Ionospheric slab thickness at the equatorial anomaly region after the deep solar minimum of cycle 23/24

Abstract

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 (NmF2). In this study the ionospheric slab thickness was obtained during one year of extremely low solar activity (from 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 (10.12°S, 48.21°O, 7.73°S dip lat), and another station located under the southern crest of the anomaly, situated at São José dos Campos (23.07°S, 45.52°O, 19.61°S dip lat). The TEC data have been obtained from dual-frequency Global Navigation Satellite System (GNSS) receivers and the NmF2 data were calculated from the foF2 parameter scaled from ionograms recorded by simultaneous measurements of digital ionosondes. The diurnal and seasonal variations of the ionospheric slab thickness at the EIA region were then analyzed. The minimum values of TEC and NmF2 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 their highest values. 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. The atmospheric neutral temperature (Tn) was also estimated from the correlation analysis between the MSIS modeled Tn and the calculated ionospheric slab thickness over the two observations sites. Other relevant aspects of the ionospheric slab thickness behavior and its comparison with International Reference Ionosphere (IRI) model results will be presented and discussed.