Regional GPS Mapping of Storm Enhanced Density During the 15-16 July 2000 Geomagnetic Storm

During geomagnetic disturbances, intense storm-time electric fields of magnetospheric origin extend across mid-latitudes and redistribute the ionospheric plasma through advection across both latitude and local time. Strong increases and sharp spatial gradients in total electron content (TEC) characterize the ionospheric storm response. In this paper, TEC measurements from GPS receivers scattered throughout the eastern and southeastern parts of the U.S., including a few located in the Caribbean, are used to monitor the ionospheric response to both the 15-16 July 2000 geomagnetic storm, one of the largest geomagnetic storms in recent history, and the more recent 31 March 2001 storm. The GPS data have been used to construct a time history of TEC perturbations in two dimensions. The data clearly show plasma advection from the lower latitudes bringing in storm-enhanced density (SED) [1] with total electron content (TEC) ~ 100 TEC units into the region immediately equatorward of the trough. During these geomagnetic storms, plasma is transported to higher latitudes and to earlier local times – approaching the noon meridian. Additional maps of storm-induced ionospheric perturbations, constructed with Millstone Hill incoherent scatter radar data spanning the mid-latitude ionosphere between 35° and 65° invariant latitude, support the GPS observations. In-situ DMSP satellite observations of electric fields and particle precipitation are used to further study the structure and dynamics of the magnetospheric and ionospheric response to these storms. During both storms, very large enhancements in the TEC are seen over the eastern part of the US. This is due to bulk transport of the F region ionosphere to mid latitudes from the vicinity of the equatorial anomaly. Large TEC gradients are observed at several individual GPS sites, impacting standard GPS data processing techniques at some sites. The fusion of these different data sources, GPS, Incoherent Scatter, and DMSP satellite observations, allows comprehensive monitoring of the magnetospheric and ionospheric interaction and of the development in time and space of the ionospheric SED phenomenon.