Recent studies have shown that the sensitivity of the circumpolar transport of channels to the westerlies is controlled by wind-driven gyre circulations. Although the form stress associated with the gyres has been shown to be controlled by eddies, bottom friction, and topographic width, the role of inertial effects has not been fully understood. In this study, we conduct a series of sensitivity analyses using the barotropic model with and without the advection term (hereinafter, the model without the advection term is denoted as linear model). Experiments showed that the sensitivity of the circumpolar transport decreased under the westerly winds compared to the linear model, while it increased under the easterly winds. We show that the inertial effect of western boundary currents generates anomalous anticyclonic circulations over the topography, producing the westward topographic form stress anomalies regardless of the wind directions. In addition, we discuss the sensitivity of the inertial effect mechanism to topographic height, width, and geometries. The inertial effect mechanism is robust as long as the gyre circulations dominate while its relative importance changes. We also found that the dynamics of the barotropic channel strongly depend on the geometries of geostrophic contours, f/h. Therefore, we conclude that the dynamics of barotropic channel models might be interpreted with caution to understand the dynamics of the Southern Ocean.
{"title":"Inertial effect and its dependency on the topographic geometries in barotropic channel models under the weakly nonlinear regime","authors":"Takuro Matsuta, H. Mitsudera","doi":"10.1175/jpo-d-23-0075.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0075.1","url":null,"abstract":"\u0000Recent studies have shown that the sensitivity of the circumpolar transport of channels to the westerlies is controlled by wind-driven gyre circulations. Although the form stress associated with the gyres has been shown to be controlled by eddies, bottom friction, and topographic width, the role of inertial effects has not been fully understood. In this study, we conduct a series of sensitivity analyses using the barotropic model with and without the advection term (hereinafter, the model without the advection term is denoted as linear model). Experiments showed that the sensitivity of the circumpolar transport decreased under the westerly winds compared to the linear model, while it increased under the easterly winds. We show that the inertial effect of western boundary currents generates anomalous anticyclonic circulations over the topography, producing the westward topographic form stress anomalies regardless of the wind directions. In addition, we discuss the sensitivity of the inertial effect mechanism to topographic height, width, and geometries. The inertial effect mechanism is robust as long as the gyre circulations dominate while its relative importance changes. We also found that the dynamics of the barotropic channel strongly depend on the geometries of geostrophic contours, f/h. Therefore, we conclude that the dynamics of barotropic channel models might be interpreted with caution to understand the dynamics of the Southern Ocean.","PeriodicalId":506940,"journal":{"name":"Journal of Physical Oceanography","volume":"11 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-03-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140077430","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. F. Sterl, J. LaCasce, S. Groeskamp, A. Nummelin, P. Isachsen, M. Baatsen
Oceanic mesoscale eddy mixing plays a crucial role in the Earth’s climate system by redistributing heat, salt and carbon. For many ocean and climate models, mesoscale eddies still need to be parameterized. This is often done via an eddy diffusivity, Κ, which sets the strength of turbulent downgradient tracer fluxes. A well known effect is the modulation of Κ in the presence of background potential vorticity (PV) gradients, which suppresses cross-PV gradient mixing. Topographic slopes can induce such suppression through topographic PV gradients. However, this effect has received little attention, and topographic effects are often not included in parameterizations for Κ. In this study, we show that it is possible to describe the effect of topography on Κ analytically in a barotropic framework, using a simple stochastic representation of eddy-eddy interactions. We obtain an analytical expression for the depth-averaged Κ as a function of the bottom slope, which we validate against diagnosed eddy diffusivities from a numerical model. The obtained analytical expression can be generalized to any constant barotropic PV gradient. Moreover, the expression is consistent with empirical parameterizations for eddy diffusivity over topography from previous studies and provides a physical rationalization for these parameterizations. The new expression helps to understand how eddy diffusivities vary across the ocean, and thus how mesoscale eddies impact ocean mixing processes.
