Retrospective analysis of GLEs and estimates of radiation risks

Abstract

28 February 2017 marked 75 years since the first confident registration of solar cosmic rays (SCRs), i.e., accelerated solar particles with energies from about 106 to ~1010 ÷ 1011 eV. Modern state of the problems related to the studies of Ground Level Enhancements (GLEs) of relativistic SCRs is critically analyzed based on available direct and proxy data. We are also taking into account extremely large fluxes of non-relativistic solar energetic particles (SEPs). Both kinds of SCR events are of great astrophysical and geo-scientific (geophysical) interests. A number of the GLE properties (total statistics, occurrence rate, longitude distribution, ranking of GLEs, a number of specific GLEs – so-called “rogue” SEP events etc.) are discussed in some detail. We note also the problems of GLE identification (definition) by ground-based observations, the difficulties in the studies of weak (“hidden”, or sub-) GLEs etc. One of serious challenges to the problem of radiation hazard in space is a lack of a clear, unambiguous relation between the fluxes (fluences) of relativistic SCR and non-relativistic SEPs. Special attention is paid to the recent debate on the validity, origin and properties of the “ancient” events AD775, AD994, AD1859 (Carrington event) and BC3372. We demonstrate that, in spite of existing uncertainties in proton fluences above 30 MeV, all of them are fitted well by a unique distribution function, at least, with the present level of solar activity. Extremely large SEP events are shown to obey a probabilistic distribution on their fluences with a sharp break in the range of large fluences (or low probabilities). The studies of this kind may be extended for periods with different levels of solar activity in the past and/or in the future. Dose rates at aircraft altitudes are also demonstrated during some GLEs. Several examples of using the SCR data and GLE properties in radiation prediction schemes are considered.

Revised GLE database: Fluences of solar energetic particles as measured by the neutron-monitor network since 1956

“…Event-integrated fluences of SEP and their energy and rigidity spectra are needed when the accumulated effects of the SEP events are assessed, such as radiation doses, atmospheric ionisation and related atmospheric response, and production of cosmogenic isotopes (e.g. Pavlov et al 2014;Oh et al 2012;Duderstadt et al 2016;Melott et al 2016;Jiggens et al 2018;Miroshnichenko 2018;Herbst et al 2020). The first systematic effort to estimate the SEP event-integrated omnidirectional fluence 7 F(>R), where R is the proton rigidity (momentum per charge) was made by Tylka & Dietrich (2009) (updated as Raukunen et al 2018) for GLE events 5 through 71 using NM count rates.…”

Revisiting the cosmic-ray induced Venusian ionization with the Atmospheric Radiation Interaction Simulator (AtRIS)

“…However, because of particle acceleration and transport mechanisms, the energy spectrum of such events is temporally and spatially variable. Although remarkable efforts revealing the temporal evolution of SEP events can be found in literature (see, e.g., Belov et al 2005;Bombardieri et al 2007;Plainaki et al 2007;Matthiä et al 2009;Miroshnichenko 2018;and references therein) to model the atmospheric effects induced by solar energetic particles often a mean energy spectrum is used.…”

Ionization effect in the Earth’s atmosphere during the sequence of October–November 2003 Halloween GLE events

“…The presented here computation of ionization effect during the sequence of three Halloween events give good basis to study the possible effect of precipitating high-energy particles in the Earth's atmosphere on a minor constituents, atmospheric physics and chemistry as well as studies related to space weather and solar-terrestrial physics (Miroshnichenko, 2003;Mishev and Velinov, 2015b;Miroshnichenko, 2018).…”