Multispectral observations of Jupiter's Aurora

in Advances in Space Research (2000), 26(10), 1453-1475

Remote sensing of Jupiter's aurora from x-ray to radio wavelengths has revealed much about the nature of the jovian aurora and about the impact of ionosphere-magnetosphere coupling on the upper atmosphere ... [more ▼]

Remote sensing of Jupiter's aurora from x-ray to radio wavelengths has revealed much about the nature of the jovian aurora and about the impact of ionosphere-magnetosphere coupling on the upper atmosphere of Jupiter, As indicated by the combination of x-ray and ultraviolet observations, both energetic heavy ions and electrons energized in the outer magnetosphere contribute to auroral excitation. Imaging with the Hubble Space Telescope in the ultraviolet and with the InfraRed Telescope Facility at infrared wavelengths shows several distinct regions of interaction: 1) a dusk sector where turbulent auroral patterns extend well into the polar cap; 2) a morning sector generally characterized by a single spatially confined auroral are originating in the outer or middle magnetosphere of Jupiter; 3) diffuse emissions associated with the Io plasma - spectroscopy has provided important information about the thermal structure of Jupiter's auroral atmosphere and the altitude distribution of auroral particle energy deposition, while Lyman alpha line profiles yield clues to the nature of thermospheric dynamical effects. Galileo observations at visible wavelengths on the nightside offer a new view of the jovian aurora with unprecedented spatial information. Infrared observations have added much to the understanding of thermal structure at all latitudes, the dynamics of the thermospheric wind system, and auroral morphology, and may hold the key to understanding the role of Joule heating in Jupiter's thermosphere. ROSAT observations have revealed soft x-ray emissions from Jupiter's lower latitudes as well as from the auroral zones, implying that energetic particle precipitation also occurs at low latitudes in regions magnetically linked to the inner radiation belts. In this review, multispectral observations of jovian auroral emissions are presented within a theoretical/modeling framework that is intended to provide some insight into magnetosphere-ionosphere coupling and its effects on the upper atmosphere. (C) 2000 COSPAR. Published by Elsevier Science Ltd. All rights reserved. [less ▲]

Séminaire de thèse

Scientific conference (1999, October 29)

HST/GHRS ultraviolet spectroscopy and model diagnostics of the Jovian aurora

Poster (1999, October 10)

Far ultraviolet Observations of Jovian low latitude regions with HST/STIS

in Bulletin of the American Astronomical Society (1999, September 01), 30(11),

Far ultraviolet observations of the Jovian disk were made at low and mid-latitudes with FUV MAMA/STIS on board HST in January 1999 both in the imaging and spectroscopic modes. An image was obtained with ... [more ▼]

Far ultraviolet observations of the Jovian disk were made at low and mid-latitudes with FUV MAMA/STIS on board HST in January 1999 both in the imaging and spectroscopic modes. An image was obtained with the Lyalpha filter in the hydrogen bulge region for comparison with the expected Lyman-alpha brightness distribution for Ly-alpha resonance scattering. Other images in the 1200-1700 { Angstroms} region show band structures parallel to the equator with fading contrast toward the center and the limb. Spectroscopic observations were made in the 1200-1700 { Angstroms} (G140L) and 1245-1298 { Angstroms} (G140M) regions at ~ 5 { Angstroms} resolution to map the H_2 airglow and the UV absorbents along the STIS slit. Preliminary results indicate that a C_2H_2 absorption signature is clearly observed in the solar ultraviolet reflected spectrum. The ethylene absorption may be mapped to derive variations of the acetylene abundance. The H_2 FUV airglow shows both the fluorescence and the electron impact components. Its spatial variation is described and compared with the expected airglow distribution. We acknowledge funding by NASA and by the PRODEX program of the European space agency. [less ▲]

HST/GHRS ultraviolet spectroscopy and model diagnostics of the Jovian aurora.

in Bulletin of the American Astronomical Society (1999)

A model coupling a detailed synthetic spectrum of the H_2 Lyman and Werner band systems with an electron energy degradation code is applied to the analysis of 7 GHRS spectra of the 1200-1700 { Angstroms ... [more ▼]

A model coupling a detailed synthetic spectrum of the H_2 Lyman and Werner band systems with an electron energy degradation code is applied to the analysis of 7 GHRS spectra of the 1200-1700 { Angstroms} region obtained with a ~ 5 { Angstroms} resolution at various locations in the north and south Jovian aurora. The observed color ratios indicate that the characteristic energy of the assumed initial Maxwellian distribution ranges between 17 and 40 keV. A clear signature of acetylene is observed near the absorption peaks at 1520, 1480 and 1440 { Angstroms}. The C_2H_2 column overlying the emission peak varies from 0.02 to 0.2 of the methane column. A better fit is obtained for some spectra when ethane absorption is added. The changing mixing ratios relative to methane are attributed to perturbations by heat released by the fast electron thermalization and/or perturbations to the hydrocarbon chemistry resulting from the production of H atoms by the aurora. A spectrum of the Io magnetic footprint and its trailing tail shows ultraviolet color and hydrocarbon absorption charateristics quite similar to some of the main oval spectra. This observation implies that the electrons of the Io flux tube are energized to a few tens of keV, similar to the electron precipitated in the main ovals and polar caps. Echelle spectra between 1216 and 1220 { Angstroms} at 0.07 { Angstroms} resolution are also compared with the model best fitting the closely spaced in time mid-resolution spectrum. It is found that the effective H_2 rovibrational temperature associated with the Echelle spectra is significantly higher than predicted by the model. A steep temperature gradient near the methane homopause due to large heating by auroral precipitation is a plausible explanation for this difference. We acknowledge funding by NASA and the PRODEX program of the European Space Agency. [less ▲]

