Mesoscale eddy buoyancy fluxes across continental slopes profoundly modulate the boundary current dynamics and shelf-ocean exchanges, but have yet to be appropriately parameterized via the Gent-McWilliams (GM) scheme in predictive ocean models. In this work, we test the prognostic performance of multiple GM variants in non-eddying simulations of upwelling slope fronts that are commonly found along the subtropical continental margins. The tested GM variants range from a set of constant eddy buoyancy diffusivities to recently developed energetically-constrained, bathymetry-aware diffusivities, whose implementation is augmented by an artificial neural network (ANN) serving to predict the mesoscale eddy energy based on the topographic and mean flow quantities online. In addition, an ANN is employed to parameterize the cross-slope eddy momentum flux (EMF) that maintains a barotropic flow field analogous to that in an eddy-resolving model. Our tests reveal that non-eddying simulations employing the bathymetry-aware forms of the Rhines scale-based scheme and GEOMETRIC scheme (Wang and Stewart, 2020; https://doi.org/10.1016/j.ocemod.2020.101579) can most accurately reproduce the heat contents and along-slope baroclinic transports as those in the eddy-resolving simulations. Further analyses reveal certain degrees of physical consistency in the ANN-inferred eddy energy, which tends to grow (decay) as isopycnal slopes are steepened (flattened), and in the parameterized EMF, which exhibits the correct strength of shaping the flow baroclinicity if a bathymetry-aware GM variant is jointly used. These findings provide a recipe of GM variants for use in non-eddying simulations with continental slopes and highlight the potential of machine learning techniques to augment physics-based mesoscale eddy parameterization schemes.
{"title":"Bathymetry-aware mesoscale eddy parameterizations across upwelling slope fronts: A machine learning-augmented approach","authors":"Chenyue Xie, Huaiyu Wei, Yan Wang","doi":"10.1175/jpo-d-23-0017.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0017.1","url":null,"abstract":"\u0000Mesoscale eddy buoyancy fluxes across continental slopes profoundly modulate the boundary current dynamics and shelf-ocean exchanges, but have yet to be appropriately parameterized via the Gent-McWilliams (GM) scheme in predictive ocean models. In this work, we test the prognostic performance of multiple GM variants in non-eddying simulations of upwelling slope fronts that are commonly found along the subtropical continental margins. The tested GM variants range from a set of constant eddy buoyancy diffusivities to recently developed energetically-constrained, bathymetry-aware diffusivities, whose implementation is augmented by an artificial neural network (ANN) serving to predict the mesoscale eddy energy based on the topographic and mean flow quantities online. In addition, an ANN is employed to parameterize the cross-slope eddy momentum flux (EMF) that maintains a barotropic flow field analogous to that in an eddy-resolving model. Our tests reveal that non-eddying simulations employing the bathymetry-aware forms of the Rhines scale-based scheme and GEOMETRIC scheme (Wang and Stewart, 2020; https://doi.org/10.1016/j.ocemod.2020.101579) can most accurately reproduce the heat contents and along-slope baroclinic transports as those in the eddy-resolving simulations. Further analyses reveal certain degrees of physical consistency in the ANN-inferred eddy energy, which tends to grow (decay) as isopycnal slopes are steepened (flattened), and in the parameterized EMF, which exhibits the correct strength of shaping the flow baroclinicity if a bathymetry-aware GM variant is jointly used. These findings provide a recipe of GM variants for use in non-eddying simulations with continental slopes and highlight the potential of machine learning techniques to augment physics-based mesoscale eddy parameterization schemes.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":" ","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-09-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46022456","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}
It is evident from hydrographic profiles in the Arctic Ocean that relatively warm and salty Canada Basin Deep Water (CBDW) flows over the Lomonosov Ridge into the Amundsen Basin, in the Eurasian Arctic. However, oceanographic data in the deep Arctic Ocean are scarce, making it difficult to analyse the spatial extent or the dynamics of this inflow. Here we present new hydrographic data from two recent expeditions as well as historical data from previous expeditions in the central Arctic. We use an end-member analysis to quantify the presence of CBDW in the Amundsen and Nansen Basin and infer new circulation pathways. We find that the inflow of CBDW is intermittent, and that it recirculates in the Amundsen Basin along Gakkel Ridge. Although the forcing mechanisms for the inflow of CBDW into the Amundsen Basin remain unclear owing to the lack of continuous observations, we demonstrate that density-driven overflows, even intermittent, and the pressure gradient across the Lomonosov Ridge are unlikely drivers. We also find multiple deep eddies with a CBDW content of up to 600 g kg-1 and a vertical extent of up to 1200 metres in the Amundsen Basin. The high CBDW content of these eddies suggests that they can efficiently trap CBDW and transport its heat and salt over long distances.
