Geographical distribution and anisotropy of the inverse kinetic energy cascade, and its role in the eddy equilibrium processes

Wang, Shihong; Liu, Zhiliang; Pang, Chongguang

doi:10.1002/2014jc010476

Cited by 21 publications

(14 citation statements)

References 53 publications

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“…The correlations between L e and regional EKE level are 0.7 and 0.6 in the upstream and downstream regions, respectively. The mean value of L e in the KE region is about 250 km, close to previous studies using altimetry observations (Wang et al, ).…”

Section: Eddy Characteristicssupporting

confidence: 89%

“…While these previous studies have significantly improved our knowledge of the decadal variability of the eddy fields in the KE region, some important issues remain unsolved. First, eddy characteristics that determine the evolution of EKE level and its interaction with the mean flow, such as the energy length scales (Qiu et al, ; Wang et al, ) and eddy shapes (Waterman & Hoskins, ), are not fully studied. Second, because of lack of detailed descriptions in the existing literatures, our understanding about the dynamic processes during the unstable period, especially in the upstream KE, remains fragmentary.…”

Section: Introductionmentioning

confidence: 99%

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Decadal Variability of Eddy Characteristics and Energetics in the Kuroshio Extension: Unstable Versus Stable States

et al. 2018

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Using the Estimating Circulation and Climate of the Ocean Phase II product, this study investigates the eddy characteristics and energetics in two dynamical regimes within the Kuroshio Extension (KE) region. Based on the empirical orthogonal function analysis, it is found that the decadal evolution of eddy kinetic energy in the KE region is characterized by a delayed negative correlation between the upstream and downstream. Besides the out-of-phase change in eddy activity levels, eddy characteristics and energetics in the upstream KE are also different from those in the downstream. In the upstream region, eddies are stretched in the zonal direction and the unstable state is characterized by strong eddy-shedding processes. During these processes, cyclonic eddies are found to be formed in the first quasi-stationary meander and finally pinched off from the KE jet. Energy budget illustrates that the eddy shedding processes are triggered by baroclinic instability, while barotropic instability becomes the dominated energy source after the meander is fully developed. Accompanied by the generation of cyclonic eddies, significant inverse energy cascade is detected. When the upstream KE is stable, the eddy activity is dominated by baroclinic instability and the inverse energy cascade occurs similarly. Distinct from the upstream, eddies in the downstream KE tend to be stretched in the meridional direction and the decadal variability of eddy kinetic energy in this region is mainly regulated by the upstream through lateral advection.Plain Language Summary Based on classic physical oceanography theory, oceanic eddies are generated mainly through the vertical shear of background mean flow, i.e. baroclinic instability (BC). A stronger mean flow should favor BC and lead to more eddy generation. However, at decadal timescales, the correlation between the strength of the Kuroshio Extension (KE) jet and the regional eddy kinetic energy (EKE) level is negative, therefore the decadal variability of mesoscale eddy field in the KE system cannot be simply explained by the classic instability theory. This study explores in great depth the dynamical processes in the unstable state in the upstream KE and analyzes the evolution of eddy energetics during these processes. It is found that unstable events in the upstream KE are characterized by strong eddy-shedding processes. During these events, cyclonic eddies are found to be formed in the first quasi-stationary meander and finally pinched off from the KE jet. During these processes, both BC and barotropic energy transfer are important in the generation of eddies. This study will be a step toward the understanding of low-frequency variability in strong oceanic current regions in the global ocean.

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Section: Eddy Characteristicssupporting

confidence: 89%

Section: Introductionmentioning

confidence: 99%

Decadal Variability of Eddy Characteristics and Energetics in the Kuroshio Extension: Unstable Versus Stable States

et al. 2018

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“…The geographic distribution of the horizontal characterization scale L in each 4°× 4°bin for all the identified eddies is shown in Figure 4a. In general, the horizontal scale of eddies is larger at low latitudes and smaller at high latitudes, an observation that has been widely recognized in previous studies Wang et al, 2015). This simple latitudinal dependence is also evident in a scatterplot of the horizontal radius and latitude (Figure 4b).…”

