Spectroscopic evidence for high-altitude Aurora at Jupiter from Galileo Extreme Ultraviolet Spectrometer and Hopkins Ultraviolet Telescope observations

The Galileo Extreme Ultraviolet Spectrometer (EUVS) and the Hopkins Ultravi olet Telescope (HUT) acquired UV spectra of Jupiter Aurora in the period fr om 1995 through 1997, The EUVS spectra spanned the wavelength range 540-128 0 Angstrom and the HUT spectra measured the extreme ultraviolet and far ult raviolet (EUV + FUV) wavelength range 830-1850 Angstrom. Both sets of spect ra present evidence of high-altitude, optically thin H-2 band emissions fro m the exobase region, The analysis of the UV spectra with a two-stream elec tron transport model and a jovian model auroral atmosphere indicates that t he primary electron flux is composed of both soft and hard electrons with c haracteristic energies in the soft electron energy range of 20-200 eV and t he hard electron range of 5-100 keV, The soft electron flux causes enhanced EUV emission intensities below 1100 Angstrom. The soft electron flux may e xplain the high temperature of the upper atmosphere above the homopause as measured from Il: rovibrational temperatures in the IR. For the deep aurora , a high primary characteristic energy above 5 keV is known to be present. The Galileo Energetic Particle Detector (EPD) has measured the electron dis tribution functions for energies above 15 keV in the middle magnetosphere. The high-energy distribution functions can be modeled by a combination of M axwellian and kappa distributions. However, the EUV (800-1200 Angstrom) por tion of the HUT spectrum cannot be modeled with a single distribution of ha rd electrons as was possible in the past for the FUV (1200-1650 Angstrom) s pectrum measured by itself, The combination of EUV and FUV spectral observa tions by HUT serves to identify the amount of soft electron flux relative t o the hard primary flux required to produce the high-altitude aurora in the neighborhood of the exobase, (C) tool academic Press.