Effects of geomagnetic storms at F1-layer heights in Irkutsk region during the decay of solar activity and at its minimum

We estimated the effect of geomagnetic storms on the electron density at F1-layer heights during the solar activity decay and minimum (2003-2008) for the Irkutsk station using the digisonde data (52° N, 104° E). We confirmed the existence of a spring-autumn asymmetry at 190 km for moderate geomagnetic storms. Notable effects at lower F-region heights (150-190 km) were found during autumn superstorms.