Freshly Developed Low-Latitude Postmidnight-To-Dawn F-Region Ionospheric Irregularities Over China on 13 November 2015

In this study, the evolutional features and underlying driving mechanisms of the postmidnight-to-dawn equatorial plasma bubble (EPB) irregularities during the weak geomagnetic activity period on 13 November 2015 were investigated based on the multiple satellite and ground-based observations. By using the coherent scatter radar operating at very high frequency at Fuke (19.5°N, 109.1°E, dip latitude 14.4°N), China, it was found that the freshly developed field-aligned irregularities (FAIs) occurred within the radar's field of view around ∼04:37 LT and sustained for more than 40 min. The remarkable EPB-related density and total electron content (TEC) depletions measured by the satellite and GNSS receivers were also observed, which indicates the persistence of EPB irregularities until ∼06 LT. The significant elevation of bottomside F-layer's virtual height obtained by the Digisonde at Fuke as well as the upward vertical F-layer plasma drifts derived from a nearby Digisonde at Sanya (18.4°N, 109.6°E, dip latitude 13.1°N) both imply the existence of strong eastward perturbation electric fields after local midnight. These findings suggest that the collective effects of eastward overshielding penetration electric field (PEF) resulted from the substorm onset and rapid northward turning of the interplanetary magnetic field (IMF) Bz, surpassed the role of westward undershielding prompt penetration electric field (PPEF) induced by the southward turning of IMF Bz. Thus, the former predominated in modulating the equatorial/low-latitude zonal electric fields and raised the F-layer considerably, which consequently boosted the growth of R-T instability and created the favorable conditions for the postmidnight-to-dawn EPBs development.