Deceleration and dispersion of large-scale coronal bright fronts^⋆

¹ Astrophysics Research Group, School of Physics, Trinity College Dublin, Dublin 2, Ireland
e-mail: longda@tcd.ie
² Harvard-Smithsonian Centre for Astrophysics, 60 Garden St., Cambridge, MA 02138, USA
³ Department of Astronomy, New Mexico State University, PO Box 30001 MSC 4500, Las Cruces, NM 88003, USA

Received: 6 October 2010
Accepted: 21 April 2011

Abstract

Context. One of the most dramatic manifestations of solar activity are large-scale coronal bright fronts (CBFs) observed in extreme ultraviolet (EUV) images of the solar atmosphere. To date, the energetics and kinematics of CBFs remain poorly understood, due to the low image cadence and sensitivity of previous EUV imagers and the limited methods used to extract the features.

Aims. In this paper, the trajectory and morphology of CBFs was determined in order to investigate the varying properties of a sample of CBFs, including their kinematics and pulse shape, dispersion, and dissipation.

Methods. We have developed a semi-automatic intensity profiling technique to extract the morphology and accurate positions of CBFs in 2.5–10 min cadence images from STEREO/EUVI. The technique was applied to sequences of 171 Å and 195 Å images from STEREO/EUVI in order to measure the wave properties of four separate CBF events.

Results. Following launch at velocities of  ~240–450 km s^-1 each of the four events studied showed significant negative acceleration ranging from  ~−290 to  −60 m s^-2. The CBF spatial and temporal widths were found to increase from  ~50 Mm to  ~200 Mm and  ~100 s to  ~1500 s respectively, suggesting that they are dispersive in nature. The variation in position-angle averaged pulse-integrated intensity with propagation shows no clear trend across the four events studied. These results are most consistent with CBFs being dispersive magnetoacoustic waves.