Volume and Transport of Eddy‐Trapped Mode Water South of the Kuroshio Extension

Shi, Fei; Luo, Yiyong; Xu, Lixiao

doi:10.1029/2018jc014176

Cited by 15 publications

(21 citation statements)

References 33 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In the North Pacific, the subtropical mode water formed in the deep mixed layer in late winter because of intense convection is known as STMW [40]. STMW is significantly modulated by mesoscale eddies and thick (thin) STMW is co-located with anticyclonic (cyclonic) eddies [31,41,42]. The potential vorticity is used to identify STMW, which is defined as [43]: The criterion of T z ≥ 0.02°C/m is adopted to identify the permanent thermocline.…”

Section: Stmwmentioning

confidence: 99%

Anatomy of a Cyclonic Eddy in the Kuroshio Extension Based on High-Resolution Observations

Zhang

Chen

2019

Atmosphere

View full text Add to dashboard Cite

Mesoscale eddies are common in the ocean and their surface characteristics have been well revealed based on altimetric observations. Comparatively, the knowledge of the three-dimensional (3D) structure of mesoscale eddies is scarce, especially in the open ocean. In the present study, high-resolution field observations of a cyclonic eddy in the Kuroshio Extension have been carried out and the anatomy of the observed eddy is conducted. The temperature anomaly exhibits a vertical monopole cone structure with a maximum of −7.3 • C located in the main thermocline. The salinity anomaly shows a vertical dipole structure with a fresh anomaly in the main thermocline and a saline anomaly in the North Pacific Intermediate Water (NPIW). The cyclonic flow displays an equivalent barotropic structure. The mixed layer is deep in the center of the eddy and thin in the periphery. The seasonal thermocline is intensified and the permanent thermocline is upward domed by 350 m. The subtropical mode water (STMW) straddled between the seasonal and permanent thermoclines weakens and dissipates in the eddy center. The salinity of NPIW distributed along the isopycnals shows no significant difference inside and outside the eddy. The geostrophic relation is approximately set up in the eddy. The nonlinearity-defined as the ratio between the rotational speed to the translational speed-is 12.5 and decreases with depth. The eddy-wind interaction is examined by high resolution satellite observations. The results show that the cold eddy induces wind stress aloft with positive divergence and negative curl. The wind induced upwelling process is responsible for the formation of the horizontal monopole pattern of salinity, while the horizontal transport results in the horizontal dipole structure of temperature in the mixed layer. species composition (EDDIES) in the Sargasso Sea off Bermuda [5], meso-and submesoscale processes in an intense front (AlborEx) [6] and the northwestern Pacific eddies, internal waves and mixing Experiment (NPEIM) [7], and so forth. Nowadays, main observation methods for field experiment include Argo floats, moored instrumentation, underwater gliders and shipboard survey.Argo profiling floats, which are designed to measure underwater ocean temperature and salinity (T/S) [8], are one of the effective methods to obtain 3D mesoscale eddy structures [9][10][11][12][13]. However, due to the drift features, the detailed structure of a specific eddy is difficult to acquire unless a large number of Argo floats are deployed inside the targeted mesoscale eddy. Reference [14] deployed 17 rapid-sampling Argo floats to study the anticyclonic eddies effects on mode water subduction in the south of the Kuroshio Extension to the east of Japan. In situ mooring observations can usually collect temperature, salinity and current data from the bottom to the surface at a fixed-point where the eddy moves through. Reference [15] designed and conducted a multi-month field campaign to capture the full-depth 3D structure of a pair of anticyclonic and c...

show abstract

Section: Stmwmentioning

confidence: 99%

Anatomy of a Cyclonic Eddy in the Kuroshio Extension Based on High-Resolution Observations

Zhang

Chen

2019

Atmosphere

View full text Add to dashboard Cite

show abstract

“…An understanding of the formation and circulation of water masses will help to improve our knowledge of long‐term thermohaline changes and variations in the upper ocean. Recently, the role of eddies in water mass formation (e.g., Kouketsu et al, ) and spreading (e.g., Shi et al, ; Zhang et al, ) has been recognized. To develop our understanding of long‐term changes in the upper ocean, further examination of the formation, circulation, and dissipation of water masses using both observational data and eddy‐resolving models will be useful.…”

