Small-scale structures in Saturn's ultraviolet aurora

Magnetospheric Physics: Field-aligned currents and current systems (2409); Magnetospheric Physics: Magnetosphere/ionosphere interactions (2431); Magnetospheric Physics: Planetary magnetospheres (5443; 5737; 6033); Planetary Sciences: Fluid Planets: Aurorae; Planetary Sciences: Solar System Objects: Saturn

Abstract :

[en] On 26 August 2008, the Ultraviolet Imaging Spectrograph Subsystem (UVIS) instrument onboard the Cassini spacecraft recorded a series of spatially resolved spectra of the northern auroral region of Saturn. Near periapsis, the spacecraft was only five Saturn radii (R[SUB]S[/SUB]) from the surface and spatially resolved auroral structures as small as 500 km across (0.5° of latitude). We report the observation of two types of UV auroral substructures at the location of the main ring of emission, bunches of spots and narrow arcs. They are found in the noon and dusk sectors, respectively, at latitudes ranging from 73 to 80° corresponding to equatorial regions located beyond 16 R[SUB]S[/SUB]. Their brightness ranges from 1 to 30 kR and their characteristic size varies from 500 km to several thousands of km. These small-scale substructures are likely associated with patterns of upward field aligned currents resulting from nonuniform plasma flow in the equatorial plane. It is suggested that magnetopause Kelvin-Helmholtz waves trigger localized perturbations in the flow, like vortices, able to give rise to the observed UV auroral substructures.

Disciplines :

Space science, astronomy & astrophysics

Author, co-author :

Grodent, Denis ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Labo de physique atmosphérique et planétaire (LPAP)

Gustin, Jacques ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Département d'astrophys., géophysique et océanographie (AGO)

Gérard, Jean-Claude ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Labo de physique atmosphérique et planétaire (LPAP)

Radioti, Aikaterini ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Labo de physique atmosphérique et planétaire (LPAP)

Bonfond, Bertrand ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Labo de physique atmosphérique et planétaire (LPAP)

Pryor, W. R.; Central Arizona College, (Coolidge, Arizona, USA) > Science Department

Language :

English

Title :

Small-scale structures in Saturn's ultraviolet aurora

Publication date :

2011

Journal title :

Journal of Geophysical Research. Space Physics

ISSN :

2169-9380

eISSN :

2169-9402

Publisher :

American Geophysical Union (AGU), Washington, United States - District of Columbia

Volume :

116

Pages :

09225

Peer reviewed :

Peer Reviewed verified by ORBi

Available on ORBi :

