The large mass differences between the ions present in the transition region between the F layer and protonosphere can cause individual ion species to drift at different velocities during periods of rapid temperature change. Calculations show that these velocity differences can be detected using incoherent scatter. Preliminary observations indicate that velocity differences between H+ and O+ can be as large as 80 m/s after sunset. Such simultaneous measurements of the fluxes of individual ion species are essential or detailed studies of the charge exchange reactions between H+ and O+ and of the morphology of ionospheric-protonospheric coupling.