Abstract
Abstract. In this work the response of the ionosphere due to the severe magnetic storm of 7–10 November 2004 is investigated by analyzing GPS Total Electron Content (TEC) maps constructed for the South America sector. In order to verify the disturbed zonal electric fields in South America during the superstorm, ionospheric vertical drift data obtained from modeling results are used in the analysis. The vertical drifts were inferred from ΔH magnetometer data (Jicamarca-Piura) following the methodology presented by Anderson et al. (2004). Also used were vertical drifts measured by the Jicamarca ISR. Data from a digisonde located at São Luís, Brazil (2.33° S, 44.2° W, dip latitude 0.25°) are presented to complement the Jicamarca equatorial data. Penetration electric fields were observed by the comparison between the equatorial vertical drifts and the Interplanetary Electric Field (IEF). The TEC maps obtained from GPS data reflect the ionospheric response over the South America low-latitude and equatorial region. They reveal unexpected plasma distributions and TEC levels during the main phase of the superstorm on 7 November, which is coincident with the local post-sunset hours. At this time an increase in the pre-reversal enhancement was expected to develop the Equatorial Ionization Anomaly (EIA) but we observed the absence of EIA. The results also reveal well known characteristics of the plasma distributions on 8, 9, and 10 November. The emphasized features are the expansion and intensification of EIA due to prompt penetration electric fields on 9 November and the inhibition of EIA during post-sunset hours on 7, 8, and 10 November. One important result is that the TEC maps provided a bi-dimensional view of the ionospheric changes offering a spatial description of the electrodynamics involved, which is an advantage over TEC measured by isolated GPS receivers.
Highlights
The complex effects of magnetospheric convection in ionospheric electric fields and currents from middle to low latitudes during geomagnetic disturbances have been documented in several studies (Blanc, 1983; Heelis and Coley, 1992; Fejer, 1997; Foster and Rich, 1998; Kelley et al, 1979, 2003; Huang et al, 2005a, b; Mannucci et al, 2008)
In the present paper the main focus is the ionospheric response to the geomagnetic disturbances that occurred during the 7–12 November 2004 superstorm
The November 2004 superstorm was marked out with recurrent Sym-H descendings and main phases lasting about 1 day (8 November and 10 November). This very disturbed period was responsible to create an ionospheric-thermospheric condition characterized by stressed modifications in electric fields and neutral composition changes
Summary
The complex effects of magnetospheric convection in ionospheric electric fields and currents from middle to low latitudes during geomagnetic disturbances have been documented in several studies (Blanc, 1983; Heelis and Coley, 1992; Fejer, 1997; Foster and Rich, 1998; Kelley et al, 1979, 2003; Huang et al, 2005a, b; Mannucci et al, 2008). The two main sources of electric fields responsible for changes in the plasma drifts and for current perturbations are the prompt penetration electric fields (PPEFs) and the long lasting ionospheric disturbance dynamo (DD) electric fields. In this work both features are observed during a very intense geomagnetic storm that occurred on November 2004. As discussed by Vasyliunas (2001, 2005a, b), the only parameter observed in the solar wind as well as in the magnetosphere and ionosphere is the plasma flow velocity V and not the electric field E.
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