Electron Energization by Alfvén Waves: Freja and Sounding Rocket Observations

Y. Khotyaintsev, N. Ivchenko¹, K. Stasiewicz, M. Berthomier
Swedish Institute of Space Physics, S-75591 Uppsala
¹Alfvén Lab, Royal Institute of Technology, S-10044 Stockholm

Abstract:

Recent sounding rockets observations highlight some space-time ambiguities in phenomena taking place in the auroral ionosphere, previously observed by the Freja spacecraft. Field aligned electron populations with energies from a few tens of eV to a few keV streaming through cold background plasma are usually observed in the auroral zone in association with strongly nonlinear electromagnetic perturbations. Simultaneous observations of bursty Langmuir emissions indicate the unstable character of these plasma distributions. A detailed analysis shows that the electromagnetic perturbations take the form of quasi-stationary nonlinear spatial structures related to inertial Alfvén waves. We suggest that inhomogeneous altitude distribution of the parallel electric field of these structures due to ionospheric density gradient is responsible for the observed electron distributions.