Streamer Waves Driven by Coronal Mass Ejections

Abstract

Between July 5th and July 7th 2004, two intriguing fast coronal mass ejection(CME)-streamer interaction events were recorded by the Large Angle and Spectrometric Coronagraph (LASCO). At the beginning of the events, the streamer was pushed aside from their equilibrium position upon the impact of the rapidly outgoing and expanding ejecta; then, the streamer structure, mainly the bright streamer belt, exhibited elegant large scale sinusoidal wavelike motions. The motions were apparently driven by the restoring magnetic forces resulting from the CME impingement, suggestive of magnetohydrodynamic kink mode propagating outwards along the plasma sheet of the streamer. The mode is supported collectively by the streamer-plasma sheet structure and is therefore named " streamer wave" in the present study. With the white light coronagraph data, we show that the streamer wave has a period of about 1 hour, a wavelength varying from 2 to 4 solar radii, an amplitude of about a few tens of solar radii, and a propagating phase speed in the range 300 to 500 km s −1 . We also find that there is a tendancy for the phase speed to decline with increasing heliocentric distance. These observations provide good examples of large scale wave phenomena carried by coronal structures, and have significance in developing seismological techniques for diagnosing plasma and magnetic parameters in the outer corona.

A review of recent studies on coronal dynamics: Streamers, coronal mass ejections, and their interactions

“…Given a fast-moving and expanding eruption and a large streamer deflection, the restoring force may be strong enough not only to deflect but also oscillate the streamer structure. This intuitive picture has been verified by Chen et al (2010) [138], as will be described in the following.…”

“…Streamer waves are first reported by Chen et al [138] with the LASCO data. The wave properties including the wavelength, wave period, and phase speed are deduced.…”

“…In recent studies, we have discovered several interesting white-light and radio phenomena associated with CMEstreamer interactions, including streamer waves manifested as the wavy motion of a streamer stalk [138][139][140], and spectral bump and break features of type II radio busts caused by the radio source propagating through a streamer from outside [141] and inside of the streamer [142]. These studies will be reviewed as follows.…”

“…This gives rise to the streamer oscillation, which propagates outwards along the plasma sheet. Accordingly, there appear "black-white and white-black" pairs on the difference images, which have been used by Chen et al [138] and Feng et al [140] to delineate the wave profiles. They further determine the locations of observable wave troughs and crests at all exposure times to calculate the wave paramteres.…”

“…They further determine the locations of observable wave troughs and crests at all exposure times to calculate the wave paramteres. Based on this case study, Chen et al [138] present the observational definition of streamer wave as a long-period largescale wave phenomenon excited in the aftermath of CMEstreamer interaction, which is carried by and propagating outwards along the plasma sheet, representing one of the largest wave phenomena ever observed in the corona.…”