Section: Geographical Distribution Of Vortex Aspect Ratiosupporting

confidence: 76%

Aspect Ratio of Eddies Inferred From Argo Floats and Satellite Altimeter Data in the Ocean

Liu

Liao

et al. 2020

JGR Oceans

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Mesoscale eddies dominate the majority of oceanic kinetic energy. The size of eddies is one of the basic properties; however, little is known about it because of lack of observations. Especially, their global vertical extent has still not been well investigated. Here, a ratio relationship of height to length scale for an eddy is derived based on dynamical constraints. Global satellite altimetry data combined with Argo float observations are used to calculate the aspect ratios of mesoscale eddies in the global ocean, and then their vertical scale is inferred. Approximately 25% of the total identified eddies with lifetimes ≥16 weeks from January 2002 to December 2017 trapped at least an Argo float near the eddy center. The result shows that the size of eddies has an obvious latitudinal dependence. Eddies at middle-low latitudes tend to be "large and shallow" with small aspect ratios, and eddies at high latitudes tend to be "small and deep-reaching" with large aspect ratios. Such results are coarsely considered as a competition between rotation and stratification. Eddy aspect ratios in middle-high-latitude regions show enhanced variance compared to those in low-latitude regions. More than half of eddies have a vertical extent smaller than 400 m. The majority of eddies extend over the mixed layer depth and are instead situated in the pycnocline. Some eddies at the middle-high latitudes penetrate through the entire pycnocline and reach deep ocean; as such, these eddies may play an important role in linking the deep-sea circulations and the surface circulations.Key Points:• The size (length and depth) of eddies has a distinct latitudinal dependence • More than half of eddies have a vertical extent smaller than 400 m • More than 70% of eddies penetrate through the entire pycnocline and reach deep ocean

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“…Wang et al . 27 further pointed out that the kinetic energy flux over the mesoscale band is anisotropic in these high EKE regions, with more kinetic energy being upscale transferred in the zonal direction. Therefore, more kinetic energy is observed in the zonal direction, which can flatten the zonal spectrum.…”

Section: Resultsmentioning

confidence: 95%

“…Using the gridded altimeter data, Scott and Wang 32 found a universal inverse kinetic energy flux from the deformation scale to larger scales. The inverse kinetic energy flux is considered to accompany the nonlinear interactions among mesoscale signals and between the mesoscale signals and mean currents 23,27 , and the EKE is redistributed in wavenumber space and the spectral slope is changed through these interactions. Wang et al .…”

Section: Summary and Discussionmentioning

confidence: 99%

Anisotropy of the sea surface height wavenumber spectrum from altimeter observations

Wang

Dai

Zhou

2019

Sci Rep

Self Cite

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In this paper, the zonal and meridional sea surface height (SSH) wavenumber spectra are systematically calculated using along-track and gridded altimeter products, and the slopes of the SSH wavenumber spectra over the mesoscale band, which is defined by the characteristic length scale of mesoscale signals, are estimated. The results show that the homogeneous spectral slopes calculated from the along-track and gridded altimeter datasets have a similar spatial pattern, but the spectral slopes from gridded altimeter data are generally steeper than that from the along-track data with an averaged difference of 1.5. Significant differences are found between the zonal and meridional spectra, which suggest that SSH wavenumber spectra are indeed anisotropic. Furthermore, the anisotropy exhibits strong regional contrast: in the equatorial region, the zonal spectrum is steeper than its corresponding meridional spectrum, while in the eastward-flowing high EKE regions the meridional spectrum is steeper than its zonal counterpart. The anisotropy of SSH wavenumber spectral slopes implies that EKE distributes anisotropically in different directions, and this distribution is closely associated with the generation and nonlinear evolution of mesoscale movements.

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Geographical distribution and anisotropy of the inverse kinetic energy cascade, and its role in the eddy equilibrium processes

Cited by 21 publications

References 53 publications

Decadal Variability of Eddy Characteristics and Energetics in the Kuroshio Extension: Unstable Versus Stable States

Decadal Variability of Eddy Characteristics and Energetics in the Kuroshio Extension: Unstable Versus Stable States

Aspect Ratio of Eddies Inferred From Argo Floats and Satellite Altimeter Data in the Ocean

Anisotropy of the sea surface height wavenumber spectrum from altimeter observations

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