{"title":"Suppression of mesoscale eddy mixing by topographic PV gradients","authors":"M. F. Sterl, J. LaCasce, S. Groeskamp, A. Nummelin, P. Isachsen, M. Baatsen","doi":"10.1175/jpo-d-23-0142.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0142.1","url":null,"abstract":"\u0000Oceanic mesoscale eddy mixing plays a crucial role in the Earth’s climate system by redistributing heat, salt and carbon. For many ocean and climate models, mesoscale eddies still need to be parameterized. This is often done via an eddy diffusivity, Κ, which sets the strength of turbulent downgradient tracer fluxes. A well known effect is the modulation of Κ in the presence of background potential vorticity (PV) gradients, which suppresses cross-PV gradient mixing. Topographic slopes can induce such suppression through topographic PV gradients. However, this effect has received little attention, and topographic effects are often not included in parameterizations for Κ. In this study, we show that it is possible to describe the effect of topography on Κ analytically in a barotropic framework, using a simple stochastic representation of eddy-eddy interactions. We obtain an analytical expression for the depth-averaged Κ as a function of the bottom slope, which we validate against diagnosed eddy diffusivities from a numerical model. The obtained analytical expression can be generalized to any constant barotropic PV gradient. Moreover, the expression is consistent with empirical parameterizations for eddy diffusivity over topography from previous studies and provides a physical rationalization for these parameterizations. The new expression helps to understand how eddy diffusivities vary across the ocean, and thus how mesoscale eddies impact ocean mixing processes.","PeriodicalId":506940,"journal":{"name":"Journal of Physical Oceanography","volume":"113 2","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139835902","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. F. Sterl, J. LaCasce, S. Groeskamp, A. Nummelin, P. Isachsen, M. Baatsen
Oceanic mesoscale eddy mixing plays a crucial role in the Earth’s climate system by redistributing heat, salt and carbon. For many ocean and climate models, mesoscale eddies still need to be parameterized. This is often done via an eddy diffusivity, Κ, which sets the strength of turbulent downgradient tracer fluxes. A well known effect is the modulation of Κ in the presence of background potential vorticity (PV) gradients, which suppresses cross-PV gradient mixing. Topographic slopes can induce such suppression through topographic PV gradients. However, this effect has received little attention, and topographic effects are often not included in parameterizations for Κ. In this study, we show that it is possible to describe the effect of topography on Κ analytically in a barotropic framework, using a simple stochastic representation of eddy-eddy interactions. We obtain an analytical expression for the depth-averaged Κ as a function of the bottom slope, which we validate against diagnosed eddy diffusivities from a numerical model. The obtained analytical expression can be generalized to any constant barotropic PV gradient. Moreover, the expression is consistent with empirical parameterizations for eddy diffusivity over topography from previous studies and provides a physical rationalization for these parameterizations. The new expression helps to understand how eddy diffusivities vary across the ocean, and thus how mesoscale eddies impact ocean mixing processes.
{"title":"Suppression of mesoscale eddy mixing by topographic PV gradients","authors":"M. F. Sterl, J. LaCasce, S. Groeskamp, A. Nummelin, P. Isachsen, M. Baatsen","doi":"10.1175/jpo-d-23-0142.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0142.1","url":null,"abstract":"\u0000Oceanic mesoscale eddy mixing plays a crucial role in the Earth’s climate system by redistributing heat, salt and carbon. For many ocean and climate models, mesoscale eddies still need to be parameterized. This is often done via an eddy diffusivity, Κ, which sets the strength of turbulent downgradient tracer fluxes. A well known effect is the modulation of Κ in the presence of background potential vorticity (PV) gradients, which suppresses cross-PV gradient mixing. Topographic slopes can induce such suppression through topographic PV gradients. However, this effect has received little attention, and topographic effects are often not included in parameterizations for Κ. In this study, we show that it is possible to describe the effect of topography on Κ analytically in a barotropic framework, using a simple stochastic representation of eddy-eddy interactions. We obtain an analytical expression for the depth-averaged Κ as a function of the bottom slope, which we validate against diagnosed eddy diffusivities from a numerical model. The obtained analytical expression can be generalized to any constant barotropic PV gradient. Moreover, the expression is consistent with empirical parameterizations for eddy diffusivity over topography from previous studies and provides a physical rationalization for these parameterizations. The new expression helps to understand how eddy diffusivities vary across the ocean, and thus how mesoscale eddies impact ocean mixing processes.","PeriodicalId":506940,"journal":{"name":"Journal of Physical Oceanography","volume":"32 3","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139776277","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Schmitt, H. T. Pham, S. Sarkar, K. Klingbeil, L. Umlauf
Diurnal Warm Layers (DWLs) form near the surface of the ocean on days with strong solar radiation, weak to moderate winds, and small surface-wave effects. Here, we use idealized second-moment turbulence modelling, validated with Large Eddy Simulations (LES), to study the properties, dynamics and energetics of DWLs across the entire physically relevant parameter space. Both types of models include representations of Langmuir turbulence (LT). We find that LT only slightly modifies DWL thicknesses and other bulk parameters under equilibrium wave conditions, but leads to a strong reduction in surface temperature and velocity with possible implications for air-sea coupling. Comparing tropical and the less frequently studied high-latitude DWLs, we find that LT has a strong impact on the energy budget and that rotation at high latitudes strongly modifies the DWL energetics, suppressing net energy turnover and entrainment. We identify the key non-dimensional parameters for DWL evolution and find that the scaling relations of Price et al. (1986) provide a reliable representation of the DWL bulk properties across a wide parameter space, including high-latitude DWLs. We present different sets of revised model coefficients that include the deepening of the DWL due to LT and other aspects of our more advanced turbulence model to describe DWL properties at midday and during the DWL temperature peak in the afternoon, which we find to occur around 15:00-16:30 for a broad range of parameters.
