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The strong increase in the flux ofrelativistic electrons during the recovery phase of magnetic storms and duringother active periods is investigated with the help of Hamiltonian formalism andsimulations of test electrons which interact with whistler waves. The intensityof the whistler waves is enhanced significantly due to injection of 10-100 keVelectrons during the substorm. Electrons which drift in the gradient andcurvature of the magnetic field generate the rising tones of VLF whistlerchorus. The seed population of relativistic electrons which bounce along theinhomogeneous magnetic field, interacts resonantly with the whistler waves.Whistler wave propagating obliquely to the magnetic field can interact withenergetic electrons through Landau, cyclotron, and higher harmonic resonantinteractions when the Doppler-shifted wave frequency equals any (positive ornegative) integer multiple of the local relativistic gyrofrequency. Because thegyroradius of a relativistic electron may be the order of or greater than theperpendicular wavelength, numerous cyclotron, harmonics can contribute to theresonant interaction which breaks down the adiabatic invariant. A similarprocess diffuses the pitch angle leading to electron precipitation. Theirreversible changes in the adiabatic invariant depend on the relative phasebetween the wave and the electron, and successive resonant interactions resultin electrons undergoing a random walk in energy and pitch angle. This resonantprocess may contribute to the 10-100 fold increase of the relativistic electronflux in the outer radiation belt, and constitute an interesting relation betweensubstorm-generated waves and enhancements in fluxes of relativistic electronsduring geomagnetic storms and other active periods.  <b>Key words.</b> Magnetospheric physics (energetic particles· trapped; plasma waves and instabilities; storms and substorms

Resonant enhancement of relativistic electron fluxes during geomagnetically active periods