Signatures of solar event at middle and low latitudes in the Europe-African sector, during geomagnetic storms, October 2013

Abstract

International audienceThis paper presents the variability of the total electron content, VTEC, the ROTI index (proxy of the scintillation index) and the transient variations of the Earth's magnetic field associated to the impacts of solar events during October 2013. The observations are from middle and low latitudes in European African longitude sector. During October 2013, there are four solar events reaching the Earth. The two first events, on October 2 and October 8 are CME, the third event on October 14, is a jet of fast solar wind flowing from a solar coronal hole, and the last event on October 30 is a slow solar wind with southward excursions of the Bz component of the Interplanetary magnetic field, associated to CME passing near the Earth. For the four events, the variation of VTEC at middle latitudes is the same and presents an increase of VTEC at the time of the impact followed by a decrease of VTEC, lasting one or several days. At low latitudes, no clear common pattern for all the events appears. For the four events the variation of the ROTI index over Africa is different showing the asymmetry between West and East Africa. For the first event, on October 2, the scintillations are not inhibited, for the second and the fourth events on October 8 and 30, the scintillations are inhibited on East Africa and for the third event (high speed solar wind stream), on October 14, the scintillations are inhibited over the whole Africa. The available data allow the full explanation of the observations of October 14, indeed, on this day, there is no post sunset increase of the virtual height h'F2 at Ascension Island. There is no Pre Reversal Enhancement (PRE) of the eastward electric field; it is this electric field which moves up the F layer, the necessary condition for the existence of scintillation. The analysis of the variations of the Earth's magnetic field at low latitudes highlights the presence of the ionospheric disturbance dynamo on October 14, which produces a decrease of the Equatorial Electrojet, several hours after the impact of the high speed solar wind. The disturbance dynamo electric field (DDEF) is westward during the day and till after sunset and turns eastward around 22.30LT. So, on October 14, the westward DDEF inhibits the eastward regular electric field

The Response of African Equatorial/Low‐Latitude Ionosphere to 2015 St. Patrick's Day Geomagnetic Storm

“…This fortunately coincided with the local time of pre‐PRE over this sector; thus, irregularities that were seen as equatorial spread F with ionosondes and scintillations in GPS receivers were intensified. Azzouzi et al () associated the nonexistence of irregularities during the storm of 14 October 2013 to the absence of the signature of the PRE on the F ‐layer height over Ascension Island. Ngwira et al () linked the absence of irregularities during the main phase of the minor storm of 13–14 September 2004 over the African sector to the negative perturbation in Δ H associated with a CEJ or westward electric field during the local postnoon period.…”

“…In equation (3), STEC is in TECU with 1 TECU = 10 16 electrons/m 3 , t k À t k À 1 is the time difference between successive epoch = 30 s. ROT is converted in TECU/min by multiplying by 60 s (Azzouzi et al, 2015;Zaourar et al, 2017).…”

“…We used the method of Fathy et al (2014) in separating the effect of DP2 signal from Ddyn signal. This entailed using a moving average filter that takes the average value of 4 hr with a sliding of 1 hour (Azzouzi et al, 2015;Fathy et al, 2014).…”

“…This indicated a reversal in Sq current and reversed electrojet as seen in the negative value of ΔH during the noon to postnoon period at low and equatorial latitudes, respectively. The ionospheric disturbance dynamo process had been analyzed by Fathy et al (2014) and Azzouzi et al (2015). The resulting westward DDEF have opposite configuration to the regular day time eastward E × B drift.…”

Inter-hourly variability of Total Electron Content during the quiet condition over Nigeria, within the Equatorial Ionization Anomaly region

“…Many studies were made using GPS derived ionospheric data (Obrou et al, 2009;Ouattara et al, 2012;Bolaji et al, 2012;Bolaji et al, 2013;Oladipo et al, 2014;Bolaji et al, 2015), on the solar cycle and the seasonal behavior of TEC (Moeketsi et al, 2007;Ackah et al, 2011;Zoundi et al, 2012;Shimeis et al, 2014), on magnetic storms Adeniyi et al, 2014;De Abreu et al, 2014;Shimeis et al, 2015;Azzouzi et al, 2015). This paper is the first paper in Africa devoted to the IHV of TEC.…”