The Disconnection Events of January 10 and April 8 1986 IN the Plasma Tail of Comet Halley

A sequence of 6 white-light pictures covering 10 hrs of the Jan. 10, 1986 Halley's comet plasma tail disconnection was analyzed in order to deduce the variation of the relative velocity of the ion tail revealing a sudden acceleration. A second sequence of 8 CO(+) pictures covering 2.5 hr of the April 8, 1986 large disconnection event was obtained and the velocity field was studied. An attempt to trace the origin of this event on early sequence of white light pictures is discussed, as well as the occurrence of sudden accelerations. The images confirm sudden increases or decreases of the velocity, but it is difficult to say whether these changes can be wholly attributed to sudden acceleration.