Dipolarization Fronts With Associated Energized Electrons in Saturn's Magnetotail

Smith, A. W.; Jackman, C. M.; Thomsen, M. F.; Sergis, N.; Mitchell, D. G.; Roussos, E.

doi:10.1002/2017ja024904

Cited by 14 publications

(27 citation statements)

References 92 publications

(192 reference statements)

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“…Dipolarization signatures occur after magnetic reconnection in the magnetotail, where the planetward magnetic field relaxes and becomes more dipolar (Bunce et al, ; Slavin et al, ). Plasmoids and dipolarizations have both been investigated at Saturn (e.g., Hill et al, ; Jackman et al, ; Smith, Jackman, Thomsen, Sergis, et al, ; Thomsen et al, ) and are also commonly observed at the magnetospheres of Mercury (e.g., Dewey et al, ) and Earth (e.g. Hones, ; Ieda et al, ; Arnold et al, ).…”

Section: Resultsmentioning

confidence: 99%

“…However, our evidence of an LT asymmetry may indicate that this region of plasma depletion may occur at Saturn's magnetosphere. Dipolarization signatures of Dungey‐style reconnection have also found density‐depleted flux tubes in the postmidnight region (Smith et al, ; Smith, Jackman, Thomsen, Sergis, et al, ). Our conclusion that this phenomenon needs to be examined more closely is similar to a recent study of Juno spacecraft data by Gershman et al () that found that the concept of a cushion region at Jupiter also needs to be reassessed.…”

Section: Summary and Discussionmentioning

confidence: 97%

“…Both the northern and southern cusp have been measured at Saturn's magnetosphere (Arridge et al, ; Jasinski, Arridge, et al, ). On the nightside, Dungey‐cycle magnetic reconnection drives open fields in the lobes to be closed, and during this process, plasma is released down the tail (e.g., Hill et al, ; Jackman et al, , ; Smith et al, , ). Therefore, the open magnetosphere is located at the polar regions where the field is tethered to only one of the polar ionospheres.…”

Section: Introductionmentioning

confidence: 99%

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Saturn's Open‐Closed Field Line Boundary: A Cassini Electron Survey at Saturn's Magnetosphere

et al. 2019

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We investigate the average configuration and structure of Saturn's magnetosphere in the nightside equatorial and high-latitude regions. Electron data from the Cassini Plasma Spectrometer's Electron Spectrometer (CAPS-ELS) is processed to produce a signal-to-noise ratio for the entire CAPS-ELS time of operation at Saturn's magnetosphere. We investigate where the signal-to-noise ratio falls below 1 to identify regions in the magnetosphere where there is a significant depletion in the electron content. In the nightside equatorial region, we use this to find that the most planetward reconnection x-line location is at 20-25 R S downtail from the planet in the midnight to dawn sector. We also find an equatorial dawn-dusk asymmetry at a radial distance of >20 R S , which may indicate the presence of plasma-depleted flux tubes returning to the dayside after reconnection in the tail. Furthermore, we find that the high-latitude magnetosphere is predominantly in a state of constant plasma depletion and located on open field lines. We map the region of high-latitude magnetosphere that is depleted of electrons to the polar cap to estimate the size and open flux content within the polar caps. The mean open flux content for the northern and southern polar caps are found to be 25 ± 5 and 32 ± 5 GWb, respectively. The average location of the open-closed field boundary is found at invariant colatitudes of 12.7 ± 0.6°and 14.5 ± 0.6°. The northern boundary is modulated by planetary period oscillations more than the southern boundary.

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Section: Resultsmentioning

confidence: 99%

Section: Summary and Discussionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

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Saturn's Open‐Closed Field Line Boundary: A Cassini Electron Survey at Saturn's Magnetosphere

et al. 2019

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“…Since then numerous in situ encounters with plasmoids (Hill et al, ; Jackman et al, , ; Russell et al, ) and dipolarizations (Jackman et al, , ; Thomsen et al, ; Yao et al, ) have been observed. More recently, wider surveys of Saturn's magnetotail aiming to identify these structures have been conducted (e.g., Jackman et al, ; Smith et al, , ; Thomsen, Jackman, et al, ).…”

