F2 Peak parameters, drifts and spread F derived from digisonde ionograms for the COPEX campaign in Brazil

Digisonde ionograms recorded in Brazil during the COPEX campaign of 2002 have been analyzed to determine the diurnal variations of the F2 peak parameters (foF2, hmF2 and the Chapman scale height, Hm) for the three COPEX stations, Boa Vista, Cachimbo and Campo Grande. Values of foF2 were derived at 15-min intervals for UT days 278–298. The autoscaled F2 traces for all ionograms recorded on several days were modified manually as required and then used to derive the F2 peak parameters. The Cachimbo ionograms have also been analyzed to determine the post-sunset vertical drifts and the occurrence of spread F echoes at the magnetic equator. Spread F occurred on ∼90% of the nights at all three sites, limiting the number of ionograms that provide well-defined peak parameters during these conditions. The ionograms provide a wealth of details not previously reported for equatorial locations, and not predicted by current models of the equatorial ionosphere. In this paper, we discuss the correlation between the observed vertical drifts and the occurrence of spread F echoes, describe the short-term variability of the three peak parameters, and provide brief interpretations of this variability in terms of the processes that control plasma production and transport.