A heliospheric vortex street?

This paper presents the hypothesis that the periodic meridional (north–south) flows observed by Voyager 2 in the neighborhood of 20–25 AU were produced by a heliospheric vortex street. The separation of the vortices was approximately 6 AU in the radial direction, and the vortices were carried away from the sun at a speed of approximately 425 km/s. This hypothesis can account for the observed ±5° deflections in the flow with a period of 25.5 days, and it predicts small amplitude fluctuations in the bulk speed with two maxima per solar rotation, which is consistent with the observations in 1986. A variety of meridional flow profiles is predicted, depending on the position of the spacecraft relative to the symmetry axis of the vortex street. A definitive test of this hypothesis would be provided by simultaneous observations from two spacecraft with a latitudinal separation of the order of the vortex diameter.