Physics
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmsh13b1550l&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #SH13B-1550
Physics
7513 Coronal Mass Ejections (2101), 7534 Radio Emissions, 7851 Shock Waves (4455)
Scientific paper
It has been a long-standing controversy whether coronal metric type II bursts are generated by CME-driven shocks or flare blast waves. Using unprecedented high-cadence observations from STEREO/SECCHI, we investigate the relationship between a metric type II event and a shock driven by the 2007 December 31 CME. The CME occurs at the east limb and its evolution is observed from about 1.1 to several tens of solar radii. The existence of the CME-driven shock is indicated by the deflection of coronal structures before the CME impinges on them, the best evidence for shocks in imaging observations. The earliest deflection of distant coronal structures occurs at 00:51:22 UT, about 2.6 min before the metric type II onset. The CME- driven shock emerges from the corona and produces a break point in the streamer north of the CME, which allows us to follow the shock propagation in imaging observations for the first time. We also have a continuous frequency coverage of the radio dynamic spectrum by combining observations from STEREO/SWAVES, BIRS and Learmonth, which successfully establishes the connection between the metric and decametric-hectometric (DH) type II bursts. The CME speed is about 600 km/s at the time of the metric type II onset, larger than the Alfven speed 420 - 490 km/s determined from the band splitting of the metric type II burst. The shock height-time curve determined from the metric and DH type II bands is consistent with the shock propagation obtained from the streamer deflection. These results provide unambiguous evidence that the metric type II burst is caused by the CME-driven shock. Implications are also discussed for particle acceleration and space weather forecasting.
Bale Stuart
Lin Runliang
Liu Ya-Ying
Luhmann Janet
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