ALBERT

Description: Over the last two decades, maps of GPS total electron content (TEC) have improved our understanding of the large perturbations in ionospheric electron density which occur during geomagnetic storms. However, previous regional and global studies of ionospheric storms have performed only a limited separation of storm-time, local time, longitudinal, and seasonal effects. Using 13 years of GPS TEC data, we present a complete statistical characterization of the ionospheric response to geomagnetic storms for midlatitudes in the North American sector where dense ground receiver coverage is available. The rapid onset of a positive phase is observed across much of the dayside and evening ionosphere followed by a longer-lasting negative phase across all latitudes and local times. Our results show clear seasonal variations in the storm-time TEC, such that summer events tend to be dominated by the negative storm response while winter events exhibit a stronger initial positive phase with minimal negative storm effects. We find no discernable difference between spring and fall equinox events with both being equivalent to the average storm-time response across all seasons. We also identify a prominent magnetic declination effect such that stronger dayside positive storm effects are observed in regions of negative declination (i.e., eastern North America). On the nightside, asymmetries in the TEC response are observed near the auroral oval and midlatitude trough which may be attributed to thermospheric zonal winds pushing plasma upward/downward along field lines of opposite declination.