Abstract
We examine Ulysses solar wind and interplanetary magnetic field (IMF) observations at 5 AU for two ~13 month intervals during the rising and declining phases of solar cycle 23 and the predicted response of the Jovian magnetosphere during these times. The declining phase solar wind, composed primarily of corotating interaction regions and high-speed streams, was, on average, faster, hotter, less dense, and more Alfvenic relative to the rising phase solar wind, composed mainly of slow wind and interplanetary coronal mass ejections. Interestingly, none of solar wind and IMF distributions reported here were bimodal, a feature used to explain the bimodal distribution of bow shock and magnetopause standoff distances observed at Jupiter. Instead, many of these distributions had extended, non-Gaussian tails that resulted in large standard deviations and much larger mean over median values. The distribution of predicted Jupiter bow shock and magnetopause standoff distances during these intervals were also not bimodal, the mean/median values being larger during the declining phase by ~1 – 4%. These results provide data-derived solar wind and IMF boundary conditions at 5 AU for models aimed at studying solar wind-magnetosphere interactions at Jupiter and can support the science investigations of upcoming Jupiter system missions. Here, we provide expectations for Juno, which is scheduled to arrive at Jupiter in July 2016. Accounting for the long-term decline in solar wind dynamic pressure reported by McComas et al. (2013), Jupiter’s bow shock and magnetopause is expected to be at least 8 – 12% further from Jupiter, if these trends continue.
Highlights
Jupiter’s magnetosphere has been explored by several spacecraft, including seven flyby missions (Pioneer 10 and 11, Voyager 1 and 2, Ulysses, Cassini, and New Horizons) and one orbiter (Galileo), as reviewed in Bagenal et al (2004). Observations from these spacecraft have uncovered the general morphology of the magnetosphere, whose primary feature is the oxygen and sulfur-rich Io torus that peaks in density at ∼6 jovian radii (1 RJ ∼71492 km), and revealed a host of dynamical processes that occur on timescales of minutes—such as plasma interchange near the Io torus (Kivelson et al, 1997), reconnection driven auroral emissions (Grodent et al, 2003), hours—such as spin period modulated radio emissions (Zarka, 2004), energetic electron injections (Mauk et al, 1998), ultraviolet (UV) auroral brightenings (Clarke et al, 2009) and days—such as reconnection driven particle bursts (Woch et al, 1998), plasmoid ejection (Kronberg et al, 2005), large scale outer boundary motion (McComas et al, 2014)
The expected bimodal nature of these standoff distance distributions is not apparent here and the predictions favor a magnetosphere in a more expanded state. This may be due to the presence of intermediate speed solar wind with dynamic pressure distributions that are not bimodal or, perhaps, because Jupiter’s magnetosphere does not immediately respond to changes in the solar wind dynamic pressure (e.g., McComas et al, 2014)
The role of the solar wind in shaping the topology of and controlling the dynamics within Jupiter’s magnetosphere is an open issue (e.g., Krupp et al, 2004) that remains under considerable debate (Cowley et al, 2008; McComas and Bagenal, 2008)
Summary
None of solar wind and IMF distributions reported here were bimodal, a feature used to explain the bimodal distribution of bow shock and magnetopause standoff distances observed at Jupiter Instead, many of these distributions had extended, non-Gaussian tails that resulted in large standard deviations and much larger mean over median values. The distribution of predicted Jupiter bow shock and magnetopause standoff distances during these intervals were not bimodal, the mean/median values being larger during the declining phase by ∼1–4%. These results provide data-derived solar wind and IMF boundary conditions at 5 AU for models aimed at studying solar wind-magnetosphere interactions at Jupiter and can support the science investigations of upcoming Jupiter system missions.
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