A study of CME and type II shock kinematics based on coronal density measurement

Abstract

Aims. The aim of this paper is to determine location and speed of a coronal shock from a type II burst spectrum without relying on any coronal density model, and to use the result to discuss the relationship between the type II burst and Coronal Mass Ejection (CME). Methods. This study is made for the 2004 August 18 solar eruption observed by Green Bank Solar Radio Burst Spectrometer (GBSRBS) and a limb CME/streamer simultaneously detected by Mauna Loa Solar Observatory (MLSO) MK4 coronameter. We determine the background density distribution over the area of interest by inverting the MLSO MK4 polarization map taken just before the CME onset. Using the two-dimensional density distribution and the type II emission frequencies, we calculate the type II shock heights along several radial directions selected to encompass the entire position angles of the CME. We then compare these emission heights with those of the CME to determine at which position angle the type II burst propagated. Along the most plausible position angle, we finally determine the height and speed of the shock as functions of time. Results. It turns out that the type II emission height calculated along a southern streamer best agrees to the observed height of the CME flank. Along this region, both the shock and CME moved at a speed ranging from 800 to 600 kms-1. We also found that the streamer boundary already had enhanced density compared to other parts before the CME and formed a low Alfvénic region. Conclusions. We therefore conclude that the type II burst was generated at the interface of the CME flank and the streamer, as favorable for the shock formation. © ESO 2007.