Are the double-peaks in solar indices during solar maxima of cycle 23 reflected in ionospheric foF2?

Abstract

The 12-month running means of solar indices indicated that during 2000–2002, all solar indices (including EUV) had two maxima, one near July 2000 and another near end of 2001, but the magnitudes of the second maximum relative to the first maximum were different for different solar indices. For EUV 26–34 nm relevant for ionospheric (foF2) 2, the second maximum was ∼3% higher than the first maximum. The 12-month running means of (foF2) 2 at some mid-latitude locations in both hemispheres showed similar two maxima, but the magnitudes of the second maximum relative to the first maximum were not similar to those of observed solar EUV (∼3%) and were very different at different locations (−3% to +18%). Even on the solar cycle time scale (solar minimum to solar maximum), changes of (foF2) 2 at different locations were not alike (factors of 3.1–4.5).