The generation of internal tides at coastal margins is an important mechanism for the loss of energy from the barotropic tide. Although some previous studies attempted to quantify energy loss from the barotropic tides into the deep ocean, global estimates are complicated by the coastal geometry and spatially and temporally variable stratification. Here, we explore the effects of supercritical, finite amplitude bottom topography, which is difficult to solve analytically. We conduct a suite of 2D linear numerical simulations of the barotropic tide interacting with a uniform along-shore coastal shelf, representing the tidal forcing by a body force derived from the vertical displacement of the isopycnals by the gravest coastal trapped wave (of which a Kelvin wave is a close approximation). We explore the effects of latitude, topographic parameters, and non-uniform stratification on the baroclinic tidal energy flux propagating into the deep ocean away from the shelf. By varying the pycnocline depth and thickness, we extend previous studies of shallow and infinitesimally thin pycnoclines to include deep permanent pycnoclines. We find that scaling laws previously derived in terms of continental shelf width and depth for shallow and thin pycnoclines generally hold for the deeper and thicker pycnoclines considered in this study. We also find baroclinic tidal energy flux is more sensitive to topographic than stratification parameters. Interestingly, we find that the slope of the shelf itself to be an important parameter, but not the width of the continental slope in the case of these steep topographies.
{"title":"Internal tides at the coast: energy flux of baroclinic tides propagating into the deep ocean in the presence of supercritical shelf topography","authors":"Varvara E. Zemskova, R. C. Musgrave, J. Lerczak","doi":"10.1175/jpo-d-23-0164.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0164.1","url":null,"abstract":"\u0000The generation of internal tides at coastal margins is an important mechanism for the loss of energy from the barotropic tide. Although some previous studies attempted to quantify energy loss from the barotropic tides into the deep ocean, global estimates are complicated by the coastal geometry and spatially and temporally variable stratification. Here, we explore the effects of supercritical, finite amplitude bottom topography, which is difficult to solve analytically. We conduct a suite of 2D linear numerical simulations of the barotropic tide interacting with a uniform along-shore coastal shelf, representing the tidal forcing by a body force derived from the vertical displacement of the isopycnals by the gravest coastal trapped wave (of which a Kelvin wave is a close approximation). We explore the effects of latitude, topographic parameters, and non-uniform stratification on the baroclinic tidal energy flux propagating into the deep ocean away from the shelf. By varying the pycnocline depth and thickness, we extend previous studies of shallow and infinitesimally thin pycnoclines to include deep permanent pycnoclines. We find that scaling laws previously derived in terms of continental shelf width and depth for shallow and thin pycnoclines generally hold for the deeper and thicker pycnoclines considered in this study. We also find baroclinic tidal energy flux is more sensitive to topographic than stratification parameters. Interestingly, we find that the slope of the shelf itself to be an important parameter, but not the width of the continental slope in the case of these steep topographies.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140749546","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}
Data from an air-sea interaction tower are used to close the turbulent kinetic energy (TKE) budget in the wave-affected surface layer of the upper ocean. Under energetic wind forcing with active wave breaking, the dominant balance is between the dissipation rate of TKE and the downward convergence in vertical energy flux. The downward energy flux is driven by pressure work, and the TKE transport is upward, opposite to the downgradient assumption in most turbulence closure models. The sign and the relative magnitude of these energy fluxes are hypothesized to be driven by an interaction between the vertical velocity of Langmuir circulation (LC) and the kinetic energy and pressure of wave groups, which is the result of small-scale wave-current interaction. Consistent with previous modeling studies, the data suggest that the horizontal velocity anomaly associated with LC refracts wave energy away from downwelling regions and into upwelling regions, resulting in negative covariance between the vertical velocity of LC and the pressure anomaly associated with the wave groups. The asymmetry between downward pressure work and upward TKE flux is explained by the Bernoulli response of the sea surface, which results in groups of waves having a larger pressure anomaly than the corresponding kinetic energy anomaly, consistent with group-bound long wave theory.
