Looping RAFOS floats in the California Current System

Collins, Curtis A.; Margolina, Tetyana; Rago, Thomas A.; Ivanov, Leonid M.

doi:10.1016/j.dsr2.2012.07.027

Cited by 45 publications

(63 citation statements)

References 39 publications

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“…For the PCUS and the CALUS in the Pacific basin, the observed eddy-types were close to those previously documented. In both of these upwelling systems, the presence of strong subsurface-intensified anticyclones, carrying warm and salty water from their nearcoastal poleward undercurrents, are well sampled by the Argo floats and match the previous observations [Simpson et al, 1984;Johnson and McTaggart, 2010;Chaigneau et al, 2011;Kurian et al, 2011;Colas et al, 2012;Collins et al, 2013]. However, we also highlighted the presence of weak surface-intensified anticyclones in the PCUS that represent 45% of the sampled eddies.…”

Section: Pacific and Atlantic Ebus: Differences Between Their Respectsupporting

confidence: 66%

Main eddy vertical structures observed in the four major Eastern Boundary Upwelling Systems

2015

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In the four major Eastern Boundary Upwelling Systems (EBUS), mesoscale eddies are known to modulate the biological productivity and transport near‐coastal seawater properties toward the offshore ocean, however little is known about their main characteristics and vertical structure. This study combines 10 years of satellite‐altimetry data and Argo float profiles of temperature and salinity, and our main goals are (i) to describe the main surface characteristics of long‐lived eddies formed in each EBUS and their evolution, and (ii) to depict the main vertical structure of the eddy‐types that coexist in these regions. A clustering analysis of the Argo profiles surfacing within the long‐lived eddies of each EBUS allows us to determine the proportion of surface and subsurface‐intensified eddies in each region, and to describe their vertical structure in terms of temperature, salinity and dynamic height anomalies. In the Peru‐Chile Upwelling System, 55% of the sampled anticyclonic eddies (AEs) have subsurface‐intensified maximum temperature and salinity anomalies below the seasonal pycnocline, whereas 88% of the cyclonic eddies (CEs) are surface‐intensified. In the California Upwelling System, only 30% of the AEs are subsurface‐intensified and all of the CEs show maximum anomalies above the pycnocline. In the Canary Upwelling System, ∼40% of the AEs and ∼60% of the CEs are subsurface‐intensified with maximum anomalies extending down to 800 m depth. Finally, the Benguela Upwelling System tends to generate ∼40–50% of weak surface‐intensified eddies and ∼50–60% of much stronger subsurface‐intensified eddies with a clear geographical distribution. The mechanisms involved in the observed eddy vertical shapes are discussed.

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Section: Pacific and Atlantic Ebus: Differences Between Their Respectsupporting

confidence: 66%

Main eddy vertical structures observed in the four major Eastern Boundary Upwelling Systems

2015

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“…They rely neither on the wind nor on local topographic features yet provide a simple mechanism for driving cyclonic subsurface currents at continental slopes that is dynamically consistent with observations. While the tendency of the cyclonic jet modeled here to undergo baroclinic instability is reminiscent of the squirts, jets and eddies that are ubiquitous in eastern oceans, observed eddies originating in the California Undercurrent are about twice as likely to be anticyclonic than cyclonic (Collins et al, 2013), with the bias perhaps explained by topographic triggering near specific points and capes or nearshore bottom stress (Molemaker et al, 2015). Nevertheless, the idealized experiment discussed here shows that forced, tidal motions of a stratified fluid at sloping boundaries has the intrinsic tendency to 'set-up' a subsurface thermocline, drive or enhance a near-bottom cyclonic jet as a consequence of geostrophy, and ultimately, to produce along-shore variability and cross-shore transport via baroclinic instability.…”

