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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2007.05.016 Byline: Tom Stallard (a), Chris Smith (b), Steve Miller (b), Henrik Melin (c), Makenzie Lystrup (b), Alan Aylward (b), Nick Achilleos (b), Michele Dougherty (d) Keywords: Aurorae; Ionospheres; Infrared observations; Saturn; magnetosphere; Saturn; atmosphere Abstract: We present a detailed analysis of the H.sup.+.sub.3 intensity and velocity profiles crossing Saturn's auroral/polar region, as described by Stallard et al. [Stallard, T., Miller, S., Melin, H., Lystrup, M., Dougherty, M., Achilleos, N., 2007. Icarus 189, 1-13], with a view to understanding the magnetospheric processes with which they are connected. The data are not consistent with the theory that Saturn's main auroral oval is associated with corotation enforcement currents in the middle magnetosphere. This implies that the main auroral oval can be associated with the open-closed field line boundary [Cowley, S.W.H., Bunce, E.J., O'Rourke, J.M., 2004. J. Geophys. Res. 109. A05212]; a third model, by Sittler et al. [Sittler, E.C., Blanc, M.F., Richardson, J.D., 2006. J. Geophys. Res. 111. A06208] associates the main oval with centrifugal instabilities in the outer magnetosphere, but does not make predictions about ionospheric plasma flows with which we can compare our data. We do, however, tentatively identify emission at latitudes lower than the main auroral oval which may be associated with the corotation enforcement currents in the middle magnetosphere. We also find that at latitudes higher than the main auroral oval there is often a region of the ionosphere that is in rigid corotation with the planet. We suggest that this region corresponds to field lines embedded in the centre of the magnetotail which are shielded from the solar wind such that their rotation is controlled only by the neutral atmosphere. Author Affiliation: (a) Radio and Space Plasma Physics Group, Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK (b) Atmospheric Physics Laboratory, Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK (c) Space Environment Technologies, Planetary and Space Science Division, 320 N. Halstead St, Suite 170, Pasadena, CA 91107, USA (d) Space and Atmospheric Physics Group, Department of Physics, Imperial College of Science, Technology and Medicine, South Kensington Campus, London SW7 2AZ, UK Article History: Received 16 September 2006; Revised 17 May 2007

Byline: Robert J. Barber (a), Steve Miller (a), Tom Stallard (a), Jonathan Tennyson (a), Paul Hirst (b), Tim Carroll (b), Andy Adamson (b) Keywords: Comets; Infrared observations Abstract: We present results from the United Kingdom Infrared Telescope observations of the impact of Deep Impact with Comet 9P/Tempel 1, on July 4, 2005 UT. These observations were carried out in conjunction with the worldwide observing campaign co-ordinated by K.J. Meech [Meech, K.J., and 208 colleagues, 2005. Science 310, 265-269]. The UKIRT team was the first to observe and announce the successful impact. At 05:50:52 ([+ or -]2.5 s) UT the visible camera that is used to guide the telescope on the comet showed the start of a rapid rise in intensity, such that the visible brightness of Tempel 1 approximately doubled in 70 s. After that time there was a steady increase in the visible flux from the comet until it reached a maximum around 35 min post-impact, at which point it was more than ten times its original intensity. From an average of the time to maximum brightness and the time to noticeable intensity decline, we deduce that the material ejected by the impact expanded with a range of velocities between [approximately equal to]125 and [approximately equal to]390 m/s. We also observed water emission lines in the spectral region from 2.8945 to 2.8985 [mu]m. We noted several water lines, which are known to be pumped by sunlight. But there was a lower intensity spectral component, which we propose may result from solar heating of icy grains freshly exposed by the impact. Author Affiliation: (a) Department of Physics and Astronomy, University College London, London WC1E 6BT, UK (b) Joint Astronomy Centre, 660 N. A'ohoku Place, University Park, Hilo, HI 96720, USA Article History: Received 12 April 2006; Revised 31 July 2006

