An isolated, bright cusp aurora at Saturn

Kinrade, Joe; Bunce, E. J.; Tao, Chihiro; Provan, G.; Cowley, S. W. H.; Grocott, Adrian; Gray, R.J.; Grodent, Denis; Kimura, Tomoki; Nichols, J. D.; Arridge, C. S.; Radioti, Aikaterini; Clarke, J. T.; Crary, F. J.; Pryor, W. R.; Melin, Henrik; Baines, K. H.; Dougherty, M. K.

doi:10.1002/2016ja023792

Cited by 9 publications

(16 citation statements)

References 86 publications

(176 reference statements)

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“…The systematic fitting of circles was limited to those images displaying clear equatorward 10.1029/2018JA025426 Journal of Geophysical Research: Space Physics emission boundaries (see section 4.2) in both the dawn and dusk sectors to constrain the fit; however, during the 2014 campaign, only 26 images were found to be suitable. The auroral oval morphology was very mixed, including periods during which the dawn arc disappeared completely (Kinrade et al, 2017). We found no statistical oscillation of the oval position using these images, but the oval (when present) was offset by a mean~3°toward a LT of~02 LT, consistent with the offset reported by Carbary (2012) and Nichols et al (2016).…”

Section: A1 Rotational Modulation Of Auroral Positionsupporting

confidence: 83%

“…Nichols et al (2016) also observed this pre-noon, LT boundary in HST images from 2011 to 2013, citing the presence of poleward auroral forms around noon to be the probable cause. Poleward forms around noon were also present during this 2014 campaign (Kinrade et al, 2017) and were identified as signatures of dayside reconnection processes. Auroral features poleward of the dayside main emission have been previously linked with cusp emission and bursty reconnection during periods of magnetospheric compression by the solar wind (e.g., Badman et al, 2013;Gérard et al, 2005;Meredith et al, 2015;Radioti et al, 2011), although reconnection signatures in the dayside aurora have also been observed during quiet solar wind conditions and in absence of any other main emission morphology (Kinrade et al, 2017).…”

Section: Boundary Locationsmentioning

confidence: 82%

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Saturn's Northern Auroras and Their Modulation by Rotating Current Systems During Late Northern Spring in Early 2014

et al. 2018

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The Hubble Space Telescope imaged Saturn's northern ultraviolet auroras during February–June 2014, when Saturn's northern and southern magnetic perturbation fields were locked in antiphase and matched in rotation period (~10.69 hr). During this coalescence period, we test for evidence of rotational modulation of the auroras using the latest rotating current system model and kilometric radio phases derived from Cassini measurements. While we see modulation of auroral intensity in the rotating frames of the planetary period current systems, the pattern is opposite to that expected and is dominated by an asymmetric local time profile that peaks at dawn. Enhancement of the north emission by rotating upward field aligned currents (FACs) is expected to peak at magnetic longitudes of ~90°, whereas here the intensity increased at ~270°. This unexpected finding is attributed to the presence of nonplanetary period oscillation dynamics having affected the auroral morphology, together with insufficient sampling of the rotational system orientations provided during such Hubble Space Telescope campaigns. Rotational modulation is clearest at dawn regardless of the pattern's orientation, suggesting that the physical relationship between rotating FACs and auroral intensity is not direct, having a local time dependence that is not generally observed in the rotating FAC magnitudes. We also find no statistically significant planetary period oscillation of the auroral circle position, but the mean center was offset from the spin pole by ~3° latitude toward early morning local times. Mean auroral boundaries were located at equatorward and poleward colatitudes of 15.0 ± 2.8° and 12.4 ± 3.0°, respectively.

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Section: A1 Rotational Modulation Of Auroral Positionsupporting

confidence: 83%

Section: Boundary Locationsmentioning

confidence: 82%

Saturn's Northern Auroras and Their Modulation by Rotating Current Systems During Late Northern Spring in Early 2014

et al. 2018

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“…These images were acquired by the HST Space Telescope Imaging Spectrograph (STIS), with the STIS FUV multianode microchannel array using the F25SrF2 long‐pass filter with an exposure time of 840 s. This filter is a band‐pass filter letting 125‐ to 190‐nm wavelengths pass while blocking the H Lyman‐ α emission line at 121 nm. All exposures were background‐subtracted and projected on a planetocentric polar grid (e.g., Clarke et al, ; Kinrade et al, ). This day clearly featured an exceptionally quiet aurora in the northern hemisphere, with none of the images including any dawn emission.…”

