Diurnal variations of the vertical total electron content under quiet heliogeomagnetic conditions

We studied character of diurnal variation of the vertical total electron content (TEC) under quiet heliogeomagnetic conditions using the GIM map analysis. This variation reflects the background behaviour of ionization,. We obtained statistical estimates of maximum and minimum TEC values within 24 hours along with amplitudes of diurnal TEC variations for different latitude-longitude sectors and for different seasons. Averaged diurnal variations of the vertical TEC were compared with behaviour of the F2-layer critical frequency and TEC registration data using the geostationary satellite ATS-3. The comparison showed that, despite the interpolation, GIM maps provide an adequate picture of the ionization behaviour under quiet heliogeomagnetic conditions.