Alfvén waves, magnetic decreases, and discontinuities in interplanetary space

Abstract

The Ulysses mission goes to the polar regions of the heliosphere and therefore is an ideal mission to study Alfvén waves and discontinuities. The polar region is dominated by a high speed solar wind with embedded outwardly propagating nonlinear (|Δ B|/ B₀ ∼ 1 to 2) Alfvén waves. Rotational discontinuities are detected at the edges of Alfvén waves and have been shown to be the phase-steepened edges of the waves. Dissipation at these phase-steepened Alfvén waves has been sought in the plasma and magnetic field data, but not found. Another phenomenon detected at high latitudes is magnetic field decreases (MDs) bounded by discontinuities. One-dimensional simulation results suggest that MDs may be a product of the evolution of nonlinear Alfvén waves.