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2006.08.014 Byline: Henrik Melin (a), Steve Miller (a), Tom Stallard (a), L.M. Trafton (b), T.R. Geballe (c) Keywords: Aurorae; Ionospheres; Saturn; atmosphere Abstract: We present an analysis of observations of the auroral/polar regions of Saturn, carried out in 1999, 2004 and 2005, making use of the facility spectrometer, CGS4, on the United Kingdom Infrared Telescope (UKIRT), Mauna Kea, Hawaii. We obtain temperatures of 380([+ or -]70) K in 1999 and 420([+ or -]70) K in 2004. (The 2005 data has insufficient spectral resolution for a temperature determination to be made.) Our most probable interpretation is that the temperature of Saturn's auroral/polar H.sup.+.sub.3 layer should be taken as 400([+ or -]50) K. This is lower than the value obtained by Miller et al. [Miller, S., and 10 colleagues, 2000. Philos. Trans. R. Soc. 358, 2485-2502], which is shown to be in error. Our analysis reveals clearly that the line emission due to H.sup.+.sub.3 varies considerably, showing nearly an order of magnitude increase when one compares the data obtained in 1999 with those of 2004. Our conclusion is that this variability is (mainly) due to the changing H.sup.+.sub.3 column density. By analogy with modelling results obtained for Jupiter, we estimate that the particle (keV electron) precipitation experienced by Saturn must be [approximately equal to]20 times greater in 2004 than in 1999, to produce this additional ionisation. The H.sup.+.sub.3 emission increases, but this is insufficient to offset most of the heating due to the extra particle precipitation, indicating that this ion does not act as a 'thermostat' on Saturn, in the same way that it does on Jupiter. Author Affiliation: (a) Atmospheric Physics Laboratory, Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK (b) McDonald Observatory, University of Texas at Austin, Austin, TX 78712, USA (c) Gemini Observatory, 670 N. A'ohoku Place, Hilo, HI 96720, USA Article History: Received 2 March 2006; Revised 9 August 2006

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2005.11.004 Byline: Henrik Melin (a), Steve Miller (a), Tom Stallard (a), Chris Smith (a), Denis Grodent (b) Keywords: Aurorae; Ionospheres; Jupiter; atmosphere; Jupiter; infrared Abstract: We present an analysis of a series of observations of the auroral/polar regions of Jupiter, carried out between September 8 and 11, 1998, making use of the high-resolution spectrometer, CSHELL, on the NASA InfraRed Telescope Facility (IRTF), Mauna Kea, Hawaii; these observations spanned an 'auroral heating event.' This analysis combines the measured line intensities and ion velocities with a one-dimensional model vertical profile of the jovian thermosphere/ionosphere. We compute the model line intensities both assuming local thermodynamic equilibrium (LTE) and, relaxing this condition (non-LTE), through detailed balance calculations, in order to compare with the observations. Taking the model parameters derived, we calculate the changes in heating rate required to account for the modelled temperature profiles that are consistent with the measured line intensities. We compute the electron precipitation rates required to give the modelled ion densities that are consistent with the measured line intensities, and derive the corresponding Pedersen conductivities. We compute the changes in heating due to Joule heating and ion drag derived from the measured ion velocities, and modelled conductivities, making use of ion-neutral coupling coefficients derived from a 3-D global circulation model. Finally, we compute the cooling due to the downward conduction of heat and the radiation-to-space from the H.sub.3.sup.+ molecular ion and hydrocarbons. Comparison of the various heating and cooling terms enables us to investigate the balance of energy inputs into the auroral/polar atmosphere. Increases in Joule heating and ion drag are sufficient to explain the observed heating of the atmosphere; increased particle precipitation makes only a minor heating contribution. But local cooling effects -- predominantly radiation-to-space -- are shown to be too inefficient to allow the atmosphere to relax back to pre-event thermal conditions. Thus we conclude that this event provides observational, i.e. empirical, evidence that heat must be transported away from the auroral/polar regions by thermally or mechanically driven winds. Author Affiliation: (a) Atmospheric Physics Laboratory, Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK (b) Laboratoire de Physique Atmospherique et Planetaire, Institut d'Astrophysique et de Geophysique, Universite de Liege, Avenue de Cointe 5, B-4000 Liege, Belgium Article History: Received 13 June 2005; Revised 28 October 2005

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2005.04.016 Byline: Henrik Melin (a), Steve Miller (a), Tom Stallard (a), Denis Grodent (b) Keywords: Aurora; Ionospheres; Jupiter; atmosphere; Jupiter; infrared; Modelling Abstract: Calculations of column intensities are performed for a number of infrared transitions of the H.sub.3.sup.+ molecular ion, using a model atmosphere recently produced by Grodent et al. [2001. A self-consistent model of the jovian auroral thermal structure. J. Geophys. Res. 106, 12933-12952]. The line intensities integrated along the line of sight through the model atmosphere are first computed assuming that all of the emitting energy levels are in local thermodynamic equilibrium (LTE). These results are compared with those derived from a detailed balance calculation using a method recently proposed by Oka and Epp [2004. Non-thermal rotational distribution of H.sub.3.sup.+. Astrophys. J. In press]. It is shown that the population of excited vibrational levels starts to depart from that derived from LTE at altitudes higher than 500 km (above the jovian cloud tops). This effect has been noted previously by Kim et al. [1992. Densities and vibrational distribution of H.sub.3.sup.+ in the jovian auroral atmosphere. J. Geophys. Res. 97, 6093-6101]. By 2000 km, all of the excited vibrational levels are populated at less than 10% of the expected LTE value. This has important implications for the jovian upper atmosphere. In particular, the H.sub.3.sup.+ cooling effect will be greatly reduced high in the atmosphere. Modelled LTE line emission is greater than that derived from non-LTE modelling. Comparison of the non-LTE modelling with recent spectral measurements of the jovian auroral/polar regions in the L- and K-infrared windows shows that the Grodent et al. [2001. A self-consistent model of the jovian auroral thermal structure. J. Geophys. Res. 106, 12933-12952] profile overestimates the measured line intensity by [approximately equal to]3. Allowing for this, the non-LTE modelling shows that the column densities derived from (quasi-)LTE treatment of the measured line intensities may underestimate the real H.sub.3.sup.+ abundance by a factor of between 6 and 200. This means that attempts to derive important ionospheric properties, such as conductivity and related energy inputs due to magnetosphere-ionosphere coupling, from observed spectra will need to take this into account, if they are not to be seriously in error. Author Affiliation: (a) Atmospheric Physics Laboratory, Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK (b) Laboratoire de Physique Atmospherique et Planetaire, Institut d'Astrophysique et de Geophysique, Universite de Liege, Avenue de Cointe 5, B-4000 Liege, Belgium Article History: Received 22 November 2004; Revised 20 March 2005

