Long‐Term Variability in Southward Atmospheric Flows Over South America: Improving the Current Understanding

ABSTRACT

The southward atmospheric flows over the Chaco region in South America are important in transporting heat and moisture from the tropics to the subtropics. The intensity and frequency of these flows are modulated by climatic variability at different time scales. However, previous studies show discrepancies in the relationships between these flows and the multidecadal variabilities, such as the Atlantic Multidecadal Oscillation (AMO) and the Pacific Decadal Oscillation (PDO). Therefore, this study utilised a longer time series from the more recent and detailed reanalysis, considering the entire time series and all seasons, without and with criteria/indices for the South American Low‐Level Jet (SALLJ), in addition to further statistical analyses and a new approach to assessing the impacts of the combined phases of the AMO and the PDO, to understand in greater detail these atmospheric relationships over the Chaco region. In synthesis, the present study found that, in an isolated form, the PDO has a stronger influence than the AMO on southward atmospheric flows over the Chaco region in South America. The PDO predominantly shows a positive relationship with these atmospheric flows (mainly in the winter and spring seasons), while the AMO shows an inverse relationship with the southward atmospheric flows over the Chaco region during the South American Monsoon. In a combined form, the association of positive phases of both the AMO and the PDO (neutral AMO and negative PDO) provides the most favourable (unfavourable) conditions for southward atmospheric flows from the tropics to the subtropics in South America.