Long-term trends in the ionospheric F2 region with different solar activity indices
Other literature type
(issn: 1432-0576, eissn: 1432-0576)
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.
Three main results have been derived:
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.
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
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.