Kinematic Properties of Globally-Propagating Waves in the Solar Corona

TL;DR

This study uses EUV observations from STEREO and SDO to analyze the kinematics of coronal bright fronts, revealing their dispersive, wave-like nature and the influence of observational cadence on measurements.

Contribution

It introduces a semi-automated, statistically rigorous method for identifying and analyzing CBFs, improving accuracy over traditional techniques.

Findings

CBFs exhibit deceleration and pulse broadening, indicating dispersive wave behavior.

Kinematic measurements are significantly affected by image cadence and passband.

CBFs are best interpreted as fast-mode magnetoacoustic waves in the solar corona.

Abstract

Globally-propagating coronal bright fronts (CBFs) in the solar corona are among the most dramatic manifestations of solar activity, but are not well understood despite strong links with both solar flares and coronal mass ejections. Extreme UltraViolet (EUV) observations from the STEREO and SDO spacecraft are used here to study their kinematics and morphology. The first STEREO observations of a CBF are presented, with the pulse observed in all available EUV passbands (171, 195, 284 and for the first time, 304A). The pulse displayed similar kinematics in all passbands, although the derived pulse velocity and acceleration were found to be strongly influenced by the observing cadence, implying that previous kinematics may have been underestimated. Different techniques for identifying CBFs and deriving their true kinematics were tested, with traditional techniques shown to be prone to undefined user-dependent errors. This was overcome through the development of a statistically rigorous, semi-automated identification algorithm, which was then used to determine the kinematics of four CBF events observed by STEREO. All of the events studied exhibited clear deceleration as well as increases in both spatial and temporal pulse width, indicating that the CBFs are dispersive. A CBF pulse observed by both STEREO and SDO was also studied using the algorithm, with lower initial velocity and weaker deceleration noted in STEREO observations compared to SDO, reaffirming the effects of image cadence on the derived kinematics. The kinematics obtained using SDO were highly passband dependent, suggesting a compressive nature. Significant pulse broadening was also noted in observations from both spacecraft, allowing the dispersion rate of the pulse to be determined. These results indicate that coronal bright fronts are best interpreted as fast-mode magnetoacoustic waves propagating in an inhomogeneous medium.