Abstract
Abstract. We have analyzed low-latitude ionospheric current responses to two intense (X-class) solar flares that occurred on 13 May 2013 and 11 March 2015. Sudden intensifications, in response to solar flare radiation impulses, in the Sq and equatorial electrojet (EEJ) currents, as detected by magnetometers over equatorial and low-latitude sites in South America, are studied. In particular we show for the first time that a 5 to 8 min time delay is present in the peak effect in the EEJ, with respect that of Sq current outside the magnetic equator, in response to the flare radiation enhancement. The Sq current intensification peaks close to the flare X-ray peak, while the EEJ peak occurs 5 to 8 min later. We have used the Sheffield University Plasmasphere-Ionosphere Model at National Institute for Space Research (SUPIM-INPE) to simulate the E-region conductivity enhancement as caused by the flare enhanced solar extreme ultraviolet (EUV) and soft X-rays flux. We propose that the flare-induced enhancement in neutral wind occurring with a time delay (with respect to the flare radiation) could be responsible for a delayed zonal electric field disturbance driving the EEJ, in which the Cowling conductivity offers enhanced sensitivity to the driving zonal electric field. Keywords. Ionosphere (equatorial ionosphere)
Highlights
During a solar flare event, a great enhancement in extreme ultraviolet (EUV) and X-ray radiation causes sudden and intense disturbances in the Earth’s upper atmosphere
We analyze the responses of the ionospheric current system during two solar flare events that occurred near midday on 13 May 2013 and 11 March 2015; both events occur during geomagnetic quiet days
Simultaneous variations in the horizontal components of the Earth’s magnetic field as measured by a number of magnetometers in South America are shown in the following successive panels
Summary
During a solar flare event, a great enhancement in extreme ultraviolet (EUV) and X-ray radiation causes sudden and intense disturbances in the Earth’s upper atmosphere. These disturbances are observed in the form of sudden increases in the ionospheric electron density in the D, E and F regions, reflecting in the ionospheric currents (Curto et al 1994a, b, Xiong et al, 2011; Tsurutani et al, 2005; Manju et al, 2009; Nogueira et al, 2015; Abdu et al, 2017). The solar flare of 13 May 2013 was classified as an X2.8 class event (the intensity peaking at 16:05 UT), and the solar flare of Published by Copernicus Publications on behalf of the European Geosciences Union
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