Simulation Studies on Formation of Earth's Radiation Belt and Ring Current

摘要

Theory and observation of electromagnetic ion cyclotron triggered emissionsElectromagnetic ion cyclotron (EMIC) waves are suggested to play a significant role in the dynamics of the Earth's radiation belt and the ring current. We develop a nonlinear wave growth theory of EMIC triggered emissions observed in the Earth's magnetosphere. After deriving the basic wave equations from Maxwell's equations and the momentum equations for the electrons and ions, we obtain equations that describe the nonlinear dynamics of resonant protons interacting with an EMIC wave. The frequency sweeprate of the wave plays an important role in forming the resonant current that controls the wave growth. Assuming an optimum condition for the maximum growth rate as an absolute instability at the magnetic equator and a self-sustaining growth condition for the wave propagating from the magnetic equator, we obtain a set of ordinary differential equations that describe the nonlinear evolution of a rising tone emission generated at the magnetic equator. Using the physical parameters inferred from observations by the Cluster spacecraft, we determine the dispersion relation for the EMIC waves. Assuming saturation of the wave amplitude, as is found in the observations, we find good agreement between the numerical solutions and the wave spectrum of the EMIC triggered emissions.