Field aligned observations of transequatorial bubbles from Rarotonga in 1969‐70

A raster scanning photometer with 0.5° field of view was used in 1969‐70 to make images in 6300 Å and 5577 Å emission from Rarotonga of tropical F region trans‐equatorial ‘bubbles’ or ‘depletions.’ From this site the F region plasma structures in the emission layer can be viewed in a magnetic field aligned configuration. A spatial resolution of approximately 15 km was achieved, and revealed a variety of shapes in the bubble cross sections, including ‘bifurcations’ and ‘pinched off’ bubbles. Eastward drift velocities averaged 125 ms −1 . Tilts were usually westward at about 45° in the equatorial plane, but some were near zero and some were eastward. The tops reached apex heights of over 800 km. The structures appeared a little less diffuse in 5577 Å emission than in 6300 Å owing to less diffusion of O¹S with its 0.75 sec. lifetime, than O¹D with its 150 sec. lifetime.