Navid Constantinou (SIO)
Eddy saturation in a barotropic model
"Eddy saturation" refers to a regime in which the total zonal volume transport of an ocean current is insensitive to the wind stress strength; the Antarctic Circumpolar Current (ACC) is the most prominent example. Baroclinicity is currently believed to be key to the development of an eddy-saturated state. Here, we show that eddy saturation occurs in a barotropic flow over topography, without baroclinicity. We show that eddy saturation is a fundamental property of barotropic dynamics above topography. We demonstrate that the main factor controlling the appearance or not of eddy saturated states is the structure of geostrophic contours, that is the contours of f/H, with f the Coriolis parameter and H the depth. Eddy saturated states occur when the geostrophic contours are open, that is when the geostrophic contours span the whole zonal extent of the domain. We demonstrate this minimal requirement for eddy saturated states in a scenario relevant to the ACC using numerical integrations of a single-layer quasi-geostrophic flow over two different topographies characterized by either open or closed geostrophic contours. We also extend the stability method of Hart [JAS, 36, 1736-1746 (1979)] to explain the flow transitions that occur in the solutions with open geostrophic contours.
A preprint of the paper submitted to JPO can be found at: http://arxiv.org/abs/1703.