The 300Â km threshold value for vertical drifts inferred from F-region heights: Past observations, present developments, and future works

The variability of the quiet time F-region vertical plasma drift in the low latitude region if well understood forms an essential subject in the equatorial ionosphere-thermosphere environment. Vertical drift velocities obtained from the time rate of change of the F-layer height have been adjudged a realistic representation of the true velocities when the F-layer altitudes are greater than a threshold value of 300 km. In this light, the sufficiency of this threshold value of some outstanding past results was discussed in relation to some present observations, especially in the African sector where there is paucity of data, and a new direction for future developments was suggested.