DOT tomography of the solar atmosphere

II. Reversed granulation in Ca II H

¹ Sterrekundig Instituut, Utrecht University, Postbus 80 000, 3508 TA Utrecht, The Netherlands e-mail: [R.J.Rutten; A.G.deWijn; P.Suetterlin]@astro.uu.nl
² Institute of Theoretical Astrophysics, Oslo University, PO Box 1029 Blindern, 0315 Oslo, Norway

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

Received: 5 November 2003
Accepted: 28 November 2003

Abstract

High-quality simultaneous image sequences from the Dutch Open Telescope (DOT) in the G band and the Ca IIH line are used to quantify the occurrence of reversed granulation as a constituent of the subsonic brightness pattern observed as a background to acoustic oscillations in the quiet-Sun internetwork atmosphere. In the middle photosphere reversed granulation constitutes a much larger part of this background than at the larger heights sampled by ultraviolet radiation. The anticorrelation with the underlying granulation reaches about 50% at a temporal delay of 2–3 min, and increases with spatial image smoothing to mesogranular resolution. We discuss the nature of reversed granulation in terms of convection reversal, gravity waves, acoustic waves, and intergranular magnetism, suggest that the internetwork background pattern is primarily a mixture of the first two ingredients, and speculate that it is also an inverse canopy mapper.