Recirculation and trapping of tidal plume fronts and internal wave generation in the Rhine ROFI

<p>River plumes dominate transport and mixing in our coastal oceans. We present data and introduce a conceptual picture showing how a multi-frontal, mid-field river plume can form, and how the newly released tidal plume fronts can generate multiple internal solitary waves. We focus on the analysis of data and 3D modelling of the Rhine ROFI, and discuss how a recirculation zone forms in the near to mid-field plume. &#160;Our data show the presence of tidal plume fronts, as well as relic tidal plume fronts. It also shows two internal solitary wave packets ahead of a new tidal plume front. Tidal advection and a strong recirculation is found to trap tidal plume fronts within 20 km from the river mouth. This trapping maintains the multi-frontal system. We find that when tidal straining is large, the tidal plume fronts re-strengthen due to increased convergence. The recirculation zone is populated by multiple tidal plume fronts that return to the near field plume, and subsequently interact with the newly forming tidal plume front that discharges freshwater on the ebb tide. Understanding near-to mid-field river plume systems is important for our understanding of along and cross-shore exchange and mixing. Ocean models typically do not resolve non-hydrostatic internal solitary waves, we discuss how this may limit our understanding of mixing in near to mid-field river plumes.</p>