References of "Pryor, W. R"
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See detailDynamic auroral storms on Saturn as observed by the Hubble Space Telescope
Nichols, J. D.; Badman, S. V.; Baines, K. H. et al

in Geophysical Research Letters (2014), 41

We present observations of significant dynamics within two UV auroral storms observed on Saturn using the Hubble Space Telescope in April/May 2013. Specifically, we discuss bursts of auroral emission ... [more ▼]

We present observations of significant dynamics within two UV auroral storms observed on Saturn using the Hubble Space Telescope in April/May 2013. Specifically, we discuss bursts of auroral emission observed at the poleward boundary of a solar wind-induced auroral storm, propagating at ˜330% rigid corotation from near ˜01 h LT toward ˜08 h LT. We suggest that these are indicative of ongoing, bursty reconnection of lobe flux in the magnetotail, providing strong evidence that Saturn's auroral storms are caused by large-scale flux closure. We also discuss the later evolution of a similar storm and show that the emission maps to the trailing region of an energetic neutral atom enhancement. We thus identify the auroral form with the upward field-aligned continuity currents flowing into the associated partial ring current. [less ▲]

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See detailAuroral counterpart of magnetic field dipolarizations in Saturn's tail
Jackman, C. M.; Achilleos, N.; Bunce, E. J. et al

in American Geophysical Union, Fall Meeting 2011, abstract #SM14A-07 (2011, December 01)

Following magnetic reconnection in a planetary magnetotail, newly closed field lines can be rapidly accelerated back towards the planet, becoming "dipolarized" in the process. At Saturn, dipolarizations ... [more ▼]

Following magnetic reconnection in a planetary magnetotail, newly closed field lines can be rapidly accelerated back towards the planet, becoming "dipolarized" in the process. At Saturn, dipolarizations can be initially identified from the magnetometer data by looking for a southward turning of the magnetic field, indicating the transition from a radially stretched configuration to a more dipolar field topology. The highly stretched geometry of the kronian magnetotail lobes gives rise to a tail current which flows eastward (dusk to dawn) in the near equatorial plane across the centre of the tail. During reconnection and associated dipolarization of the field, the inner edge of this tail current can be diverted through the ionosphere, in a situation analogous to the substorm current wedge picture at Earth [McPherron et al. 1973]. We present a picture of the current circuit arising from this tail reconfiguration, and outline the equations which govern the field-current relationship. We show a number of examples of dipolarizations as identified in the Cassini magnetometer data and use this formalism to calculate limits for the ionospheric current density that would arise for these examples. In addition to the magnetometer data, we also present data from the Cassini VIMS and UVIS instruments which have observed small 'spots' of auroral emission lying near the main oval - features thought to be associated with dipolarizations in the tail. We compare the auroral intensities as predicted from our calculation with the observed spot sizes and intensities. [less ▲]

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See detailSaturn's aurora as viewed by Cassini VIMS
Melin, H.; Stallard, T.; Badman, S. V. et al

Conference (2011, December 01)

The stunning views of the kronian aurora captured by the Visual and Infrared Imaging Spectrograph (VIMS) onboard the Cassini spacecraft continues to provide crucial observations of the fervent interaction ... [more ▼]

The stunning views of the kronian aurora captured by the Visual and Infrared Imaging Spectrograph (VIMS) onboard the Cassini spacecraft continues to provide crucial observations of the fervent interaction between the upper atmosphere and the magnetosphere of Saturn. Here, we present recent findings of VIMS auroral research, which includes both statistical studies and case studies of auroral events and morphology. In addition to stand-alone observations, there is a small subset of VIMS observations during which UVIS was also acquiring data. These observations enable the comparison between observations of H, H2 in the ultraviolet and H3+ in the infrared that are both spatially overlapping and temporally simultaneous. Whilst emission tends to coincide for these three species on the main oval, there are significant differences both pole-ward and equator-ward, such that observations of H and H2 is generally a poor proxy for emissions of H3+. VIMS is sensitive to infrared thermal emission from the H3+ molecule, which is formed very efficiently via the ionisation of H2. Therefore, the morphology of H3+ emission becomes a tracer of energy injected into the upper atmosphere - the most striking of which is auroral particle precipitation. [less ▲]

