Clear air turbulence (CAT) poses a significant threat to aviation. CAT usually occurs in the lower stratosphere and the upper troposphere. It is generally associated with large scale waves, mountain waves, jet streams, upper-level fronts and tropopause folds. Aircraft can experience CAT when flying in proximity of a tropopause fold. To better understand and diagnose tropopause fold- associated CAT we selected a series of cases from among those reported by pilots between June 2017 and December 2018 in the Romanian airspace. Data on turbulence were used in conjunction with meteorological data, satellite imagery, and vertical profiles. Additionally, a set of indices as Ellrod, horizontal temperature gradient, Dutton, and Brown were computed to diagnose CAT associated with tropopause folding. These indices were also analyzed to test the physics mechanisms that may explain the occurrence of severe turbulence. Results show that out of the 420 cases announced by pilots, severe turbulence was reported in 80 cases of which 13 were associated with tropopause folding.

中文翻译：

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与罗马尼亚领空对流层褶皱有关的晴空湍流研究

晴空湍流（CAT）对航空业构成重大威胁。CAT通常发生在平流层下部和对流层上部。它通常与大规模海浪，山浪，急流，高层锋和对流层顶褶皱有关。飞机在对流层褶皱附近飞行时会遇到CAT。为了更好地理解和诊断与对流层顶褶皱相关的CAT，我们从2017年6月至2018年12月在罗马尼亚领空的飞行员报告的病例中选择了一系列病例。湍流数据与气象数据，卫星图像和垂直剖面一起使用。另外，计算了一组指标，如Ellrod，水平温度梯度，Dutton和Brown，以诊断与对流层顶折叠相关的CAT。还分析了这些指标以测试可能解释严重湍流发生的物理机制。结果显示，在飞行员宣布的420例病例中，据报道有80例严重湍流，其中13例与对流层顶折叠有关。