Equatorial plasma bubbles developing around sunrise observed by an all-sky imager and global navigation satellite system network during storm time

Kun Wu,Chao Xiong,Yajun Zhu,Wenbin Wang,Ji Luo,Xinan Yue,Wei Yuan,Chi Wang,Jiyao Xu

doi:10.5194/angeo-38-163-2020

Abstract

Abstract. A large number of studies have shown that equatorial plasma bubbles (EPBs) occur mainly after sunset, and they usually drift eastward. However, in this paper, an unusual EPB event was simultaneously observed by an all-sky imager and the global navigation satellite system (GNSS) network in southern China, during the recovery phase of a geomagnetic storm that happened on 6–8 November 2015. Observations from both techniques show that the EPBs appeared near dawn. Interestingly, the observational results show that the EPBs continued to develop after sunrise, and they disappeared about 1 h after sunrise. The development stage of EPBs lasted for at least about 3 h. To our knowledge, this is the first time that the evolution of EPBs developing around sunrise was observed by an all-sky imager and the GNSS network. Our observation showed that the EPBs drifted westward, which was different from the usual eastward drifts of post-sunset EPBs. The simulation from the Thermosphere–Ionosphere–Electrodynamics General Circulation Model (TIE-GCM) suggest that the westward drift of EPBs should be related to the enhanced westward winds at storm time. Besides this, bifurcation and merging processes of EPBs were observed by the all-sky imager in the event. Associated with the development of EPBs, an increase in the peak height of the ionospheric F region was also observed near sunrise, and we suggest the enhanced upward vertical plasma drift during the geomagnetic storm plays a major role in triggering the EPBs near sunrise.

Highlights

After sunset, plasma density depletions, called equatorial plasma bubbles (EPBs), sometime occur in the equatorial- and low-latitude ionosphere
Some of the results showed that geomagnetic storms can affect the development of EPBs (e.g., Abdu et al, 2003; Tulasi et al, 2008; Carter et al, 2016), and in some extreme cases, the EPBs can extend to middle latitudes during intense geomagnetic storms (e.g., Sahai et al, 2009; Patra et al, 2016; Katamzi-Joseph et al, 2017; Aa et al, 2018)
Santos et al (2016) showed some EPBs of zonal drifts reversal during a geomagnetic storm, and they suggested the reversal was caused by a vertical Hall electric field which was induced by a zonal prompt penetration electric field (PPEF) in the presence of enhanced conductivity in the E region during night

Summary

Introduction

Plasma density depletions, called equatorial plasma bubbles (EPBs), sometime occur in the equatorial- and low-latitude ionosphere. During storm time, EPBs near sunrise were occasionally observed by some instruments such as radar and satellite. During storm periods westward-drifting EPBs have been observed (Abdu et al, 2003; Basu et al, 2010; Santos et al, 2016). Abdu et al (2003) reported some cases of EPBs that showed eastward drifts after sunset which later reversed to westward drifts. Santos et al (2016) showed some EPBs of zonal drifts reversal (eastward to westward) during a geomagnetic storm, and they suggested the reversal was caused by a vertical Hall electric field which was induced by a zonal prompt penetration electric field (PPEF) in the presence of enhanced conductivity in the E region during night.

All-sky imager

Digisonde

Observations and results

Discussion

Summary