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Title: Where is the cosmic-ray modulation boundary of the heliosphere?

The intensity of Galactic cosmic rays in the heliosphere is modulated by solar activities. The outer boundary where the solar modulation begins has always been a subject matter of debate in the cosmic-ray and heliophysics community. Various experimental methods and theoretical model calculations have been used to determine the boundary. Although the heliopause was always suspected to be the boundary, it is only until very recently after Voyager 1 had crossed the heliopause did we confirm that the boundary is indeed the heliopause. In this paper, we use a model simulation and detailed Voyager observation of cosmic rays at the heliopause crossing to show that the modulation boundary, in fact, is a fraction of an AU beyond the heliopause. Such a conclusion requires a very low turbulence level of the interstellar magnetic field in the outer heliosheath. According to the quasi-linear theory, a low level of turbulence should result in a very large diffusion coefficient parallel to the magnetic field and a very small perpendicular diffusion coefficient. For the first time, we are confident that Voyager 1 has obtained the truly pristine local interstellar cosmic-ray spectra down to the energies below 1 MeV. The cosmic-ray intensity is rapidly filtered by amore » thin layer of the interstellar magnetic field immediately outside of the heliopause. Its filtration amount depends on the conditions of magnetic field turbulence on the both sides of the heliopause, thus making it solar-cycle dependent as well.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4]
  1. Department of Physics and Space Sciences, Florida Institute of Technology, Melbourne, Florida 32901 (United States)
  2. Center for Space Research, North-West University, Potchefstroom 2520 (South Africa)
  3. (China)
  4. Center for Space Plasma and Aeronomic Research and Department of Space Science, University of Alabama in Huntsville, Huntsville, Alabama 35899 (United States)
Publication Date:
OSTI Identifier:
22490123
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 22; Journal Issue: 9; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; 79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; COSMIC RADIATION; DIFFUSION; HELIOSPHERE; INTERSTELLAR MAGNETIC FIELDS; MEV RANGE; MODULATION; SIMULATION; SOLAR ACTIVITY; SOLAR CYCLE; SPECTRA; TURBULENCE; VOYAGER SPACE PROBES