Y. Troitskaya, A. Kandaurov, A. Zotova, E. Korsukova, D. Sergeev
Recent studies indicate that the dominant mechanism for generating sprays in hurricane winds is “a bag breakup” fragmentation. This fragmentation process is typically characterized by inflation and consequent bursting of short-lived objects, referred to as ”bags” (sail-like pieces of water film surrounded by a rim). Both the number of spray droplets and their size distribution substantially affect the air-sea heat and momentum exchange. Due to a lack of experimental data, the early spray generation function (SGF) for the ”bag breakup” mechanism was based on the assumed similarity with resembling processes. Here we present experimental results for the case with a single isolated ”bag breakup” fragmentation event. These experiments revealed several differences from similar fragmentation events that control the droplet sizes, such as secondary disintegration of droplets in gaseous flows and bursting of bubbles. In contrast to the bubble bursting, the film thickness of the ”bag” canopy is not constant but is random with lognormal distribution. Additionally, its average value does not depend on the canopy radius but is determined by the wind speed. The lognormal size distribution of the canopy droplets is observed in conjunction with the established mechanism of liquid film fragmentation. The rim fragmentation results in two types of droplets, and their size distribution has been found to be lognormal distribution. The constructed SGF is verified by comparing it with experimental data from the literature. The perspectives of transferring the results from laboratory to field environment have also been discussed.
{"title":"Statistical characteristics of droplets formed due to the “bag breakup” fragmentation event at the interface between water and high-speed air flow.","authors":"Y. Troitskaya, A. Kandaurov, A. Zotova, E. Korsukova, D. Sergeev","doi":"10.1175/jpo-d-23-0037.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0037.1","url":null,"abstract":"\u0000Recent studies indicate that the dominant mechanism for generating sprays in hurricane winds is “a bag breakup” fragmentation. This fragmentation process is typically characterized by inflation and consequent bursting of short-lived objects, referred to as ”bags” (sail-like pieces of water film surrounded by a rim). Both the number of spray droplets and their size distribution substantially affect the air-sea heat and momentum exchange. Due to a lack of experimental data, the early spray generation function (SGF) for the ”bag breakup” mechanism was based on the assumed similarity with resembling processes. Here we present experimental results for the case with a single isolated ”bag breakup” fragmentation event. These experiments revealed several differences from similar fragmentation events that control the droplet sizes, such as secondary disintegration of droplets in gaseous flows and bursting of bubbles. In contrast to the bubble bursting, the film thickness of the ”bag” canopy is not constant but is random with lognormal distribution. Additionally, its average value does not depend on the canopy radius but is determined by the wind speed. The lognormal size distribution of the canopy droplets is observed in conjunction with the established mechanism of liquid film fragmentation. The rim fragmentation results in two types of droplets, and their size distribution has been found to be lognormal distribution. The constructed SGF is verified by comparing it with experimental data from the literature. The perspectives of transferring the results from laboratory to field environment have also been discussed.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":" ","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45852751","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 process of water-column stratification breakdown in Antarctic coastal polynyas adjacent to an ice shelf with a cavity underneath. This first part of a two-part sequence seeks to quantify the influence of offshore katabatic winds, alongshore winds, air temperature, and initial ambient stratification on the timescales of polynya destratification through combining process-oriented numerical simulations and analytical scaling. In particular, the often-neglected influence of wind-driven circulation on the lateral transport of the water formed at the polynya surface — which we call Polynya Source Water (PSW) — is systematically examined here. First, an ice-shelf/sea-ice/ocean coupled numerical model is adapted to simulate the process of PSW formation in polynyas of various configurations. The simulations highlight that i) before reaching the bottom, majority of the PSW is actually carried away from the polynya by katabatic wind-induced offshore outflow, diminishing water-column mixing in the polynya and intrusion of the PSW into the neighboring ice shelf cavity, and ii) alongshore coastal easterly winds, through inducing onshore Ekman transport, reduce offshore loss of the PSW and enhance polynya mixing and PSW intrusion into the cavity. Second, an analytical scaling of the destratification timescale is derived based on fundamental physical principles to quantitatively synthesize the influence of the physical factors, which is then verified by independent numerical sensitivity simulations. This work provides insights into the mechanisms that drive temporal and cross-polynya variations in stratification and PSW formation in Antarctic coastal polynyas, and establishes a framework for studying differences among the polynyas in the ocean.