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See detailSimultaneous Cassini VIMS and UVIS observations of Saturn's southern aurora: Comparing emissions from H, H2 and H3+ at a high spatial resolution
Melin, H.; Stallard, T.; Miller, S. et al

in Geophysical Research Letters (2011), 38

Here, for the first time, temporally coincident and spatially overlapping Cassini VIMS and UVIS observations of Saturn's southern aurora are presented. Ultraviolet auroral H and H[SUB]2[/SUB] emissions ... [more ▼]

Here, for the first time, temporally coincident and spatially overlapping Cassini VIMS and UVIS observations of Saturn's southern aurora are presented. Ultraviolet auroral H and H[SUB]2[/SUB] emissions from UVIS are compared to infrared H[SUB]3[/SUB][SUP]+[/SUP] emission from VIMS. The auroral emission is structured into three arcs - H, H[SUB]2[/SUB] and H[SUB]3[/SUB][SUP]+[/SUP] are morphologically identical in the bright main auroral oval (˜73°S), but there is an equatorward arc that is seen predominantly in H (˜70°S), and a poleward arc (˜74°S) that is seen mainly in H[SUB]2[/SUB] and H[SUB]3[/SUB][SUP]+[/SUP]. These observations indicate that, for the main auroral oval, UV emission is a good proxy for the infrared H[SUB]3[/SUB][SUP]+[/SUP] morphology (and vice versa), but for emission either poleward or equatorward this is no longer true. Hence, simultaneous UV/IR observations are crucial for completing the picture of how the atmosphere interacts with the magnetosphere. [less ▲]

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See detailSmall-scale structures in Saturn's ultraviolet aurora
Grodent, Denis ULg; Gustin, Jacques ULg; Gérard, Jean-Claude ULg et al

in Journal of Geophysical Research. Space Physics (2011), 116

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 ... [more ▼]

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. [less ▲]

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See detailSaturn's polar auroral emissions
Radioti, Aikaterini ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

Conference (2010, June 07)

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See detailSaturn's aurora seen by HST and UVIS
Grodent, Denis ULg; Radioti, Aikaterini ULg; Bonfond, Bertrand ULg et al

Conference (2010, June 07)

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See detailSaturn Auroral Movies from Cassini UVIS
Pryor, W. R.; Stewart, I.; Esposito, L. W. et al

in American Geophysical Union, Fall Meeting 2009 (2009, December 01)

Cassini's Ultraviolet Imaging Spectrograph (UVIS) continues to obtain Saturn auroral data. Two long slit spectral channels are used to obtain EUV data from 56.3-118.2 nm and FUV data from 111.5-191.3 nm ... [more ▼]

Cassini's Ultraviolet Imaging Spectrograph (UVIS) continues to obtain Saturn auroral data. Two long slit spectral channels are used to obtain EUV data from 56.3-118.2 nm and FUV data from 111.5-191.3 nm. 64 spatial pixels along each slit are combined with slit motion to construct spectral images of Saturn. Auroral emissions are seen from electron-excited molecular and atomic hydrogen. In 2007-2009 UVIS obtained data with the spacecraft well out of Saturn's ring plane, permitting UVIS to obtain a number of short movies of the rotating auroral structures. Selected movies will be presented with geometric overlays and in polar projections. In some movies a cusp-like feature is present near noon inside the oval. One movie from 2008 day 201 shows parallel linear features on the day side almost at right angles to the main auroral oval that appear, then lengthen, separate in the middle, and then fade away. Other movies show similar cusp-related structures that resemble the letter "Q" where a dynamical feature at right angles to the oval moves away from the cusp region. The 2008 day 201 movie also shows one bright "polar flare" inside the oval with a spectrally distinct signature indicating the presence of higher energy electrons. A few of the most recent images were obtained at sufficiently close range that 2 spacecraft slews were needed to completely cover the oval. These images provide almost 100 pixels of information across the oval and clearly show multiple arcs of emission on the main oval and scattered emissions inside the oval. Several frames show emissions associated with the footprint of the Enceladus field line. We will discuss these features, their locations, and possible interpretations. [less ▲]

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See detailRecurrent energization of plasma in the midnight-to-dawn quadrant of Saturn's magnetosphere, and its relationship to auroral UV and radio emissions
Mitchell, D. G.; Krimigis, S. M.; Paranicas, C. et al

in Planetary and Space Science (2009), 57

We demonstrate that under some magnetospheric conditions protons and oxygen ions are accelerated once per Saturn magnetosphere rotation, at a preferred local time between midnight and dawn. Although ... [more ▼]

