Gyrokinetic particle simulation of low frequency compressional modes in dipole geometry

Details Gyrokinetic particle simulation of low frequency compressional modes in dipole geometry Gyrokinetic particle simulation of low frequency compressional modes in dipole geometry

Dec 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsm13b2072p&link_type=abstract

American Geophysical Union, Fall Meeting 2011, abstract #SM13B-2072

Physics

Plasma Physics

[2772] Magnetospheric Physics / Plasma Waves And Instabilities, [7829] Space Plasma Physics / Kinetic Waves And Instabilities

Scientific paper

Compressional Pc5 pulsations with high azimuthal wave number are common in the morning and afternoon magnetosphere. Several causes have been proposed for these waves including drift mirror instability driven by pressure anisotropy or ion temperature gradients and drift-bounce ballooning-mirror instability. To examine the origin of such waves we have developed a gyrokinetic particle simulation of low frequency compressional modes using flux coordinates in a global magnetic dipole geometry including anistropy in the equilibrium distribution function. The compressional component is formulated in a scalar form of the parallel magnetic perturbation and the gyro-averaging is performed explicitly in the configuration space. A reduced gyrokinetic model, in which the compressional perturbations are decoupled from the shear Alfvén and electrostatic perturbations, has been implemented. The code has been benchmarked in slab geometry and produces results consistent with the linear dispersion relation. Global simulations of unstable drift-compressional modes in the dipole geometry with kinetic ions find that finite Larmor radius (FLR) effects reduce the linear growth rate significantly but do not significantly alter the real frequency. Global eigenmode structures show that the modes are even along the equilibrium magnetic field and broadened by the FLR effects in the radial direction. Radial propagation away from the region of excitation is observed. We examine the relative role of anistropy and configuration/velocity space nonuniformities on stability and implications for low frequency compressional Pc5 waves that may arise at plasmaspheric boundaries or edges of plasmaspheric plumes.

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