Density depletions and current singularities observed by Freja

Details Density depletions and current singularities observed by Freja Density depletions and current singularities observed by Freja

Mar 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998jgr...103.4251s&link_type=abstract

Journal of Geophysical Research, Volume 103, Issue A3, p. 4251-4260

Physics

Plasma Physics

39

Ionosphere: Auroral Ionosphere, Ionosphere: Plasma Temperature And Density, Ionosphere: Plasma Waves And Instabilities, Space Plasma Physics: Turbulence

Scientific paper

High time resolution data collected by the Freja spacecraft in the topside ionosphere (h~1500km) reveal that the ``low-frequency turbulence'' observed commonly below the ion gyrofrequency consists of a large number of coherent plasma structures which represent intense field-aligned currents (j∥~30-300μAm-2) accompanied by plasma density depletions (cavities). The electromagnetic fluctuations are identified with inertial electron Alfvén waves (IEAW) at perpendicular wavelengths <~6km. The coherent structures with singularly strong j∥ are consistent with being the resonance cones of IEAW generated by localized sources at h>=1RE. The density cavities are observed to be directly related to the magnetic field gradient, i.e., intensity of field-aligned current. Using multiresolution wavelet analysis we have investigated also the wave impedance and the polarization of the electromagnetic structures at different scales. The polarization records show phase discontinuities at small-scale electromagnetic structures which is consistent with the hypothesis that they represent resonance cones or interference patterns of IEAW.

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