A Fisk‐Parker Hybrid Heliospheric Magnetic Field with a Solar‐Cycle Dependence

Abstract

We present a refinement of the Fisk-Parker hybrid field of Burger and Hitge which now includes a region bordering the solar rotational equator where magnetic field footpoint motion occurs only through diffusive reconnection. The hybrid field, therefore, only occurs above a certain latitude in a given hemisphere, and in the equatorial region the field is a pure Parker field. We also propose a simple qualitative model for the solar cycle dependence of the hybrid field, taking into account changes in the tilt angle of the heliospheric current sheet and the latitudinal extend of the polar coronal hole on the photosphere and on the source surface over the course of a solar activity cycle. We find that the amplitude of magnetic field fluctuations for assumed solar minimum parameters would not be observable above the background noise (see Roberts and coworkers). We also show that for these parameters, periodicities associated with differential footpoint motion would be barely distinguishable from rigid rotation at the solar equatorial rate. We point out that the question of periodicities in magnetic field data is perhaps more complicated than previously thought. We confirm the result of Burger and Hitge that a Fisk-type heliospheric magnetic field provides a natural explanation for the observed linear relationship between the amplitude of the recurrent cosmic-ray variations and the global latitude gradient (see Zhang). We show that this relationship holds for helium, protons, and electrons. Moreover, we show that the constant of proportionality is larger when qA > 0 than when qA < 0, as inferred from observations by Richardson and coworkers.

Modelling anomalous cosmic ray oxygen in the heliosheath

“…thus consisting of one component directed along the mean HMF, κ || is taken from Burger et al (2008), and two component perpendicular to it, κ ⊥r/θ is taken from Burger et al (2000). As input for κ || various turbulence quantities are needed, most notable the HMF variance δB 2 .…”

A Generalized Two-Component Model of Solar Wind Turbulence and Ab Initio Diffusion Mean-Free Paths and Drift Lengthscales of Cosmic Rays

“…To this end, we present here results for the rigidity and spatial dependences of the proton parallel and perpendicular mean-free paths using outputs yielded by the new, generalized, self-consistent two-component turbulence transport model discussed above. The parallel mean-free path used here is that employed by, e.g., Burger et al (2008), and derives from quasilinear theory (QLT). We present a novel expression for the proton perpendicular mean-free path, derived from the random ballistic decorrelation (RBD) interpretation of the nonlinear guiding center (NLGC) theory of Matthaeus et al (2003) as presented by Ruffolo et al (2012).…”

Hale cycle and long-term trend in variation of galactic cosmic rays related to solar rotation

“…Alania et al (2008) studied the phase distribution of the 27-day variation in SW speed and found more stable and long-lived heliolongitudinal structures during A > 0 minima, possibly affecting the amplitude of 27-day variation of GCR intensity and causing the observed Hale cycle dependence. Burger et al (2008) used a Fisk-type hybrid field in modeling the GCR intensity variation and also found a larger 27-day variation during positive-polarity minima.…”