06 m s−1 at t = 2 days. The transverse circulation modifies the salinity/density field, producing a downward-bending of density contours and horizontal density gradients in BBL on the southern flank of the channel which, in accordance with the thermal wind relation, click here can provide a geostrophically

balanced decrease of the gravity current velocity towards the bottom without the Ekman veering; such a process is referred to as Ekman layer arrest ( Garrett et al. 1993). As a result, the northward (positive) transverse velocities summing the Ekman velocities and the geostrophic velocities due to the down-channel pressure gradient fade below the core and even become slightly negative, while the southward transverse jet-like flow with speeds of about 0.03 m s−1 still persists in the density interface just above the core (see the bottom right-hand plot in Figure 4). Such a reversal of the near-bottom transverse

current is caused by the thermal wind shear due to the presence of lateral, cross-channel density gradients below the interface ( Umlauf & Arneborg buy CYC202 2009b, Umlauf et al. 2010). All the above-mentioned features of the channelized gravity current revealed by means of simulation, including the pinching-spreading effect, the existence of a lateral density gradient and vertical density homogenization in the southern flank below the core of the current, the establishment of a transverse circulation with a southward transverse interfacial jet and a near-bottom current reversal, have been observed in a channel-like constriction Sinomenine of the Arkona Basin (Umlauf & Arneborg 2009a) and reproduced numerically by Burchard et al. (2009). To check whether a rotating gravity current is frictionally

controlled, one has to estimate different terms of the bulk (vertically integrated) down- channel momentum balance and the non-dimensional Froude and Ekman numbers characterizing the variety of flow regimes. Following e.g. Arneborg et al. (2007), the bulk buoyancy B   and thickness H   of a gravity current may be defined as equation(1) BH=∫zb∞bdz,12BH2=∫zb∞b(z−zb)dz,where b=−g(ρ−ρ∞)/ρ∞b=−g(ρ−ρ∞)/ρ∞ is the negative buoyancy of gravity flow with respect to the overlying ambient fluid of density ρ∞ρ∞ and zero buoyancy (b → 0 at z → ∞), g   = 9.81 m s−2 is the acceleration due to gravity, and the lower integration limit lies at the bottom (z   = zb  ). The Froude number (Fr), the Ekman number (Ek) and the Ekman layer depth are introduced as equation(2) Fr=U(−BH)1/2,Ek=(δEH)2,δE=u*2fU,where U   is the vertically averaged (bulk) velocity of the gravity current, u*2=−τx/ρ∞ is the squared friction velocity, τx is the down-channel bottom stress and f is the Coriolis parameter.