{"title":"Diurnal Warm Layers in the ocean: Energetics, non-dimensional scaling, and parameterization","authors":"M. Schmitt, H. T. Pham, S. Sarkar, K. Klingbeil, L. Umlauf","doi":"10.1175/jpo-d-23-0129.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0129.1","url":null,"abstract":"\u0000Diurnal Warm Layers (DWLs) form near the surface of the ocean on days with strong solar radiation, weak to moderate winds, and small surface-wave effects. Here, we use idealized second-moment turbulence modelling, validated with Large Eddy Simulations (LES), to study the properties, dynamics and energetics of DWLs across the entire physically relevant parameter space. Both types of models include representations of Langmuir turbulence (LT). We find that LT only slightly modifies DWL thicknesses and other bulk parameters under equilibrium wave conditions, but leads to a strong reduction in surface temperature and velocity with possible implications for air-sea coupling. Comparing tropical and the less frequently studied high-latitude DWLs, we find that LT has a strong impact on the energy budget and that rotation at high latitudes strongly modifies the DWL energetics, suppressing net energy turnover and entrainment. We identify the key non-dimensional parameters for DWL evolution and find that the scaling relations of Price et al. (1986) provide a reliable representation of the DWL bulk properties across a wide parameter space, including high-latitude DWLs. We present different sets of revised model coefficients that include the deepening of the DWL due to LT and other aspects of our more advanced turbulence model to describe DWL properties at midday and during the DWL temperature peak in the afternoon, which we find to occur around 15:00-16:30 for a broad range of parameters.","PeriodicalId":506940,"journal":{"name":"Journal of Physical Oceanography","volume":"50 ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139841042","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Despite its relatively small magnitude, cross-channel circulation in estuaries can influence the along-channel momentum balance, dispersion, and transport. We investigate spatial and temporal variation in cross-channel circulation at two contrasting sites in the Hudson River estuary. The two sites differ in the relative strength and direction of Coriolis and curvature forcing. We contrast the patterns and magnitudes of flow at the two sites during varying conditions in stratification driven by tidal amplitude and river discharge. We found well-defined flows during flood tides at both sites, characterized by mainly two-layer structures when the water column was more homogeneous and three- or more-layer structures when the water column was more stratified. Ebb tides had generally weaker and less definite flows, except at one site where curvature and Coriolis reinforced each other during spring tide ebbs. Cross-channel currents had similar patterns, but were oppositely directed at the two sites, demonstrating the importance of curvature even in channels with relatively gradual curves. Coriolis and curvature dominated the measured terms in the cross-channel momentum balance. Their combination was generally consistent with driving the observed patterns and directions of flow, but local acceleration and cross-channel advection made some notable contributions. A large residual in the momentum balance indicates that some combination of vertical stress divergence, baroclinic pressure gradients, and along-channel and vertical advection must play an essential role, but data limitations prevented an accurate estimation of these terms. Cross-channel advection affected the along-channel momentum balance at times, with implications for the exchange flow’s strength.
