Saturn's equinoctial auroras

Nichols, J. D.; Bunce, E. J.; Clarke, J. T.; Cowley, S. W. H.; Crary, F. J.; Dougherty, M. K.; Gérard, Jean‐Claude; Grodent, Denis; Hansen, K. C.; Kurth, W. S.; Mitchell, D. G.; Pryor, W. R.; Stallard, T.; Talboys, D. L.; Wannawichian, S.

doi:10.1029/2009gl041491

Cited by 41 publications

(60 citation statements)

References 22 publications

(31 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Table 2 Comparison of emitted auroral power in the two hemispheres. Blob S 16.6 ± 0.6 9.9 4(3) Blob S 14.0 ± 0.6 9.9 4(4) Blob N 7.2 ± 0.4 13.3 In the case of the equinoctial observations of Saturn's FUV aurora, Nichols et al (2009) argued that the larger emitted power in the north where the magnetic field is stronger indicates that the field-aligned currents are responsible for this emission.…”

Section: Discussionmentioning

confidence: 99%

“…The emitted power is then proportional to the product of strength of the magnetic field by the square of the Pedersen conductivity, assuming a common source population. In the more general case for arbitrary geometry, the UV power is proportional to the total current squared multiplied by the ionospheric field strength (Nichols et al, 2009). We note however that the Pedersen conductivity itself varies as the inverse of the magnetic field intensity so that the auroral power then varies as 1/B i , similar to the diffuse aurora.…”

Section: Discussionmentioning

confidence: 99%

“…Such data were obtained at equinox by Nichols et al (2009). They showed that individual auroral features can exhibit distinct hemispheric asymmetries.…”

Section: Introductionmentioning

confidence: 95%

“…Given the longer time separating images of the two hemispheres, these features will not be discussed in detail in this study. Instead, the main emission structure is generally stable over several hours (Nichols et al, 2009) as evidenced by observations of the morphology during one or several successive HST orbits (movie available as supporting material in Nichols et al (2009); jgra19860-sup-0003-ms01.mp4).…”

Section: Morphological Featuresmentioning

confidence: 99%

See 3 more Smart Citations

Hubble observations of Jupiter’s north–south conjugate ultraviolet aurora

Gérard

Grodent

Radioti

et al. 2013

Icarus

Self Cite

View full text Add to dashboard Cite

a b s t r a c tComparisons of the northern and southern far ultraviolet (UV) auroral emissions of Jupiter from the Hubble Space Telescope (HST) or any other ultraviolet imager have mostly been made so far on a statistical basis or were not obtained with high sensitivity and resolution. Such observations are important to discriminate between different mechanisms responsible for the electron acceleration of the different components of the aurora such as the satellite footprints, the «main oval» or the polar emissions. The field of view of the ACS and STIS cameras on board HST is not wide enough to provide images of the full jovian disk. We thus compare the morphology of the north and south aurora observed 55 min apart and we point out similarities and differences. On one occasion HST pointed successively the two polar regions and auroral images were seen separated by only 3 min. This makes it possible to compare the emission structure and the emitted FUV power of corresponding regions. We find that most morphological features identified in one hemisphere have a conjugate counterpart in the other hemisphere. However, the power associated with conjugate regions of the main oval, diffuse or discrete equatoward emission observed quasi-simultaneously may be different in the two hemispheres. It is not directly nor inversely proportional to the strength of the B-field as one might expect for diffuse precipitation or field-aligned acceleration with equal ionospheric electron density in both hemispheres. Finally, the lack of symmetry of some polar emissions suggests that some of them could be located on open magnetic field lines.

show abstract

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

“…Such data were obtained at equinox by Nichols et al (2009). They showed that individual auroral features can exhibit distinct hemispheric asymmetries.…”

Section: Introductionmentioning

confidence: 95%

Section: Morphological Featuresmentioning

confidence: 99%

See 2 more Smart Citations

Hubble observations of Jupiter’s north–south conjugate ultraviolet aurora

Gérard

Grodent

Radioti

et al. 2013

Icarus

Self Cite

View full text Add to dashboard Cite

show abstract

“…That is, it is unlikely that each radio occultation observation at high latitudes occurred above an auroral event. Auroral morphologies at Saturn have been studied using HST (e.g., Clarke et al, 2005;Nichols et al, 2009 ), groundbased telescopes ( Stallard et al, 2008a ), and Cassini ( Stallard et al, 2008b;Melin et al, 2011 ). While considerable variations occur from the equatorward edge of the auroral oval to across the polar cap, there are no dramatic cases of equatorward excursions of auroral storms-as often seen on Earth.…”

