Mirror instability and L-mode electromagnetic ion cyclotron instability: Competition in the Earth's magnetosheath

Details Mirror instability and L-mode electromagnetic ion cyclotron instability: Competition in the Earth's magnetosheath Mirror instability and L-mode electromagnetic ion cyclotron instability: Competition in the Earth's magnetosheath

Oct 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009jgra..11410203s&link_type=abstract

Journal of Geophysical Research, Volume 114, Issue A10, CiteID A10203

Physics

Plasma Physics

6

Magnetospheric Physics: Plasma Waves And Instabilities (2471), Magnetospheric Physics: Magnetosheath, Space Plasma Physics: Wave/Particle Interactions (2483, 6984), Space Plasma Physics: Nonlinear Phenomena (4400, 6944), Space Plasma Physics: Kinetic Waves And Instabilities

Scientific paper

We performed both two- and three-dimensional hybrid simulations of the competing processes between the L-mode electromagnetic ion cyclotron (EMIC) and mirror instabilities, assuming anisotropic energetic ions with T $\perp$ /T $\parallel$ = 4.0. In the two-dimensional model, the energy of the EMIC waves is higher at the linear growth phase because its growth rate is larger than that of the mirror mode. In the three-dimensional model, however, the energy of the mirror mode waves is larger than that of the EMIC waves for all times because the wave number spectra of mirror mode waves form torus-like structures. We also theoretically derived a necessary condition for the dominance of the mirror instability. As the mirror mode waves relax the temperature anisotropy effectively, the linear growth rates of the EMIC waves become smaller before saturation. The EMIC waves cause heating of protons trapped by the nonlinear potentials due to coexistence of forward and backward propagating waves and inverse cascading. They terminate the linear growth of EMIC waves. Because of these parallel heatings, the temperature anisotropy decreases to the threshold of the mirror instability and thus the mirror mode wave saturates. At the nonlinear stage, coalescence of the mirror mode waves takes place in both models. The quick dissipation of the EMIC waves occurs due to the heating by the nonlinear processes. On the other hand, the coalescence is a much slower process than the nonlinear processes of EMIC waves, and thus the mirror mode waves remain in the three-dimensional model.

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