We demonstrate that under some magnetospheric conditions protons and oxygen ions are accelerated once per Saturn magnetosphere rotation, at a preferred local time between midnight and dawn. Although enhancements in energetic neutral atom (ENA) emission may in general occur at any local time and at any time in a Saturn rotation, those enhancements that exhibit a recurrence at a period very close to Saturn's rotation period usually recur in the same magnetospheric location. We suggest that these events result from current sheet acceleration in the 15-20 Rs range, probably associated with reconnection and plasmoid formation in Saturn's magnetotail. Simultaneous auroral observations by the Hubble Space Telescope (HST) and the Cassini Ultraviolet Imaging Spectrometer (UVIS) suggest a close correlation between these dynamical magnetospheric events and dawn-side transient auroral brightenings. Likewise, many of the recurrent ENA enhancements coincide closely with bursts of Saturn kilometric radiation, again pointing to possible linkage with high latitude auroral processes. We argue that the rotating azimuthal asymmetry of the ring current pressure revealed in the ENA images creates an associated rotating field aligned current system linking to the ionosphere and driving the correlated auroral processes. [less ▲]

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See detailSaturn Auroral Images and Movies from Cassini UVIS
Pryor, W. R.; Grodent, Denis ULg; Gérard, Jean-Claude ULg

Conference (2009, July 27)

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See detailSaturn's equinoctial auroras
Nichols, J. D.; Badman, S. V.; Bunce, E. J. et al

in Geophysical Research Letters (2009), 36

We present the first images of Saturn's conjugate equinoctial auroras, obtained in early 2009 using the Hubble Space Telescope. We show that the radius of the northern auroral oval is similar to 1.5 ... [more ▼]

We present the first images of Saturn's conjugate equinoctial auroras, obtained in early 2009 using the Hubble Space Telescope. We show that the radius of the northern auroral oval is similar to 1.5 degrees smaller than the southern, indicating that Saturn's polar ionospheric magnetic field, measured for the first time in the ionosphere, is similar to 17% larger in the north than the south. Despite this, the total emitted UV power is on average similar to 17% larger in the north than the south, suggesting that field-aligned currents (FACs) are responsible for the emission. Finally, we show that individual auroral features can exhibit distinct hemispheric asymmetries. These observations will provide important context for Cassini observations as Saturn moves from southern to northern summer. Citation: Nichols, J. D., et al. (2009), Saturn's equinoctial auroras, Geophys. Res. Lett., 36, L24102, doi: 10.1029/2009GL041491. [less ▲]

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See detailAuroral Processes
Kurth, W. S.; Bunce, E. J.; Clarke, J. T. et al

in Dougherty, M. K.; Esposito, L. W.; Krimigis, S. M. (Eds.) Saturn from Cassini-Huygens (2009)

Cassini has afforded a number of unique opportunities to understand auroral processes at Saturn and to highlight both differences and similarities with auroral physics at both Earth and Jupiter. A number ... [more ▼]

Cassini has afforded a number of unique opportunities to understand auroral processes at Saturn and to highlight both differences and similarities with auroral physics at both Earth and Jupiter. A number of campaigns were coordinated with the Hubble Space Telescope such that Cassini could provide either ground truth on the impinging solar wind or in situ measurements of magnetospheric conditions leading to qualitative and sometimes quantitative relationships between the solar wind influence on the intensity, the morphology and evolution of the auroras, and magnetospheric dynamics. The Hubble UV images are enhanced by Cassini’s own remote sensing of the auroras. Cassini’s in situ studies of the structure and dynamics of the magnetosphere discussed in other chapters of this book provide the context for understanding the primary drivers of Saturn’s auroras and the role of magnetospheric dynamics in their variations. Finally, Cassini’s three dimensional prime mission survey of the magnetosphere culminates in high inclination orbits placing it at relatively small radial distances while on auroral field lines, providing the first such in situ observations of auroral particles and fields at a planet other than Earth. The new observations have spawned a number of efforts to model the interaction of the solar wind with the magnetosphere and how such dynamics influence the auroras. [less ▲]

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See detailSaturn Auroral Movies from Cassini UVIS
Pryor, W. R.; Stewart, I.; Esposito, L. et al

Conference (2008, December 01)

Cassini's Ultraviolet Imaging Spectrograph (UVIS) has completed four years of study of Saturn's atmosphere and auroras. Two long slit spectral channels are used to obtain EUV data from 56.3-118.2 nm and ... [more ▼]

