Response of Jupiter's and Saturn's auroral activity to the solar wind

Abstract

While the terrestrial aurorae are known to be driven primarily by the interaction of the Earth's magnetosphere with the solar wind, there is considerable evidence that auroral emissions on Jupiter and Saturn are driven primarily by internal processes, with the main energy source being the planets' rapid rotation. Prior observations have suggested there might be some influence of the solar wind on Jupiter's aurorae and indicated that auroral storms on Saturn can occur at times of solar wind pressure increases. To investigate in detail the dependence of auroral processes on solar wind conditions, a large campaign of observations of these planets has been undertaken using the Hubble Space Telescope, in association with measurements from planetary spacecraft and solar wind conditions both propagated from 1 AU and measured near each planet. The data indicate a brightening of both the auroral emissions and Saturn kilometric radiation at Saturn close in time to the arrival of solar wind shocks and pressure increases, consistent with a direct physical relationship between Saturnian auroral processes and solar wind conditions. At Jupiter the correlation is less strong, with increases in total auroral power seen near the arrival of solar wind forward shocks but little increase observed near reverse shocks. In addition, auroral dawn storms have been observed when there was little change in solar wind conditions. The data are consistent with some solar wind influence on some Jovian auroral processes, while the auroral activity also varies independently of the solar wind. This extensive data set will serve to constrain theoretical models for the interaction of the solar wind with the magnetospheres of Jupiter and Saturn.

Jupiter’s magnetosphere and aurorae observed by the Juno spacecraft during its first polar orbits

“…In the northern hemisphere at ~12:13 UT, JADE observed three ion Ganymede footprints [34], the large regions of UV emission associated with plasma injection signatures [35,36] and the main emission discontinuity around noon. The overall aurora brightness level is somewhat dim, but not atypically so [37], and the UV color ratio values are similar to previous observations [26,27]. While there is much similarity between UV and IR auroras, there are differences related to the emission mechanisms at work in both cases.…”

“…The overall aurora brightness level is somewhat dim, but not atypically so [37], and the UV color ratio values are similar to previous observations [26,27]. While there is much similarity between UV and IR auroras, there are differences related to the emission mechanisms at work in both cases.…”

“…While there is much similarity between UV and IR auroras, there are differences related to the emission mechanisms at work in both cases. UV emissions are more directly responsive to precipitating particles and as such evidence rapid time variations [37]. In contrast, IR emissions are thermally exited and provide a measurement of upper atmospheric temperature and thereby a measure of energy deposition, whether by particle precipitation or Joule heating.…”

What characterizes planetary space weather?

“…The magnetospheric dynamics as demonstrated by increases in the output of the aurora and auroral kilometric radiation (AKR) at Saturn has been found to be driven by the rotation of the planet except during periods of strong solar wind compression of the magnetosphere (Desch 1982;Clarke et al 2009;Crary et al 2005;Badman and Cowley 2007;Masters et al 2014;Badman et al 2014). The influence of the solar wind at Jupiter is thought to be less strong although solar wind compressions have been associated with changes in the aurora (Baron et al 1996;Gurnett et al 2002;Nichols et al 2007;Cowley et al 2007;Clarke et al 2009). …”

Hungarian national report on IAGA 2007–2010

“…Propagated solar wind data upstream of Jupiter and Saturn for the last 13 years are published at the MSWiM web site http:/ /mswim.engin.umich.edu/, which are freely available for registered users. Our solar wind propagation data were used in, among many other studies, the interpretation of auroral observations at Jupiter and Saturn by the Hubble Space Telescope (Clarke et al 2009). …”