Section: Summary and Discussionmentioning

confidence: 99%

“…The θ anomaly derived from MLT in the outcrop region is detected widely on the isopycnal surface at lags of 2 and 3 years (Figures c and d), suggesting a rapid southward spread of the θ anomalies. Since eddy activity is elevated in the western to central part of the subtropical gyre compared to the eastern part (e.g., Qiu & Chen, ), mesoscale eddies (Shi et al, ; Zhang et al, ) and/or submesoscale phenomena may play important roles in the rapid distribution of the θ anomalies. The high‐correlation regions shrink to the east of 150°E at lags of 4 and 5 years and do not reach regions farther west (Figures e and f).…”

Section: Mechanism Of Long‐term Variationsmentioning

confidence: 99%

“…On the surfaces σ θ = 23.5, 24.0, and 24.5 kg m −3 that correspond to NPTW in the southern part of the subtropical gyre, both θ and S have a decadal variation, with maxima around 2004and minima around 1998, 2008, and 2018). The S variations on the NPTW surfaces are similar to the S variation in the salinity maximum region on the pressure coordinate (region 2) ( Figure 3b) in terms of both phase and amplitude.…”

Section: North Pacific Tropical Water (Nptw)mentioning

confidence: 99%

See 1 more Smart Citation

Long‐Term Thermohaline Variations in the North Pacific Subtropical Gyre From a Repeat Hydrographic Section Along 165°E

et al. 2020

View full text Add to dashboard Cite

Long-term thermohaline variability in the North Pacific subtropical gyre for 1996-2018 was investigated by repeat hydrography along 165°E conducted by the Japan Meteorological Agency. Potential temperature (θ) and salinity (S) in North Pacific Tropical Water (NPTW), characterized by the salinity maximum, exhibit an interannual or longer-timescale variation with significant warming and salinification. The θ-S of NPTW originates from mixed layer temperature (MLT) and salinity (MLS) in the isopycnal outcrop region. In the NPTW formation region, the MLS determines surface density and controls the meridional position of the outcrop region. High (low) MLS and the associated southward (northward) migration of the outcrop region increase (decrease) θ-S anomalies in NPTW. The θ-S in the main thermocline/halocline associated with subtropical mode water (STMW) shows a decadal-scale variation, with a significant cooling and freshening. These properties also derive from MLT and MLS in the isopycnal outcrop region. In the central North Pacific, including the eastern part of the STMW formation region, the MLT controls meridional migration of the outcrop region; during high (low) MLT, the outcrop region migrates northward (southward), and cold and fresh (warm and salty) STMW is formed. The signals are passed into the main thermocline/halocline through subduction of STMW. Consideration of the mechanism that generates θ-S anomalies via migration of the outcrop regions leads us to suggest surface warming and salinification in the subtropical gyre associated with global warming cause a cooling and freshening in the main thermocline/halocline and warming and salinification in NPTW, respectively. Plain Language Summary Thermohaline (potential temperature (θ) and salinity (S)) changes and variations in the upper ocean are essential elements of climate variability. Monitoring and understanding of the ocean variability are necessary to predict the coming climate changes and adapt to them. We examine the long-term thermohaline changes and variations in subsurface layers of the North Pacific subtropical gyre using shipboard observations along a section at 165°E. Significant warming and salinification in North Pacific Tropical Water, which is the saltiest water in the North Pacific, and a cooling and freshening in the main thermocline/halocline are detected. In addition, in those regions, θ and S fluctuate on an interannual to decadal timescale. The thermohaline variations in the subsurface layers originate in the surface mixed layer in the central part of the North Pacific. The θ -S anomalies that form in the mixed layer are transported into the subsurface ocean and circulate in the anticyclonic North Pacific subtropical gyre along isopycnal (i.e., isentropic) surfaces. Furthermore, through this subduction process, large-scale long-term changes at the ocean surface associated with global warming, such as warming and salinification in the North Pacific subtropical gyre, can change the thermohaline structure in the subsurface ocean.

