Magnetosphere-ionosphere mapping at Jupiter: Quantifying the effects of using different internal field models

The lack of global field models accurate beyond the inner magnetosphere (< 30 RJ) makes it difficult to relate Jupiter’s polar auroral features to magnetospheric source regions. Vogt et al. [2011] map Jupiter’s equatorial magnetosphere to the ionosphere using a flux equivalence calculation that requires equal flux at the equatorial and ionospheric ends of flux tubes. This approach is more accurate than tracing field lines in a global field model, but only if it is based on an accurate model of Jupiter’s internal field. At present there are three widely used internal field models – VIP4, the Grodent anomaly model (GAM), and VIPAL. We will present results of a recently published study that quantifies how the choice of an internal field model affects the mapping of various auroral features using the Vogt et al. [2011] flux equivalence calculation. We find that different internal field models can shift the ionospheric mapping of points in the equatorial plane by several degrees and shift the magnetospheric mapping to the equator by ~30 Jovian radii radially and by less than one hour in local time. These shifts are consistent with differences in how well each model maps the Ganymede footprint, underscoring the need for more accurate Jovian internal field models. Understanding these differences is important for the continued analysis of HST images and in planning for Juno’s arrival at Jupiter in 2016. We will discuss differences in the size and location of the open/closed field line boundary and the mapping of specific auroral features, like polar dawn spots. We will also present some new analysis of the mapping of Jupiter’s main auroral oval and relate this to temporal variability observed in Jupiter’s magnetodisk.