The measured motions inside equatorial plasma bubbles

A preliminary study of the vertical and north‐south horizontal ion motions in plasma bubbles in the near‐equatorial ionosphere utilizing drift meter data from Atmosphere Explorer E is presented. High‐resolution data show that the vertical ion velocity in some bubbles increases approximately linearly with (No‐N)/N, where No is the background ion concentration and N is the bubble ion concentration. At sufficiently large No/N the vertical ion velocity saturates, but often at a value substantially larger than the ratio of the gravitational acceleration to the ion neutral collision frequency (g/νin), which is the nominal collision‐dominated velocity limit for cylindrical bubbles. These larger than nominal velocities may result from background eastward electric fields and/or from a vertically elongated bubble cross section. The unanticipated observation that large poleward horizontal drifts accompany these vertical drifts seems to follow naturally from a redistribution of plasma along flux tubes as the plasma convects from the bottomside of the F region to high altitudes.