The height dependence of the perturbation of the mid-latitude F-region by Pi2 pulsations

Observations are presented of the perturbation of the mid-latitude bottom-side F-layer by Pi2 geomagnetic pulsations using vertical HF sounding by several well-spaced frequencies simultaneously. It is found that the amplitude and phase of the Doppler velocity oscillation are constant with height. The observations were compared with three mechanisms previously proposed for such perturbations. The detailed numerical model of Sutcliffe and Poole [ J. geophys. Res. 94, 13,505 (1989)] is interpreted as predicting that, for Pi2 pulsations at night, the dominant mechanism of the three will be vertical electron drift driven by the pulsation electric field. In the framework of this theory, the observed amplitude of Doppler velocity and its height profile show that vertical drift indeed dominates. Simple models, assuming hydromagnetic wave fields uniform with height and neglecting collisions, are developed for each mechanism. These confirm features of Sutcliffe and Poole's model and, taken with the observations presented, again indicate that vertical electron drift dominates for Pi2. The height profile of Doppler velocity phase is consistent with the dominance of vertical drift, but is a poor diagnostic for distinguishing the three mechanisms in the case of Pi2 pulsations.