Physics
Scientific paper
Nov 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995jgr...10021669w&link_type=abstract
Journal of Geophysical Research, Volume 100, Issue A11, p. 21669-21682
Physics
Magnetospheric Physics: Planetary Magnetospheres, Planetology: Solid Surface Planets: Interactions With Particles And Fields, Planetology: Solid Surface Planets: Magnetic Fields And Magnetism, Radio Science: Magnetospheric Physics
Scientific paper
Two empirical models were developed for the location and beam structure of Neptune's right-hand (RH) polarized corotating smooth component radio source. The O8 magnetic field model was assumed. In both models the usual assumptions were also made that (1) the source is distributed within a region such that X mode emission toward the spacecraft would be RH elliptically polarized, (2) the resultant beam is the sum of elementary hollow cone beam components for which the cone axes are tangent to the magnetic field at the individual source elements, and (3) all the source elements lie just above the surface on which the electron cyclotron frequency equals the frequency of the emitted radiation. (The resultant beam was found also to be confined to a hollow cone, indicating a relatively small source area.) In the second model, which is the more realistic of the two, an additional requirement was imposed that all ray paths to the spacecraft must lie entirely outside this surface, i.e., within the radio horizon. At each of several frequencies between about 40 and 400 kHz, the adjustable model parameters were varied to yield calculated intensity versus time curves at the spacecraft location that most closely matched the observed intensity versus time curves. The model indicated that the source is located within or near the the northern auroral zone at L=20. At 116 kHz it was found that the half angle of the hollow cone emission beam was approximately 80° (at its midpoint) with a beam wall thickness of about 15°. At higher frequencies the beam half angle and wall thickness were somewhat less than these values. A new component of the Neptunian radio emission is also described. This component is left-hand polarized and is of extremely narrow bandwidth. It is believed to be confined within an unusually thin-walled hollow cone emission beam. It is referred to as the LNT component. Evidence is presented suggesting that it is O mode emission from the same source that produces the X mode smooth component.
Carr Thomas D.
Wang Liyun
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