Longitudinal Responses of the Equatorial/Low‐Latitude Ionosphere Over the Oceanic Regions to Geomagnetic Storms of May and September 2017

Abstract

This study presents the longitudinal dependence of responses of the equatorial/low‐latitude ionosphere over the oceanic regions to geomagnetic storms of 28 May and 8 September 2017. We investigated the interplanetary origins of the storms. Total electron content (TEC) data were obtained from Global Navigation Satellite System stations, located around the oceanic areas in the equatorial/low‐latitude regions. The Rate of change of TEC Index (ROTI) was used as a proxy for ionospheric irregularities over the study locations. Further, variations of the horizontal component of the Earth's magnetic fields, obtained from ground‐based magnetometers were studied. We used ionospheric disturbance currents, polar cap and auroral electrojet indices to monitor the storm time electric fields. The May 2017 storm was driven by sheath and magnetic cloud fields, while the September 2017 storm was driven by sheath fields. We observed a comparative dominance of TEC intensities over the Oceans than over the landlocked areas. Empirically, our results validated a theoretical suggestion of the existence of a dynamic ocean‐ionosphere coupling made by Godin et al. (2015, http://10.0.4.162/s40623-015-0212-4). Prompt Penetration Electric Fields (PPEF) was observed to be a key factor that controls TEC responses to storms. PPEFs caused TEC enhancements, mainly over the Pacific Ocean longitudes during the May 2017 storm and enhanced TEC over the Atlantic Ocean and the Pacific Oceans longitudes during the September 2017 storm. These PPEFs triggered irregularities over the Pacific Ocean longitudes, particularly during the main phase of May 2017 storm. Irregularities were generally inhibited by the September 2017 storm.

Solar Origins of August 26, 2018 Geomagnetic Storm: Responses of the Interplanetary Medium and Equatorial/Low‐Latitude Ionosphere to the Storm

“…The SYMmetric Horizontal magnetic field (SYM-H) index data were used to compute ionospheric electric current disturbance (Diono). Detailed methodology for determining Diono is thoroughly presented by Akala et al (2020). Over the middle-latitude and low-latitude regions, Diono is the sum of DP2 and Ddyn (Le Huy & Amory- Mazaudier, 2005).…”

“…At the equatorial/low-latitude region, during geomagnetic storms, when IMF Bz is southward, PPEFs are eastward during the local daytime. The eastward orientation of the PPEFs intensifies ionospheric forward plasma fountain (Fagundes et al, 2016;Huang et al, 2005;Kikuchi et al, 2008), while the westward orientation of the PPEF drives a reverse fountain (Akala et al, 2020), causing reduction in ionospheric plasma density around the EIA crest and subsequent equator-ward movement of the EIA crests (Narayanan et al, 2013). In the dayside equatorial ionosphere, E × B drift due to strong eastward PPEF drives plasma upward so fast that it cannot recombine (Balan et al, 2018).…”

Interplanetary Origins of Some Intense Geomagnetic Storms During Solar Cycle 24 and the Responses of African Equatorial/Low‐Latitude Ionosphere to Them

“…During nighttime hours, plasma density ionization around the EIA change direction due to westward orientation of PPEF, during southward turning of IMF, causing plasma to move equator-ward and build up at locations around the magnetic equator (A. O. Akala et al, 2020;Fagundes et al, 2016). where TEC responded positively to the later part of the main phase of the storm.…”

“…The eastward orientation of PPEF intensifies ionospheric forward plasma fountain (Fagundes et al, 2016;Huang et al, 2005;Kikuchi et al, 2008), while the westward orientation of PPEF drives a reverse fountain (A. O. Akala et al, 2020), causing reduction in ionospheric plasma density around the EIA crest and subsequent equator-ward movement of the EIA crests (Narayanan et al, 2013). Previously, in the African sector, Adewale et al (2011) studied the responses of African low-latitude ionosphere to geomagnetic storms during 2000-2007 at Libreville, Gabon.…”

Ground‐Based GNSS and C/NOFS Observations of Ionospheric Irregularities Over Africa: A Case Study of the 2013 St. Patrick’s Day Geomagnetic Storm

“…The formation of EPBs can be significantly altered during geomagnetic storm mostly by the Prompt Penetration Electric Field (PPEF) (Nishida et al., 1966), the disturbance dynamo electric field (DDEF) (Blanc & Richmond, 1980) and trans‐equatorial neutral wind (Maruyama & Matuura, 1984; Mendillo et al., 1992). For example, the regular pre‐reversal enhancement (PRE) in the vertical E × B drift which is responsible for the uplift of the equatorial F‐layer can be enhanced (reduced) by eastward (westward) PPEF (DDEF) in the postsunset period thereby, promoting the generation (inhibition) of EPBs (A. O. Akala et al., 2020; Amaechi et al, 2020a; Bhattacharyya et al., 2019; Dungey, 1956; B. J. Fejer et al., 1999; X. Luo et al., 2019; Tulasi Ram et al., 2006; Whalen, 2002).…”