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Solar cycle variations of the amplitudes of the 27-day solar rotation periodreflected in the geomagnetic activity index Ap, solar radio flux F10.7cmand critical frequency foF2 for mid-latitude ionosonde station Moscowfrom the maximum of sunspot cycle 18 to the maximum of cycle 23 are examined.The analysis shows that there are distinct enhancements of the 27-dayamplitudes for foF2 and Ap in the late declining phase of each solarcycle while the amplitudes for F10.7cm decrease gradually, and the foF2 and Ap amplitude peaks are much larger for even-numbered solar cyclesthan for the odd ones. Additionally, we found the same even-high and odd-lowpattern of foF2 for other mid-latitude ionosonde stations in Northernand Southern Hemispheres. This property suggests that there exists a 22-yearcycle in the F2-layer variability coupled with the 22-year cycle in the27-day recurrence of geomagnetic activity. Key words. Ionosphere (mid-latitude ionosphere; ionosphere-magnetosphere interactions) – Magnetosphericphysics (solar wind-magnetosphere interactions

The 22-year cycle in the geomagnetic 27-day recurrences reflecting on the F2-layer ionization