The brightness ratio of H Lyman- alpha /H sub(2) bands in FUV auroral emissions: A diagnosis for the energy of precipitating electrons and associated magnetospheric acceleration processes applied to Saturn

• Published in: Geophysical research letters Vol. 41; no. 19; pp. 6644 - 6651
• Main Authors: Tao, Chihiro, Lamy, Laurent, Prange, Renee
• Format: Journal Article
• Language: English
• Published: 01.10.2014
• Subjects: Acceleration; Bands; Brightness; Cassini mission; Electron density; Electron energy; Indicators; Magnetospheres
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1002/2014GL061329

We propose that the ratio of the auroral brightness of H Lyman- alpha to that of far ultraviolet H sub(2) and the absolute value of the H sub(2) brightness provide good indicators of the acceleration versus nonacceleration processes for field-aligned auroral electron precipitation in the Saturn magnetosphere-ionosphere coupled system. This finding is based on model results indicating that this ratio is a decreasing function of the auroral electron energy over the whole auroral energy range, as previously suggested by Cassini observations. For electron energies above 5keV, the results agree with the Knight relation, as in the environments of the Earth and Jupiter. On the other hand, decreasing electron flux with increasing electron energies below a few keV is also found and alternately explained as a nonacceleration reflecting the magnetospheric plasma distribution and/or wave-particle interactions. Key Points * H Lyman- alpha /H sub(2) brightness ratio is a good indicator for auroral electron energy * Electron flux-energy relation is obtained from observed Saturn FUV brightness * Acceleration and nonacceleration processes of auroral electrons are discussed