Open AccessMultiscale current structures observed by Freja
Author(s) -
Stasiewicz K.,
Potemra T.
Publication year - 1998
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/97ja02396
Subject(s) - physics , computational physics , polarization (electrochemistry) , current density , geophysics , electron , vortex , magnetic field , current (fluid) , magnetometer , plasma , mechanics , chemistry , quantum mechanics , thermodynamics
Multiscale structure of field‐aligned currents and plasma density records are analyzed with multiresolution wavelet technique. We show that field‐aligned currents measured by Freja in the auroral region have a spectrum of scales from ∼ 500 km down to about a hundred meters. The intensity of currents has a maximum of ∼100–300 μAm −2 at the subkilometer scales. The locations of small‐scale currents (corresponding presumably to discrete auroral structures) is not coincident neither with strong macroscopic density gradients, nor with the most intense large‐scale currents. These structures are observed to cluster inside medium scale density cavities and represent most likely interference patterns of short (λ ⊥ ≥ c /ω pe ) inertial Alfvén waves. At kilometer scales the energetic electrons (30 eV to 30 keV) carry less than ∼ 20% of the magnetometer current, indicating that thermal electrons are the major current carriers. We discuss also vector polarization of the magnetic perturbations at various scales which may be used as a tool for resolving polarization patterns and sense of rotation for Alfvén waves, vortices, and current filaments.