Dynamics of the solar chromosphere. V. High-frequency modulation in ultraviolet image sequences from TRACE

TL;DR

This study investigates high-frequency oscillations in the solar chromosphere using ultraviolet images from TRACE, revealing acoustic modulation up to 20 mHz, which may contribute to understanding stellar atmospheric heating.

Contribution

It provides the first reliable detection of high-frequency acoustic oscillations in the solar chromosphere using high-cadence ultraviolet imaging data.

Findings

Detection of acoustic modulation up to 20 mHz in internetwork areas.

Identification of high-frequency features that are likely artifacts.

Use of phase difference measurement as a sensitive diagnostic.

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 k-f 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 f=20 mHz (periods down to 50 seconds) in internetwork areas.