Alfven waves, magnetic decreases, and discontinuities in interplanetary space

The Ulysses mission goes to the polar regions of the heliosphere and therefore is an ideal mission to study Alfven waves and discontinuities. The polar region is dominated by a high speed solar wind with embedded outwardly propagating nonlinear (\DeltaB\/B-0 similar to 1 to 2) Alfven waves. Rotational discontinuities are detected at the edges of Alfven waves and have been shown to be the phase-steepened edges of the waves. Dissipation at these phase-steepened Alfven 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 Alfven waves. Published by Elsevier Science Ltd on behalf of COSPAR.