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|Title:||A hexagon in Saturn's northern stratosphere surrounding the emerging summertime polar vortex.|
|Authors:||Fletcher, L. N.|
Orton, G. S.
Sinclair, J. A.
Read, P. L.
Achterberg, R. K.
Flasar, F. M.
Irwin, P. G. J.
Bjoraker, G. L.
Hesman, B. E.
Calcutt, S. B.
|Publisher:||Nature Publishing Group|
|Citation:||Nature Communications, 2018, 9 (1), 3564|
|Abstract:||Saturn's polar stratosphere exhibits the seasonal growth and dissipation of broad, warm vortices poleward of ~75° latitude, which are strongest in the summer and absent in winter. The longevity of the exploration of the Saturn system by Cassini allows the use of infrared spectroscopy to trace the formation of the North Polar Stratospheric Vortex (NPSV), a region of enhanced temperatures and elevated hydrocarbon abundances at millibar pressures. We constrain the timescales of stratospheric vortex formation and dissipation in both hemispheres. Although the NPSV formed during late northern spring, by the end of Cassini's reconnaissance (shortly after northern summer solstice), it still did not display the contrasts in temperature and composition that were evident at the south pole during southern summer. The newly formed NPSV was bounded by a strengthening stratospheric thermal gradient near 78°N. The emergent boundary was hexagonal, suggesting that the Rossby wave responsible for Saturn's long-lived polar hexagon-which was previously expected to be trapped in the troposphere-can influence the stratospheric temperatures some 300 km above Saturn's clouds.|
|Rights:||Copyright © the authors, 2018. This is an open-access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.|
|Description:||All data can be obtained from the primary author (L.N.F., email: leigh.fletcher@leicester. ac.uk) upon request or can be accessed from the following GitHub repository doi:10.5281/zenodo.1286856, which contains the temporally and latitudinally averaged spectra used in this study. Raw and calibrated Cassini Composite Infrared Spectrometer observations are available from NASA’s Planetary Data System (PDS). The entire CIRS database was used in this study, but we provide unique data identifiers where data subsets were used in our figures. The NEMESIS spectral retrieval tool is available upon reasonable request from P.G.J.I. (firstname.lastname@example.org). The reconstructed temperature and hydrocarbon fields are also available at the DOI listed above.|
|Appears in Collections:||Published Articles, Dept. of Physics and Astronomy|
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