{"title":"Stratification Breakdown in Antarctic Coastal Polynyas, Part I: Influence of Physical Factors on the Destratification Timescale","authors":"Yilang Xu, W. Zhang, T. Maksym, R. Ji, Yun Li","doi":"10.1175/jpo-d-22-0218.1","DOIUrl":"https://doi.org/10.1175/jpo-d-22-0218.1","url":null,"abstract":"\u0000This study examines the process of water-column stratification breakdown in Antarctic coastal polynyas adjacent to an ice shelf with a cavity underneath. This first part of a two-part sequence seeks to quantify the influence of offshore katabatic winds, alongshore winds, air temperature, and initial ambient stratification on the timescales of polynya destratification through combining process-oriented numerical simulations and analytical scaling. In particular, the often-neglected influence of wind-driven circulation on the lateral transport of the water formed at the polynya surface — which we call Polynya Source Water (PSW) — is systematically examined here. First, an ice-shelf/sea-ice/ocean coupled numerical model is adapted to simulate the process of PSW formation in polynyas of various configurations. The simulations highlight that i) before reaching the bottom, majority of the PSW is actually carried away from the polynya by katabatic wind-induced offshore outflow, diminishing water-column mixing in the polynya and intrusion of the PSW into the neighboring ice shelf cavity, and ii) alongshore coastal easterly winds, through inducing onshore Ekman transport, reduce offshore loss of the PSW and enhance polynya mixing and PSW intrusion into the cavity. Second, an analytical scaling of the destratification timescale is derived based on fundamental physical principles to quantitatively synthesize the influence of the physical factors, which is then verified by independent numerical sensitivity simulations. This work provides insights into the mechanisms that drive temporal and cross-polynya variations in stratification and PSW formation in Antarctic coastal polynyas, and establishes a framework for studying differences among the polynyas in the ocean.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":" ","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43471792","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 is Part II of a study examining wintertime destratification in Antarctic coastal polynyas, focusing on providing a qualitative description of the influence of ice tongues and headlands, both common geometric features neighboring the polynyas. The model of a coastal polynya used in Part I is modified to include an ice tongue and a headland to investigate their impacts on the dispersal of water formed at the polynya surface, which is referred to as Polynya Source Water (PSW) here. The model configuration qualitatively represents the settings of some coastal polynyas, such as the Terra Nova Bay Polynya. The simulations highlight that an ice tongue next to a polynya tends to break the alongshore symmetry in the lateral return flows toward the polynya, creating a stagnant region in the corner between the ice tongue and polynya where outflow of the PSW in the water column is suppressed. This enhances sinking of the PSW and accelerates destratification of the polynya water column. Adding a headland to the other side of the polynya tends to restore the alongshore symmetry in the lateral return flows, which increases the offshore PSW transport and slows down destratification in the polynya. This work stresses the importance of resolving small-scale geometric features in simulating vertical mixing in the polynya. It provides a framework to explain spatial and temporal variability in rates of destratification and Dense Shelf Water formation across Antarctic coastal polynyas, and helps understand why some polynyas are sources of Antarctic Bottom Water while other are not.
