Permanent Meanders in the California Current System

Abstract

Surface Velocity Program (SVP) drifter data from 1987 through 2005; Archiving, Validation, and Interpretation of Satellite Oceanographic data (AVISO) sea level anomalies; and NCEP reanalysis winds are used to assemble a time-averaged map of the 15-m-deep geostrophic velocity field in the California Current System seaward of about 50 km from the coast. The wind data are used to compute the Ekman currents, which are then subtracted from the drifter velocity measurements. The resulting proxy for geostrophic velocity anomalies computed from drifters and from satellite sea level measurements are combined to form an unbiased mean geostrophic circulation map. The result shows a California Current System that flows southward with four permanent meanders that can extend seaward for more than 800 km. Bands of alternating eastward and westward zonal currents are connected to the meanders and extend several thousand kilometers into the Pacific Ocean. This observed time-mean circulation and its associated eddy energy are compared to those produced by various high-resolution OGCM solutions: Regional Ocean Modeling System (ROMS; 5 km), Parallel Ocean Program model (POP; 1/10°), Hybrid Coordinate Ocean Model (HYCOM; 1/12°), and Naval Research Laboratory (NRL) Layered Ocean Model (NLOM; 1/32°). Simulations in closest agreement with observations come from ROMS, which also produces four meanders, geostrophic time-mean currents, and geostrophic eddy energy consistent with the observed values. The time-mean ageostrophic velocity in ROMS is strongest within the cyclonic part of the meanders and is similar to the ageostrophic velocity produced by nonlinear interaction of Ekman currents with the nearsurface vorticity field.

The mesoscale eddies and Kuroshio transport in the western North Pacific east of Taiwan from 8-year (2003–2010) model reanalysis

“…Both are averaged over 8 years (2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010), with a 120-h filter to remove the short-term fluctuations. The two have similar patterns except in the Kuroshio region where the altimetry is known to underestimate the EKE (e.g., Centurioni et al 2008), mainly because of its inadequate spatial resolution. The spatial resolution of the merged data set is estimated to be~150 km by Ducet et al (2000), which is about the same as the width of Kuroshio at the region.…”

“…Centurioni et al 2008;Maximenko et al 2009). The altimetry spatial resolution, however, is too coarse to map the Kuroshio transport.…”

Western boundary upwelling dynamics off Oman

“…We see this feature as an analog of the quasi-standing meanders observed in EBUs. Such meanders are the manifestation of topographic steering on the unstable current system (Marchesiello et al 2003;Centurioni et al 2008).…”

Global observations of quasi‐zonal bands in microwave sea surface temperature

“…Referred to as quasi-zonal in reference to their departure from a strictly zonal orientation and latent owing to their O(1 cm s 21 ) magnitude relative to the more dominant O(10 cm s 21 ) eddy field, these jet-like structures have been observed globally [Maximenko et al, 2005[Maximenko et al, , 2008 and regionally in studies involving each or a combination of the aforementioned data sets (altimeter SSH, MDT, and Argo). Regional studies include those in the subtropics Centurioni et al, 2008;Scott et al, 2008;Ivanov et al, 2009Ivanov et al, , 2010van Sebille et al, 2011;Buckingham and Cornillon, 2013], Southern Ocean [Sokolov and Rintoul, 2007] and near-equatorial waters [Cravatte et al, 2012;Qiu et al, 2013]. Some suggestion of their existence is also found within the trajectories of Lagrangian isopycnal floats in the Deep Brazil Basin [Hogg and mesoscale eddies identified and tracked by Chelton et al [2011a] but that two characteristics were inconsistent with their model of random eddies: the (i) variance of u did not decay as expected and (ii) number of eddies, as well as the size and amplitude of these eddies, correlated with the observed jet-like structures was large and broad in spectrum.…”