Wind-Enhanced Separation of Large-Scale River Plumes From Coastal Corners

Abstract

Idealized models are analyzed to quantify how large-scale river plumes interact with coastal corners with and without wind-driven currents. The configuration has a corner formed by two perpendicular shelves (with constant slope) that are joined with a coastal radius of curvature (r_c). The buoyant plume originates from an upstream point source. The r_c and wind forcing are varied among runs. Steep- and gentle-slope runs are compared for some situations. Without winds, plumes separate from corners with r_c smaller than two inertial radii (r_i); this threshold is twice the r_c < r_i theoretical separation criterion. After separation, no-wind plumes form an anticyclonic bulge, and reattach farther downstream. Offshore excursion increases as r_c decreases. A downwelling-favorable wind component along the upstream coast (τ_sx) favors separation by increasing total plume speed. An upwelling-favorable wind component along the downstream coast (τ_sy) also increases offshore excursion. Winds blowing obliquely offshore with both these wind components advect the plume farther offshore. Wind-driven currents that steer plumes in this situation include a downshelf jet originating on the upstream shelf and continuing around the coastal corner and beyond, offshore and upshelf surface transport downstream of the corner, and surface Ekman transport on the outer shelf. Multiple linear regressions quantify plume position sensitivity to r_c, τ_sx, and τ_sy; results are discussed in a dynamical context. Globally, many river plumes interact with coastal corners under various wind conditions.