Relaxation in the Heliosphere

The solar wind is a driven, non-linear, open, non-equilibrium system. Streams, slow flows, ejecta, shocks, and turbulence produced near the Sun interact to create an evolving complex multiscale structure. During the declining phase of the solar cycle, large structures (seen as Corotating Merged Interaction Regions, CMIRs and Large-Scale Fluctuations) grow from 1 AU to ~15 AU. During solar maximum, Global Merged Interaction Regions (GMIRs) grow out to ~40 AU by the merging of systems of transient flows and other flows. After the formation of CMIRs, GMIRs, and Large-Scale Fluctuations, the solar wind tries to relax toward an equilibrium state. The relaxation as a function of distance out to the termination shock can be described by the evolution of the multi- scale probability distributions of increments of B (q-Gaussian functions), multifractal spectra, and correlation functions, using observations made by Voyager. Tsallis suggested that the evolution toward equilibrium could be described by a "q-triplet" derived from these properties, and the Voyager observations support this hypothesis. Voyager 1 observations show that the solar wind remains complex and non-linear in the heliosheath, after passing through the TS, but in some respects the heliosheath is closer to equilibrium than the supersonic solar wind.