从北冰洋的水文剖面可以明显看出，相对温暖和咸的加拿大盆地深水（CBDW）流经罗蒙诺索夫山脊，流入欧亚北极的阿蒙森盆地。然而，北冰洋深处的海洋学数据很少，因此很难分析这种流入的空间范围或动力学。在这里，我们展示了最近两次探险的新水文数据，以及之前在北极中部探险的历史数据。我们使用末端成员分析来量化CBDW在阿蒙森和南森盆地的存在，并推断新的环流路径。我们发现CBDW的流入是间歇性的，并且它沿着Gakkel山脊在阿蒙森盆地再循环。尽管由于缺乏连续观测，CBDW流入阿蒙森盆地的强迫机制仍不清楚，但我们证明，密度驱动的溢流，甚至是间歇性的，以及罗蒙诺索夫山脊的压力梯度不太可能是驱动因素。我们还在阿蒙森盆地发现了多个CBDW含量高达600 g kg-1、垂直范围高达1200米的深层涡旋。这些涡流的高CBDW含量表明，它们可以有效地捕获CBDW，并将其热量和盐分远距离输送。
{"title":"Recirculation of Canada Basin Deep Water in the Amundsen Basin, Arctic","authors":"S. Karam, C. Heuzé, Vasco Müller, Yixi Zheng","doi":"10.1175/jpo-d-22-0252.1","DOIUrl":"https://doi.org/10.1175/jpo-d-22-0252.1","url":null,"abstract":"\u0000It is evident from hydrographic profiles in the Arctic Ocean that relatively warm and salty Canada Basin Deep Water (CBDW) flows over the Lomonosov Ridge into the Amundsen Basin, in the Eurasian Arctic. However, oceanographic data in the deep Arctic Ocean are scarce, making it difficult to analyse the spatial extent or the dynamics of this inflow. Here we present new hydrographic data from two recent expeditions as well as historical data from previous expeditions in the central Arctic. We use an end-member analysis to quantify the presence of CBDW in the Amundsen and Nansen Basin and infer new circulation pathways. We find that the inflow of CBDW is intermittent, and that it recirculates in the Amundsen Basin along Gakkel Ridge. Although the forcing mechanisms for the inflow of CBDW into the Amundsen Basin remain unclear owing to the lack of continuous observations, we demonstrate that density-driven overflows, even intermittent, and the pressure gradient across the Lomonosov Ridge are unlikely drivers. We also find multiple deep eddies with a CBDW content of up to 600 g kg-1 and a vertical extent of up to 1200 metres in the Amundsen Basin. The high CBDW content of these eddies suggests that they can efficiently trap CBDW and transport its heat and salt over long distances.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":" ","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-09-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46644309","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}
E. Masunaga, M. Alford, Andrew J. Lucas, Andrea Rodriguez-Marin Freudmann
This study investigates three-dimensional semidiurnal internal tide (IT) energetics in the vicinity of La Jolla Canyon, a steep shelf submarine canyon off the South California Coast, with the SUNTANS numerical simulator. Numerical simulations show vertical structure and temporal phasing consistent with detailed field observations. ITs induce large (approximately 34-m peak-to-peak) isotherm displacements and net onshore IT energy flux up to 200 W m-1. Although the net IT energy flux is onshore, the steep supercritical slope around the canyon results in strong reflection. The model provides the full life span of internal tides around the canyon, including internal tide generation, propagation and dissipation. ITs propagate into the canyon from the south and are reflected back towards offshore from the canyon’s north side. In the inner part of the canyon, elevated mixing occurs in the middle layer due to an interaction between incident mode-1 ITs and reflected higher-mode ITs. The magnitude of IT flux, generation and dissipation on the south side of the canyon are higher than those on the north side. An interference pattern in horizontal kinetic energy and available potential energy with a scale of approximately 20–50 km arises due to low-mode wave reflections. Our results provide new insight into IT dynamics associated with a small scale canyon topography.
