The water mass produced during wintertime convection in the Labrador Sea (i.e. the Labrador Sea Water or LSW) is characterized by distinct thermohaline properties. It has been shown to exert critical impact on the property and circulation fields of the North Atlantic. However, a quantitative understanding of the transformation and formation processes that produce LSW is still incomplete. Here we evaluate the mean water mass transformation and formation rates in the Labrador Sea, along with their forcing attributions, in both density and thermohaline coordinates using observation-based datasets during 2014–2019. We find that while surface buoyancy loss results in an expected densification of the basin and thus LSW formation, interior mixing has an indispensable and more complex impact. In particular, mixing across density surfaces is estimated to account for 63% of the mean formation rate in the LSW layer (4.9 Sv) and does so by converting both upper layer and overflow layer waters into the LSW layer. In addition, mixing along density surfaces is shown to be responsible for the pronounced diathermohaline transformation (~ 10 Sv) west of Greenland. This is the primary process through which the cold and fresh LSW in the basin interior is exchanged with the warm and salty Irminger water in the boundary current. Results from this study underline the critical role of mixing (both across and along density surfaces) in determining the volume and properties of the LSW, with implications for better understanding and simulating deep water evolution under climate change.
{"title":"Observation-based estimates of water mass transformation and formation in the Labrador Sea","authors":"Sijia Zou, T. Petit, Feili Li, M. Lozier","doi":"10.1175/jpo-d-23-0235.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0235.1","url":null,"abstract":"\u0000The water mass produced during wintertime convection in the Labrador Sea (i.e. the Labrador Sea Water or LSW) is characterized by distinct thermohaline properties. It has been shown to exert critical impact on the property and circulation fields of the North Atlantic. However, a quantitative understanding of the transformation and formation processes that produce LSW is still incomplete. Here we evaluate the mean water mass transformation and formation rates in the Labrador Sea, along with their forcing attributions, in both density and thermohaline coordinates using observation-based datasets during 2014–2019. We find that while surface buoyancy loss results in an expected densification of the basin and thus LSW formation, interior mixing has an indispensable and more complex impact. In particular, mixing across density surfaces is estimated to account for 63% of the mean formation rate in the LSW layer (4.9 Sv) and does so by converting both upper layer and overflow layer waters into the LSW layer. In addition, mixing along density surfaces is shown to be responsible for the pronounced diathermohaline transformation (~ 10 Sv) west of Greenland. This is the primary process through which the cold and fresh LSW in the basin interior is exchanged with the warm and salty Irminger water in the boundary current. Results from this study underline the critical role of mixing (both across and along density surfaces) in determining the volume and properties of the LSW, with implications for better understanding and simulating deep water evolution under climate change.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-04-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140655162","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}
Dongxue Mo, Po Hu, Jian Li, Yijun Hou, Shuiqing Li
The wave effect is crucial to coastal ocean dynamics, but the roles of the associated wave-dependent mechanisms, such as the wave-enhanced surface stress, wave-enhanced bottom stress, and three-dimensional wave force, are not yet fully understood. In addition, the parameterizations of each mechanism vary and need to be assessed. In this study, a coupled wave-current model based on the Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST) model system was established to identify the effect of the wave-dependent mechanism on storm surges and currents during three typical extreme weather systems, i.e., cold wave, extratropical cyclone, and typhoon systems, in a semi-enclosed sea. The effects of the three coupled mechanisms on the surface or bottom stress, in terms of both the magnitude and direction, were investigated and quantified separately based on numerical sensitive analysis. A total of seven parameterizations is used to evaluate these mechanisms, resulting in significant variations in the storm surge and current vectors. The similarities and differences of the wave-induced surge and wave-induced current among the various mechanisms were summarized. The change in the surface stress and bottom stress and the excessive momentum flux due to waves were found to mainly occur in shallow nearshore regions. Optimal choice of the combination of parameterization schemes was obtained through comparison with measured data. The wave-induced current in the open waters with a deep-water depth and complex terrain could generate cyclonic or anticyclonic current vorticities, the number and intensity of which always increased with the enhanced strength and rotation of the wind field increased.