{"title":"Vertical Energy Fluxes Driven by the Interaction Between Wave Groups and Langmuir Turbulence","authors":"M. E. Scully, Seth F. Zippel","doi":"10.1175/jpo-d-23-0193.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0193.1","url":null,"abstract":"\u0000Data from an air-sea interaction tower are used to close the turbulent kinetic energy (TKE) budget in the wave-affected surface layer of the upper ocean. Under energetic wind forcing with active wave breaking, the dominant balance is between the dissipation rate of TKE and the downward convergence in vertical energy flux. The downward energy flux is driven by pressure work, and the TKE transport is upward, opposite to the downgradient assumption in most turbulence closure models. The sign and the relative magnitude of these energy fluxes are hypothesized to be driven by an interaction between the vertical velocity of Langmuir circulation (LC) and the kinetic energy and pressure of wave groups, which is the result of small-scale wave-current interaction. Consistent with previous modeling studies, the data suggest that the horizontal velocity anomaly associated with LC refracts wave energy away from downwelling regions and into upwelling regions, resulting in negative covariance between the vertical velocity of LC and the pressure anomaly associated with the wave groups. The asymmetry between downward pressure work and upward TKE flux is explained by the Bernoulli response of the sea surface, which results in groups of waves having a larger pressure anomaly than the corresponding kinetic energy anomaly, consistent with group-bound long wave theory.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140795154","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}
The ocean surrounding Antarctica, also known as the Antarctic margins, is characterised by complex and heterogeneous process interactions which have major impacts on the global climate. A common way to understand changes in the Antarctic margins is to categorise regions into similar ‘regimes’, thereby guiding process-based studies and observational analyses. However, this categorisation is traditionally largely subjective and based on temperature, density and bathymetric criteria that are bespoke to the dataset being analysed. In this work, we introduce a method to classify Antarctic shelf regimes using unsupervised learning. We apply Gaussian Mixture Modelling to the across-shelf temperature and salinity properties along the Antarctic margins from a high-resolution ocean model, ACCESS-OM2-01. Three clusters are found to be optimum based on the Bayesian Information Criterion and an assessment of regime properties. The three clusters correspond to the fresh, dense and warm regimes identified canonically via subjective approaches. Our analysis allows us to track changes to these regimes in a future projection of the ACCESS-OM2-01 model. We identify the future collapse of dense water formation, and the merging of dense and fresh shelf regions into a single fresh regime that covers the entirety of the Antarctic shelf except for the West Antarctic. Our assessment of these clusters indicates that the Antarctic margins may shift into a two-regime system in the future, consisting only of a strengthening warm shelf in the West Antarctic and a fresh shelf regime everywhere else.
{"title":"Unsupervised classification identifies warm, fresh and dense regimes of the Antarctic margins","authors":"T. Sohail, J.D. Zika","doi":"10.1175/jpo-d-23-0153.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0153.1","url":null,"abstract":"\u0000The ocean surrounding Antarctica, also known as the Antarctic margins, is characterised by complex and heterogeneous process interactions which have major impacts on the global climate. A common way to understand changes in the Antarctic margins is to categorise regions into similar ‘regimes’, thereby guiding process-based studies and observational analyses. However, this categorisation is traditionally largely subjective and based on temperature, density and bathymetric criteria that are bespoke to the dataset being analysed. In this work, we introduce a method to classify Antarctic shelf regimes using unsupervised learning. We apply Gaussian Mixture Modelling to the across-shelf temperature and salinity properties along the Antarctic margins from a high-resolution ocean model, ACCESS-OM2-01. Three clusters are found to be optimum based on the Bayesian Information Criterion and an assessment of regime properties. The three clusters correspond to the fresh, dense and warm regimes identified canonically via subjective approaches. Our analysis allows us to track changes to these regimes in a future projection of the ACCESS-OM2-01 model. We identify the future collapse of dense water formation, and the merging of dense and fresh shelf regions into a single fresh regime that covers the entirety of the Antarctic shelf except for the West Antarctic. Our assessment of these clusters indicates that the Antarctic margins may shift into a two-regime system in the future, consisting only of a strengthening warm shelf in the West Antarctic and a fresh shelf regime everywhere else.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140384904","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}
The seasonal and interannual variations of the Mindanao Current retroflection are studied using surface geostrophic currents of satellite altimeters covering January 1993 through December 2019. The results show that the Mindanao Current mainstream retroflects back to the Pacific Ocean north of the Talaud Island in boreal summer, and intrudes into the northern Maluku Sea in boreal winter. The variation of the Mindanao Current retroflection has resulted in the seasonal movement of the sea surface color fronts at the entrance of the Indonesian seas, both of which are highly correlated to the seasonal transport variations of the North Equatorial Countercurrent, lagging the latter due to the westward propagation of the seasonal Rossby waves. The MC retroflection and sea surface color fronts are found to move synchronously on interannual time scales at the Pacific entrance of the Indonesian seas, with the Niño 3.4 index lagging by about 2 months. The MC retroflection intrudes anomalously deeper than the seasonal cycle into the northern Maluku Sea in El Niño winters, while tends to take a leaping path in La Niña winters. During El Niño summers, the leaping path of the MC is changed into a penetrating path sometimes.
