Revisiting substorm events with preonset aurora

Miyashita, Yukinaga; Ieda, A.

doi:10.5194/angeo-36-1419-2018

Cited by 10 publications

(23 citation statements)

References 75 publications

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“…The transient spots observed in Jupiter's aurora share several morphological and temporal characteristics with transient mesoscale features on Earth, sometimes associated with poleward boundary intensifications and sometimes with streamers (Forsyth et al., 2020). Both are often observed before the substorm onset (Nishimura et al., 2011), even if the exact relationship between streamers and substorms is disputed (Miyashita & Ieda, 2018). Both phenomena are associated with reconnection in the magnetotail and the subsequent inward flow of plasma and dipolarizing field lines (Angelopoulos et al., 2008).…”

Section: Discussionmentioning

confidence: 99%

Are Dawn Storms Jupiter's Auroral Substorms?

et al. 2021

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The specificity of the dawn storms among the various auroral morphologies at Jupiter was recognized as soon as the first high resolution ultraviolet (UV) images of the aurorae on Jupiter became available (Gérard et al., 1994). As observed from the Hubble Space Telescope (HST), having only access to the Earth-facing side of the aurora, they consist of a thickening and a major enhancement of the brightness of the dawn arc of the main auroral emission (main oval). They seem to last for at least 1-2 h (Ballester et al., 1996), but given the typical length of HST sequences is ∼45 min, HST could not provide a complete and uninterrupted view of the process. Dawn storms are also characterized by clear signatures of methane absorption, indicating that the charged particles causing them can precipitate deep below the methane homopause, with energies up to 460 keV (Gustin et al., 2006) in the case of electrons. Based on the large HST observation campaign carried out in 2007, dawn storms appeared rare (3 cases out of 54 observations) and occurred independently from the state of the solar wind (Nichols et al., 2009). However, the dawn storm observed Abstract Dawn storms are among the brightest events in the Jovian aurorae. Up to now, they had only been observed from Earth-based observatories, only showing the Sun-facing side of the planet. Here, we show for the first time global views of the phenomenon, from its initiation to its end and from the nightside of the aurora onto the dayside. Based on Juno's first 20 orbits, some patterns now emerge. Small short-lived spots are often seen a couple of hours before the main emission starts to brighten and evolve from a straight arc to a more irregular one in the midnight sector. As the whole feature rotates dawnward, the arc then separates into two arcs with a central initially void region that is progressively filled with emissions. A gap in longitude then often forms before the whole feature dims. Finally, it transforms into an equatorward-moving patch of auroral emissions associated with plasma injection signatures. Some dawn storms remain weak and never fully develop. We also found cases of successive dawn storms within a few hours. Dawn storms thus share many fundamental features with the auroral signatures of the substorms at Earth, despite the substantial differences between the dynamics of the magnetosphere at the two planets. Plain Language Summary Polar aurorae are a direct consequence of the dynamics of the plasma in the magnetosphere. The sources of mass and energy differ between the Earth's and Jupiter's magnetospheres, leading to fundamentally distinct auroral morphologies and very different responses to solar wind variations. Here, we report on the imaging of all development stages of spectacular auroral events at Jupiter, called dawn storms, including, for the first time, their initiation on the nightside. Our results reveal surprising similarities with auroral substorms at Earth, which are auroral events stemming from explosive magnetospheric reconfigurations. These...

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Section: Discussionmentioning

confidence: 99%

Are Dawn Storms Jupiter's Auroral Substorms?

et al. 2021

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“…( 2014 ). Recently, Miyashita and Ieda ( 2018 ) revisited three substorm events reported by Nishimura et al. ( 2010 , 2011 ), particularly with a focus of the arrival timing of the preonset aurora relative to the thee steps of auroral onset arc development, initial brightening, wave-like structure, and poleward expansion.…”

