Estimating Decadal Changes in the South American Low Level Jet

Rainfall in the Amazon is seasonal, particularly in the southwest region. In the northern regions, precipitation tends to be more consistent throughout the year, but in the southwest, a dry season exists from June to October. In the southwest region, precipitation is primarily driven by the Low Level Jet, which transports moisture from the Atlantic Ocean to the southwestern Amazon region near the Andes mountain range. In the last 10 to 15 years, precipitation has decreased in the southwest Amazon where the Low Level Jet has changed over time, and we need to determine the causes of these changes. In this study, we investigated the changes in specific humidity and wind velocity in this region. Using the ERA5 reanalysis dataset, we calculated the 42-year average specific humidity and horizontal wind velocity, as well as the decadal averages for three decadal periods (1981-1990, 1996-2005, and 2011-2020). For the southwest Amazon, we found increases in specific humidity during the rainy season, and decreases during the dry season. This suggests that the kinematic advection of specific humidity increased during the rainy season, while decreases prevailed during the dry season.