Abstract
Abstract. The ionospheric response at middle and high latitudes in the Antarctica American and Australian sectors to the 26–27 September 2011 moderately intense geomagnetic storm was investigated using instruments including an ionosonde, riometer, and GNSS receivers. The multi-instrument observations permitted us to characterize the ionospheric storm-enhanced density (SED) and tongues of ionization (TOIs) as a function of storm time and location, considering the effect of prompt penetration electric fields (PPEFs). During the main phase of the geomagnetic storm, dayside SEDs were observed at middle latitudes, and in the nightside only density depletions were observed from middle to high latitudes. Both the increase and decrease in ionospheric density at middle latitudes can be attributed to a combination of processes, including the PPEF effect just after the storm onset, dominated by disturbance dynamo processes during the evolution of the main phase. Two SEDs–TOIs were identified in the Southern Hemisphere, but only the first episode had a counterpart in the Northern Hemisphere. This difference can be explained by the interhemispheric asymmetry caused by the high-latitude coupling between solar wind and the magnetosphere, which drives the dawn-to-dusk component of the interplanetary magnetic field. The formation of polar TOI is a function of the SED plume location that might be near the dayside cusp from which it can enter the polar cap, which was the case in the Southern Hemisphere. Strong GNSS scintillations were observed at stations collocated with SED plumes at middle latitudes and cusp on the dayside and at polar cap TOIs on the nightside.
Highlights
The magnetosphere–ionosphere–thermosphere system is strongly disturbed during geomagnetic storms
To characterize the ionospheric response to the geomagnetic storm that occurred on 26–27 September 2011 as a function of storm time, local time, and station geomagnetic location, we use GNSS and ionosonde data from receivers operating at stations located from middle to high latitudes in the Antarctica American and Australian sectors (Fig. 2), which are representative of daytime and nighttime sectors, respectively
The NmF2 and VTEC parameters have values always above the quiet day level, showing that the positive phase of the ionospheric storm is dominant during the main phase storm at middle latitudes (Fig. 3a) where it started to develop at the geomagnetic storm onset
Summary
The magnetosphere–ionosphere–thermosphere system is strongly disturbed during geomagnetic storms. The precipitation of energetic particles into the thermosphere enhances ionospheric conductivities and generates intense electrical currents (Buonsanto, 1999) The dissipation of these currents by the Joule effect heats the auroral zone, which expands, changing the lower thermospheric composition and driving large-scale neutral winds (Fuller-Rowell et al, 1994; Buonsanto, 1999; Danilov and Lastovicka, 2001). The combination of these ionospheric processes during major geomagnetic storms results in a large-scale thermal plasma redistribution involving the equatorial through the polar latitude regions
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