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Ann. Geophys., 20, 1663-1675, 2002
www.ann-geophys.net/20/1663/2002/
© European Geosciences Union 2002
A revised approach to the ƒoF2 long-term trends analysis
A. V. Mikhailov1, D. Marin2, T. Yu. Leschinskaya1, and M. Herraiz3
1Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation, Troitsk, Moscow Region 142190, Russia
2Atmospheric Sounding Station “El Arenosillo", INTA, Spain
3Faculty of Physics, Complutense University, Spain
Correspondence to: A. V. Mikhailov (avm71@orc.ru)
Abstract. A new approach to extract foF2
long-term trends, which are free to a great extent from solar and geomagnetic
activity effects, has been proposed. These trends are insensitive to the phase
(increasing/decreasing) of geomagnetic activity, with long-term variations
being small and insignificant for such relatively short time periods. A small
but significant residual foF2 trend, with the slope Kr
= - 2.2 × 10-4 per year, was obtained over a 55-year period (the
longest avail-able) of observations at Slough. Such small trends have no
practical importance. On the other hand, negative (although insignificant)
residual trends obtained at 10 ionosonde stations for shorter periods (31
years) may be considered as a manifestation of a very long-term geomagnetic
activity increase which did take place during the 20th century. All of the
revealed foF2 long-term variations (trends) are shown to have a natural
origin related to long-term variations in solar and geomagnetic activity. There
is no indication of any manmade foF2 trends.
Key words. Ionosphere (ionosphere-atmosphere
interactions, ionospheric disturbances)
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