GPS phase fluctuations in the equatorial region during sunspot minimum

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Abstract
GPS multisite and multisatellite observations of phase fluctuations are used to characterize irregularity development in the equatorial region. We use 30‐s samples of total electron content obtained from phase differences between 1.2 and 1.6‐GHz signals as gathered by the International GPS Service for Geodynamics (IGS). These observations from a number of ground receivers allowed for simultaneous studies over a range of latitudes and longitudes in the region near and distant from the magnetic equator. Several storm periods were analyzed in the time period from November 3,1993, to October 2,1995. By examining phase fluctuations at latitudes near the magnetic equator, in the anomaly region, and poleward of the anomaly region, it was found that very high altitudes were reached by plumes of irregularities during seven magnetic storms in solar minimum years. These also occurred during periods of magnetic quiet. The data set allowed the determination of effective altitudes of equatorial irregularities. During low solar flux years, there was a plethora of different altitude regimes from thin layers to altitudes over 2000 km.