No 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.

[1] Space weather studies have increased due to human society dependence on spaceborne and terrestrial infrastructure vulnerable to its effects. In this paper, we present an interdisciplinary study of the effects of solar activity on the Earth's environment; specifically, we focus on the effects on the ionosphere and the geomagnetic field. A timeline of effects occurring on the Earth produced by one of the first relevant events of the present solar cycle (24-25 October 2011) is given. We have analyzed the solar wind shockwave from satellite data, the storm-time development, the ionospheric effects at global and local scales using the National Center for Atmospheric Research Thermosphere-Ionosphere-Electrodynamics General Circulation Model fed with geomagnetic field-aligned current data from the Active Magnetosphere and Planetary Electrodynamics Response Experiment, and ground ionosonde data from both hemispheres, at Ebre Observatory and Port Stanley locations. We have compared observed geomagnetic variations at high latitudes with those modeled by the National Center for Atmospheric Research Thermosphere-Ionosphere-Electrodynamics General Circulation Model. We have analyzed rapid geomagnetic variations (e.g., solar flare effect, storm commencement, Pi2) also on both hemispheres, at Ebre Observatory and Livingston Island locations. Finally, we have estimated geoelectric field and geomagnetically induced currents in the northeast of Spain (Catalonia) produced by this geomagnetic disturbance.

The Service of Rapid Magnetic Variations (RMV) was created by the International Association of Geomagnetism and Aeronomy (IAGA) with the aim of obtaining an overall view of the temporal and spatial distribution of RMV as a base for further study of these phenomena. The Ebro Observatory participated in the creation of this service and has been administering it from the beginning; consequently, the histories of these two organizations are intertwined.