Resonant enhancement of relativistic electron fluxes during geomagnetically active periods

The strong increase in the flux of relativistic electrons during the recove ry phase of magnetic storms and during other active periods is investigated with the help of Hamiltonian formalism and simulations of test electrons w hich interact with whistler waves. The intensity of the whistler waves is e nhanced significantly due to injection of 10-100 keV electrons during the s ubstorm. Electrons which drift in the gradient and curvature of the magneti c field generate the rising tones of VLF whistler chorus. The seed populati on of relativistic electrons which bounce along the inhomogeneous magnetic field, interacts resonantly with the whistler waves. Whistler wave propagat ing obliquely to the magnetic field can interact with energetic electrons t hrough Landau, cyclotron, and higher harmonic resonant interactions when th e Doppler-shifted wave frequency equals any (positive or negative) integer multiple of the local relativistic gyrofrequency. Because the gyroradius of a relativistic electron may be the order of or greater than the perpendicu lar wavelength, numerous cyclotron, harmonics can contribute to the resonan t interaction which breaks down the adiabatic invariant. A similar process diffuses the pitch angle leading to electron precipitation. The irreversibl e changes in the adiabatic invariant depend on the relative phase between t he wave and the electron, and successive resonant interactions result in el ectrons undergoing a random walk in energy and pitch angle. This resonant p rocess may contribute to the 10-100 fold increase of the relativistic elect ron flux in the outer radiation belt, and constitute an interesting relatio n between substorm-generated waves and enhancements in fluxes of relativist ic electrons during geomagnetic storms and other active periods.