{"title":"Effect of wave-dependent mechanisms on storm surge and current simulation during three extreme weather systems","authors":"Dongxue Mo, Po Hu, Jian Li, Yijun Hou, Shuiqing Li","doi":"10.1175/jpo-d-23-0190.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0190.1","url":null,"abstract":"\u0000The wave effect is crucial to coastal ocean dynamics, but the roles of the associated wave-dependent mechanisms, such as the wave-enhanced surface stress, wave-enhanced bottom stress, and three-dimensional wave force, are not yet fully understood. In addition, the parameterizations of each mechanism vary and need to be assessed. In this study, a coupled wave-current model based on the Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST) model system was established to identify the effect of the wave-dependent mechanism on storm surges and currents during three typical extreme weather systems, i.e., cold wave, extratropical cyclone, and typhoon systems, in a semi-enclosed sea. The effects of the three coupled mechanisms on the surface or bottom stress, in terms of both the magnitude and direction, were investigated and quantified separately based on numerical sensitive analysis. A total of seven parameterizations is used to evaluate these mechanisms, resulting in significant variations in the storm surge and current vectors. The similarities and differences of the wave-induced surge and wave-induced current among the various mechanisms were summarized. The change in the surface stress and bottom stress and the excessive momentum flux due to waves were found to mainly occur in shallow nearshore regions. Optimal choice of the combination of parameterization schemes was obtained through comparison with measured data. The wave-induced current in the open waters with a deep-water depth and complex terrain could generate cyclonic or anticyclonic current vorticities, the number and intensity of which always increased with the enhanced strength and rotation of the wind field increased.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-04-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140674152","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}
Efforts to parameterize ice shelf basal melting within climate models are limited by an incomplete understanding of the influence of ice base slope on the turbulent ice shelf-ocean boundary current (ISOBC). Here we examine the relationship between ice base slope, boundary current dynamics, and melt rate using 3-D, turbulence-permitting large-eddy simulations (LES) of an idealized ice shelf-ocean boundary current forced solely by melt-induced buoyancy. The range of simulated slopes (3-10%) is appropriate to the grounding zone of small Antarctic ice shelves and to the flanks of relatively wide ice base channels, and the initial conditions are representative of warm-cavity ocean conditions. In line with previous studies, the simulations feature the development of an Ekman boundary layer adjacent to the ice, overlaying a broad pycnocline. The time-averaged flow within the pycnocline is in thermal wind balance, with a mean shear that is only weakly dependent on the ice base slope angle α, resulting in a mean gradient Richardson number 〈Rig〉 that decreases approximately linearly with sinα. Combining this inverse relationship with a linear approximation to the density profile, we derive formulations for the friction velocity, thermal forcing, and melt rate in terms of slope angle and total buoyancy input. This theory predicts that melt rate varies like the square root of slope, which is consistent with the LES results and differs from a previously proposed linear trend. The derived scalings provide a potential framework for incorporating slope-dependence into parameterizations of mixing and melting at the base of ice shelves.