Calculations of column intensities are performed for a number of infrared transitions of the [H.sup.+.sub.3] molecular ion, using a model atmosphere recently produced by Grodent et al. [2001. A self-consistent model of the jovian auroral thermal structure. J. Geophys. Res. 106, 12933-12952]. The line intensities integrated along the line of sight through the model atmosphere are first computed assuming that all of the emitting energy levels are in local thermodynamic equilibrium (LTE). These results are compared with those derived from a detailed balance calculation using a method recently proposed by Oka and Epp [2004. Non-thermal rotational distribution of [H.sup.+.sub.3]. Astrophys. J. In press]. It is shown that the population of excited vibrational levels starts to depart from that derived from LTE at altitudes higher than 500 km (above the jovian cloud tops). This effect has been noted previously by Kim et al. [1992. Densities and vibrational distribution of [H.sup.+.sub.3] in the jovian auroral atmosphere. J. Geophys. Res. 97, 6093-6101]. By 2000 km, all of the excited vibrational levels are populated at less than 10% of the expected LTE value. This has important implications for the jovian upper atmosphere. In particular, the [H.sup.+.sub.3] cooling effect will be greatly reduced high in the atmosphere. Modelled LTE line emission is greater than that derived from non-LTE modelling. Comparison of the non-LTE modelling with recent spectral measurements of the jovian auroral/polar regions in the L- and K-infrared windows shows that the Grodent et al. [2001. A self-consistent model of the jovian auroral thermal structure. J. Geophys. Res. 106, 12933-12952] profile overestimates the measured line intensity by ~3. Allowing for this, the non-LTE modelling shows that the column densities derived from (quasi-)LTE treatment of the measured line intensities may underestimate the real [H.sup.+.sub.3] abundance by a factor of between 6 and 200. This means that attempts to derive important ionospheric properties, such as conductivity and related energy inputs due to magnetosphere-ionosphere coupling, from observed spectra will need to take this into account, if they are not to be seriously in error. Keywords: Aurora; Ionospheres; Jupiter, atmosphere; Jupiter, infrared; Modelling

We use the fully coupled, three-dimensional, global circulation Jovian Ionospheric Model (JIM) to calculate the coupling between ions in the jovian auroral ovals and the co-existing neutral atmosphere. The model shows that ions subject to drift motion around the auroral oval, as a result of the E x B coupling between a meridional, equatorward electric field and the jovian magnetic field, generate neutral winds in the planetary frame of reference. Unconstrained by the magnetic field, these neutral winds have a greater latitudinal extent than the corresponding ion drifts. Values of the coupling coefficient, k (h), are presented as a function of altitude and cross-auroral electric field strength, for different incoming electron fluxes and energies. The results show that, with ion velocities of several hundred metres per second to over 1 kms -1, k(h) can attain values greater than 0.5 at the ion production peak. This parameter is key to calculating the effective conductivities required to model magnetosphere-ionosphere coupling correctly. The extent to which angular momentum (and therefore energy) is transported vertically in JIM is much more limited than earlier, one-dimensional, studies have predicted. Keywords: Aurora; Ionospheres; Jupiter, atmosphere; Jupiter, magnetosphere; Modelling

