Axisymmetric intrusions

Intrusions occur, for example, when a localized mixed patch collapses and moves horizontally in a stratified ambient. Compared with studies of gravity currents that move over rigid boundaries, relatively little is known about intrusions and, in particular, their interaction with internal waves. Following up on experimental studies of intrusions in a two-layer fluid, which were performed in a rectilinear tank, in this work we examine the radial spreading of a mixed patch of fluid released from a cylinder in a two-layer fluid. In the symmetric case with equal upper and lower layer fluid depth and with the mixed patch having the average density of the ambient, surprisingly we find that the current spreads at constant radial speed. In asymmetric circumstances the current spreads a finite distance before stopping, instead imparting its kinetic energy to interfacial wave motions. These qualitative observations are essentially unchanged by the action of weak Coriolis forces that act primarily to limit the ultimate radial spreading distance and to trap a fraction of mixed fluid at the release site.