Section: Resultsmentioning

confidence: 99%

Observations of Continuous Quasiperiodic Auroral Pulsations on Saturn in High Time‐Resolution UV Auroral Imagery

et al. 2019

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Saturn's aurora represents the ionospheric response to plasma processes occurring in the planet's entire magnetosphere. Short-lived ∼1-hr quasiperiodic high-energy electron injections, frequently observed in in situ particle and radio measurements, should therefore entail an associated flashing auroral signature. This study uses high time-resolution ultraviolet (UV) auroral imagery from the Cassini spacecraft to demonstrate the continuous occurrence of such flashes in Saturn's northern hemisphere and investigate their properties. We find that their recurrence periods of order 1 hr and preferential occurrence near dusk match well with previous observations of electron injections and related auroral hiss features. A large spread in UV auroral emission power, reaching more than 50% of the total auroral power, is observed independent of the flash locations. Based on an event observed both by the Hubble Space Telescope and the Cassini spacecraft, we propose that these auroral flashes are not associated with low-frequency waves and instead directly caused by recurrent small-scale magnetodisc reconnection on closed field lines. We suggest that such reconnection processes accelerate plasma planetward of the reconnection site toward the ionosphere inducing transient auroral spots while the magnetic field rapidly changes from a bent-back to a more dipolar configuration. This manifests as a sawtooth-shaped discontinuity observed in magnetic field data and indicates a release of magnetospheric energy through plasmoid release.Recent surveys have statistically investigated the occurrence of such short periodicities throughout the Kronian magnetosphere. Roussos et al. (2016) and analyzed quasiperiodic injections of relativistic electrons and found that most events occurred at ∼1-hr periodicities and outside of Titan's orbit (∼20 R S ), spread through almost all the outer magnetosphere-although with a significant location bias toward dusk local times (LTs). further observed strong radio bursts in the auroral hiss collocated with the electron injections and higher growth rates of the pulses at high latitudes, suggesting a high-latitude acceleration region. The observed location at which these injections take place points to magnetopause or Vasyliunas-cycle reconnection as possible trigger mechanisms . Kelvin-Helmholtz waves are deemed unlikely to effectuate the observed LT disparity.Based on radio measurements from the entire Cassini mission, Carbary et al. (2016) observed similarly increased occurrence rates of periodicities in plasma wave intensity near dusk and at high latitudes, although noting that this bias might be explained with higher auroral hiss observation rates in these regions. They

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“…impinging on Jupiter's magnetosphere. This model is used extensively by the outer planets magnetosphere community [11][12][13] in the absence of in-situ measurements of the solar-wind conditions.…”

Section: Methodsmentioning

confidence: 99%

A brightening of Jupiter’s auroral 7.8-μm CH4 emission during a solar-wind compression

et al. 2019

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Enhanced mid-infrared emission from CH 4 and other stratospheric hydrocarbons have been observed coincident with Jupiter's ultraviolet auroral emission 1-3 , which demonstrates that auroral processes and the neutral stratosphere of Jupiter are coupled. However, the exact nature of this coupling has remained an open question. Here, we present a time series of Subaru-COMICS images of Jupiter at 7.80 µm measured between January 11-14th, February 4-5th and May 17-20th (UT) 2017, which show both the morphology and magnitude of the auroral CH 4 emission to vary on daily timescales in relation to external solar-wind conditions. The southern auroral CH 4 emission increased in brightness temperature (T b) by ∆T b = 3.8 ± 0.9 K between January 11th 15:50 UT-12th 12:57 UT during a predicted solarwind compression. During the same compression, the northern auroral emission exhibited a dusk-side brightening, which mimicks the morphology observed in the ultraviolet auroral emission during periods of enhanced solar-wind pressures 4, 5. These results suggest that changes in external solar wind conditions perturb the jovian magnetosphere such that ener

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An isolated, bright cusp aurora at Saturn

Cited by 9 publications

References 86 publications

Saturn's Northern Auroras and Their Modulation by Rotating Current Systems During Late Northern Spring in Early 2014

Saturn's Northern Auroras and Their Modulation by Rotating Current Systems During Late Northern Spring in Early 2014

Observations of Continuous Quasiperiodic Auroral Pulsations on Saturn in High Time‐Resolution UV Auroral Imagery

A brightening of Jupiter’s auroral 7.8-μm CH4 emission during a solar-wind compression

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