Evolution and instability of monopolar vortices in a stratified fluid

Abstract

The evolution of initially axisymmetric shielded pancake-like vortices in a nonrotating linearly stratified fluid has been investigated experimentally and numerically. The evolution process and the shape of tripoles in laboratory experiments depend on the experimental parameter values. In order to investigate this phenomenon we have considered the influence of the Reynolds (Re) and Froude (F) numbers on the tripole formation process. Also, the role of the (absolute) ratio γ between the vorticity values of the satellite vortices and the core vortex on the tripole evolution has been investigated. Additionally, a set of numerical simulations has been performed to enable an examination of the role of Reynolds numbers (up to Re=10 000) and Froude numbers (F=0.1, 0.2, 0.4, and 0.8) outside the experimentally accessible range. The steepness parameter α was varied between 2 and 8 in order to estimate the relative importance of the different modes constituting the perturbation. From this study we conclude that tripole formation and dipole splitting in a linearly stratified fluid can be well described in terms of the parameter set (Re,F,α).