Journal of Atmospheric and Solar-Terrestrial Physics
A new version of the NeQuick ionosphere electron density model
Introduction
The NeQuick (Hochegger et al., 2000, Radicella and Leitinger, 2001) is an ionospheric electron density model developed at the Aeronomy and Radiopropagation Laboratory of The Abdus Salam International Centre for Theoretical Physics (ICTP), Trieste, Italy, and at the Institute for Geophysics, Astrophysics and Meteorology (IGAM) of the University of Graz, Austria. Historically the NeQuick has to be considered as an evolution of the DGR profiler proposed by Di Giovanni and Radicella (1990), and subsequently modified by Radicella and Zhang (1995).
The first version of the model has been used by the European Space Agency (ESA) European Geostationary Navigation Overlay Service (EGNOS) project for assessment analysis and has been adopted for single-frequency positioning applications in the framework of the European Galileo project. It has also been adopted by the International Telecommunication Union, Radiocommunication Sector (ITU-R) as a suitable method for total electron content (TEC) modeling (ITU, 2003). In addition, the NeQuick has been implemented in the simulation toolkit developed in Australia to conduct a qualitative assessment of the performance characteristics of the future GNSS infrastructure (Seynat et al., 2004) and it has been adapted by the Rutherford-Appleton Laboratory of the UK to forecast vertical TEC from forecasted values of foF2 and MUF(3000)F2 (Cander, 2003). NeQuick (FORTRAN 77) source code is available at http://www.itu.int/ITU-R/index.asp?category=documents&link=rsg3&lang=en.
As in the case of other models, like for example the IRI (Bilitza, 2001), many efforts have been done to improve the NeQuick analytical formulation and taking advantage of the increasing amount of available data, the NeQuick has been continuously updated. In particular the modifications have been done taking into account the necessity for the model to provide better representations of the median ionosphere at global scales. Recently major changes have been introduced in the bottomside (Leitinger et al., 2005) and in the topside (Coïsson et al., 2006) description of the model. In addition, specific revisions have been applied to the computer package associated with NeQuick model in order to improve its computational efficiency. All these efforts, directed toward the developments of a new version of the model, have therefore led to the implementation of the NeQuick 2. In the following paragraphs the main features of the new version of the NeQuick will be described and the analytical formulation of the model will be reported.
Section snippets
The NeQuick 2
Being the version 2 of the NeQuick an evolution of the version 1, the conceptual structure of the model has been kept unchanged. Nevertheless, the formulation of some specific parameter related to the bottomside and topside description has been modified.
In the following, only the main features of the NeQuick 2 will be indicated, and the complete analytical formulation of the model will be given subsequently.
To describe the electron density of the ionosphere above 90 km and up to the peak of the
Model validation
In the present paragraph the main reasons that lead to the major changes in the NeQuick 2 are indicated and the corresponding improvements obtained in terms of ionosphere electron density representation are summarized.
As indicated by Leitinger et al. (2005), when the first version of NeQuick is used to compute electron density grids at fixed heights below the peak, in some cases strong gradients and strange structures appear in E and layer heights. The strategy used to solve these
Conclusions
In recent years several changes have been introduced in the version 1 of the NeQuick model. The most important modifications are related to the bottomside formulation in terms of the modeling of the layer peak electron density, height and thickness parameter.
Concerning the model topside, a new formulation of the shape parameter k has been adopted.
All the model improvements have therefore been considered to finalize a new version of the model: the NeQuick 2.
Correspondingly, the computer
Acknowledgments
The authors are grateful to Prof. Reinhart Leitinger of the University of Graz, Austria, who has strongly contributed to the development of the NeQuick model and to all its implementations.
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