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Field-Aligned Photoelectron Energy Peaks at High Altitude and on the Nightside of Titan

Cao, YT; Wellbrock, A; Coates, AJ; Caro-Carretero, R; Jones, GH; Cui, J; Galand, M; (2020) Field-Aligned Photoelectron Energy Peaks at High Altitude and on the Nightside of Titan. Journal of Geophysical Research: Planets , 125 (1) , Article e2019JE006252. 10.1029/2019JE006252. Green open access

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Abstract

The ionization of N2 by strong solar He II 30.4-nm photons produces distinctive spectral peaks near 24.1 eV in Titan's upper atmosphere, which have been observed by the Electron Spectrometer (ELS) as part of the Cassini Plasma Spectrometer. The ELS observations reveal that, in addition to the dayside, photoelectron peaks were also detected on the deep nightside where photoionization is switched off, as well as at sufficiently high altitudes where the ambient neutral density is low. These photoelectron peaks are unlikely to be produced locally but instead must be contributed by transport along the magnetic field lines from their dayside source regions. In this study, we present a statistical survey of all photoelectron peaks identified with an automatic finite impulse response algorithm based on the available ELS data accumulated during 56 Titan flybys. The spatial distribution of photoelectron peaks indicates that most photoelectrons detected at an altitude above 4,000 km and a solar zenith angle above 100° are field aligned, which is consistent with the scenario of photoelectron transport along the magnetic field lines. Our analysis also reveals the presence of a photoelectron gap in the deep nightside ionosphere where almost no photoelectrons were detected. It appears to be very difficult for photoelectrons to travel to this region, and such a feature may not be driven by the changes in the orientation between the solar and corotation wakes.

Type: Article
Title: Field-Aligned Photoelectron Energy Peaks at High Altitude and on the Nightside of Titan
Open access status: An open access version is available from UCL Discovery
DOI: 10.1029/2019JE006252
Publisher version: https://doi.org/10.1029/2019JE006252
Language: English
Additional information: This version is the author accepted manuscript. For information on re-use, please refer to the publisher’s terms and conditions.
Keywords: Titan, photoelectron, ionosphere
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics
URI: https://discovery.ucl.ac.uk/id/eprint/10091472
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