Voyagers 1 and 2 Observe a GMIR and Associated Cosmic Ray Decreases at 61 and 78 AU

Voyager 2 (V2) observed a Global Merged Interaction Region (GMIR) during the year 2000, when V2 was located near 61 AU and 21.5° south heliographic latitude. This GMIR produced the first major step-like decrease in the cosmic ray intensity in the distant heliosphere during solar cycle 23. Voyager 1 (V1) observed a similar step-like decrease in the cosmic ray intensity near 82 AU and 33.7° north, approximately two months after the event seen at V2. The step decrease at V1 was produced by the same GMIR that was observed by V2. The maximum magnetic field strength in the GMIR was near 0.2 nT, but the field strength fluctuated, indicating that the GMIR was a cluster of strong fields. The magnetic field enhancement in this GMIR is smaller than in the GMIRs observed by V2 closer to the sun, possibly owing to the relatively high thermal pressure of pickup protons in the high-density regions. The radial extent of the GMIR was >15 AU at V2 and ≈30 AU at V1.