Competition Between the Mirror- and L-mode Electromagnetic Ion Cyclotron Instabilities in the Earth's magnetosheath: Comparison Between 2-D and 3-D Simulations

Details Competition Between the Mirror- and L-mode Electromagnetic Ion Cyclotron Instabilities in the Earth's magnetosheath: Comparison Between 2-D and 3-D Simulations Competition Between the Mirror- and L-mode Electromagnetic Ion Cyclotron Instabilities in the Earth's magnetosheath: Comparison Between 2-D and 3-D Simulations

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufmsm31c0573s&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #SM31C-0573

Physics

2728 Magnetosheath, 2772 Plasma Waves And Instabilities (2471), 7839 Nonlinear Phenomena (4400, 6944), 7867 Wave/Particle Interactions (2483, 6984), 7868 Wave/Wave Interactions

Scientific paper

Spacecraft observations show that the mirror instability dominates over the L-mode electromagnetic ion cyclotron (EMIC) instability in the magnetosheath, although the theoretical linear growth rate of the L-mode EMIC wave is higher than that of the mirror mode waves. This has been a long-standing puzzle. To analyze the competing processes between the L-mode instability and the mirror instability, we performed both two-D and three-D hybrid simulations, assuming anisotropic energetic ions. In the two-D model, the energy of the L-mode wave is higher at the initial stage because its linear growth rate is larger than that of the mirror mode. However, in the three-D simulation, we find that the mirror mode wave can consume more free energy than the L-mode wave at the initial state of wave growth. To understand this apparent discrepancy, we performed parametric analyses on the nonlinear evolution of the proton temperature anisotropy. We find that the nonlinear evolution of the mirror instability in the three-D model is much different from that in the two-D model. Coalescence of the magnetic field structures of the mirror modes takes place in both models. In the two-D case, the coalescence of the magnetic structures proceeds slowly, while in the three-D case the mirror mode structures changes on a much faster time scale. Through this change of structures, electric fields are induced, and the energy of the electromagnetic fields is converted to the thermal energy of particles.

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