{"title":"Curves, Coriolis, and cross-channel circulation in the Hudson River estuary","authors":"Margaret M. Conley, J. Lerczak","doi":"10.1175/jpo-d-23-0093.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0093.1","url":null,"abstract":"\u0000Despite its relatively small magnitude, cross-channel circulation in estuaries can influence the along-channel momentum balance, dispersion, and transport. We investigate spatial and temporal variation in cross-channel circulation at two contrasting sites in the Hudson River estuary. The two sites differ in the relative strength and direction of Coriolis and curvature forcing. We contrast the patterns and magnitudes of flow at the two sites during varying conditions in stratification driven by tidal amplitude and river discharge. We found well-defined flows during flood tides at both sites, characterized by mainly two-layer structures when the water column was more homogeneous and three- or more-layer structures when the water column was more stratified. Ebb tides had generally weaker and less definite flows, except at one site where curvature and Coriolis reinforced each other during spring tide ebbs. Cross-channel currents had similar patterns, but were oppositely directed at the two sites, demonstrating the importance of curvature even in channels with relatively gradual curves. Coriolis and curvature dominated the measured terms in the cross-channel momentum balance. Their combination was generally consistent with driving the observed patterns and directions of flow, but local acceleration and cross-channel advection made some notable contributions. A large residual in the momentum balance indicates that some combination of vertical stress divergence, baroclinic pressure gradients, and along-channel and vertical advection must play an essential role, but data limitations prevented an accurate estimation of these terms. Cross-channel advection affected the along-channel momentum balance at times, with implications for the exchange flow’s strength.","PeriodicalId":506940,"journal":{"name":"Journal of Physical Oceanography","volume":"118 20","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139810040","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Despite its relatively small magnitude, cross-channel circulation in estuaries can influence the along-channel momentum balance, dispersion, and transport. We investigate spatial and temporal variation in cross-channel circulation at two contrasting sites in the Hudson River estuary. The two sites differ in the relative strength and direction of Coriolis and curvature forcing. We contrast the patterns and magnitudes of flow at the two sites during varying conditions in stratification driven by tidal amplitude and river discharge. We found well-defined flows during flood tides at both sites, characterized by mainly two-layer structures when the water column was more homogeneous and three- or more-layer structures when the water column was more stratified. Ebb tides had generally weaker and less definite flows, except at one site where curvature and Coriolis reinforced each other during spring tide ebbs. Cross-channel currents had similar patterns, but were oppositely directed at the two sites, demonstrating the importance of curvature even in channels with relatively gradual curves. Coriolis and curvature dominated the measured terms in the cross-channel momentum balance. Their combination was generally consistent with driving the observed patterns and directions of flow, but local acceleration and cross-channel advection made some notable contributions. A large residual in the momentum balance indicates that some combination of vertical stress divergence, baroclinic pressure gradients, and along-channel and vertical advection must play an essential role, but data limitations prevented an accurate estimation of these terms. Cross-channel advection affected the along-channel momentum balance at times, with implications for the exchange flow’s strength.
