Dynamics of the solar chromosphere

III. Ultraviolet brightness oscillations from TRACE

¹ Sterrekundig Instituut, Postbus 80 000, 3508 TA Utrecht, The Netherlands e-mail: J.M.Krijger@astro.uu.nl, R.J.Rutten@astro.uu.nl
² High Altitude Observatory, National Center for Atmospheric Research, PO Box 3000, Boulder CO 80307-3000, USA e-mail: lites@hao.ucar.edu
³ Osservatorio Astronomico di Capodimonte, Via Moiariello 16, 80131 Napoli, Italy e-mail: straus@na.astro.it
⁴ Lockheed Martin Solar and Astrophysics Lab, Dept. L9-41, Building 252, 3251 Hanover Street, Palo Alto, CA 94304, USA e-mail: shine@lmsal.com; tarbell@lmsal.com

Corresponding author: J. M. Krijger, J.M.Krijger@astro.uu.nl

Received: 13 June 2001
Accepted: 14 September 2001

Abstract

We analyze oscillations in the solar atmosphere using image sequences from the Transition Region and Coronal Explorer (TRACE) in three ultraviolet passbands which sample the upper solar photosphere and low chromosphere. We exploit the absence of atmospheric seeing in TRACE data to furnish comprehensive Fourier diagnostics (amplitude maps, phase-difference spectra, spatio-temporal decomposition) for quiet-Sun network and internetwork areas with excellent sampling statistics. Comparison displays from the ground-based Caii H spectrometry that was numerically reproduced by Carlsson & Stein are added to link our results to the acoustic shock dynamics in this simulation. The TRACE image sequences confirm the dichotomy in oscillatory behaviour between network and internetwork and show upward propagation above the cutoff frequency, the onset of acoustic shock formation in the upper photosphere, phase-difference contrast between pseudo-mode ridges and the interridge background, enhanced three-minute modulation aureoles around network patches, a persistent low-intensity background pattern largely made up of internal gravity waves, ubiquitous magnetic flashers, and low-lying magnetic canopies with much low-frequency modulation. The spatio-temporal occurrence pattern of internetwork grains is found to be dominated by acoustic and gravity wave interference. We find no sign of the high-frequency sound waves that have been proposed to heat the quiet chromosphere, but such measurement is hampered by non-simultaneous imaging in different passbands. We also find no signature of particular low-frequency fluxtube waves that have been proposed to heat the network. However, internal gravity waves may play a role in their excitation.