II. Transport of Nearly Incompressible Magnetohydrodynamic Turbulence from 1 to 75 au

Abstract

The thermal plasma beta in the solar wind and the solar corona is of the order of and . Zank et al. developed 2D and slab turbulence transport model equations of the order of and using nearly incompressible (NI) theory. We solve the Zank et al. NI MHD coupled turbulence transport equations for the inhomogeneous solar wind from 1 to 75 au, and compare the numerical solutions to Voyager 2 observations. We find that (1) the 2D turbulent energies are larger than the slab energies throughout the heliosphere; (2) the 2D turbulent energies decrease more slowly than the slab turbulent energies within ∼4 au, while the slab energies increase and the 2D energies flatten in the outer heliosphere; (3) the 2D normalized cross-helicity decreases faster than the slab normalized cross-helicity within ∼4 au; (4) the 2D normalized residual energy is more magnetically dominated than the slab; (5) the variance of density fluctuations decreases more rapidly than within ∼10 au, and more slowly in the outer heliosphere; and (6) the observed variance in magnetic field fluctuations as a function of the thermal plasma beta is described by the two-component turbulence transport model. In summary, the NI MHD two-component Zank et al. turbulence transport model captures the behavior of the forward, backward, and total energies in the fluctuating Elsässer variables, the variance in the magnetic field, kinetic energy, and density fluctuations, the cross-helicities and residual energies, the thermal temperature and plasma beta, and the various correlation lengths.