A Comparison of FUV Auroral Emissions During the April 2002 Events as seen by the IMAGE/FUV and TIMED/GUVI Instruments

The auroral emissions that resulted from the series of solar particle events and magnetic storms during 14-24 April 2002 provide an excellent data set for the cross-comparison of the IMAGE/FUV and TIMED/GUVI auroral imagers. The IMAGE/FUV instrument comprises the SI spectral imager (121.8 nm and 135.6 nm) and the WIC imaging photometer (LBH) and observes the entire Earth from high Earth orbit. The TIMED/GUVI spectral imager (121.6 nm, 130.4 nm, 135.6 nm, LBH short, and LBH long) scans a nadir-to-limb swath from low Earth orbit. Although there is a large difference in spatial resolution, preliminary comparison of simultaneously-observed diffuse auroral emissions indicates fairly good agreement between the calibrated brightnesses determined for common spectral features. We will present a detailed simulation of one or more of the April 2002 events as seen by each imager to determine if a single description of the auroral precipitation can self-consistently account for the proton- and electron-generated FUV emissions observed from the two spacecraft

H[SUB]2[/SUB] temperature and self-absorption: analysis of Jovian auroral spectra obtained with the FUSE satellite

High-resolution spectra of the Jovian aurora have been obtained with unprecedented spectral resolution in the 900-1190 Ì· window with the the Far Ultraviolet Spectroscopic Explorer (FUSE), using the 30"x30" LWRS aperture. All observed features belong to the H[SUB]2[/SUB] transitions from the B, C, B', D, B" and D' electronic states to the ground-state. These emissions are excited by inelastic collisions of the primary and secondary auroral electrons with H[SUB]2[/SUB] molecules. The relative intensity distribution of the observed lines depends on the rotational temperature of the emitting layer and self-absorption. Below 1100 Ì· , the transitions leading to the v" = 0, 1 and 2 levels of ground-state are partially or totally absorbed by H[SUB]2[/SUB], giving indications about the vibrational H[SUB]2[/SUB] distribution and overlying column. After a validation with an unabsorbed and a self-absorbed laboratory spectrum obtained in controlled conditions (100K, 300 eV), this study compares the observations and synthetic spectra, generated by a code including the B, C and B', D, B" and D' Rydberg states. The rotational and vibrational H[SUB]2[/SUB] temperatures are determined as well as the overlying H[SUB]2[/SUB] column. The combination of these parameters is used to determine the depth of the auroral energy deposition. This work is based on data obtained for the Guaranteed Time Team by the NASA-CNES-CSA FUSE mission operated by the Johns Hopkins University. French participants are supported by CNES. Financial support to U.S. participants has been provided by NASA contract NAS5-32985

Jovian auroral spectroscopy with FUSE: analysis of self-absorption and implications for electron precipitation

High-resolution (similar to 0.22 Angstrom) spectra of the north jovian aurora were obtained in the 905-1180 Angstrom window with the Far Ultraviolet Spectroscopic Explorer (FUSE) on October 28, 2000. The FUSE instrument resolves the rotational structure of the H-2 spectra and the spectral range allows the study of self-absorption. Below 1100 Angstrom, transitions connecting to the upsilon" less than or equal to 2 levels of the H-2 ground state are partially or totally absorbed by the overlying H2 molecules. The FUSE spectra provide information on the overlying H2 column and on the vibrational distribution of H-2. Transitions from high-energy H-2 Rydberg states and treatment of self-absorption are considered in our synthetic spectral generator. We show comparisons between synthetic and observed spectra in the 920-970, 1030-1080, and 1090-1180 Angstrom spectral windows. In a first approach (single-layer model), the synthetic spectra are venerated in a thin emitting layer and the emerging photons are absorbed by a layer located above the source. It is found that the parameters of the single-layer model best fitting the three spectral windows are 850, 800, and 800 K respectively for the H-2 gas temperature and 1.3 x 10(18), 1.5 x 10(20), and 1.3 x 10(20) cm(-2) for the H-2 self-absorbing vertical column respectively. Comparison between the H-2 column and a 1-D atmospheric model indicates that the short-wavelength FUV auroral emission originates from just above the homopause. This is confirmed by the high H-2 rovibrational temperatures, close to those deduced from spectral analyses of H-3(+) auroral emission. In a second approach, the synthetic spectral generator is coupled with a vertically distributed 3 energy degradation model, where the only input is the energy distribution of incoming electrons (multi-layer model). The model that best fits globally the three FUSE spectra is a sum of Maxwellian functions, with characteristic energies ranging from 1 to 100 keV, giving rise to an emission peak located at 5 mubar, that is similar to 100 km below the methane homopause. This multi-layer model is also applied to a re-analysis of the Hopkins Ultraviolet Telescope (HUT) auroral spectrum and accounts for the H2 self-absorption as well as the methane absorption. It is found that no additional discrete soft electron precipitation is necessary to fit either the FUSE or the HUT observations. (C) 2004 Elsevier Inc. All rights reserved