The hydrological cycle in South America during austral summer, including extreme precipitation and floods, is significantly influenced by northerly low-level jets (LLJs) along the eastern Andes. These synoptic weather events have been associated with three different types of LLJs (Central, Northern, and Andes) and are sensitive to remote large-scale forcings. This study investigates how tropical forcings related to El Niño/Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) regulate the duration and frequency of each LLJ type and their impacts on extreme precipitation. Our analysis reveals that ENSO and PDO are important in driving the variability of LLJs over the past 65 years. Specifically, the Central LLJ type is more prevalent during El Niño and Warm/Neutral PDO phases, leading to heightened extreme precipitation in southern South America. Conversely, La Niña years during Cold PDO phases tend to favor the Northern and Andes LLJs, which are associated with increased precipitation extremes in the western Amazon and southeastern South America. Central and Andes LLJs tend to persist longer during these favored conditions, causing more pronounced precipitation events in the areas under their influence. This study enhances our understanding of the influence of large-scale atmospheric forcings on the regional precipitation dynamics in South America.

南美洲在南半球夏季的水文循环，包括极端降水和洪水，受到安第斯山脉东部偏北低空急流 （LLJ） 的显著影响。这些天气事件与三种不同类型的 LLJ（中部、北部和安第斯山脉）有关，并且对遥远的大尺度强迫很敏感。本研究调查了与厄尔尼诺/南方涛动 （ENSO） 和太平洋年代际涛动 （PDO） 相关的热带强迫如何调节每种 LLJ 类型的持续时间和频率及其对极端降水的影响。我们的分析表明，ENSO 和 PDO 在过去 65 年中在驱动 LLJ 的可变性方面很重要。具体来说，中部 LLJ 类型在厄尔尼诺和暖/中性 PDO 阶段更为普遍，导致南美洲南部的极端降水增加。相反，寒冷 PDO 阶段的拉尼娜年往往有利于北部和安第斯山脉 LLJ，这与亚马逊西部和南美洲东南部的极端降水增加有关。在这些有利的条件下，中部和安第斯山脉 LLJ 往往持续更长时间，从而在其影响的地区导致更明显的降水事件。这项研究增强了我们对大尺度大气强迫对南美洲区域降水动态影响的理解。