The correct depiction of atmospheric blocking still poses a key challenge for current numerical weather prediction (NWP) and climate models. This study evaluates the representation of blocking in the new global ICOsahedral Non-hydrostatic NWP and climate model ICON and links model mean state biases to observed blocking deviations. Blocking is identified using both an anomaly and a flow reversal approach in an eight member ensemble of 15-year AMIP-type ICON simulations and verified against ERA Interim reanalyses. Either approach demonstrates a good representation of annual blocking frequencies in ICON. Deviations emerge when considering individual seasons. In the anomaly framework, enhanced blocking occurrence in the mid-latitude Pacific domain during winter and spring and a marked underestimation of blocking in the Euro-Atlantic region are found during summer. Moreover, this approach indicates a general underestimation of blocking at higher latitudes. The flow reversal index reveals the often reported underestimation of blocking in the Euro-Atlantic region during winter. Furthermore, increased blocking activity in the Pacific and Greenland region during spring and decreased blocking occurrence at high latitudes in summer are found. Focusing on the anomaly approach, we assess how the model mean state influences blocking identification. A systematically higher tropopause, forced by a cold bias in the lower stratosphere, reduces diagnosed blocking frequencies at higher latitudes especially during summer. This goes along with a reduction in blocking size, duration, and intensity. While confirming an overall good representation of blocking in ICON, this study demonstrates how mean state biases can crucially affect the identification of blocking and that blocking deviations have to be interpreted with caution as they are highly dependent on the exact diagnostic used.

中文翻译：

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新的全球非静力学天气预报模型 ICON 中大气阻塞的表示

对大气阻塞的正确描述仍然是当前数值天气预报 (NWP) 和气候模型的关键挑战。本研究评估了新的全球 ICOsahedral Non-hydrostatic NWP 和气候模型 ICON 中阻塞的表示，并将模型平均状态偏差与观察到的阻塞偏差联系起来。在 15 年 AMIP 型 ICON 模拟的 8 名成员集合中，使用异常和流动反转方法识别阻塞，并根据 ERA 临时再分析进行验证。这两种方法都展示了 ICON 中年度阻塞频率的良好表示。考虑个别季节时会出现偏差。在异常框架中，冬季和春季期间中纬度太平洋区域的阻塞发生增强，而夏季欧洲大西洋地区的阻塞发生明显低估。此外，这种方法表明普遍低估了高纬度地区的阻塞。逆流指数揭示了欧洲大西洋地区冬季经常报告的阻塞情况。此外，发现春季太平洋和格陵兰地区的阻塞活动增加，夏季高纬度地区的阻塞发生率降低。专注于异常方法，我们评估模型平均状态如何影响阻塞识别。受低平流层冷偏压的系统性更高的对流层顶降低了高纬度地区的诊断阻塞频率，尤其是在夏季。这伴随着阻塞大小、持续时间和强度的减少。在确认 ICON 中阻塞的总体良好表现的同时，这项研究证明了平均状态偏差如何对阻塞的识别产生重大影响，并且必须谨慎解释阻塞偏差，因为它们高度依赖于所使用的确切诊断。