North-south asymmetry of solar-particle fluxes in polar-cap regions

On January 24, 1969, an experiment on the Esro 1/Aurorae satellite recorded a flux over the central north pole that at times was a factor of 7 greater than that seen over the south pole. This asymmetry is discussed in relation to the interplanetary-field direction measured at the same time by the Heos spacecraft, and comparison is made with the opposite asymmetrical configuration observed by Evans and Stone (1969) on November 2, 1967. From the evidence of two events it would appear that a southward interplanetary field plays a significant role in permitting direct access, while the magnitude and polarity of the asymmetry are determined by, respectively, interplanetary-particle anisotropy and the ‘toward’ or ‘away’ nature of the field.