Transient heliosheath modulation
File(s)
Accepted version
Author(s)
Quenby, JJ
Webber, WR
Type
Journal Article
Abstract
Voyager 1 has explored the solar wind–interstellar medium interaction region between the terminal shock and heliopause, following the intensity distribution of Galactic cosmic ray protons above 200 MeV energy. Before this component reached the expected galactic flux level at 121.7 au from the Sun, four episodes of rapid intensity change occurred with a behaviour similar to that found in Forbush Decreases in the inner Solar system, rather than that expected from a mechanism related to models for the long-term modulation found closer to the Sun. Because the mean solar wind flow is both expected and observed to be perpendicular to the radial direction close to the heliopause, an explanation is suggested in terms of transient radial flows related to possible heliopause boundary flapping. It is necessary that the radial flows are of the order either of the sound speed found for conditions downstream of the terminal shock or of the fluctuations found near the boundary by the Voyager 1 Low Energy Charged Particle detector and that the relevant cosmic ray diffusion perpendicular to the mean field is controlled by ‘slab’ fluctuations accounting for about 20 per cent of the total power in the field variance. However, additional radial drift motion related to possible north to south gradients in the magnetic field may allow the inclusion of some diffusion according to the predictions of a theory based upon the presence of 2D turbulence. The required field gradients may arise due to field variation in the field carried by solar plasma flow deflected away from the solar equatorial plane. Modulation amounting to a total 30 per cent drop in galactic intensity requires explanation by a combination of transient effects.
Date Issued
2015-10-21
Date Acceptance
2015-07-01
Citation
Monthly Notices of the Royal Astronomical Society, 2015, 453 (2), pp.1297-1304
ISSN
1365-2966
Publisher
Oxford University Press (OUP)
Start Page
1297
End Page
1304
Journal / Book Title
Monthly Notices of the Royal Astronomical Society
Volume
453
Issue
2
Copyright Statement
© 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved. This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society
Subjects
Diffusion
Sun: heliosphere
Solar wind
Cosmic rays
ISM: magnetic fields
Publication Status
Published