Impacts of Northerly Low-Level Jets on Mesoscale Convective Systems East of the Andes

Low-level jets (LLJs) play a critical role in moisture transport, vertical motion enhancement, and orographic lifting, frequently leading to deep, organized convection formation in South America. This study examines the impacts of three types of LLJs (Central, Northern, and Andes) on Mesoscale Convective Systems (MCSs), using a 4 km horizontal grid spacing Weather Research and Forecasting (WRF) model simulation and satellite-based data. The Central and Andes LLJ types facilitate significant moisture flux convergence over the La Plata Basin (LPB), contributing to intense MCS activity and heavy precipitation. In contrast, the Northern LLJ type, operating over the eastern slopes of the northern Andes, exerts a weaker impact on MCS development over the Amazon Basin, leading to more scattered convection. Stronger LLJs support larger, longer-lived MCSs with higher mean precipitation in jet exit regions. El Niño Southern Oscillation modulates these relationships, with El Niño increasing MCS size and duration in the Central LLJ region, while La Niña enhances MCS frequency in the Andes and Northern LLJ regions. The WRF model captures many of these dynamics but produces higher extreme MCS mean precipitation than IMERG. These findings highlight the importance of LLJ variability in modulating MCSs and suggest that future LLJ changes could alter the hydroclimate and extreme weather patterns in the region. This study underscores the utility of km-scale models in representing the complex interactions of LLJs and MCSs, making them a promising tool to improve our understanding of these interactions and to assess the potential impacts of climate change on water resources and extreme weather in South America.