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Title: Equatorial Oscillation and Planetary Wave Activity in Saturn's Stratosphere Through the Cassini Epoch
Authors: Guerlet, S.
Fouchet, T.
Spiga, A.
Flasar, F. M.
Fletcher, Leigh N.
Hesman, B. E.
Gorius, N.
First Published: 9-Jan-2018
Publisher: American Geophysical Union
Citation: Journal of Geophysical Research: Planets, 2018, 123 (1), pp. 246-261
Abstract: 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.
DOI Link: 10.1002/2017JE005419
ISSN: 2169-9097
eISSN: 2169-9100
Version: Publisher Version
Status: Peer-reviewed
Type: Journal Article
Rights: Copyright © 2018, American Geophysical Union. Deposited with reference to the publisher’s open access archiving policy. (
Description: 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.
Appears in Collections:Published Articles, Dept. of Physics and Astronomy

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