A NEW LOOK AT THE NATURE OF COMET HALLEYS LF ELECTROMAGNETIC-WAVES - GIOTTO OBSERVATIONS

All of the comet Halley high-time resolution magnetic field data have been examined to determine the nature of the ''turbulence'' and its di fference from that of comets Giacobini-Zinner and Grigg-Skjellerup. Al though much of the wave appears unpolarized, occasionally there are in tervals of clear order. We find several interesting new wave polarizat ions: arc-, left-hand/arc- (sunglass) and left-hand circular polarized waves (in the spacecraft frame). The former two types have separation s of similar to 120 s between individual pulses, indicating that the w aves are generated from pickup of the H2O group cometary ions. The thi rd type of waves occurs in a wave-train and may be a detached whistler packet. The unusual polarizations could be caused by wave refraction in the highly turbulent (and high beta) Halley environment or by nonli near evolution due to strong growth rates. It is noted that some of th e large amplitude waves are non-planar. These results are further deta ils of the ''linear polarization'' of Halley waves determined by previ ous coherency analyses, and may explain some of the evolution leading to its plasma turbulence.