Observation of kinetic Alfvén waves by the FREJA spacecraft

It is shown that the low‐frequency (from 1 to 20 Hz) auroral electromagnetic turbulence consists of two kinds of phenomena: (1) magnetic fluctuations due to quasi‐static currents and (2) strong electric spikes (larger than 100 mV/m) with associated magnetic (30 nT) and density (dn/n ≥ 30%) fluctuations. These spikes are interpreted as kinetic Alfvén waves. They have transverse scale of the order of the electron inertia length (1 km) and then, could dissipate via the generation of a parallel electric field by finite electron mass effects. Given their strong Poynting flux (10−3 to 10−2 W/m²), they likely significantly contribute to the auroral plasma energization.