Deceleration and dispersion of large-scale coronal bright fronts

Abstract

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 angstrom and 195 angstrom images from STEREO/EUVI in order to measure the wave properties of four separate CBF events.

Results. Following launch at velocities of similar to 240-450 km s(-1) each of the four events studied showed significant negative acceleration ranging from similar to-290 to -60 ms(-2). The CBF spatial and temporal widths were found to increase from similar to 50 Mm to similar to 200 Mm and similar to 100 s to similar 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.