Extraordinary Solar Modulation Effects On Galactic Cosmic Rays Observed By V1 Near The Heliopause

TL;DR

Voyager 1 observed two significant cosmic ray intensity increases near the heliopause, revealing new insights into heliospheric modulation effects that differ from those observed at Earth, with implications for understanding cosmic ray behavior.

Contribution

This study presents the first detailed observations of large cosmic ray increases near the heliopause, highlighting a different modulation mechanism than previously understood.

Findings

Cosmic ray increases of over 50% for nuclei and 2x for electrons were observed.

Magnetic field variations correlated with cosmic ray changes during the second increase.

The observed modulation resembles a simple force-field model with a potential of about 80MV.

Abstract

We discuss two extraordinary increases of cosmic ray intensity observed by Voyager 1 in the last 1.1 AU before heliopause crossing, Aug 2012 at 121.7 AU. The two increases are roughly similar in amplitude and result in a total increase of cosmic ray nuclei around 1 GV of over 50 percent and of 0.01 GV electrons of a factor about 2. During the first increase, the changes in the magnetic, B, field are small. After the first increase, the B field variations and cosmic ray changes become large and during the second increase the B field variations and the cosmic ray changes are correlated to within a day. The intensity variations of H and He nuclei during these time intervals are measured from 0.1 to over 1 GV. The total GCR increse over the two events resemble those expected from a simple force-field 'like' solar modulation model with a modulation potential of about 80MV. This is nearly one third of the total modulation potential of about 250 GV required to produce the modulation of these particles observed at the earth at the 2009 sunspot minimum and adds a new aspect to ideas about heliospheric modulation.