The Asymmetric Hydrodynamic Structure of a Wind‐Dominated River Plume

Abstract This study investigates the velocity and salinity structure of the large surface‐attached, low‐latitude, and microtidal plume of the Magdalena River (southern Caribbean Sea) during a period of high freshwater discharge and variable wind conditions. The plume was analyzed through observations at multiple transects along, across, and diagonal to the shoreline, using ADCP measurements and a CTD chain. Results show that the plume is very shallow, with a large aspect ratio of O(10 4 ) and rapid changes in its extension and direction within hours in response to forcing variability. The plume's dynamics are primarily governed by the river momentum in the near‐field, a competition between river momentum and wind stress in the mid‐field, and the wind stress in the far‐field, while the ambient ocean currents influence the plume only during mild winds. The velocity and salinity structures reveal a marked asymmetry between the downwind and upwind sides of the plume. Downwind, the plume is faster, narrower, and more mixed and remains supercritical beyond the near‐field. Upwind, the interaction between opposing river momentum and wind‐driven flows generates vortices and fronts. Finally, the plume Kelvin and Rossby numbers indicate that the Coriolis effect, often neglected in low‐latitude coastal systems, also influences the plume dynamics when the system exceeds a critical horizontal extension. The findings are rationalized to provide insights into the dynamics of low‐latitude wind‐dominated river plumes.