Type II radio emission and ESP events
Abstract
We report on a survey of energetic storm particle (ESP) events associated with radio-quiet (RQ) and radio-loud (RL) interplanetary (IP) shocks observed during 1996-2006. Shocks were classified into RL or RQ events based on the existence of type II radio bursts. We consider only shocks driven by coronal mass ejections (CMEs). Particle observations are provided by the Electron, Proton and Alpha Monitor (EPAM) instrument on the Advanced Composition Explorer (ACE) spacecraft and the Energetic and Relativistic Nuclei and Electron (ERNE) experiment on the Solar and Heliospheric Observatoty (SOHO). We find that 32% of RQ shocks produced an ESP event at energies >1.8 MeV, compared to 52% of RL shocks. Electron enhancements were detected in 20% of RQ shocks and 39% of RL shocks. The ESP events associated with RQ shocks are less intense than those associated with RL shocks. In addition, RQ shocks with ESP events are predominately quasi-perpendicular shocks, and their solar sources located generally to the east of the central meridian. The size of ESP increases showed a modest positive correlation with the CME and shock speeds and with the Alfvenic Mach number. Our results indicate that some RQ shocks can accelerate particles at 1 AU, but less efficiently than RL shocks, even though they do not produce observable type II radio bursts. This variability is probably related to differences in the shock formation in the low corona, changes in the properties of the shocks as they propagate through interplanetary space, and the escape efficiency of accelerated particles from the shock front.
- Publication:
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Solar Heliospheric and INterplanetary Environment (SHINE 2010)
- Pub Date:
- July 2010
- Bibcode:
- 2010shin.confE..87M