GLE analysis

Application of the updated NM yield function and GLE database for an improved GLE analysis

A. Mishev, I. Usoskin, S. Koldobsky, G. Kovaltsov, L. Kocharov

Systematic studies of solar energetic particles (SEPs) provide an important basis to understand their acceleration and propagation in the interplanetary space. During solar eruptive processes, solar ions can be are accelerated to high energy. In majority of cases, the maximum energy of accelerated solar ions is several tens of MeV/nucleon, but in some cases, it exceeds 100 MeV/nucleon or even reaches a GeV/nucleon range. In this case, the energy is high enough, so that solar ions can generate an atmospheric cascade in the Earth's atmosphere, where secondary particles reach the ground, being eventually registered by ground-based detectors, specifically neutron monitors (NMs). Such events form a special class of SEP events known as ground-level enhancements (GLEs). Several methods for the analysis of GLEs, using neutron monitor data have been developed over the years. Here, we discuss a method for derivation of the spectral and angular characteristics of the GLEs using data from the world-wide NM network, namely by modeling the global NM network response with the new verified yield function computed for different atmospheric depths using records from the updated GLE database. The method is based on consecutive steps, including detailed computation of asymptotic cones and rigidity cut-off of each station used in the analysis and optimization of the global NM network response over experimental and modeled count rate increases. The method is compared with other methods, including in-situ measurements. A very good agreement between our method and space-borne measurements by the PAMELA space mission, specifically the derived fluence of solar protons during GLE 71 was achieved, providing a verification of the method is performed. Several issues of GLE analysis and possible applications are discussed.


Reconstruction of SEP fluences during GLE events: description of the new method and its application to the data

S. Koldobskiy(1,2), I. Usoskin(2,3), G. Kovaltsov(4), A. MIshev(2), A. Gil(5)
(1) National Research Nuclear University MEPhI, Moscow, Russia
(2) Space Physics and Astronomy Research Unit, University of Oulu, Finland
(3) Sodankyla Geophysical Observatory, University of Oulu, Finland
(4) Ioffe Physical-Technical Institute, St. Petersburg, Russia
(5) Space Research Center, Polish Academy of Sciences, Warsaw, Poland
(6) Institute ofMathematics, Siedlce University, Siedlce, Poland

During solar eruptive events, such as solar flares and coronal mass ejections, charged particle can be accelerated from the vicinity of the Sun into the heliosphere. These particles are known as solar energetic particles (SEPs). When SEPs reach Earth, they can be registered using satellite experiments. At present, there is the AMS-02 experiment, which can be used for registration of high-energy SEP fluxes. But from the historical perspective, the only instruments that allow us to get information about SEP events over a long-term period, are neutron monitors. They register the products of SEP interaction with nuclei of atmospheric gases, if the rigidity of incoming SEP is above 1 GV. Such events are called ground level enhancements (GLE). Up to date, we know 72 GLE events (
One way of GLE data representation is the reconstruction of the integral SEP fluence, which can be used in several applications, such as the study of radiation hazards, ionization of the atmosphere, etc. Here we present a new reconstruction of GLE fluences, which is based on NM yield function, updated and cross-calibrated with PAMELA and AMS-02 experiments, and a new method of non-parametric analysis of GLE data.


SEP spectra derived from neutron monitor data and from EPHIN space detector data during recent GLEs and sub-GLEs

R. Bütikofer 1, P. Kühl 2, A. Papaioannou 3,4
1 Physikalisches Institut, University of Bern, Switzerland
2 CAU, Kiel, Germany
3 IAASARS, National Observatory of Athens, Penteli, Greece
4 Nuclear and Particle Physics Department, Faculty of Physics, National and Kapodistrian University of Athens, Athens, Greece

The Electron Proton Helium Instrument (EPHIN) aboard the Solar Heliospheric Observatory (SOHO) observed several SEP events with protons accelerated to energies >500 MeV, whereas no neutron monitor (NM) of the worldwide network showed a significant increase in the counting rate. For instance the SEP event on 9 November 2000 with maximum proton intensity at 500 MeV of >0.1 (cm^2 s sr MeV)^-1 is outstanding, as this maximum proton flux is comparable with the GLEs on 14 July 2000 (max. NM increase in 5-min data of almost 60% at the South Pole NM) and on 15 April 2001 (max. NM increase in 5-min data of 225% at the South Pole NM). In a first step we executed a forward modelling of the SEP event on 9 November 2000, i.e. we computed the expected NM count rate increases for selected stations, utilizing as input parameter the SEP spectra determined from EPHIN data. However, we were not able to model any NM count rate increase during this SEP, particularly at high latitude and high altitude NM stations. Therefore, in a next step, we investigated recent GLEs and sub-GLEs. For four selected SEP events we made on the one hand a GLE analysis based on the data of the worldwide network of NMs and on the other hand again a forward modelling. In this work, we will show, if the SEP spectra during the selected GLEs and sub-GLEs as determined from EPHIN measurements agree with the results obtained from NM data in this investigation as well as presented in other publications. In addition, we will discuss the outcome of these investigations and what those may imply for the SEP characteristics of the event on 9 November 2000.


Relativistic solar particle events, pion decay gamma rays, and magnetic connectivity

Karl-Ludwig Klein, Observatoire de Paris

Relativistic solar particle events detected by neutron monitors come preferentially from activity in the western solar hemisphere, but may also come from eruptions in the eastern hemisphere or from behind the solar limb. This can in principle be explained by transient interplanetary magnetic field configurations that differ from the nominal Parker spiral, especially when the heliosphere has been perturbed by numerous successive CMEs (S. Masson et al. 2012 A&A). In this contribution an attempt will be reported to use the radio emission of electrons (type III bursts) as a tracer of magnetic connectivity. A type III burst is electromagnetic emission from electron beams. At low frequencies it is observed down to the electron plasma frequency at the spacecraft, together with locally generated Langmuir waves, when the electron beams intercept the spacecraft. When the beams travel far from the spacecraft, a clear gap is observed between the low-frequency limit of the electromagnetic emission and the local plasma frequency. This feature will be applied here to GLEs, in order to confirm their magnetic connection to the Earth and to discuss the significance for identifying the acceleration region.