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- Title
Variations in Thermosphere Composition and Ionosphere Total Electron Content Under "Geomagnetically Quiet" Conditions at Solar-Minimum.
- Authors
Xuguang Cai; Burns, Alan G.; Wenbin Wang; Liying Qian; Pedatella, Nicholas; Coster, Anthea; Shunrong Zhang; Solomon, Stanley C.; Eastes, Richard W.; Daniell, Robert E.; McClintock, William E.
- Abstract
We conducted observational and modeling studies of thermospheric composition and ionospheric total electron content (TEC) variations during two geomagnetically quiet periods (maximum Kp = 1.7) at solar minimum. Daytime thermospheric O and N2 column density ratio (SO/N2) observed by Global-scale Observations of the Limb and Disk and TEC from a network of ground-based Global Navigation Satellites System receivers both exhibited large (~30% of reference values) and long-lived (5-11 h) day-to-day variations in roughly the same mid-latitude geographic regions. Numerical simulations replicated the observed variability, though not perfectly. Analysis of the simulations suggested that the variations were mainly generated in the high-latitudes and were subsequently advected equatorward and westward. When high-latitudes input was turned off in simulations, the variations were negligible. This suggested the potentially important role of high-latitude geomagnetic forcing in thermospheric composition and ionospheric density variations at mid-latitudes even during some "geomagnetically quiet" periods at solar-minimum. Plain Language Summary This study presents two cases when geomagnetic forcing can be a plausible source of mid-latitude thermospheric composition and ionosphere density variations even during what is typically considered as geomagnetically quiet times (magnetic activity index Kp < 2). The column density ratio of thermospheric O and N2 (SO/N2) plays a major role in the daytime ionospheric F-region plasma density at mid-latitudes. In this study, thermospheric and ionospheric variations during geomagnetically quiet times are investigated with the two-dimensional images of SO/N2 provided by a satellite located in geostationary orbit and the ground-based total electron content (TEC) maps. Both SO/N2 and TEC displayed similar strong, long-lived and localized depletions and enhancements at mid-latitudes. Numerical simulations driven by an empirical model of geomagnetic activity, but with a climatological tide in the lower boundary, qualitatively produced the patterns of observed variations. Analysis of simulations revealed that SO/N2 variations were initially formed at high-latitudes and then transported equatorward and westward. When geomagnetic forcing was turned off in simulations, the modeled SO/N2 and TEC variations were negligible. This study suggests the potentially important roles of high-latitude forcing in thermosphere and ionosphere variations at mid-latitudes even during some "geomagnetically quiet" periods at solar-minimum.
- Subjects
GEOMAGNETISM; THERMOSPHERE; GLOBAL Positioning System; IONOSPHERE; GEOSTATIONARY satellites; IONOSPHERIC plasma
- Publication
Geophysical Research Letters, 2021, Vol 48, Issue 11, p1
- ISSN
0094-8276
- Publication type
Article
- DOI
10.1029/2021GL093300