DISAPPEARANCE OF THE HELIOSPHERIC SECTOR STRUCTURE AT ULYSSES

In May, 1993, the heliospheric current sheet (HCS) ceased to be seen b y the Ulysses spacecraft at a heliocentric latitude of approximately 3 0-degrees-S and distance of 4.7 AU. The disappearance of the HCS coinc ided with the solar wind speed remaining >560 km/s and with the disapp earance of one of four interaction regions previously seen on each sol ar rotation. The heliographic latitude of the disappearance of die HCS at Ulysses was 11-degrees equatorward of the latitude of the magnetic neutral sheet computed at the source surface at 2.5 solar radii, and it occurred a half year earlier than predicted on the basis of the per sistence of the time profile of the neutral sheet tilt from one solar cycle to the next.