Acceleration of solar wind ions to 1 MeV by electromagnetic structures upstream of the Earth's bow shock

¹ Swedish Institute of Space Physics - Uppsala, Sweden, EU
² Space Research Centre, Polish Academy of Sciences - Poland, EU
³ KTH Royal Institute of Technology, High Performance Computing and Visualization Department Stockholm, Sweden, EU
⁴ Institute of Theoretical Physics, Ruhr-University Bochum - Germany, EU
⁵ Swedish Institute of Space Physics - Kiruna, Sweden, EU
⁶ Department of Physics and Astronomy, University of Zielona Gora - Poland, EU

Received: 10 April 2013
Accepted: 6 May 2013

Abstract

We present measurements from the ESA/NASA Cluster mission that show in situ acceleration of ions to energies of 1 MeV outside the bow shock. The observed heating can be associated with the presence of electromagnetic structures with strong spatial gradients of the electric field that lead to ion gyro-phase breaking and to the onset of chaos in ion trajectories. It results in rapid, stochastic acceleration of ions in the direction perpendicular to the ambient magnetic field. The electric potential of the structures can be compared to a field of moguls on a ski slope, capable of accelerating and ejecting the fast running skiers out of piste. This mechanism may represent the universal mechanism for perpendicular acceleration and heating of ions in the magnetosphere, the solar corona and in astrophysical plasmas. This is also a basic mechanism that can limit steepening of nonlinear electromagnetic structures at shocks and foreshocks in collisionless plasmas.