THE EVOLUTION OF SLAB FLUCTUATIONS IN THE PRESENCE OF PRESSURE-BALANCED MAGNETIC-STRUCTURES AND VELOCITY SHEARS

The traditional view that solar wind fluctuations are well-described a s a spectrum of parallel-propagating Alfven waves has been challenged many times but is still a frequently encountered perspective. Here we examine whether it remains consistent to view most of the fluctuation energy as resident in parallel-propagating Alfven waves in situations in which there are also present either transverse pressure-balanced (P B) magnetic structures or transverse velocity shears. We address these questions through direct simulation of compressible magnetohydrodynam ics, with expansion effects neglected. We show that parallel-propagati ng Alfven waves are redirected to large oblique angles after refractiv e interactions with PB structures or advective interactions with veloc ity shears, reflecting the nonequilibrium nature of the initial spectr al distribution. The timescale for these processes ranges from 2-8 edd y-turnover times or characteristic nonlinear times. Relatively small a mounts of PB structure and/or shear energy can redirect initially para llel-propagating Alfven waves to highly oblique angles. Velocity micro streams appear to be particularly efficient at creating highly oblique waves. Even though the excited wave vectors are eventually primarily oblique, the magnetic variance ratios show a minimum variance in the m ean magnetic field direction.