Linear and Nonlinear Wave Processes in Inner Magnetosphere Dynamics
Abstract
Earth's inner magnetosphere,which contains the radiation belts,ring current and plasmasphere,is a complex dynamical region that evolves in response to energy inputs from the Sun. The Radiation Belt Storm Probes (RBSP) mission promises to provide the best ever particle,field and wave measurements of the radiation belts. The broad objectives of RBSP are to determine (a) the physical processes that produce radiation belt enhancements, (b) the dominant processes causing relativistic electron loss,and (c) how radiation belt behavior links to the ring current and plasmasphere,and is affected by geomagnetic disturbances. Wave-particle interactions undoubtedly play a leading role in controlling radiation belt dynamics. While wave-particle interactions in the magnetosphere have traditionally been treated using linear and quasi-linear theories,it is becoming increasingly evident that nonlinear wave processes can significantly influence radiation belt particle behavior. Whistler-mode chorus waves can both accelerate and induce precipitation loss of radiation belt electrons.Here we examine the linear and nonlinear growth of whistler-mode chorus waves in the inner magnetosphere. According to recently developed nonlinear cyclotron resonance theory,the generation of whistler-mode rising-tone chorus elements at the magnetic equator can be modeled by a pair of nonlinear coupled ordinary differential equations. We generalize these wave equations to an arbitrary energetic electron distribution,and calculate the associated threshold wave amplitudes for sustained nonlinear growth. For three distinct particle distributions and various sets of parameters,we obtain solutions for the wave magnetic field amplitude,wave frequency,total nonlinear growth rate and temporal nonlinear growth rate. Further,we obtain time-profiles for the wave amplitude that smoothly match at the interface of the linear and nonlinear growth phases. The matching process and consequently nonlinear wave growth can only take place over restricted regions of parameter space. We propose to compare our results with both full-scale kinetic simulations and RBSP wave data.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFMSM32A..09S
- Keywords:
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- 2730 MAGNETOSPHERIC PHYSICS / Magnetosphere: inner;
- 2772 MAGNETOSPHERIC PHYSICS / Plasma waves and instabilities;
- 2774 MAGNETOSPHERIC PHYSICS / Radiation belts