Journal of Physical Oceanography最新文献

{"title":"Eddy acceleration and decay driven by internal tides","authors":"Callum J. Shakespeare","doi":"10.1175/jpo-d-23-0127.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0127.1","url":null,"abstract":"Abstract Recent observations and numerical simulations have demonstrated the potential for significant interactions between mesoscale eddies and smaller-scale tidally generated internal waves — also known as internal tides. Here we develop a simple theoretical model that predicts the one-way upscale transfer of energy from internal tides to mesoscale eddies through a critical level mechanism. We find that — in the presence of a critical level — the internal tide energy flux into an eddy is partitioned according to the wave frequency Ω and local inertial frequency f : a fraction of 1 – f /Ω is transferred to the eddy kinetic energy while the remainder is viscously dissipated or supports mixing. These predictions are validated by comparison with a suite of numerical simulations. The simulations further show that the wave-driven energisation of the eddies also accelerates the onset of hydrodynamical instabilities and the break down of the eddies, thereby increasing eddy kinetic energy, but reducing eddy lifetimes. Our estimates suggest that in regions of the ocean with both significant eddy fields and internal tides—such as parts of the Gulf Stream and Antarctic Circumpolar Current—the critical level effect could drive a ∼10% per month increase in the kinetic energy of a typical eddy. Our results provide a basis for parameterising internal tide-eddy interactions in global ocean models where they are currently unrepresented.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":"6 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135592432","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Vertical Exchange Induced by Mixed-Layer Instabilities","authors":"Yangcheng Luo, Jörn Callies","doi":"10.1175/jpo-d-23-0059.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0059.1","url":null,"abstract":"Abstract Submesoscale turbulence in the upper ocean consists of fronts, filaments, and vortices that have horizontal scales of order 100 m to 10 km. High-resolution numerical simulations have suggested that submesoscale turbulence is associated with strong vertical motion that could substantially enhance the vertical exchange between the thermocline and mixed layer, which may have an impact on marine ecosystems and climate. Theoretical, numerical, and observational work indicates that submesoscale turbulence is energized primarily by baroclinic instability in the mixed layer, which is most vigorous in winter. This study demonstrates how such mixed-layer baroclinic instabilities induce vertical exchange by drawing filaments of thermocline water into the mixed layer. A scaling law is proposed for the dependence of the exchange on environmental parameters. Linear stability analysis and nonlinear simulations indicate that the exchange, quantified by how much thermocline water is entrained into the mixed layer, is proportional to the mixed-layer depth, is inversely proportional to the Richardson number of the thermocline, and increases with increasing Richardson number of the mixed layer. The results imply that the tracer exchange between the thermocline and mixed layer is more efficient when the mixed layer is thicker, when the mixed-layer stratification is stronger, when the lateral buoyancy gradient is stronger, and when the thermocline stratification is weaker. The scaling suggests vigorous exchange between the permanent thermocline and deep mixed layers in winter, especially in mode water formation regions.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":"8 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135591473","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Effects of Wind Stress Uncertainty on Short-term Prediction of the Kuroshio Extension State Transition Process","authors":"Hui Zhang, Qiang Wang, Mu Mu, Kun Zhang, Yu Geng","doi":"10.1175/jpo-d-23-0047.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0047.1","url":null,"abstract":"Abstract Based on the Conditional Nonlinear Optimal Perturbation for boundary condition method and Regional Ocean Modeling System (ROMS), this study investigates the influence of wind stress uncertainty on predicting the short-term state transitions of the Kuroshio Extension (KE). The optimal time-dependent wind stress errors that lead to maximum prediction errors are obtained for two KE stable-to-unstable and two reverse transitions, which exhibit local multi-eddies structures with decreasing magnitude as the end time of prediction approaches. The optimal boundary errors initially induce small oceanic errors through Ekman pumping. Subsequently, these errors grow in magnitude as oceanic internal processes take effect, which exerts significant influences on the short-term prediction of the KE state transition process. Specifically, during stable-to-unstable (unstable-to-stable) transitions, the growing error induces an overestimation (underestimation) of the meridional sea surface height gradient across the KE axis, leading to the predicted KE state being more (less) stable. Furthermore, the dynamics mechanism analysis indicates that barotropic instability is crucial for the error growth in the prediction of both the stable-to-unstable and the reverse transition processes due to the horizontal shear of flow field. But work generated by wind stress error plays a more important role in the prediction of the unstable-to-stable transitions because of the synergistic effect of strong wind stress error and strong oceanic error. Eventually, the sensitive areas have been identified based on the optimal boundary errors. Reducing wind stress errors in sensitive areas can significantly improve prediction skills, offering theoretical guidance for devising observational strategies.