This study applies a Lagrangian approach to identify the origin of moisture for subtropical cyclones (SCs) along their tracks in the South Atlantic Ocean (SAO) basin from 1980 to 2015. The analysis shows that the local evaporation cannot fully explain the moisture gained by SCs, highlighting the role of external sources in moisture support, mainly through the northeasterly winds associated with the South Atlantic Subtropical Anticyclone. Overall, the northwestern SAO was the principal moisture source for SCs. It was noticeable that its contribution (~40%–45%) remained quasi‐constant during the year. Conversely, the moisture supplied from the northeastern SAO, southwestern SAO and the terrestrial source southeastern Brazil exhibited a marked seasonal variability. While contributions from the southwestern SAO intensify (weaken) in austral winter (summer), the southeastern Brazil source is more intense (weak) in summer (winter). In addition, SCs predominantly gain atmospheric humidity from sources close to their position, which reduces the mean water vapor residence time to ~3.2 days. Interestingly, we also found that ~42%–47% of the moisture that reached the SCs precipitates. These findings constitute a further step toward improving our knowledge of mechanisms underlying SC activity in the SAO basin.

中文翻译：

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量化南大西洋盆地副热带气旋生命周期中的相关降水和水分来源

本研究应用拉格朗日方法来识别 1980 年至 2015 年南大西洋 (SAO) 盆地副热带气旋 (SC) 路径上的水分来源。分析表明，局部蒸发不能完全解释副热带气旋 (SC) 获得的水分，强调了外部来源在水分支持中的作用，主要是通过与南大西洋副热带反气旋相关的东北风。总体而言，西北部 SAO 是 SC 的主要水分来源。值得注意的是，其贡献（约 40%–45%）在这一年中保持准恒定。相反，来自SAO东北部、SAO西南部和巴西东南部陆地来源的水分呈现出明显的季节变化。虽然西南 SAO 的贡献在南方冬季（夏季）增强（减弱），但巴西东南部的贡献在夏季（冬季）更加强烈（弱）。此外，SC 主要从靠近其位置的来源获得大气湿度，这将平均水蒸气停留时间减少到约 3.2 天。有趣的是，我们还发现到达 SC 的约 42%–47% 的水分会沉淀。这些发现进一步加深了我们对 SAO 盆地 SC 活动机制的了解。