An Integrated Study of Offshore Mesoscale Eddy Dynamics in the California Current System

Abstract In computational simulations of an idealized subtropical eastern boundary upwelling current system, similar to the California Current, a submesoscale transition occurs in the eddy variability as the horizontal grid scale is reduced to O(1) km. This first paper (in a series of three) describes the transition in terms of the emergent flow structure and the associated time-averaged eddy fluxes. In addition to the mesoscale eddies that arise from a primary instability of the alongshore, wind-driven currents, significant energy is transferred into submesoscale fronts and vortices in the upper ocean. The submesoscale arises through surface frontogenesis growing off upwelled cold filaments that are pulled offshore and strained in between the mesoscale eddy centers. In turn, some submesoscale fronts become unstable and develop submesoscale meanders and fragment into roll-up vortices. Associated with this phenomenon are a large vertical vorticity and Rossby number, a large vertical velocity, relatively flat horizontal spectra (contrary to the prevailing view of mesoscale dynamics), a large vertical buoyancy flux acting to restratify the upper ocean, a submesoscale energy conversion from potential to kinetic, a significant spatial and temporal intermittency in the upper ocean, and material exchanges between the surface boundary layer and pycnocline. Comparison with available observations indicates that submesoscale fronts and instabilities occur widely in the upper ocean, with characteristics similar to the simulations.

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Offshore transport of particulate organic carbon in the California Current System by mesoscale eddies

Nature Communications ◽

10.1038/s41467-019-12783-5 ◽

2019 ◽

Vol 10 (1) ◽

Cited By ~ 4

Author(s):

Caitlin M. Amos ◽

Renato M. Castelao ◽

Patricia M. Medeiros

Keyword(s):

Organic Carbon ◽

Particulate Organic Carbon ◽

Coastal Water ◽

Large Scale ◽

Current System ◽

Mesoscale Eddy ◽

California Current ◽

California Current System ◽

Upwelled Water ◽

Offshore Transport

Abstract The California Current System is characterized by upwelling and rich mesoscale eddy activity. Cyclonic eddies generally pinch off from meanders in the California Current, potentially trapping upwelled water along the coast and transporting it offshore. Here, we use satellite-derived measurements of particulate organic carbon (POC) as a tracer of coastal water to show that cyclones located offshore that were generated near the coast contain higher carbon concentrations in their interior than cyclones of the same amplitude generated offshore. This indicates that eddies are in fact trapping and transporting coastal water offshore, resulting in an offshore POC enrichment of 20.9 ± 11 Gg year−1. This POC enrichment due to the coastally-generated eddies extends for 1000 km from shore. This analysis provides large-scale observational-based evidence that eddies play a quantitatively important role in the offshore transport of coastal water, substantially widening the area influenced by highly productive upwelled waters in the California Current System.

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The Physical Structure and Behavior of the California Current System

10.1101/2020.02.10.942730 ◽

2020 ◽

Cited By ~ 2

Author(s):

Lionel Renault ◽

James C. McWilliams ◽

Alexandre Jousse ◽

Curtis Deutsch ◽

Hartmut Frenzel ◽

...

Keyword(s):

