Relative maximum slow mode density perturbation in the corona. We divided this by to allow this plot to be used as a reference. Left: as a function of the density contrast between the chromosphere and the corona for different transition region widths, Δy. Right: as a function of the density gradient at y = y₀ and the corona for different transition region widths, Δy. The horizontal dashed-dotted lines give the value of the perturbation for a loop with no atmosphere. Connecting lines have been included to both plots as visual aids.