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Simulations of the ionospheric annual asymmetry: Sun‐Earth distance effect
Author(s) -
Dang Tong,
Wang Wenbin,
Burns Alan,
Dou Xiankang,
Wan Weixing,
Lei Jiuhou
Publication year - 2017
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1002/2017ja024188
Subject(s) - ionosphere , thermosphere , solstice , atmospheric sciences , asymmetry , ambipolar diffusion , ionization , physics , environmental science , daytime , computational physics , latitude , electron , ion , astronomy , quantum mechanics
It has been suggested that the difference of the Sun‐Earth distance between the December and June solstices has a great impact on the ionospheric annual asymmetry. In this study, the physical mechanisms of the Sun‐Earth distance effects on the ionospheric annual asymmetry are investigated using Thermosphere‐Ionosphere Electrodynamics General Circulation Model simulations. The main findings are the following: (1) The Sun‐Earth distance affects the ionospheric annual asymmetry mainly through photochemical processes. (2) During the daytime, this photochemical process results from the combined effect of ionization rate of atomic oxygen and the recombination with neutral species. The solar irradiation variation between December and June directly leads to about 6% December‐June electron density difference via ionization of atomic oxygen, whereas the recombination with neutral composition contributes to 12%–15% December‐June electron density difference. (3) In the plasma fountain‐prominent region (between 20° and 40° magnetic latitude), ambipolar diffusion can also be modulated by the Sun‐Earth distance effect and contribute to the ionospheric annual asymmetry. (4) During the nighttime, the Sun‐Earth distance effect impacts the annual asymmetry by changing thermospheric composition and ionospheric diffusion.