{"title":"Seasonal and interannual movement of the Mindanao Current retroflection at the Pacific entrance of the Indonesian seas","authors":"Kunxiang Wang, Dongliang Yuan, Kaixin Ren","doi":"10.1175/jpo-d-23-0125.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0125.1","url":null,"abstract":"\u0000The seasonal and interannual variations of the Mindanao Current retroflection are studied using surface geostrophic currents of satellite altimeters covering January 1993 through December 2019. The results show that the Mindanao Current mainstream retroflects back to the Pacific Ocean north of the Talaud Island in boreal summer, and intrudes into the northern Maluku Sea in boreal winter. The variation of the Mindanao Current retroflection has resulted in the seasonal movement of the sea surface color fronts at the entrance of the Indonesian seas, both of which are highly correlated to the seasonal transport variations of the North Equatorial Countercurrent, lagging the latter due to the westward propagation of the seasonal Rossby waves. The MC retroflection and sea surface color fronts are found to move synchronously on interannual time scales at the Pacific entrance of the Indonesian seas, with the Niño 3.4 index lagging by about 2 months. The MC retroflection intrudes anomalously deeper than the seasonal cycle into the northern Maluku Sea in El Niño winters, while tends to take a leaping path in La Niña winters. During El Niño summers, the leaping path of the MC is changed into a penetrating path sometimes.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-02-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140441067","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}
Y. Gong, Zhiwu Chen, Ruixiang Zhao, Jiexin Xu, Juan Li, Jiesuo Xie, Yinghui He, X. Zhu, Yuhan Sun, Shuqun Cai
Joint effects of winds and tides on near-inertial internal waves (NIWs) are numerically investigated via a series of three-dimensional quasi-realistic simulations in the northern South China Sea (NSCS). Model results demonstrate that in the presence of wind-induced NIWs, more tidal energy is transferred to NIWs, while in the presence of tide-induced NIWs, the extreme wind (cyclone) would inject less near-inertial kinetic energy (NIKE). The interaction between wind-induced and tide-induced NIWs produces total NIKE more (or less) than a linear superposition of that generated by wind and tide forcing alone at different sites in the NSCS. Specifically, near the Luzon Strait, both tides and winds make positive contributions to the local near-inertial energy input, resulting in more than 30% enhancement of total NIKE (>0.5 kJ m−2). However, in some deep-water regions along the cyclone paths, energy is transferred from cyclones to NIWs and also from NIWs to internal tides. Due to this “energy pipeline” effect, tide- and wind-induced NIWs contribute to weakening of total NIKE (∼0.3 kJ m−2 or 30%). Additionally, sensitivity experiments with varying initial tidal phases indicate that the interaction between wind-induced NIKE and tide-induced NIKE is robust in most model domain (over 80%) under different phase alignments between wind- and tide-induced NIWs. From the perspective of cyclones, tide-induced NIKE is comparable to wind-induced NIKE in the Luzon Strait before the arrival of cyclones, while tide-induced NIKE is two orders of magnitude smaller than wind-induced NIKE in most of the NSCS after the arrival of cyclones. Overall, our results highlight the joint effects of wind and tide forcing on the local NIW dynamics in the NSCS.
