Abstract
Abstract. Using OI6300 airglow images collected over São João do Cariri (7.4∘ S, 36.5∘ W) from 2000 to 2007, the equatorial plasma bubble (EPB) zonal drifts were calculated. A strong day-to-day variability was observed in the EPB zonal drifts, which is directly associated with the very complex dynamics of the nighttime thermosphere–ionosphere system near the Equator. The present work investigated the contribution of the semidiurnal lunar tide M2 for the EPB zonal drifts. The M2 presented an amplitude of 3.1 m s−1 in the EPB zonal drifts, which corresponds to 5.6 % of the average drifts. The results showed that the M2 amplitudes in the EPB zonal drifts were solar cycle and seasonally dependent. The amplitude of the M2 was stronger during the high solar activity, reaching over 10 % of the EPB zonal drift average. Regarding the seasons, during the Southern Hemisphere summer, the M2 amplitude was twice as large (12 %) compared to the equinox ones. The seasonality agrees with other observations of the M2 in the ionospheric parameters such as vertical drifts and electron concentration, for instance. On the other hand, the very large M2 amplitudes found during the high solar activity agree with previous observations of the lunar tide in the ionospheric E region.
Highlights
Equatorial plasma bubbles (EPBs) appear during the nighttime near the magnetic equator and extend across the tropics along the magnetic field lines (e.g., Weber et al, 1978)
One can see that the solid line fits very well to the data, indicating that the lunar semidiurnal tide was present during the whole studied period, with an amplitude of 3.1 m s−1 corresponding to 5.6 % of the zonal drift average
Another relevant aspect of being considered is that, the amplitude is relatively small, this oscillation is always present in data producing an interesting day-to-day variability in the dynamics of the EPBs
Summary
Equatorial plasma bubbles (EPBs) appear during the nighttime near the magnetic equator and extend across the tropics along the magnetic field lines (e.g., Weber et al, 1978). As the EPBs contain plasma irregularities, radio techniques have been used to investigate them (e.g., Woodman and La Hoz, 1976; Abdu et al, 1985, 1998; Fejer et al, 1996; de Paula and Hysell, 2004; Chu et al, 2005). The zonal electric field controls the vertical movement of the F layer. During the daytime the plasma moves upward, while during the nighttime, the motion is downward. After the sunset, the pre-reversal enhancement (PRE) can occur, which is a rapid upward movement of the F region before it reverses, i.e., before the motion becomes downward (Farley et al, 1986). The PRE has well-defined temporal dependencies, being more intense during the summer and with high solar activity (Fejer et al, 1991)
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