Cassini's Ultraviolet Imaging Spectrograph (UVIS) has completed four years of study of Saturn's atmosphere and auroras. Two long slit spectral channels are used to obtain EUV data from 56.3-118.2 nm and FUV data from 111.5-191.3 nm. 64 spatial pixels along each slit are combined with slit motion to construct spectral images of Saturn. Auroral emissions are seen from electron-excited molecular and atomic hydrogen. In 2008 UVIS obtained data with the spacecraft well out of Saturn's ring plane, permitting UVIS to obtain a number of short movies of the rotating auroral structures. In some movies a cusp-like feature is present near noon inside the oval. One movie from 2008 day 201 shows parallel linear features on the day side almost at right angles to the main auroral oval that appear, then lengthen, separate in the middle, and then fade away. The same movie also shows one bright "polar flare" inside the oval. A few of the most recent images were obtained at sufficiently close range that 2 spacecraft slews were needed to completely cover the oval. These images provide almost 100 pixels of information across the oval and clearly show multiple arcs of emission on the main oval and scattered emissions inside the oval. We will discuss these features, their locations, and possible interpretations. [less ▲]

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See detailCoordinated measurements of auroral processes at Saturn from the Cassini spacecraft and HST
Mitchell, D. G.; Kurth, William; Hospodarsky, G. B. et al

Conference (2008, December 01)

One of the primary Cassini mission objectives at Saturn is to characterize Saturn's aurora-its spatial morphology, associated particle energization, radio wave generation, and magnetospheric currents ... [more ▼]

One of the primary Cassini mission objectives at Saturn is to characterize Saturn's aurora-its spatial morphology, associated particle energization, radio wave generation, and magnetospheric currents, relationship with solar wind pressure and magnetic field, and its large scale mapping to the magnetosphere. By design, the Cassini orbital tour included high inclination and low periapsis orbits late in the prime mission specifically to address many of these topics. In this presentation, we will provide a snapshot of the current state of our investigation into the relationship between magnetospheric measurements of particles and fields, and the aurora. For in situ data, we will show measurements of upward traveling light ion conics (~30 keV to 200 keV), often accompanied by electron beams (<20 keV to ~1 MeV) and enhanced broadband noise (10 Hz to a few kHz), throughout the outer magnetosphere on field lines that nominally map from well into the polar cap (dipole L > 50) to well into the closed field region (dipole L < 10). Sometimes the particle phenomena and the broadband noise occur in pulses of roughly five-minute duration, separated by tens of minutes. At other times they are relatively steady over an hour or more. Magnetic signatures associated with some of the pulsed events are consistent with field aligned current structures. Correlative observations of solar wind (Cassini) and aurora (HST) have established a strong relationship between solar wind pressure and auroral activity (brightness) (Crary et al., Nature, 2005; Clarke et al., JGR, 2008). A similar correspondence between bright auroral arcs and ring current ion acceleration will be shown here. So while some auroral forms seem to be associated with the open/closed field boundary (i.e. in the cusp-Bunce et al., JGR, 2008), we also demonstrate that under some magnetospheric conditions for which protons and oxygen ions are accelerated once per Saturn magnetosphere rotation at a preferred local time between midnight and dawn, simultaneous auroral observations by the HST reveal a close correlation between these dynamical magnetospheric events and dawn-side transient auroral brightenings. Likewise, many of the recurrent energetic neutral atom enhancements coincide closely with bursts of Saturn kilometric radiation, again suggesting a linkage with high latitude auroral processes. Finally, we will show some intriguing results of auroral movie sequences from the Cassini UVIS instrument with corresponding ring current movies from the Magnetospheric Imaging Instrument Ion and Neutral Camera (MIMI/INCA). [less ▲]

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See detailAuroral Movies and Spectroscopy from Cassini UVIS
Pryor, W. R.; West, R.; Stewart, I. et al

Conference (2007, December 01)

Cassini's Ultraviolet Imaging Spectrograph (UVIS) has completed three years of study of Saturn's atmosphere and auroras. Two long slit spectral channels are used to obtain EUV data from 56.3-118.2 nm and ... [more ▼]