{"title":"Numerical simulations of internal tide dynamics in a steep submarine canyon","authors":"E. Masunaga, M. Alford, Andrew J. Lucas, Andrea Rodriguez-Marin Freudmann","doi":"10.1175/jpo-d-23-0040.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0040.1","url":null,"abstract":"\u0000This study investigates three-dimensional semidiurnal internal tide (IT) energetics in the vicinity of La Jolla Canyon, a steep shelf submarine canyon off the South California Coast, with the SUNTANS numerical simulator. Numerical simulations show vertical structure and temporal phasing consistent with detailed field observations. ITs induce large (approximately 34-m peak-to-peak) isotherm displacements and net onshore IT energy flux up to 200 W m-1. Although the net IT energy flux is onshore, the steep supercritical slope around the canyon results in strong reflection. The model provides the full life span of internal tides around the canyon, including internal tide generation, propagation and dissipation. ITs propagate into the canyon from the south and are reflected back towards offshore from the canyon’s north side. In the inner part of the canyon, elevated mixing occurs in the middle layer due to an interaction between incident mode-1 ITs and reflected higher-mode ITs. The magnitude of IT flux, generation and dissipation on the south side of the canyon are higher than those on the north side. An interference pattern in horizontal kinetic energy and available potential energy with a scale of approximately 20–50 km arises due to low-mode wave reflections. Our results provide new insight into IT dynamics associated with a small scale canyon topography.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":" ","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43897568","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}
Eric Kunze, R. Lien, C. Whalen, J. Girton, Barry Ma, M. Buijsman
Six profiling floats measured water-mass properties (Т, S), horizontal velocities (u, v) and microstructure thermal-variance dissipation rates χT in the upper ~1 km of Iceland and Irminger Basins in the eastern sub-polar North Atlantic from June 2019 to April 2021. The floats drifted into slope boundary currents to travel counterclockwise around the basins. Pairs of velocity profiles half an inertial period apart were collected every 7-14 days. These half-inertial-period pairs are separated into subinertial eddy (sum) and inertial/semidiurnal (difference) motions. Eddy flow speeds are ~O(0.1 m s−1) in the upper 400 m, diminishing to ~O(0.01 m s−1) by ~800-m depth. In late summer through early spring, near-inertial motions are energized in the surface layer and permanent pycnocline to at least 800-m depth almost simultaneously (within the 14-day temporal resolution), suggesting rapid transformation of large-horizontal-scale surface-layer inertial oscillations into near-inertial internal waves with high vertical group velocities through interactions with eddy vorticity-gradients (effective β). During the same period, internal-wave vertical shear variance was 2-5 times canonical midlatitude magnitudes and dominantly clockwise-with-depth (downward energy propagation). In late spring and early summer, shear levels are comparable to canonical midlatitude values and dominantly counterclockwise-with-depth (upward energy propagation), particularly over major topographic ridges. Turbulent diapycnal diffusivities K ~O(10−4 m2 s−1) are an order of magnitude larger than canonical mid-latitude values. Depth-averaged (10-1000 m) diffusivities exhibit factor-of-three month-by-month variability with minima in early August.
