Implication of kinetic Alfvén waves to magnetic field turbulence spectra : Earth's magnetosheath

• In the present paper, we investigate the power-law behaviour of the magnetic field spectra in the Earth's magnetosheath region using Cluster spacecraft data under solar minimum condition. The power spectral density of the magnetic field data and spectral slopes at various frequencies are analysed. Propagation angle, kB, and compressibility, R vertical bar, are used to test the nature of turbulent fluctuations. The magnetic field spectra have the spectral slopes, , between -1.5 to 0 down to spatial scales of 20i (where i is ion gyroradius), and show clear evidence of a transition to steeper spectra for small scales with a second power-law, having between -2.6 to -1.8. At low frequencies, fsc<0.3fci (where fci is ion gyro-frequency), kB approximate to 90 degrees to the mean magnetic field, B0, and R vertical bar shows a broad distribution, 0.1R vertical bar 0.9. On the other hand at fsc>10fci, kB exhibits a broad range, 30 degrees kB90 degrees, while R vertical bar has a small variation: 0.2R vertical bar 0.5. We conjecture that at high frequencies, the perpendicularly propagating Alfven waves could partly explain the statistical analysis of spectra. To support our prediction of kinetic Alfven wave dominated spectral slope behaviour at high frequency, we also present a theoretical model and simulate the magnetic field turbulence spectra due to nonlinear evolution of kinetic Alfven waves. The present study also shows the analogy between the observational and simulated spectra.

Ämnesord

NATURVETENSKAP  -- Fysik -- Fusion, plasma och rymdfysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Fusion, Plasma and Space Physics (hsv//eng)

NATURVETENSKAP  -- Fysik -- Astronomi, astrofysik och kosmologi (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Astronomy, Astrophysics and Cosmology (hsv//eng)

Nyckelord

Turbulence

Magnetic field spectra

Spectralslope

Kinetic Alfven wave

Nonlinearity

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