The shock driving capability of a CME inferred from multiwavelength observations

Abstract: The radial speed of a coronal mass ejection (CME) determines the shock-driving capability of a CME as indicated by the presence of a type II radio burst. Here we report on the April 18, 2014 CME that was associated with a type II radio burst in the metric and interplanetary domains. We used the radio-burst data provided by the San Vito Solar Observatory of the Radio Solar Telescope Network and data from the Wind spacecraft. The CME is a full halo in the field of view of the coronagraphs on board the Solar and Heliospheric Observatory (SOHO). The CME was also observed by the coronagraphs on board the Solar Terrestrial Relations Observatory (STEREO). We computed the CME shock and flux rope speeds based on the multi-view observations by the different coronagraphs and by EUV instruments. We determined the shock speed from metric and interplanetary radio observations and found them to be consistent with white-light observations, provided the metric type II burst and its continuation into the decameter-hectometric domain are produced at the shock flanks, where the speed is still high enough to accelerate electrons that produce the type II bursts. Interestingly, there was an interplanetary type II burst segment consistent with an origin at the shock nose suggesting that the curved shock was crossing plasma levels separated by a few solar radii. We conclude that the CME speed is high enough to produce the interplanetary Type II burst and a solar energetic particle (SEP) event. However, the speed is not high enough to produce a ground level enhancement (GLE) event, which requires the shock to form at a height of ~1.5 Rs.