GPS tomography in the polar cap: comparison with ionosondes and in situ spacecraft data
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Tomographic 4D reconstructions of ionospheric anomalies appearing in the high-latitude polar cap region are compared with plasma density measurements by digital ionosonde located near the north magnetic pole at Eureka station and with in situ plasma measurements on-board DMSP spacecraft. The moderate magnetic storm of 14–17 October 2002 is taken as an example of a geomagnetic disturbance which generates large-scale ionospheric plasma anomalies at mid-latitudes and in the polar cap region. Comparison of the GPS tomographic reconstructions over Eureka station with the ionosonde measurements of the F layer peak densities indicates that the GPS tomography correctly predicts the time of arrival and passage of the ionospheric tongue of ionization over the magnetic pole area, although the tomographic technique appears to under-estimate the value of F peak plasma density. Comparison with the in situ plasma measurements by the DMSP SSIES instruments shows that the GPS tomography correctly reproduces the large-scale spatial structure of ionospheric anomalies over a wide range of latitudes from mid-latitudes to the high-latitude polar cap region, though the tomographic reconstructions tend to over-estimate the density of the topside ionosphere at 840 km DMSP orbit. This study is essential for understanding the quality and limitations of the tomographic reconstruction techniques, particularly in high-latitude regions where GPS TEC measurements and other ionospheric data sources are limited.
KeywordsIonosphere Geomagnetic storms GPS tomography
The Canadian authors would like to acknowledge the financial support from the Natural Sciences and Engineering Research Council of Canada. The UK authors acknowledge the financial support from the UK Science and Technology Facilities Council and the Royal Society Wolfson Research Award. CADI and CHAIN operation is conducted in collaboration with the Canadian Space Agency. DMSP SSIES data is provided by the University of Texas in Dallas. We would like to thank the International GNSS Service for making the GPS data available, University of Kyoto for providing geomagnetic indices and the NASA OMNIweb service for providing the solar wind data.
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