Conjugate localized enhancement of total electron content at low latitudes in the American sector

We report evidence for a discrete localized enhancement of total electron content (TEC) in magnetic-conjugate regions at dusk in the American sector during large magnetic storms. After their formation, the conjugate enhancements persist at these longitudes and corotate into the night sector. We use ground-based GPS TEC and Millstone Hill radar observations, and DMSP overflights to investigate this phenomenon. Both poleward and eastward components of the disturbance electric field are needed to account for the observed redistribution of cold plasma at low and mid latitudes inside the plasmapause. We conclude that horizontal plasma transport associated with disturbance electric fields is the dominant mechanism for producing the conjugate TEC enhancements. The repeatability and geographic localization of this feature indicate a longitudinal specificity for the process associated with its formation. This long-lasting conjugate enhancement in TEC serves as a corotating source for the erosion plumes of storm-enhanced density seen during such events.