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

Abstract

The radial density gradient (G r ) 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 X G r ). This effect is called the north-south anisotropy (£NS) 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 £NS-Furthermore, we have used determined yearly amplitudes of £NS to infer the magnitude of G r for particles with rigidities in excess of 10 GV.

Raios cósmicos e a heliosfera

“…(2) A Anisotropia Norte-Sul deve-se ao fato de que ao gradiente de população de GCR que aponta para fora do Sol. Como há maior população de raios cósmicos no espaço voltado para o lado noturno da Terra e menor no lado diurno a configuração das linhas do IMF apontando para fora (away) ou para dentro (toward ) do Sol faz com que haja uma maior incidência de partículas no hemisfério Norte ou no hemisfério Sul da Terra devido a força eletromagnética de Lorentz [51]. Esta anisotropia permite localizar a Terra em relação a HCS.…”

Australian Cosmic Ray Modulation Research

“…Figure 12 shows the results of such an analysis by . Finally, analysis of the difference between the response to the sidereal diurnal anisotropy in the toward and away sectors of the IMF can be employed to derive the anisotropy Hall, Humble & Duldig 1994a;Hall, Duldig & Humble 1995a).…”