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Ann. Geophys., 21, 751-760, 2003
www.ann-geophys.net/21/751/2003/
© European Geosciences Union 2003
Long-term trends of foE and geomagnetic activity variations
A. V. Mikhailov1 and B. A. de la Morena2
1Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation, Troitsk, Moscow Region 142190, Russia
2National Institute of Aerospace Technology, Atmospheric Sounding Station El Arenosillo, 21130 Mazagon-Moguerssia (Huelva), Spain
Abstract. A relationship between foE
trends and geomagnetic activity long-term variations has been revealed for the
first time. By analogy with earlier obtained results on the foF2 trends
it is possible to speak about the geomagnetic control of the foE
long-term trends as well. Periods of increasing geomagnetic activity correspond
to negative foE trends, while these trends are positive for the
decreasing phase of geomagnetic activity. This "natural" relationship
breaks down around 1970 (on some stations later) when pronounced positive foE
trends have appeared on most of the stations considered. The dependence of foE
trends on geomagnetic activity can be related with nitric oxide variations at
the E-layer heights. The positive foE trends that appeared after the
"break down" effect may also be explained by the [NO] decrease which
is not related to geomagnetic activity variations. But negative trends or
irregular foE variations on some stations for the same time period
require some different mechanism. Chemical pollution of the lower thermosphere
due to the anthropogenic activity may be responsible for such abnormal foE
behavior after the end of the 1960s.
Key words. Ionosphere
(ionosphere-atmosphere interactions; ionospheric disturbances)
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