Dynamics of the solar chromosphere IV. Evidence for atmospheric gravity waves from TRACE

Sterrekundig Instituut, Postbus 80 000, 3508 TA Utrecht, The Netherlands e-mail: R.J.Rutten@astro.uu.nl;J.M.Krijger@astro.uu.nl

Corresponding author: R. J. Rutten, R.J.Rutten@astro.uu.nl

Received: 23 July 2002
Accepted: 6 June 2003

Abstract

We study the low-frequency brightness modulation of internetwork regions in the low solar chromosphere using simultaneous ultraviolet and white-light image sequences from the Transition Region and Coronal Explorer (TRACE). The ultraviolet sequences exhibit a slowly varying brightness pattern in internetwork regions on which the more familiar acoustic three-minute oscillation is superimposed, with about half of the peak brightness reached in internetwork grains contributed by the low-frequency background. We address the nature of the latter, applying two-dimensional Fourier filtering to isolate it from the acoustic modulation. Spatio-temporal comparisons and selective time-delay scatter correlations between the ultraviolet and white-light low-frequency sequences establish that reversed granulation constitutes at most a minor part of the ultraviolet background. Fourier analysis shows that the meso-scale contribution dominates and consists of atmospheric gravity waves.