Ray tracing of Jovian decametric radiation from southern and northern hemisphere sources: Comparison with Voyager observations

Abstract

Because of a lack of readily usable information pertaining to the polarization of the Voyager 1 and 2 high‐frequency band data, a technique has been developed that aids the identification of Io‐dependent decametric radiation originating from the southern hemisphere of Jupiter. This technique compares the results of model ray tracing calculations with the Planetary Radio Astronomy (PRA) observations. A large portion of the Voyager 1 and 2 PRA observations are sorted into bins (±3° wide) centered on a specific Io central meridian longitude. When the data are plotted (as a frequency‐longitude spectrogram) in this coordinate system, Io‐dependent features can be identified and compared with ray tracing calculations performed in a model Jovian magnetosphere where it is assumed that the decametric emissions are generated in the RX mode from low‐altitude source regions along the instantaneous Io flux tube. Two different magnetic field models are used, and the results are contrasted. In this study, we compare the observations for constant sub‐Io longitudes of 260° and 300° with the corresponding model ray tracings. The results permit the identification of decametric spectral features from source locations in both the northern and southern hemispheres: (1) The emission traditionally designated “Io‐B” originates at the Io flux tube footprint in the northern hemisphere when the sub‐Io system III longitude λIII is equal to 260°. (2) The component traditionally designated “Io‐C” is a combination of emissions emanating from the Io flux tube footprints in both northern and southern hemispheres when Io is located at longitudes 260° and 300°. (3) The traditional “non‐Io‐A” emission is, in fact, Io related at both Io configurations studied. When Io is located at λIII = 260°, this emission originates in the southern hemisphere flux tube footprint. When Io is at λIII = 300°, this component (“non‐Io‐A”) originates from the flux tube footprint in the northern hemisphere.