A Comparison of Recent Reanalysis Datasets Using Objective Feature Tracking: Storm Tracks and Tropical Easterly Waves
A Comparison of Recent Reanalysis Datasets Using Objective Feature Tracking: Storm Tracks and Tropical Easterly Waves
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使用客观特征跟踪的最近再分析数据集的比较：风暴轨迹和热带东风波
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发表时间：
2003
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通讯作者：
C. Thorncroft
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作者：
K. Hodges;B. Hoskins;J. Boyle;C. Thorncroft
最近的四个再分析项目[ECMWF、NCEP-NCAR、NCEP-能源部(DOE)、NASA]使用客观特征跟踪方法在天气系统的尺度上进行了诊断。跟踪统计表明，总体来说，再分析在北半球对流层低层符合得很好，尽管平均强度空间分布的差异表明，ECMWF再分析在主要风暴路径区域系统性地较强，而在主要地形特征附近较弱。对轨道集合的直接比较表明，在重新分析中，具有广泛强度范围的一些系统可以很好地进行比较。此外，还发现了一些小尺度弱系统，它们在重新分析之间没有对应关系，或者只有在放宽匹配标准后才对应，这表明可能存在位置和/或时间一致性方面的差异。它们分布在风暴路径上，特别是在以小规模活动著称的区域，如次级发展区域和地中海。对于南半球(SH)，在对流层下部通常不太一致，路径密度和平均强度都有显著差异。在各种再分析之间对应的系统大大减少，而那些不匹配的系统跨越了广泛的风暴强度范围。放宽匹配标准表明，与NH相比，系统的位置和强度都存在更大程度的不确定性。在对流层上层，在NH和SH冬季，ECMWF再分析与其他再分析之间的活动水平存在显著差异。这是由于ERA15中系统的表面传播缺乏连贯性造成的，在500百帕以上显得最为严重。这可能是由于ERA15中使用了最佳内插数据同化。还显示了基于使用相同技术诊断热带东风波活动的结果。结果表明，波的活动性不仅对所使用的分辨率和同化方法敏感，而且对模式公式也很敏感。
Data from four recent reanalysis projects [ECMWF, NCEP‐NCAR, NCEP‐Department of Energy (DOE), NASA] have been diagnosed at the scale of synoptic weather systems using an objective feature tracking method. The tracking statistics indicate that, overall, the reanalyses correspond very well in the Northern Hemisphere (NH) lower troposphere, although differences for the spatial distribution of mean intensities show that the ECMWF reanalysis is systematically stronger in the main storm track regions but weaker around major orographic features. A direct comparison of the track ensembles indicates a number of systems with a broad range of intensities that compare well among the reanalyses. In addition, a number of small-scale weak systems are found that have no correspondence among the reanalyses or that only correspond upon relaxing the matching criteria, indicating possible differences in location and/or temporal coherence. These are distributed throughout the storm tracks, particularly in the regions known for small-scale activity, such as secondary development regions and the Mediterranean. For the Southern Hemisphere (SH), agreement is found to be generally less consistent in the lower troposphere with significant differences in both track density and mean intensity. The systems that correspond between the various reanalyses are considerably reduced and those that do not match span a broad range of storm intensities. Relaxing the matching criteria indicates that there is a larger degree of uncertainty in both the location of systems and their intensities compared with the NH. At upper-tropospheric levels, significant differences in the level of activity occur between the ECMWF reanalysis and the other reanalyses in both the NH and SH winters. This occurs due to a lack of coherence in the apparent propagation of the systems in ERA15 and appears most acute above 500 hPa. This is probably due to the use of optimal interpolation data assimilation in ERA15. Also shown are results based on using the same techniques to diagnose the tropical easterly wave activity. Results indicate that the wave activity is sensitive not only to the resolution and assimilation methods used but also to the model formulation.