Nighttime dynamics of the F region near Arecibo as mapped by airglow features

A scanning photometer was used to obtain red line airglow measurements at Arecibo in order to determine the direction and phase velocity of propagation of major airglow enhancements. The scans were made in the N-S direction on 13 nights and in the E-W direction on five nights. The most common type of descent begins in the south and progresses northward, with an apparent phase velocity of the order of 300 m/s. Neutral winds are apparently the cause of this type of descent. Observed descents of the equatorial ionosphere are described, and their relation to airglow enhancement is considered. A second type of airglow enhancement was seen occasionally and travels from north to south; this enhancement is probably due to traveling ionospheric disturbances. A third type previously unreported involves sudden descents lasting an hour or so and sometimes ocurring nearly simultaneously over regions extending at least 1000 km in the N-S or E-W direction.