On the turbulent structures generated by intruding downslope rotating gravity currents

Gravity currents play a crucial role in the formation of deep waters in the ocean, contributing to the vorticity and energy transfers towards the ocean interior. We present results from an experimental study on downslope intruding and rotating gravity currents into an initially two-layer stably stratified ambient at high buoyancy Reynolds numbers. A new turbulent process of downslope transport, intermittent and localized, is identified, taking the form of cascades. The lifetime of cascades presents a power law relationship, and the related transport does not exhibit any characteristic length scale, suggesting self-organized criticality. Cascades reveal to be the main contributor to the vorticity and turbulence in the ocean interior, with a dependence on the Coriolis parameter and the density anomaly to the surrounding ambient. Vorticity is produced both by the spreading of the cascade into the interior, and by the meandering and the break up of the deep boundary current (formed from downward Ekman transport). When the intrusion spreads at the pycnocline only, anticyclonic eddies are formed in the intrusion and top layers, whereas for intrusions spreading through the full bottom layer, vortices of both signs are generated due to bottom friction. The turbulence in the receiving ambient reveals to be horizontally isotropic, non-stationary and non-homogeneous. In the intrusion area close to the slope, the turbulence is forced by energy injection at the penetration length scale through the cascades. The central area far from the boundaries is characterized, instead, by freely evolving two-dimensional turbulence, forced at large scales.