2019年6月至2021年4月，六个剖面浮标测量了北大西洋东部亚极地冰岛和伊明格尔盆地上游约1公里的水体性质（Т，S）、水平速度（u，v）和微观结构热变化耗散率χT。漂浮物漂移到斜坡边界流中，沿逆时针方向在盆地周围流动。每隔7-14天收集一对相隔半惯性周期的速度剖面。这些半惯性周期对被分为亚惯性涡（和）和惯性/半日（差）运动。涡流速度在上部400 m处为~O（0.1 m s−1），在800 m深度处降至~O（0.01 m s−2）。在夏末至早春，表层和永久性比重跃层中的近惯性运动几乎同时被激发到至少800-m的深度（在14天的时间分辨率内），这表明通过与涡度梯度（有效β）的相互作用，大水平尺度表层惯性振荡迅速转变为具有高垂直群速度的近惯性内波。在同一时期，内波垂直剪切方差是标准中纬度震级的2-5倍，并且主要是顺时针方向随深度变化（向下能量传播）。在春末夏初，剪切水平与典型的中纬度值相当，并且主要是逆时针方向随深度变化（向上能量传播），特别是在主要地形山脊上。湍流滞流扩散系数K~O（10−4 m2 s−1）比标准中纬度值大一个数量级。深度平均（10-1000m）扩散系数表现出三个月的变化因子，8月初最小。
{"title":"Seasonal Variability of Near-Inertial/Semidiurnal Fluctuations and Turbulence in the Sub-Arctic North Atlantic","authors":"Eric Kunze, R. Lien, C. Whalen, J. Girton, Barry Ma, M. Buijsman","doi":"10.1175/jpo-d-22-0231.1","DOIUrl":"https://doi.org/10.1175/jpo-d-22-0231.1","url":null,"abstract":"\u0000Six profiling floats measured water-mass properties (Т, S), horizontal velocities (u, v) and microstructure thermal-variance dissipation rates χT in the upper ~1 km of Iceland and Irminger Basins in the eastern sub-polar North Atlantic from June 2019 to April 2021. The floats drifted into slope boundary currents to travel counterclockwise around the basins. Pairs of velocity profiles half an inertial period apart were collected every 7-14 days. These half-inertial-period pairs are separated into subinertial eddy (sum) and inertial/semidiurnal (difference) motions. Eddy flow speeds are ~O(0.1 m s−1) in the upper 400 m, diminishing to ~O(0.01 m s−1) by ~800-m depth. In late summer through early spring, near-inertial motions are energized in the surface layer and permanent pycnocline to at least 800-m depth almost simultaneously (within the 14-day temporal resolution), suggesting rapid transformation of large-horizontal-scale surface-layer inertial oscillations into near-inertial internal waves with high vertical group velocities through interactions with eddy vorticity-gradients (effective β). During the same period, internal-wave vertical shear variance was 2-5 times canonical midlatitude magnitudes and dominantly clockwise-with-depth (downward energy propagation). In late spring and early summer, shear levels are comparable to canonical midlatitude values and dominantly counterclockwise-with-depth (upward energy propagation), particularly over major topographic ridges. Turbulent diapycnal diffusivities K ~O(10−4 m2 s−1) are an order of magnitude larger than canonical mid-latitude values. Depth-averaged (10-1000 m) diffusivities exhibit factor-of-three month-by-month variability with minima in early August.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":" ","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42017403","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}
Turbulence in the ocean surface layer is forced by a mixture of buoyancy, wind, and wave processes that evolves over time scales from the diurnal scale of buoyancy forcing, through storm time scales, to the annual cycle. This study seeks a predictor for root-mean-square w (rmsw), a time and surface layer average of turbulent vertical velocity w measured by bottom-mounted vertical-beam acoustic Doppler current profilers, in terms of concurrently measured surface forcing fields. Data used are from two coastal sites, one shallow (LEO, 15-m depth) and one deeper (R2, 26-m depth). The analysis demonstrates that it is possible to predict observed rmsw with a simple linear combination of two scale velocities, one the convective scale velocity familiar from the atmospheric literature, the other a scale velocity wS representing combined wind and wave effects. Three variants are considered for this latter scale velocity, the wind stress velocity alone and two forms using both and US, a Stokes velocity characteristic of the surface wave field. At both sites, the two-parameter fit using alone is least accurate, while fits using the other two variants are essentially indistinguishable. At both sites, the coefficient multiplying is the same, within error bounds, and within the range of previous observations. At the deeper site, the coefficient multiplying the wind/wave scale velocity wS is approximately half that at the shallow site, a difference here attributed to difference in wave character.
