[en] Observation of an exceptionally bright (peaking at similar to 1.8 MR) Jovian auroral morning arc was obtained with the Space Telescope Imaging Spectrograph (STIS) on 21 September 1999, both in the imaging and spectral modes. The images of the HST orbit are used to describe the variation of the position of the bright arc, while the time-tagged spectra are examined to derive the properties of the precipitating auroral electrons, such as their mean energy and the electron current density at the top of the atmosphere. The first and the last images of the HST orbit, separated by 37 min, show that the bright morning emission is situated on the reference oval, with a "leading" edge fixed in lambda(III) longitudes (i.e., rotating with the planet), and a "trailing" edge that extends into the nightside. The auroral arc is divided in two branches, as was also observed in some previous analyses. An isolated bright spot is also observed at lambda(III) similar to 184 degrees. Its brightness reaches 500 kR and it also approximately corotates with Jupiter. Four regions of the auroral morning arc captured by the STIS aperture were extracted from the spectral observation. The four associated low-resolution spectra (similar to 4.8 degrees) show very different characteristics. In particular, two spectra reveal unusually high color ratios (18.5 and 45.5), with corresponding mean electron energies of similar to 280 and similar to 460 keV, respectively. The current densities associated with three of the spectra lie in the range 0.09-0.2 mu A m(-2), consistent with previous estimates, while the fourth spectrum is characterized by a mean current density of 0.54 mu A m(-2), outside the range similar to 0.04-0.4 mu A m(-2) obtained in a previous study of G140L spectra of the Jovian main oval. Assuming that main oval aurorae are caused by field-aligned electric fields, the relationship between the energy flux and the current density derived from the spectra has been compared to the Knight's theory of field-aligned currents. Because of the very high acceleration potential derived from two of the extracted spectra, a relativistic treatment of the Knight theory was used. Assuming an electron temperature T-e = 2.5 keV, it is seen that the two regions corresponding to earlier local times (higher lambda(III) longitudes) reveal an electron source density lower than the values observed in the equatorial plane during the Voyager flybys. On the other hand, the equatorward region (lowest latitude) exhibits an electron source density in the upper range of usual values. Analysis of time-tag spectra reveals that the variations of the energy flux and the color ratios are large but continuous and generally covary.
Disciplines :
Earth sciences & physical geography
Author, co-author :
Gustin, Jacques ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Labo de physique atmosphérique et planétaire (LPAP)
Grodent, Denis ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Labo de physique atmosphérique et planétaire (LPAP)
Clarke, J. T.
Language :
English
Title :
Characteristics of Jovian morning bright FUV aurora from Hubble Space Telescope/Space Telescope Imaging Spectrograph imaging and spectral observations
Publication date :
28 September 2006
Journal title :
Journal of Geophysical Research. Space Physics
ISSN :
2169-9380
eISSN :
2169-9402
Publisher :
Amer Geophysical Union, Washington, United States - District of Columbia
Ballester, G. E., and the WFPC 2 Science Team (1996), Time-resolved observations of Jupiter's far-ultraviolet aurora, Science, 274, 409.
Broadfoot, A. L., et al. (1979), Extreme ultraviolet observations from Voyager 1 encounter with Jupiter, Science, 204, 979.
Clarke, J. T., and the WFPC 2 Science Team (1996), Far-UV imaging of Jupiter's aurora with HST/WFPC 2, Science, 274, 404.
Clarke, J. T., et al. (1998), Hubble Space Telescope imaging of Jupiter's UV aurora during the Galileo orbiter mission, J. Geophys. Res., 103, 20,217.
Clarke, J. T., et al. (2002), Ultraviolet Auroral Emissions from the magnetic footprints of Io, Ganymede, and Europa on Jupiter, Nature, 415, 997.
Connerney, J. E. P. (1992), Doing more with Jupiter's magnetic field, in Planetary Radio Emissions III, Austrian Acad. of Sci. Press, Vienna.
Connerney, J. E. P., M. H. Acuna, N. F. Ness, and T. Satoh (1998), New models of Jupiter's magnetic field constrained by the Io flux tube footprint, J. Geophys. Res., 103, 11,929.
Cowley, S. W. H. (2006), Current-voltage and kinetic energy flux relations for relativistic field-aligned acceleration of auroral electrons, Ann. Geophys., 24, 325-338.
Cowley, S. W. H., and E. J. Bunce (2001), Origin of the main auroral oval in Jupiter's coupled magnetosphere-ionosphere system, Planet. Space Sci., 49, 1067.
Cowley, S. W. H., I. I. Alexeev, E. S. Belenkaya, E. J. Bunce, C. E. Cottis, V. V. Kalegaev, J. D. Nichols, R. Prangé, and F. J. Wilson (2005), A simple axi-symmetric model of magnetosphere-ionosphere coupling currents in Jupiter's polar ionosphere, J. Geophys. Res., 110, A11209, doi:10.1029/2005JA011237.
