Multifractal structure of the interplanetary magnetic field: Voyager 2 observations near 25 AU, 19871988
Abstract
This paper analyzes the largescale fluctuations of the interplanetary magnetic field strength observed by Voyager 2 from 23.3 AU to 27.8 AU during the period from day 190, 1987 to day 345, 1988. The qth moments of B_{τ} show scaling behavior in the range of scales from 16 hours to 21 days for 10 ≤ q ≤ 10, i.e., <B_{τ}^{q}> ∼ τ^{s(q)} in this range. s(q) is approximately a quadratic function of q for 4 ≤ q ≤ 4, as one expects for a distribution that is approximately lognormal, but the higher moments diverge from those of a lognormal distribution. The function D_{q} (q) = 1 + s(q)/(q  1) has the form that is characteristic of multifractals. For a multifractal magnetic field, the moments of the field should scale as τ^{α} on a set with fractal dimension f (α), where α has a continuum of values over some limited range. For the largescale magnetic field fluctuations, the function f(α) computed from D_{q} (q) is approximately a fourth order polynomial for 10 ≤ q ≤ 10, and positive values of f(α) occur for 0.8 ≤ α ≤ 1.2. The multifractal character of the magnetic field strength fluctuations generalizes the concept that the magnetic field is organized into interaction regions (regions in which the magnetic field strength and pressure are higher than average for several hours) and rarefaction regions (regions in which the magnetic field strength and pressure are lower than average). Near solar maximum the interaction regions in the distant heliosphere might be viewed as clusters of strong disturbed fields with considerable fine structure on various scales. The multifractal description of the magnetic field suggests several problems for future study.
 Publication:

Geophysical Research Letters
 Pub Date:
 January 1991
 DOI:
 10.1029/90GL02596
 Bibcode:
 1991GeoRL..18...69B
 Keywords:

 Fractals;
 Interplanetary Magnetic Fields;
 Magnetic Field Configurations;
 Magnetic Flux;
 Flux Density;
 Magnetic Storms;
 Temporal Distribution;
 Voyager 2 Spacecraft;
 Astrophysics;
 Interplanetary Physics: Interplanetary magnetic fields