Annales Geophysicae
Annales Geophysicae
ANGEO
Articles | Volume 43, issue 1
Articles | Volume 43, issue 1
https://doi.org/10.5194/angeo-43-73-2025
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
Special issue:
https://doi.org/10.5194/angeo-43-73-2025
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
Articles | Volume 43, issue 1
Regular paper
 | 
21 Jan 2025
Regular paper |  | 21 Jan 2025

Long-term changes in the dependence of NmF2 on solar flux at Juliusruh

Maria Gloria Tan Jun Rios, Claudia Borries, Huixin Liu, and Jens Mielich

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This study analyzes changes in the ionospheric response to solar flux over five complete solar cycles (1957 to 2023). We use Juliusruh hourly data of the peak electron density of the F2 layer, NmF2, and three solar extreme ultraviolet (EUV) radiation proxies. The response is better represented by a cubic regression, and F30 shows the highest correlation for describing NmF2 dependence over time. These results reveal a decrease in NmF2 influenced by the intensity of the solar activity index.
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Long-term trends in the stratosphere–mesosphere–thermosphere–ionosphere...