Abstract
Ion velocities associated with nighttime equatorial plasma depletions near 800 km altitude have been investigated utilizing data from the Defense Meteorological Satellite Program. Observations of upward ion drifts exceeding 800 m s−1, within the depleted regions, are shown to have a strong dependence on solar zenith angle. Given the existence of bubble plasma, the probability of observing large upward drifts is as high as 40% just after sunset, when the solar zenith angle is 110°, but it decreases rapidly, falling below 5% for solar zenith angles above 140°. It is suggested that irregularity formation in the bottomside F region during a period of postsunset enhanced electric fields will cause magnetic flux tubes of depleted plasma to accelerate upward, reaching a velocity maximum at apex heights corresponding to the peak in the flux‐tube‐integrated conductivity of the background plasma. In the presence of a postsunset enhanced electric field, this peak may exist at apex heights above 500 km.
Published Version
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