Ionospheric variability for quiet and perturbed conditions Original Research Article

An F2 region critical frequency database, from 75 ionosonde stations and 25 storms, covering a full solar cycle, was built as the basis of the STORM Time Empirical Ionospheric Correction Model. This database has been sorted by season (five intervals from summer to winter, including intermediate seasons), geomagnetic latitude (four regions, 0–20, 20–40, 40–60, and 60–80), and storm intensity (as a function of filtered ap). For each bin of latitude-season, the standard deviation was used to quantify the scatter around the fit, i.e. the geophysical variability. The first interval, between 0 and 500 units of the filtered ap, corresponds to non-perturbed conditions; where approximately one half of the data lay. The rest of the intervals, with increments of 500 units, cover perturbed conditions. For quiet conditions, the lowest variability of the data was found to be about 0.15, in the summer hemisphere. The standard deviation of the data increases up to 0.23 for intermediate seasons, up to 0.22 for equinox, and up to 0.40 for the winter hemisphere. In general, low latitudes show higher variability for both perturbed and un-perturbed conditions, while the summer hemisphere, mid-latitudes have the lowest.