这是一项研究的第二部分，该研究考察了南极沿海波利尼亚斯冬季的退化，重点是对冰舌和海岬的影响进行定性描述，这两种特征都是波利尼亚斯附近的常见几何特征。第一部分中使用的沿海波利尼亚模型被修改为包括冰舌和岬，以研究它们对波利尼亚表面形成的水扩散的影响，这里称为波利尼亚水源水（PSW）。模型配置定性地代表了一些沿海波利尼亚的环境，如Terra Nova Bay Polynya。模拟结果表明，在朝向波尼亚的横向回流中，波尼亚旁边的冰舌往往会打破沿岸对称性，在冰舌和波尼亚之间的角落形成一个停滞区域，在该区域，水柱中PSW的流出受到抑制。这增强了PSW的下沉并加速了polynya水柱的破坏。在波利尼亚河的另一侧增加一个海岬往往会恢复横向回流中的沿岸对称性，这增加了海上PSW的输送，减缓了波利尼亚河中的破坏速度。这项工作强调了在模拟多边形中的垂直混合时解决小尺度几何特征的重要性。它提供了一个框架来解释南极沿海波利尼亚斯的破坏率和密集大陆架水形成率的空间和时间变化，并有助于理解为什么一些波利尼亚斯是南极底层水的来源，而另一些则不是。
{"title":"Stratification Breakdown in Antarctic Coastal Polynyas, Part II: Influence of an Ice Tongue and Coastline Geometry","authors":"Yilang Xu, W. Zhang, T. Maksym, R. Ji, Yun Li","doi":"10.1175/jpo-d-22-0219.1","DOIUrl":"https://doi.org/10.1175/jpo-d-22-0219.1","url":null,"abstract":"\u0000This is Part II of a study examining wintertime destratification in Antarctic coastal polynyas, focusing on providing a qualitative description of the influence of ice tongues and headlands, both common geometric features neighboring the polynyas. The model of a coastal polynya used in Part I is modified to include an ice tongue and a headland to investigate their impacts on the dispersal of water formed at the polynya surface, which is referred to as Polynya Source Water (PSW) here. The model configuration qualitatively represents the settings of some coastal polynyas, such as the Terra Nova Bay Polynya. The simulations highlight that an ice tongue next to a polynya tends to break the alongshore symmetry in the lateral return flows toward the polynya, creating a stagnant region in the corner between the ice tongue and polynya where outflow of the PSW in the water column is suppressed. This enhances sinking of the PSW and accelerates destratification of the polynya water column. Adding a headland to the other side of the polynya tends to restore the alongshore symmetry in the lateral return flows, which increases the offshore PSW transport and slows down destratification in the polynya. This work stresses the importance of resolving small-scale geometric features in simulating vertical mixing in the polynya. It provides a framework to explain spatial and temporal variability in rates of destratification and Dense Shelf Water formation across Antarctic coastal polynyas, and helps understand why some polynyas are sources of Antarctic Bottom Water while other are not.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":" ","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44399974","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The large-scale ocean circulation in an ocean basin was previously thought to be impacted cumulatively by all the overlying tropical cyclones (TCs). Based on idealized numerical experiments and altimetry observation, this study reveals that, unnecessarily by cumulative impacts, a single TC actually has the ability of plowing the large-scale sea surface height (SSH) field due to the TC-induced geostrophic response. This ability is dictated by the along-track length scale of the geostrophic response, i.e. the total track length. Some of observed along-track signals including SSH trough, jet and SSH rise can confirm the TC-induced large-scale impacts. Shortly after the TC passage, the observable large-scale signals are generally the SSH trough. However, the jet and the SSH rise easily emerge from the evolved SSH trough due to Rossby wave dispersion. By identifying and tracking the observable signals, this study demonstrates that the subtropical gyre primarily over [4-20 °N, 122-180 °E] are plowed by 9 typhoons (2015) into several large blocks of SSH trough and SSH rise. These long-lived SSH troughs and SSH rises dominate the upper-layer circulation from April to December in 2015. If the large-scale signals cannot be observed, the estimated TC-induced mean SSH decreases suggest that the large-scale impacts may still exist but merely cannot be seen intuitively. This study provides compelling observational evidence for the TC-induced large-scale impacts, further highlighting that TCs may play a non-negligible role in the upper ocean dynamics in the subtropical gyre.
