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Title: Saturn's Seasonally Changing Atmosphere: Thermal Structure, Composition and Aerosols
Authors: Fletcher, L. N.
Greathouse, T. K.
Moses, J. I.
Guerlet, S.
West, R. A.
First Published: Jun-2018
Publisher: Cambridge University Press (CUP)
Citation: Chapter in Saturn in the 21st Century, 2018
Abstract: The longevity of Cassini's exploration of Saturn's atmosphere (a third of a Saturnian year) means that we have been able to track the seasonal evolution of atmospheric temperatures, chemistry and cloud opacity over almost every season, from solstice to solstice and from perihelion to aphelion. Cassini has built upon the decades-long ground-based record to observe seasonal shifts in atmospheric temperature, finding a thermal response that lags behind the seasonal insolation with a lag time that increases with depth into the atmosphere, in agreement with radiative climate models. Seasonal hemispheric contrasts are perturbed at smaller scales by atmospheric circulation, such as belt/zone dynamics, the equatorial oscillations and the polar vortices. Temperature asymmetries are largest in the middle stratosphere and become insignificant near the radiative-convective boundary. Cassini has also measured southern-summertime asymmetries in atmospheric composition, including ammonia (the key species for the topmost clouds), phosphine and para-hydrogen (both disequilibrium species) in the upper troposphere; and hydrocarbons deriving from the UV photolysis of methane in the stratosphere (principally ethane and acetylene). These chemical asymmetries are now altering in subtle ways due to (i) the changing chemical efficiencies with temperature and insolation; and (ii) vertical motions associated with large-scale overturning in response to the seasonal temperature contrasts. Similarly, hemispheric contrasts in tropospheric aerosol opacity and coloration that were identified during the earliest phases of Cassini's exploration have now reversed, suggesting an intricate link between the clouds and the temperatures. [Abridged]
Embargo on file until: 1-Jan-10000
Version: Post-print
Status: Peer-reviewed
Type: Chapter
Rights: Copyright in the Chapter, L.N. Fletcher, T.K. Greathouse, S. Guerlet, J.I. Moses and R.A. West Copyright in the Volume, Cambridge University Press
Description: 34 pages, 20 figures, accepted for publication by Cambridge University Press as part of a multi-volume work edited by Kevin Baines, Michael Flasar, Norbert Krupp, and Thomas Stallard, entitled "Saturn in the 21st Century." The copy of the Chapter, as displayed on this website, is a draft, pre-publication copy only
The file associated with this record is under embargo until 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:Books & Book Chapters, Dept. of Physics and Astronomy

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