Latitudinal beaming of Jovian decametric radio emissions as viewed from Juno and the Nancay Decameter Array

Two well-defined Jovian decametric radio arcs were observed at latitudinal separations of 11 degrees-16 degrees from the Juno spacecraft near Jupiter and the Nancay Decameter Array (NDA) at Earth on 17 May and 25 August 2016. These discrete arcs are from the so-called A source covering both Io-related and non-Io-related emissions. By measuring the wave arrival time at two distant observers with propagation time correction, the remaining delay times are 92.8 +/- 1.3 min for the first arc and 116.0 +/- 1.2 min for the second arc. This implies that both radio sources are not controlled by the orbital motion of Io but Jupiter's rotation itself. The geometrical information for Juno and NDA and the loss cone-driven electron cyclotron maser instability theory provide these radio sources that are located at about 173 degrees +/- 10 degrees in system III longitude projected onto Jupiter's north surface and imply resonant electron energy ranges from 0.5 to 11 keV.