Frontal Dynamics at the Mouth of the Columbia River

We use COAWST modeling system (Warner et al., 2010) to investigate the mechanisms behind frontogenesis in the near–field plume region outside the mouth of the Columbia River. The Columbia River is a tidally dominated estuary with tidal velocities ranging from 1 m/s on flood to over 2 m/s on ebb. In the near plume region, strong fronts perpendicular to the coast are generated during ebb of each tidal cycle. These fronts are exhibit strong horizontal velocity and density gradients on a scale ~ 100 m in width with normalized relative vorticity (ζ/f) values reaching up to 50. We specifically focus on the separate fronts on the north and south edges of the plume where we examine the evolution in plume characteristics such as the frontogenetic sharpening, the temporal and spatial variability of the stratification, vertical velocity, and vertical mixing along these fronts, and the decay and fragmentation phase after the turn of the tide. Surface gravity wave Stokes drift vortex forces and material advection are included in the model. Observational validation is presented.