Relationship between generation of equatorial F-region plasma bubbles and thermospheric dynamics

Abstract

Simultaneous zenith measurements of the OI 630.0 nm and 557.7 nm nightglow emissions, using a multi-channel tilting filter type photometer and nighttime thermospheric neutral wind velocities from the Doppler shifts of the OI 630.0 nm emission line, using a Fabry-Perot interferometer, have been carried out at Cachoeira Paulista (23°S, 45°W), Brazil, during 1988–1991. These measurements constitute a unique opportunity to study the relationship between the generation of F-region plasma bubbles (regions of depleted electron densities) and thermospheric dynamics. During the period of March 1988 to June 1991, we have 9 nights on which there were nearly full nights of simultaneous observations of thermospheric wind velocities (zonal and meridional) and the OI 630.0 nm and 557.7 nm emissions showing formation of plasma bubbles. On the night of March 18, 1991, the zonal wind was unusually strong in the beginning of the night (300 m/s) and this night shows very strong formation of plasma bubbles, indicating that a strong zonal wind in some way may be connected with plasma bubble formation through the electric field created by the interaction between the zonal wind and the Earth's magnetic field. However, both the zonal and meridional winds on several nights with, and without plasma bubbles, are comparable. This feature possibly indicates only a secondary role of thermospheric winds in the generation of the equatorial ionospheric plasma depletions. It should be pointed out that an analysis of the nocturnal intensity variations of simultaneous mesospheric (E-region) emissions (OI 557.7 nm, O 2 atm. 864.5 nm, NaD 589.0 nm and OH (9-4) 775.0 nm) on all the nine nights studied, shows the presence of gravity waves, indicating possible relation between wave processes in the mesosphere and F-region irregularities.