由于不完全了解冰基坡度对湍流冰架-海洋边界流（ISOBC）的影响，气候模式中冰架基底融化参数化的努力受到限制。在此，我们利用三维、湍流允许的大涡流模拟（LES），研究了仅由融化引起的浮力强迫的理想化冰架-海洋边界流的冰基坡度、边界流动力学和融化率之间的关系。模拟的坡度范围（3-10%）适合南极小型冰架的接地区和相对较宽的冰基通道的侧翼，初始条件代表了暖腔海洋条件。与之前的研究一致，模拟的特点是在冰层附近形成埃克曼边界层，并覆盖在宽阔的冰跃层上。pycnocline内的时均流处于热风平衡状态，平均切变只与冰基斜角α有微弱关系，导致平均梯度理查森数〈Rig〉随sinα近似线性下降。将这种反比关系与密度剖面的线性近似值相结合，我们得出了摩擦速度、热强迫和熔融率与斜坡角和总浮力输入有关的公式。根据该理论预测，熔化率的变化与坡度的平方根有关，这与 LES 结果一致，与之前提出的线性趋势不同。推导出的标度为将坡度依赖性纳入冰架底部混合和融化参数提供了一个潜在框架。
{"title":"Ice base slope effects on the turbulent ice shelf-ocean boundary current","authors":"J. Anselin, P. Holland, A. Jenkins, J. R. Taylor","doi":"10.1175/jpo-d-23-0256.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0256.1","url":null,"abstract":"\u0000Efforts to parameterize ice shelf basal melting within climate models are limited by an incomplete understanding of the influence of ice base slope on the turbulent ice shelf-ocean boundary current (ISOBC). Here we examine the relationship between ice base slope, boundary current dynamics, and melt rate using 3-D, turbulence-permitting large-eddy simulations (LES) of an idealized ice shelf-ocean boundary current forced solely by melt-induced buoyancy. The range of simulated slopes (3-10%) is appropriate to the grounding zone of small Antarctic ice shelves and to the flanks of relatively wide ice base channels, and the initial conditions are representative of warm-cavity ocean conditions. In line with previous studies, the simulations feature the development of an Ekman boundary layer adjacent to the ice, overlaying a broad pycnocline. The time-averaged flow within the pycnocline is in thermal wind balance, with a mean shear that is only weakly dependent on the ice base slope angle α, resulting in a mean gradient Richardson number 〈Rig〉 that decreases approximately linearly with sinα. Combining this inverse relationship with a linear approximation to the density profile, we derive formulations for the friction velocity, thermal forcing, and melt rate in terms of slope angle and total buoyancy input. This theory predicts that melt rate varies like the square root of slope, which is consistent with the LES results and differs from a previously proposed linear trend. The derived scalings provide a potential framework for incorporating slope-dependence into parameterizations of mixing and melting at the base of ice shelves.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-04-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140675879","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}
Gong Shang, Zhiwei Zhang, S. Guan, Xiaodong Huang, Chun Zhou, Wei Zhao, Jiwei Tian
Diapycnal mixing in the South China Sea (SCS) is commonly attributed to the vertical shear variance (S2) of horizontal ocean current velocity, but the seasonal modulation of the S2 is still poorly understood due to the scarcity of long-term velocity observations. Here, this issue is explored in detail based on nearly 10-year-long ADCP velocity data from a mooring in the northern SCS. We find that the S2 in the northern SCS exhibits significant seasonal variations at both the near-surface (90–180 m) and sub-surface (180–400 m) layers, but their seasonal cycles and modulation mechanisms are quite different. For the near-surface layer, the S2 is stronger in late summer, autumn, and winter but weaker in spring and early summer, while in the sub-surface layer, it is much stronger in winter than other seasons. Further analysis suggests that in the near-surface layer, the stronger S2 in autumn and winter is primarily caused by typhoons-induced near-inertial internal waves (NIWs) and the large sub-inertial velocity shear of the baroclinic mesoscale eddies, respectively. With respect to the sub-surface layer, the enhanced wintertime S2 is primarily associated with the “inertial chimney” effect of anticyclonic eddies, trapping wind-forced downward-propagating NIWs and significantly increasing the near-inertial shear at the critical layer. The findings in this study highlight the potentially important roles of mesoscale eddies and NIWs in modulating the seasonality of upper-ocean mixing in the northern SCS. This modulation is attributed not only to the strong shear of these features but also to their interactions.
