The geomagnetic storm time response of GPS total electron content in the North American sector

Abstract

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.

High‐latitude topside ionospheric vertical electron density profile changes in response to large magnetic storms

“…The Northern Hemisphere has the best coverage of topside N e (h) profiles and allows pairs of storms to be compared for three different conditions: winter nighttime, winter daytime, and spring daytime. The nighttime storm‐induced enhancements and daytime storm‐induced depletions during these seasons shown in Table are consistent with the high northern latitude nighttime topside enhancements and daytime depletions observed by Nishida [] during the large magnetic storm of 21–23 September 1963 and with the statistical TEC results of Thomas et al [] at lower MLAT (near 60 ° north) during moderate magnetic storms (see their Figures , c, and d).…”

Alfvén wave‐driven ionospheric mass outflow and electron precipitation during storms

“…These field lines map to the heart of the ring current, where observations of Alfvén waves and highly energized ionospheric ions arriving in the equatorial plane directly from the ionosphere below have been reported [ Chaston et al ., ]. Besides the role of Alfvén waves in contributing to ionospherically sourced ion populations in the ring current, Alfvén wave‐induced electron precipitation may also play a role in the complex but significant modification of ionospheric density during geomagnetic storms [see, e.g., Thomas et al ., , and references therein].…”

The story of plumes: the development of a new conceptual framework for understanding magnetosphere and ionosphere coupling

“…As multipoint measurements became more common (e.g., Su et al, 2001b), the name plumes began to appear, and with the seminal work of connecting the ionospheric SED signature with the plasmaspheric plume feature, the term SED plume began to appear regularly (e.g., Yizengaw et al, 2006;. These SED plumes are observed in all MLT sectors but are preferentially observed in the American sector due to the tilt of the dipole geomagnetic field (e.g., Foster et al, 2008;Yizengaw et al, 2006;Coster et al, 2007;Thomas et al, 2016). The largest values of TEC are also observed in the American sector .…”