On modulation instability in a system of jets, waves and eddies off California

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Author
Ivanov, L.M.
Collins, C.A.
Margolina, T.
Date
2014-02-20Metadata
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SSH altimetry observations for 1992 to 2009 off Central and Southern California are
used to show that observed quasi-zonal jets were likely driven by near-resonance interactions
between different scales of the flow. Quartet (modulational) instability dominated and caused non-local transfer of energy from waves and eddies to bi-annual
oscillations and quasi-zonal jets. The total number of quartets induced off California
was approximately 10 times larger than the number of existing triads, and quartet amplitudes
in general were larger than triad amplitudes. The spectral centroid regularly
shifted into the domain of low-order modes. Local “negative” viscosity probably did not generate a classical inverse cascade because the spectrum of SSHs did not demonstrate
power behavior. Two types of quartets were identified: (a) quasi-zonal jets, annual
and semi-annual Rossby waves and eddies, and (b) bi-annual oscillations, semiannual
Rossby waves and eddies. For a case with bottom friction, quartet instability
required the existence of a certain level of dissipativity in the flow.
Description
The article of record as published may be found at http://dx.doi.org/10.5194/npgd-1-97-2014
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