During November 17-18, 1975, a magnetic cloud was observed by the IMP 8 sat
ellite. The cloud was analyzed in several papers. It draws attention becaus
e it is the most clear example where the magnetic field components behave d
ifferently from the current single flux rope model. Various models and fits
have been presented to explain the magnetic field measurements for this pa
rticular event: single-polarity cylindrical flux rope, spheromak, toroidal
flux rope, and two subsequent flux ropes (flux rope twins). We critically e
xamine these models and fits and stress that not only magnetic field data b
ut also plasma data must be taken into account. There is a remarkably sharp
drop in the density inside the magnetic cloud. The most consistent explana
tion of the behavior of magnetic field and plasma data for this event is th
at the magnetic cloud consists of a dual-polarity flux rope with a low dens
ity and strong magnetic field core surrounded by an annular region of the s
ame chirality but opposite polarity. An implication of this possibility to
explain other magnetic cloud observations is discussed.