Evolution of Power Anisotropy in Magnetic Field Fluctuations Throughout the Heliosphere

Anisotropy is an important property of the solar wind turbulence. Solar wind fluctuations are thought to be highly anisotropic in the presence of large-scale magnetic field. We develop a theoretical model describing the evolution of the power anisotropy in the inertial range throughout the heliosphere for three possibilities: i) no in situ sources of turbulence, ii) stream shear sources of 2D and slab turbulence, and iii) a pickup ion source of slab turbulence, using the Zank et al. (2017) nearly incompressible turbulence transport model equations. We use dimensional analysis to relate the variances of the 2D and slab fluctuating magnetic energy in the energy-containing range to those in the inertial range. We consider different assumptions (80:20, 70:30, 60:40, and 55:45) about the ratio of the variances of the 2D and slab fluctuating magnetic energy in the energy containing range. We find that the anisotropy in the inertial range is typically larger than in the energy-containing range. The anisotropy in the inertial range changes differently than in the energy containing range.