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":"8 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135592438","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Enhanced Dissipation of Internal Tides in a Mesoscale Baroclinic Eddy","authors":"Yang Wang, Sonya Legg","doi":"10.1175/jpo-d-23-0045.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0045.1","url":null,"abstract":"Abstract The dissipation of low-mode internal tides as they propagate through mesoscale baroclinic eddies is examined using a series of numerical simulations, complemented by three-dimensional ray tracing calculations. The incident mode-1 internal tide is refracted into convergent energy beams, resulting in a zone of reduced energy flux in the lee of the eddy. The dissipation of internal tides is significantly enhanced in the upper water column within strongly baroclinic (anticyclonic) eddies, exhibiting a spatially asymmetric pattern, due to trapped high-mode internal tides. Where the eddy velocity opposes the internal tide propagation velocity, high-mode waves can be trapped within the eddy, whereas high modes can freely propagate away from regions where eddy and internal wave velocities are in the same direction. The trapped high modes with large vertical shear are then dissipated, with the asymmetric distribution of trapping leading to the asymmetric distribution of dissipation. Three-dimensional ray tracing solutions further illustrate the importance of the baroclinic current for wave trapping. Similar enhancement of dissipation is also found for a baroclinic cyclonic eddy. However, a barotropic eddy is incapable of facilitating robust high modes and thus cannot generate significant dissipation of internal tides, despite its strong velocities. Both energy transfer from low to high modes in the baroclinic eddy structure and trapping of those high modes by the eddy velocity field are therefore necessary to produce internal wave dissipation, a conclusion confirmed by examining the sensitivity of the internal tide dissipation to eddy radius, vorticity, and vertical scale. Significance Statement The oceanic tides drive underwater waves at the tidal frequency known as internal tides. When these waves break, or dissipate, they can lead to mixing of oceanic heat and salt which impacts the ocean circulation and climate. Accurate climate predictions require computer models that correctly represent the distribution of this mixing. Here we explore how an oceanic eddy, a swirling vortex of order 100–400 km across, can locally enhance the dissipation of oceanic internal tides. We find that strong ocean eddies can be hotspots for internal tide dissipation, for both clockwise and anticlockwise rotating vortices, and surface-enhanced eddies are most effective at internal tide dissipation. These results can improve climate model representations of tidally driven mixing, leading to more credible future predictions.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":"35 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134976791","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Local mixing determines spatial structure of diahaline exchange flow in a mesotidal estuary – a study of extreme runoff conditions","authors":"Lloyd Reese, Ulf Gräwe, Knut Klingbeil, Xiangyu Li, Marvin Lorenz, Hans Burchard","doi":"10.1175/jpo-d-23-0052.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0052.1","url":null,"abstract":"Abstract Salt mixing enables the transport of water between the inflow and outflow layers of estuarine circulation and therefore closes the circulation by driving a diahaline exchange flow. A recently derived universal law links the salt mixing inside an estuarine volume bounded by an isohaline surface to freshwater discharge: it states that on long-term average, the area-integrated mixing across the bounding isohaline is directly proportional to the freshwater discharge entering the estuary. However, even though numerous studies predict that periods of extreme discharge will become more frequent with climate change, the direct impact of such periods on estuarine mixing and circulation has yet to be investigated. Therefore, this numerical modeling study focuses on salinity mixing and diahaline exchange flows during a low-discharge and an extreme high-discharge period. To this end, we apply a realistic numerical setup of the Elbe estuary in northern Germany, using curvilinear coordinates that follow the navigational channel. This is the first time the direct relationship between diahaline exchange flow and salt mixing as well as the spatial distribution of the diahaline exchange flow are shown in a realistic tidal setup. The spatial distribution is highly correlated with the local mixing gradient for salinity, such that inflow occurs near the bottom at the upstream end of the isohaline. Meanwhile, outflow occurs near the surface at its downstream end. Lastly, increased vertical stratification occurs within the estuary during the high-discharge period, while estuarine-wide mixing strongly converges to the universal law for averaging periods of the discharge event time scale.