The quasi-pure pitch-angle scattering of energetic electrons driven by field-aligned propagating whistler mode waves during the 9～15 October 1990 magnetic storm at L≈ 3 ～ 4 is studied, and numerical calculations for energetic electrons in gyroresonance with a band of frequency of whistler mode waves distributed over a standard Gaussian spectrum is performed. It is found that the whistler mode waves can efficiently drive energetic electrons from the larger pitchangles into the loss cone, and lead to a flat-top distribution during the main phase of geomagnetic storms. This result perhaps presents a feasible interpretation for observation of time evolution of the quasi-isotropic pitch-angle distribution by Combined Release and Radiation Effects Satellite （CRRES） spacecraft at L ≈ 3 ～ 4.
The left-hand superluminous electromagnetic waves, L-O mode and L-X mode, can be excited and observed in the auroral cavity of the Earth during the magnetic storms. The two modes can propagate into outer radiation zone and encounter enhanced resonant interactions with the trapped energetic electrons over a wide range of magnetosphere. A current first-order resonant model is extended to evaluate the stochastic acceleration of electrons by the L-O mode and L-X mode at the higher-order resonance. Similar to the first-order resonance, L-O mode can produce significant acceleration of electrons at the higher harmonic resonances over a wide range of wave normal angles and spatial regions. However, the higher harmonic resonance＇s contribution for significant electron acceleration by L-X mode is less than that of the first order resonance, with the requirement of higher minimum energies, e.g., -1 MeV in the outer radiation belt. This indicates that L-O mode may be one of the efficient mechanisms for the stochastic acceleration of electrons within the outer radiation zone.
