Optical Signatures and Models of Dispersive Nonlinear Field Line Resonances

Details Optical Signatures and Models of Dispersive Nonlinear Field Line Resonances Optical Signatures and Models of Dispersive Nonlinear Field Line Resonances

Dec 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufmsm21c..03r&link_type=abstract

American Geophysical Union, Fall Meeting 2003, abstract #SM21C-03

Physics

2451 Particle Acceleration, 2471 Plasma Waves And Instabilities, 2730 Magnetosphere: Inner, 2753 Numerical Modeling

Scientific paper

The nightside auroral zone is threaded by geomagnetic field lines that support localized ultra-low frequency (ULF) shear Alfven field line resonances (FLRs). Small-scale dispersive FLRs are excited through resonant mode conversion of global scale compressional waves that propagate isotropically through the magnetosphere. In the more distant magnetotail, warm plasma dispersive effects exclude the excitation of latitudinally narrow FLR wave fields. Closer to Earth, flux tubes are loaded with colder plasma that favors inertial scale dispersive effects and nonlinear wave processes. We identify preferential locations in the magnetosphere where small-scale discrete arcs preferentially form, and analyze their spatiotemporal characteristics. We demonstrate that the smallest scales form on field lines where two competing wave dispersion mechanisms cancel. Over realistic timescales, this situation naturally occurs as a result of shear Alfven wave ponderomotive forces that are associated with up-flowing ions and Earthward motion of the resonance position in the magnetosphere. The amplitudes, perpendicular widths, and latitudinal dependence of dispersive scale ULF waves are analyzed and compared with CANOPUS magnetometer and meridian scanning photometer data. Optical signatures of FLR-related arcs are also presented, and differences between dawn and midnight region arcs are discussed in the context of anomalously low FLR frequencies (1-4 mHz between L~7-11).

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