Intraseasonal Modulation of the Chocó Low-Level Jet by the Madden–Julian Oscillation

The Madden–Julian Oscillation (MJO) is the dominant mode of intraseasonal variability (30–90 days) in the tropical atmosphere, characterized by eastward-propagating convective and circulation anomalies that strongly modulate tropical and regional climate. Through its large-scale dynamical perturbations, the MJO influences moisture transport, low-level circulation, and precipitation over regions far removed from its primary convective center. However, its role in regulating low-level moisture fluxes over northwestern South America has received comparatively limited attention. In this study, we investigate the influence of the MJO on moisture transport toward Colombia, with particular emphasis on its modulation of the Chocó Low-Level Jet. Using MERRA-2 reanalysis, we characterize intraseasonal variability in low-level moisture advection and wind fields associated with different MJO phases defined by the Real-time Multivariate MJO (RMM) index. The analysis examines changes in low-level moisture transport, wind intensity, and large-scale convergence associated with the zonal displacement of the MJO convective envelope. Results show that the strength of the Chocó Jet depends strongly on the longitudinal position of the MJO convective center. Certain MJO phases enhance moisture transport from the eastern Pacific toward Colombia, favoring orographic ascent along the Andes and organized convection over the Colombian Pacific region, while other phases are associated with weaker moisture fluxes and reduced convergence. These findings highlight the role of the MJO in regulating intraseasonal moisture transport and low-level circulation over northwestern South America.