We present profiles of the line-of-sight (l.o.s.) ionospheric wind velocities in the southern auroral/polar region of Saturn. Our velocities are derived from the measurement of Doppler shifting of the [H+.sub.3] [v.sub.2]Q(1, 0-) line at 3.953 microns. The data for this study were obtained using the facility high-resolution spectrometer CSHELL on the NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii, during the night of February 6, 2003 (UT). The l.o.s, velocity profiles finally derived are consistent with an extended region of the upper atmosphere sub-corotating with the planet: the ion velocities in the inertial reference are only 1/3 of those expected for full planetary corotation. We discuss the results in the light of recent proposals for the kronian magnetosphere, and suggest that, in this region, Saturn's ion winds may he under solar wind control. Keywords: Atmospheres, dynamics; Aurorae; Infrared observations; Saturn, atmosphere; Saturn, magnetosphere

Recent work has been concerned with calculating the three-dimensional ion concentrations and Pedersen and Hall conductivities within the auroral region of Jupiter for varying conditions of incident electron precipitation. Using the jovian ionospheric model, we present results that show the auroral ionospheric response to changing the incoming flux of precipitating electrons (for constant initial energy) and also the response to changing the initial energy (for both constant flux and constant energy flux). The results show that, for expected energy fluxes of precipitating particles, the average auroral integrated Pedersen conductivity attains values in excess of 1 mho. In addition, it is shown that electrons with an initial energy of around 60 keV are particularly effective at generating auroral conductivity: Particles of this energy penetrate most effectively to the layer of the jovian ionosphere at which the auroral conductivity is at a maximum. Key Words: aurorae; ionospheres; Jupiter, atmosphere; Jupiter, magnetosphere; modelling.

We present the first reported measurements of the intensity of a 'hotband' transition for the [H.sup.+.sub.3] molecular ion in the northern auroral/polar region of Jupiter. This transition is identified as the R(3, [4.sup.+]) line of the (2[v.sub.2]2(l = 0) [vector] v2) hotband, with a wavelength of 3.94895/[micro]m. This is the first time such a transition has been measured outside the laboratory, and the wavelength as measured on Jupiter is within the experimental accuracy of the lab measurement. This detection makes it possible to investigate [H.sup.+.sub.3] transitions that simultaneously originate from different vibrational levels. We use the intensity ratio between this line and the Q(1, [0.sup.-]) fundamental transition to derive effective vibrational temperatures, column densities, and total emission parameters as a function of position across the auroral/polar region. Effective temperatures range from ~900 to ~1250 K; an increase in average temperature during our observing run of ~100 K is noted. The derived temperatures are toward the high end or in excess of the auroral temperature range that has been reported in the literature to date. The relationship among emission intensity, temperature, and density is shown to be complex. This may reflect the nonthermalization of the vibrational levels at the gas densities prevailing in the jovian thermosphere. An alternative analysis allowing for this effect is presented. But this approach requires thermospheric temperatures to be 41500 K at the level that the majority of [H.sup.+.sub.3] is being produced, higher than has previously been proposed. Key Words: aurorae; infrared observations; ionospheres; Jupiter, atmosphere; spectroscopy.

We present profiles of the line-of-sight ionospheric wind velocities in the northern auroral/polar region of Jupiter. Our velocities are derived from the measurement of Doppler shifting of the [H.sup.+.sub.3] [v.sub.2] Q(1,[0.sup.-]) line at 3.953 [micro]m. The data for this study were obtained using the facility high-resolution spectrometer CSHELL on the NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii, during the nights of September 7-11, 1998 (UT). A detailed analysis, allowing for several effects on the measured wavelength, is presented. The velocity profiles finally derived are consistent with an [H.sup.+.sub.3] electrojet of ~1.2 to 1.5 km [s.sup.-1] flowing clockwise (as viewed from above the north rotational pole)--i.e., counter to the rotation of the planet--around the main auroral oval, for the night of September 11, and with somewhat lower velocities for September 8 and 10. In addition, we note two main regions inside (poleward of) the main auroral oval, which we call the Dark Polar Region (DPR) and the Bright Polar Region (DPR). These features correspond to the yin-yang structure noted by T. Satoh and J. E. P. Connerney (1999, Icarus 141, 236-252). The DPR appears to be strongly redshifted, with poleward winds in the line of sight up to -2.5 km [s.sup.-1]. The BPR may have weakly blueshifted emission. The detection of the auroral electrojet continuously over our observing run confirms the initial electrojet detection of D. Rego, N. Achilleos, T. Stallard, S. Miller, R. Prange, M. Dougherty, and R. D. Joseph (1999, Nature 399, 121-124), as well the mechanism proposed by T. W. Hill (1979, J. Geophys. Res. 84, 6554-6558) to explain how Jupiter's equatorial magnetospheric plasmasheet is kept in corotation with the planet. We discuss the results in light of recent proposals and analyses of the jovian middle magnetosphere, and suggest that our DPR winds may be under solar wind control. Key Words: atmospheres, dynamics; aurorae; infrared observations; jupiter, atmosphere; jupiter, magnetosphere.