Induced Nonlinear Scattering of Magnetospherically Reflecting Whistlers
Abstract
Whistler waves play an important role in regulating the energetic electron population of the Earth’s inner magnetosphere through pitch angle scattering of resonant electrons. There are many potential sources of whistlers in the lower magnetosphere (L=2-3 ), e.g., lightening discharges, VLF transmitters, and unstable particle distributions. Once the whistler waves are generated, they are maintained in an effective cavity around the lower-hybrid resonant surface where the waves are ultimately dissipated. Before the waves are dissipated they participate in pitch angle scattering of energetic resonant electrons. In this paper we demonstrate that when the energy density of whistler wave turbulence exceeds a threshold, which we estimate occurs at δB=30-50 pT, the process of nonlinear induced scattering by thermal electrons [1] dominates both electron-ion collisional damping and linear Landau damping due to superthermal electrons [2]. This occurs primarily by scattering of waves before the wave-packet settles down on a lower-hybrid surface (where the wave is heavily damped). This has two important intermediate consequences: 1) the lifetime of whistler wave turbulence is increased from seconds to 10s of seconds, 2) the whistler wave packets spend more time away from the lower-hybrid surface and thus interact more efficiently with energetic electrons [1]. Thus the lifetime of energetic electrons is reduced due to the induced nonlinear scattering of whistler waves. [1] Ganguli et al., Phys. of Plasmas, 17, 052310 (2010). [2] Innan et al., J. Geophys. Res., 108, 1186 (2003).
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFMSM11B1724C
- Keywords:
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- 2716 MAGNETOSPHERIC PHYSICS / Energetic particles: precipitating;
- 2772 MAGNETOSPHERIC PHYSICS / Plasma waves and instabilities;
- 2774 MAGNETOSPHERIC PHYSICS / Radiation belts