Images in the 6300-Å and 7774-Å plasma recombination emissions have been made that show the development and dynamics of field-aligned bubbles of low density plasma in the tropical nighttime F region. An intensified charge coupled device detector was used with an eight-filter camera to view a field-aligned section of the F region that mapped to magnetic apex heights from 400 to 900 km above the dip equator and up to 700 km in east-west extent from a ground-based observation site on Mount Haleakala, Hawaii. Field-aligned bubbles were observed to grow from near-stationary wavelike perturbations with horizontal scale sizes of about 100 km at the lower apex altitude regions during the evening hours. The bubbles were seen to elongate toward higher apex levels as they accelerated eastward, sometimes reaching eastward velocities of over 100 m/s. In general, field-aligned depletions were observed to occur over all portions of the night. A characteristic shape was often observed with a rather sharp vertical wall bounding the depletion on the eastward side and with several tilted branches on the westward side. The structures were often observed to develop westward tilts as shear motions yielded eastward drifts that decreased with increasing apex altitude. During periods of extreme levels of shear, isolated depletions were seen to drift separately from neighboring depletion structures.
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