Momentum coupling in ionospheric critical ionization velocity experiments*

The critical ionization velocity (CIV) effect is a process that can rapidly ionize a neutral gas which moves through a magnetized plasma. The process has been studied for several decades in laboratory experiments, but presently the emphasis has moved to ionospheric injection experiments. In these experiments, the neutral gas component is released at high velocity, with respect to the ionosphere, from a rocket or a satellite. Efficient momentum coupling between the injected cloud and the ambient ionosphere is achieved by means of Alfvén waves that are launched along the magnetic field. A computer model is presented for the momentum exchange between a cloud of injected ions and the ionosphere, and the model electric fields and particle spectra are shown to agree in detail with measurements from the Critical Ionization Test II (CRIT II); [Swenson et al., Geophys. Res. Lett. 17, 2337 (1990)] ionospheric injection experiment.