Abstract. The tropopause layer plays a key role in manifold processes in atmospheric chemistry and physics. Here we compare the representation and characteristics of the lapse rate tropopause according to the definition of the World Meteorological Organization (WMO) as estimated from European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis data. Our study is based on ten-year records (2009 to 2018) of ECMWF's state-of-the-art reanalysis ERA5 and its predecessor ERA-Interim. The intercomparison reveals notable differences between ERA5 and ERA-Interim tropopause data, in particular on small spatiotemporal scales. The monthly mean differences of ERA5 minus ERA-Interim tropopause heights vary between −300 m at the transition from the tropics to the extratropics (near 30° S and 30° N) to 150 m around the equator. Mean tropopause temperatures are mostly lower in ERA5 than in ERA-Interim, with a maximum difference of up to −1.5 K in the tropics. Monthly standard deviations of tropopause heights of ERA5 are up to 350 m or 60 % larger than for ERA-Interim. Monthly standard deviations of tropopause temperatures of ERA5 exceed those of ERA-Interim by up to 1.5 K or 30 %. The occurrence frequencies of double tropopause events in ERA5 exceed those of ERA-Interim by up to 25 percentage points at mid latitudes. We attribute the differences between the ERA5 and ERA-Interim tropopause data and the larger, more realistic variability of ERA5 to improved spatiotemporal resolution and better representation of geophysical processes in the forecast model as well as improvements in the data assimilation scheme and the utilization of additional observations in ERA5. The improved spatiotemporal resolution of ERA5 allows for a better representation of mesoscale features, in particular of gravity waves, which affect the temperature profiles in the upper troposphere and lower stratosphere and thus the tropopause height estimates. We evaluated the quality of the ERA5 and ERA-Interim reanalysis tropopause data by comparisons with COSMIC and MetOp Global Positioning System (GPS) satellite observations as well as high-resolution radiosonde profiles. The comparison indicates an uncertainty of the first tropopause for ERA5 (ERA-Interim) of about ±150 m to ±200 m (±250 m) based on radiosonde data and ±120 m to ±150 m (±170 to ±200 m) based on the coarser resolution GPS data at different latitudes. Consequently, ERA5 will provide more accurate information than ERA-Interim for future tropopause-related studies.

中文翻译：

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对 ERA5 和 ERA-Interim 气象再分析的对流层顶特征的评估

摘要。对流层顶层在大气化学和物理的多种过程中起着关键作用。在这里，我们根据欧洲中期天气预报中心 (ECMWF) 再分析数据估计的世界气象组织 (WMO) 的定义，比较了对流层顶递减率的表示和特征。我们的研究基于 ECMWF 最先进的再分析 ERA5 及其前身 ERA-Interim 的十年记录（2009 年至 2018 年）。比对揭示了 ERA5 和 ERA-Interim 对流层顶数据之间的显着差异，特别是在小时空尺度上。ERA5 减去 ERA-临时对流层顶高度的月平均差异在从热带过渡到温带地区（南纬 30°和北纬 30°附近）到赤道周围 150 米的 -300 米之间变化。ERA5 的平均对流层顶温度大多低于 ERA-Interim，热带地区的最大差异高达 -1.5 K。ERA5 的对流层顶高度的月标准偏差高达 350 m 或比 ERA-Interim 大 60%。ERA5 的对流层顶温度的月标准偏差超过 ERA-Interim 高达 1.5 K 或 30%。ERA5中双对流层顶事件的发生频率在中纬度地区比ERA-Interim高出25个百分点。我们将 ERA5 和 ERA-Interim 对流层顶数据之间的差异以及 ERA5 更大、更现实的可变性归因于预测模型中改进的时空分辨率和地球物理过程的更好表示，以及数据同化方案的改进和额外的利用ERA5 中的观察结果。ERA5 改进的时空分辨率允许更好地表示中尺度特征，特别是重力波，这些特征影响对流层上部和平流层下部的温度剖面，从而影响对流层顶高度估计。我们通过与 COSMIC 和 MetOp 全球定位系统 (GPS) 卫星观测以及高分辨率无线电探空仪剖面进行比较，评估了 ERA5 和 ERA-Interim 再分析对流层顶数据的质量。根据无线电探空仪数据，比较表明 ERA5（ERA-Interim）第一对流层顶的不确定性约为 ±150 m 至 ±200 m（±250 m）和 ±120 m 至 ±150 m（±170 至 ±200 m）基于不同纬度的较粗分辨率的 GPS 数据。因此，ERA5 将为未来的对流层顶相关研究提供比 ERA-Interim 更准确的信息。