MHD-Kinetic Transition in Imbalanced Alfvénic Turbulence
De Keyser, J.
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Alfvénic turbulence in space is usually imbalanced: amplitudes of waves propagating parallel and anti-parallel to the mean magnetic field B0 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 B0. 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.
CitationVoitenko, Y.; De Keyser, J. (2016). MHD-Kinetic Transition in Imbalanced Alfvénic Turbulence. , Astrophysical Journal Letters, Vol. 832, Issue 2, L20, DOI: 10.3847/2041-8205/832/2/L20.