{"title":"Joint Effects of Winds and Tides on Near-Inertial Internal Waves in the Northern South China Sea: A Three-Dimensional Numerical Study","authors":"Y. Gong, Zhiwu Chen, Ruixiang Zhao, Jiexin Xu, Juan Li, Jiesuo Xie, Yinghui He, X. Zhu, Yuhan Sun, Shuqun Cai","doi":"10.1175/jpo-d-23-0182.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0182.1","url":null,"abstract":"\u0000Joint effects of winds and tides on near-inertial internal waves (NIWs) are numerically investigated via a series of three-dimensional quasi-realistic simulations in the northern South China Sea (NSCS). Model results demonstrate that in the presence of wind-induced NIWs, more tidal energy is transferred to NIWs, while in the presence of tide-induced NIWs, the extreme wind (cyclone) would inject less near-inertial kinetic energy (NIKE). The interaction between wind-induced and tide-induced NIWs produces total NIKE more (or less) than a linear superposition of that generated by wind and tide forcing alone at different sites in the NSCS. Specifically, near the Luzon Strait, both tides and winds make positive contributions to the local near-inertial energy input, resulting in more than 30% enhancement of total NIKE (>0.5 kJ m−2). However, in some deep-water regions along the cyclone paths, energy is transferred from cyclones to NIWs and also from NIWs to internal tides. Due to this “energy pipeline” effect, tide- and wind-induced NIWs contribute to weakening of total NIKE (∼0.3 kJ m−2 or 30%). Additionally, sensitivity experiments with varying initial tidal phases indicate that the interaction between wind-induced NIKE and tide-induced NIKE is robust in most model domain (over 80%) under different phase alignments between wind- and tide-induced NIWs. From the perspective of cyclones, tide-induced NIKE is comparable to wind-induced NIKE in the Luzon Strait before the arrival of cyclones, while tide-induced NIKE is two orders of magnitude smaller than wind-induced NIKE in most of the NSCS after the arrival of cyclones. Overall, our results highlight the joint effects of wind and tide forcing on the local NIW dynamics in the NSCS.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-02-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140444161","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}
Shipboard ADCP velocity and towed CTD chain density measurements from the eastern North Pacific pycnocline are used to segregate energy between linear internal waves (IW) and linear vortical motion (quasi-geostrophy, QG) in 2-D wavenumber space spanning submesoscale horizontal wavelengths λx ∼ 1 – 50 km and finescale vertical wavelengths λz ∼ 7 – 100 m. Helmholtz decomposition and a new Burger-number Bu decomposition yield similar results despite different methodologies. Partition between IW and QG total energies depends on 𝐵𝑢. For Bu < 0.01, available potential energy EP exceeds horizontal kinetic energy EK and is contributed mostly by QG. In contrast, energy is nearly equipartitioned between QG and IW for Bu » 1. For Bu < 2, EK is contributed mainly by IW, and EP by QG, while, for Bu > 2, contributions are reversed. Vertical shear variance is contributed primarily by near-inertial IW at small λz, implying negligible QG contribution to vertical shear instability. Conversely, both QG and IW at the smallest λx ∼ 1 km contribute large horizontal shear variance, such that both may lead to horizontal shear instability. Both QG and IW contribute to vortex-stretching at small vertical scales. For QG, the relative vorticity contribution to linear potential vorticity anomaly increases with decreasing horizontal and increasing vertical scales.
