Influence of local ionization on ionospheric densities in Titan's upper atmosphere

Luc B M Sagnières, Marina Galand, Jun Cui, Panayotis P. Lavvas, Erik Vigren, Véronique Vuitton, Roger Yelle, Anne Wellbrock, Andrew J. Coates

Research output: Contribution to journalArticle

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Abstract

Titan has the most chemically complex ionosphere of the solar system. The main sources of ions on the dayside are ionization by EUV solar radiation and on the nightside include ionization by precipitated electrons from Saturn's magnetosphere and transport of ions from the dayside, but many questions remain open. How well do models predict local ionization rates? How strongly do the ionization processes drive the ionospheric densities locally? To address these questions, we have carried out an analysis of ion densities from the Ion and Neutral Mass Spectrometer (INMS) from 16 close flybys of Titan's upper atmosphere. Using a simple chemical model applied to the INMS data set, we have calculated the ion production rates and local ionization frequencies associated with primary ions N2+ and CH4+. We find that on the dayside the solar energy deposition model overestimates the INMS-derived N2+ production rates by a factor of 2. On the nightside, however, the model driven by suprathermal electron intensities from the Cassini Plasma Spectrometer Electron Spectrometer sometimes agrees and other times underestimates the INMS-derived N2+ production rates by a factor of up to 2-3. We find that below 1200 km, all ion number densities correlate with the local ionization frequency, although the correlation is significantly stronger for short-lived ions than long-lived ions. Furthermore, we find that, for a given N<inf>2</inf> local ionization frequency, CH5+ has higher densities on the dayside than on the nightside. We explain that this is due to CH<inf>4</inf> being more efficiently ionized by solar photons than by magnetospheric electrons for a given amount of N<inf>2</inf> ionization. Key Points Overestimation of ionization rates of dayside compared with observations Short-lived ion densities are driven by local ionization Long-lived ion densities are influenced by chemical survival.

Original languageEnglish (US)
Pages (from-to)5899-5921
Number of pages23
JournalJournal of Geophysical Research: Space Physics
Volume120
Issue number7
DOIs
StatePublished - Jul 1 2015

Fingerprint

Upper atmosphere
Titan
upper atmosphere
ionospherics
Ionization
ionization
Ions
ion
ionization frequencies
ions
mass spectrometers
spectrometer
Mass spectrometers
electron
Electrons
ion production rates
spectrometers
electron flux density
Spectrometers
electrons

Keywords

  • Cassini
  • ionization processes
  • Titan
  • upper atmosphere

ASJC Scopus subject areas

  • Space and Planetary Science
  • Geophysics

Cite this

Sagnières, L. B. M., Galand, M., Cui, J., Lavvas, P. P., Vigren, E., Vuitton, V., ... Coates, A. J. (2015). Influence of local ionization on ionospheric densities in Titan's upper atmosphere. Journal of Geophysical Research: Space Physics, 120(7), 5899-5921. https://doi.org/10.1002/2014JA020890

Influence of local ionization on ionospheric densities in Titan's upper atmosphere. / Sagnières, Luc B M; Galand, Marina; Cui, Jun; Lavvas, Panayotis P.; Vigren, Erik; Vuitton, Véronique; Yelle, Roger; Wellbrock, Anne; Coates, Andrew J.

In: Journal of Geophysical Research: Space Physics, Vol. 120, No. 7, 01.07.2015, p. 5899-5921.

Research output: Contribution to journalArticle

Sagnières, LBM, Galand, M, Cui, J, Lavvas, PP, Vigren, E, Vuitton, V, Yelle, R, Wellbrock, A & Coates, AJ 2015, 'Influence of local ionization on ionospheric densities in Titan's upper atmosphere', Journal of Geophysical Research: Space Physics, vol. 120, no. 7, pp. 5899-5921. https://doi.org/10.1002/2014JA020890
Sagnières, Luc B M ; Galand, Marina ; Cui, Jun ; Lavvas, Panayotis P. ; Vigren, Erik ; Vuitton, Véronique ; Yelle, Roger ; Wellbrock, Anne ; Coates, Andrew J. / Influence of local ionization on ionospheric densities in Titan's upper atmosphere. In: Journal of Geophysical Research: Space Physics. 2015 ; Vol. 120, No. 7. pp. 5899-5921.
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