edu.ucar.opensky::articles:20913 UCAR/NCAR - Library OpenSky Support PO Box 3000 Boulder CO 80307-3000 opensky@ucar.edu http://opensky.ucar.edu/ homepage pointOfContact 2025-12-26T02:29:19.300528 ISO 19115-2 Geographic Information - Metadata - Part 2: Extensions for Imagery and Gridded Data ISO 19115-2:2009(E) https://n2t.org/ark:/85065/d7736tb1 Simulations of the ionospheric annual asymmetry: Sun-Earth distance effect 2017-06-01T00:00:00Z publication https://n2t.org/ark:/85065/d7736tb1 https://doi.org/10.1002/2017JA024188 Dang, T. author Wang, Wenbin author Burns, Alan author Dou, X. author Wan, W. author Lei, J. author UCAR/NCAR - Library publisher 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 degrees and 40 degrees 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. UCAR/NCAR - Library OpenSky Support PO Box 3000 Boulder CO 80307-3000 opensky@ucar.edu http://opensky.ucar.edu/ homepage pointOfContact PDF Text theme Resource Type 2016-01-01T00:00:00Z publication Copyright 2017 American Geophysical Union. None eng geoscientificInformation