利用对北太平洋东部pycnocline的船载ADCP速度和拖曳CTD链密度的测量结果，在二维波数空间中将能量分为线性内波（IW）和线性涡旋运动（准地动仪，QG），横跨亚目尺度水平波长λx ∼ 1 - 50千米和细目尺度垂直波长λz ∼ 7 - 100米。尽管方法不同，但亥姆霍兹分解和新的布尔格数布分解得到的结果相似。IW 和 QG 总能量的划分取决于 𝐵𝑢。当 Bu < 0.01 时，可用势能 EP 超过水平动能 EK，且主要由 QG 贡献。相反，当 Bu " 1 时，能量几乎在 QG 和 IW 之间均衡分配。当 Bu < 2 时，EK 主要由 IW 贡献，EP 由 QG 贡献，而当 Bu > 2 时，两者的贡献正好相反。在小λz时，垂直切变方差主要由近惯性IW贡献，这意味着QG对垂直切变不稳定性的贡献可以忽略不计。相反，在最小 λx ∼ 1 km 处，QG 和 IW 都贡献了很大的水平切变方差，因此两者都可能导致水平切变不稳定性。QG和IW都会导致小垂直尺度的涡旋伸展。就 QG 而言，随着水平尺度的减小和垂直尺度的增大，对线性潜在涡度异常的相对涡度贡献会增大。
{"title":"Energy partition between submesoscale internal waves and quasi-geostrophic vortical motion in the pycnocline","authors":"A. Vladoiu, R. Lien, Eric Kunze","doi":"10.1175/jpo-d-23-0090.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0090.1","url":null,"abstract":"\u0000Shipboard ADCP velocity and towed CTD chain density measurements from the eastern North Pacific pycnocline are used to segregate energy between linear internal waves (IW) and linear vortical motion (quasi-geostrophy, QG) in 2-D wavenumber space spanning submesoscale horizontal wavelengths λx ∼ 1 – 50 km and finescale vertical wavelengths λz ∼ 7 – 100 m. Helmholtz decomposition and a new Burger-number Bu decomposition yield similar results despite different methodologies. Partition between IW and QG total energies depends on 𝐵𝑢. For Bu < 0.01, available potential energy EP exceeds horizontal kinetic energy EK and is contributed mostly by QG. In contrast, energy is nearly equipartitioned between QG and IW for Bu » 1. For Bu < 2, EK is contributed mainly by IW, and EP by QG, while, for Bu > 2, contributions are reversed. Vertical shear variance is contributed primarily by near-inertial IW at small λz, implying negligible QG contribution to vertical shear instability. Conversely, both QG and IW at the smallest λx ∼ 1 km contribute large horizontal shear variance, such that both may lead to horizontal shear instability. Both QG and IW contribute to vortex-stretching at small vertical scales. For QG, the relative vorticity contribution to linear potential vorticity anomaly increases with decreasing horizontal and increasing vertical scales.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-02-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140449589","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}
Upper-ocean turbulence results from a complex set of interactions between submesoscale turbulence and local boundary layer processes. The interaction between larger-scale currents and turbulent fluctuations is two-way: large-scale shearing motions generate turbulence, and the resulting coherent turbulent fluxes of momentum and buoyancy feed back onto the larger flow. Here we examine the evolution and role of turbulence in the intensification, instability, arrest, and decay (i.e., the life cycle) of a dense filament undergoing frontogenesis in the upper-ocean boundary layer, i.e., cold filament frontogenesis (CFF). This phenomenon is examined in large-eddy simulations (LES) with resolved turbulent motions in large horizontal domains using 109 grid points. The boundary layer turbulence is generated by surface buoyancy loss (cooling flux) and is allowed to freely interact with an initially imposed cold filament, and the evolution is followed through the frontal life cycle. Two control parameters are explored: the initial frontal strength M2 = ∂xb and the surface flux . The former is more consequent: initially weaker fronts sharpen more slowly and become arrested at a later time with a larger width. This reflects a competition between the frontogenetic rate induced by the secondary circulation associated with vertical momentum mixing by the turbulence and the instability rate for the along-filament shear flow. The frontal turbulence is energized by the shear production of the latter, is nonlocally transported away from the primary production zone at the filament centerline, and cascades to dissipation in a broad region surrounding the filament. The turbulent momentum fluxes arresting the frontogenesis are supported across a wide range of horizontal scales.
