The ionospheric spectrum of the critical frequency of the F2 region, ƒ0F2, is studied in detail at 35 locations during solar maximum and at 21 stations during solar minimum. The spectra contain prominent lines superposed on background continua. The most prominent lines correspond to solar periods of 24, 12, and 8 hours. Lines at half a lunar day (period of 12.48 solar hours) and at two lunisolar periods have also been detected in all the spectra investigated. The lunisolar lines have statistically significant amplitudes only at the low-latitude stations. Our analysis indicates the influence in the F region of plasma transport processes such as E×B drift, ambipolar diffusion, and ion-drag effects of the neutral air wind generated by the thermospheric diurnal density variations. An assessment of the roles of some of these processes is attempted in terms of the results obtained from our analysis.