Left: total magnetic field strength across the centre of the tube as a function of height. Right: Vertical slice through the centre of the flux tube showing the difference in density between the initial condition with the flux tube and the purely hydrodynamic initial condition. A reduced density (negative) will cause the tube to rise, and an increased density (positive) will cause it to sink. The contour of the magnetic field value of 25 kG is shown in green. The relative density perturbation is constant as a function of height in the background Model S atmosphere.