The peak height hmF2 of the ionosphere F2 layer is controlled by ambipolar diffusion, recombination and neutrals wind and the changes in the condition of recombination causes changes in the ions vertical velocity.

The ground-based inferred vertical plasma drift, as well as radar measurements especially during the evening and early morning hours are regarded to be apparent. This is because of the additional contribution from photochemical loss and production. As a result, it becomes very necessary to explain the role of chemistry processes from these drift measurements for realistic understanding of the actual movement of plasma in the ionosphere. Read Sumod et al. (2012), Indian Journal of Radio and Space Physics, 41, 130.

Additionaly, Ambili et al. (2012, Geophys. Res. Lett., 39, L16102, doi:10.1029/2012GL052, 876 had disclosed that the apparent surge of the equatorial F-region peak at sunrise is produced majorly by photochemistry as against the general believed dynamics. They investigated the behavior of the early morning ionosphere using a Digisonde located at Trivandrum. They observed that as the peak rate of photo-ionization moves down in altitude and increases in magnitude, the newly formed charged particles follows a comparable pattern. Subsequently, a jump, which was followed by a quick downward motion of the increasingly strong F-region peak altitude, was observed as the density becomes large enough to be detected by the digisonde. They concluded that the rationale behind the downward motion of the F peak ending around 250 km is chemistry and not the usual electrodynamics.

paper about chemical corrections for the vertical plasma drift calculation is for example:

Bitencourt, J. A., Abdu, M. A., A theoretical comparison between apparent and real vertical ionization drift velocities in the equatorial F-region. Journal of Geophysical Research 86: 2451-2454, 1981.