Upwelling flow dynamics in long canyons at low Rossby number

Submarine canyons, topographic features incising the continental slope, vary in both shape and size. The dynamics of short canyons have been observed and described in the field, in the laboratory, and with numerical simulations. Flow within long canyons, such as Juan de Fuca canyon, located between Vancouver Island and Washington State in the Pacific Northwest, is less well understood. Physical models of both long and short canyons have been constructed to understand the upwelling dynamics in long canyons and how upwelling changes, as compared with the dynamics of short canyons, at low Rossby number. Stratification and rotation, both important parameters in determining the dynamics in canyons, can be controlled and scaled accordingly for replication of oceanic conditions. The physical model is spun up to an initial rotation rate, and the flow is forced by increasing the rotation rate over the equivalent of several days. Flow visualization is used to determine the strength and location of upwelling, the strength and mechanisms generating vorticity, as well as the differences between the flow within the long and short canyons. The pattern of upwelling between the two canyons is significantly different in the horizontal with upwelling occurring through the canyon head in the short canyon and upwelling occurring close to the mouth along the downstream rim in the long canyon. At high Rossby number, upwelling is similar in both the long and short canyon and is driven by advection. However, as Rossby number decreases, the flow in the long canyon is more strongly affected by the strong convergence of the isobaths near the canyon than by advection alone.