HAPpy Hour- Global scale forcing of SALLJ and associated local impacts on precipitation extremes

Abstract: Increasing floods and droughts in South America underscore the urgent need toexamine the driving forces behind these precipitation extremes. The South American Low-level Jet (SALLJ) is important for the hydrological cycle over South America due to its control on precipitation. This study delves into the remote forcings, and trends associated with various types of the SALLJ (Central, Northern, and Andes), and their impacts on precipitation extremes using global reanalysis data (ERA5). The El Niño Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) drive SALLJ trends. In their positive phases, Central SALLJ occurs more frequently (38.9%), intensifying precipitation extremes in Southern South America. In contrast, negative phases favor Northern (20.3%) and Andes (37.3%) SALLJ, enhancing precipitation extremes in the western and southeastern Amazon. SALLJ persists longer in its favored phases, resulting in more intense precipitation events in its exit region. This framework explains the
large-scale forcings of historical trends and helps with understanding the frequency and intensity increases in future extreme precipitation events.