{"title":"Oceanic Frontal Turbulence","authors":"Peter P. Sullivan, James C. McWilliams","doi":"10.1175/jpo-d-23-0033.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0033.1","url":null,"abstract":"\u0000Upper-ocean turbulence results from a complex set of interactions between submesoscale turbulence and local boundary layer processes. The interaction between larger-scale currents and turbulent fluctuations is two-way: large-scale shearing motions generate turbulence, and the resulting coherent turbulent fluxes of momentum and buoyancy feed back onto the larger flow. Here we examine the evolution and role of turbulence in the intensification, instability, arrest, and decay (i.e., the life cycle) of a dense filament undergoing frontogenesis in the upper-ocean boundary layer, i.e., cold filament frontogenesis (CFF). This phenomenon is examined in large-eddy simulations (LES) with resolved turbulent motions in large horizontal domains using 109 grid points. The boundary layer turbulence is generated by surface buoyancy loss (cooling flux) and is allowed to freely interact with an initially imposed cold filament, and the evolution is followed through the frontal life cycle. Two control parameters are explored: the initial frontal strength M2 = ∂xb and the surface flux . The former is more consequent: initially weaker fronts sharpen more slowly and become arrested at a later time with a larger width. This reflects a competition between the frontogenetic rate induced by the secondary circulation associated with vertical momentum mixing by the turbulence and the instability rate for the along-filament shear flow. The frontal turbulence is energized by the shear production of the latter, is nonlocally transported away from the primary production zone at the filament centerline, and cascades to dissipation in a broad region surrounding the filament. The turbulent momentum fluxes arresting the frontogenesis are supported across a wide range of horizontal scales.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139687009","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}
Jinghong Wang, Y. Shu, Dongxiao Wang, Ju Chen, Yang Yang, Weiqiang Wang, Binbin Guo, Ke Huang, Yunkai He
In the eastern off-equatorial Indian Ocean, deep current intraseasonal variability within a typical period of 10–20 days was revealed by a mooring at 5°N, 90.5°E, accounting for over 50% of the total bottom subtidal velocity variability. The 10–20-day oscillations were more energetic in the cross-isobathic direction (STD = 3.02 cm s−1) than those in the along-isobathic direction (STD = 1.50 cm s−1). The oscillations were interpreted as topographic Rossby waves (TRWs) because they satisfied the TRWs dispersion relation that considered the smaller Coriolis parameter and stronger β effect at low latitude. Further analysis indicated significant vertical coupling between the deep cross-slope oscillations and cross-isobathic 10–20-day perturbations at the depth of 300–950 m. The 10–20-day TRWs were generated by cross-isobathic motions under the potential vorticity conservation adjustment. The Mercator Ocean output reproduced the generation of kinetic energy (KE) of deep current variability. The associated diagnostic analysis of multiscale energetics showed that the KE of TRWs was mainly supplied by vertical pressure work. In the seamount region (2°–10°N, 89°–92°E), vertical and horizontal pressure works were identified to be the dominant energy source (contributing to 94% of the total KE source) and sink (contributing to 98% of the total KE sink) of the deep current variability, transporting energy downward and redistributing energy horizontally, respectively.
