Vortex pairing in an unstable anticyclonic shear flow: discrete subharmonics of one pendulum day

Type Article
Date 2001-08
Language English
Author(s) Flament Pierre, Lumpkin Rick, Tournadre Jean, Armi Laurence
Affiliation(s) Inst Francais Rech Exploitat Mer, Dept Oceanog Spatiale, F-29280 Plouzane, France.
Univ Hawaii, Sch Ocean & Earth Sci & Technol, Dept Oceanog, Honolulu, HI 96822 USA.
Florida State Univ, Dept Oceanog, Tallahassee, FL 32306 USA.
Univ Calif San Diego, Scripps Inst Oceanog, Inst Geophys & Planetary Phys, La Jolla, CA 92093 USA.
Source Journal of Fluid Mechanics (0022-1120) (Cambridge University Press), 2001-08 , Vol. 440 , P. 401-409
DOI 10.1017/S0022112001004955
WOS© Times Cited 32
Keyword(s) Vortex, Oceanic shear flow
Abstract Observations of the downstream evolution of an oceanic zonal horizontal shear flow at a Reynolds number of about 10(11), formed as the westward North Equatorial Current passes the island of Hawai'i, reveal finite-amplitude anticyclonic vortices resulting from instability of the shear. The initial orbital period of the vortices is exactly one pendulum day (3.1 days at this latitude), centrifugal instability presumably inhibiting stronger vortices from forming. As they move downstream, they appear to pair and merge into successively larger vortices, in a geometric sequence of longer orbital periods; three subharmonic transitions are suggested with final orbital periods near 6, 12 and 24 days.
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