Persistent Eastward EEJ Enhancement During the Geomagnetic Storm Recovery Phases

Abstract

Recent case studies disclosed that sometimes the dayside ionospheric equatorial electric field underwent persistent long‐duration (>4 hr) eastward enhancements during geomagnetic storm recovery phases, rather than anticipated decrease or reversal. However, it is still unknown the occurrence and morphology of the persistent enhancement as well as its impact on the low‐latitude ionospheric plasma distribution. For the first time, we examined the issue with superposed epoch analyses of equatorial electrojet (EEJ) and GNSS total electron content (TEC) responses in the American (49°W) and Indian (78°E) sectors. The occurrence rates of the persistent enhancement during storm recovery phases are more than 30%, with higher occurrence rates in second to fourth days of the recovery phase, equinoxes, and American sector. The corresponding averaged EEJ and TEC responses were disclosed and compared with those storm samples without the persistent enhancement. On the first day of recovery phase, the dayside equatorial ionosphere was dominated by the prevalent westward electric field and causative inhibited equatorial fountain. In contrast, after the first day, the dayside morphologies showed different patterns: (a) for the persistent cases, the large eastward EEJ and TEC enhancement indicated the enhanced eastward electric field at forenoon and causative intensified equatorial fountain. (b) For the storms without the persistent cases, the general westward EEJ and equatorial TEC enhancements were dominated. Our study indicates that dayside eastward enhancement is an important disturbed pattern of equatorial ionospheric electric field during the late recovery phases, and the enhancement generally causes the intensification of equatorial ionization anomaly.

Different Response of the Ionospheric TEC and EEJ to Ultra‐Fast Kelvin Waves in the Mesosphere and Lower Thermosphere

“…Seen from Figure 6b, the EIA is not only asymmetrical, but also the peak position is shifted in latitude. Magnetic storms (Dst < −50 nT) can have an impact on the EEJ (Li et al., 2022). It means EEJ may be affected to some extent during this period.…”

Anomalous Disturbance of the Ionosphere in the East Asia Region During the Geomagnetically Quiet Day on 1 November 2016

“…In the daytime, the zonal electric fields generated by neutral winds through the dynamo process map to the F region along magnetic field lines and subsequently produce vertical plasma drifts. When poleward meridional winds or westward zonal winds in the E region increase, the zonal electric field enhances through the ionospheric E region dynamo, increasing in the eastward EEF, thus intensifying the equatorial ionospheric fountain effect (Lei et al., 2018; Li et al., 2022; Xiong et al., 2022). Tidal winds from the lower atmosphere drive the E region dynamo and mainly control the daytime electric fields (Ren et al., 2010).…”

A Case Study of Ionospheric Storm‐Time Altitudinal Differences at Low Latitudes During the May 2021 Geomagnetic Storm

“…Lei et al (2018) pointed out that the lower atmospheric forcing may be one of the factors driving the TEC changes during the recovery phase of the September 2017 storm. Not coincidentally, Li et al (2022) similarly noted that the influences of lower atmospheric sources cannot be excluded in the study of persistent eastward EEJ enhancements during the recovery phase of geomagnetic storms. More observational data and model calculations are needed to further analyze the effects of driving sources on the opposite hmF2/NmF2 variations during both the storms and the quiet periods in the future.…”