean currents) on the other. Of an already small number of models which do show a realistic amount of sea ice, we identify that some do so for the wrong reasons. However, there is one model using established model components which shows realistic behavior. This model is able to match observations of sea ice drift. This demonstrates that the existing climate models are capable of representing Antarctic sea ice without further increases in sophistication. Focusing on such models for climate projections may improve the reliability of projections of the future.