Model of the Jovian magnetic field topology constrained by the Io auroral emissions

Abstract

[1] The determination of the internal magnetic field of Jupiter has been the object of many studies and publications. These models have been computed from the Pioneer, Voyager, and Ulysses measurements. Some models also use the position of the Io footprints as a constraint: the magnetic field lines mapping to the footprints must have their origins along Io's orbit. The use of this latter constraint to determine the internal magnetic field models greatly improved the modeling of the auroral emissions, in particular the radio ones, which strongly depends on the magnetic field geometry. This constraint is, however, not sufficient for allowing a completely accurate modeling. The fact that the footprint field line should map to a longitude close to Io's was not used, so that the azimuthal component of the magnetic field could not be precisely constrained. Moreover, a recent study showed the presence of a magnetic anomaly in the northern hemisphere, which has never been included in any spherical harmonic decomposition of the internal magnetic field. We compute a decomposition of the Jovian internal magnetic field into spherical harmonics, which allows for a more accurate mapping of the magnetic field lines crossing Io, Europa, and Ganymede orbits to the satellite footprints observed in UV. This model, named VIPAL, is mostly constrained by the Io footprint positions, including the longitudinal constraint, and normalized by the Voyager and Pioneer magnetic field measurements. We show that the surface magnetic fields predicted by our model are more consistent with the observed frequencies of the Jovian radio emissions than those predicted by previous models.

A Panchromatic View of Brown Dwarf Aurorae

“…By contrast, numerous authors have used these similar assumptions to try to directly constrain the properties of individual objects through models of their dynamic spectra (Yu et al 2011;Lynch et al 2015;Leto et al 2016). Although interesting, these efforts require many assumptions of typically uncertain parameters for a problem that is difficult to answer accurately, even with much more information, as has been attempted with radio observations of Jupiter (see Hess et al 2011). …”

Hubble observations of Jupiter’s north–south conjugate ultraviolet aurora

“…In the present observations, the discontinuity extends over 11,450 km in the north (AB) and 20,700 km in the south (CD). If we magnetically map the size of the north discontinuity to the south using the VIPAL model (Hess et al, 2011), we find that it would extend over 15,000 km, that is less than the observed length. The presence of these segments of the main oval showing no or weak emission in a confined magnetic local time sector was studied by Radioti et al (2008).…”

“…The error associated with the background subtraction is small in comparison with the other two sources. We note that a ''blind'' determination of a given magnetically conjugate point from one hemisphere to the other with the VIPAL model (Hess et al, 2011) leads to localization errors on the order of 2-3°of great circle. We have therefore manually corrected the selected location based on visual inspection of the conjugate features.…”

“…Important statistical differences between the morphology of the main emission in the north and in the south have been pointed out since the two polar regions have been observed. They reflect the large asymmetry of the surface magnetic field which is strongly non-dipolar and presents a magnetic anomaly in the north Hess et al, 2011). Accumulation of observations in both hemispheres at different central meridian longitudes has made it possible to obtain statistical maps of the morphology of the main emissions and satellite footprints Grodent et al, 2003aGrodent et al, , 2008.…”

Zebra-like fine spectral structures in Jovian decametric radio emission

“…This is also consistent with the distribution of the surface (1-bar pressure level) magnetic field of Jupiter and, therefore, with the maximum electron cyclotron frequency. As was shown by Genova and Aubier [1985] and Hess et al [2011] the maximum radio frequency for the northern Io-DAM (Io-A and Io-B sources) is ≈ 38 MHz, while the southern Io-DAM sources (Io-C and Io-D) are mainly observed at lower frequencies < 25 MHz.…”