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Article ReferenceLarge-scale ionospheric gradients over Europe observed in October 2003
It is well known that ionospheric perturbations are characterised by strong horizontal gradients and rapid changes of the ionisation. Thus, space weather induced severe ionosphere perturbations can cause serious technological problems in Global Navigation Satellite Systems (GNSS) such as GPS. During the severe ionosphere storm period of 29–31 October 2003, reported were several significant malfunctions due to the adverse effects of the ionosphere perturbations such as interruption of the WAAS service and degradation of mid-latitudes GPS reference services. To properly warn service users of such effects, a quick evaluation of the current signal propagation conditions expressed in a suitable ionospheric perturbation index would be of great benefit. Preliminary results of a comparative study of ionospheric gradients including vertical sounding and Total Electron Content (TEC) data are presented. Strong enhancements of latitudinal gradients and temporal changes of the ionisation are observed over Europe during the 29–30 October storm period. The potential use of spatial gradients and rate of change of foF2 and TEC characterising the actual perturbation degree of the ionosphere is discussed. It has been found that perturbation induced spatial gradients of TEC and foF2 strongly enhance during the ionospheric storm on 29 October over the Central European region in particular in North–South direction exceeding the gradients in East–West direction by a factor of 2.
Article ReferenceTopside ionosphere and plasmasphere: Use of NeQuick in connection with Gallagher plasmasphere model
The NeQuick ionospheric electron density model has a very simple topside formulation, which allows taking into account the electron content up to 20,000 km. In the present work, the Gallagher model has been used in connection with NeQuick to provide a more realistic representation of the electron concentration distribution in the plasmasphere. An analysis of the impact of the proposed modification in low geomagnetic latitudes (±40°) on modeled vertical total electron content has been performed for different levels of solar activity, season, and universal time. In addition, GPS vertical total electron content values obtained from seven IGS (International GPS Service) station data have been compared with the NeQuick and NeQuick+Gallagher vertical total electron content values, confirming the importance of including a plasmaspheric formulation in the NeQuick model.
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