Periodic cosmic-ray variations associated with the sector structure of the interplanetary magnetic field

Abstract

Observations by IMP-1 satellite have established that the interplanetary magnetic field is divided into sectors of opposing polarity. These observations have been confirmed by observations with IMP-2 and Mariner 4. The effect of this sector structure on the cosmic-ray intensity observed on the earth has been studied using daily averages of pressure-corrected neutron monitor data from several locations. These data have been analyzed using the method of superposition of epochs, beginning at the edge of the observed sector. The results indicate periodic variations of 6–8-day periods and 0.5 to 1.0% amplitude in cosmic-ray intensity, associated with the passage of positive and negative sectors moving past the earth, including a weak recurrence at 27 days. Theoretical implications of these observations are discussed.