Gyroresonant pitch angle scattering by coherent and incoherent whistler mode waves in the magnetosphere

Journal Article · Thu Jan 01 00:00:00 EST 1987 · J. Geophys. Res.; (United States)

DOI:https://doi.org/10.1029/JA092iA01p00127· OSTI ID:7078215

Inan, U S

A test particle approach is used to compare gyroresonant pitch angle scattering of energetic electrons by coherent versus incoherent whistler mode waves, for the case in which the coherent wave amplitude is below the nonlinear phase trapping threshold. Wave packets of 400 ms duration propagating along the magnetic field at L = 4 within the plasmasphere are considered, and the wave-induced pitch angle scattering along the propagation path from one hemisphere to the other and the resulting precipitation flux are computed. An incoherent wave spectrum is simulated by random modulation of the wave frequency at intervals of 1 ms, thereby generating signals with nearly constant power spectral density over a bandwidth of 2 kHz centered at 5.5 kHz. The associated pitch angle scattering is compared with that of a monochromatic 5.5-kHz signal of 400 ms duration. Results of the test particle analysis are compared with those expected on the basis of a classical diffusion treatment, and an expression is derived for an effective ''diffusion'' coefficient for pitch angle scattering by coherent waves. The trajectory followed by a particle when interacting with incoherent waves essentially represents a random walk in velocity space, while for coherent waves the pitch angle of the particle varies in a well-defined manner. In spite of the fact that individual particle scattering are typically larger for coherent waves, the peak precipitation fluxes induced by incoherent waves are found to be approximately the same as those for coherent waves having the same total power. This results from the fact that incoherent waves interact with particles over a wider range of energies. As a consequence, the energy spectrum and the temporal extent of transient precipitation pulses due to incoherent wave packets are broader than those for equivalent coherent ones.

• Research Organization: STAR Laboratory, Stanford University, Stanford, California
• OSTI ID: 7078215
• Journal Information: J. Geophys. Res.; (United States), Vol. 92:A1
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
RADIATION BELTS
CHARGED-PARTICLE PRECIPITATION
EARTH MAGNETOSPHERE
INCLINATION
SCATTERING
TRAPPED ELECTRONS
TRAPPED PROTONS
WHISTLERS
BARYONS
EARTH ATMOSPHERE
ELECTROMAGNETIC RADIATION
ELECTRONS
ELEMENTARY PARTICLES
FERMIONS
HADRONS
LEPTONS
NOISE
NUCLEONS
PROTONS
RADIATIONS
RADIO NOISE
RADIOWAVE RADIATION
640201* - Atmospheric Physics- Auroral
Ionospheric
& Magetospheric Phenomena