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Session 19 - Solar Flares.
Oral session, Monday, June 10
Wisconsin Center,
There exists a controversy regarding the origin of coronal and interplanetary (IP) shocks. Present observations shows that coronal shocks are associated with flares while the IP shocks are associated with coronal mass ejections (CMEs). An important question in this connection is whether the IP shocks are extensions of the coronal shocks or they are independently driven by CMEs. The coronal shocks have traditionally been inferred from metric type II radio bursts. The ionospheric cut-off around 20 MHz had been a hurdle in arriving at a firm conclusion regarding the continuation of type II bursts to frequencies lower than the ionospheric cut off. The WAVES experiment on board the WIND spacecraft has essentially removed this hurdle so that we are able to track metric radio bursts to hectometric wavelengths. We have identified about two dozen type II bursts observed by the Hiraiso Radio Spectrograph (HiRAS) after the launch of the WIND satellite. Most of these type II bursts were accompanied by type III bursts. We have positively identified the solar flares associated with all the events. When we examined the WIND Radio and Plasma waves (WAVES) data, we found the following: (i) Most of the metric (Hiraiso) type III bursts have counterparts in the WAVES data; (ii) None of the metric type II bursts have counterparts in the WAVES data. This result suggest that coronal shocks responsible for metric type II bursts are blast waves which decay rapidly within the inner corona while the electron beams producing type III bursts continue to propagate to the IP medium.
