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Ann. Geophys., 17, 631-638, 1999
www.ann-geophys.net/17/631/1999/
© European Geosciences Union 1999
Resonant enhancement of relativistic electron fluxes during geomagnetically active periods
I. Roth1, M. Temerin1, and M. K. Hudson2
1Space Sciences Laboratory, University of California, Berkeley, CA 94720, USA
e-mail: ilan@ssl.berkeley.edu
2Physics and Astronomy Department, Dartmouth College, Hanover, NH 03755, USA
Abstract. The strong increase in the flux of
relativistic electrons during the recovery phase of magnetic storms and during
other active periods is investigated with the help of Hamiltonian formalism and
simulations of test electrons which interact with whistler waves. The intensity
of the whistler waves is enhanced significantly due to injection of 10-100 keV
electrons during the substorm. Electrons which drift in the gradient and
curvature of the magnetic field generate the rising tones of VLF whistler
chorus. The seed population of relativistic electrons which bounce along the
inhomogeneous magnetic field, interacts resonantly with the whistler waves.
Whistler wave propagating obliquely to the magnetic field can interact with
energetic electrons through Landau, cyclotron, and higher harmonic resonant
interactions when the 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
perpendicular wavelength, numerous cyclotron, harmonics can contribute to the
resonant interaction which breaks down the adiabatic invariant. A similar
process diffuses the pitch angle leading to electron precipitation. The
irreversible changes in the adiabatic invariant depend on the relative phase
between the wave and the electron, and successive resonant interactions result
in electrons undergoing a random walk in energy and pitch angle. This resonant
process may contribute to the 10-100 fold increase of the relativistic electron
flux in the outer radiation belt, and constitute an interesting relation between
substorm-generated waves and enhancements in fluxes of relativistic electrons
during geomagnetic storms and other active periods.
Key words. Magnetospheric physics (energetic particles
ยท trapped; plasma waves and instabilities; storms and substorms)
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