Section: Onset Mechanismsmentioning

confidence: 99%

Explosive Magnetotail Activity

et al. 2019

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Modes and manifestations of the explosive activity in the Earth’s magnetotail, as well as its onset mechanisms and key pre-onset conditions are reviewed. Two mechanisms for the generation of the pre-onset current sheet are discussed, namely magnetic flux addition to the tail lobes, or other high-latitude perturbations, and magnetic flux evacuation from the near-Earth tail associated with dayside reconnection. Reconnection onset may require stretching and thinning of the sheet down to electron scales. It may also start in thicker sheets in regions with a tailward gradient of the equatorial magnetic field ; in this case it begins as an ideal-MHD instability followed by the generation of bursty bulk flows and dipolarization fronts. Indeed, remote sensing and global MHD modeling show the formation of tail regions with increased , prone to magnetic reconnection, ballooning/interchange and flapping instabilities. While interchange instability may also develop in such thicker sheets, it may grow more slowly compared to tearing and cause secondary reconnection locally in the dawn-dusk direction. Post-onset transients include bursty flows and dipolarization fronts, micro-instabilities of lower-hybrid-drift and whistler waves, as well as damped global flux tube oscillations in the near-Earth region. They convert the stretched tail magnetic field energy into bulk plasma acceleration and collisionless heating, excitation of a broad spectrum of plasma waves, and collisional dissipation in the ionosphere. Collisionless heating involves ion reflection from fronts, Fermi, betatron as well as other, non-adiabatic, mechanisms. Ionospheric manifestations of some of these magnetotail phenomena are discussed. Explosive plasma phenomena observed in the laboratory, the solar corona and solar wind are also discussed.

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“…However, we reclassified the events morphologically according to occurrence of auroral poleward expansion by visual inspection of THEMIS all-sky images. Miyashita & Ieda, 2018), but we adopted them as zero epoch time for the present statistical analyses. The rest of 54 events were discarded in the following statistical analyses, since auroral onset arcs were observed near the edge of imagers' fields of view or the auroral morphology was not clear due to cloud.…”

Section: Classification Of Pseudosubstorms and Substormsmentioning

confidence: 99%

“…Furthermore, the onset (initial auroral brightening) times given in the present list may have some delay, potentially a few minutes (cf. Miyashita & Ieda, 2018), but we adopted them as zero epoch time for the present statistical analyses. Figure 1 shows examples of auroral onset arc development for the pseudosubstorm and the substorm (see also Movies S1 and S2).…”

Section: Classification Of Pseudosubstorms and Substormsmentioning

confidence: 99%

A Statistical Study of Near‐Earth Magnetotail Evolution During Pseudosubstorms and Substorms With THEMIS Data

et al. 2020

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Pseudosubstorms (pseudobreakups) and substorms are similar phenomena. In terms of auroral morphology, however, the former are not accompanied by poleward expansion, while the latter are. To understand what causes this difference, we studied temporal and spatial development of the near-Earth magnetotail at X = −7 to −11R E around pseudosubstorm and substorm onsets, based on superposed epoch analysis of Time History of Events and Macroscale Interactions during Substorms (THEMIS) data. We find that the earthward flow begins to increase at X = −10 to −11R E just before onset and dipolarization for both pseudosubstorms and substorms, possibly due to near-Earth magnetic reconnection or the preceding relaxation of the thin current sheet in a tailward region, but the earthward flow is slower for pseudosubstorms than for substorms. Dipolarization, together with magnetic field fluctuation, is nearly the same at X = −8R E for both cases, but it is weaker at other distances for pseudosubstorms than for substorms. This result suggests that the current disruption related to dipolarization does not expand tailward and hence auroral poleward expansion does not occur for pseudosubstorms. Furthermore, the total pressure is larger at X = −8 to −11R E for several minutes before onset for substorms than for pseudosubstorms. The total pressure gradient increases more largely after onset for substorms than for pseudosubstorms. We suggest that these differences are important factors for determining whether ballooning instability causing current disruption grows in a wide area, that is, whether the initial action develops into a substorm or subsides as a pseudosubstorm.

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Revisiting substorm events with preonset aurora

Cited by 10 publications

References 75 publications

Are Dawn Storms Jupiter's Auroral Substorms?

Are Dawn Storms Jupiter's Auroral Substorms?

Explosive Magnetotail Activity

A Statistical Study of Near‐Earth Magnetotail Evolution During Pseudosubstorms and Substorms With THEMIS Data

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