Statistical analysis of shock properties driven by coronal mass ejections based on observations of type II radio bursts

Abstract

In this paper, we investigate 77 type-II radio burst events' data observed by Wind/WAVES and STEREO/SWAVES from January 2007 to December 2015. By fitting the frequency-time profile to obtain the corresponding shock velocity, we study the relationship between the parameters of shock and those of coronal mass ejection (CME), solar flare and the associated SEP events, and explore the influences of type II radio enhancement on these relationships. Our findings are as follows. 1) In general, at the onset time of type II radio bursts within deca-hectometric (DH) waveband, the shock front is about 0.4Rs ahead of the leading edge of CME (shock standoff distance), and this distance increases as the CME propagates outward. In the low and high corona, the relationship between shock standoff distance and CME speed indicates a significant difference; the shock standoff distance is correlated with the CME speed positively at the low altitude, but negatively at high altitude. 2) The CME speed of the events with radio enhancement is significantly larger than that with no radio enhancement; and comparing with the events with no radio enhancement, the correlation coefficient between the shock speed and the mass and kinetic energy of the associated CME is significantly high for the events with radio enhancement. 3) There is no correlation between the duration of type II radio burst in DH waveband with enhancement and the speed, mass and kinetic energy of CME. However, it presents a positive correlation for the events with no radio enhancement. 4) Usually the speed of shock that can produce SEP event is obviously higher than that with producing no SEP event. The probability of the SEP generated by the events associated with radio enhancement is slightly higher than with no radio enhancement (73.5% > 67.4%), but for the large SEP events, the generation probability (67.6%) associated with radio enhancement is about one-order of magnitude higher than that with no radio enhancement (37.2%). This conclusion indicates that the type II radio enhancement can be used as one of the signatures of the shock or the radio source that more probably produces a large SEP event.