Stereoscopic Observation of Recurrent Streamer Waves Driven by Successive Slow Coronal Mass Ejections

TL;DR

This study uses stereoscopic observations to show that recurrent streamer waves can be driven by slow CMEs, revealing that wave periods are governed by the streamer’s eigenmodes rather than CME speed or energy.

Contribution

It demonstrates that streamer waves can be excited by slow CMEs and that their periods are primarily determined by the streamer’s inherent eigenmodes, challenging previous assumptions.

Findings

Recurrent streamer waves driven by slow CMEs with speeds <500 km/s.

Wave periods are similar despite differences in CME energy and wave scales.

Wave amplitude and wavelength exhibit specific propagation trends with distance.

Abstract

We report the stereoscopic observations of two recurrent streamer waves in a single streamer structure, utilizing coordinated observations from the SOHO, STEREO, and SDO missions. Contrary to the long-held view that fast coronal mass ejections (CMEs) are necessary drivers, we demonstrate that these recurrent waves were excited by two consecutive slow CMEs (<500 km/s} accompanied by only modest flare activity. Three-dimensional reconstruction reveals that the first and second waves propagated with significant decelerations of - 7.93 and - 10.26 m s^-2, respectively. Their average amplitudes were 0.41 and 0.77 solar radii, wavelengths were 4.02 and 6.17, and periods were 2.66 and 2.53 hours, respectively. While the amplitude of the first wave declined with heliocentric distance (consistent with conventional energy convection), the second wave exhibited an intriguing increasing trend in amplitude. Both waves showed a linear increase in wavelength and period with distance, indicating a non-stationary and dispersive medium. Crucially, despite the disparity in driver energy and wave scales, the periods and their change rates remained nearly identical for both events. This provides compelling case-specific evidence that the streamer wave period is primarily determined by the inherent eigenmodes of the streamer plasma slab rather than the specific characteristics of the trigger. We conclude that the generation of observable streamer waves is a combined consequence of the streamer's structural stability and the energy transfer efficiency of the triggering disturbance.