Wave-number spectra and intermittency in the terrestrial foreshock region.
Wave-number spectra of magnetic field fluctuations are directly determined in the terrestrial foreshock region (upstream of a quasiparallel collisionless shock wave) using four-point Cluster spacecraft measurements. The spectral curve is characterized by three ranges reminiscent of turbulence: energy injection, inertial, and dissipation range. The spectral index for the inertial range spectrum is close to Kolmogorov's slope, -5/3. On the other hand, the fluctuations are highly anisotropic and intermittent perpendicular to the mean magnetic field direction. These results suggest that the foreshock is in a weakly turbulent and intermittent state in which parallel propagating Alfvén waves interact with one another, resulting in the phase coherence or the intermittency.
Narita
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Institute of Geophysics and Extraterrestrial Physics, Mendelssohnstrasse 3, D-38106 Braunschweig, Germany. y.narita@tu-bs.de
Glassmeier
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KH
Treumann
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