Ionospheric electron density perturbations during the 7–10 March 2012 geomagnetic storm period

Abstract

From 7 to 10 March 2012 a series of magnetospheric disturbances caused perturbations in the ionospheric electron density. Analyzing the interplanetary causes in each phase of this disturbed period, in comparison with the total electron content (TEC) disturbances, we have concluded that the interplanetary solar wind controls largely the ionospheric response. An interplanetary shock detected at 0328UT on 7 March caused the formation of prompt penetrating electric fields in the dayside that transported plasma from the near-equatorial region to higher in attitudes and latitudes forming a giant plasma fountain which is part of the so-called dayside ionospheric super-fountain. The super-fountain produces an increase in TEC which is the dominant effect at middle latitude, masking the effect of the negative storm. Simultaneously, inspecting the TEC maps, we found evidence for a turbulence in TEC propagating southward probably caused by large scale travelling ionospheric disturbances (LSTIDs) linked to auroral electrojet intensification. On 8 March, a magnetospheric sudden impulse at 1130UT accompanied with strong pulsations in all interplanetary magnetic field (IMF) components and with northward Bz component during the growth phase of the storm. These conditions triggered a pronounced directly driven substorm phase during which we observe LSTID. However, the analysis of DMSP satellite observations, provided with strong evidence for Sub-Auroral Polarization Streams (SAPS) formation that erode travelling ionospheric disturbances (TID) signatures. The overall result of these mechanisms can be detected in maps of de-trended TEC, but it is difficult to identify separately each of the sources of the observed perturbations, i.e. auroral electrojet activity and LSTIDs, super-fountain and SAPS.In order to assess the capability of the ionospheric profiler called Topside Sounder Model - assisted Digisonde (TaD model) to detect such perturbations in the electron density, electron density disturbances at heights from 200 to 1000km have been calculated with the TaD model and compared with slant TEC parameters obtained from GPS receivers co-located with the Digisondes whose data were used to generate the TaD model predictions. The model matches in qualitative terms the GPS TEC observed perturbations independently from the source. The physical mechanisms that govern the ionosphere, such as ion drag by neutral winds along magnetic field lines, E×B drifts, and increased recombination due to the neutral composition changes, offer various combinations of foF2, hmF2 and TEC variations, which TaD resolves. Counterwise, TaD can help the interpretation of various physical scenarios which cannot be achieved if solely TEC or F layer variations are considered.