Streamer Wave Events Observed in Solar Cycle 23

Abstract

In this paper we conduct a data survey searching for well-defined streamer wave events observed by the Large Angle and Spectrometric Coronagraph (LASCO) on-board the Solar and Heliospheric Observatory (SOHO) throughout Solar Cycle 23. As a result, 8 candidate events are found and presented here. We compare different events and find that in most of them the driving CMEs ejecta are characterized by a high speed and a wide angular span, and the CME-streamer interactions occur generally along the flank of the streamer structure at an altitude no higher than the bottom of the field of view of LASCO C2. In addition, all front-side CMEs have accompanying flares. These common observational features shed light on the excitation conditions of streamer wave events. We also conduct a further analysis on one specific streamer wave event on 5 June 2003. The heliocentric distances of 4 wave troughs/crests at various exposure times are determined; they are then used to deduce the wave properties like period, wavelength, and phase speeds. It is found that both the period and wavelength increase gradually with the wave propagation along the streamer plasma sheet, and the phase speed of the preceding wave is generally faster than that of the trailing ones. The associated coronal seismological study yields the radial profiles of the Alfv\'en speed and magnetic field strength in the region surrounding the streamer plasma sheet. Both quantities show a general declining trend with time. This is interpreted as an observational manifestation of the recovering process of the CME-disturbed corona. It is also found that the Alfv\'enic critical point is at about 10 R$_\odot$ where the flow speed, which equals the Alfv\'en speed, is $\sim$ 200 km s$^{-1}$

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

“…The mothod can be used to dianose the variations of the Alfvén speed and magnetic field strength from 3-10 Rs along the streamer plasma sheet. This study inspires further theoretical investigations on MHD wave modes supported by magnetized shear flows [138][139][140]157].…”

“…Besides the above event, Feng et al [140] also conducted a similar seismological study on the 5 June 2003 event.…”

“…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.…”

“…Most data are from the CDAW datacenter. The events with * represent questionable wave events, in which the streamer wavy motions may get disturbed by CME trailing structures (taken from [140]). effect of its field lines.…”