Abstract
Abstract. Sea surface height (SSH) altimetry observations for 1992 to 2009 off 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 biannual oscillations and quasi-zonal jets. Two types of quartets were identified: those composed of scales corresponding to (a) quasi-zonal jets, annual and semiannual Rossby waves and mesoscale eddies, and (b) biannual oscillations, semiannual Rossby waves and mesoscale eddies. The spectral centroid regularly shifted into the domain of low-order modes. However, the spectrum of SSHs does not demonstrate a power behavior. This says that the classical inverse cascade is absent. For a case with bottom friction, quartet instability required the existence of a certain level of dissipativity in the flow.
Highlights
In recent years, there has been growing recognition of the existence of persistent quasi-zonal jets (QZJs) in the midlatitude atmosphere as well as in the atmospheres of gaseous planets
The results presented here do not agree with Srinivasan and Young (2012) because in our opinion, nonlinearity played a very important role in the jet generation; results were not compared to those obtained by Srinivasan and Young (2012)
Note that horizontal velocity was not estimated from Sea surface height (SSH) using geostrophic relationships, because non-geostrophic motions in the studied coastal oceanic area may contain up to 30 % of the total kinetic energy of horizontal circulation (Marchesiello et al, 2003), and frontal dynamics plays an important role in forming circulation in the California Current system (Castelao et al, 2006)
Summary
There has been growing recognition of the existence of persistent quasi-zonal jets (QZJs) in the midlatitude atmosphere as well as in the atmospheres of gaseous planets (an intensive review of such QZJs is given by Baldwin et al, 2007). A Debaucher sixth-order wavelet transform was used in this study This allowed for the introduction of six frequency bands (FBs): (1) 1 month (ω ≈ 2 × 10−5 rad) to 2 months (ω ≈ 4 × 10−5 rad) (referred to as the mesoscale eddy II (ME-II) band), (2) 2 months (ω ≈ 4 × 10 −5 rad) to 4 months (ω ≈ 8 × 10 −5 rad) (ME-I band), (4) 4 months (ω ≈ 8 × 10 −5 rad) to 8 months (ω ≈ 16 × 10 −5 rad) (semiannual Rossby waves or SARW band), (5) 8 months (ω ≈ 1.6 × 10 −6 rad) to 18 months (ω ≈ 3, 6 × 10 −6 rad) (annual Rossby waves or ARW band), (6) 18 months (ω ≈ 3, 6 × 10 −6 rad) to 36 months (ω ≈ 7.2 × 10 −6 rad) (biannual oscillations or BAO band), and (7) longer than 36 months (ω ≈ 7.2 × 10 −6 rad) (quasi-zonal jets or QZJ band). The mesoscale coherent structures observed in SSH observations off California shared overlapping spatial scales, but had distinct timescales This allowed for detection and selection of QZJs, BAOs, RWs and MEs. Time-averaged spectra for each of the six frequency bands are shown, b as a function of mode number. SSH in the jets reached 4–5 cm and was not less than 2.5–3 cm within the 17-year observational www.nonlin-processes-geophys.net/21/887/2014/
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