LAUSR

Synoptic decametric (DAM) radio observations at Jupiter were made in a broad Jovicentric latitudinal range of −21∘ to +15∘ by the Juno polar orbiting spacecraft from 21 June to 10 December, 2016. We investigated the occurrence probability of non-Io-related DAM. At 19.5 MHz, as Juno's latitude varies from +15∘ to −21∘, a peak of non-Io-B occurrence probability at 175∘ System III central meridian longitude (CML) gradually shifts in longitude to 140∘ CML. Also, another peak occurs at 110∘ CML between −15∘ and −9∘, merging into the bottom edge of the former peak. This J-shaped feature is similarly seen at 16.5 MHz. Using the Jovian magnetic field models, the fixed hollow cone model can reasonably account for the J-shaped structure for radio sources traced along active magnetic flux tubes onto Jupiter's surface projected at about 135∘–149∘ System III longitude. Moreover, these non-Io-B spectral profiles extend from 13.5 to 23.5 MHz.