The role of Shabansky orbits in the generation of compression-related EMIC waves
Abstract
Electromagnetic ion-cyclotron (EMIC) waves arise from temperature anisotropies in trapped warm plasma populations. In particular, EMIC waves at high L values near local noon are often found to be related to magnetospheric compression events. There are several possible mechanisms that can generate these temperature anisotropies: energizing processes, including adiabatic compression and shock-induced and radial transport; and non-energizing processes, such as drift shell splitting and the effects of off-equatorial minima on particle populations. In this work we investigate the role of off-equatorial minima in the generation of temperature anisotropies both at the magnetic equator and at higher latitudes. There are two kinds of behavior particles undergo in response: particles with high equatorial pitch angles (EPAs) are forced to execute so-called Shabanksy orbits and mirror at high latitudes without passing through the equator, and those with lower EPAs will pass through the equator with higher EPAs than before; as a result, perpendicular energies increase at the cost of parallel energies. By using a 3D particle tracing code in a tunable analytic compressed-dipole field, we parameterize the effects of Shabansky orbits on the anisotropy of the warm plasma. These results as well as evidence from simulations of a real event in which EMIC waves were observed (the compression event of 29 June 2007) are presented.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFMSM43C..08M
- Keywords:
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- 2753 MAGNETOSPHERIC PHYSICS / Numerical modeling;
- 2772 MAGNETOSPHERIC PHYSICS / Plasma waves and instabilities;
- 2778 MAGNETOSPHERIC PHYSICS / Ring current;
- 2784 MAGNETOSPHERIC PHYSICS / Solar wind/magnetosphere interactions