The first estimation of the energy cascade rate |εC| of magnetosheath turbulence is obtained using the Cluster and THEMIS spacecraft data and an exact law of compressible isothermal magnetohydrodynamics turbulence. The mean value of |εC| is found to be close to 1013Jm3s1, at least 2 orders of magnitude larger than its value in the solar wind (1016Jm3s1 in the fast wind). Two types of turbulence are evidenced and shown to be dominated either by incompressible Alfvénic or compressible magnetosoniclike fluctuations. Density fluctuations are shown to amplify the cascade rate and its spatial anisotropy in comparison with incompressible Alfvénic turbulence. Furthermore, for compressible magnetosonic fluctuations, large cascade rates are found to lie mostly near the linear kinetic instability of the mirror mode. New empirical power-laws relating |εC| to the turbulent Mach number and to the internal energy are evidenced. These new findings have potential applications in distant astrophysical plasmas that are not accessible to in situ measurements.

L. Z. Hadid, F. Sahraoui, S. Galtier, and S. Y. Huang
Phys. Rev. Lett. 120, 055102 – Published 29 January 2018

DOI: https://doi.org/10.1103/PhysRevLett.120.055102