Properties of solar energetic particle events inferred from their associated radio emission^⋆

¹ Section of Astrogeophysics, Department of PhysicsUniversity of Ioannina, 45110 Ioannina, Greece
e-mail: akouloumvak@phys.uoa.gr
² Department of Physics and Astronomy, University of Turku, 20014 Turku, Finland
³ IAASARS, National Observatory of Athens, 15236 Penteli, Greece
⁴ Department of Electronics, Technological Educational Institute of Lamia, 35100 Lamia, Greece
⁵ Section of Astrophysics, Astronomy and Mechanics, Department of Physics, National and Capodistrian University of Athens, 15783 Athens, Greece

Received: 13 June 2014
Accepted: 4 June 2015

Abstract

Aims. We study selected properties of solar energetic particle (SEP) events as inferred from their associated radio emissions.

Methods. We used a catalogue of 115 SEP events, which consists of entries of proton intensity enhancements at one AU, with complete coverage over solar cycle 23 based on high-energy (~68 MeV) protons from SOHO/ERNE. We also calculated the proton release time at the Sun using velocity dispersion analysis (VDA). After an initial rejection of cases with unrealistic VDA path lengths, we assembled composite radio spectra for the remaining events using data from ground-based and space-borne radio spectrographs. We registered the associated radio emissions for every event, and we divided the events in groups according to their associated radio emissions. In cases of type III-associated events, we extended our study to the timings between the type III radio emission, the proton release, and the electron release as inferred from VDA based on Wind/3DP 20–646 keV data.

Results. The proton release was found to be most often accompanied by both type III and II radio bursts, but a good association percentage was also registered in cases accompanied by type IIIs only. The worst association was found for the cases only associated with type II. In the type III-associated cases, we usually found systematic delays of both the proton and electron release times as inferred by the particles’ VDAs, with respect to the start of the associated type III burst. The comparison of the proton and electron release times revealed that, in more than half of the cases, the protons and electrons were simultaneously released within the statistical uncertainty of our analysis. For the cases with type II radio association, we found that the distribution of the proton release heights had a maximum at ~2.5 R_⊙. Most (69%) of the flares associated with our SEP events were located in the western hemisphere, with a peak within the well-connected region of 50°–60° western longitude.

Conclusions. Both flare- and shock-related particle release processes are observed in major proton events at >50 MeV. Typically, the protons are released after the start of the associated type III bursts and simultaneously or before the release of energetic electrons. Our study indicates that a clear-cut distinction between flare-related and CME-related SEP events is difficult to establish.