In polar regions, where the boundary layer is often stably stratified, atmospheric models produce large biases depending on the boundary-layer parametrizations and the parametrization of the exchange of energy at the surface. This model intercomparison focuses on the very stable stratification encountered over the Antarctic Plateau in 2009. Here, we analyze results from 10 large-eddy-simulation (LES) codes for different spatial resolutions over 24 consecutive hours, and compare them with observations acquired at the Concordia Research Station during summer. This is a challenging exercise for such simulations since they need to reproduce both the 300-m-deep convective boundary layer and the very thin stable boundary layer characterized by a strong vertical temperature gradient (10 K difference over the lowest 20 m) when the sun is low over the horizon. A large variability in surface fluxes among the different models is highlighted. The LES models correctly reproduce the convective boundary layer in terms of mean profiles and turbulent characteristics but display more spread during stable conditions, which is largely reduced by increasing the horizontal and vertical resolutions in additional simulations focusing only on the stable period. This highlights the fact that very fine resolution is needed to represent such conditions. Complementary sensitivity studies are conducted regarding the roughness length, the subgrid-scale turbulence closure as well as the resolution and domain size. While we find little dependence on the surface-flux parametrization, the results indicate a pronounced sensitivity to both the roughness length and the turbulence closure.

中文翻译：

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南极边界层非常稳定分层的大涡模拟的比对

在边界层通常稳定分层的极地地区，大气模型会根据边界层参数化和地表能量交换参数化产生很大的偏差。该模型比对侧重于 2009 年南极高原上空遇到的非常稳定的分层。在这里，我们分析了连续 24 小时内不同空间分辨率的 10 个大涡模拟 (LES) 代码的结果，并将它们与在 2009 年获得的观测结果进行比较。夏季的康考迪亚研究站。对于此类模拟而言，这是一项具有挑战性的练习，因为它们需要重现 300 米深的对流边界层和以强烈垂直温度梯度（最低 20 米上有 10 K 差异）为特征的非常薄的稳定边界层在地平线上低。突出显示了不同模型之间表面通量的巨大变化。LES 模型在平均剖面和湍流特性方面正确地再现了对流边界层，但在稳定条件下显示出更多的扩散，通过增加仅关注稳定期的附加模拟中的水平和垂直分辨率而大大减少。这突出了一个事实，即需要非常精细的分辨率来表示此类条件。对粗糙度长度、亚网格尺度湍流闭合以及分辨率和域大小进行了补充敏感性研究。虽然我们发现对表面通量参数化的依赖性很小，但结果表明对粗糙度长度和湍流闭合都有明显的敏感性。