Ionospheric Slab Thickness at the Equatorial Anomaly Region after the Deep Solar Minimum of Cycle 23/24

Abstract:

This paper reports the first results of equivalent ionospheric slab thickness estimated in the Brazilian longitudinal sector. The ionospheric slab thickness is a measure of the shape of the ionospheric profile and can be obtained from the ratio of total electron content (TEC) to the F-region peak electron density (N_mF₂). In this study the ionospheric slab thickness was obtained during one year of extremely low solar activity (March 2009 to February 2010). The period analyzed were separated in three seasonal groups: equinoxes, June solstice (winter) and December solstice (summer) months. The ionospheric slab thickness was studied at two stations located around the southern crest of the Equatorial Ionization Anomaly (EIA). One station located in the inner edge of the anomaly region, named Palmas (10.12º S, 48.21º O, 7.73º S dip lat), and another station located under the crest of the anomaly, situated at São José dos Campos (23.07º S, 45.52º O, 19.61º S dip lat). The TEC data have been obtained from dual-frequency GPS receivers and the N_mF₂ data were calculated from the f₀F₂ parameter scaled from ionograms recorded by simultaneous measurements of digital ionosondes. The diurnal, seasonal and latitudinal variations of the ionospheric slab thickness were then analyzed. The minimum values of TEC and N_mF₂ were observed in both stations during the early morning, and the maximum values during afternoon hours. During the summer and equinoctial periods the slab thickness reached the higher values compared to those observed during the winter solstice months. The nearly equatorial site of Palmas showed values of daytime slab thickness larger than those observed at the low latitude station of São José dos Campos, except during the June solstice months. At São José dos Campos, a pronounced pre-dusk increase in the equivalent slab thickness was observed during the winter solstice months. From the calculated slab thickness we also inferred the atmospheric neutral temperature (T_n) over both the stations. Other relevant aspects of the ionospheric slab thickness behaviour and its comparison with International Reference Ionosphere (IRI) model results will be presented and discussed.