Study of emission cone of Io-controlled Jovian decameter radiation

We have investigated the angular distribution of the Jovian decameter radiation occurrence probability, relatively to the local magnetic field B and its gradient ∇B in the source region, using the magnetic field model for Jupiter, based on Juno’s first nine orbits observations, JRM09, was recently proposed by Connerney et al. [Geophys. Res. Lett., 45, 2590-2596, 2018]. The results were compared to those obtained earlier using older models (O6, VIP4, VIT4 and VIPAL). The JRM09 model confirms the former results: the radio emission is beamed in a hollow cone presenting a flattening in a specific direction. The Jovian decameter radiation is supposed to be produced by the cyclotron maser instability (CMI). We interpret this flattening by the fact that the magnetic field in the radio source does not have any axial symmetry because B and ∇B are not parallel. This hypothesis is confirmed by the amplitude of the flattening of the emission cone which appears to be more important for the northern emission (34.8%) than for the southern emission (12.5%) probably due to the fact that the angle between the directions of B and ∇B is greater in the North (~10°) than in the South (~4°). A theory of CMI is being developed in this context of a magnetized plasma not exhibiting axial symmetry.