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":"2015 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135200012","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The current feedback on stress modifies the Ekman buoyancy flux at fronts","authors":"Jacob O. Wenegrat","doi":"10.1175/jpo-d-23-0005.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0005.1","url":null,"abstract":"Abstract Ocean surface currents introduce variations into the surface wind-stress that can change the component of the stress aligned with the thermal wind shear at fronts. This modifies the Ekman buoyancy flux, such that the current feedback on the stress tends to generate an effective flux of buoyancy and potential vorticity to the mixed-layer. Scaling arguments and idealized simulations resolving both mesoscale and submesoscale turbulence suggest that this pathway for air-sea interaction can be important both locally at individual submesoscale fronts with strong surface currents—where it can introduce equivalent advective heat fluxes exceeding several hundredWm −2 —and in the spatial mean where it reduces the integrated Ekman buoyancy flux by approximately 50%. The accompanying source of surface potential vorticity injection suggests that at some fronts the current feedback modification of the Ekman buoyancy flux may be significant in terms of both submesoscale dynamics and boundary layer energetics, with an implied modification of symmetric instability growth rates and dissipation that scales similarly to the energy lost through the negative wind work generated by the current feedback. This provides an example of how the shift of dynamical regimes into the submesoscale may promote the importance of air-sea interaction mechanisms that differ from those most active at larger scale.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":"82 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135536479","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A rigorous derivation of the Water Mass Transformation framework, the relation between mixing and dia-surface exchange flow, and links to recent theories in estuarine research","authors":"Knut Klingbeil, Erika Henella","doi":"10.1175/jpo-d-23-0130.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0130.1","url":null,"abstract":"Abstract In this paper we present the analytical derivation of a local Water Mass Transformation (WMT) framework for an individual water column. We exactly formulate the mapping of the governing equations from geopotential coordinates to an arbitrary tracer space. Unique definitions for the local effective vertical dia-surface fluxes are given. In tracer space we derive new relations between the local dia-tracer fluxes and the mixing per tracer class. The key relation between the effective vertical dia-tracer velocity and the mixing per tracer class directly formulates how the overturning circulation is linked to local tracer variance dissipation. Horizontal integration of the governing equations in tracer space and the relations between the dia-tracer quantities finally recovers the well-known integral WMT formulations.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":"116 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135815969","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Reflection and Scattering of Low-mode Internal Tides on the Continental Slope of the South China Sea","authors":"Wei Li, Xiaohui Xie","doi":"10.1175/jpo-d-23-0087.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0087.1","url":null,"abstract":"Abstract It is well known that strong low-mode internal tides generated in Luzon Strait propagate westward to impinge continental slopes in the northeastern South China Sea (SCS). The reflection and scattering of these internal tides including diurnal and semidiurnal components on the slopes are quantitatively investigated using two sets of mooring data and a linear internal tide model with realistic topography and stratification. Flux reflections computed from mooring data collected on the continental slopes are consistent with the linear model. Based on the results of the observations and simulations, a map of low-mode internal tide reflection and scattering coefficients along the continental margin in the northeastern SCS is revealed. On average, diurnal internal tides lose 38% of their energy to high modes (≥ mode-4) that are assumed to dissipate on the slopes, transmit 28% onto the continental shelf, and reflect 31% back to the deep ocean. On the contrary, most of the semidiurnal energy (89%) transmit onto the continental shelf, and only 11% is scattered to high modes (7%), and reflected back to the deep ocean (4%). For diurnal internal tides, a large fraction of energy that is scattered to high modes and reflected back to the deep sea can be attributed to the critical-supercritical slopes, while the weak reflection for the semidiurnal energy is due to the subcritical slopes. These quantitative descriptions for evolutions of low-mode internal tides incident to the slopes provide an energy budget map on the continental slopes in the northeastern SCS.