The kinetic Alfvén-like nature of turbulent fluctuations in the Earth's magnetosheath: MMS measurement of the electron Alfvén ratio

The Magnetospheric MultiScale (MMS) mission is used to investigate turbulent fluctuations in the Earth's magnetosheath. The unique combination of multiple spacecraft and high time resolution plasma and electromagnetic field data provided by MMS makes it an ideal mission to study the nature of turbulence and energy conversion. The multiple spacecraft allow the determination of the wavevector directions and plasma frame frequencies of the fluctuations. Moreover, the particle velocities allow the determination of the ion and electron Alfvén ratios, giving an additional diagnostic to reveal the nature of the turbulent fluctuations. Finally, the currents (determined from plasma moments) and the three-dimensional electric field measurements allow the determination of a scale-dependent energy conversion rate. The results reveal that the fluctuations predominantly have kinetic Alfvén wave-like properties at wavenumbers near kρi∼1 (where ρi is the ion gyroradius) and that Landau damping is an important pathway for converting energy.