{"title":"Mesoscale eddies and near-inertial internal waves modulate seasonal variations of vertical shear variance in the northern South China Sea","authors":"Gong Shang, Zhiwei Zhang, S. Guan, Xiaodong Huang, Chun Zhou, Wei Zhao, Jiwei Tian","doi":"10.1175/jpo-d-23-0070.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0070.1","url":null,"abstract":"\u0000Diapycnal mixing in the South China Sea (SCS) is commonly attributed to the vertical shear variance (S2) of horizontal ocean current velocity, but the seasonal modulation of the S2 is still poorly understood due to the scarcity of long-term velocity observations. Here, this issue is explored in detail based on nearly 10-year-long ADCP velocity data from a mooring in the northern SCS. We find that the S2 in the northern SCS exhibits significant seasonal variations at both the near-surface (90–180 m) and sub-surface (180–400 m) layers, but their seasonal cycles and modulation mechanisms are quite different. For the near-surface layer, the S2 is stronger in late summer, autumn, and winter but weaker in spring and early summer, while in the sub-surface layer, it is much stronger in winter than other seasons. Further analysis suggests that in the near-surface layer, the stronger S2 in autumn and winter is primarily caused by typhoons-induced near-inertial internal waves (NIWs) and the large sub-inertial velocity shear of the baroclinic mesoscale eddies, respectively. With respect to the sub-surface layer, the enhanced wintertime S2 is primarily associated with the “inertial chimney” effect of anticyclonic eddies, trapping wind-forced downward-propagating NIWs and significantly increasing the near-inertial shear at the critical layer. The findings in this study highlight the potentially important roles of mesoscale eddies and NIWs in modulating the seasonality of upper-ocean mixing in the northern SCS. This modulation is attributed not only to the strong shear of these features but also to their interactions.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-04-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140684550","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}
Subtropical mode water (STMW) is a thick layer of water mass characterized by homogeneous properties within the main pycnocline, important for oceanic oxygen utilization, carbon sequestration, and climate regulation. North Pacific STMW is formed in the Kuroshio Extension region, where vigorous mesoscale eddies strongly interact with the atmosphere. However, it remains unknown how such mesoscale ocean-atmosphere (MOA) coupling affects the STMW formation. By conducting twin simulations with an eddy-resolving global climate model, we find that approximately 25% more STMW is formed with the MOA coupling than without it. This is attributable to a significant increase in ocean latent heat release primarily driven by higher wind speed over the STMW formation region, which is associated with the southward deflection of storm tracks in response to oceanic mesoscale imprints. Such enhanced surface latent heat loss overwhelms the stronger upper-ocean restratification induced by vertical eddy and turbulent heat transport, leading to the formation of colder and denser STMW in the presence of MOA coupling. Further investigation of a multi-model and multi-resolution ensemble of global coupled models reveals that the agreement between the STMW simulation in eddy-present/rich coupled models and observations is superior to that of eddy-free ones, likely due to more realistic representation of MOA coupling. However, the ocean-alone model simulations show significant limitations in improving STMW production, even with refined model resolution. This indicates the importance of incorporating the MOA coupling into Earth system models to alleviate biases in STMW and associated climatic and biogeochemical impacts.
{"title":"Mesoscale ocean-atmosphere coupling effects on the North Pacific subtropical mode water","authors":"Jingjie Yu, Bolan Gan, Haiyuan Yang, Zhaohui Chen, Lixiao Xu, Lixin Wu","doi":"10.1175/jpo-d-23-0148.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0148.1","url":null,"abstract":"\u0000Subtropical mode water (STMW) is a thick layer of water mass characterized by homogeneous properties within the main pycnocline, important for oceanic oxygen utilization, carbon sequestration, and climate regulation. North Pacific STMW is formed in the Kuroshio Extension region, where vigorous mesoscale eddies strongly interact with the atmosphere. However, it remains unknown how such mesoscale ocean-atmosphere (MOA) coupling affects the STMW formation. By conducting twin simulations with an eddy-resolving global climate model, we find that approximately 25% more STMW is formed with the MOA coupling than without it. This is attributable to a significant increase in ocean latent heat release primarily driven by higher wind speed over the STMW formation region, which is associated with the southward deflection of storm tracks in response to oceanic mesoscale imprints. Such enhanced surface latent heat loss overwhelms the stronger upper-ocean restratification induced by vertical eddy and turbulent heat transport, leading to the formation of colder and denser STMW in the presence of MOA coupling. Further investigation of a multi-model and multi-resolution ensemble of global coupled models reveals that the agreement between the STMW simulation in eddy-present/rich coupled models and observations is superior to that of eddy-free ones, likely due to more realistic representation of MOA coupling. However, the ocean-alone model simulations show significant limitations in improving STMW production, even with refined model resolution. This indicates the importance of incorporating the MOA coupling into Earth system models to alleviate biases in STMW and associated climatic and biogeochemical impacts.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-04-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140689797","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}
F. Sévellec, A. Colin de Verdière, N. Kolodziejczyk
Observations of deep Argo displacements (located between 950 and 1150 dbar) and their associated integrated Lagrangian velocities allow for the first time to compute worldwide deep horizontal transfers of Kinetic Energy (KE) between the 3°×3°-Mean and the Eddy reservoirs (MKE and EKE, respectively). This diagnostic reveals that the transfers are mainly localized along western boundaries and in the Southern Ocean. Overall the MKE-to-EKE transfers appear dominant globally and in all specifically tested regions (i.e., Gulf Stream, Kuroshio, Agulhas Current, and Antarctic Circumpolar Current). However an important exception is the Zapiola gyre where the EKE-to-MKE transfers dominate. Beyond that, we find that horizontal KE transfers are better described by the horizontal properties of the mean flow deformation (divergence and strain) than by the horizontal properties of the turbulent velocities. Our theoretical analysis also demonstrates that the mean flow vorticity does not contribute to KE transfers. We show the existence of two consistent transfer modes: one from MKE to EKE and one from EKE to MKE, which are based on the eigendirections of the mean flow deformation tensor. The alignment of the turbulence along these directions selects the transfer modes and it is the competition between these two transfer modes that leads to the actual transfers. We compute these transfer modes globally, regionally, and locally. We explain the distinctive situation of the Zapiola gyre by the favoured alignment of the turbulence with the EKE-to-MKE transfer mode. Overall, the dominance of the large-scale flow properties on the structure of the MKE-to-EKE transfers suggests the potential for a large-scale parameterization.
