Generation Mechanisms of Plasma Density Irregularity in the Equatorial Ionosphere During a Geomagnetic Storm on 21–22 December 2014

Abstract

The equatorial ionosphere endured plasma density irregularities during a geomagnetic storm on 21–22 December 2014. To understand the underlying mechanism, we analyzed the rate of the total electron content change (ROTI) data obtained from a global navigation satellite system, along with solar wind, interplanetary magnetic field (IMF), geomagnetic indices, Jicamarca incoherent scatter radar, and magnetometer data. The results indicate that the ROTI enhancement related to plasma density irregularities (plasma bubbles) occurred three times in the equatorial and low latitude regions of the American sector during the geomagnetic storm. The first, second, and third enhancements which have a longitudinal extent of ∼20° appeared in the post‐sunset, pre‐midnight, and post‐midnight sectors, respectively. The second enhancement occurred during the recovery phase of the storm‐time substorm even though the IMF remained southward. During this period, the direction of the dayside equatorial electrojet (EEJ) changed from eastward to westward, while the nightside upward plasma velocity at Jicamarca increased to 28.8 m/s. The response of the EEJ and upward ion drift implies that the westward and eastward electric fields were intensified on the dayside and nightside, respectively. Therefore, these results suggest that an over‐shielding electric field penetrates the dayside/nightside equator simultaneously in association with a substorm recovery phase, and that the electric field generates plasma bubbles by the Rayleigh‐Taylor instability mechanism. Plasma bubbles induced by the penetration of an over‐shielding electric field due to substorm activity have not previously been reported.

First Observations of Equatorial Ionospheric Electric Fields Driven by Storm‐Time Rapidly Recurrent Magnetospheric Substorms

“…This is also the case for electric fields driven by enhanced high latitude convection. Over the last few years, several new studies (e.g., Hashimoto et al., 2017; Hui et al., 2017; Sori et al., 2022) examined in more detail the role of magnetospheric substorms as drivers of low latitude ionospheric electric field and currents. Veendhari et al.…”

“…This is also the case for electric fields driven by enhanced high latitude convection. Over the last few years, several new studies (e.g., Hashimoto et al, 2017;Hui et al, 2017;Sori et al, 2022) examined in more detail the role of magnetospheric substorms as drivers of low latitude ionospheric electric field and currents. Veendhari et al (2019) discussed observations of day side equatorial counter electrojets (indicative of westward penetration electric fields) over the Indian and Japanese sectors during steady southward IMF Bz periods.…”

First Detection of Midlatitude Plasma Bubble by SuperDARN During a Geomagnetic Storm on May 27 and 28, 2017

“…Following by Sori, Shinbori, et al. (2022), EEJ values are defined by: $$$\mathrm{E}\mathrm{E}\mathrm{J}={X}_{\mathrm{H}\mathrm{U}\mathrm{A}}^{\prime }-\left(\frac{{X}_{\mathrm{P}\mathrm{I}\mathrm{L}}^{\prime }}{\mathrm{cos}\,{\theta }_{\mathrm{P}\mathrm{I}\mathrm{L}}}\right)\mathrm{cos}\,{\theta }_{\mathrm{H}\mathrm{U}\mathrm{A}}$$$ …”

“…Plasma bubbles contain plasma density irregularities (Booker & Wells, 1938; Woodman & La Hoz, 1976) and have field‐aligned structures connecting the Northern and Southern Hemispheres (Martinis & Mendillo, 2007; Otsuka et al., 2002; Tsunoda, 1980a). There are many studies conducted on plasma bubbles using ionosondes (Abdu et al., 2003), all‐sky imagers (Otsuka et al., 2002; Martinis & Mendillo, 2007), VHF radars (Ajith et al., 2015; de Paula et al., 2019; Saito et al., 2008; Tulasi Ram et al., 2008, 2017; Woodman & La Hoz, 1976), and global navigation satellite system (GNSS) networks (Cherniak & Zakharenkova, 2016; Li et al., 2018; Ma & Maruyama, 2006; Otsuka et al., 2021; Sori, Shinbori, et al., 2022; Sori, Otsuka, et al., 2022; Valladares et al., 2004).…”

Multi-process driven unusually large equatorial perturbation electric fields during the April 2023 geomagnetic storm

“…Prompt penetration and disturbance electric fields have long been known to significantly affect the generation and evolution of equatorial nighttime F-region plasma irregularities by changing the instability growth rate (e.g., Rastogi et al, 1978;Fejer et al, 1999;Abdu, 2012). Substorms were recently shown to cause strong structuring on equatorial spread F (e.g., Fejer et al, 2021;Sori et al, 2022;Sousasantos et al, 2023). Storm-time ionospheric electric field also have major effects on the temporal and spatial variation of ionospheric plasma from auroral to equatorial latitudes (e.g., Astafyeva et al, 2016;Aa et al, 2018).…”