High Resolution ◽

Boundary Conditions ◽

Current System ◽

Mesoscale Eddy ◽

California Current ◽

Open Boundary ◽

Biogeochemical Model ◽

California Current System ◽

Synoptic Wind ◽

The Impact

AbstractThis paper is the first of two that present a 16-year reanalysis solution from a coupled physical and biogeochemical model of the California Current System (CCS) along the U. S. West Coast and validate the solution with respect to mean and seasonal fields and, to a lesser degree, eddy variability. Its companion paper is Deutsch et al. (2019a). The intent is to construct and demonstrate a modeling tool that will be used for mechanistic explanations, attributive causal assessments, and forecasts of future evolution for circulation and biogeochemistry, with particular attention to the increasing oceanic stratification, deoxygenation, and acidification. A well-resolved mesoscale (dx = 4 km) simulation of the CCS circulation is made with the Regional Oceanic Modeling System over a reanalysis period of 16 years from 1995 to 2010. The oceanic solution is forced by a high-resolution (dx = 6 km) regional configuration of the Weather and Research Forecast (WRF) atmospheric model. Both of these high-resolution regional oceanic and atmospheric simulations are forced by lateral open boundary conditions taken from larger-domain, coarser-resolution parent simulations that themselves have boundary conditions from the Mercator and Climate Forecast System reanalyses, respectively. We first show good agreement between the simulated atmospheric forcing of the ocean and satellite observations for the spatial patterns and seasonal variability of the cloud cover and for the surface fluxes of momentum, heat, and freshwater. The simulated oceanic physical fields are then evaluated with satellite and in situ observations. The simulation reproduces the main structure of the climatological upwelling front and cross-shore isopycnal slopes, the mean current patterns (including the California Undercurrent), and the seasonal and interannual variability. It also shows agreement between the mesoscale eddy activity and the wind-work energy exchange between the ocean and atmosphere modulated by influences of surface current on surface stress. Finally, the impact of using a high frequency wind forcing is assessed for the importance of synoptic wind variability to realistically represent oceanic mesoscale activity and ageostrophic inertial currents.

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Faculty Opinions recommendation of Rapid progression of ocean acidification in the California Current System.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.717953148.793458716 ◽

2012 ◽

Author(s):

Russell Moll

Keyword(s):

Ocean Acidification ◽

Current System ◽

California Current ◽

Rapid Progression ◽

California Current System

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Improved Ecosystem Predictions of the California Current System via Accurate Light Calculations

10.21236/ada557196 ◽

2011 ◽

Author(s):

Curtis D. Mobley

Keyword(s):

Current System ◽

California Current ◽

California Current System

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Reconstruction of Diffusion Coefficients and Power Exponents from Single Lagrangian Trajectories

Fluids ◽

10.3390/fluids6030111 ◽

2021 ◽

Vol 6 (3) ◽

pp. 111

Author(s):

Leonid M. Ivanov ◽

Collins A. Collins ◽

Tetyana Margolina

Keyword(s):

Black Sea ◽

Diffusion Coefficients ◽

Current System ◽

Mean Square Displacement ◽

California Current ◽

The Black Sea ◽

Mean Square ◽

California Current System ◽

The Mean ◽

Non Gaussian

Using discrete wavelets, a novel technique is developed to estimate turbulent diffusion coefficients and power exponents from single Lagrangian particle trajectories. The technique differs from the classical approach (Davis (1991)’s technique) because averaging over a statistical ensemble of the mean square displacement (<X2>) is replaced by averaging along a single Lagrangian trajectory X(t) = {X(t), Y(t)}. Metzler et al. (2014) have demonstrated that for an ergodic (for example, normal diffusion) flow, the mean square displacement is <X2> = limT→∞τX2(T,s), where τX2 (T, s) = 1/(T − s) ∫0T−s(X(t+Δt) − X(t))2 dt, T and s are observational and lag times but for weak non-ergodic (such as super-diffusion and sub-diffusion) flows <X2> = limT→∞≪τX2(T,s)≫, where ≪…≫ is some additional averaging. Numerical calculations for surface drifters in the Black Sea and isobaric RAFOS floats deployed at mid depths in the California Current system demonstrated that the reconstructed diffusion coefficients were smaller than those calculated by Davis (1991)’s technique. This difference is caused by the choice of the Lagrangian mean. The technique proposed here is applied to the analysis of Lagrangian motions in the Black Sea (horizontal diffusion coefficients varied from 105 to 106 cm2/s) and for the sub-diffusion of two RAFOS floats in the California Current system where power exponents varied from 0.65 to 0.72. RAFOS float motions were found to be strongly non-ergodic and non-Gaussian.

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