Non-propagating electric and density structures formed through non-linear interaction of Alfvén waves

Abstract

In the auroral zone of the Earth, the electron acceleration by Alfvén waves is sometimes seen as a precursor of the non-propagating acceleration structures. In order to investigate how Alfvén waves could generate non-propagating electric fields, a series of simulations of counter-propagating waves in a homogeneous medium is presented. The waves propagate along the ambient magnetic field direction. It is shown that non-propagating electric fields are generated at the locus of the Alfvén waves crossing. These electric fields have a component orientated along the direction of the ambient magnetic field, and they generate a significant perturbation of the plasma density. The non-linear interaction of down and up-going Alfvén waves might be a cause of plasma density fluctuations (with gradients along the magnetic field) on a scale comparable to those of the Alfvén wavelengths. The present paper is mainly focused on the creation process of the non-propagating parallel electric field.