On quartet interactions in the California Current system

The article of record as published may be located at http://dx.doi.org/10.5194/npg-21-887-2014Sea 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.Support for LI (CC) was provided by NSF grant OCE-0827527 (OCE-0827160)

Detection of Oceanic Quasi-Zonal Jets from Altimetry Observations

The article of record as published may be located at http://dx.doi.org/10.1175/JTECH-D-11-00130.1Recent 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

On model validation for meso/submesoscale currents: Metrics and application to ROMS off Central California

The article of record as published may be located at http://dx.doi.org/10.1016/j.ocemod.2009.02.003ROMS with horizontal grid spacing of 3.5 km for the region off Central California was compared to RAFOS float observations and satellite altimetry on meso/submesoscales. The approach introduced and used two new metrics for model-data comparison, as well as suggested how to calculate these metrics for different spatio-temporal scales. The first metric consisted of the first two moments of exit time and was used to compare ROMS against RAFOS float observations at mid-depths (between 300 m and 350 m). Exit time is the time a float launched at a point takes to leave a domain for the first time. The second metric was spectral entropy and was used to estimate how well ROMS reproduced variability of the sea surface height (SSH) anomaly field extracted from an AVISO data set (1992–2007) for specified temporal and spatial scales. Calculations showed that ROMS reproduced the mid-depth mesoscale/submesoscale currents next to the coast in a very accurate manner (low-order exit time statistics of floats were reproduced by ROMS with an accuracy better than 95%); but ROMS overestimated the speed of westward drift of floats by as much as 20–30% at distances greater than 350 km from the coastline. ROMS predicted the variability of the mesoscale (100–400 km) SSH anomaly field for temporal scales of 1–12 months with a reasonable accuracy. A wavelet transform modulus maxima technique applied to the spectral entropy of SSH anomaly also demonstrated good agreement between ROMS and satellite altimetry for mesoscales characterized by singular exponents and multi-fractal spectra for 1–12 month time scales

Reconstruction of Shelf Circulation in Northern Gulf of Mexico Circulation From Drifter Buoy Data

Fourth Conference on Coastal Meteorology and Oceanography, American Meteorological Societ

Lagrangian predictabilty of high-resolution regional ocean models

Nonlinear Processes in Geophysics, European Geosciences Union/American Geophysical Union, 11, 47-66

Reconstruction of Ocean Currents From Sparse and Noisy Data

M-I-P-