Dynamics of the solar chromosphere

V. High-frequency modulation in ultraviolet image sequences from TRACE

¹ Sterrekundig Instituut, Utrecht University, Postbus 80 000, 3508 TA Utrecht, The Netherlands e-mail: [A.G.deWijn; R.J.Rutten]@astro.uu.nl
² Institute of Theoretical Astrophysics, Oslo University, PO Box 1029 Blindern, 0315 Oslo, Norway
³ Lockheed Martin Solar and Astrophysics Lab, Dept. ADBS, Building 252, 3251 Hanover Street, Palo Alto, CA 94304, USA e-mail: tarbell@lmsal.com

Received: 24 July 2004
Accepted: 12 October 2004

Abstract

We search for signatures of high-frequency oscillations in the upper solar photosphere and low chromosphere in the context of acoustic heating of outer stellar atmospheres. We use ultraviolet image sequences of a quiet center-disk area from the Transition Region and Coronal Explorer (TRACE) mission which were taken with strict cadence regularity. The latter permits more reliable high-frequency diagnosis than in earlier work. Spatial Fourier power maps, spatially averaged coherence and phase-difference spectra, and spatio-temporal () decompositions all contain high-frequency features that at first sight seem of considerable intrinsic interest but actually are more likely to represent artifacts of different nature. Spatially averaged phase difference measurement provides the most sensitive diagnostic and indicates the presence of acoustic modulation up to (periods down to 50 s) in internetwork areas.