Dols, V., J.-C. Gérard, J. T. Clarke, J. Gustin, and D. Grodent (2000), Diagnostics of the Jovian aurora deduced from ultraviolet spectroscopy: Model and GHRS observations, Icarus, 147, 251.
Gérard, J.-C., V. Dols, R. Prangé, and F. Paresce (1994), The morphology of the north Jovian ultraviolet aurora observed with the Hubble Space Telescope, Planet. Space Sci., 42, 905.
Gérard, J.-C., J. Gustin, D. Grodent, P. Delamere, and J. T. Clarke (2002), The excitation of the FUV Io tail on Jupiter: Characterization of the electron precipitation, J. Geophys. Res., 107(A11), 1394, doi:10.1029/ 2002JA009410.
Gérard, J.-C., J. Gustin, D. Grodent, and J. T. Clarke (2003), Spectral observations of transient features in the FUV Jovian polar aurora, J. Geophys. Res., 108(A8), 1319, doi:10.1029/2003JA009901.
Gladstone, G. R., M. Allen, and Y. L. Yung (1996), Hydrocarbon photochemistry in the upper atmosphere of Jupiter, Icarus, 119, 1.
Grodent, D., J. H. Waite Jr., and J.-C. Gérard (2001), A self-consistent model of the Jovian auroral thermal structure, J. Geophys. Res., 106, 12,933.
Grodent, D., J. T. Clarke, J. H. Waite, J. Kim, and S. W. H. Cowley (2003a), Jupiter's main auroral oval observed with HST-STIS, J. Geophys. Res., 108(A11), 1389, doi:10.1029/2003JA009921.
Grodent, D., J. T. Clarke, J. H. Waite, S. W. H. Cowley, J.-C. Gérard, and J. Kim (2003b), Jupiter's polar auroral emissions, J. Geophys. Res., 108(A10), 1366, doi:10.1029/2003JA010017.
Grodent, D., J.-C. Gérard, J. Gustin, B. H. Mauk, J. E. P. Connerney, and J. T. Clarke (2006), Europe's FUV auroral tail on Jupiter, Geophys. Res. Lett., 33, L06201, doi:10.1029/2005GL025487.
Gustin, J., D. Grodent, J.-C. Gérard, and J. T. Clarke (2002), Spatially resolved far ultraviolet spectroscopy of the Jovian aurora, Icarus, 157, 91.
Gustin, J., J.- C. Gérard, D. Grodent, S. W. H. Cowley, J. T. Clarke, and A. Grard (2004), Energy - flux relationship in the FUV Jovian aurora deduced from HST-STIS spectral observations, J. Geophys. Res., 109, A10205, doi:10.1029/2003JA010365.
Hill, T. W. (1979), Inertial limit on corotation, J. Geophys. Res., 84, 6554.
Hill, T. W. (1980), Corotation lag in Jupiter's magnetosphere: Comparison of observation and theory, Science, 207, 301.
Hill, T. W. (2001), The Jovian auroral oval, J. Geophys. Res., 106, 8101.
Knight, S. (1973), Parallel electric fields, Planet. Space Sci., 21, 741.
Lundin, R., and I. Sandahl (1978), Some characteristics of the parallel electric field acceleration of electrons over discrete auroral arcs as observed from two rocket flights, Eur. Space Agency Spec. Publ., ESA SP-135.
Nichols, J. D., and S. W. H. Cowley (2004), Magnetosphere-ionosphere coupling currents in Jupiter's middle magnetosphere: Effect of precipitation-induced enhancement of the ionospheric Pedersen conductivity, Ann. Geophys., 22, 1799.
Nichols, J. D., and S. W. H. Cowley (2005), Magnetosphere-ionosphere coupling currents in Jupiter's middle magnetosphere: Effect of magnetosphere-ionosphere decoupling by field-aligned auroral voltages, Ann. Geophys., 23, 799.
Prangé, R., D. Rego, L. Pallier, J. E. P. Connerney, P. Zarka, and J. Queinnec (1998), Detailed study of FUV Jovian features with the post-COSTAR HST faint object camera, J. Geophys. Res., 103, 20,195.
Scudder, J. D., E. C. Sittler Jr., and H. S. Bridge (1981), A survey of the plasma electron environment of Jupiter: A view from Voyager, J. Geophys. Res., 86, 8157.
Southwood, D. J., and M. G. Kivelson (2001), A new perspective concerning the influence of the solar wind on the Jovian magnetosphere, J. Geophys. Res., 106, 6123.
Waite, J. H., Jr., et al. (2001), An auroral flare at Jupiter, Nature, 410, 787.
Yung, Y. L., G. R. Gladstone, K. M. Chang, J. M. Ajello, and S. K. Srivastaya (1982), H2 fluorescence spectrum from 1200 to 1700 Å by electron impact: Laboratory study and application to jovian aurora, Astrophys. J., 254, L65.