{"title":"Global Observations of Deep Ocean Kinetic Energy Transfers","authors":"F. Sévellec, A. Colin de Verdière, N. Kolodziejczyk","doi":"10.1175/jpo-d-23-0150.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0150.1","url":null,"abstract":"\u0000Observations of deep Argo displacements (located between 950 and 1150 dbar) and their associated integrated Lagrangian velocities allow for the first time to compute worldwide deep horizontal transfers of Kinetic Energy (KE) between the 3°×3°-Mean and the Eddy reservoirs (MKE and EKE, respectively). This diagnostic reveals that the transfers are mainly localized along western boundaries and in the Southern Ocean. Overall the MKE-to-EKE transfers appear dominant globally and in all specifically tested regions (i.e., Gulf Stream, Kuroshio, Agulhas Current, and Antarctic Circumpolar Current). However an important exception is the Zapiola gyre where the EKE-to-MKE transfers dominate. Beyond that, we find that horizontal KE transfers are better described by the horizontal properties of the mean flow deformation (divergence and strain) than by the horizontal properties of the turbulent velocities. Our theoretical analysis also demonstrates that the mean flow vorticity does not contribute to KE transfers. We show the existence of two consistent transfer modes: one from MKE to EKE and one from EKE to MKE, which are based on the eigendirections of the mean flow deformation tensor. The alignment of the turbulence along these directions selects the transfer modes and it is the competition between these two transfer modes that leads to the actual transfers. We compute these transfer modes globally, regionally, and locally. We explain the distinctive situation of the Zapiola gyre by the favoured alignment of the turbulence with the EKE-to-MKE transfer mode. Overall, the dominance of the large-scale flow properties on the structure of the MKE-to-EKE transfers suggests the potential for a large-scale parameterization.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140709195","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}
T. Morrison, J. McClean, Sarah T. Gille, M. Maltrud, Detelina P. Ivanova, Anthony P. Craig
Meltwater from the Greenland Ice Sheet can alter the continental shelf/slope circulation, cross-shelf freshwater fluxes, and limit deep convection in adjacent basins through surface freshening. We explore the impacts on the West Greenland Current and Eastern Labrador Sea with different vertical distributions of the meltwater forcing. In this study, we present results from global coupled ocean/sea-ice simulations, forced with atmospheric reanalysis, that are mesoscale eddy-active (~2–3 km horizontal spacing) and eddy-permitting (~6–7 km horizontal spacing) in the study region. We compare the West Greenland Current in mesoscale eddy-active and eddy-permitting without meltwater to highlight the role of small scale features. The mesoscale eddy-active configuration is then used to assess the change in the Eastern Labrador Sea when meltwater is added to the surface or vertically distributed to account for mixing within fjords. In both simulations with meltwater, the West Greenland and West Greenland Coastal Currents are faster than in the simulation with no meltwater; their mean surface speeds are highest in the vertical distribution case. In the latter case, there is enhanced baroclinic conversion at the shelf break compared to the simulation with no meltwater. When meltwater is vertically distributed, there is an increase in baroclinic conversion at the shelf break associated with increased eddy kinetic energy. In addition, in the Eastern Labrador Sea the salinity is lower and the meltwater volume greater when meltwater is vertically distributed. Therefore, the West Greenland Current is sensitive to how meltwater is added to the ocean with implications for the freshening of the Labrador Sea.
