By using the data of total electron content (TEC) obtained from the Faraday rotation of signals from geostationary satellites recorded at several locations, the day-to-day variability of the daily range and hour of maximum of TEC is studied. Fluctuations sometimes as large as ¿50% in the magnitude of TEC and ¿4 hours in the time of the maximum are observed, even on quiet days. Changes in TEC and Nmax even at the same location are not always completely parallel. Also TEC changes at locations separated by more than about 3000 km in latitude or longitude show poor correlations. No relation with changes in solar EUV is indicated. It is suggested that erratic neutral winds blow away from the polar regions toward the equator even during quiet times and create convection cells which may result in ionospheric irregularities of scale lengths of about 3000 km which wander about the globe slowly and give the observed day-to-day variability of TEC and the equivalent slab thickness &tgr;.