{"title":"Observable large-scale impacts of tropical cyclones on subtropical gyre","authors":"Zhumin Lu, Guihua Wang, X. Shang","doi":"10.1175/jpo-d-22-0230.1","DOIUrl":"https://doi.org/10.1175/jpo-d-22-0230.1","url":null,"abstract":"\u0000The large-scale ocean circulation in an ocean basin was previously thought to be impacted cumulatively by all the overlying tropical cyclones (TCs). Based on idealized numerical experiments and altimetry observation, this study reveals that, unnecessarily by cumulative impacts, a single TC actually has the ability of plowing the large-scale sea surface height (SSH) field due to the TC-induced geostrophic response. This ability is dictated by the along-track length scale of the geostrophic response, i.e. the total track length. Some of observed along-track signals including SSH trough, jet and SSH rise can confirm the TC-induced large-scale impacts. Shortly after the TC passage, the observable large-scale signals are generally the SSH trough. However, the jet and the SSH rise easily emerge from the evolved SSH trough due to Rossby wave dispersion. By identifying and tracking the observable signals, this study demonstrates that the subtropical gyre primarily over [4-20 °N, 122-180 °E] are plowed by 9 typhoons (2015) into several large blocks of SSH trough and SSH rise. These long-lived SSH troughs and SSH rises dominate the upper-layer circulation from April to December in 2015. If the large-scale signals cannot be observed, the estimated TC-induced mean SSH decreases suggest that the large-scale impacts may still exist but merely cannot be seen intuitively. This study provides compelling observational evidence for the TC-induced large-scale impacts, further highlighting that TCs may play a non-negligible role in the upper ocean dynamics in the subtropical gyre.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":" ","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42164087","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}
Lina Yang, Xinyang Zhao, Peng Liang, Tianyu Zhang, L. Xie, R. Murtugudde
Sea level variabilities in the southwest Pacific contribute to the variations of equatorial current bifurcation and the Indonesian Throughflow transport. These processes are closely related to the recharge/discharge of equatorial heat content and dynamic distribution of anthropogenic ocean heating over the Indo-Pacific basin, thus being of profound significance for climate variability and change. Here we identify the major features of seasonal and interannual sea level variabilities in this region, confirming the dominance of the first baroclinic mode in the tropics (contributing 60–80% of the variances) and higher baroclinic modes in the extra-tropics (40–60% of the seasonal variance). Seasonally, except in the western Coral Sea where the Ekman pumping is significant, the wind-driven first-mode baroclinic Rossby waves originating to the east of the dateline control the sea level variations over most tropical Pacific regions. In the domain where the 1.5-layer reduced gravity model becomes deficient, the surface heat fluxes dominate, explaining ~40–80% of sea level variance. For interannual variability, ~40–60% of the variance are El Niño-Southern Oscillation (ENSO)-related. The wind-driven Rossby and Kelvin waves east of the dateline explain ~40–78% of the interannual variance in the tropical Pacific. Outside the tropics, small-scale diffusive processes are presumed critical for interannual variability according to a thermodynamic analysis using an eddy-permitting ocean model simulation. Further process and predictive understandings can be achieved with the coupled climate models properly parameterizing the sub-grid-scale processes.
{"title":"Wind and heat forcings of the seasonal and interannual sea level variabilities in the southwest Pacific","authors":"Lina Yang, Xinyang Zhao, Peng Liang, Tianyu Zhang, L. Xie, R. Murtugudde","doi":"10.1175/jpo-d-23-0018.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0018.1","url":null,"abstract":"\u0000Sea level variabilities in the southwest Pacific contribute to the variations of equatorial current bifurcation and the Indonesian Throughflow transport. These processes are closely related to the recharge/discharge of equatorial heat content and dynamic distribution of anthropogenic ocean heating over the Indo-Pacific basin, thus being of profound significance for climate variability and change. Here we identify the major features of seasonal and interannual sea level variabilities in this region, confirming the dominance of the first baroclinic mode in the tropics (contributing 60–80% of the variances) and higher baroclinic modes in the extra-tropics (40–60% of the seasonal variance). Seasonally, except in the western Coral Sea where the Ekman pumping is significant, the wind-driven first-mode baroclinic Rossby waves originating to the east of the dateline control the sea level variations over most tropical Pacific regions. In the domain where the 1.5-layer reduced gravity model becomes deficient, the surface heat fluxes dominate, explaining ~40–80% of sea level variance. For interannual variability, ~40–60% of the variance are El Niño-Southern Oscillation (ENSO)-related. The wind-driven Rossby and Kelvin waves east of the dateline explain ~40–78% of the interannual variance in the tropical Pacific. Outside the tropics, small-scale diffusive processes are presumed critical for interannual variability according to a thermodynamic analysis using an eddy-permitting ocean model simulation. Further process and predictive understandings can be achieved with the coupled climate models properly parameterizing the sub-grid-scale processes.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":" ","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-06-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42665178","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}