{"title":"Sensitivities of the West Greenland Current to Greenland Ice Sheet Meltwater in a Mesoscale Ocean/Sea ice Model","authors":"T. Morrison, J. McClean, Sarah T. Gille, M. Maltrud, Detelina P. Ivanova, Anthony P. Craig","doi":"10.1175/jpo-d-23-0102.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0102.1","url":null,"abstract":"\u0000Meltwater from the Greenland Ice Sheet can alter the continental shelf/slope circulation, cross-shelf freshwater fluxes, and limit deep convection in adjacent basins through surface freshening. We explore the impacts on the West Greenland Current and Eastern Labrador Sea with different vertical distributions of the meltwater forcing. In this study, we present results from global coupled ocean/sea-ice simulations, forced with atmospheric reanalysis, that are mesoscale eddy-active (~2–3 km horizontal spacing) and eddy-permitting (~6–7 km horizontal spacing) in the study region. We compare the West Greenland Current in mesoscale eddy-active and eddy-permitting without meltwater to highlight the role of small scale features. The mesoscale eddy-active configuration is then used to assess the change in the Eastern Labrador Sea when meltwater is added to the surface or vertically distributed to account for mixing within fjords. In both simulations with meltwater, the West Greenland and West Greenland Coastal Currents are faster than in the simulation with no meltwater; their mean surface speeds are highest in the vertical distribution case. In the latter case, there is enhanced baroclinic conversion at the shelf break compared to the simulation with no meltwater. When meltwater is vertically distributed, there is an increase in baroclinic conversion at the shelf break associated with increased eddy kinetic energy. In addition, in the Eastern Labrador Sea the salinity is lower and the meltwater volume greater when meltwater is vertically distributed. Therefore, the West Greenland Current is sensitive to how meltwater is added to the ocean with implications for the freshening of the Labrador Sea.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-04-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140724321","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}
R. C. Musgrave, D. Winters, V. E. Zemskova, J. Lerczak
A series of idealized numerical simulations is used to examine the generation of mode-one superinertial coastally trapped waves (CTW). In the first set of simulations, CTW are resonantly generated when freely propagating mode-one internal tides are incident on the coast such that the angle of incidence of the internal wave causes the projected wavenumber of the tide on the coast to satisfy a triad relationship with the wavenumbers of the bathymetry and the CTW. In the second set of simulations, CTW are generated by the interaction of the barotropic tide with topography that has the same scales as the CTW. Under resonant conditions superinertial coastally trapped waves are a leading order coastal process, with along-shore current magnitudes that can be larger than the barotropic or internal tides from which they are generated.
{"title":"The generation of superinertial coastally trapped waves by scattering at the coast","authors":"R. C. Musgrave, D. Winters, V. E. Zemskova, J. Lerczak","doi":"10.1175/jpo-d-23-0180.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0180.1","url":null,"abstract":"\u0000A series of idealized numerical simulations is used to examine the generation of mode-one superinertial coastally trapped waves (CTW). In the first set of simulations, CTW are resonantly generated when freely propagating mode-one internal tides are incident on the coast such that the angle of incidence of the internal wave causes the projected wavenumber of the tide on the coast to satisfy a triad relationship with the wavenumbers of the bathymetry and the CTW. In the second set of simulations, CTW are generated by the interaction of the barotropic tide with topography that has the same scales as the CTW. Under resonant conditions superinertial coastally trapped waves are a leading order coastal process, with along-shore current magnitudes that can be larger than the barotropic or internal tides from which they are generated.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-04-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140728173","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}
Anna Lo Piccolo, Christopher Horvat, B. Fox-Kemper
During polar winter, refreezing of exposed ocean areas results in the rejection of brine, i.e., salt-enriched plumes of water, a source of available potential energy that can drive ocean instabilities. As this process is highly localized, and driven by sea ice physics, not gradients in oceanic or atmospheric buoyancy, it is not currently captured in modern climate models. This study aims to understand the energetics and lateral transfer of density at a semi-infinite, instantaneously-opened and continuously re-freezing sea ice edge through a series of high resolution model experiments. We show that kilometer-scale submesoscale eddies grow from baroclinic instabilities via an inverse energy cascade. These eddies meander along the ice edge and propagate laterally. The lateral transfer of buoyancy by eddies is not explained by existing theories. We isolate the fundamental forcing-independent quantities driving lateral mixing, and discuss the implications for the overall strength of submesoscale activity in the Arctic Ocean.
