Reconnection and Dipolarization Driven Auroral Dawn Storms and Injections

Yao, Zhonghua; Bonfond, Bertrand; Clark, G.; Grodent, Denis; Dunn, W. R.; Vogt, M. F.; Guo, Ruilong; Mauk, B. H.; Connerney, J. E. P.; Levin, S. M.; Bolton, S. J.

doi:10.1002/essoar.10503657.1

Cited by 10 publications

(19 citation statements)

References 71 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Overall, then, we have shown that this dawn storm was associated with significant plasma dynamics and heating in the dawnside middle to outer magnetosphere, likely initiated by reconnection and/or disruption of the azimuthal current. The schematic in Figure 7 shows the expected generation and evolution of the dawn storm, with reconnection at an earlier local time triggering the reconfiguration of field lines as suggested previously (Kimura et al., 2017; Yao et al., 2020). The reconfiguration front rapidly expands radially outward and through local dawn, corresponding to the poleward and noonward expansion of the auroral emission, until most of the dawn outer magnetosphere is reconfigured at the full extent of the dawn storm.…”

Section: Discussionsupporting

confidence: 52%

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

et al. 2021

View full text Add to dashboard Cite

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

show abstract

Section: Discussionsupporting

confidence: 52%

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

et al. 2021

View full text Add to dashboard Cite

show abstract

“…Based on the final measurement by Cassini, energetic neutral atom enhancements and conjugate periodic enhancements of energetic electrons were observed simultaneously with Saturn's aurora (Radioti et al., 2019). Moreover, at Jupiter, contemporaneous in situ and remote sensing observations from the Juno spacecraft and the Hubble Space telescope allowed to directly connect the latest stage of an auroral dawn storm to energetic electron injection in the middle magnetosphere (Z. H. Yao et al., 2020). These previous studies suggested a close relationship between energetic electrons generated by DFs and auroral intensifications.…”

Section: Discussionmentioning

confidence: 99%

Successive Dipolarization Fronts With a Stepwise Electron Acceleration During a Substorm in Saturn's Magnetotail

Huang

Yuan

et al. 2022

Geophysical Research Letters

View full text Add to dashboard Cite

Studies on substorms originated from the discovery of consistent patterns of auroral activity in Earth's ionosphere (Akasofu, 1964). After decades of intense studies, several features of Earth's substorms have become well known (e.g., Haerendel, 2015). At the beginning of a substorm, dayside magnetopause reconnection occurs, and the corresponding magnetic flux is transported to the lobes and loaded into the magnetotail (Dungey, 1961). Then, the increased magnetic pressure within the lobes thins the central current sheet and promotes magnetic reconnection in the magnetotail (Coroniti & Kennel, 1972). Moreover, a pair of connected X-and O-lines form in the plasma sheet (Russell & McPherron, 1973). As the rate of magnetotail reconnection increases, the O-line evolves to the plasmoid and will be released from the central magnetotail. Magnetic dipolarization is generated near the earthward X-line, and then transports the energetic particles into the inner magnetosphere (Russell & McPherron, 1973). Saturn's space environment is different from Earth's, suggesting that Saturn has a different substorm driving mechanism. Compared with Earth (1 AU), Saturn is farther away from the Sun (9.58 AU), and the solar wind near Saturn is relatively weak, with a dynamic pressure of 0.015 nPa (1.7 nPa for Earth). Although magnetopause reconnections occasionally occur at Saturn's magnetopause (Desroche et al., 2013;Masters et al., 2014;Fuselier et al., 2014), the solar wind is not the most important driver of magnetopause reconnection at Saturn. The water-group neutrals released from Enceladus are ionized and serve as the internal plasma source in Saturn's inner magnetosphere (Bagenal & Delamere, 2011). Moreover, due to Saturn's rapid rotation, the magnetic field configuration and the plasmas in Saturn's magnetosphere present the characteristic of rotation. The rotational energy arises from the corotational kinetic energy that planetary rotation exerts on magnetospheric plasma (Ge Abstract Substorms are a fundamental phenomenon in planetary magnetospheric systems. Using Cassini measurements, we report a typical event in which four successive dipolarization fronts (DFs) were observed within 1 hour during the substorm in Saturn's magnetotail. The last three DFs caused a type of stepwise electron acceleration and generated energetic electrons. The pitch angle distributions of the electrons show evidence of the Fermi acceleration mechanism behind these DFs. Therefore, we infer the magnetotail dynamics process during Saturn's substorm: The stepwise acceleration by successive DFs powerfully accelerates the field-aligned electrons and generates field-aligned energetic electrons. These high-energy electrons are injected into the inner magnetosphere and become an important trigger of Saturn's aurora. Our results show an efficient acceleration mechanism for the electrons caused by successive DFs and confirm an important source of energetic particles during the substorm in Saturn, and these findings improve our understanding of Saturn's substorm ...

show abstract

“…Some magnetic field reversals appear to have a helical or loop‐like magnetic field structure that is characteristic of plasmoid events (Vogt et al., 2014). Also seen are magnetic signatures of “dipolarizations,” which are the result of plasma compression due to fast planetward flows in the so‐called “exhausts” emanating from the reconnection sites (Artemyev et al., 2013, 2020; Yao et al., 2020).…”

Section: Introductionmentioning

confidence: 99%

Properties of Ion‐Inertial Scale Plasmoids Observed by the Juno Spacecraft in the Jovian Magnetotail

et al. 2022

View full text Add to dashboard Cite

We expand on previous observations of magnetic reconnection in Jupiter's magnetosphere by constructing a survey of ion‐inertial scale plasmoids in the Jovian magnetotail. We developed an automated detection algorithm to identify reversals in the Bθ ${B}_{\theta }$ component and performed the minimum variance analysis for each identified plasmoid to characterize its helical structure. The magnetic field observations were complemented by data collected using the Juno Waves instrument, which is used to estimate the total electron density, and the JEDI energetic particle detectors. We identified 87 plasmoids with “peak‐to‐peak” durations between 10 and 300 s. Thirty‐one plasmoids possessed a core field and were classified as flux‐ropes. The other 56 plasmoids had minimum field strength at their centers and were termed O‐lines. Out of the 87 plasmoids, 58 had in situ signatures shorter than 60 s, despite the algorithm's upper limit being 300 s, suggesting that smaller plasmoids with shorter durations were more likely to be detected by Juno. We estimate the diameter of these plasmoids assuming a circular cross section and a travel speed equal to the Alfven speed in the surrounding lobes. Using the electron density inferred by Waves, we contend that these plasmoid diameters were within an order of the local ion‐inertial length. Our results demonstrate that magnetic reconnection in the Jovian magnetotail occurs at ion scales like in other space environments. We show that ion‐scale plasmoids would need to be released every 0.1 s or less to match the canonical 1 ton/s rate of plasma production due to Io.

show abstract

Reconnection and Dipolarization Driven Auroral Dawn Storms and Injections

Cited by 10 publications

References 71 publications

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

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

Successive Dipolarization Fronts With a Stepwise Electron Acceleration During a Substorm in Saturn's Magnetotail

Properties of Ion‐Inertial Scale Plasmoids Observed by the Juno Spacecraft in the Jovian Magnetotail

Contact Info

Product

Resources

About