Detection of Oceanic Quasi-Zonal Jets from Altimetry Observations
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Authors
Ivanov, L.M.
Collins, C.A.
Margolina, T.M.
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2012-08
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Abstract
Recent analyses of observations and ocean model outputs have revealed coherent low-frequency quasizonal
jets in observed sea surface height (SSH) anomaly and model velocity fields. The jets were latent, that is,
they were not detectable by eye, but revealed and selected by time-averaging procedures. Time-averaging
procedures, when applied to fields that contain propagating features (eddies and waves), can create jetlike
structures of nonphysical nature (artifacts). This paper suggests the application of three criteria to distinguish
real jets from these artifacts, and demonstrates that quasi-zonal jets extracted from satellite altimetry observations
off California were not artifacts. First, quasi-zonal jets off California were stronger than artifacts:
the observed SSH for the jets reached 4–5 cm, which is considerably larger than SSH artifacts, which did not
exceed 0.9–1.2 cm. Second, axes of the observed jets were not always oriented along the paths of propagating
mesoscale features (waves and eddies). Observed jet axes rotated as late as 12 months after propagating
mesoscale features changed their propagation direction. This behavior differed from that of artifacts, the axes
of which should be oriented in the same direction as propagation paths of mesoscale features. Third, generation
(amplification) of quasi-zonal jets was accompanied by phase synchronization or locking of flow time
scales resulting from interactions between these scales. Because artifacts were a result of linear averaging
procedures, they cannot exhibit such phase synchronization.
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The article of record as published may be located at http://dx.doi.org/10.1175/JTECH-D-11-00130.1
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Journal of Atmospheric and Oceanic Technology, Volume 29, August 2012
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This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. Copyright protection is not available for this work in the United States.