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The North–South Anisotropy and the Radial Density Gradient of Galactic Cosmic Rays at 1 AU

Published online by Cambridge University Press:  25 April 2016

D. L. Hall
Affiliation:
Physics Department, University of Tasmania, GPO Box 252C, Hobart, Tas. 7001, Australia. dhall@physvax.phys.utas.edu.au, humble@physvax.phys.utas.edu.au
M. L. Duldig
Affiliation:
Australian Antarctic Division, c/o Physics Department, University of Tasmania, GPO Box 252C, Hobart, Tas. 7001, Australia. duldig@physvax.phys.utas.edu.au
J. E. Humble
Affiliation:
Physics Department, University of Tasmania, GPO Box 252C, Hobart, Tas. 7001, Australia. dhall@physvax.phys.utas.edu.au, humble@physvax.phys.utas.edu.au

Abstract

The radial density gradient (Gr) of Galactic cosmic rays in the ecliptic plane points outward from the Sun. This indicates an increasing density of cosmic ray particles beyond the Earth’s orbit. Due to this gradient and the direction of the Sun’s interplanetary magnetic field (IMF) above and below the IMF wavy neutral sheet, there exists an anisotropic flow of cosmic ray particles approximately perpendicular to the ecliptic plane (i.e. in the direction parallel to BIMF × Gr). This effect is called the north–south anisotropy (ξNS) and manifests as a diurnal variation in sidereal time in the particle intensity recorded by a cosmic ray detector. By analysing the yearly averaged sidereal diurnal variation recorded by five neutron monitors and six muon telescopes from 1957 to 1990, we have deduced probable values of the average rigidity spectrum and magnitude of ξNS. Furthermore, we have used determined yearly amplitudes of ξNS to infer the magnitude of Gr for particles with rigidities in excess of 10 GV.

Type
High-energy Astrophysics
Copyright
Copyright © Astronomical Society of Australia 1995

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The North–South Anisotropy and the Radial Density Gradient of Galactic Cosmic Rays at 1 AU
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