since 22 August 2011

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Bibliography

Bunce, E. J., et al. (2008a), Origin of Saturn's aurora: Simultaneous observations by Cassini and the Hubble Space Telescope, J. Geophys. Res., 113, A09209, doi:10.1029/2008JA013257.
Bunce, E. J., C. S. Arridge, S. W. H. Cowley, and M. K. Dougherty (2008b), Magnetic field structure of Saturn's dayside magnetosphere and its mapping to the ionosphere: Results from ring current modeling, J. Geophys. Res., 113, A02207, doi:10.1029/2007JA012538.
Bunce, E. J., et al. (2010), Extraordinary field-aligned current signatures in Saturn's high-altitude magnetosphere: Analysis of Cassini data during Revolution 89, J. Geophys. Res., 115,A10238, doi:10.1029/2010JA015612.
Clarke, J. T., et al. (2005), Morphological differences between Saturn's ultraviolet aurorae and those of Earth and Jupiter, Nature, 433, 717-719, doi:10.1038/nature03331. (Pubitemid 40292974)
Clarke, J. T., et al. (2009), The response of Jupiter's and Saturn's auroral activity to the solar wind, J. Geophys. Res., 114, A05210, doi:10.1029/ 2008JA013694.
Cowley, S. W. H., E. J. Bunce, and J. M. O'Rourke (2004), A simple quantitative model of plasma flows and currents in Saturn's polar ionosphere, J. Geophys. Res., 109, A05212, doi:10.1029/2003JA010375.
Delamere, P. A., R. J. Wilson, and A. Masters (2011), Kelvin-Helmholtz instability at Saturn's magnetopause: 2. Hybrid simulations, J. Geophys. Res., doi:10.1029/2011JA016724, in press.
Esposito, L. W., et al. (2004), The Cassini Ultraviolet Imaging Spectrograph Investigation, Space Sci. Rev., 115, 299-361, doi:10.1007/ s11214-004-1455-8.
Fukazawa, K., T. Ogino, and R. J. Walker (2007), Vortex-associated reconnection for northward IMF in the Kronian magnetosphere, Geophys. Res. Lett., 34, L23201, doi:10.1029/2007GL031784. (Pubitemid 351246980)
Galopeau, P. H. M., P. Zarka, and D. Le Quéau (1995), Source location of Saturn's kilometric radiation: The Kelvin-Helmholtz instability hypothesis, J. Geophys. Res., 100(E12), 26,397-26,410, doi:10.1029/95JE02132.
Gérard, J.-C., D. Grodent, J. Gustin, A. Saglam, J. T. Clarke, and J. T. Trauger (2004), Characteristics of Saturn's FUV aurora observed with the Space Telescope Imaging Spectrograph, J. Geophys. Res., 109, A09207, doi:10.1029/2004JA010513.
Gérard, J.-C., E. J. Bunce, D. Grodent, S. W. H. Cowley, J. T. Clarke, and S. V. Badman (2005), Signature of Saturn's auroral cusp: Simultaneous Hubble Space Telescope FUV observations and upstream solar wind monitoring, J. Geophys. Res., 110, A11201, doi:10.1029/2005JA011094. (Pubitemid 44971518)
Gérard, J.-C., et al. (2006), Saturn's auroral morphology and activity during quiet magnetospheric conditions, J. Geophys. Res., 111, A12210, doi:10.1029/2006JA011965.
Gérard, J.-C., B. Bonfond, J. Gustin, D. Grodent, J. T. Clarke, D. Bisikalo, and V. Shematovich (2009), Altitude of Saturn's aurora and its implications for the characteristic energy of precipitated electrons, Geophys. Res. Lett., 36, L02202, doi:10.1029/2008GL036554.
Grodent, D., J.-C. Gérard, S. W. H. Cowley, E. J. Bunce, and J. T. Clarke (2005), Variable morphology of Saturn's southern ultraviolet aurora, J. Geophys. Res., 110, A07215, doi:10.1029/2004JA010983. (Pubitemid 44116582)
Grodent, D., A. Radioti, B. Bonfond, and J.-C. Gérard (2010), On the origin of Saturn's outer auroral emission, J. Geophys. Res., 115, A08219, doi:10.1029/2009JA014901.
Gustin, J., J.-C. Gérard, W. Pryor, P. D. Feldman, D. Grodent, and G. Holsclaw (2009), Characteristics of Saturn's polar atmosphere and auroral electrons derived from HST/STIS, FUSE and Cassini/UVIS spectra, Icarus, 200, 176-187, doi:10.1016/j.icarus.2008.11.013.
Hess, S. L. G., P. A. Delamere, V. Dols, and L. C. Ray (2011), Comparative study of the power transferred from satellite-magnetosphere interactions to auroral emissions, J. Geophys. Res., 116, A01202, doi:10.1029/ 2010JA015807.
Masters, A., N. Achilleos, C. Bertucci, M. K. Dougherty, S. J. Kanani, C. S. Arridge, H. J. McAndrews, and A. J. Coates (2009), Surface waves on Saturn's dawn flank magnetopause driven by the Kelvin-Helmholtz instability, Planet. Space Sci., 57, 1769-1778, doi:10.1016/j.pss.2009. 02.010.
Masters, A., et al. (2010), Cassini observations of a Kelvin-Helmholtz vortex in Saturn's outer magnetosphere, J. Geophys. Res., 115, A07225, doi:10.1029/2010JA015351.
Nichols, J. D., J. T. Clarke, S. W. H. Cowley, J. Duval, A. J. Farmer, J.-C. Gérard, D. Grodent, and S. Wannawichian (2008), Oscillation of Saturn's southern auroral oval, J. Geophys. Res., 113, A11205, doi:10.1029/ 2008JA013444.
Nichols, J. D., et al. (2009), Saturn's equinoctial auroras, Geophys. Res. Lett., 36, L24102, doi:10.1029/2009GL041491.
Nichols, J. D., S. W. H. Cowley, and L. Lamy (2010), Dawn-dusk oscillation of Saturn's conjugate auroral ovals, Geophys. Res. Lett., 37, L24102, doi:10.1029/2010GL045818.
Pryor, W. R., et al. (2011), The auroral footprint of Enceladus on Saturn, Nature, 472, 331-333, doi:10.1038/nature09928.
Pu, Z. Y., and M. G. Kivelson (1983), Kelvin-Helmholtz instability at the magnetopause: Solution for compressible plasmas, J. Geophys. Res., 88(A2), 841-852, doi:10.1029/JA088iA02p00841.
Radioti, A., D. Grodent, J.-C. Gérard, E. Roussos, C. Paranicas, B. Bonfond, D. G. Mitchell, N. Krupp, S. Krimigis, and J. T. Clarke (2009), Transient auroral features at Saturn: Signatures of energetic particle injections in the magnetosphere, J. Geophys. Res., 114, A03210, doi:10.1029/ 2008JA013632.
Radioti, A., D. Grodent, J.-C. Gérard, S. E. Milan, B. Bonfond, J. Gustin, and W. Pryor (2011), Bifurcations of the main auroral ring at Saturn: Ionospheric signatures of consecutive reconnection events at the magnetopause, J. Geophys. Res., doi:10.1029/2011JA016661, in press.
Talboys, D. L., C. S. Arridge, E. J. Bunce, A. J. Coates, S. W. H. Cowley, and M. K. Dougherty (2009a), Characterization of auroral current systems in Saturn's magnetosphere: High-latitude Cassini observations, J. Geophys. Res., 114, A06220, doi:10.1029/2008JA013846.
Talboys, D. L., C. S. Arridge, E. J. Bunce, A. J. Coates, S. W. H. Cowley, M. K. Dougherty, and K. K. Khurana (2009b), Signatures of fieldaligned currents in Saturn's nightside magnetosphere, Geophys. Res. Lett., 36, L19107, doi:10.1029/2009GL039867.
Talboys, D. L., E. J. Bunce, S. W. H. Cowley, C. S. Arridge, A. J. Coates, and M. K. Dougherty (2011), Statistical characteristics of field-aligned currents in Saturn's nightside magnetosphere, J. Geophys. Res., 116, A04213, doi:10.1029/2010JA016102.
Vo, H. B., and J. S. Murphree (1995), A study of dayside auroral bright spots seen by the Viking auroral imager, J. Geophys. Res., 100(A3), 3649-3655, doi:10.1029/94JA03138.
Walker, R. J., K. Fukazawa, T. Ogino, and D. Morozoff (2011), A simulation study of Kelvin-elmholtz waves at Saturn's magnetopause, J. Geophys. Res., 116, A03203, doi:10.1029/2010JA015905.