A SEMIKINETIC MODEL FOR IONOSPHERIC LANGMUIR TURBULENCE

Langmuir turbulence during ionospheric heating experiments is studied by a model which treats the low-frequency ion dynamics from a lineariz ed kinetic description, where the usual high frequency Zakharov equati on describing the electron dynamics is retained. The main objective is to compare the predictions from this model with results previously ob tained from quasi-fluid Zakharov models. Our findings are that the pre dictions from the two types of models are in good qualitative agreemen t. At high values of the frequency mismatch and moderate values of the driving electric field, the saturated dynamics is cascade-dominated, while at lower-frequency mismatch, that is, nearer to the reflection h eight, or at higher drive, the dynamics is of the cavitation type. In cascade dominated cases the perturbation of the ion velocity distribut ion is mainly around the ion acoustic velocity, while in cavitation-do minated cases the whole velocity range is perturbed.