The effect of the July 14, 2000 "Bastille Day" solar flare event on >70 MeV galactic cosmic rays observed at V1 and V2 in the distant heliosphere

Abstract

Decreases in the >70 MeV rates of galactic cosmic rays are observed in the outer heliosphere in 2001 at V2 (63 AU) and V1 (80 AU) coincident with the arrival of the interaction region from the Bastille Day event in 2000 at the Earth. These decreases began ∼180 days after the event at the Sun at V2 and ∼245 days at V1 corresponding to average propagation speeds of 605 and 567 km/s respectively. The intensity decrease was 13.1% at V2 and 9.3% at V1. The intensity of these galactic cosmic rays recovered very slowly at V2 and V1 this recovery continuing for ∼150-120 days or more after the transient passed these spacecraft. The intensity time profiles show no obvious effects at the time when the interaction region might be expected to encounter the termination shock and suggest that the modulation associated with interaction region continued well beyond the location of the termination shock, into the heliosheath and perhaps to the heliopause.