NON-MARKOVIAN ELECTRON-DIFFUSION IN THE AURORAL IONOSPHERE AT HIGH LANGMUIR-WAVE INTENSITIES

A generalized non-Markovian diffusion model which describes the intera ction of Langmuir waves with field-aligned electrons in the auroral io nosphere is found to be relevant to the large amplitude Langmuir waves measured by UC Berkeley sounding rockets and by the Freja satellite. This model is valid for any ordering of the diffusion time and the aut ocorrelation time (the standard quasilinear diffusion model requires t he diffusion time to be much longer than the autocorrelation time). We demonstrate that, while the quasilinear diffusion approximation is va lid for the lower altitudes studied by the Berkeley sounding rockets, the non-Markovian model is needed for the intense waves observed at th e higher altitudes probed by Freja. A test particle simulation is empl oyed to quantify our estimates of the relevant timescales.