{"title":"Predicting Turbulent Vertical Velocity in the Ocean Surface Layer under Mixed Convective and Wind/Wave Forcing","authors":"A. Gargett","doi":"10.1175/jpo-d-22-0213.1","DOIUrl":"https://doi.org/10.1175/jpo-d-22-0213.1","url":null,"abstract":"\u0000Turbulence in the ocean surface layer is forced by a mixture of buoyancy, wind, and wave processes that evolves over time scales from the diurnal scale of buoyancy forcing, through storm time scales, to the annual cycle. This study seeks a predictor for root-mean-square w (rmsw), a time and surface layer average of turbulent vertical velocity w measured by bottom-mounted vertical-beam acoustic Doppler current profilers, in terms of concurrently measured surface forcing fields. Data used are from two coastal sites, one shallow (LEO, 15-m depth) and one deeper (R2, 26-m depth). The analysis demonstrates that it is possible to predict observed rmsw with a simple linear combination of two scale velocities, one the convective scale velocity familiar from the atmospheric literature, the other a scale velocity wS representing combined wind and wave effects. Three variants are considered for this latter scale velocity, the wind stress velocity alone and two forms using both and US, a Stokes velocity characteristic of the surface wave field. At both sites, the two-parameter fit using alone is least accurate, while fits using the other two variants are essentially indistinguishable. At both sites, the coefficient multiplying is the same, within error bounds, and within the range of previous observations. At the deeper site, the coefficient multiplying the wind/wave scale velocity wS is approximately half that at the shallow site, a difference here attributed to difference in wave character.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":" ","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46520031","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}
Zhang Kun, Wang Qiang, Baoshu Yin, Dezhou Yang, Yang Lina
Deep vertical velocity is a critical factor causing deficiencies in Sverdrup theory. However, few studies have focused on its influence in the low-latitude western Pacific. Through multiple analyses of observational, reanalysis, and simulation data, this study explored the contribution of deep non-zero vertical velocity to the Sverdrup transport inaccuracy in the low-latitude North Pacific. The vertical velocities inducing relatively small non-Sverdrup transport exist within 1500–2500 m, which exhibit similar patterns with opposite values to the south and north of 13°N. The zonally integrated meridional volume transport associated with these vertical velocities displays non-negligible dipolar zonal bands west of approximately 150°W. The positive and negative transport bands, centered at 11°N and 17°N, can reach an amplitude of approximately 8.0 Sv when integrated from the eastern boundary to 140°E. On average, such integrated meridional transport makes up roughly half of the prominent Sverdrup transport discrepancies in the central-western Pacific. Further investigation indicated that the spatial pattern of these vertical velocities is modulated by ocean topography and deep southward currents. Moreover, a near-global test suggested that the meridional non-Sverdrup transport related to deep vertical velocity is widespread and undergoes remarkable multidecadal variation. This study reveals the disruptive role of deep vertical velocity in disturbing the Sverdrup balance and emphasizes the consideration of its long-term variation when diagnosing wind-driven circulation changes using Sverdrup theory.
