A MECHANISM OF FORMATION OF PULSATING AURORAE

We consider a mechanism of pulsating aurora formation relevant for the substorm recovery phase. It is based on the spikelike regime of whistler cyclotron instability in auroral ducts with enhanced plasma density, elongated with geomagnetic field lines. We present the rigorously derived self-consistent quasi-linear theory of flow cyclotron maser operation, which describes spikelike regimes of whistler wave generation and energetic particle precipitation in a duct. We show that pulsations are formed due to broadening of the resonance region in velocity space in the course of instability development. We have obtained theoretical estimations for temporal characteristics of pulsating auroral patches. Pulsating regime is realized when the energetic electron number density is below some critical value depending on background plasma density and particle source parameters. Pulsation ''on'' time is determined by the nonlinear instability dynamics whereas ''off'' time is nearly equal to the time of reaching the wave excitation threshold. We compare our analytical and numerical results with known experimental data and show that the model explains reasonably most observations concerning pulsation time pattern, electron precipitation fluxes, VLF wave spectrum dynamics, latitudinal and longitudinal dependencies of pulsation characteristics, etc. We have made also preliminary estimations of nonlinear particle trapping effects during the maximum of the on phase that can give rise to a fine temporal structure of pulsations.