Miriam A. Forman

Cosmic-ray streaming and anisotropies

The principal result of this paper is the demonstration that in interplanetary space the electric-field drifts and convective flow parallel to the magnetic field of cosmic-ray particles combine as a simple convective flow with the solar wind. In addition there are diffusive currents and transverse gradient drift currents. With this interpretation direct reference to the interplanetary electric-field drifts is eliminated and the study of steady-state and transient cosmic-ray anisotropies is both more systematic and simpler.Following a discussion of our present knowledge of the diffusion coefficient in the interplanetary medium, the theory is applied to steady-state anisotropies near Earth in the kinetic energy (T) range 7.5 MeV<T<20 GeV. First the theory of the diurnal variation atT>-2 GeV is examined and it is suggested that the azimuthal streaming associated with the observations be regarded simply as proof that there is no significant net radial flow of cosmic rays at these energies. Second, it is predicted that, near Earth, the radial anisotropy will have a (+−+) variation with energy and this prediction is very insensitive to the precise values of the parameters used: intensity spectrum, solar wind speed, radial density gradient, and diffusion coefficient. Then, third, the small and radial steady-state anisotropies reported by Raoet al. (1967) in the intervals 7.5<T<45 MeV and 45<T<90 MeV are re-examined and it is found that the gradients and diffusion coefficients required to produce the reported anisotropies in 7.5<T<45 MeV are inconsistent with those expected from other data.

Large‐scale speed fluctuations at 1 AU on scales from 1 hour to ≈1 year: 1999 and 1995

[1]xa0This paper describes the solar wind speed fluctuations, V(τi), observed on a wide range of scales (from 1 hour to ≈1 year) at 1 AU, both during 1999 approaching solar maximum and during 1995 during the descending phase of solar activity. The fluctuations extend from the inertial turbulence range, throughout the scales dominated by interaction regions and streams, and through the largest scales where the fluctuations reflect the variability of the characteristics of the streams. The general properties of the fluctuations of the speed differences, dVn, on all of these scales, τn, are described by the three functions: skewness S(τn), kurtosis K(τn), and standard deviation SD(τn). These three functions have the same qualitative form for both the 1999 data and the 1995 data, in the range of scales of τn = 10.7–341 days (the “Gaussian range”), S(τn) ≈ 0, and K(τn) ≈ 3, consistent with Gaussian distribution functions for both 1999 and 1995. The skewness is positive for τn 10.7 days, the PDFs are Gaussian for the 1999 data and approximately Gaussian for the 1995 period. For scales defined by streams, the PDFs are like Gaussians but fatter on the dVn > 0 side. The PDFs are cubic on a semilog scale for the 1999 data and are approximately cubic for the 1995 data. At scales characteristic of the sizes of interaction regions, the PDFs have a large tail for dVn > 0 that is produced by the large positive dVn at leading edges of streams. At the smallest scales, the PDFs have a form that is characteristic of intermittent turbulence. The power spectra for the 1999 and 1995 data are power laws in frequency throughout the interaction region range and the stream range, the slopes being β = −2.02 ± 0.01 and −2.12 ± 0.04, respectively, consistent with the dominance of shocks and jumps over turbulence. The fluctuations of V(τn) have a multifractal scaling structure, described by a function s(q), the exponent of the structure function versus moment number q in the inertial range, the interaction region range, and extending to the stream range. In the interaction region and stream ranges, s(3) > 1.