For the artificial channel shown in Figure 3cmax is estimated at cmax = 1.1 m s−1, so that the time scale twave for the disturbances (shallow water waves) generated at the boundaries to reach the mid section is twave = 150 km/1.1 m s−1 ≈ 1.6 days. In fact, the numerical simulations showed that strong wave-like disturbances appeared in front of the downstream boundary 4 days after the simulation onset and reached the mid-section in 2 extra days. For this reason the analysis that follows will be restricted to a time limit of 6 days. Figure 4 presents the distributions of salinity as well as along-channel and cross-channel

velocities in the mid cross-section of the channel click here obtained by POM after 2 and

4 days from the start of the simulation. The dense saline water flows down the channel with a velocity U of about 0.4 m s−1, so the formation of a gravity current is clearly seen. The interface between the saline water involved in the gravity current and the overlying fresher water slopes down to the north, entirely in accordance with geostrophic equilibration in the y (i.e. cross-channel) direction. The highest speeds are observed right below the interface, and there is a continuous decrease of the along-channel velocity towards the bottom. The cross-channel salinity/density structure displays, apart from the interface tilt caused by the geostrophic adjustment of the underlying gravity current, a well-pronounced asymmetry consisting of the pinching and spreading LDK378 clinical trial of the interfacial isohalines/isopycnals on the left- and right- hand sides of the gravity current (looking downstream) and a displacement of the pool of densest water to the left-hand side (i.e. to the north in our case). Moreover, the salinity contours below the interface become vertical Dynein in the southern and central parts, displaying the presence of considerable horizontal salinity/density gradients along with the vanishingly small vertical gradients. In the northern part such horizontal salinity/density gradients are absent. Note that the simulated features of the transverse salinity/density structure

(Figure 4) show reasonable quantitative correspondence with the observations (Figure 2): both the observations and simulations display a vertically quasi-homogeneous BBL about 20 m thick with a horizontal salinity gradient of about 0.2 PSU km−1 in the centre and the right-hand flank of the gravity flow. The evolution of a transverse circulation in the course of the formation of a channelized rotating gravity current is illustrated in the bottom panels of Figure 4. The formation is accompanied by a clockwise (looking downstream) transverse circulation caused by the geostrophically balanced interfacial jet (Umlauf & Arneborg 2009b), and the sum of the Ekman transport and the opposite geostrophic transport below the interface.