The ideal response of a Gulf of Mexico estuary plume to wind forcing: Its connection with salt flux and a Lagrangian view

The plume structure of Perdido Bay Estuary (PBE), a typical bay on the Florida‐Alabama coast along the Gulf of Mexico, was simulated using an existing calibrated model. To better understand plume dynamics in the PBE and similar bay systems, idealized sensitivity experiments were conducted to examine the influence of wind stress on the 3‐D plume signature: the results indicate that wind speed and direction significantly influence plume orientation, area, width, length, and depth. The plume size was reduced under the effect of wind and increased wind forcing. Among wind‐forced cases, the plume is largest for northerly (offshore) winds and smallest for southerly (onshore) winds. Bay‐shelf salt flux and water flux were also investigated, since they are important for the formation of a 3‐D plume structure. Model simulations show that water outflow to the coastal ocean is strongest under northerly winds and can be stopped by southerly winds. For moderately strong winds, the outflow and plume size are larger for easterly downwelling‐favorable winds than for westerly upwelling‐favorable winds; the opposite is true for outflow and plume size for these two wind directions under stronger winds. For all wind directions, the ratio of salt flux and water flux at the bay mouth increases with wind speed. This ratio trend is consistent with higher outflow salinities, and this decreased buoyancy signature, along with more energetic vertical mixing, reduces plume size. A detailed understanding of this water and salt flux is essential to the plume dynamics studied here and for other plumes. Additional particle transport analysis using variable wind forcing was conducted to determine the influence of the plume on particle movement. The results showed a consistency between the surface plume, salt flux, and particle transport and illustrate the strong effects that winds have on particle fate and dispersion.