{"title":"Curves, Coriolis, and cross-channel circulation in the Hudson River estuary","authors":"Margaret M. Conley, J. Lerczak","doi":"10.1175/jpo-d-23-0093.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0093.1","url":null,"abstract":"\u0000Despite its relatively small magnitude, cross-channel circulation in estuaries can influence the along-channel momentum balance, dispersion, and transport. We investigate spatial and temporal variation in cross-channel circulation at two contrasting sites in the Hudson River estuary. The two sites differ in the relative strength and direction of Coriolis and curvature forcing. We contrast the patterns and magnitudes of flow at the two sites during varying conditions in stratification driven by tidal amplitude and river discharge. We found well-defined flows during flood tides at both sites, characterized by mainly two-layer structures when the water column was more homogeneous and three- or more-layer structures when the water column was more stratified. Ebb tides had generally weaker and less definite flows, except at one site where curvature and Coriolis reinforced each other during spring tide ebbs. Cross-channel currents had similar patterns, but were oppositely directed at the two sites, demonstrating the importance of curvature even in channels with relatively gradual curves. Coriolis and curvature dominated the measured terms in the cross-channel momentum balance. Their combination was generally consistent with driving the observed patterns and directions of flow, but local acceleration and cross-channel advection made some notable contributions. A large residual in the momentum balance indicates that some combination of vertical stress divergence, baroclinic pressure gradients, and along-channel and vertical advection must play an essential role, but data limitations prevented an accurate estimation of these terms. Cross-channel advection affected the along-channel momentum balance at times, with implications for the exchange flow’s strength.","PeriodicalId":506940,"journal":{"name":"Journal of Physical Oceanography","volume":"44 5","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139869883","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Observations in the Pacific Equatorial Undercurrents (EUC) show that the nighttime deep-cycle turbulence (DCT) in the marginal-instability (MI) layer of the EUC exhibits seasonal variability that can modulate heat transport and sea surface temperature. Large-eddy simulations (LES), spanning a wide range of control parameters, are performed to identify the key processes that influence the turbulent heat flux at multiple time scales ranging from turbulent (minutes to hours) to daily to seasonal. The control parameters include wind stress, convective surface heat flux, shear magnitude, and thickness of the MI layer. In the LES, DCT occurs in discrete bursts during the night, exhibits high temporal variability within a burst, and modulates the mixed layer depth. At the daily time scale, turbulent heat flux generally increases with increasing wind stress, MI-layer shear, or nighttime convection. Convection is found to be important to mixing under weak wind, weak shear conditions. A parameterization for the daily averaged turbulent heat flux is developed from the LES suite to infer the variability of heat flux at the seasonal time scale. The LES-based parameterized heat flux, which takes into account the effects of all control parameters, exhibits a seasonal variability that is similar to the observed heat flux from the χ-pods.
对太平洋赤道暗流（EUC）的观测表明，EUC 边缘不稳定层（MI）的夜间深循环湍流（DCT）表现出季节性变化，可调节热传输和海面温度。为了确定影响湍流热通量的关键过程，在从湍流（分钟到小时）到日到季节的多个时间尺度上进行了大涡度模拟（LES），其中包括多种控制参数。控制参数包括风应力、对流表面热通量、切变幅度和 MI 层厚度。在 LES 中，DCT 在夜间以离散爆发的形式出现，在爆发中表现出较高的时变性，并调节混合层深度。在日时间尺度上，湍流热通量通常会随着风压、混合层切变或夜间对流的增加而增加。在弱风、弱切变条件下，对流对混合非常重要。根据 LES 套件开发了日平均湍流热通量参数化，以推断热通量在季节时间尺度上的变化。基于 LES 的参数化热通量考虑了所有控制参数的影响，其季节变化与来自 χ 模式的观测热通量相似。
{"title":"Deep-Cycle Turbulence in the Upper Pacific Equatorial Ocean: Characterization by LES and Heat Flux Parameterization","authors":"H. Pham, S. Sarkar, W. Smyth, J. Moum, S. Warner","doi":"10.1175/jpo-d-23-0015.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0015.1","url":null,"abstract":"\u0000Observations in the Pacific Equatorial Undercurrents (EUC) show that the nighttime deep-cycle turbulence (DCT) in the marginal-instability (MI) layer of the EUC exhibits seasonal variability that can modulate heat transport and sea surface temperature. Large-eddy simulations (LES), spanning a wide range of control parameters, are performed to identify the key processes that influence the turbulent heat flux at multiple time scales ranging from turbulent (minutes to hours) to daily to seasonal. The control parameters include wind stress, convective surface heat flux, shear magnitude, and thickness of the MI layer. In the LES, DCT occurs in discrete bursts during the night, exhibits high temporal variability within a burst, and modulates the mixed layer depth. At the daily time scale, turbulent heat flux generally increases with increasing wind stress, MI-layer shear, or nighttime convection. Convection is found to be important to mixing under weak wind, weak shear conditions. A parameterization for the daily averaged turbulent heat flux is developed from the LES suite to infer the variability of heat flux at the seasonal time scale. The LES-based parameterized heat flux, which takes into account the effects of all control parameters, exhibits a seasonal variability that is similar to the observed heat flux from the χ-pods.","PeriodicalId":506940,"journal":{"name":"Journal of Physical Oceanography","volume":"6 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139890441","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Observations in the Pacific Equatorial Undercurrents (EUC) show that the nighttime deep-cycle turbulence (DCT) in the marginal-instability (MI) layer of the EUC exhibits seasonal variability that can modulate heat transport and sea surface temperature. Large-eddy simulations (LES), spanning a wide range of control parameters, are performed to identify the key processes that influence the turbulent heat flux at multiple time scales ranging from turbulent (minutes to hours) to daily to seasonal. The control parameters include wind stress, convective surface heat flux, shear magnitude, and thickness of the MI layer. In the LES, DCT occurs in discrete bursts during the night, exhibits high temporal variability within a burst, and modulates the mixed layer depth. At the daily time scale, turbulent heat flux generally increases with increasing wind stress, MI-layer shear, or nighttime convection. Convection is found to be important to mixing under weak wind, weak shear conditions. A parameterization for the daily averaged turbulent heat flux is developed from the LES suite to infer the variability of heat flux at the seasonal time scale. The LES-based parameterized heat flux, which takes into account the effects of all control parameters, exhibits a seasonal variability that is similar to the observed heat flux from the χ-pods.
