Statistical analysis of the relationship between type II radio enhancement and solar energetic particle event

Abstract

In this paper, we investigated 82 type-II radio burst events detected by some ground stations Learmonth, YNAO, and BIRS and spacecraft Wind/WAVES, STEREO/WAVES from January 2007 to December 2015. And we identified 39 events associated with radio enhancement and 43 events without enhancement. We found that: 1) The CME velocity, mass, kinetic energy and flare class with respect to type II radio enhancement events were generally higher than that of no enhancement events, and these properties in the solar energetic particle (SEP) events were significantly higher than that no SEP event, regardless of whether radio enhancement or not. 2) As shown in the characteristic time analysis, the initial release time of SEPs is generally earlier than the start time of radio enhancement, so we can the radio enhancement is only as a signature of the shock enhancement rather than the direct generator of SEP events. 3) Whether radio enhancement or not, the onset height of type IIs associated with SEP event is slightly lower than that of event without SEP. For the absence height, the SEP events are significantly higher than the no-SEP events, and that the absence height of enhancement events are also distinctly higher than that non-enhancement events, which reveals that the enhanced CME shock characterized by enhanced radio burst can keep propagating to more higher or further space. 4) When one fast and wide CME fully sweeps over another slow and narrow preceding CME, CME interaction can more easily generate radio enhancement, but no distinctive difference between SEP events and non-SEP events. So the results of this paper reveal that radio enhancement can be regarded as a manifestation of CME shock becoming strong during interacting with other CME, and the enhanced shock can accelerate the particle to generate large SEP events more easily. However, the type II radio enhancement is not the direct producer or causer that generate large SEP event.