4 Ionospheric conductance effects
The model includes a height-integrated conductance in Jupiter’s ionosphere. The runs presented so far all considered a Pedersen conductance of 1 S. However, Gérard et al. (2020) have used data from the Ultraviolet Spectral Imager (UVS) on Juno to make estimates of the Pedersen conductance, showing that it can range from 0.1 S to about 10 S, consistent with results from ionospheric modeling (Millward et al., 2002; Ray et al., 2014). We have done a series of runs to see the effect of the variation of the conductance at Jupiter, using the low-density model discussed above. Figure 7 shows the Poynting flux for runs in which Io is near the equator as in Figures 2a. Figure 7a shows the 0.1 S case, while Figure 7b gives the results for a Pedersen conductance of 10 S. In the low-conductance case, the ionosphere is closely matched to the Alfvén wave impedance and the wave is largely absorbed there. It can be seen that the reflection from the torus boundary is stronger than the reflection from the ionosphere. On the other hand, the reflection from the ionosphere in the 10 S case is very strong and does not lead to damping of the wave. In this case the secondary waves are enhanced compared to the lower conductance case.