Wave structures observed in the equatorial F-region plasma density and temperature during the sunset period

Electron density and temperature measurements were carried out with Langmuir probes (LP) on board Brazilian sounding rockets launched soon after the local sunset from Natal (5.8°S, 35.2°W, dip 23.7°S) and Alcântara (2.3°S, 44.4°W, dip 7°S), Brazil, on December 02, 2011, and December 08, 2012, respectively. Digisondes operating near the launching sites revealed a rapid rise in the F-region base indicating a probable pre-reversal enhancement of the vertical plasma drift. Strong spread-F traces are also visible on the ionograms simultaneously recorded, suggesting the occurrence of ionospheric bubbles during these campaigns. Electron density and temperature vertical profiles estimated from the LP data exhibit in the E-F region valley (120-300 km) the presence of large-amplitude wave activity, and electron temperature values higher than 1600 K, respectively, phenomena probably related to the electrodynamic processes that occur during the sunset period.