Influence of the Coriolis Force on Spreading of River Plumes

Abstract

Wind is the main external force that governs the spreading of river plumes in the sea. Many previous studies demonstrated that the spreading direction of river plumes (especially small plumes) generally coincides with wind direction. At the same time, the majority of river plumes are strongly affected by the Coriolis force, which is also among the baseline knowledge about the plumes. In this study, we focus on the deflection of plumes from wind direction induced by the Coriolis force, which received little attention before. For this purpose, we analyzed an extensive set of Landsat 8 and Sentinel-2 satellite images of multiple small- and medium-sized river plumes at different parts of the World Ocean and synchronous wind reanalysis data. We demonstrated that the deflection angle is stable for individual river plumes for different wind directions, albeit with certain limitations related to wind speed and coastal morphology. Moreover, the deflection angle is similar for river plumes located at similar latitudes and varies from ~0° near the Equator to 15–25° in temperate zones and ~30° in polar zones. Finally, we derived a direct relation between latitude and the deflection angle. The obtained results contribute to our understanding of universal features of river plume dynamics, which is important for monitoring and forecasting of delivery and fate of fluvial water and river-borne matter in different coastal regions of the World Ocean.

Keywords

• river plume
• Coriolis force
• wind forcing
• coastal circulation
• Ekman transport