On the Decadal Variability of the Eddy Kinetic Energy in the Kuroshio Extension

Yang, Yang; Liang, Xin‐Zhong; Qiu, Bo; Chen, Shuiming

doi:10.1175/jpo-d-16-0201.1

Cited by 52 publications

(72 citation statements)

References 99 publications

(124 reference statements)

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“…The data used in this study are Estimating the Circulation and Climate of the Ocean (ECCO), Phase II product (ECCO2, http://apdrc.soest.hawaii.edu/data/; cube 92 version), which is also used by Yang et al (). It is based on the Massachusetts Institute of Technology General Circulation Model (MITgcm; Marshall et al, ).…”

Section: Datamentioning

confidence: 99%

“…Thus, the solution is both realistic and dynamically consistent, which makes the solution useful for process and budget analyses (Wunsch et al, ). The ECCO2 state estimate has been used in the past to diagnose the eddy dynamics and oceanic energetics in the KE region (e.g., Chen et al, ; Yang et al, ). In this study, the 3‐day‐averaged data set in the KE region (140°E–180°E, 25°N–45°N) from 1993 to 2015 is used.…”

Section: Datamentioning

confidence: 99%

“…Here EKE is defined as

EKE = \frac{1}{2} ((), u'^{2} + v'^{2}),

where u ′ and v ′ denote zonal and meridional surface velocity deviation from their 270‐day running‐mean values. This definition is based on the eddy characteristic periods in the KE region suggested by previous studies (Itoh & Yasuda, ; Yang et al, ). Changing this running‐mean window within the range of 180 to 400 days does not affect the following analysis results qualitatively.…”

Section: Eddy Characteristicsmentioning

confidence: 99%

“…Based on both observations and an idealized model study, Waterman and Jayne () and Waterman et al () indicated that the KE jet is subject to a mixed instability mechanism. Using a multiscale energy and vorticity analysis method, Yang and Liang () and Yang et al () suggested the important role of barotropic instability (BT) in the eddy energy budget within the KE region. They claimed that both BT and BC are important for the growth of EKE in the time‐mean sense, while the decadal modulation of EKE is mainly controlled by BT.…”

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: Datamentioning

confidence: 99%

Section: Datamentioning

confidence: 99%

“…Here EKE is defined as

EKE = \frac{1}{2} ((), u'^{2} + v'^{2}),

Section: Eddy Characteristicsmentioning

confidence: 99%

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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“…Dong et al () suggest that the global oceanic eddy movement can significantly influence distribution of the heat and fresh water in the ocean. The Kuroshio Extension (KE) region, from Japan eastward to the mid‐Pacific, is one of the two largest eddy kinetic energy (EKE) bands in the northern Pacific Ocean (the other being the subtropical frontal zone; Chow et al, ; Liu et al, ; Qiu & Chen, ; Yang et al, ). Eddy activities in the KE play an important role in the decade variations in the KE system circulation (Qiu & Chen, , ) and air‐sea interaction (Ma et al, ).…”

Section: Introductionmentioning

confidence: 99%

Oceanic Eddy Characteristics and Generation Mechanisms in the Kuroshio Extension Region

Dong

Zhang

et al. 2018

JGR Oceans

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The Kuroshio Extension region is well known for its strong eddy activity. In this paper, using satellite altimetry‐measured sea surface height anomaly data from 1993 to 2012 in an extended Kuroshio Extension region (140–180°E, 25–45°N), we analyze eddy characteristics: eddy size, polarity, lifetime, intensity, trajectory, and spatial and temporal distributions. Using temperature and salinity vertical profiles measured by Argo floats, we examine the eddy impact on vertical stratification. During the 20‐year period, 7,574 eddies are identified (based on following complete eddy trajectories) with a lifetime equal to or longer than 4 weeks. The numbers of cyclonic and anticyclonic eddies are found to be approximately the same. The distribution of eddy sizes peaks at a radius of about 40 km. The radius at the peak is at the same order as the first baroclinic deformation radius or the horizontal shear scale of the Kuroshio flow. The normalized eddy statistical characteristics show that eddies have different characteristics at different stages of their lifetimes. Among eddies with lifetimes longer than 50 weeks, more anticyclonic (cyclonic) eddies are found north (south) of 35°N. In contrast, among eddies with lifetimes shorter than 20 weeks, more cyclonic (anticyclonic) eddies are found north (south) of 35°N. The asymmetric distribution of eddies suggests two different eddy generation mechanisms: (1) the development of meanders in the Kuroshio path leading to the pinch off of eddies with longer lifetime (larger size) and (2) horizontal shear instability (barotropic instability) leading to eddies of shorter life (smaller size). We further apply an eddy‐resolved numerical product to quantitatively investigate the eddy generation mechanisms.

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The fastest growing initial error in prediction of the Kuroshio Extension state transition processes and its growth

Wang

Pierini

2020

Clim Dyn

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On the Decadal Variability of the Eddy Kinetic Energy in the Kuroshio Extension

Cited by 52 publications

References 99 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

Oceanic Eddy Characteristics and Generation Mechanisms in the Kuroshio Extension Region

The fastest growing initial error in prediction of the Kuroshio Extension state transition processes and its growth

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