We study ionospheric variability using HF radio facilities within three latitudinal regions: polar zone (Norilsk ionosonde; 69.4N, 88.1E), sub-polar zone (Ekaterinburg SuperDARN radar; 56.4N, 58.5E) and mid-latitude zone (Hokkaido East SuperDARN radar; 43.53N, 143.61E). As characteristics we select the peak electron density (NmF2) measured with the ionosonde and the ground backscatter range corresponding to the skip distance (Rmin) from HF radar measurements. The disturbances of characteristics are the deviations of characteristics from their 27-day running median values. The variability is considered as the root mean square of disturbances. For different tasks we used different types of averaging. Annual averaging was used for studying year-to-year changes in the variability (solar cycle variations). To obtain the seasonal pattern of the variability we performed averaging over years for the daytime of each day of year. In the paper we discuss similarities and differences between the selected characteristics and between the polar, sub-polar and mid-latitude ionospheric variability.