Comparative studies of short-term ionospheric variability in the F region ionosphere during rapid sequence sounding campaign "HIRAC/ SolarMax" (23-29 April 2001) are presented. The ionospheric short-term fluctuations have been studied in detail using measurements from vertical sounding at Ebro (40.8 °N, 0.5 °E) and Průhonice (49.9 °N, 14.5 °E) in the period range from 15 minutes to 2 hours. The electron density measurements contain variations that indicate the possible presence of propagating gravity waves. Regular wave-like bursts were found during quiet days at both stations in electron concentration in F region, with an increase of the oscillation activity after sunrise and then during late afternoon, and at sunset and after sunset. Solar Terminator is assumed to be one of the sources of the regular wave bursts detected in the ionosphere during campaign HIRAC. As expected, substantial intensification in longer period gravity waves was found to occur during the disturbed period on April 28. Particular enhancement of the wave-like activity during disturbed day is discussed, being significant evidences of a change of the wave-like activity pattern at a height around 200 km.