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Ann. Geophys., 20, 511-521, 2002
www.ann-geophys.net/20/511/2002/
© European Geosciences Union 2002
The method of determination of the long-term trends in the F2 region independent of geomagnetic activity
A. D. Danilov
Institute of Applied Geophysics, Rostokinskays 9, Moscow 129 128, Russia
Correspondence to: A. D. Danilov (adanilov99@mail.ru)
Abstract. A detailed analysis of
the f oF2 data at the Sverdlovsk station is performed to answer the question:
whether the long-term trends of the F2-layer parameter detected recently are
mainly due to the long-term changes in geomagnetic activity during the recent
decades. Two methods to derive trends independent of geomagnetic activity are
developed. It is found that both methods agree well and give a relative
nongeomagnetic trend of about - 0.0015 per year (or an absolute nongeomagnetic
trend of about - 0.015 MHz per year). The close relation of foF2 to Ap
found by several authors is mainly due to a high correlation between the foF2
deviations from the regression line and year-to-year changes in the Ap
index rather than to systematic long-term changes of Ap as has been
suggested earlier.
Key words. Ionosphere (ionospheric
distances; modeling and forecasting)
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