Observation of short and long timescale variability of the jovian UV aurora

in Bulletin of the American Astronomical Society (1998, September 01)

Three sets of Hubble Space Telescope far-ultraviolet images of Jupiter's North pole aurora have been obtained with the Wide Field and Planetary Camera 2 in June 1996, May 1997 and August 1997. The ... [more ▼]

Three sets of Hubble Space Telescope far-ultraviolet images of Jupiter's North pole aurora have been obtained with the Wide Field and Planetary Camera 2 in June 1996, May 1997 and August 1997. The exposure time was limited to 160 seconds in order to reveal short timescale auroral features that are normally averaged during longer exposures and blurred by the rapid jovian rotation. The 3 sets of images show the aurora in a comparable (quiet) activity level, exhibiting long term persistent features such as : (i) a stable thin morning arc, (ii) a morning-afternoon emission dichotomy, (iii) a minimum of low latitude emission around CML=175 deg, (iv) bright localized afternoon structures. The equatorward boundary of the arc closely follows but is not coincident with the footprint of the 20 RJ magnetic field line given by the VIP4 model. These stable structures contrast with rapidly changing features like small size spots blasting in one single image, bright regions connecting trans-auroral structures, and the inner diffuse emission. The question of temporal variability and spatial extent of the auroral features is of major importance in understanding the origin and acceleration mechanisms of the auroral particles exciting the jovian UV aurora. In particular, short timescale processes can be related to field aligned currents generating acceleration structures and discrete aurora. [less ▲]

The longitudinal variation of the color ratio of the Jovian ultraviolet aurora: a geometric effect?

in Geophysical Research Letters (1998), 25(10), 1601-1604

A three-dimensional model is used to assess the role of the viewing geometry on the auroral color ratio. The simulations show that both an auroral are with a geometry deduced from images obtained with the ... [more ▼]

A three-dimensional model is used to assess the role of the viewing geometry on the auroral color ratio. The simulations show that both an auroral are with a geometry deduced from images obtained with the Hubble Space Telescope (HST) and a uniform polar cap emission produce no modulation or a minimum absorption when the longitude of the Jovian central meridian (CML) is close to 200 degrees. This result is in contrast with the statistical measurements made with the International Ultraviolet Explorer (IUE) spectrograph that the hydrocarbon optical depth above the auroral emission maximizes for CMLs about 180 degrees. In the frame of this simplified model, we examine a possible way to reconcile the model with the IUE data. An intrinsic longitudinal dependence of the column of methane above the level of the auroral emission is introduced in the simulation. It may result from a combination of a vigorous upwelling in sectors of strong acid stable precipitation and/or a longitudinal dependence of the characteristic energy of the auroral particles. [less ▲]

Simulation of the morphology of the Jovian UV north aurora observed with the Hubble Space Telescope

in Icarus: International Journal of Solar System Studies (1997), 128(2), 306-321

A model simulating Earth views of UV auroral arcs and diffuse emissions in the Jovian north polar region is described. It assumes a Chapman profile of vertical brightness distribution and various ... [more ▼]

A model simulating Earth views of UV auroral arcs and diffuse emissions in the Jovian north polar region is described. It assumes a Chapman profile of vertical brightness distribution and various horizontal structures, Simple geometric cases are described to illustrate the dependence on the altitude, atmospheric scale height, and central meridian planetary longitude (CML) of an idealized amoral morphology seen from Earth orbit, The numerical simulation makes it possible to assess the importance of limb brightening and the contribution from high altitude auroral emission located behind the planetary limb. As an application of the simulation model, four images obtained with the Wide Field and Planetary Camera 2 (WFPC2) on board the Hubble Space Telescope are used to determine the characteristics of their auroral (discrete and diffuse) structures, The apparent brightness distribution along the arcs can only be reproduced if intrinsic longitudinal (or local time) variations are introduced, in addition to the path length effects of the viewing geometry, A composite average auroral distribution is built by mapping 10 WFPC2 images from the same dataset, It illustrates the dichotomy frequently observed between a narrow single structure are at System III longitudes larger than 180 degrees (or morning sector) and the multiple are and broad diffuse emission at longitudes less than 180 degrees (or afternoon sector), It is shown that the equatorial auroral emission boundary is located between the 6R(J) and the 30R(J) magnetic field line footprints of the Goddard Space Flight Center (GSFC) O-6 model. (C) 1997 Academic Press. [less ▲]

The equatorial boundary of the ultraviolet Jovian north aurora observed with multispectral Hubble Space Telescope images

in Journal of Geophysical Research (1996), 101(E1), 2163-2168

Multispectral observations of the far ultraviolet Jovian aurora with the faint object camera (FOC) on board the Hubble Space Telescope are reported. They are used to describe and compare the morphology ... [more ▼]

Multispectral observations of the far ultraviolet Jovian aurora with the faint object camera (FOC) on board the Hubble Space Telescope are reported. They are used to describe and compare the morphology and the mean brightness of the H-2 Lyman and Werner bands observed at 153, 125, and 130 nm. It is shown that most of the emissions are confined inside the 6 R(J) O-6-GSFC auroral oval and fill a large fraction of the polar cap. During the similar to 50 hours time span of the observations following a very strong aurora, no bright are was observed along the oval mapping the 30 R(J) O-6 oval. Hydrogen emissions at 125 and 130 nm are observed down to 50 degrees N and somewhat below, a region not accessible to previous FOC observations at longer wavelengths. Temporal variations are also observed on timescales of hours to days. [less ▲]

La comète qui rencontra Jupiter

Conference given outside the academic context (1995)