对太平洋赤道暗流（EUC）的观测表明，EUC 边缘不稳定层（MI）的夜间深循环湍流（DCT）表现出季节性变化，可调节热传输和海面温度。为了确定影响湍流热通量的关键过程，在从湍流（分钟到小时）到日到季节的多个时间尺度上进行了大涡度模拟（LES），其中包括多种控制参数。控制参数包括风应力、对流表面热通量、切变幅度和 MI 层厚度。在 LES 中，DCT 在夜间以离散爆发的形式出现，在爆发中表现出较高的时变性，并调节混合层深度。在日时间尺度上，湍流热通量通常会随着风压、混合层切变或夜间对流的增加而增加。在弱风、弱切变条件下，对流对混合非常重要。根据 LES 套件开发了日平均湍流热通量参数化，以推断热通量在季节时间尺度上的变化。基于 LES 的参数化热通量考虑了所有控制参数的影响，其季节变化与来自 χ 模式的观测热通量相似。
{"title":"Deep-Cycle Turbulence in the Upper Pacific Equatorial Ocean: Characterization by LES and Heat Flux Parameterization","authors":"H. Pham, S. Sarkar, W. Smyth, J. Moum, S. Warner","doi":"10.1175/jpo-d-23-0015.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0015.1","url":null,"abstract":"\u0000Observations in the Pacific Equatorial Undercurrents (EUC) show that the nighttime deep-cycle turbulence (DCT) in the marginal-instability (MI) layer of the EUC exhibits seasonal variability that can modulate heat transport and sea surface temperature. Large-eddy simulations (LES), spanning a wide range of control parameters, are performed to identify the key processes that influence the turbulent heat flux at multiple time scales ranging from turbulent (minutes to hours) to daily to seasonal. The control parameters include wind stress, convective surface heat flux, shear magnitude, and thickness of the MI layer. In the LES, DCT occurs in discrete bursts during the night, exhibits high temporal variability within a burst, and modulates the mixed layer depth. At the daily time scale, turbulent heat flux generally increases with increasing wind stress, MI-layer shear, or nighttime convection. Convection is found to be important to mixing under weak wind, weak shear conditions. A parameterization for the daily averaged turbulent heat flux is developed from the LES suite to infer the variability of heat flux at the seasonal time scale. The LES-based parameterized heat flux, which takes into account the effects of all control parameters, exhibits a seasonal variability that is similar to the observed heat flux from the χ-pods.","PeriodicalId":506940,"journal":{"name":"Journal of Physical Oceanography","volume":"119 ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139830900","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The scale-to-scale kinetic energy (KE) cascade induced by the nonlinear interaction among topography, Kuroshio Current, and mesoscale eddies is systematically investigated in the coarse-graining framework based on simulated data from the well-validated Regional Ocean Model System. The KE transfer exhibits inhomogeneous spatial and temporal distributions and varies with length scale. During current-topography interaction, the KE transfers downscale across larger scales and reversely across smaller scales with an inherent separation scale of 150 km northeast of Taiwan, resulting in a significant positive net KE flux for mesoscale motions. The transfer around Suao Ridge is consistently downscaled with significant seasonal variation that is stronger in summer and weaker in winter. South of Suao Ridge, the transfer is one order of magnitude weaker and changes greatly with time. The cyclonic (anticyclonic) eddy weakens (enhances) KE transfer in most study area. In particular, the cyclonic eddy reverses the transfer direction around Suao Ridge. The anticyclonic eddy triggers a significant bidirectional transfer south of Suao Ridge. Analyses show that the special arc-shaped topographic feature and northwestward Kuroshio intrusion current are responsible for the nature of bidirectional KE transfer northeast of Taiwan. The direction of mean current relative to the topography gradient determines the Rossby number magnitude and the KE transfer direction. The large-scale circulation determines the transfer intensity by changing the horizontal shear and barotropic instabilities. The KE transfer caused by nonlinear dynamics contributes significantly to the total anticyclonic eddy-induced net KE flux changes. In particular, inverse KE cascade plays a key role in net KE flux changes in mesoscale motions east of Taiwan.