show abstract

“…The other is the southward translation of the anticyclone itself, which accompanies large volume of low PV water. Shi et al () compared the differences between different mesoscale oceanic eddies based on the shape of their isopycnals in transporting the STMW. Liu and Peiliang () found that in the nongeneration months (from May to Dec), the “trapped depth” of the anticyclone is deeper than that of the cyclone, namely, the anticyclone can trap thicker STMW to its center and then transports it southward.…”

Section: Introductionmentioning

confidence: 99%

Different Influences of Mesoscale Oceanic Eddies on the North Pacific Subsurface Low Potential Vorticity Water Mass Between Winter and Summer

Wen

Song

et al. 2020

JGR Oceans

View full text Add to dashboard Cite

The generation and dissipation of North Pacific subsurface low potential vorticity water mass (SLPVW) affect various ocean-atmosphere dynamic and thermodynamic processes on a wide range of time scales. Mesoscale oceanic eddies are believed to play an important role in the variation of SLPVW. National Centers for Environmental Prediction (NCEP)/NCEP-Climate Forecast System Reanalysis coupled data set during 1979-2010 has been analyzed to investigate the different influences of mesoscale oceanic eddies on the SLPVW between winter and summer. It is found that the correlation between the sea surface height and SLPVW volume in winter is positive on the north of 30°N but negative on the south of 30°N, which is mainly caused by the eddy vorticity strength. The negative correlation value region has more strong anticyclones than the positive correlation value region, so the mixed layer depth in the negative (positive) correlation value region tends to be deeper (shallower) caused by stronger (weaker) anticyclones, which leads to the decreasing (increasing) of the low PV water mass under mixed layer depth (namely, SLPVW). Eddies also have obvious impacts on the subduction rate. The climatological eddy subduction rate can reach to 1.88 Sv in the NCEP-Climate Forecast System Reanalysis, which accounts for 36.4% of the total subduction rate. In summer, the correlation between the sea surface height and SLPVW volume is remarkably negative. It is found that water diverges (converges) in the composite anticyclone (cyclone), which leads to the increasing (decreasing) of PV value in the composite anticyclone (cyclone), finally accelerates (hinders) the dissipation of SLPVW. Plain Language SummaryThe study researched different influences of mesoscale oceanic eddies on the North Pacific subsurface low potential vorticity water mass (SLPVW) between winter and summer. The results revealed that eddies influence the formation of low potential vorticity water by changing turbulent heat flux in winter. Moreover, it is found that the relationship between oceanic eddies and SLPVW volume is influenced by the eddy vorticity strength. The mixed layer depth in the stronger (weaker) anticyclones tends to be deeper (shallower), which leads to the increasing (decreasing) of the low PV water mass but decreasing (increasing) of the low PV water mass under mixed layer depth (namely, SLPVW). The subduction rate varies greatly from year to year, suggesting the role of the interannual variation of eddies. In summer, the rotation of the eddies leads to the convergence and divergence, thus changing the stratification of the ocean and ultimately affecting the dissipation of SLPVW. The results might give the new insight to studies the role of mesoscale eddies on SLPVW, which have important implications for North Pacific climate scientists and predictions.

show abstract

Volume and Transport of Eddy‐Trapped Mode Water South of the Kuroshio Extension

Cited by 15 publications

References 33 publications

Anatomy of a Cyclonic Eddy in the Kuroshio Extension Based on High-Resolution Observations

Anatomy of a Cyclonic Eddy in the Kuroshio Extension Based on High-Resolution Observations

Long‐Term Thermohaline Variations in the North Pacific Subtropical Gyre From a Repeat Hydrographic Section Along 165°E

Different Influences of Mesoscale Oceanic Eddies on the North Pacific Subsurface Low Potential Vorticity Water Mass Between Winter and Summer

Contact Info

Product

Resources

About