Signs of anomalous behavior of the ionosphere in 2003-2014 at F1-layer heights over Irkutsk

We have detected an anomalous electron density Ne increase in winter months in Irkutsk in some years of the period 2003-2014. This effect was manifested when we compared the experimental values obtained by the Irkutsk ionosonde with model calculations at F1-layer heights (120-200 km). Two anomalous time zones have been found. The first was observed in the period 2003-2006 near solar minimum. In this zone, 2003 is the year of maximum manifestation of the winter Ne increase over the entire research period. The second anomalous zone - 2012, 2013, 2014 - was detected during solar maximum. We have explored possible causes of the Ne change in winter at the F1-layer heights in all the years under study. We have found that the main factor causing the winter increase in Ne is significant geomagnetic disturbances in the above time periods.