Tracing shock waves from the corona to 1 AU: Type II radio emission and relationship with CMEs

Abstract

We report on 10 type II bursts observed with ground‐based spectrographs in the meter‐decameter range, and with the Radio and Plasma Wave Investigation on the Wind spacecraft from 13.8 to 0.01 MHz. We have selected events with contemporaneous observations of flares and of coronal mass ejections (CMEs) by Large‐Angle and Spectrometric Coronagraph (LASCO) telescopes. We trace the history of each event from the time of the impulsive phase of the flare, the CME liftoff time, and the start time of the radio bursts. We derive the speed of the type II shock by using a coronal/solar wind density model, and the height‐time progression is compared with that of the CME as observed in the plane of the sky and then converted into the radial direction. For most events a shock at 1 AU was observed in situ. The results show the following: (1) All type II bursts occurred within 2 or 3 min of the impulsive phase of a flare. (2) The speeds of the disturbances from the time of the flares to the time of the shocks at 1 AU were very similar to the speeds of the type II‐emitting shocks; they were in the range of 600 to 1300 km s−1. (3) When the type II burst was observed far out in the solar wind, the progression of the type II source had about the same speed in the solar wind as in the corona. (4) The CME liftoffs were before the flares and the type II bursts by 1–24 min for most of the selected events. As a consequence, in the corona, the type II bursts, being behind the fronts of the CMEs, are usually blast waves. (5) When a shock and CME material are observed at 1 AU, the time of arrival implies a deceleration of the CME in the solar wind, as is observed in the LASCO data. (6) Somewhere in the solar wind the shocks very likely become piston‐driven, related to the CME.