Cassini's Ultraviolet Imaging Spectrograph (UVIS) has completed three years of study of Saturn's atmosphere and auroras. Two long slit spectral channels are used to obtain EUV data from 56.3-118.2 nm and FUV data from 111.5-191.3 nm. 64 spatial pixels along each slit are combined with slit motion to construct spectral images of Saturn. Auroral emissions are seen from electron-excited molecular and atomic hydrogen. In 2007 UVIS obtained data with the spacecraft well out of Saturn's ring plane, permitting us to create images, spectra, and at times movies. We will present an auroral movie from 2007-145 that has been processed to remove flat-fielding artifacts and deconvolved to remove scattering along the slit. The movie shows near co- rotation of N polar auroral features with the planet's rotation. An auroral oval is present. The oval appears doubled on the midnight side. Other images from this year show emissions inside the auroral oval. We will discuss these images and their spectra. Additional images and movies are planned in coming months. [less ▲]

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See detailSaturn's Auroras and Polar Atmosphere from Cassini UVIS
Pryor, W. R.; West, R.; Larsen, K. et al

Conference (2006, December 01)

Cassini's Ultraviolet Imaging Spectrograph (UVIS) has completed two years of study of Saturn's atmosphere and auroras. Two long slit spectral channels are used to obtain EUV data from 56.3-118.2 nm and ... [more ▼]

Cassini's Ultraviolet Imaging Spectrograph (UVIS) has completed two years of study of Saturn's atmosphere and auroras. Two long slit spectral channels are used to obtain EUV data from 56.3-118.2 nm and FUV data from 111.5-191.3 nm. 64 spatial pixels along each slit are combined with slit motion to construct spectral images of Saturn, with sufficient spatial resolution to image Saturn's auroral oval when Cassini leaves Saturn's equatorial plane. We will present new images and time-series data from summer 2006. Detailed spectral models of molecular hydrogen auroral emissions that include hydrocarbon absorption and hydrogen self- absorption have now been compared to UVIS data. We are analyzing a UV spectral feature detected in an auroral oval image from 2005. The feature is an absorption feature concentrated inside the oval, at wavelengths dominated by reflected sunlight and acetylene absorption. The absorption feature appears as a broad absorption "scoop". One plausible molecule that has a similar absorption feature is benzene, which has a cross-section some 500 times larger than acetylene in this spectral region. Thus UVIS is sensitive to small quantities of benzene. Enhanced polar benzene has been previously observed at Jupiter and can be generated in coupled photochemical/auroral models. We will explore the uniqueness of this interpretation, and compare the inferred benzene abundances to results from complementary Cassini CIRS infrared observations. Additional out of the equatorial plane UVIS Saturn data planned for the coming months will improve the signal- to-noise ratio and spatial resolution on the auroral ovals and their interior. Coordinated observations with Cassini VIMS and Hubble Space Telescope are being scheduled for 2007. [less ▲]

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See detailHST/ACS UV Imaging of Saturn's Southern Aurora in a Quiet State
Wannawichian, S.; Clarke, J. T.; Gérard, Jean-Claude ULg et al

Conference (2005, December 01)

Prior observations of Saturn's aurora have suggested that the aurora are highly variable, with much of the activity controlled by conditions in the solar wind. Observations of Saturn's UV aurora on 17 ... [more ▼]

Prior observations of Saturn's aurora have suggested that the aurora are highly variable, with much of the activity controlled by conditions in the solar wind. Observations of Saturn's UV aurora on 17 February 2005 were performed with the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope (HST) to further test this. The UV Solar Blind Camera (SBC) imaged the UV emissions from 115.0 to 170.0 nm for a period of 5 HST orbits, or 8 hours, corresponding to 74% of a Saturn rotation. In that observation period, HST imaged the southern auroral region in sunlight, but not the northern auroral region because of the tilt of Saturn rotation axis. Saturn's aurora appeared in its most quiet state, comparable or fainter than those observed by HST's Space Telescope Imaging Spectrograph (STIS) in January 2004. Discrete emissions were detected, with some evidence of latitudinal variations of localized emissions and motions. At the same time, Cassini's Ultraviolet Imaging Spectrograph (UVIS) studied the intensity and spectral distribution of Saturn's northern night side emission region. With the benefit of simultaneous observations, we found that the characteristics of Saturn's emission region in the day side southern aurora appeared correlated with Saturn kilometric radio (SKR) emissions, charged particles and magnetic field measurements in the night side Saturn magnetosphere. The faint UV aurora are consistent with the previously reported correlation between radio and UV emissions, and the low disturbance in Saturn's magnetosphere observed by Cassini. In this quiet state, the auroral oval brightness is a few kilorayleighs (KR). The summed images show evidence of an offset auroral oval toward midnight responding to solar wind pressure and more diffuse features in the dusk side. The specific properties of Saturn's aurora in its minimum state will be presented, and compared with more active periods. [less ▲]

