Within the ocean's interior away from the top and bottom Ekman layers, the ocean circulation for time scales exceeding a few days is dominated by geostrophic currents, in which horizontal pressure gradients in the ocean almost exactly balance the Coriolis force. Pure geostrophic currents do not have vertical component of velocity and follow isobars. Vertical motions and associated ageostrophic overturning circulations arise when flow is deflected from geostrophic balance due to the effects of advection, vertical mixing or interaction with high-frequency components. In this study I consider different mechanisms, resulting in generation of ageostrophic circulations: effects of advection and vertical mixing in mesoscale eddies; frontal convection and interaction of frontal processes with abyssal circulation, and generation of quasi-steady vertical motions by tides over rough topography. To examine processes contributing to the ageostropic circulation I apply the semi-geostrophic methods, as extended Sawyer- Eliasson equation of frontal dynamics, omega-equation. I will discuss the applications to Arctic Ocean mass formation, convection in the Sea of Japan, and restratification of mixed layer depth by mesoscale eddies.
Temperature and quasi-steady vertical motions in simulations with and without tides