Slow halo CMEs with shock signatures

Abstract

Context. In the solar corona, shocks are formed when the speed of a disturbance exceeds the local magnetosonic speed. In the active region corona the Alfvén speed can drop to a few hundred km s −1 , but globally it is much higher. There has been a long debate on whether the shocks responsible for type II bursts are created by bow shocks in front of coronal mass ejections (CMEs), shocks in the flanks of CMEs, or by flare (blast) waves. Aims. We study the alternative explanations for type II bursts in events where we have a slow CME, flare(s), and associated type II burst emission. Methods. We use multi-wavelength observations to analyse the height-time evolution of CMEs and compare it with the evolution of shock signatures in radio and EUV. Results. Three flare-associated halo-type CME events were observed on October 30, 2004. Velocity estimates (260, 325, and 920 km s −1 ) from the first plane-of-the-sky CME leading front observations suggested that the first two were very slow compared to halo CMEs, on average. The CMEs were associated with flares (M 4.2, X1.2, and M 5.9) and each event was also associated with coronal (metric) type II emission that is known to be a signature of a propagating shock front. After the flare starts, loop displacements and large-scale dimmings were observed in EUV. The two slow halo CMEs started as filament eruptions, but the CME velocities and/or bulk motions were affected at the times of flares. We find support for the idea that the cause of metric type II bursts in these two events is flare-related. The later CME velocity changes (acceleration around 4-5 solar radii) could also be explained by eruptions associated with later flares. The repeating homologous flare-halo CME events indicate a restoration of the same large-scale structures within 5-6 h.

Origin of Coronal Shock Waves

“…The situation is different for Moreton-wave associated type II bursts, which tend to have considerably higher starting frequencies, with emission in the harmonic band occasionally extending to > 300 MHz range (Warmuth et al, 2004b;Vršnak et al, 2006). In such events both the CME and the flare are observed, so over the years a flare vs. fast ejection controversy has arisen regarding the origin of coronal shocks (Cliver, Webb, and Howard, 1999;Vršnak, 2001;Hudson et al, 2003;Hudson and Warmuth, 2004;Cho et al, 2005;Shanmugaraju et al, 2005;Gopalswamy, 2006;Pohjolainen and Lehtinen, 2006;Reiner et al, 2007;Magdalenić et al, 2008).…”

On the relationship of shock waves to flares and coronal mass ejections

“…Classen & Aurass 2002;Shanmugaraju et al 2006;Hudson & Warmuth 2004;Cho et al 2005Cho et al , 2007Pohjolainen & Lehtinen 2006;Reiner et al 2007;Vršnak et al 2006;Dauphin et al 2006;Liu et al 2009). Most type II bursts that lack a clear CME association occur with flares within 30…”

Probability of Solar Flares Turn out to Form a Coronal Mass Ejections Events due to the Characterization of Solar Radio Burst Type II and III

“…There have been many studies of the possible association of SRBT II with either flares or CMEs [153][154][155][156][157][158][159][160][161][162]. SRBT II has extensively studied to understand their sources and in connection with CMEs and Solar Energetic Particles (SEP) events [50,163] based on signatures of the shock-associated plasma oscillate signatures of type II bursts occurred near off after the maximum of chromosphere flare.…”