{"title":"Energetics and Transfer of Submesoscale Brine Driven Eddies at a Sea Ice Edge","authors":"Anna Lo Piccolo, Christopher Horvat, B. Fox-Kemper","doi":"10.1175/jpo-d-23-0147.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0147.1","url":null,"abstract":"\u0000During polar winter, refreezing of exposed ocean areas results in the rejection of brine, i.e., salt-enriched plumes of water, a source of available potential energy that can drive ocean instabilities. As this process is highly localized, and driven by sea ice physics, not gradients in oceanic or atmospheric buoyancy, it is not currently captured in modern climate models. This study aims to understand the energetics and lateral transfer of density at a semi-infinite, instantaneously-opened and continuously re-freezing sea ice edge through a series of high resolution model experiments. We show that kilometer-scale submesoscale eddies grow from baroclinic instabilities via an inverse energy cascade. These eddies meander along the ice edge and propagate laterally. The lateral transfer of buoyancy by eddies is not explained by existing theories. We isolate the fundamental forcing-independent quantities driving lateral mixing, and discuss the implications for the overall strength of submesoscale activity in the Arctic Ocean.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-04-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140738805","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}
This study examines the link between near-bottom outflows of dense water formed in Antarctic coastal polynyas and onshore intrusions of Circumpolar Deep Water (CDW) through prograde troughs cutting across the continental shelf. Numerical simulations show that the dense water outflow is primarily in the form of cyclonic eddies. The trough serves as a topographic guide that organizes the offshore-moving dense water eddies into a chain pattern. The offshore migration speed of the dense water eddies is similar to the velocity of the dense water offshore flow in the trough, which scaling analysis finds to be proportional to the reduced gravity of the dense water and the slope of the trough side walls and to be inversely proportional to the Coriolis parameter. Our model simulations indicate that, as these cyclonic dense water eddies move across the trough mouth into the deep ocean, they entrain CDW from offshore and carry CDW clockwise along their periphery into the trough. Subsequent cyclonic dense water eddies then entrain the intruding CDW further toward the coast along the trough. This process of recurring onshore entrainment of CDW by a topographically constrained chain of offshore-flowing dense water eddies is consistent with topographic hotspots of onshore intrusion of CDW around Antarctica identified by other studies. It can bring CDW from offshore to close to the coast and thus impact the heat flux into Antarctic coastal regions, affecting interactions among ocean, sea ice, and ice shelves.
{"title":"Cross-Shelf Exchange in Prograde Antarctic Troughs Driven by Offshore Propagating Dense Water Eddies","authors":"Alan Gaul, W. Zhang, C. Cenedese","doi":"10.1175/jpo-d-23-0088.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0088.1","url":null,"abstract":"\u0000This study examines the link between near-bottom outflows of dense water formed in Antarctic coastal polynyas and onshore intrusions of Circumpolar Deep Water (CDW) through prograde troughs cutting across the continental shelf. Numerical simulations show that the dense water outflow is primarily in the form of cyclonic eddies. The trough serves as a topographic guide that organizes the offshore-moving dense water eddies into a chain pattern. The offshore migration speed of the dense water eddies is similar to the velocity of the dense water offshore flow in the trough, which scaling analysis finds to be proportional to the reduced gravity of the dense water and the slope of the trough side walls and to be inversely proportional to the Coriolis parameter. Our model simulations indicate that, as these cyclonic dense water eddies move across the trough mouth into the deep ocean, they entrain CDW from offshore and carry CDW clockwise along their periphery into the trough. Subsequent cyclonic dense water eddies then entrain the intruding CDW further toward the coast along the trough. This process of recurring onshore entrainment of CDW by a topographically constrained chain of offshore-flowing dense water eddies is consistent with topographic hotspots of onshore intrusion of CDW around Antarctica identified by other studies. It can bring CDW from offshore to close to the coast and thus impact the heat flux into Antarctic coastal regions, affecting interactions among ocean, sea ice, and ice shelves.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-04-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140736173","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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