Abstract
Abstract. Using the extensive and uniform data on coronal mass ejections (CMEs), solar energetic particle (SEP) events, and type II radio bursts during the SOHO era, we discuss how the CME properties such as speed, width and solar-source longitude decide whether CMEs are associated with type II radio bursts and SEP events. We discuss why some radio-quiet CMEs are associated with small SEP events while some radio-loud CMEs are not associated with SEP events. We conclude that either some fast and wide CMEs do not drive shocks or they drive weak shocks that do not produce significant levels of particle acceleration. We also infer that the Alfvén speed in the corona and near-Sun interplanetary medium ranges from <200 km/s to ~1600 km/s. Radio-quiet fast and wide CMEs are also poor SEP producers and the association rate of type II bursts and SEP events steadily increases with CME speed and width (i.e. energy). If we consider western hemispheric CMEs, the SEP association rate increases linearly from ~30% for 800 km/s CMEs to 100% for ≥1800 km/s. Essentially all type II bursts in the decametre-hectometric (DH) wavelength range are associated with SEP events once the source location on the Sun is taken into account. This is a significant result for space weather applications, because if a CME originating from the western hemisphere is accompanied by a DH type II burst, there is a high probability that it will produce an SEP event.
Highlights
Coronal mass ejections (CMEs) associated with type radio II bursts are more energetic on the average and there is a hierarchical relationship between CME kinetic energy and the wavelength range of type II radio bursts (Gopalswamy et al, 2001a, 2005; Lara et al, 2003; Gopalswamy, 2006)
This work concerns the ability of CMEs to produce type II radio bursts and solar energetic particle (SEP), through the common process of particle acceleration by fast mode MHD shocks
Using the extensive and uniform data on CMEs, SEPs, and type II radio bursts that became available during the Solar and Heliospheric Observatory (SOHO) era, we discuss how the CME properties such as speed, width and solar source longitude decide whether CMEs are associated with type II radio bursts and SEP events
Summary
Coronal mass ejections (CMEs) associated with type radio II bursts are more energetic on the average and there is a hierarchical relationship between CME kinetic energy and the wavelength range of type II radio bursts (Gopalswamy et al, 2001a, 2005; Lara et al, 2003; Gopalswamy, 2006). The average speed (1524 km/s) of CMEs associated with large solar energetic particle (SEP) events is very similar to that of CMEs with mkm type II bursts. This is consistent with the idea that CME-driven shocks accelerate both ions and electrons. When CMEs move faster than the characteristic speed of the ambient medium (say, the Alfven speed), they drive fast-mode MHD shocks, which in turn accelerate electrons to produce the type II bursts. To get a complete picture on the ability of CMEs in driving shocks and producing energetic particles, we need to understand how CMEs, SEPs, and type II radio bursts are interrelated. A list of DH type II bursts with information on the associated CMEs is available online at the CDAW Data Center (http://cdaw.gsfc.nasa.gov/CME list/radio/waves type2.html)
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