Powerful Solar Flares of 2017 September: Correspondence between Parameters of Microwave Bursts and Proton Fluxes near Earth

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. The GOES time history of proton fluxes of September 4–12, 2017 and frequency spectra of the associated radio bursts.

PDF file Research Notes of the American Astronomical Society. V. 2. Id. 20. 2018. DOI:

10.3847/2515-5172/aaaab7

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