Long-term trends in the ionospheric F2 region with different solar activity indices

• Main Authors: J. Mielich, J. Bremer
• Format: Article
• Language: English
• Published: Copernicus Publications 2013-02-01
• Series: Annales Geophysicae
• Online Access: https://www.ann-geophys.net/31/291/2013/angeo-31-291-2013.pdf

A new comprehensive data collection by Damboldt and Suessmann (2012a) with monthly <I>fo</I>F2 and M(3000)F2 median values is an excellent basis for the derivation of long-term trends in the ionospheric F2 region. Ionospheric trends have been derived only for stations with data series of at least 22 years (124 stations with <I>fo</I>F2 data and 113 stations with M(3000)F2 data) using a twofold regression analysis depending on solar and geomagnetic activity. <br><br> Three main results have been derived: <br><br> Firstly, it could be shown that the solar 10.7 cm radio flux F10.7 is a better index for the description of the solar activity than the relative solar sunspot number <I>R</I> as well as the solar EUV proxy E10.7. <br><br> Secondly, the global mean <I>fo</I>F2 and <I>hm</I>F2 trends derived for the interval between 1948 and 2006 are in surprisingly good agreement with model calculations of an increasing atmospheric greenhouse effect (Rishbeth and Roble, 1992). <br><br> Thirdly, during the years 2007 until 2009, the <I>hm</I>F2 values and to a smaller amount the <I>fo</I>F2 values strongly decrease. The reason for this effect is a reduction of the thermospheric density and ionization due to a markedly reduced solar EUV irradiation and extremely small geomagnetic activity during the solar cycle 23/24 minimum.