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Abstract
Abstract. A previous approach to the ionospheric long-term trend analysis has been applied to the foF1 observations from Slough and Rome in order to investigate a possible relationship between the foF1 and the long-term variation of geomagnetic activity. A 40-year period, starting in 1962, has been used for the analysis. According to the results obtained earlier for F2 and E-region trends, geomagnetic control of the long-term variation has also been revealed for the foF1. Thus, it is now possible to speak about the geomagnetic control of the ionospheric trends in the whole ionosphere. This is not surprising as the Earth's ionosphere is a single entity that is strongly controlled, either directly or indirectly, by the magnetic field. As with the F2-region, this geomagnetic control is provided via neutral composition and temperature changes. A very long-term (centennial) increase in geomagnetic activity in the 20th century is seen in the long-term foF1 variations as well. After its removal, the residual foF1 trends are very small and insignificant. In principal, this means that the observed foF1 long-term variations have a natural origin and can be attributed to solar and geomagnetic activity long-term variations. However, the situation in the thermosphere has been changing since 1997 and available foF2 observations at the two stations reveal information about the "break down" of the geomagnetic control in the F2-region. Possible reasons of these changes are discussed.
Highlights
During the last few decades, long-term trends of ionospheric parameters have been widely discussed due to general interest to the anthropogenic impact on the ecological system and on the Earth’s upper atmosphere as a part of it
Using an earlier developed approach to the ionospheric long-term trend analysis, it was shown for the first time the relationship between foF1 trends and the geomagnetic activity long-term variations
With the earlier obtained results for the foF2 and foE trends, the periods of increasing geomagnetic activity correspond to negative foF1 trends while these trends are positive for the decreasing phase in geomagnetic activity
Summary
During the last few decades, long-term trends of ionospheric parameters have been widely discussed due to general interest to the anthropogenic impact on the ecological system and on the Earth’s upper atmosphere as a part of it. The interest to the problem has been greatly stimulated by the model calculations by Roble and Dickinson (1989), Rishbeth (1990), Rishbeth and Roble (1992) who predicted the ionospheric effects of the atmosphere greenhouse gas concentrations increase. These trends are very small and have no practical importance, they may serve as an indicator of longterm changes in the Earth’s upper atmosphere, and their investigation may be interesting and important from this point of view.
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