On some features of the solar proton event on 2021 October 28 – GLE73

I.M. Chertok

Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation (IZMIRAN), Troitsk, Moscow, Russia

MNRAS   Volume 517, Issue 2, Pages 2709–2713,     2022

Abstract.  In addition to several recent articles devoted to the rare event of ground-level enhancement of the solar relativistic proton flux observed on 2021 October 28 – GLE73, we study the 10–100 MeV solar energetic particle (SEP) component of this event. Based on the GOES satellite data for 26 GLEs recorded since 1986, we have formed a scatter plot displaying the ratio of the peak fluxes of the >10 MeV (J10 ) and >100 MeV (J100 ) protons and their energy spectra. Two extreme characteristics of the prompt component of the SEP–GLE73 event were revealed: (1) very small J10 and J100 proton fluxes and (2) a very hard energetic spectrum in the 10–100 MeV range. There are only two events with these characteristics similar to SEP–GLE73 namely, GLE40 (1989 July 25) and GLE46 (1989 November 15). A correspondence was demonstrated between the hard frequency spectrum of microwave radio bursts of initiating flares and the hard SEP energy spectrum of these two and other GLEs. These results suggest that the flare magnetic reconnection both in the impulsive and post-eruption phases plays an important role in the acceleration of the SEP–GLE protons.

 Figure 1. Time profiles of the GOES-16 proton fluxes with E > 10, 50, and 100 MeV.  The prompt SEP component is marked with a vertical arrow.


Table 1. Parameters of the prompt component of the >10 MeV and >100 MeV proton fluxes in GLEs under consideration.


Figure 2. Scatter of the western GLEs observed in Cycles 22–25 on the J10J100 proton flux plane. Numbers indicate the generally accepted GLE numbers (see Table 1). Red square belongs
to SEP–GLE73. The blue lines correspond to the specified power-low spectral indexes γ in the energy range of 10–100 MeV.


Figure 3. Frequency spectra of radio bursts of the GLE events with the hard (panel a) and relatively soft (b) SEP energy spectra in the 10–100 MeV range. The indicated numbers correspond to the GLE numbers presented in Fig. 2 and Table 1. The incomplete available data of GLE73 are shown on panel a.


PDF file        MNRAS   Volume 517, Issue 2, Pages 2709–2713,     2022





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