Evolution of a Density Enhancement in a Stratified Atmosphere With Uniform Vertical Magnetic Field

In this paper the evolution of a density enhancement under the effect of gravity in a stratified atmosphere is considered in a 2D simulation. The stratified atmosphere is chosen with a high-density photosphere, transition region and low-density corona where the enhancement is added in non-equilibrium to the corona. The atmosphere is also threaded with an initially uniform vertical magnetic field. If sufficiently strong, the magnetic field plays an important role in the evolution of the density enhancement as it tries to gain equilibrium. It not only enables the density enhancement to maintain its shape as it falls, but if strong enough results in the density enhancement rebounding a number of times. Therefore both upward and downward velocities of the enhancement are obtained. In all cases the density enhancement is found to fall with speeds much less than the free-fall speed and can remain in the corona at least 11 times longer than a free-fall particle. The relevance of the simulations to the solar atmosphere is then discussed. Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1005266330720