Wind-Driven Coastal Generation of Annual Mesoscale Eddy Activity in the California Current

1993 ◽  
Author(s):  
Alejandro Pares-Sierra ◽  
Warren B. White ◽  
C-K Tai
Keyword(s):  
Mesoscale Eddy ◽  
California Current ◽  
Eddy Activity

scholarly journals Assymmetric eddy populations in adjacent basins – a high resolution numerical study of the Tyrrhenian and Ligurian Seas

2012 ◽  
Vol 9 (6) ◽  
pp. 3521-3566 ◽  
Author(s):  
R. M. A. Caldeira ◽  
X. Couvelard ◽  
E. Casella ◽  
A. Vetrano
Keyword(s):  
High Resolution ◽  
Ocean Circulation ◽  
Numerical Solutions ◽  
Numerical Study ◽  
Mesoscale Eddy ◽  
Leeward Side ◽  
Boundary Current ◽  
High Concentration ◽  
Eddy Activity ◽  
Tyrrhenian Basin

Abstract. A high-resolution ocean circulation modelling system forced with a high-resolution numerical wind product was used to study the mesoscale and sub-mesoscale eddy population of the North-Western Mediterranean Sea, contrasting eddy-activity between the Tyrrhenian and Ligurian sub-basins. Numerical solutions reproduced some of the known regional dynamics, namely the occurrence and oceanic implications of Mistral events, the convective cell leeward of the Gulf of Lion, as well as the Balearic frontal system. Calculated transport across the Corsica Channel followed a similar trend, when compared to the transport computed from a moored current meter. The analysis of the results showed that surface eddy activity is mostly confined to the boundary-currents, whereas in the deeper layers most eddies are concentrated on the central-deeper part of the basins. The Liguro-Provençal basin shows a much higher concentration of intermediate and deep-water eddies, when compared to the Tyrrhenian basin. Sub-mesoscale surface eddies tend to merge and migrate vertically onto intermediate waters. Intense eddy activity in the boundary-current surrounding the Liguro-Provençal Gyre, concentrate high-productivity, manifested by higher concentrations of mean sea surface chlorophyll, in the central part of the gyre, defined herein as the Ligurian Productive Pool (LPP). On average, the Tyrrhenian was mostly oligotrophic except for a small productive vortice in the south-eastern (leeward) side of Corsica. The transport in the Tyrrhenian Gyre, and across the basin is one order of magnitude higher than the transport calculated for the Liguro-Provençal basin. A high concentration of eddies in the passage between the Balearic Archipelago and Sardinia suggests retention and longer residence times of nutrient rich water in the "Ligurian pool", compared to a "fast draining" Tyrrhenian basin. Previous studies support the cyclonic gyre circulation generated in the Liguro-Provençal basin but more studies are needed to address the surface and deep mesoscale activity of the Tyrrhenian basin.

Decadal variability of the Kuroshio Extension

2020 ◽  
Author(s):  
Guidi Zhou ◽  
Xuhua Cheng
Keyword(s):  
Decadal Variability ◽  
Kuroshio Extension ◽  
Relaxation Oscillation ◽  
Mesoscale Eddy ◽  
Height Anomaly ◽  
Intrinsic Variability ◽  
Mean Flow ◽  
The Real ◽  
Eddy Activity ◽  
The Kuroshio

<p>The decadal variability of the Kuroshio Extension (KE) is investigated using altimeter observations (AVISO) and the output of an ocean model (OFES). It is shown that the KE decadal variability is manifested in its strength, latitudinal position, and zonal extent, as well as the associated mesoscale eddy activity. Two differences between the two datasets are identified: (a) In OFES, the eddy activity positively correlates with the KE mode index when it leads by a few years, whereas in AVISO the two are negatively and concurrently correlated. (b) In OFES, the positive KE mode is associated with large meanders of the Kuroshio south of Japan, but in AVISO they are irrelevant. These differences indicate that the generation mechanism of KE's decadal variability is different in OFES and the real ocean. The sea surface height anomaly (SSHA) is then decomposed into major components including the wind-driven Rossby waves and residual (intrinsic) variability. The relationship between the two components are virtually the same in OFES and in AVISO, showing a negative correlation when the wind-driven part leads by a few years. Further diagnostics based on OFES reveals that the residual SSHA originates from the downstream region over the Shatsky Rise, slowly propagates westward, and is driven by eddy potential energy transfer. The OFES results partly conform to the intrinsic relaxation oscillation theory put forth by idealized model analyses, but in the latter the SSHA signal originates from the upstream Kuroshio. A new mechanism is then proposed for OFES: the decadal variability of the KE is first a result of the intrinsic relaxation oscillation probably excited by wind forcing, which regulates the strength of the KE’s inflow and thus modulates the downstream topography interaction, resulting in different downstream mesoscale eddy activity that further feeds back on the mean-flow. The mechanism for the real ocean is also reassessed.</p>

scholarly journals Seasonal Modulation of Eddy Kinetic Energy and Its Formation Mechanism in the Southeast Indian Ocean

2011 ◽  
Vol 41 (4) ◽  
pp. 657-665 ◽  
Author(s):  
Fan Jia ◽  
Lixin Wu ◽  
Bo Qiu
Keyword(s):  
Indian Ocean ◽  
Kinetic Energy ◽  
Vertical Velocity ◽  
Baroclinic Instability ◽  
Mesoscale Eddy ◽  
Eddy Kinetic Energy ◽  
Velocity Shear ◽  
Austral Spring ◽  
Eddy Activity ◽  
South Indian

