Statistical study of latitudinal beaming of Jupiter's decametric radio emissions using Juno

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.