Merged interaction regions observed by Voyagers 1 and 2 during 1998

Abstract

A broad region of relatively intense magnetic fields (a “merged interaction region” (MIR)) was observed by Voyager 2 (V2) from approximately calendar day (DOY) 264–313, 1998, at a distance of 56.1 ± 0.2 AU and latitude −23.4°. From the average speed of the material in the MIR at V2, 450 ± 19 km/s, we estimate that the radial extent of the MIR was ≈ 13 AU. The average magnetic field strength B at V2 was (0.10 ± 0.03) nT. A MIR was observed by Voyager 1 (V1) from ≈DOY 257–302, 1998, when the heliocentric distance of V1 was R = 71.6 ± 0.2 AU and its heliographic latitude was 33.4°. The average magnetic field strength in this region at V1 was (0.05 ± 0.01) nT. If the MIRs observed by V1 and V2 left the Sun at the same time, then the mean speed at V1 was ∼1.3 times the mean speed at V2, i.e., ∼600 km/s. The radial extent of the MIR at V1 was ∼16 AU. The distribution of the azimuthal angles of the magnetic fields observed by V2 was double peaked, with both toward and away polarities, consistent with the location of V2 within the sector zone. The distribution of the azimuthal angles observed by V1 was single peaked with a positive polarity, consistent with the location of V1 above the sector zone. These distinctly different distributions of magnetic field directions suggests that V1 and V2 observed two related MIRs, rather than two parts of a single “global merged interaction region”.