Indonesian throughflow (ITF) waters move along multiple pathways within the Indian Ocean. The western route is within the thermocline of the South Equatorial Current (SEC), and the southern via injection into the Leeuwin Current (LC) along western Australia. We use gridded Argo data to examine heat content anomaly (HCa) within three boxes in the eastern Indian Ocean, one adjacent to the ITF outflow from the Indonesian Seas (ITF box), one in the eastern portion of the SEC (SEC box), and the third in the LC (LC box). Although interannual HCa variability in the SEC and ITF boxes is well correlated, a large increase in HCa within the ITF box does not appear in the SEC box in 2011, but is evident in the LC box. The 2011 change in the SEC/LC partitioning is investigated using GODAS reanalysis by examining the strength of the SEC and LC during a 2009 HCa increase within the ITF box, and the subsequent increase in 2011. During 2009 a strong SEC and weakened LC spread the increased ITF HCa into the central Indian Ocean; whereas a weak SEC and strengthened LC during 2011 transmit the HCa signal to the south. Near surface winds and mean sea level pressure from NCEP/NCAR reanalysis reveal that Ningaloo Niño events led to shifts in ocean circulation during 2000, and 2011. LC and SEC exports show a high negative correlation at interannual timescales, indicating that a reduction of outflow from one pathway is partially compensated by an increase from the other.
{"title":"Indonesian Throughflow Partitioning Between Leeuwin and South Equatorial Currents","authors":"L. Gruenburg, A. Gordon, A. Thurnherr","doi":"10.1175/jpo-d-22-0205.1","DOIUrl":"https://doi.org/10.1175/jpo-d-22-0205.1","url":null,"abstract":"\u0000Indonesian throughflow (ITF) waters move along multiple pathways within the Indian Ocean. The western route is within the thermocline of the South Equatorial Current (SEC), and the southern via injection into the Leeuwin Current (LC) along western Australia. We use gridded Argo data to examine heat content anomaly (HCa) within three boxes in the eastern Indian Ocean, one adjacent to the ITF outflow from the Indonesian Seas (ITF box), one in the eastern portion of the SEC (SEC box), and the third in the LC (LC box). Although interannual HCa variability in the SEC and ITF boxes is well correlated, a large increase in HCa within the ITF box does not appear in the SEC box in 2011, but is evident in the LC box. The 2011 change in the SEC/LC partitioning is investigated using GODAS reanalysis by examining the strength of the SEC and LC during a 2009 HCa increase within the ITF box, and the subsequent increase in 2011. During 2009 a strong SEC and weakened LC spread the increased ITF HCa into the central Indian Ocean; whereas a weak SEC and strengthened LC during 2011 transmit the HCa signal to the south. Near surface winds and mean sea level pressure from NCEP/NCAR reanalysis reveal that Ningaloo Niño events led to shifts in ocean circulation during 2000, and 2011. LC and SEC exports show a high negative correlation at interannual timescales, indicating that a reduction of outflow from one pathway is partially compensated by an increase from the other.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":" ","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-06-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48205498","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}
Directional wave spectra are of importance for numerous practical applications such as seafaring and ocean engineering. The wave spectral densities at a certain point in the open ocean are significantly correlated to the local wind field and historical remote wind field. This feature can be used to predict the wave spectrum at that point using the wind field. In this study, a Convolutional Neural Network (CNN) model was established to estimate wave spectra at a target point using the wind field from the ERA5 dataset. A geospatial range where the wind could impact the target point was selected and then the historical wind field data within the range was analyzed to extract the nonlinear quantitative relationships between wind fields and wave spectra. For the spectral densities at a given direction, the wind data along the direction where waves come from were used as the input of the CNN. The model was trained to minimize the Mean Square Error (MSE) between the CNN-predicted and ERA5 re-analysis spectral density. The data structure of the wind input is reorganized into a polar grid centered on the target point to make the model applicable to different open-ocean locations worldwide. The results show that the model can well predict the wave spectrum shapes and integral wave parameters. The model allows for the prediction of single-point wave spectra in the open ocean with low computational cost and can be helpful for the study of spectral wave climate.
