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The excitation of the far ultraviolet electroglow emissions on Uranus, Saturn, and Jupiter

Clarke, John T. and Hudson, Mary K. and Yung, Yuk L. (1987) The excitation of the far ultraviolet electroglow emissions on Uranus, Saturn, and Jupiter. Journal of Geophysical Research A, 92 (A13). pp. 15139-15147. ISSN 0148-0227. https://resolver.caltech.edu/CaltechAUTHORS:20140923-142045443

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Abstract

We propose that the diffuse FUV emissions of H and H_2 in excess of photoelectron excitation observed from the sunlit atmospheres of Uranus, Saturn, and Jupiter are produced by electric field acceleration of photoelectrons and ions locally in the upper atmospheres. This in situ acceleration is required to satisfy the many observational constraints on the altitude distribution, exciting particle energy, and total input energy requirements of the electroglow mechanism. We further suggest that a primary mechanism leading to this acceleration is an ionospheric dynamo, which is created in the same manner as the Earth's dynamo. The calculated altitude of charge separation by the neutral wind drag on ions across magnetic field lines is consistent with the observed peaks in electroglow emissions from the Voyager ultraviolet spectrometer limb scan data on both Saturn (near the homopause) and Uranus (just above the homopause). This dynamo action therefore appears to initiate the acceleration process, which must have the form of field-aligned potentials to accelerate the magnetized electrons. We propose that these field-aligned potentials are due to anomalous resistivity, which results from sufficiently high field-aligned currents in the ionosphere to generate plasma instabilities and therefore runaway electrons and ions above some critical lower initial energy. There are multiple candidate processes for inducing these currents, including polarization in the equivalent F regions and inner magnetospheric convection, and each of these processes should exhibit latitudinal structure. The acceleration of low-energy electrons in an H_2 atmosphere preferentially results in FUV radiation and further ionization, whereas electron acceleration in a nitrogen/oxygen atmosphere such as the Earth' is dominated by elastic scattering and thus results in electric currents. Individual electron and proton collisions with H_2 molecules will result in excitation, ionization, and heating, so that considerable enhancement of the ionospheric density and heating of the upper atmosphere will accompany the FUV emission.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://onlinelibrary.wiley.com/doi/10.1029/JA092iA13p15139/abstractPublisherArticle
http://dx.doi.org/10.1029/JA092iA13p15139DOIArticle
ORCID:
AuthorORCID
Yung, Yuk L.0000-0002-4263-2562
Additional Information:© 1987 by the American Geophysical Union. Received March 25, 1987; revised October 5, 1987; accepted October 9, 1987. Paper number 7A9027. We wish to acknowledge helpful discussions with A. Dessler, W.-H. Ip, H. Mayr, J. Moses, D. Shemansky, H. Waite, J. Warren, and R. Yelle. M.K.H. acknowledges support from NASA grant NAGW-809 to Dartmouth College, and Y.L.Y. acknowledges support from NASA grant NSG 7376 to the California Institute of Technology. The Editor thanks R. V. Yelle and another referee for their assistance in evaluating this paper.
Funders:
Funding AgencyGrant Number
NASANAGW-809
NASANSG 7376
Issue or Number:A13
Record Number:CaltechAUTHORS:20140923-142045443
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20140923-142045443
Official Citation:Clarke, J. T., M. K. Hudson, and Y. L. Yung (1987), The excitation of the far ultraviolet electroglow emissions on Uranus, Saturn, and Jupiter, J. Geophys. Res., 92(A13), 15139–15147, doi:10.1029/JA092iA13p15139.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:49953
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:23 Sep 2014 21:34
Last Modified:09 Mar 2020 13:19

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