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\begin{document}

\title{What is happening with the Sun - and ionospheric impact?}



\author[1]{Jan Lastovicka}%
\author[2]{Dalia Buresova}%
\affil[1]{Institute of Atmospheric Physics, Czech Academy of Sciences}%
\affil[2]{Institute of Atmospheric Physics}%


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  \date{June 18, 2024}


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\begin{abstract}
To model ionospheric climate and to study its long-term changes we need
solar activity proxies, because long and homogeneous data series of
solar ionizing flux are not available. Here we use solar activity
proxies/indices F10.7, sunspot numbers, F30, Mg II, He II and solar
Lyman-\selectlanguage{greek}α \selectlanguage{english}flux, and yearly average foF2 values from six midlatitude
ionospheric stations from four continents (Juliusruh, Pruhonice, Roma,
Boulder, Kokubunji and Canberra) over 1976-2014. Main results are as
follows: (1) Relationships among solar activity indices/proxies differ
between solar cycles 21 and 22 (represented by years 1976-1995) on the
one hand, and cycles 23 and 24 (represented by years 1996-2014) on the
other hand. (2) Consequently the relationships between midlatitude foF2
and solar activity proxies also differ except for F30. (3) The
variability of yearly values of foF2 at middle latitudes appears to be
described best by solar activity proxies F30 and Mg II.%
\end{abstract}%



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