Simultaneous Observation of an Auroral Dawn Storm With the Hubble Space Telescope and Juno

Abstract

Jupiter's ultraviolet auroras are dominated by the main auroral oval, an almost continuous narrow band or series of bands of emission encircling the magnetic poles of the planet (e.g., Clarke et al., 2004;Grodent et al., 2003). This emission maps to the middle magnetosphere, and is generally believed to be driven by the breakdown in corotation of iogenic plasma at radial distances of several tens of planetary radii (Cowley & Bunce, 2001;Hill, 2001;Southwood & Kivelson, 2001). While the overall morphology of the main emission is fixed in System-III longitude and is relatively stable over observation timescales (Clarke et al., 2004), there also exist more dynamic features known to develop over timescales of minutes to tens of minutes. An example of these dynamic phenomena is dawn storms, a brightening of the main emission fixed at dawn. These events produce the most powerful auroral emissions observed at Jupiter and are likely associated with significant reconfigurations of the magnetosphere, but the precise mechanisms of their generation and evolution are currently unknown. Dawn storms were first observed in Jupiter's northern far ultraviolet (FUV) aurora using the Faint Object Camera (FOC) and Wide Field Planetary Camera 2 (WFPC2) on HST (Ballester et al., 1996;Clarke et al., 1998;Gérard et al., 1994), and were characterized as bright enhancements of the dawnward arc of the main emission. These enhancements expand poleward and eastward longitudinally over several tens of minutes, then appear fixed near dawn for several hours before returning to typical auroral intensities. Auroral intensities often peak at several MR to tens of MR, and additionally high color ratios have previously been measured for dawn storm emissions (Gustin et al., 2006), indicating significant hydrocarbon absorption of the auroral emission. This suggests electrons precipitating in the region penetrate to greater depths in the upper atmosphere, requiring higher electron energies than are typically calculated for the

Large-scale episodic enhancements of relativistic electron intensities in Jupiter's radiation belt

“…Vogt et al (2010) and Vogt et al (2020) identified reconnection events in the middle and outer magnetosphere observed by Galileo and Juno, revealing that a similar LT asymmetry of predominant occurrence at dawn also exists for the reconnection sites. Recently, Yao et al (2020) and Swithenbank‐Harris et al (2021) analyzed the storm‐time dynamics at dawn in the context of auroral emissions, suggesting that inward bursts of energetic electrons and protons associated with reconnection could be linked to common occurrences of auroral dawn storms in Jovian magnetosphere (Grodent et al, 2018). Similar local time asymmetries of storm‐time dynamics and associated injections have also been observed in Saturn's magnetosphere.…”

Are Dawn Storms Jupiter's Auroral Substorms?

“…Simultaneous in situ measurements in the dawn-side magnetosphere with Juno and auroral images from the HST showed that dawn storms are associated with reconnection, dipolarization and particle acceleration signatures (Z. H. Yao et al, 2020a, Swithenbank-Harris et al 2021. Observations from Galileo also showed signatures of dipolarization, plasmoid release, and plasma energization in the magnetotail, which were associated with substorm-like events (Ge et al, 2007;Kronberg et al, 2005Kronberg et al, , 2008; Krupp et al, 1998), because of the analogy with similar processes taking place during terrestrial substorms.…”

Relation of Jupiter's Dawnside Main Emission Intensity to Magnetospheric Currents During the Juno Mission

“…The first three of these exhibited dawn storms, when the dawnside main emission was significantly brightened. The origin of dawn storms is unclear but recent suggestions relate to nightside reconnection (Swithenbank‐Harris et al., 2021; Yao et al., 2020), rather than more directly to the M‐I coupling current system. The other two excluded images were obtained when Juno was outside of the magnetosphere, such that no simultaneous current measurements could be made.…”