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":"133 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136313135","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Propagation Features of Diurnal Internal Tides West of the Luzon Strait Revealed by a Large PIES Array","authors":"Min Wang, Xiao-Hua Zhu, Hua Zheng, Juntian Chen, Ruixiang Zhao, Zhao-Jun Liu, Qiang Ren, Yansong Liu, Feng Nan, Fei Yu, Jianfeng Wang, Qiang Li","doi":"10.1175/jpo-d-22-0206.1","DOIUrl":"https://doi.org/10.1175/jpo-d-22-0206.1","url":null,"abstract":"Abstract Energetic internal tides (ITs) are generated from the Luzon Strait (LS) and propagate westward into the South China Sea (SCS). Owing to the lack of large-scale synchronous measurements, the propagation features and seasonal variations of diurnal ITs remain unclear. From 2018 to 2019, mode-1 diurnal ITs west of the LS were continuously observed using a large-scale moored array of 27 pressure inverted echo sounders (PIESs) and a thermistor chain. Measurements confirmed that diurnal ITs radiate from the LS with a north–south asymmetrical pattern, with the most energetic channel located in the middle and south of the LS. The total energy radiated into the SCS across 120°E is 2.67 GW for the K 1 and 1.54 GW for O 1 ITs, approximately two times larger than those inferred from satellite observations. K 1 dominates among the diurnal ITs, with its maximum isopycnal displacement (amplitude) and energy input to the SCS being the strongest in summer (i.e., 16.3 m and 2.81 GW, respectively). The propagation speed of K 1 is higher in summer and autumn along the main channel (i.e., 4.33 and 4.36 m s −1 , respectively). Seasonal stratification and circulation play important roles in the seasonal variation of amplitude and propagation speed of the K 1 ITs. The seasonal variability of diurnal-band ITs, which includes all diurnal constituents, is location-dependent and primarily results from the superposition of the K 1 and P 1 ITs. In particular, vertical displacement is strong in summer and winter along the main channel of the K 1 and P 1 ITs. The seasonal amplitude of K 1 can modulate this seasonal feature.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":"213 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134913035","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Mixing processes at the southwestern entrance to the Japan/East Sea","authors":"Hemantha W. Wijesekera, Conrad A. Luecke, David W. Wang, Ewa Jarosz, Sergio DeRada, William J. Teague, Kyung-Il Chang, Jae Hak Lee, Hong-Sik Min, SungHyun Nam","doi":"10.1175/jpo-d-23-0061.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0061.1","url":null,"abstract":"Abstract Small-scale processes at the southwestern boundary of the Ulleung Basin (UB) in the Japan/East Sea (JES) were examined using combined ship-based and moored observations along with model output. Model results show baroclinic semidiurnal tides are generated at the shelf break and corresponding slope connecting the Korea/Tsushima Strait with the UB, and propagate into the UB with large barotropic to baroclinic energy conversion over the slope. Observations show high-frequency internal-wave packets and indicate strong velocity shear and energetic turbulence associated with baroclinic tides in the stratified bottom-layer. Solitary-like waves with frequencies 0.2 N to 0.5 N (buoyancy frequency, N ) were found at the edge of the shelf break with supercritical flow. For subcritical flow, a hydraulic jump formed over the shelf break with weakly-dispersive internal lee waves with frequencies varying from 0.5 N to N . These high-frequency lee waves were trapped in the stratified bottom-layer, with wave stress similar to the turbulent stress near the bottom. The power loss due to turbulent bottom drag can be an important factor for energy loss associated with the hydraulic jump. Turbulent-kinetic-energy dissipation rates of ~10 −4 W kg −1 were found. Large downward heat and salt fluxes below the high-salinity core mix warm/salty Tsushima Current Water with cold/low-salinity JES intermediate water. Mixing over the shelf break could be very important to the JES circulation since the calculated diapycnal upwelling (1-6 m d −1 ) at the shelf break and slope is substantially greater than the basin-averaged estimate from chemical tracers and modeling studies.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":"8 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135740865","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}