Zonal drift velocity variations with 30% amplitudes and several minute time scales are observed in Jicamarca radar interferometer data collected from bottomside F region altitudes during two different periods with 70--90 m/s and 100--155 m/s mean zonal drifts. These fluctuations are indicative of intermediate scale vertical structuring of F region plasma to be expected in periods of Rayleigh-Taylor bubble formation, and may contribute significantly to the decorrelation of forward scattered satellite signals detected for scintillation spaced receiver analysis.