MHD-kinetic transition in imbalanced Alfvénic turbulence

Abstract

Alfvénic turbulence in space is usually imbalanced: amplitudes of waves propagating parallel and anti-parallel to the mean magnetic field $B_0$ are unequal. It is commonly accepted that the turbulence is driven by (counter-)collisions between these counter-propagating wave fractions. Contrary to this, we found a new ion-scale dynamical range of the turbulence established by (co-)collisions among waves co-propagating in the same direction along $B_0$. Co-collisions become stronger than counter-collisions and produce steep non-universal spectra above certain wavenumbers dependent on the imbalance. Spectral indexes of the strong turbulence vary around -3, such that steeper spectra follow larger imbalances. Intermittency steepens the -3 spectra further, up to -3.7. Our theoretical predictions are compatible with steep variable spectra observed in the solar wind at ion kinetic scales, but further verifications are needed by correlating observed spectra with measured imbalances.

References in corpus (7)

• Imbalanced Strong MHD Turbulence
• Strong Imbalanced Turbulence
• Strong Anisotropic MHD Turbulence with Cross Helicity
• Spectral Slope Variation at Proton Scales from Fast to Slow Solar Wind
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Cited by in corpus (5)

• The Ion Transition Range of Solar Wind Turbulence in the Inner Heliosphere: Parker Solar Probe Observations
• Imbalanced kinetic Alfvén wave turbulence: from weak turbulence theory to nonlinear diffusion models for the strong regime
• Solar wind magnetic field background spectrum from fluid to kinetic scales
• Modeling imbalanced collisionless Alfvén wave turbulence with nonlinear diffusion equations
• Solar plasma radio emission in the presence of imbalanced turbulence of kinetic-scale Alfvén waves