Evolution of large-scale solar wind structures beyond 1 AU

The evolution of solar wind speed fluctuations beyond 1 AU is considered under the assumption that turbulent dissipation is negligible (except at shock fronts). Both a dimensional argument, giving the distance scale on which a shell of high-speed solar wind is ‘smoothed’ into the ambient, and numerical solutions of the nonlinear fluid equations indicate that the solar wind structures observed near 1 AU persist to well beyond 5–10 AU. In fact, the shock fronts associated with such structures under this set of assumptions are found to strengthen with increasing heliocentric distance. The comparison of these predictions with future solar wind observations should reveal the importance of large-scale turbulent processes in the interplanetary plasma.