Jupiter decametric emission: Jovian active longitude
Long term ground observations of the jovian decameter radio emission (DAM) show that the occurrence probability of the radiation depends on two essential parameters:
the central meridian longitude (CML, System III), which is linked to the rotating magnetic field, and the orbital phase of the satellite Io. The CML-Io diagram, which
displays the occurrence of the emission as a function of the CML and Io, reveals several zones of enhanced occurrence probability which have been named Io-controlled sources: Io-A, Io-B, Io-C and Io-D. The generation of planetary radio emissions (in particular the jovian decametric emissions) is attributed to the cyclotron maser instability (CMI).
 - Figure 2 left
 - Figure 2 right
Theoretical evidence of Jovian active longitudes was provided by Galopeau et al. [2004]. A schematic illustration of the parameters of this model is shown in Figure 1. The radiation is supposed to be emitted at the local gyrofrequency along an active magnetic field line intersecting Io’s wake with a lead angle δ. The radio emission is beamed into a hollow cone with half-angle θ and axis parallel to the direction of the gradient of the magnetic field modulus ∇B . The authors supposed that the occurrence probability of the radiation was linked to the amplification efficiency of the radio waves by the CMI. Figure 2 shows the modeled (left-panel) and observed (right-panel) CM-Io phase diagrams.
|
