Steady wind forcing of a density front over a circular bank
Additional Document Info
The response of a density front along the edge of a circular bank to steady wind forcing is examined using a primitive equation numerical model. Initially, the fluid is at rest with relatively light, vertically homogeneous water over the bank. The density field is allowed to adjust geostrophically and frictionally for ten days, after which a spatially uniform wind stress is applied for three days. The resulting surface velocity field over the bank is asymmetrical, with a relative maximum on the downwind side of the bank to the left of the wind direction and a relative minimum on the upwind side of the bank to the right of the wind direction. For the small Ekman number considered here, the density-driven flow persists beneath the surface Ekman layer. Light fluid is advected off the bank near the surface in the direction of Ekman transport, weakening the surface density gradients. On the opposite side of the bank, the vertical structure of the density field is weakened and the surface density gradients remain relatively constant. When the wind stress is abruptly turned off, the anti-cyclonic surface velocity is restored within one inertial period, and some light fluid remains off the bank. The loss of neutrally buoyant near-surface particles released over the bank primarily occurs from the region of the bank downwind and to the right. The presence of the density front slightly increases the number of particles lost from the bank. A simple formula for the particle loss is presented.