Study of the Equatorial and Low‐Latitude Electrodynamic and Ionospheric Disturbances During the 22–23 June 2015 Geomagnetic Storm Using Ground‐Based and Spaceborne Techniques

Abstract

We use a set of ground‐based instruments (Global Positioning System receivers, ionosondes, magnetometers) along with data of multiple satellite missions (Swarm, C/NOFS, DMSP, GUVI) to analyze the equatorial and low‐latitude electrodynamic and ionospheric disturbances caused by the geomagnetic storm of 22–23 June 2015, which is the second largest storm in the current solar cycle. Our results show that at the beginning of the storm, the equatorial electrojet (EEJ) and the equatorial zonal electric fields were largely impacted by the prompt penetration electric fields (PPEF). The PPEF were first directed eastward and caused significant ionospheric uplift and positive ionospheric storm on the dayside, and downward drift on the nightside. Furthermore, about 45 min after the storm commencement, the interplanetary magnetic field (IMF) Bz component turned northward, leading to the EEJ changing sign to westward, and to overall decrease of the vertical total electron content (VTEC) and electron density on the dayside. At the end of the main phase of the storm, and with the second long‐term IMF Bz southward turn, we observed several oscillations of the EEJ, which led us to conclude that at this stage of the storm, the disturbance dynamo effect was already in effect, competing with the PPEF and reducing it. Our analysis showed no significant upward or downward plasma motion during this period of time; however, the electron density and the VTEC drastically increased on the dayside (over the Asian region). We show that this second positive storm was largely influenced by the disturbed thermospheric conditions.

Dynamic Response of Ionospheric Plasma Density to the Geomagnetic Storm of 22‐23 June 2015

“…AMBER (Yizengaw & Moldwin, 2009) and LISN (Valladares & Chau, 2012) data were used to derive the EEJ for American (station pair PUER-LETI, Puerto Maldonado and Leticia) and Asian (BANG-PUKT, Bangkok and Phuket) sectors, respectively, as described in the previous section. Furthermore, the E × B drift variations shown in the present study for both American and Asian sectors are well correlated with C/NOFS vertical plasma drift and SWARM EEJ in situ satellite measurements (see Astafyeva et al, 2018, for comparison). Figure 3a clearly demonstrates that after Shock S3 the dayside American sector experienced a rapid enhancement of the E×B drift increasing from −3 m/s starting at about 18:36 UT (13:20 LT) to a peak value of 28 m/s at about 18:42 UT (13:26 LT).…”

“…In the Asian sector (Figure 3b), daytime E × B drift was characterized by several upward and downward oscillations between 01:00-11:00 UT. These oscillations are considered to be the competing effect between PPEFs and the disturbance dynamo effect (Astafyeva et al, 2018). Downward (negative) drifts can move the ionospheric plasma to lower altitudes where recombination rates are higher resulting in reduced TEC.…”

“…Understanding the basic geophysical processes that pertain to divergent storm features is one of the priority areas of ionospheric physics (including, Astafyeva et al, 2018;Crowley, Emery, Roble, Carlson, Salah, et al, 1989;Mendillo, 2006;Ngwira, McKinnell, Cilliers, & Coster, 2012;Ngwira & Coster, 2017;Yizengaw et al, 2005, and references therein). Understanding the basic geophysical processes that pertain to divergent storm features is one of the priority areas of ionospheric physics (including, Astafyeva et al, 2018;Crowley, Emery, Roble, Carlson, Salah, et al, 1989;Mendillo, 2006;Ngwira, McKinnell, Cilliers, & Coster, 2012;Ngwira & Coster, 2017;Yizengaw et al, 2005, and references therein).…”

“…In another study of the June 2015 storm, Astafyeva et al (2017) investigated the global ionospheric and thermospheric response. More recently, Astafyeva et al (2018) performed a global evaluation of equatorial and low-latitude effects for 22-23 June and revealed that the equatorial electrojet (EEJ) and equatorial zonal electric fields were strongly disturbed by PPEFs at the beginning of the storm (22 June) but the enhanced electron density during the main phase on 23 June was largely due to disturbed thermospheric conditions. Similarly, Singh and Sripathi (2017), using ground-based ionosondes and GPS (Global Positioning System) receivers over India, found that after the storm commencement on 22 June, plasma bubbles were suppressed in the Indian sector in contrast to the European sector.…”

“…Storm time disturbances in the ionosphere can lead to production of positive (increase) and/or negative (decrease) electron density structures. Understanding the basic geophysical processes that pertain to divergent storm features is one of the priority areas of ionospheric physics (including, Astafyeva et al, 2018;Crowley, Emery, Roble, Carlson, Salah, et al, 1989;Mendillo, 2006;Ngwira, McKinnell, Cilliers, & Coster, 2012;Ngwira & Coster, 2017;Yizengaw et al, 2005, and references therein). There is a consensus within the ionospheric community that negative storms are caused by the movement of neutral composition changes (e.g., Crowley, Emery, Roble, Carlson, & Knipp, 1989;Fuller-Rowell et al, 1996;Yizengaw et al, 2005).…”