UNUSUAL GALACTIC COSMIC RAY INTENSITY AND SPECTRAL CHANGES OBSERVED BY $V1$ NEAR THE HELIOPAUSE

Abstract

We discuss here two unusual increases of cosmic ray intensity that were observed by V1 in the last 1.1 AU before it crossed the heliopause in 2012 August, at 121.5 AU. These two increases are roughly similar in amplitude and result in a total increase in ?1 GV cosmic ray nuclei of over 50% and 0.01 GV electrons of a factor ?2. During the first increase the changes in the B field are small. After the first increase the B field changes become large and during the second increase the B field variations and cosmic ray changes are correlated to within ? one day. During these time intervals, the rigidity dependence of the increases of GCR H and He nuclei from 100?600 MeV/nuc resemble those used to describe the solar modulation near the Earth during a large transient decrease but the ratio between the intensity changes of H, He, and electrons are different. The magnitude of these increases at Voyager is ?1/3 of the modulation that is required to produce the total modulation of protons, helium nuclei, and electrons between the local interstellar intensities and those observed at the Earth at the 2009 sunspot minima. This may imply that a significant part of the residual solar modulation at times of sunspot minima occurs near the heliopause itself.