Theory and Transport of Nearly Incompressible Magnetohydrodynamics Turbulence. III. Evolution of power anisotropy in magnetic field fluctuations throughout the heliosphere
Abstract
A theoretical model that describes the evolution of the power anisotropy in the energy-containing and inertial ranges throughout the heliosphere is developed for three possibilities: (i) no in situ sources of turbulence; (ii) stream-shear sources of 2D and slab turbulence; and (iii) a fully driven turbulence model that includes both stream- shear driving and a pickup ion source of slab turbulence. At the inner boundary (1 au), we assume that the ratios of the 2D to slab fluctuating magnetic energy variances in the energy-containing range are 80:20, 70:30, 60:40, and 55:45. For case (i), <B^2_2D>/<b^2_slab> in the energy-containing range increases monotonically throughout the heliosphere, whereas the inertial range ratio increases until _20 au and then decreases. For case (ii), the energy-containing range ratio increases initially and then remains approximately constant and ordered beyond _2 au, according to the inner boundary assumptions. The inertial range ratio for the 80:20 case increases with heliocentric distance, whereas for the 70:30, 60:40, and 55:45 cases, the rations increase between _2 to _10-20 au, and then generally decrease at larger heliocentric distances. For case (iii), the energy-containing and inertial range ratios increase initially, remain approximately constant and increase slightly, respectively, and then decrease more rapidly between _8 and 30 au, and more gradually thereafter, approaching a ratio of _1 at 75 au. We present preliminary results that show the power anisotropy in magnetic field fluctuations observed by Ulysses spacecraft increasing with heliocentric distance from _1.5 to 4.5 au.
- Publication:
-
42nd COSPAR Scientific Assembly
- Pub Date:
- July 2018
- Bibcode:
- 2018cosp...42E..28A