{"title":"A Deep Learning-Based Approach for Empirical Modelling of Single-Point Wave Spectra in Open Oceans","authors":"Yuhao Song, Haoyu Jiang","doi":"10.1175/jpo-d-22-0198.1","DOIUrl":"https://doi.org/10.1175/jpo-d-22-0198.1","url":null,"abstract":"\u0000Directional wave spectra are of importance for numerous practical applications such as seafaring and ocean engineering. The wave spectral densities at a certain point in the open ocean are significantly correlated to the local wind field and historical remote wind field. This feature can be used to predict the wave spectrum at that point using the wind field. In this study, a Convolutional Neural Network (CNN) model was established to estimate wave spectra at a target point using the wind field from the ERA5 dataset. A geospatial range where the wind could impact the target point was selected and then the historical wind field data within the range was analyzed to extract the nonlinear quantitative relationships between wind fields and wave spectra. For the spectral densities at a given direction, the wind data along the direction where waves come from were used as the input of the CNN. The model was trained to minimize the Mean Square Error (MSE) between the CNN-predicted and ERA5 re-analysis spectral density. The data structure of the wind input is reorganized into a polar grid centered on the target point to make the model applicable to different open-ocean locations worldwide. The results show that the model can well predict the wave spectrum shapes and integral wave parameters. The model allows for the prediction of single-point wave spectra in the open ocean with low computational cost and can be helpful for the study of spectral wave climate.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":" ","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-06-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46420736","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}
Qinbo Xu, Chun Zhou, Linlin Zhang, Fan Wang, Wei Zhao, D. Hu
The deep western boundary current (DWBC) was studied based on a full-depth mooring east of Luzon Island in the Northern Philippine Sea deep basin during the period from January 2018 to May 2020. On average, the DWBC in the Philippine Sea flows southward with a velocity of approximately 1.18 cm s−1 at a depth of 3050 m. Significant intraseasonal and seasonal variations of the DWBC are identified. The intraseasonal variations have multiple spectral peaks in the range of 30-200 days, with the most obvious peak at approximately 120 days. On the seasonal time scale, the DWBC intensifies in summer/autumn and weakens in winter/spring, corresponding well with the seasonal variation of the ocean bottom pressure (OBP) from the Gravity Recovery and Climate Experiment. Both intraseasonal and seasonal variations have no significant correlation with the temporal variations in the upper and middle layers but have a certain correlation with transport through the Yap-Mariana Junction (YMJ). A set of experiments based on an inverted-reduced-gravity model and the OBP data reveal that the temporal variations originating from the YMJ could propagate counterclockwise along the boundary of the deep basin to the western boundary of the deep Philippine Sea, dominating the temporal variations of DWBC.
