Despite the increasing number of atmospheric moisture tracking tools, their validation is challenging due to the lack of observations. This work contributes to a better understanding of uncertainties in the moisture sources analysis for the precipitation of tropical cyclones (TCs) by assessing eight combinations of threshold values in tracking methods based on the Lagrangian water budget equation. We selected as a study case Hurricane Ida that formed in the North Atlantic basin in late August 2021 and extracted the air parcel trajectories from the global outputs of the Lagrangian FLEXPART model. Results indicate that the choice of relative humidity (RH) threshold for filtering precipitating parcels has a noticeable impact on the Lagrangian precipitation estimates. In addition, methods applying the atmospheric boundary layer restriction produce a weaker moisture source pattern than those accounting for moisture uptakes in the whole atmospheric column. In particular, methods imposing an RH restriction along the air parcel trajectories to filter out noise in moisture losses outperform the others, providing more reliable moisture source contributions. We also introduced a simple bias correction approach that further improves the reliability of moisture source representation.

中文翻译：

---

通过一个研究案例了解热带气旋降水水分来源拉格朗日分析中的不确定性


尽管大气水分跟踪工具的数量不断增加，但由于缺乏观测，它们的验证具有挑战性。这项工作通过评估基于拉格朗日水收支方程的跟踪方法中的八种阈值组合，有助于更好地了解热带气旋 （TCs） 降水水分来源分析中的不确定性。我们选择了 2021 年 8 月下旬在北大西洋盆地形成的飓风艾达作为研究案例，并从拉格朗日 FLEXPART 模型的全球输出中提取了气团轨迹。结果表明，选择相对湿度 （RH） 阈值来过滤沉淀地块对拉格朗日降水估计有显著影响。此外，应用大气边界层限制的方法产生的水分源模式比考虑整个大气柱中水分吸收的方法产生更弱的水分源模式。特别是，沿气团轨迹施加 RH 限制以过滤掉水分损失中的噪声的方法优于其他方法，从而提供更可靠的水分来源贡献。我们还引入了一种简单的偏差校正方法，进一步提高了水分源表示的可靠性。