Large‐scale fluctuations between 13 AU and 25 AU and their effects on cosmic rays

Abstract

Measurements made by Voyagers 1 and 2 between 13 AU and 25 AU show that large‐scale fluctuations in the strength of the magnetic field were quasiperiodic and had large amplitudes in 1984, when large recurrent merged interaction regions were present, and the fluctuations were aperiodic and had small amplitudes in 1985. Both near the solar equatorial plane and at latitudes between 22° and 27° the spectra of low‐frequency fluctuations (periods between ∼5 days and 26 days) were ƒ−2 during 1984 and significantly flatter than ƒ−2 during 1985. Near the equator, the power at 26 days during 1984 was an order of magnitude greater than that during 1985. The spectrum of intermediate frequency fluctuations (periods from several hours to approximately 5 days) near the equator was ƒ−2 for both 1984 and 1985, but the spectrum at latitudes near 24° was ƒ−5/3 for both 1984 and 1985. The magnetic field strength distribution was skewed owing to the presence of an exponential tail, which was larger in 1984 than in 1985. During 1984 the tail was larger near the equator than near 23°, but during 1985 there was no latitudinal gradient in the tail. The ratio of magnetic field intensity near 23° to that near the ecliptic was approximately 0.8 in 1984, and the ratio of the magnetic field strength measured near 25° to that measured near the solar equatorial plane was 0.7 in 1985. The ratio of the magnetic field strength near the equatorial plane in 1985 to that in 1984 was 0.8. The model of Burlaga et al. (1985a) provides good first approximations to the intensity profiles of cosmic rays > 75 MeV in 1984 and 1985.