在粗粒度框架内，根据经过充分验证的区域海洋模式系统的模拟数据，系统地研究了地形、黑潮和中尺度涡流之间的非线性相互作用引起的尺度-尺度动能（KE）级联。KE 转移表现出不均匀的时空分布，并随长度尺度而变化。在海流-地形相互作用过程中，KE 在较大尺度上向下转移，在较小尺度上反向转移，其固有分离尺度为台湾东北 150 公里，从而导致中尺度运动产生显著的正净 KE 通量。苏澳海脊周围的传输持续降尺度，具有显著的季节性变化，夏季较强，冬季较弱。在苏澳海脊以南，传输弱一个数量级，且随时间变化很大。在大部分研究区域，气旋（反气旋）涡减弱（增强）了 KE 的传输。尤其是苏澳海脊附近的气旋性涡旋会逆转传递方向。反气旋涡流在苏澳海脊以南引发了显著的双向转移。分析表明，特殊的弧形地形特征和西北向的黑潮侵入流是造成台湾东北部双向 KE 转移性质的原因。平均海流相对于地形梯度的方向决定了罗斯比数的大小和 KE 的转移方向。大尺度环流通过改变水平切变和气压不稳定性来决定传输强度。非线性动力学引起的 KE 转移在反气旋涡引起的总净 KE 通量变化中起着重要作用。特别是反KE级联在台湾以东中尺度运动的净KE通量变化中起了关键作用。
{"title":"Kinetic energy cascade induced by the interaction of mean flow, topography, and mesoscale eddies east of Taiwan: a scale-to-scale analysis","authors":"Lingjing Xu, Dezhou Yang, Zhiwei He, Xingru Feng, Guandong Gao, Xuan Cui, Baoshu Yin","doi":"10.1175/jpo-d-23-0077.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0077.1","url":null,"abstract":"\u0000The scale-to-scale kinetic energy (KE) cascade induced by the nonlinear interaction among topography, Kuroshio Current, and mesoscale eddies is systematically investigated in the coarse-graining framework based on simulated data from the well-validated Regional Ocean Model System. The KE transfer exhibits inhomogeneous spatial and temporal distributions and varies with length scale. During current-topography interaction, the KE transfers downscale across larger scales and reversely across smaller scales with an inherent separation scale of 150 km northeast of Taiwan, resulting in a significant positive net KE flux for mesoscale motions. The transfer around Suao Ridge is consistently downscaled with significant seasonal variation that is stronger in summer and weaker in winter. South of Suao Ridge, the transfer is one order of magnitude weaker and changes greatly with time. The cyclonic (anticyclonic) eddy weakens (enhances) KE transfer in most study area. In particular, the cyclonic eddy reverses the transfer direction around Suao Ridge. The anticyclonic eddy triggers a significant bidirectional transfer south of Suao Ridge. Analyses show that the special arc-shaped topographic feature and northwestward Kuroshio intrusion current are responsible for the nature of bidirectional KE transfer northeast of Taiwan. The direction of mean current relative to the topography gradient determines the Rossby number magnitude and the KE transfer direction. The large-scale circulation determines the transfer intensity by changing the horizontal shear and barotropic instabilities. The KE transfer caused by nonlinear dynamics contributes significantly to the total anticyclonic eddy-induced net KE flux changes. In particular, inverse KE cascade plays a key role in net KE flux changes in mesoscale motions east of Taiwan.","PeriodicalId":506940,"journal":{"name":"Journal of Physical Oceanography","volume":"52 12","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-01-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139386387","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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