基于2018年1月至2020年5月期间菲律宾海北部深盆吕宋岛以东的全深度系泊，研究了西部深边流（DWBC）。菲律宾海的DWBC平均以约1.18 cm s−1的速度向南流动，深度为3050 m。发现了DWBC的显著季节内和季节变化。季节内变化在30-200天的范围内有多个光谱峰值，最明显的峰值在120天左右。在季节性时间尺度上，DWBC在夏季/秋季增强，在冬季/春季减弱，这与重力恢复和气候实验中海底压力的季节变化非常吻合。季节内和季节变化与上层和中层的时间变化没有显著相关性，但与通过雅普-马里亚纳交界处（YMJ）的运输有一定相关性。基于反向重力模型和OBP数据的一组实验表明，源自YMJ的时间变化可以沿深盆地边界逆时针传播到菲律宾海西部边界，主导DWBC的时间变化。
{"title":"Variability of the Deep Western Boundary Current in the Northern Philippine Sea","authors":"Qinbo Xu, Chun Zhou, Linlin Zhang, Fan Wang, Wei Zhao, D. Hu","doi":"10.1175/jpo-d-23-0025.1","DOIUrl":"https://doi.org/10.1175/jpo-d-23-0025.1","url":null,"abstract":"\u0000The deep western boundary current (DWBC) was studied based on a full-depth mooring east of Luzon Island in the Northern Philippine Sea deep basin during the period from January 2018 to May 2020. On average, the DWBC in the Philippine Sea flows southward with a velocity of approximately 1.18 cm s−1 at a depth of 3050 m. Significant intraseasonal and seasonal variations of the DWBC are identified. The intraseasonal variations have multiple spectral peaks in the range of 30-200 days, with the most obvious peak at approximately 120 days. On the seasonal time scale, the DWBC intensifies in summer/autumn and weakens in winter/spring, corresponding well with the seasonal variation of the ocean bottom pressure (OBP) from the Gravity Recovery and Climate Experiment. Both intraseasonal and seasonal variations have no significant correlation with the temporal variations in the upper and middle layers but have a certain correlation with transport through the Yap-Mariana Junction (YMJ). A set of experiments based on an inverted-reduced-gravity model and the OBP data reveal that the temporal variations originating from the YMJ could propagate counterclockwise along the boundary of the deep basin to the western boundary of the deep Philippine Sea, dominating the temporal variations of DWBC.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":" ","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-06-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41902155","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}
Zifei Chen, F. Yu, Zhiwu Chen, Jianfeng Wang, Feng Nan, Qiang Ren, Yibo Hu, A. Cao, Tongtong Zheng
Mesoscale eddies can alter the propagation of wind-generated near-inertial waves (NIWs). Different from previous studies, the subsurface mooring observed NIWs are generated outside an anticyclonic eddy (ACE) and then interact with the arriving ACE. It is found that with the arrival of the ACE, the NIWs accelerate to propagate downward and the maximum vertical wavelength and group velocity of NIWs reach ~500 m and ~35 m/day, respectively. When entering the core of the ACE, the near-inertial energy is trapped, and finally stalls at a critical depth, which basically corresponds to the base of the ACE located at around 750 m depth. Through a ray-tracing model and dynamic analyses, this critical depth is much deeper than that of NIWs generated directly inside an ACE. By using depth-time varying stratification and relative vorticity, ray-tracing experiments further demonstrate that NIWs generated outside and passed over by an ACE can propagate to deep depths. Furthermore, energy budget analyses indicate that the net energy transfer from the ACE to NIWs plays an important role in the enhancement of downward-propagating near-inertial energy and its long-term persistence (~45 days) in the critical layer. Within the critical layer, the enhancement of shear instability and nonlinear interactions among internal waves account for the loss of the trapped near-in ertial energy and provide energy for furnishing deep ocean mixing.
{"title":"Downward Propagation and Trapping of Near-Inertial Waves by a Westward-moving Anticyclonic Eddy in the Subtropical Northwestern Pacific Ocean","authors":"Zifei Chen, F. Yu, Zhiwu Chen, Jianfeng Wang, Feng Nan, Qiang Ren, Yibo Hu, A. Cao, Tongtong Zheng","doi":"10.1175/jpo-d-22-0226.1","DOIUrl":"https://doi.org/10.1175/jpo-d-22-0226.1","url":null,"abstract":"\u0000Mesoscale eddies can alter the propagation of wind-generated near-inertial waves (NIWs). Different from previous studies, the subsurface mooring observed NIWs are generated outside an anticyclonic eddy (ACE) and then interact with the arriving ACE. It is found that with the arrival of the ACE, the NIWs accelerate to propagate downward and the maximum vertical wavelength and group velocity of NIWs reach ~500 m and ~35 m/day, respectively. When entering the core of the ACE, the near-inertial energy is trapped, and finally stalls at a critical depth, which basically corresponds to the base of the ACE located at around 750 m depth. Through a ray-tracing model and dynamic analyses, this critical depth is much deeper than that of NIWs generated directly inside an ACE. By using depth-time varying stratification and relative vorticity, ray-tracing experiments further demonstrate that NIWs generated outside and passed over by an ACE can propagate to deep depths. Furthermore, energy budget analyses indicate that the net energy transfer from the ACE to NIWs plays an important role in the enhancement of downward-propagating near-inertial energy and its long-term persistence (~45 days) in the critical layer. Within the critical layer, the enhancement of shear instability and nonlinear interactions among internal waves account for the loss of the trapped near-in ertial energy and provide energy for furnishing deep ocean mixing.