Magnetohydrodynamic simulation of the radial evolution and stream structure of solar-wind turbulence

We present a unified interpretation of observations of interplanetary fluctuations in terms of nearly incompressible magnetohyrodynamics. Incompressive effects explain the rapid evolution of turbulence in slow wind containing the heliospheric current sheet. The relative constancy of the spectrum of ``inward propagating'' fluctuations compared to the rapid decline in ``outward'' fluctuations results from incompressive spectral transfer combined with strong dissipation of the outward fluctuations. Secondary compressive effects account for nearly pressure-balanced structures and the density fluctuation levels.