Nearly incompressible magnetohydrodynamic (NI MHD) theory for beta similar to 1 (or beta > 1 plasma is fully incompressible and admits both structures (flux ropes or magnetic islands) and slab (Alfven waves) fluctuations. This paper couples the NI MHD turbulence transport equations with three fluid (proton, electron, and pickup ion) equations, and solves the 1D steady-state equations from 1-75 au.
The model is tested against 27 yr of Voyager 2 data, and Ulysses and NH SWAP data. The results agree remarkably well, with some scatter, about the theoretical predictions.