The collapse of a mixed patch in stratified fluid

Abstract

Lock-release laboratory experiments are performed to examine the collapse of a localized mixed patch of fluid in a uniformly stratified ambient with constant buoyancy frequency, N. The intrusion speed is approximately 0.13NHℓ, in which Hℓ is the depth of the mixed patch. This is consistent with the speed of intrusions released from a full-depth lock where Hℓ=H is the depth of the ambient. The vertically propagating waves have frequency set by N (ω≃0.7N) and the horizontal wavelength, λx, is set by Hℓ (λx≃1.5Hℓ). The amplitude is found to scale as the depth of the mixed region cubed at small Hℓ, and saturates at large Hℓ≳10cm due to nonlinear effects.