Structures far from the head of comet Kohoutek: II. A discussion of the swan cloud of January 11 and of the general morphology of cometary plasma tails

Photographs taken in New Mexico and in Japan during 1974 January 9–11 show that the “Swan Cloud” observed in comet Kohoutek on January 11 (C. L. Hyder, J. C. Brandt, and R. G. Roosen, 1974, Icarus23, 601–610: Paper I) was an advanced stage of a plasma tail disconnection event (DE). The event commenced and evolved with the development of strong tail ray activity, the actual tail disconnection, the merging of the disconnected tail with the new tail to form the Swan, and a new feature not discussed in recent disconnection models—the formation of arcade loops in the space between closing tail rays. An unusual aspect of the event was the deceleration of the rejected tail as it receded from the head.The observed morphological sequence is easily understood in the sector boundary model (M. B. Niedner, Jr., and J. C. Brandt, 1978, Astrophys. J.223, 655–670; 1979, Astrophys. J.234 723–732), in which dayside reconnection of captured interplanetary fields at sector boundary crossings strips away the existing tail, and field capture in the new sector builds a new tail. The associated sector boundary for the event passed Earth of 1974 January 14.The arcade loops are proposed to be reconnected flux tubes between oppositely polarized tail rays in the incipient new tail which followed the disconnection. This interpretation is not only consistent with the magnetic field topology advocated in Alfvén's original model (H. Alfvén, 1957 Tellus9 92–96), but it may also provide a physical model for some of the features known historically as “condensation,” at least some of which appear to have formed in the same manner.