Measurements of the interplanetary magnetic field taken with Explorer 33 and 35 in 1967 and 1968 indicate that for a given polarity the north-south component or, more precisely, the θ component in a spherical polar coordinate system (r, θ, ϕ) has, in general, a 27-day mean value that is significantly different from zero. The initial evidence for this effect was discovered in a study of magnetic-field records from Mariner 2, 4, and 5 recently published by Coleman and Rosenberg. For an interplanetary field directed outward from the sun the mean value of Bθ is negative above the solar equatorial plane and positive below it, and vice versa for an inward field. Thus, for an outward field, the rθ component of a line of magnetic force above or below the equatorial plane is skewed relative to r in the direction away from the equatorial field.
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Rosenberg et al. (1971) studied this question.