A case study of ionospheric storm effects during long‐lasting southward IMF B_z‐driven geomagnetic storm

Abstract

Multiple instrumental observations including GPS total electron content (TEC), f o F 2 and h m F 2 from ionosondes, vertical ion drift measurements from Communication/Navigation Outage Forecasting System, magnetometer data, and far ultraviolet airglow measured by Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics/Global Ultraviolet Imager (TIMED/GUVI) are used to investigate the profound ionospheric disturbances at midlatitude and low latitude during the 14-17 July 2012 geomagnetic storm event, which was featured by prolonged southward interplanetary geomagnetic field component for about 30 h below À10 nT. In the East Asian/Australian sector, latitudinal profile of TEC variations in the main phase were characterized by three bands of increments and separated by weak depressions in the equatorial ionospheric anomaly (EIA) crest regions, which were caused by the combined effects of disturbance dynamo electric fields (DDEF) and equatorward neutral winds. In the recovery phase, strong inhibition of EIA occurred and the summer crest of EIA disappeared on 16 July due to the combined effects of intrusion of neutral composition disturbance zone as shown by the TIMED/GUVI O/N 2 measurements and long-lasting daytime westward DDEF inferred from the equatorial electrojet observations. The transit time of DDEF over the dip equator from westward to eastward is around 2200 LT. In the American longitude, the salient ionospheric disturbances in the summer hemisphere were characterized by daytime periodical intrusion of negative phase for three consecutive days in the recovery phase, preceded by storm-enhanced density plume in the initial phase. In addition, multiple short-lived prompt penetration electric fields appeared during stable southward interplanetary magnetic field (IMF) B z in the recovery phase and were responsible for enhanced the EIA and equatorial ionospheric uplift around sunset.

Regional differences of the ionospheric response to the July 2012 geomagnetic storm

“…The disappearance of the one or two crests is most likely caused by the disturbed electric fields in the low‐latitude and equatorial regions. The effects of the neutral composition disturbance to the depletion in both the topside and bottomside TEC are mainly reflected in the region from 10°N to 50°N, which are consistent with the TIMED/GUVI [O]/[N 2 ] [ Bagiya et al , ; Liu et al , ]. The decline in TEC of the south of 20°S is inconspicuous.…”

“…They thought that the positive storm features are caused by the combined effects of DDEF and the equatorward neutral winds (traveling ionospheric disturbances) on 15 July and the strong negative storm effects are due to the combined effects of neutral composition disturbances and DDEF on 16 July. The combined effects of the multiple PEF on 15 July and the DDEF on 16 July in the American sector were also reported by Liu et al []. Especially, they considered that the nighttime EIA intensification (positive storm effect) on 16 July in the American sector is caused by the nighttime eastward DDEF which could uplift the F 2 region to higher altitudes.…”

“…Liu et al [] analyzed the mechanisms for the storm time features of TEC during this storm, discovering the outstanding role of disturbed electric fields by using the data of dH. They found that the westward DDEF appears twice on the two days 15 and 16 July in the Asian‐Australian sector, giving the effects to cause the positive storm and the negative storm, respectively.…”

“…As shown in Figure , the intense ionospheric negative storm effects on 16 July obviously appear at all the 17 stations in this sector. Bagiya et al [] and Liu et al [] reported the [O]/[N 2 ] data obtained from Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics (TIMED)/Global Ultraviolet Imager (GUVI) showing the neutral composition disturbance zone (depleted [O]/[N 2 ]) over this region on 16 July. It is generally accepted that the ionospheric negative storms should be caused by the changes in the neutral composition due to the heating of the thermosphere during the geomagnetic storms.…”

“…Wang et al [] reported the ionospheric storm effect over North China during this geomagnetic storm. Liu et al [] investigated the profound ionospheric disturbances at middle and low latitudes during this ionospheric storm and discussed the pronounced effects of the storm time‐disturbed electric fields. Bagiya et al [] also analyzed the significant changes in the ionospheric electron density over Indian region during 15 and 16 July 2012.…”