Properties of High-Frequency Type II Radio Bursts and Their Relation to the Associated Coronal Mass Ejections

Abstract

Solar radio bursts are often early indicators of space weather events such as coronal mass ejections (CMEs). In this study, we determined the properties of a sample of 40 high-starting-frequency (≥ 150 MHz) type II radio bursts and the characteristics of the associated CMEs such as width, location and speed during 2010–2016. The high starting frequency implies shock formation closer to the solar surface, which has important ramifications for the analysis of particle acceleration near the Sun. We found the CME heliocentric distances at the onset time of metric type II bursts range from 1.16 to 1.90 solar radii (Rs). The study was also extended to 128 metric type II bursts to include lower-starting-frequency events for further analysis. The projected CME heights range from 1.15 to 2.85 Rs. The lower starting frequency correspond to shocks forming at larger heights. A weak correlation was found between the type-II starting frequency and CME heights, which is consistent with the density decline in the inner corona. The analysis confirmed a good correlation between the drift rate and the starting frequency of type II bursts (correlation coefficient ∼ 0.8). Taking into account the radial variation of CMEs speeds from the inner corona to the interplanetary medium, we observed the deviations from the universal drift-rate spectrum of type II bursts and confirmed the previous results relating type II bursts to CMEs.