Abstract
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)
Highlights
IntroductionDue to an increasing interest in the anthropogenic impact on the Earth’s atmosphere the ionospheric parameter longterm trends are widely discussed in recent publications (Bremer, 1992, 1998; Givishvili and Leshchenko, 1994, 1995; Givishvili et al, 1995; Danilov, 1997, 1998; Ulich and Turunen, 1997; Rishbeth, 1997; Jarvis et al, 1998; Upadhyay and Mahajan, 1998; Sharma et al, 1999; Foppiano et al, 1999; Danilov and Mikhailov, 1999; Mikhailov and Marin, 2000; Deminov et al, 2000; Danilov and Mikhailov, 2001)
The interest in the ionospheric trend analysis was greatly stimulated by the model calculations of Rishbeth (1990) and Rishbeth and Roble (1992), who predicted the ionospheric effects of the atmosphere greenhouse gas concentration in
From a physical point of view, the obtained result is interesting, telling us that practically all observed foF2 long-term variations may be attributed to the variations in solar and geomagnetic activity, i.e. they are of a natural origin
Summary
Due to an increasing interest in the anthropogenic impact on the Earth’s atmosphere the ionospheric parameter longterm trends are widely discussed in recent publications (Bremer, 1992, 1998; Givishvili and Leshchenko, 1994, 1995; Givishvili et al, 1995; Danilov, 1997, 1998; Ulich and Turunen, 1997; Rishbeth, 1997; Jarvis et al, 1998; Upadhyay and Mahajan, 1998; Sharma et al, 1999; Foppiano et al, 1999; Danilov and Mikhailov, 1999; Mikhailov and Marin, 2000; Deminov et al, 2000; Danilov and Mikhailov, 2001). Further efforts are required in this direction to find out the physical mechanism of the F2-layer trends
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