Latitudinal variation of ionospheric slab thickness Original Research Article

The ionospheric slab thickness τ, defined as a ratio of the total electron content (TEC) to the F-region peak electron density NmF2, is a first order measure of the shape of the electron density profile. In the present study, we use GPS-derived TEC and vertical electron content estimates ITEC from ground-based ionosonde observations together with the corresponding foF2 (F2 layer critical frequency) and hmF2 (F2 layer peak height) at 14 world-wide stations lying at different latitude regions from the geomagnetic equator to north pole. The period of study is during 2001–2002, which is close to the solar maximum phase of the 23rd solar cycle. Hourly values of TEC, ITEC, foF2, hmF2 and τ during the period of study are used to compare τ values from the observation and model predictions using the International Reference Ionosphere extended towards the plasmapause with the plasmasphere option of the Russian standard model of the ionosphere, IRI*. For the three latitudinal zones (high, mid and low latitudes) the IRI* predictions of τ are compared with observed τ values for the bottomside ionosphere (below hmF2), topside ionosphere (between hmF2 and 1000 km), plasmasphere (from 1000 to 20,000 km), and the total height range through the ionosphere and plasmasphere. Significant overestimation of τ has been revealed when using IRI*, particularly for the topside ionosphere at high latitudes. Relation of the topside part of slab thickness with the topside half peak density height above the F2 layer peak provides new characteristic parameter for modeling of the topside shape of electron density profile.