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Ann. Geophys., 26, 335-344, 2008
www.ann-geophys.net/26/335/2008/
© European Geosciences Union 2008
Global electron content: a new conception to track solar activity
E. L. Afraimovich1, E. I. Astafyeva1, A. V. Oinats1, Yu. V. Yasukevich1, and I. V. Zhivetiev2
1Institute Solar-Terrestrial Physics SB RAS, Irkutsk, Russia
2Institute of Cosmophysical Research and Radiowave Propagation, FEB RAS, Petropavlovsk-Kamchatskii, Russia
Abstract. We developed a method and programs for estimation of the global electron
content (GEC) from GPS measurements, using the ionosphere models IRI-2001
and NeQuick. During the 23rd cycle of solar activity, the value of GEC varied
from 0.8 to 3.2×1032 electrons, following changes in the solar extreme
ultra violet (EUV) radiation and solar radio emission at 10.7-cm wavelength.
We found a strong resemblance of these variations, with discernible 11-year
and 27-day periodicities. A saturation effect of GEC is found when F10.7
increases. We found that GEC is characterized by strong seasonal
(semiannual) variations with maximum relative amplitude at about 10% during
the rising and falling parts of the solar activity and up to 30% during
the period of maximum. It was found that the relative difference between model
and experimental GEC series increase as the smoothing time window decreases. We
found that GEC-IRI seasonal variations are out-of-phase with experimental
GEC values. The lag between model and experimental maximum of GEC values can
reach several tens of days. The variations of GEC lag, on average, 2 days
after those of F10.7 and UV. GEC completely reflects the dynamics of the active
regions on the solar surface. The amplitude of the 27-day GEC variations
decreases from 8% at the rising and falling solar activity to 2% at
the maximum and at the minimum. We also found that the lifetime of contrast
long-living active formations on the Sun's surface in EUV range for more
than 1 month exceeds the one in radio range (10.7 cm).
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