Statistical Characterization of Storm-Time GPS Total Electron Content Variations in the North American Sector

Abstract:

Maps of vertically-integrated total electron content (TEC) based on data collected by worldwide networks of ground-based Global Positioning System (GPS) receivers are useful for characterizing large-scale structure in the Earth's ionosphere. Several previous event studies have used GPS TEC maps to monitor the dynamics of prominent storm-time ionospheric features, such as plumes of storm enhanced density (SED), the tongue of ionization (TOI), and polar cap patches. In this study, we focus on developing a statistical characterization of the storm-time response of GPS TEC in the North American sector. A superposed epoch analysis is carried out using GPS TEC variations collected over North America during 139 geomagnetic storms which occurred between 2001 and 2013. The epoch time used to order the data is the onset of the main phase determined by the Sym-H index. Clear seasonal variations in the TEC storm response are identified, such that summer events tend to be dominated by the negative (decrease) phase while winter events exhibit a stronger initial positive (increase) phase with minimal negative storm effects. We find no discernible difference between spring and fall equinox events with both being equal to the seasonal average. We also find a prominent magnetic declination effect such that stronger positive storm effects are observed in regions of negative declination (i.e. eastern North America).