Large‐scale distant heliospheric magnetic field: Voyager 1 and 2 observations from 1986 through 1989

Abstract

We analyze the magnetic field observed by Voyagers 1 and 2 (V1 and V2) as solar activity increased from near minimum in 1986 to near maximum at the end of 1989. The radial distance of V1 and V2 increased from 25.4 to 39.9 AU and from 18.9 to 30.2 AU, respectively. The elevation angle of the magnetic field observed by both V1 and V2 for each of the years was δ = 0° ± 4.5°. The azimuthal angle λ was consistent with Parker's spiral angle when the solar activity was low but not during 1988 and 1989 when there were many transient ejecta. V1 observed predominantly a single negative polarity from 1986 through 1988, when its latitude was in the range 27.8°‐30.8°N, because the heliospheric current sheet (HCS) was below V1. V1 observed both polarities during 1989, when the maximum latitude of the HCS was far above V1. During 1988 and 1989, V2 observed sectors but no sector pattern, even though an extrapolation of the neutral line near the Sun would imply a two‐sector pattern. This indicates a significant radial evolution of the sector structure and the HCS. We suggest that the numerous transient ejecta perturb the HCS and the radial positions of the sector boundaries randomly when the Sun is active. There was no relation among the sector boundaries, sectors, and interaction regions at either V1 or V2. This implies a considerable evolution of the relation between interaction regions and sector boundaries with increasing distance from the Sun.