UV and radio observations of the coronal shock associated with the 2002 July 23 coronal mass ejection event

We report on the analysis of a fast coronal mass ejection (CME)-driven shock observed on 2002 July 23 with the Ultraviolet Coronagraph Spectrometer (UVCS) on board the Solar and Heliospheric Observatory (SOHO). The CME was first detected in white light by the Large Angle and Spectrometric Coronagraph Experiment (LASCO), and shock-associated type II metric emission was recorded by several ground-based radio spectrographs. The evolution of the excess broadening of the O VI lambda 1032 line profiles observed by UVCS at 1.63 R-circle dot is consistent with the passage of a CME-driven shock surface enveloping a bubble-type, conically expanding CME, and its dynamics is found to be well associated with the complex, multiple type II radio emission detected in the metric band. Our results suggest that there might be a deficiency of ion heating in the present event with respect to what was observed in previous CME shocks detected by UVCS, and that this paucity might be attributed to different local plasma conditions, such as higher ambient coronal plasma beta. We conclude that plasma beta could be an important parameter in determining the effect of ion heating at collisionless shock fronts in the solar corona.