Section: Introductionmentioning

confidence: 99%

“…At Earth, direct ion (Eastwood et al, ; Nagai et al, ; Øieroset et al, ) and electron (Burch et al, ) diffusion region encounters have been identified. However, at Saturn, only a single encounter with the magnetotail ion diffusion region has been reported (Arridge et al, ), and so modeling (Jia et al, ) or indirect evidence such as bursts of energetic ions (e.g., Mitchell et al, ) or the orientation of reconnection products (Smith et al, , ) have been used to infer its location.…”

Section: Introductionmentioning

confidence: 99%

Multi‐instrument Investigation of the Location of Saturn's Magnetotail X‐Line

et al. 2018

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Reconnection is a fundamentally important process in planetary magnetospheres, with both local and global effects. At Saturn, observations of the magnetotail reconnection site (or x‐line) are rare, with only one in situ encounter reported to date. In this work, an extensive database of plasmoids and dipolarizations (Smith et al., 2016, https://doi.org/10.1002/2015JA022005) was investigated from a multi‐instrument perspective in order to probe the location and variability of the magnetotail x‐line. Several clear intervals were identified in which the x‐line location could be indirectly inferred to move on relatively short timescales. Two case studies are presented, the first of which concerns short‐lived flows, suggesting the reconnection sites can be either short‐lived (∼10 minutes) or extremely azimuthally limited (∼3RS/0.4 hr of local time). The second interval concerns the tailward motion of the reconnection site (or sites), inferred from the increasing electron temperature (and diminishing electron density) associated with the flows. This tailward motion occurs over ∼2.5 hr (approximately a quarter of a planetary rotation). The composition of the suprathermal plasma suggests that this could be an example of the gradual depletion of mass‐loaded flux tubes (that must occur prior to lobe reconnection). These case studies are consistent with previous statistical work that suggested that the site of reconnection in the Kronian magnetotail can be highly dynamic.

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Recurrent Magnetic Dipolarization at Saturn: Revealed by Cassini

et al. 2018

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Planetary magnetospheres receive plasma and energy from the Sun or moons of planets and consequently stretch magnetic field lines. The process may last for varied timescales at different planets. From time to time, energy is rapidly released in the magnetosphere and subsequently precipitated into the ionosphere and upper atmosphere. Usually, this energy dissipation is associated with magnetic dipolarization in the magnetosphere.This process is accompanied by plasma acceleration and field-aligned current formation, and subsequently auroral emissions are often significantly enhanced. Using measurements from multiple instruments on board the Cassini spacecraft, we reveal that magnetic dipolarization events at Saturn could reoccur after one planetary rotation and name them as recurrent dipolarizations. Three events are presented, including one from the dayside magnetosphere, which has no known precedent with terrestrial magnetospheric observations. During these events, recurrent energizations of plasma (electrons or ions) were also detected, which clearly demonstrate that these processes shall not be simply attributed to modulation of planetary periodic oscillation, although we do not exclude the possibility that the planetary periodic oscillation may modulate other processes (e.g., magnetic reconnection) which energizes particles. We discuss the potential physical mechanisms for generating the recurrent dipolarization process in a comprehensive view, including aurora and energetic neutral atom emissions. Plain Language SummaryUsing measurements from the Cassini spacecraft, we reveal a new feature of magnetic dipolarization at Saturn, that is, the magnetic signature repeat after one planetary rotation, which is named recurrent dipolarization. Up to hundreds of kiloelectron volt electrons and ions are identified for the recurrent dipolarization events, suggesting that these particles have experienced efficient acceleration and cannot be purely due to planetary modulation. It remains a mystery why the magnetic dipolarization process associated with energetic ions and electrons could reoccur after one planetary rotation. Moreover, dipolarization process in Saturn's dayside magnetosphere is reported for the first time at Saturn, which has no known precedent with terrestrial or other planetary magnetospheric observations. The results demonstrate that magnetosphere-ionosphere coupling dynamics at Saturn and Earth have fundamental similarities and differences.

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Dipolarization Fronts With Associated Energized Electrons in Saturn's Magnetotail

Cited by 14 publications

References 92 publications

Saturn's Open‐Closed Field Line Boundary: A Cassini Electron Survey at Saturn's Magnetosphere

Saturn's Open‐Closed Field Line Boundary: A Cassini Electron Survey at Saturn's Magnetosphere

Multi‐instrument Investigation of the Location of Saturn's Magnetotail X‐Line

Recurrent Magnetic Dipolarization at Saturn: Revealed by Cassini

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