Diagnostic Analysis of the Solar Proton Flares of September 2017 by Their Radio Bursts

I.M. Chertok

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

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Abstract.  The powerful flares that occurred in the Sun on September 4–10, 2017 are analyzed on the basis of the technique for the quantitative diagnostics of proton flares developed in IZMIRAN in 1970–1980s. It is shown that the fluxes and energy spectra of protons with energy of tens of MeV coming to Earth qualitatively and quantitatively correspond to the intensity and frequency spectra of microwave radio bursts in the range 2.7–15.4 GHz. In particular, the flare of 4 Sept. with a peak radio flux S ~ 2000 sfu at the frequency f ~ 3 GHz (i.e., with a soft radio spectrum) was accompanied by a significant proton flux J (> 10 MeV) ~ 100 pfu and soft energy spectrum with the exponent γ ~ 3.0, and the powerful flare of 10 Sept. with S ~ 21000 sfu at f ~ 15 GHz (i.e., with a hard radio spectrum) led to a very intense proton event with J (> 10 MeV) ~ 1000 pfu with a hard energy spectrum (γ ~ 1.4), including a ground level enhancement (GLE72). This is further evidence that data on microwave radio bursts can be successfully used to diagnose proton flares, regardless of the particular source of acceleration of particles on the Sun.

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Figure 1. Time profiles of the soft X-ray emission (a) and the proton fluxes (b) according to the data of the GOES satellites on September 4–12, 2017.

Figure 2. Frequency spectra of radio bursts related to the three proton events under consideration.

PDF file  Geomagnetism and Aeronomy, 2018, Vol. 58, No. 4, pp. 457–463. DOI:

10.1134/S0016793218040035

Original Russian Text: Geomagnetizm i Aeronomiya, 2018, Vol. 58, No. 4, pp. 471–478.

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