Analysis of the Solar Flare Effects of 6 September 2017 in the Ionosphere and in the Earth's Magnetic Field Using Spherical Elementary Current Systems

Abstract

The interval 4-10 September 2017 was one of the most flare-productive periods of the solar cycle 24, producing strong-to-severe space weather episodes. Thus, on 6 September, the solar active region AR 30023 produced an X-9 level flare. The arrival of the associated coronal mass ejection produced severe geomagnetic storming on 7 and 8 September, preceded by two significant solar flare effects (Sfe) that could be seen in the lit hemisphere. In this article, we analyze the impact of these flares on the ionosphere as registered on the vertical incidence ionospheric sounder located at Ebre Observatory. We put the emphasis on the use of this instrument to detect solar flares by means of the absorption observed in its ionograms. We also analyze the impacts of these flares on the Earth's magnetic field and the temporal evolution of the second Sfe event using the technique of spherical elementary current systems, which allows tracing in detail the current system evolution during the Sfe lifetime. As expected, a sharp increase in current intensities occurred at the beginning. The peak of the disturbance was reached after a few minutes, when hard X-rays were dominant, while a slow decay followed the advent of soft X-rays and EUV rays. The modeled current systems appear abnormally displaced in longitude with respect to the subsolar point. The northern vortex shows up about 2 hr in advance of the subsolar point meridian, while the southern vortex is about 3 hr behind it. Both remain static, showing no significant shift over the whole episode. Although the event occurred during the equinox, a clear prevalence of the Northern Hemisphere was observed.Tracing the temporal evolution of the currents producing Sfe was already attempted by some authors (Van Sabben, 1961;Veldkamp & van Sabben, 1960). With a limited number of observatories, they only achieved CURTO ET AL.

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