A revised approach to the ƒ<i>o</i>F2 long-term trends analysis

• Main Authors: A. V. Mikhailov, D. Marin, T. Yu. Leschinskaya, M. Herraiz
• Format: Article
• Language: English
• Published: Copernicus Publications 2002-10-01
• Series: Annales Geophysicae
• Online Access: https://www.ann-geophys.net/20/1663/2002/angeo-20-1663-2002.pdf

A new approach to extract <i>fo</i>F2 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 <i>fo</i>F2 trend, with the slope <i>K_r</i> = - 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 <i>fo</i>F2 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 <i>fo</i>F2 trends.&nbsp;</p> <p style="line-height: 20px;"><b>Key words.</b> Ionosphere (ionosphere-atmosphere interactions, ionospheric disturbances)