A model for Meddy formation

Abstract

A particular feature of “Meddies” is that the water within them has stable gradients of salinity and temperature. In this paper a model for a dense turbulent plume falling in a stationary, linearly-stratified environment is described. The density of the plume is assumed to be a linear function of two components, while the ambient density gradient is due to a gradient in only one of these components (labelled component one). The ratio of the contributions to the source buoyancy flux of the two components within the plume is identified as the important parameter for this type of flow. After deriving the steady equations for the plume, a simplified model for the filling process which creates the Meddy is described, which shows how a layer of fluid may be formed with stable gradients in both components in the lower part of the intrusion. The intrusion is shown to be less stratified than the surrounding fluid, with relatively weak gradients in component one (identified with temperature in the Meddy) that vary from unstable at the top to stable at the bottom of the intrusion and a fairly constant (stable) gradient in the second component (salinity for a Meddy). If the stable gradients in a Meddy are due solely to the filling process then, during formation, the top of the Meddy must become cooler than the surrounding water at the same level. The observed stable temperature gradient in Meddies is likely to be due to mixing processes after their formation, whereas the stable salanity gradient is mainly due to the filling process during formation.