{"title":"Observed 10–20-Day Deep-Current Variability at 5°N, 90.5°E in the Eastern Indian Ocean","authors":"Jinghong Wang, Y. Shu, Dongxiao Wang, Ju Chen, Yang Yang, Weiqiang Wang, Binbin Guo, Ke Huang, Yunkai He","doi":"10.1175/jpo-d-23-0082.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0082.1","url":null,"abstract":"\u0000In the eastern off-equatorial Indian Ocean, deep current intraseasonal variability within a typical period of 10–20 days was revealed by a mooring at 5°N, 90.5°E, accounting for over 50% of the total bottom subtidal velocity variability. The 10–20-day oscillations were more energetic in the cross-isobathic direction (STD = 3.02 cm s−1) than those in the along-isobathic direction (STD = 1.50 cm s−1). The oscillations were interpreted as topographic Rossby waves (TRWs) because they satisfied the TRWs dispersion relation that considered the smaller Coriolis parameter and stronger β effect at low latitude. Further analysis indicated significant vertical coupling between the deep cross-slope oscillations and cross-isobathic 10–20-day perturbations at the depth of 300–950 m. The 10–20-day TRWs were generated by cross-isobathic motions under the potential vorticity conservation adjustment. The Mercator Ocean output reproduced the generation of kinetic energy (KE) of deep current variability. The associated diagnostic analysis of multiscale energetics showed that the KE of TRWs was mainly supplied by vertical pressure work. In the seamount region (2°–10°N, 89°–92°E), vertical and horizontal pressure works were identified to be the dominant energy source (contributing to 94% of the total KE source) and sink (contributing to 98% of the total KE sink) of the deep current variability, transporting energy downward and redistributing energy horizontally, respectively.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139684906","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}
The large scatter of the drag coefficient CD at a given wind speed and its discrepancy in coastal regions and open oceans have received increasing attention. However, the parameterization of CD is still an open question, especially in coastal regions. Therefore, this study systematically investigated the influence of surface waves on wind stress based on in situ observations of surface waves and air-sea fluxes on three coastal tower-based platforms in different regions. A formulation that is a function of only wind speed was established in the wind speed range of 1-20 m/s, and when extended to 30 m/s, it could predict the saturation of coastal CD at a 20 m/s wind speed and then the attenuation. However, this wind-based formulation does not simulate the scatter of CD in practice. By further analyzing the effect of wave states on wind stress, the parameters of wave age and directionality of wind and waves were incorporated into the wind-based formulation, and a new wave-state-based parameterization on CD was proposed, which can estimate the widely spread CD values to a large extent and the saturation of CD. The RMSE between this new parameterization and observations reduce approximately 20% and 9% relative to the COARE and wind-based formula. The applicability of this new parameterization was further demonstrated through a comparison between the newly parameterized CD and observed asymmetric CD in different quadrants of a tropical cyclone. The wave-state-based parameterization scheme requires three parameters, wind speed U10, wave age β, and wave off-wind angle θ, and it is expected to be applied to coastal regions.
在给定风速下，阻力系数 CD 的巨大分散性及其在沿岸地区和开阔大洋中的差异已受到 越来越多的关注。然而，CD 的参数化仍然是一个悬而未决的问题，尤其是在沿岸地区。因此，本研究根据在不同区域的三个沿岸塔式平台上对面波和海气通量的现场观测，系统地研究了面波对风应力的影响。在风速 1-20 m/s 范围内，建立了仅与风速有关的公式，当扩展到 30 m/s 时，可以预测风速 20 m/s 时沿岸 CD 的饱和度和衰减。然而，这种基于风速的公式并不能模拟实际中 CD 的散射。通过进一步分析波浪状态对风应力的影响，将波龄、风浪方向性等参数纳入基于风力的公式中，提出了一种新的基于波浪状态的 CD 参数化方法，可以在很大程度上估算出散布较广的 CD 值以及 CD 的饱和度。与 COARE 和基于风的公式相比，新参数化与观测值之间的均方根误差分别降低了约 20% 和 9%。通过比较新参数化 CD 和热带气旋不同象限的非对称 CD 观测值，进一步证明了这种新参数化的适用性。基于波浪状态的参数化方案需要三个参数，即风速 U10、波龄 β 和波浪离风角 θ。
{"title":"A New Wave-state-based Drag Coefficient Parameterization for Coastal Regions","authors":"Sheng Chen, Wen Zheng Jiang, Yuhuan Xue, Hongyu Ma, Yong Qing Yu, Zhanli Wang, Fangli Qiao","doi":"10.1175/jpo-d-23-0081.