The E ect of the Tilt of the HCS on the Solar Wind Speed in the Outer

The ow of solar wind from the Sun is bimodal. High speed, low density plasma comes from high magnetic latitude regions and low speed, high density ow from near the heliospheric current sheet (HCS). We investigate whether this bimodal ow combined with the HCS tilt controls the solar wind velocities in the outer heliosphere near solar minimum when the Sun's magnetic eld is roughly dipolar. We present a simple model of radial solar wind ow with regions of fast and slow ow and a HCS tilt provided by the Wilcox Solar Observatory. This is the rst time a model has been used to make quantitative predictions of the solar wind speed in the outer heliosphere based on solar observations. A reasonable t to the main features of the observed velocity pro le at Voyager 2 is obtained if the full-width of the slow speed region is 30 . We conclude that the main physical parameter determining the solar wind speed observed by Voyager 2 near solar minimum in the outer heliosphere is the tilt of the HCS.