Abstract Mesoscale eddy activity in the southeast Indian Ocean (15°–30°S, 60°–110°E) is investigated based on available satellite altimetry observations. The observed sea level anomaly data show that this region is the only eastern basin among the global oceans where strong eddy activity exists. Furthermore, the eddy kinetic energy (EKE) level in this region displays a distinct seasonal cycle with the maximum in austral summer and minimum in austral winter. It is found that this seasonal modulation of EKE is mediated by baroclinic instability associated with the surface-intensified South Indian Countercurrent (SICC) and the underlying South Equatorial Current (SEC) system. In austral spring and summer the enhanced flux forcing of combined meridional Ekman and geostrophic convergence strengthens the upper-ocean meridional temperature gradient, intensifying the SICC front and its vertical velocity shear. Modulation of the vertical velocity shear results in the seasonal changes in the strength of baroclinic instability, leading to the seasonal EKE variations in the southeast Indian Ocean.

scholarly journals An Index for Depicting the Long-Term Variability of Mesoscale Eddy Activity over the Kuroshio Extension Region

Atmosphere ◽  
2020 ◽  
Vol 11 (8) ◽  
pp. 792
Author(s):  
Peilong Yu ◽  
Chao Zhang ◽  
Lifeng Zhang ◽  
Xiong Chen ◽  
Quanjia Zhong ◽  
...  
Keyword(s):  
Activity Index ◽  
Kuroshio Extension ◽  
Mesoscale Eddy ◽  
Low Frequency ◽  
Climatic Effects ◽  
Near Surface ◽  
Eddy Activity ◽  
Frequency Changes ◽  
The Kuroshio

Using high-resolution satellite-derived sea surface temperature (SST) data from September 1981 to December 2015, the present study develops a new index to detect the long-term variation in mesoscale eddy activity over the Kuroshio Extension (KE) region. This eddy activity index (EAI) highlights the strength of eddy-induced poleward heat transport and has obvious advantages over the other existing KE indices in depicting the low-frequency changes in KE eddy activity. An analysis of the EAI shows that over the long term, the KE eddy activity variability presents a significant spectral peak of about 8 years and is not directly modulated by wind-driven oceanic Rossby waves generated in the central North Pacific. When the EAI is positive, the strengthened KE eddy activity significantly enhances the heat release from ocean to atmosphere over the Kuroshio–Oyashio confluence region (KOCR). This induces an anomalous dipole pattern of near-surface baroclinicity over this region that can persist for up to 6 months, favoring a weakened and northward-moving East Asian jet, and vice versa. It is believed that the new EAI will facilitate future studies focusing on the climatic effects of the KE eddy activity variation.

Mesoscale to Submesoscale Transition in the California Current System. Part I: Flow Structure, Eddy Flux, and Observational Tests

2008 ◽  
Vol 38 (1) ◽  
pp. 29-43 ◽  
Author(s):  
X. Capet ◽  
J. C. McWilliams ◽  
M. J. Molemaker ◽  
A. F. Shchepetkin
Keyword(s):  
Flow Structure ◽  
Current System ◽  
Mesoscale Eddy ◽  
California Current ◽  
Upper Ocean ◽  
Surface Boundary ◽  
Surface Boundary Layer ◽  
California Current System ◽  
System Part ◽  
Wind Driven Currents

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.

A mesoscale eddy dipole in the offshore California Current

1990 ◽  
Vol 95 (C8) ◽  
pp. 13009 ◽  
Author(s):  
James J. Simpson ◽  
Ronald J. Lynn
Keyword(s):  
Mesoscale Eddy ◽  
California Current

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

2019 ◽  
Vol 10 (1) ◽  
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.

scholarly journals Winter mixing, mesoscale eddies and eastern boundary current: Engines for biogeochemical variability of the central Red Sea during winter/early spring period

2018 ◽  
Author(s):  
Nikolaos D. Zarokanellos ◽  
Burton H. Jones
Keyword(s):  
Remote Sensing ◽  
Red Sea ◽  
Mixed Layer ◽  
Mesoscale Eddy ◽  
Early Spring ◽  
Boundary Current ◽  
Surface Cooling ◽  
Eddy Activity ◽  
Eastern Boundary ◽  
Eastern Boundary Current

Abstract. The central Red Sea (CRS) has been shown to be characterized by significant eddy activity throughout the year. Weakened stratification in winter may lead to enhanced vertical exchange contributing to physical and biogeochemical processes. In the winter of 2014–2015, we began an extended glider time series to monitor the CRS where eddy activity is significant. Remote sensing and glider observations that include temperature, salinity, oxygen, carbon dissolved organic matter (CDOM), chlorophyll fluorescence (CHL) and multi-wavelength optical backscatter have been used to characterize the effects of winter mixing, eddy activity and lateral advection. During winter and early spring, mixing up to 90m driven by surface cooling and strong winds combined with eddy features was insufficient to penetrate the nutricline and supply nutrients into the upper layer. However, the mixing events did disperse the phytoplankton from the deep chlorophyll maximum throughout the upper mixed layer (ML) increasing the chlorophyll signature detected by ocean colour imagery. In early spring, the eastern boundary current (EBC) is evident in CRS. The EBC brings relative high concentrations of CHL and CDOM along with lower oxygen concentrations indicative of previous nutrient availability. In addition to the vertical mixing, mesoscale eddy activity cause 160 m vertical displacement of the 180 µM isopleth of oxygen, proxy of the nutricline interface. Within the cyclonic feature, this oxygen isopleth shallowed to 60 m, well within the euphotic layer. Remote sensing analyses indicate that these eddies also contribute to significant horizontal dispersion, including the exchange between the open sea and coastal coral reef ecosystems. When the phytoplankton is distributed through the mixed layer clear diel variability was evident in CHL concentration. The biogeochemical responses provide a sensitive indicator of the mixing and eddy processes that may not be detectable via remote sensing. Sustained in situ autonomous observations were essential to understand these processes.

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