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0081.1","url":null,"abstract":"\u0000The large scatter of the drag coefficient CD at a given wind speed and its discrepancy in coastal regions and open oceans have received increasing attention. However, the parameterization of CD is still an open question, especially in coastal regions. Therefore, this study systematically investigated the influence of surface waves on wind stress based on in situ observations of surface waves and air-sea fluxes on three coastal tower-based platforms in different regions. A formulation that is a function of only wind speed was established in the wind speed range of 1-20 m/s, and when extended to 30 m/s, it could predict the saturation of coastal CD at a 20 m/s wind speed and then the attenuation. However, this wind-based formulation does not simulate the scatter of CD in practice. By further analyzing the effect of wave states on wind stress, the parameters of wave age and directionality of wind and waves were incorporated into the wind-based formulation, and a new wave-state-based parameterization on CD was proposed, which can estimate the widely spread CD values to a large extent and the saturation of CD. The RMSE between this new parameterization and observations reduce approximately 20% and 9% relative to the COARE and wind-based formula. The applicability of this new parameterization was further demonstrated through a comparison between the newly parameterized CD and observed asymmetric CD in different quadrants of a tropical cyclone. The wave-state-based parameterization scheme requires three parameters, wind speed U10, wave age β, and wave off-wind angle θ, and it is expected to be applied to coastal regions.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-01-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140494265","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}
Intrathermocline eddies (ITEs), characterized by subsurface lens-shaped low potential vorticity (PV), are pervasive in the ocean. However, the abundance and generation mechanisms of these low-PV lenses are poorly understood owing to their weak surface signals and awkward sizes, which present an observational barrier. Using in-situ observations of the northern South China Sea (NSCS), a typical ITE with a lens-shaped low PV at a core depth of 30-150 m and a horizontal size of ~150 km was captured in May 2021. Combined with PV budget analysis, we investigate the underlying generation mechanism of low PVs within these ITEs using high-resolution reanalysis products. The results suggest that wintertime surface buoyancy loss driven by atmospheric diabatic forcing rather than frictional forcing is a crucial favorable condition for the ITE formation. These enhanced surface buoyancy losses produce a net upward PV flux and decrease PV in the weakly-stratified and deep winter mixed layer, which are preconditioned by anticyclonic eddies (AEs). While surface heating in the following spring tends to weaken the surface buoyancy loss and gradually causes a downward PV flux, the surface-injected high PV subsequently caps the low-PV water within the surface-intensified AEs and transforms them into ITEs. Approximately 22% of the 58 AEs detected by satellite altimetry in the NSCS are ITEs. More importantly, the lens-shaped low PVs within them are produced primarily by the enhanced surface buoyancy loss during wintertime. These findings provide a new dynamic explanation for the low-PV generation in ITEs, highlighting the crucial role of atmospheric diabatic forcing.
{"title":"Intrathermocline eddy with lens-shaped low potential vorticity and diabatic forcing mechanism in the South China Sea","authors":"Yuyi Liu, Zhiyou Jing","doi":"10.1175/jpo-d-23-0149.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0149.1","url":null,"abstract":"\u0000Intrathermocline eddies (ITEs), characterized by subsurface lens-shaped low potential vorticity (PV), are pervasive in the ocean. However, the abundance and generation mechanisms of these low-PV lenses are poorly understood owing to their weak surface signals and awkward sizes, which present an observational barrier. Using in-situ observations of the northern South China Sea (NSCS), a typical ITE with a lens-shaped low PV at a core depth of 30-150 m and a horizontal size of ~150 km was captured in May 2021. Combined with PV budget analysis, we investigate the underlying generation mechanism of low PVs within these ITEs using high-resolution reanalysis products. The results suggest that wintertime surface buoyancy loss driven by atmospheric diabatic forcing rather than frictional forcing is a crucial favorable condition for the ITE formation. These enhanced surface buoyancy losses produce a net upward PV flux and decrease PV in the weakly-stratified and deep winter mixed layer, which are preconditioned by anticyclonic eddies (AEs). While surface heating in the following spring tends to weaken the surface buoyancy loss and gradually causes a downward PV flux, the surface-injected high PV subsequently caps the low-PV water within the surface-intensified AEs and transforms them into ITEs. Approximately 22% of the 58 AEs detected by satellite altimetry in the NSCS are ITEs. More importantly, the lens-shaped low PVs within them are produced primarily by the enhanced surface buoyancy loss during wintertime. These findings provide a new dynamic explanation for the low-PV generation in ITEs, highlighting the crucial role of atmospheric diabatic forcing.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-01-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139594652","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}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：