Intrusive gravity currents and internal gravity wave generation in stratified fluid

Abstract

The excitation of internal gravity waves by fluid intrusions that propagate along the interface between a uniform upper layer and a uniformly stratified lower layer is examined by way of laboratory experiments. Intrusions are generated using a simple lock-release apparatus. Experiments are conducted in which the density gradient of the uniformly stratified layer, the density jump across the interface and the density difference between the lock fluid and the uniform upper layer are varied.In all cases, the fluid intrusions traveled at a constant speed. The forcing imparted by the generated internal gravity waves did not deform the intrusion head or significantly retard the intrusion's rate of forward advance. For a limited range of density parameters, good agreement was obtained between the experimental data and the two-layer analytical theory of Holyer & Huppert (1980) which provides estimates for the intrusion speed and depths of penetration into the upper and lower layers. Internal gravity wave excitation is due to the initial collapse of the lock fluid and the forcing imparted by the head of the intrusion. Waves are visualised and their amplitudes measured using "synthetic schlieren".The vertical flux of horizontal momentum due to internal gravity wave excitation is related to measurable properties of the fluid intrusion. This analysis suggests that outflows produced by tall convective storms that travel along the tropopause may excite non-hydrostatic internal gravity waves in the stratosphere whose momentum flux, at least during the transient generation time, is comparable to that of waves generated by topographic forcing.

Effect of thermal stratification on interflow travel time in stratified reservoir

“…A density current into stratified surroundings is also called as intrusive gravity current (IGC) which travels horizontally with a constant velocity U in stratified surroundings for a time after releasing (Flynn and Sutherland, 2004;Shin et al, 2004;Ungarish, 2005;2006;Nokes et al, 2008). Overflow and underflow are similar to the IGC travel along the top and bottom boundaries of stratified surroundings when its density is less or greater than the ambient water.…”

An intrusion layer in stationary incompressible fluids: Part 1: Periodic waves

“…An experimental investigation of the propagation of an intrusion gravity current flow into a stationary two-layer fluid has been undertaken by Sutherland et al [14]. A similar situation may occur in the atmosphere, and Flynn & Sutherland [15], for example, have described how the anvil cloud of a thunderstorm can form an intrusion layer at about the level of the tropopause. Manins [16] has conducted an experimental investigation of the initial stages of an intrusion layer entering a linearly stratified fluid.…”

An intrusion layer in stationary incompressible fluids Part 2: A solitary wave

“…Flynn & Sutherland [9] have described how the anvil cloud of a thunderstorm may form an intrusion layer at about the level of the tropopause, for example. Two-layer atmospheric intrusion flows can arise when a heavier layer penetrates beneath a lighter one, and such a process is believed to be involved in the remarkable 'Morning Glory' phenomenon in the Gulf of Carpentaria in the far north of Australia, as described by Clarke et al [10].…”