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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 ,
M. L. Duldig  and
J. E. Humble
D. L. Hall
Affiliation:
Physics Department, University of Tasmania, GPO Box 252C, Hobart, Tas. 7001, Australia. [email protected], [email protected]
M. L. Duldig
Affiliation:
Australian Antarctic Division, c/o Physics Department, University of Tasmania, GPO Box 252C, Hobart, Tas. 7001, Australia. [email protected]
J. E. Humble
Affiliation:
Physics Department, University of Tasmania, GPO Box 252C, Hobart, Tas. 7001, Australia. [email protected], [email protected]
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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.

Keywords

cosmic raysinterplanetary magnetic fieldsenergetic particlestransport processes
Type
High-energy Astrophysics
Information
Publications of the Astronomical Society of Australia , Volume 12 , Issue 2 , August 1995 , pp. 153 - 158
Copyright
Copyright © Astronomical Society of Australia 1995

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