Mixing at Camarinal Sill in the Strait of Gibraltar

摘要: During the Gibraltar Experiment in 1985–1986, observations of shear, stratification, microstructure, and acoustic backscatter revealed a complex mixing regime at Camarinal Sill Strait Gibraltar. The is forced by strong semidiurnal tidal currents weaker, but more steady, baroclinic flows. Flows are characterized as outflow or inflow, nearly equivalent to westward eastward. Rising water coincides with all depths. We observed two modes sill. In May 1986 transition layer separating Atlantic Mediterranean was between 0.75 MPa 1 when we sampled east sill near neap tide. turned down just before reaching crest, where flow became critical. Increasing shear soon destabilized transition, producing billows which grew 30–75 m on west flank overturning generated intense turbulence, peak dissipation rates, e, exceeding 10−2 W kg−1. This turbulence rapidly thickened from Δz = 30–50 130–150 within 1–2 km From rate thickening, estimate formation new transitional during tide (0.8–1.2) × 105 m3 s−1. mode did not release eastward-propagating internal bores inflow appear arrest deep outflow. May, largest average over had same magnitude estimates net energy lost adjustment velocity mass across Other averages smaller than loss, presumably because limited sampling severely underestimates rate. outflow, shears were rise 100 times those background wave field. However, probably owing spatial offsets ship's Doppler current profiler our tethered free-fall profiler, only statistically significant correlations found scales measured directly estimated e profile. other October 1985, profiled spring sill, centered 1.5 MPa. After encountering rose sharply remained 10–20 surface plunging steeply downward past edge accompanied least one rebound transition. observe eastward propagating Armi Farmer (1988) April released regimes similar 1985.