{"title":"Contribution of deep vertical velocity to deficiency of Sverdrup transport in the low-latitude North Pacific","authors":"Zhang Kun, Wang Qiang, Baoshu Yin, Dezhou Yang, Yang Lina","doi":"10.1175/jpo-d-23-0006.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0006.1","url":null,"abstract":"\u0000Deep vertical velocity is a critical factor causing deficiencies in Sverdrup theory. However, few studies have focused on its influence in the low-latitude western Pacific. Through multiple analyses of observational, reanalysis, and simulation data, this study explored the contribution of deep non-zero vertical velocity to the Sverdrup transport inaccuracy in the low-latitude North Pacific. The vertical velocities inducing relatively small non-Sverdrup transport exist within 1500–2500 m, which exhibit similar patterns with opposite values to the south and north of 13°N. The zonally integrated meridional volume transport associated with these vertical velocities displays non-negligible dipolar zonal bands west of approximately 150°W. The positive and negative transport bands, centered at 11°N and 17°N, can reach an amplitude of approximately 8.0 Sv when integrated from the eastern boundary to 140°E. On average, such integrated meridional transport makes up roughly half of the prominent Sverdrup transport discrepancies in the central-western Pacific. Further investigation indicated that the spatial pattern of these vertical velocities is modulated by ocean topography and deep southward currents. Moreover, a near-global test suggested that the meridional non-Sverdrup transport related to deep vertical velocity is widespread and undergoes remarkable multidecadal variation. This study reveals the disruptive role of deep vertical velocity in disturbing the Sverdrup balance and emphasizes the consideration of its long-term variation when diagnosing wind-driven circulation changes using Sverdrup theory.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":" ","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44478598","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":"Equity, Inclusion, and Justice: An Opportunity for Action for AMS Publications Stakeholders","authors":"","doi":"10.1175/jpo-d-23-0160.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0160.1","url":null,"abstract":"","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":" ","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44835444","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}
We present the first continuous mooring records of the West Greenland Coastal Current (WGCC), a conduit of fresh, buoyant outflow from the Arctic Ocean and the Greenland Ice Sheet. Nearly two years of temperature, salinity, and velocity data from 2018-2020 demonstrate that the WGCC on the Southwest Greenland shelf is a well-formed current distinct from the shelfbreak jet but exhibits strong chaotic variability in its lateral position on the shelf, ranging from the coastline to the shelfbreak (50 km offshore). We calculate the WGCC volume and freshwater transports during the 35% of the time when the mooring array fully bracketed the current. During these periods, the WGCC remains as strong (0.83 +/− 0.02 Sverdrup; 1 Sv = 106 m3/s) as the East Greenland Coastal Current (EGCC) on the Southeast Greenland shelf (0.86 +/− 0.05 Sv) but is saltier than the EGCC and thus transports less liquid freshwater (30 × 10−3 Sv in the WGCC versus 42 x 10−3 Sv in the EGCC). These results indicate that a significant portion of the liquid freshwater in the EGCC is diverted from the coastal current as it rounds Cape Farewell. We interpret the dominant spatial variability of the WGCC as an adjustment to upwelling-favorable wind forcing on the West Greenland shelf and a separation from the coastal bathymetric gradient. An analysis of the winds near southern Greenland supports this interpretation, with non-local winds on the Southeast Greenland shelf impacting the WGCC volume transport more strongly than local winds over the Southwest Greenland shelf.
{"title":"Moored observations of the West Greenland Coastal Current along the Southwest Greenland Shelf","authors":"N. Foukal, R. Pickart","doi":"10.1175/jpo-d-23-0104.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0104.1","url":null,"abstract":"\u0000We present the first continuous mooring records of the West Greenland Coastal Current (WGCC), a conduit of fresh, buoyant outflow from the Arctic Ocean and the Greenland Ice Sheet. Nearly two years of temperature, salinity, and velocity data from 2018-2020 demonstrate that the WGCC on the Southwest Greenland shelf is a well-formed current distinct from the shelfbreak jet but exhibits strong chaotic variability in its lateral position on the shelf, ranging from the coastline to the shelfbreak (50 km offshore). We calculate the WGCC volume and freshwater transports during the 35% of the time when the mooring array fully bracketed the current. During these periods, the WGCC remains as strong (0.83 +/− 0.02 Sverdrup; 1 Sv = 106 m3/s) as the East Greenland Coastal Current (EGCC) on the Southeast Greenland shelf (0.86 +/− 0.05 Sv) but is saltier than the EGCC and thus transports less liquid freshwater (30 × 10−3 Sv in the WGCC versus 42 x 10−3 Sv in the EGCC). These results indicate that a significant portion of the liquid freshwater in the EGCC is diverted from the coastal current as it rounds Cape Farewell. We interpret the dominant spatial variability of the WGCC as an adjustment to upwelling-favorable wind forcing on the West Greenland shelf and a separation from the coastal bathymetric gradient. An analysis of the winds near southern Greenland supports this interpretation, with non-local winds on the Southeast Greenland shelf impacting the WGCC volume transport more strongly than local winds over the Southwest Greenland shelf.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":" ","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-08-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41997630","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}
As they rim the basin from the southern tip of Greenland to the southern Labrador coast, the waters in the Labrador Sea boundary current undergo a significant transformation in salinity and temperature, but much less so in density. Motivated by these observations, a previously developed simple three-layer model is adapted to understand the processes responsible for this density-compensated overturning in the Labrador Sea. From our model simulations, we find that the density-compensating water mass transformation in the boundary current can be largely attributed to the combined effect of 1) direct atmospheric cooling of the relatively warm boundary current and 2) freshening due to mixing with the shallower and fresh waters derived from Greenland meltwater discharge and Arctic Ocean inflow. Freshening of the boundary current waters due to the excess of precipitation over evaporation in the basin has an important, but less impactful role in the density compensation. Studies examining the sensitivity of the density compensation to the freshwater entry location reveal a larger impact when the freshwater enters the boundary current on the Greenland side of the basin, compared to the Labrador side. These results yield insights into how increasing meltwater in the subpolar North Atlantic will affect the overturning.