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":" ","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44075578","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}
A. Solodoch, R. Barkan, V. Verma, H. Gildor, Y. Toledo, P. Khain, Y. Levi
The East Mediterranean Sea (EMS) circulation has previously been characterized as dominated by gyres, mesoscale eddies, and disjoint boundary currents. We develop nested high-resolution numerical simulations in the EMS to examine the circulation variability with an emphasis on the yet unexplored regional submesoscale currents. Rather than several disjoint currents, a continuous cyclonic boundary current (BC) encircling the Levantine basin is identified in both model solution and altimetry data. This EMS BC advects eddy chains downstream and is identified as a principle source of regional mesoscale and submesoscale current variability. During the seasonal fall to winter mixed layer deepening, energetic submesoscale (O(10 km)) eddies, fronts, and filaments emerge throughout the basin, characterized by O(1) Rossby numbers. A submesoscale time scale range of ≈1–5 days is identified using spatiotemporal analysis of the numerical solutions, and confirmed through mooring data. The submesoscale kinetic energy (KE) wavenumber (k) spectral slope is found to be k−2, shallower than the quasigeostrophic-like ~ k−3 slope diagnosed in summer. The shallowness of the winter spectral slope is shown to be due to divergent subinertial motions, consistent with the Boyd 1992 theoretical model, rather than with the surface quasigeostrophic model. Using a coarse graining approach, we diagnose a seasonal inverse (forward) KE cascade above (below) 30 km scales due to rotational (divergent) motions, and show that these commence after completion of the fall submesosacle energization. We also show that at scales larger than several 100 kms, the spectral density becomes near-constant and a weak forward cascade occurs, from gyre scales to mesoscales.
{"title":"Basin Scale to Submesoscale Variability of the East-Mediterranean Sea Upper Circulation","authors":"A. Solodoch, R. Barkan, V. Verma, H. Gildor, Y. Toledo, P. Khain, Y. Levi","doi":"10.1175/jpo-d-22-0243.1","DOIUrl":"https://doi.org/10.1175/jpo-d-22-0243.1","url":null,"abstract":"\u0000The East Mediterranean Sea (EMS) circulation has previously been characterized as dominated by gyres, mesoscale eddies, and disjoint boundary currents. We develop nested high-resolution numerical simulations in the EMS to examine the circulation variability with an emphasis on the yet unexplored regional submesoscale currents. Rather than several disjoint currents, a continuous cyclonic boundary current (BC) encircling the Levantine basin is identified in both model solution and altimetry data. This EMS BC advects eddy chains downstream and is identified as a principle source of regional mesoscale and submesoscale current variability. During the seasonal fall to winter mixed layer deepening, energetic submesoscale (O(10 km)) eddies, fronts, and filaments emerge throughout the basin, characterized by O(1) Rossby numbers. A submesoscale time scale range of ≈1–5 days is identified using spatiotemporal analysis of the numerical solutions, and confirmed through mooring data. The submesoscale kinetic energy (KE) wavenumber (k) spectral slope is found to be k−2, shallower than the quasigeostrophic-like ~ k−3 slope diagnosed in summer. The shallowness of the winter spectral slope is shown to be due to divergent subinertial motions, consistent with the Boyd 1992 theoretical model, rather than with the surface quasigeostrophic model. Using a coarse graining approach, we diagnose a seasonal inverse (forward) KE cascade above (below) 30 km scales due to rotational (divergent) motions, and show that these commence after completion of the fall submesosacle energization. We also show that at scales larger than several 100 kms, the spectral density becomes near-constant and a weak forward cascade occurs, from gyre scales to mesoscales.","PeriodicalId":56115,"journal":{"name":"Journal of Physical Oceanography","volume":" ","pages":""},"PeriodicalIF":3.5,"publicationDate":"2023-06-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41593585","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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