Section: Discussionmentioning

confidence: 98%

Tidally-forced flow in a rotating, stratified, shoaling basin

Winters

2015

Ocean Modelling

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a b s t r a c tBaroclinic flow of a rotating, stratified fluid in a parabolic basin is computed in response to barotropic tidal forcing using the nonlinear, non-hydrostatic, Boussinesq equations of motion. The tidal forcing is derived from an imposed, boundary-enhanced free-surface deflection that advances cyclonically around a central amphidrome. The tidal forcing perturbs a shallow pycnocline, sloshing it up and down over the shoaling bottom. Nonlinearities in the near-shore internal tide produce an azimuthally independent 'set-up' of the isopycnals that in turn drives an approximately geostrophically balanced, cyclonic, near-shore, sub-surface jet. The sub-surface cyclonic jet is an example of a slowly evolving, nearly balanced flow that is excited and maintained solely by forcing in the fast, super-inertial frequency band. Baroclinic instability of the nearly balanced jet and subsequent interactions between eddies produce a weak transfer of energy back into the inertia-gravity band as swirling motions with super-inertial vorticity stir the stratified fluid and spontaneously emit waves. The sub-surface cyclonic jet is similar in many ways to the poleward flows observed along eastern ocean boundaries, particularly the California Undercurrent. It is conjectured that such currents may be driven by the surface tide rather than by winds and/or along-shore pressure gradients.

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“…Technically, this was rather easy to achieve (by expanding or contracting the float's volume by a small amount), but the measurements proved difficult to put into a larger context because local thickness variations often masked low-order baroclinic stretching (Rossby & Prater 2005). Nonetheless, the method could be useful in studies of large-amplitude adjustment processes such as the formation of lenses (Bower et al 1997, Collins et al 2013) and the formation of eddies and lenses at steep topography (Prater 2002, Lilly et al 2003, Köhl 2007, Bracco et al 2008, Hormazabal et al 2013. The slow response of the buoyancy-driven cycling of floats to neighboring density surfaces could be improved with a small vertical thrust propeller.…”

Section: Property Change Along Lagrangian Tracksmentioning

confidence: 97%

“…Coherent lenses and eddies are present throughout the world ocean (e.g., Maximenko & Yamagata 1995, Kassis 2000, Shoosmith et al 2005, Collins et al 2013. Some appear to be inherently stable, with lifetimes measured in years (Richardson et al 2000, Johnson & McTaggart 2010, Rossby 2014, clear testimony to the very low rate of viscous dissipation in the ocean.…”

Section: Lenses and Eddiesmentioning

confidence: 97%

“…With the impressive improvements in sensor technology for the global Argo float array, no doubt a conductivity sensor could be added, but because such a sensor would substantially increase the cost of the float, most investigators would prefer to deploy more floats. However, it is possible to determine salinity variations along a float track given the float's equation of state, meaning its compressibility and coefficient of thermal expansion, because these properties determine its in situ density (e.g., Boebel et al 1995, Pérez-Brunius et al 2004a, Collins et al 2013. Boebel et al (1995) estimated that variations in salinity along a trajectory could be determined to ±0.02 PSU.…”

Section: Property Change Along Lagrangian Tracksmentioning

confidence: 99%

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Visualizing and Quantifying Oceanic Motion

Rossby

2016

Annu. Rev. Mar. Sci.

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Here I review the use of two highly complementary acoustical technologies for measuring currents in the ocean: acoustically tracked neutrally buoyant floats and vessel-mounted acoustic Doppler current profilers (ADCPs). The beauty of floats lies in their ability to efficiently and accurately visualize fluid motion in fronts and vortices and the dispersion caused by mesoscale eddy processes. Floats complement classical hydrography by articulating mechanisms and pathways by which waters spread out from their source region. Vessel-mounted ADCPs can profile the water column at O(1 km) horizontal resolution to depths greater than 1,000 m. These vessel-based scans capture in detail the cross-stream structure of fronts and eddies as well as the impact of bathymetry on currents. Sustained sampling along selected routes builds up valuable databases both for statistical studies of the submesoscale velocity field and for accurate estimates of fluid transport, as well as how these vary over time.

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Looping RAFOS floats in the California Current System

Cited by 45 publications

References 39 publications

Main eddy vertical structures observed in the four major Eastern Boundary Upwelling Systems

Main eddy vertical structures observed in the four major Eastern Boundary Upwelling Systems

Tidally-forced flow in a rotating, stratified, shoaling basin

Visualizing and Quantifying Oceanic Motion

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