Model-based reproduction and validation of the total spectrum of solar flare and their impact on the global environment at the X9.3 event of September 6, 2017

Abstract

We tried to reproduce the total electron content (TEC) variation in the Earth's atmosphere from the temporal variation of the solar flare spectrum of the X9.3 flare on September 6, 2017. The flare spectrum of the Flare Irradiance Spectral Model (FISM) which is most widely used and the flare spectrum from the 1D hydrodynamic model which considers the physics of plasma in the flare loop are used in the GAIA model which is a simulation model of the Earth's whole atmosphere and ionosphere, and calculate the difference of TEC. And then, we compared these results with the observed TEC. When we used the FISM flare spectrum, difference of TEC from the background was in a good agreement with the observation. On the other hand, when the flare spectrum of the 1D-hydro model was used, the result varied depending on the presence or absence of the background. This difference which depends on the models is thought to represent which EUV radiation is primarily responsible for increasing TEC. From the flare spectrum obtained from these models and the calculation result of TEC fluctuation using GAIA, it is considered that the enhancement in EUV emission about 15 to 35 nm is mainly contributes to increasing TEC rather than that of X-ray emission that has been thought to be mainly responsible for sudden ionospheric disturbance (SID). Also, from the altitude/wavelength distribution of the ionization rate of Earth's atmosphere by GAIA, it was found that EUV radiation of about 15–35 nm affects a wide altitude range of 120–300 km, and TEC enhancement is mainly caused by ionization of nitrogen molecules. (265 words)