GPS

The satellites of the GPS constellation are in 12-hr circular orbits (~20,000-km altitude) with orbital inclination ~55°. Over 1000 ground GPS receivers monitor the signals received from any of the 28 active GPS satellites within their field of view. The trans-ionospheric perturbation imposed on the received signals can be inverted to determine a measure of the integrated total electron content (TEC) along the path traversed. The vertical TEC determined is the combined contribution of the ionosphere and overlying plasmasphere.

Extensive analyses of the body of GPS TEC observations have been undertaken in recent years at the Haystack Observatory. Automated processing and analysis routines have been developed, enabling studies of the plasma environment of Earth to be undertaken in a variety of circumstances. During large magnetosphere/ionosphere storms, wholesale redistribution of this cold plasma envelope takes place driven by the effects of storm-generated electric field and modulated by magnetosphere-ionosphere coupling processes. Studies by Foster et al [2002] linked the ground-based TEC imagery to the perturbation and erosion of the overlying plasmasphere seen from space by the IMAGE EUV instrument. Work combining GPS TEC with Millstone Hill radar observations of ionospheric characteristics identified the magnitude of the plasma transport (flux) involved in these events and outlined its systemwide consequences [Foster et al., 2004]. The multi-instrument observations combining ground-based ionospheric imagery obtained with GPS TEC, with radar and satellite measurements of ionospheric structures and boundaries has led to the development of a global picture of these large space weather events in which disturbances originating in the low-latitude ionosphere propagate poleward bringing strong Space Weather consequences to the populous mid latitudes (over the USA) and into the high-latitude auroral and polar cap regions [Foster et al, 2005a; 2005b].

Foster, J. C., A. J. Coster, P. J. Erickson, J. Goldstein, and F. J. Rich, Ionospheric Signatures of Plasmaspheric Tails, Geophys. Res. Lett., 29(13), 10.1029/2002GL015067, 2002.

Foster, J. C., A. J. Coster, P. J. Erickson, F. J. Rich, and B. R. Sandel (2004), Stormtime observations of the flux of plasmaspheric ions to the dayside cusp/magnetopause, Geophys. Res. Lett., 31, L08809, doi:10.1029/2004GL020082, 2004.

Foster, J. C., A. J. Coster, P. J. Erickson, W. Rideout, F. J. Rich, T. J. Immel, and B. R. Sandel, Redistribution of the Stormtime Ionosphere and the Formation of the Plasmaspheric Bulge, in Inner Magnetosphere Interactions: New Perspectives from Imaging, J. Burch and M. Schultz, eds., AGU Press, Washington, DC, 2005a.

Foster, J. C., A. J. Coster, P. J. Erickson, J. M. Holt, F. D. Lind, W. Rideout, M. McCready, A. van Eyken, R. A. Greenwald, F. J. Rich, Foster, J. C., et al. (2005b), Multiradar observations of the polar tongue of ionization, J. Geophys. Res., 110, A09S31, doi:10.1029/2004JA010928.

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