A vertical soap film supported on a rectangular wire frame of height 3.5 cm and width 15 cm drains under the influence of gravity in an unsaturated environment. Evaporation at the top of the film disrupts the film shape, giving rise to a horizontal bump which grows in amplitude until becoming gravitationally unstable and generating a series of sinking plumes of relatively thick film. The plumes penetrate a finite distance into the film, giving rise to a turbulent mixed layer which slowly erodes the underlying region of stably stratified film. Note the black film adjoining the wire frame at the top of the film, and the relatively weak convective motions, associated with marginal regeneration, evident near the base of the film.
See article: Skotheim & Bush (2000)