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Spirals on the sea

Munk, Walter and Armi, Laurence and Fischer, Kenneth and Zachariasen, F. (2000) Spirals on the sea. Proceedings of the Royal Society A: Mathematical, physical, and engineering sciences, 456 (1997). pp. 1217-1280. ISSN 1364-5021. doi:10.1098/rspa.2000.0560.

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Spiral eddies were first seen in the sunglitter on the Apollo Mission 30 years ago; they have since been recorded on synthetic aperture radar (SAR) images and in the infrared. We present a small sample of images. The spirals are broadly distributed over the world's oceans, 10–25 km in size and overwhelmingly cyclonic. Under light winds favourable to visualization, linear surface features with high surfactant density and low surface roughness are of common occurrence. The linear features are wound into spirals in vortices associated with horizontal shear instability, modified by rotation, in regions where the shear is comparable with the Coriolis frequency. Two models for concentrating shear are presented: a softened version of the classical sharp Margules front, and the time–dependent Lagrangian model of Hoskins & Bretherton. Horizontal shear instabilities and both frontal models favour cyclonic shear and cyclonic spirals, but for different reasons.

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Additional Information:© 2000 The Royal Society. Received 23 September 1999; revised 15 December 1999; accepted 20 January 2000. We acknowledge the singular contribution of Paul Scully-Power, the first and last (so far) Oceanographer-Astronaut. Half of the photographs reproduced in this paper were taken by Scully-Power with a hand-held Hasselblad camera. We thank C. Cox, C. Dysthe, T. Eldevik, D. Farmer, C. Garrett, O. M. Johannessen, J. Miles, R. Parker, S. Thorpe and the two referees for their helpful comments. Support was received from MEDEA. We are indebted to Ms Susan Runco, curator of the Still Photo Archive, NASA Johnson Space Flight Center. We are greatly indebted to D. Rudnick for clarification of the Hoskins-Bretherton model. W.M. holds the Secretary of the Navy Chair in Oceanography. L.A.’ s research is supported by the Office of Naval Research. F.Z. conducted his work as Green Fellow at the Scripps Institution of Oceanography. Illustrations were prepared by Breck Betts.
Funding AgencyGrant Number
Oceanography SocietyUNSPECIFIED
Office of Naval Research (ONR)UNSPECIFIED
Scripps Institution of OceanographyUNSPECIFIED
Subject Keywords:spirals; shear instabilities; frontogenesis
Issue or Number:1997
Record Number:CaltechAUTHORS:20200929-143508182
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Official Citation:Munk Walter, Armi Laurence, Fischer Kenneth and Zachariasen F. 2000 Spirals on the sea Proc. R. Soc. Lond. A. 456:1217–1280
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:105653
Deposited By: George Porter
Deposited On:30 Sep 2020 14:33
Last Modified:16 Nov 2021 18:45

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