Simultaneous GPS and Incoherent Scatter Radar Observations of Ionospheric Density Gradients During Geomagnetically Disturbed Conditions

P. J. Erickson, M. M. Pratt

Abstract:	Ionospheric phenomena such as post-sunset storm-time en-hancements of density (the so-called ”dusk effect”) are all regularly observed by the worldwide chain of incoherent scatter radars. The density gradients during these events can cause large changes in the total electron content (TEC) over fairly short baselines. Depending on what correction algorithm is used to model the total electron content, these gradients can impact the use of GPS for navigation. This paper discusses the size and extent of density gradient-driven ionospheric electron content variations as measured simultaneously by the Millstone Hill incoherent scatter radar facility and several closely located GPS re-ceivers. During October 18 - 21, 1998, the Millstone Hill UHF incoherent scatter radar system operated as part of an extensive wide-latitude substorm (WLS) campaign. Eleva-tion and azimuth scans of its 46 meter steerable antenna yielded ionospheric density profiles as a function of lati-tude to beyond 600 km altitude. At the same time, GPS receivers measured total electron content at Millstone Hill and three other latitudinally separate sites. In response to magnetic disturbances commencing at 0 UT on October 19, the Millstone radar saw significant dusk effect total con-tent enhancements moving downwards in latitude, causing GPS receivers to experience maximum differences in iono-spheric delay of 1.5 meters at L1 frequencies. We also discuss electron content comparisons from the colocated ISR and GPS systems at Millstone Hill, which show storm-driven density depletion and subsequent recovery only for electron content below 800 km altitude.
Published in:	Proceedings of the 55th Annual Meeting of The Institute of Navigation (1999) June 27 - 30, 1999 Royal Sonesta Hotel Cambridge, MA
Pages:	363 - 371
Cite this article:	Erickson, P. J., Pratt, M. M., "Simultaneous GPS and Incoherent Scatter Radar Observations of Ionospheric Density Gradients During Geomagnetically Disturbed Conditions," Proceedings of the 55th Annual Meeting of The Institute of Navigation (1999), Cambridge, MA, June 1999, pp. 363-371.
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