North-South Asymmetry in a closed Magnetophere

Abstract

Observations during anisotropie solar proton events of North-South asymmetry in flux structures over polar caps have been usually explained in terms of a difference in the topology of interconnected geomagnetic and interplanetary field lines in both hemospheres. The present work shows that a North-South asymmetry can exist also in a closed magnetosphere, in which case the flux profiles asymmetry is due to the N-S geomagnetic field asymmetry (this being strongers when the dipolar axis forms a large angle with the perpendicular to the solar wind flow direction) and to the presence of a northern (or southern) component of the interplanetary flux anisotropy with respect to the geomagnetic equator. The observations for the January 24, 1969 event are analyzed within the frame of arguments presented in this paper and the agreement with theoretical predictions is shown to be very satisfactory.