Guerlet_et_al-2018-Journal_of_Geophysical_Research%3A_Planets.pdf (2.79 MB)
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Equatorial Oscillation and Planetary Wave Activity in Saturn's Stratosphere Through the Cassini Epoch

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journal contribution
posted on 16.04.2018, 08:40 by S. Guerlet, T. Fouchet, A. Spiga, F. M. Flasar, Leigh N. Fletcher, B. E. Hesman, N. Gorius
Thermal infrared spectra acquired by Cassini/Composite InfraRed Spectrometer (CIRS) in limb‐viewing geometry in 2015 are used to derive 2‐D latitude‐pressure temperature and thermal wind maps. These maps are used to study the vertical structure and evolution of Saturn's equatorial oscillation (SEO), a dynamical phenomenon presenting similarities with the Earth's quasi‐biennal oscillation (QBO) and semi‐annual oscillation (SAO). We report that a new local wind maximum has appeared in 2015 in the upper stratosphere and derive the descent rates of other wind extrema through time. The phase of the oscillation observed in 2015, as compared to 2005 and 2010, remains consistent with a ∼15 year period. The SEO does not propagate downward at a regular rate but exhibits faster descent rate in the upper stratosphere, combined with a greater vertical wind shear, compared to the lower stratosphere. Within the framework of a QBO‐type oscillation, we estimate the absorbed wave momentum flux in the stratosphere to be on the order of ∼7 × 10−6 N m−2. On Earth, interactions between vertically propagating waves (both planetary and mesoscale) and the mean zonal flow drive the QBO and SAO. To broaden our knowledge on waves potentially driving Saturn's equatorial oscillation, we searched for thermal signatures of planetary waves in the tropical stratosphere using CIRS nadir spectra. Temperature anomalies of amplitude 1–4 K and zonal wave numbers 1 to 9 are frequently observed, and an equatorial Rossby (n = 1) wave of zonal wave number 3 is tentatively identified in November 2009.

History

Citation

Journal of Geophysical Research: Planets, 2018, 123 (1), pp. 246-261

Author affiliation

/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy

Version

VoR (Version of Record)

Published in

Journal of Geophysical Research: Planets

Publisher

American Geophysical Union

issn

2169-9097

eissn

2169-9100

Acceptance date

02/01/2018

Copyright date

2018

Available date

09/07/2018

Publisher version

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1002/2017JE005419

Notes

The file associated with this record is under embargo until 6 months after publication, in accordance with the publisher's self-archiving policy. The full text may be available through the publisher links provided above.

Language

en