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

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.

Solar flares, coronal mass ejections and solar energetic particle event characteristics

“…Radio emissions have a rich diagnostic potential about the acceleration and propagation of solar energetic particles (Kouloumvakos et al 2015). Additionally, they provide important information on the location and temporal evolution of the particle release processes from the corona into the IP medium (Agueda et al 2014).…”

Ultra-wideband Detection of 22 Coherent Radio Bursts on M Dwarfs

“…Solar Type III bursts are produced by electron beams moving at speeds of order 10% of the speed of light, with radio frequency decreasing exponentially on a timescale of seconds; when these bursts occur at low frequencies, they indicate that energetic electrons (and likely protons as well) are escaping the solar corona on open magnetic field lines. Both of these classes of bursts are correlated with solar space weather events that impact Earth: coronal mass ejections and solar energetic particle (SEP) events (Kouloumvakos et al 2015). Analogous events, tracing bulk motion of plasma, may be detectable from nearby stars; and based on Sun-as-a-star data, such stellar radio bursts can be used to recover approximate dynamical properties of CMEs (Crosley et al 2017).…”

Energy dependence of SEP electron and proton onset times

“…Although both SEP solar particle release (SPR) times and EM onsets have been discussed at length in the past, comparison between electron release times and proton release times has been discussed only in a few papers [e.g., Cliver et al , ; Haggerty and Roelof , ; Kouloumvakos et al , ; Kahler et al , ; Posner , ]. In Posner []'s study, the author adopted the prevailing assumption of simultaneous release of electrons and protons, but he also pointed out that “release of protons before electrons (and vice versa) is possible (E. Roelof and D. Haggerty, personal communication, 2006)”.…”

“…They found that half of GLE events the relativistic proton injection preceded that of electrons; however, the low‐intensity GLEs tend to have a later time for the proton injection. Recently, Kouloumvakos et al [] compared the proton and electron release as inferred from velocity dispersion analysis (VDA) based on Wind/3DP and Energetic and Relativistic Nuclei and Electron instrument (ERNE) data and found a 7 min average delay of near‐relativistic electrons with respect to deka‐MeV protons. Haggerty and Roelof [] studied 19 electron beam events using Electron, Proton, and Alpha Monitor (EPAM) 38–315 keV data and found that for 11 of the 19 events the arrival of 50–100 MeV protons followed by electrons within ∼3 min.…”