Terrestrial AKR Beaming: Implications for Jovian DAM Beaming Models

Recent studies of terrestrial auroral kilometric radiation (AKR) angular beaming patterns using the WBD instrument on the Cluster spacecraft array demonstrate that emission from individual bursts is confined to a narrow solid angle within a plane containing the magnetic field vector at the source and tangent to the auroral oval. Assuming that the electron cyclotron maser instability (CMI) mechanism is driven by a shell distribution, the propagation direction at the source must be nearly perpendicular (k||~0). Since the angular beaming is observed at low tangent plane longitudes, the rays are must be refracted upward within the auroral cavity, typically θr >45°. We apply these results to models of Jovian decametric emission (DAM) which is also assumed to be generated by the CMI mechanism above the auroral zone. If the terrestrial and Jovian mechanisms and source environments are indeed similar, then Jovian DAM models invoking loss-cone electron distributions to explain the DAM angular power pattern are likely not correct. We suggest that a shell distribution is driving the DAM emission and that refraction causes the observing beaming angles.