{"title":"Fresh water and atmospheric cooling control on density-compensated overturning in the Labrador Sea","authors":"Y. Bebieva, M. Lozier","doi":"10.1175/jpo-d-22-0238.1","DOIUrl":"https://doi.org/10.1175/jpo-d-22-0238.1","url":null,"abstract":"\u0000As they rim the basin from the southern tip of Greenland to the southern Labrador coast, the waters in the Labrador Sea boundary current undergo a significant transformation in salinity and temperature, but much less so in density. Motivated by these observations, a previously developed simple three-layer model is adapted to understand the processes responsible for this density-compensated overturning in the Labrador Sea. From our model simulations, we find that the density-compensating water mass transformation in the boundary current can be largely attributed to the combined effect of 1) direct atmospheric cooling of the relatively warm boundary current and 2) freshening due to mixing with the shallower and fresh waters derived from Greenland meltwater discharge and Arctic Ocean inflow. Freshening of the boundary current waters due to the excess of precipitation over evaporation in the basin has an important, but less impactful role in the density compensation. Studies examining the sensitivity of the density compensation to the freshwater entry location reveal a larger impact when the freshwater enters the boundary current on the Greenland side of the basin, compared to the Labrador side. These results yield insights into how increasing meltwater in the subpolar North Atlantic will affect the overturning.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":" ","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-08-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46763311","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}
One of the most fundamental uses of ocean models is for the prediction of sea level. Vertical integration of the hydrostatic equation leads to the partitioning of sea level in terms of atmospheric pressure, steric height, and bottom pressure. In an effort to validate the baroclinic wave dynamics of numerical ocean models, some researchers have compared the steric height from models with the sea level anomaly derived from satellite altimetry. The use of steric height in these comparisons captures the qualitative aspects of the baroclinic waves, but it neglects a non-negligible contribution from bottom pressure. A more accurate evaluation of baroclinic wave dynamics using sea level would involve projecting the pressure field onto orthogonal barotropic and baroclinic components to isolate the baroclinic sea level anomaly. This note illustrates the quantitative difference between steric height and baroclinic sea level, which amounts to approximately a 20% bias of steric height over baroclinic sea level, depending on location.
{"title":"Clarifying the Distinction Between Steric and Baroclinic Sea Surface Height","authors":"E. Zaron, R. Ray","doi":"10.1175/jpo-d-23-0073.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0073.1","url":null,"abstract":"\u0000One of the most fundamental uses of ocean models is for the prediction of sea level. Vertical integration of the hydrostatic equation leads to the partitioning of sea level in terms of atmospheric pressure, steric height, and bottom pressure. In an effort to validate the baroclinic wave dynamics of numerical ocean models, some researchers have compared the steric height from models with the sea level anomaly derived from satellite altimetry. The use of steric height in these comparisons captures the qualitative aspects of the baroclinic waves, but it neglects a non-negligible contribution from bottom pressure. A more accurate evaluation of baroclinic wave dynamics using sea level would involve projecting the pressure field onto orthogonal barotropic and baroclinic components to isolate the baroclinic sea level anomaly. This note illustrates the quantitative difference between steric height and baroclinic sea level, which amounts to approximately a 20% bias of steric height over baroclinic sea level, depending on location.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":" ","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42756067","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}
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