Enhanced Pitch Angle Diffusion due to Electron-Whistler Interactions   during Disturbed Times
  During periods of increased magnetospheric activity, whistler wave emissions have been observed with increased wave amplitudes. We consider a pitch angle diffusion mechanism that is shown to scale with whistler wave amplitude and hence is 'switched on' during these periods of intense activity.   We consider the interaction between relativistic electrons and two oppositely directed, parallel propagating whistler mode waves. We show that for intense whistlers this process is stochastic and results in strong electron pitch angle diffusion.   We show that the interaction is rapid, occur on timescales of the order of tens of electron gyroperiods and that the interaction is sensitive to wave amplitude, wave frequency and electron energy. 
W Wykes, S C Chapman, G Rowlands