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Isolated Peak of Oxygen Ion Fraction in the Post‐Noon Equatorial F‐Region: ICON and SAMI3/WACCM‐X
Author(s) -
Park Jaeheung,
Huba J. D.,
Heelis Roderick,
Englert Christoph
Publication year - 2021
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1029/2021ja029217
Subject(s) - noon , middle latitudes , ionosphere , thermosphere , atmospheric sciences , latitude , earth's magnetic field , local time , ion , fraction (chemistry) , altitude (triangle) , physics , environmental science , geology , geodesy , chemistry , geophysics , magnetic field , geometry , mathematics , statistics , organic chemistry , quantum mechanics
In the equatorial region, the fraction of oxygen ions (O + ) in the topside ionosphere contains information on the source altitude of the plasma, which is controlled, in part, by the vertical plasma motion in the F‐region. Previous studies on this topic are restricted by limited coverage of local time, latitude, and season, leaving a significant knowledge gap in the distribution of the topside ionospheric composition. In this study, we statistically investigate the O + fraction measured by ICON/IVM over all the local time sectors and seasons at low‐/midlatitudes. For the first time, we have found that an isolated peak in the O + fraction emerges in the post‐noon equatorial region. The peak is most prominent during equinoxes, while during solstices it is connected to the O + fraction bulges in the local summer midlatitudes. Simulations with SAMI3 coupled with thermospheric parameters from WACCM‐X reproduce the peak of the O + fraction. The post‐noon equatorial peak can be explained by the net vertical motion of plasma consisting of transports either parallel or perpendicular to geomagnetic field lines.