Cosmic ray variations and magnetic field fluctuations in the outer heliosphere

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[1] The major features of the profile of >70 MeV/nuc cosmic ray intensity (CRI) observed by Voyager 1 (V1) in the heliosheath from 2005.8-2010.24 are described by the empirical "CR-B" relation as the cumulative effect of variations of the magnetic field strength B. The CRI profile observed by Voyager 2 (V2) from 2008.60 to 2010.28 in the heliosheath is also described by the CR-B relation. On a smaller scale, of the order of a hundred days, a sequence of 3 CRI decreases observed by V1 during 2006 was interpreted as the effect of a propagating interplanetary shock first interacting with the termination shock, then moving past V1, and finally reflecting from the heliopause and propagating back to V1. Our observations show that the second CRI decrease in this sequence began during the passage of a "Global Merged Interaction Region" (GMIR), $40 days after the arrival of the GMIR and its possible shock. The first and third CRI decreases in the sequence were associated with local enhancements of B.

Section: Summary and Discussionmentioning

confidence: 99%

Voyager observations of magnetic fields and cosmic rays in the heliosheath

Burlaga¹,

Ness²,

Stone³

et al. 2011

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“…They could be peculiar to underground muons only, or, more generally, could be a response of all cosmic rays to the series of large radial solar wind shocks in 1982 [Cliver et al, 1987] which resulted in a rapid increase in modulation, seen throughout the heliosphere. This last conjecture receives some support from the fact that the presence of minicycles is recognizable in several spacecraft observations of cosmic rays carried out during the years 1980-1982 [Venkatesan et al, 1984;Pyle and Simpson, 1985;Perko and Burlaga, 1987].…”

Section: Analysis Of Statistical Propertiesmentioning

confidence: 92%

Effects of the solar cycle on the fractal and statistical properties of deep underground muons

Bergamasco¹,

Provenzale²,

Castagnoli³

et al. 1990

We investigate the fractal and statistical properties of underground muons recorded at 570 hg/cm² and study their response to solar activity variations in the second part of solar cycle 21. A constant feature detected throughout the whole period considered is the self‐affine nature of the underground muon fluctuations which display a scaling range extending approximately from a few hours to more than 2 months. An important result of our study is that the scaling and spectral exponents are positively correlated with the sunspot cycle. In addition, the intensity distribution shows a more marked presence of short‐ and long‐term fluctuations near solar maximum. The presence of solar modulation in the muon record suggests dimensions of the heliosphere at least as large as a few scattering mean free paths of the 1.8‐TV primaries.

“…To improve the physics of this approach, Perko and Burlaga [1987] used the force field approximation of the one-dimensional Parker [1965] where f is the omnidirectional particle distribution in phase space, r is the radial distance from the Sun, P is the particle rigidity, V is the solar wind speed, and K is the radial diffusion coefficient. This time-independent equation retains the main physics of the Parker equation: diffusionconvection and adiabatic energy loss.…”

Section: Paper Number 92ja00321mentioning

confidence: 99%

Intensity variations in the interplanetary magnetic field measured by Voyager 2 and the 11‐year solar cycle modulation of galactic cosmic rays

Perko¹,

Burlaga²

1992

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We present new evidence to support the hypothesis that the l 1-year solar cycle modulation of galactic cosmic rays is caused by strong particle diffusion inside long-lived, merged interaction regions. These regions are represented by local enhancements in the heliospheric magnetic field strength. To test this hypothesis, we solved the one-dimensional, force field approximation of the cosmic ray modulation equation. The only variables were the strength of the local magnetic field and the position of the spacecraft, both taken directly from Voyager 2 data. We assume that a constant solar wind speed convects magnetic field compressions and rarefactions unchanged through a model heliosphere. The result is a reasonable simulation of the integrated, high-energy cosmic ray intensity profile from about 1982 to mid-1989. This period encompasses both the full recovery portion of the last 11-year cosmic ray cycle and the first year and a half of the new cycle. In particular, this model responds to the Voyager 2 magnetic field data by correctly timing the beginning of the new modulation cycle in late 1987. We conclude that our hypothesis is consistent with the results of this simulation.