THE LATITUDINAL STRUCTURE OF THE SOLAR-WIND IN THE VICINITY OF THE SOLAR EQUATOR NEAR SOLAR MINIMUM - 1986 AND PREDICTIONS FOR 1997

In situ observations by different spacecraft have shown that the helio spheric current sheet (HCS) is associated with a narrow band of low sp eed high density solar wind. The inclination of the HCS and the three- dimensional structure of solar wind streams is related to the inclinat ion of the coronal neutral line. Observations from the Ulysses spacecr aft during the descending phase of solar cycle 22, when Wilcox Solar O bservatory coronal field models suggest that the inclination of the co ronal neutral line was between 50 degrees and 70 degrees, showed that the inclination of the HCS was similar or equal to 20 degrees while so lar wind streams were confined to heliographic latitudes less than 35 degrees. At higher latitudes, low and medium speed solar wind disappea red and the solar wind speed was uniformly high. Observations from the Pioneer 11-Voyager 2 spacecraft pair near the time of the 1986 solar minimum revealed a different structure. At that time the inclination o f the coronal neutral line wits unusually low (<10 degrees-15 degrees) . Solar wind streams vanished near the solar equator end may have disa ppeared at most heliographic latitudes in the outer heliosphere. This has implications for the forthcoming Ulysses equatorial pass at the en d of 1997, when the inclination of the coronal neutral line and the HC S are again expected to be low. If the HCS is sufficiently flat, condi tions may resemble those observed near the time of the 1986 solar mini mum and the solar wind stream structure may disappear at Ulysses near the solar equator.