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See detailObservations of Saturn's Atmosphere and Auroras by Cassini UVIS and VIMS
Pryor, W. R.; Baines, K.; West, R. et al

Conference (2005, December 01)

Cassini's Ultraviolet Imaging Spectrograph (UVIS) has completed a year of study of Saturn's atmosphere and auroras. Two long slit spectral channels are used to obtain EUV data from 56.3-118.2 nm and FUV ... [more ▼]

Cassini's Ultraviolet Imaging Spectrograph (UVIS) has completed a year of study of Saturn's atmosphere and auroras. Two long slit spectral channels are used to obtain EUV data from 56.3-118.2 nm and FUV data from 111.5-191.3 nm. 64 spatial pixels along each slit are combined with slit motion to build up spectral images of Saturn, with sufficient spatial resolution to reveal Saturn's auroral oval. Saturn images include evidence for rapid auroral variations and polar UV-dark regions mostly inside the auroral ovals. Absorption bands of acetylene are clearly seen in the reflected sunlight spectrum. The auroral emission spectrum is similar to that of Jupiter, showing H2 band emission and H Lyman-alpha emission. Saturn's auroral, dayglow, and nightglow spectra show significant differences. Saturn's aurora is observed to vary in brightness by at least a factor of four. The brightest auroral emissions seen so far occurred after 2004 day 207 19:30 when Cassini CAPS and MAG recorded passage of a solar wind shock. The enhanced auroral brightness persisted for days, and is seen at both poles of Saturn. Cassini RPWS observed enhanced auroral kilometric emissions during several auroral brightening events seen by UVIS. A campaign of Hubble Space Telescope UV imaging with ACS (Advanced Camera for Surveys) of Saturn's dayside southern auroral zone took place on 2005 February 17. Cassini UVIS and VIMS observed Saturn's nightside northern aurora during this period. The UVIS long slit was aligned with lines of latitude on Saturn, providing information about intensity and spectral variations along the auroral oval. Cassini VIMS has now obtained an initial image and spectrum of Saturn's H3}+ auroral emissions. [less ▲]

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See detailUltraviolet Spectroscopy of Saturn: Determination of Auroral characteristics with FUSE, STIS and UVIS Spectra
Gustin, Jacques ULg; Gérard, Jean-Claude ULg; Feldman, P. D. et al

Poster (2005, September 01)

Ultraviolet (UV) lines from Saturn's aurorae are emitted following inelastic collisions between energetic electrons and H[SUB]2[/SUB] molecules. De-excitation by radiative process lead to Far Ultraviolet ... [more ▼]

Ultraviolet (UV) lines from Saturn's aurorae are emitted following inelastic collisions between energetic electrons and H[SUB]2[/SUB] molecules. De-excitation by radiative process lead to Far Ultraviolet (FUV) and Extreme Ultraviolet (EUV) emissions in the 750-1750 Å spectral window. Low resolution spectra ( 12 Å) obtained with HST/STIS in the 900-1700 Å window are employed to derive the absorption of the auroral photons by hydrocarbons (mainly methane) and depth of the auroral energy deposition. Determination of H[SUB]2[/SUB] temperature and overlying H[SUB]2[/SUB] column is achieved by analyzing spectra obtained with the FUSE instrument ( 0.2 Å resolution with the LWRS aperture in the 900-1200 Å spectral window). Below 1100 Å, transitions connecting to the v" = 0 and 1 levels of ground-state H[SUB]2[/SUB] are partially or totally absorbed by ambient H[SUB]2[/SUB] (self-absorption). Comparisons between observed and synthetic spectra allow to derive the gaz temperature and the overlying H[SUB]2[/SUB] column, which is an indicator of the depth of the aurora, hence of the energy of the precipitated electrons. Auroral spectra of Saturn at 12 Å resolution were also obtained with Cassini's Ultraviolet Imaging Spectrograph (UVIS), both in the EUV and FUV spectral bands. While the spectral resolution of UVIS is too low to estimate temperatures, the coverage of the entire UV domain allows to determine the energy of precipitated particles through the quantification of the methane and molecular hydrogen columns. Results from observations with these three instruments are presented and compared in order to characterize the auroral atmosphere and auroral electrons precipitated from Saturn's magnetosphere. [less ▲]

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