Section: Sources Of Variability At High Latitudes: Models Of Changingmentioning

confidence: 99%

Comparative ionospheres: Terrestrial and giant planets

Mendillo

Trovato

Moore

et al. 2018

Icarus

View full text Add to dashboard Cite

a b s t r a c tThe study of planetary ionospheres within our solar system offers a variety of settings to probe mechanisms of photo-ionization, chemical loss, and plasma transport. Ionospheres are a minor component of upper atmospheres, and thus their mix of ions observed depends on the neutral gas composition of their parent atmospheres. The same solar irradiance (x-rays and extreme-ultra-violet vs. wavelength) impinges upon each of these atmospheres, with solar flux magnitudes changed only by the inverse square of distance from the Sun. If all planets had the same neutral atmosphere-with ionospheres governed by photochemical equilibrium (production = loss)-their peak electron densities would decrease as the inverse of distance from the Sun, and any changes in solar output would exhibit coherent effects throughout the solar system.Here we examine the outer planet with the most observations of its ionosphere (Saturn) and compare its patterns of electron density with those at Earth under the same-day solar conditions. We show that, while the average magnitudes of the major layers of molecular ions at Earth and Saturn are approximately in accord with distance effects, only minor correlations exist between solar effects and day-to-day electron densities. This is in marked contrast to the strong correlations found between the ionospheres of Earth and Mars. Moreover, the variability observed for Saturn's ionosphere (maximum electron density and total electron content) is much larger than found at Earth and Mars. With solar irradiance changes far too small to cause such effects, we use model results to explore the roles of other agents. We find that water sources from Enceladus at low latitudes, and 'ring rain' at middle latitudes, contribute substantially to variability via water ion chemistry. Thermospheric winds and electrodynamics generated at auroral latitudes are suggested causes of high latitude ionospheric variability, but remain inconclusive due to the lack of relevant observations.

show abstract

Long‐term modulations of Saturn's auroral radio emissions by the solar wind and seasonal variations controlled by the solar ultraviolet flux

et al. 2013

Self Cite

View full text Add to dashboard Cite

[1] Saturn's auroral activities have been suggested to be controlled by the seasonal variations of the polar ionospheric conductivities and atmospheric conditions associated with the solar extreme ultraviolet (EUV) flux. However, they have not yet been explained self-consistently by only the seasonal solar EUV effects. This study investigates the long-term variations of Saturnian Kilometric Radiation (SKR) as a proxy of the auroral activities, which were observed by Cassini's Radio and Plasma Wave Science experiment mostly during the southern summer (DOY (day of year) 001 2004001 to DOY 193 2010. We deduced the height distribution of the SKR source region in the Northern (winter) and Southern (summer) Hemispheres from the remote sensing of SKR spectra. The peak spectral density of the southern (summer) SKR was found to be up to 100 times greater than that of the northern (winter) SKR, and the altitude of the peak flux was similar ( 0.8 R s ) in the Northern and Southern Hemispheres. The spectral densities in both hemispheres became comparable with each other around equinox in August 2009. These results suggest a stronger SKR source region during the summer than the winter related to the seasonal EUV effect, which is opposite to the trend observed in the Earth's kilometric radiation. A long-term correlation analysis was performed for the SKR, solar EUV flux, and solar wind parameters extrapolated from Earth's orbit by an magnetohydrodynamical simulation focusing on variations on timescales longer than several weeks. We confirmed clear positive correlations between the solar wind dynamic pressure and peak flux density in both the Southern and Northern Hemispheres during the declining phase of the solar cycle. We conclude that the solar wind variations on the timescale of the solar cycle control the SKR source region. In addition, it was also confirmed that the south-to-north ratios of SKR power flux and source altitudes are positively correlated with the solar EUV flux. This result strongly supports a seasonal EUV effect on the SKR source region. The variations of SKR activity over both seasonal and solar cycles are discussed in comparison to the terrestrial case.Citation: Kimura, T., et al. (2013), Long-term modulations of Saturn's auroral radio emissions by the solar wind and seasonal variations controlled by the solar ultraviolet flux,

show abstract

Saturn's equinoctial auroras

Cited by 41 publications

References 22 publications

Hubble observations of Jupiter’s north–south conjugate ultraviolet aurora

Hubble observations of Jupiter’s north–south conjugate ultraviolet aurora

Comparative ionospheres: Terrestrial and giant planets

Long‐term modulations of Saturn's auroral radio emissions by the solar wind and seasonal variations controlled by the solar ultraviolet flux

Contact Info

Product

Resources

About