Journal articles on the topic 'Eddies'
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Wu, Xiaoci, Pengchao Jin, Yang Zhang, and Wei Yu. "Changing Humboldt Squid Abundance and Distribution at Different Stages of Oceanic Mesoscale Eddies." Journal of Marine Science and Engineering 12, no. 4 (April 7, 2024): 626. http://dx.doi.org/10.3390/jmse12040626.
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Humboldt squid, Dosidicus gigas, is one of the main economic cephalopod species off Peruvian waters, and their abundance and distribution are regulated by localized oceanic mesoscale dynamical processes. To this end, the present study employs normalization and frequency distribution methods, combining mesoscale eddy, oceanic environment, and D. gigas fishery data. This is the first exploration into the different stages of mesoscale eddies during their evolution off Peruvian waters and their influence on the regional marine environment, as well as the abundance and distribution of D. gigas resources. The results indicate that across the four stages of eddies, namely formation, intensification, mature, and aged, their kinetic energy and structure follow a pattern of “growth–equilibration–decay”. The abundance of D. gigas within the eddy’s covered zone undergoes an initial increase, followed by a decrease during the evolution of the four stages, peaking during the eddy’s mature stage. The abundance of D. gigas was higher in the anticyclonic eddies than that in the cyclonic eddies under different stages. The environmental factors conducive to D. gigas in eddies exhibited similar changes to D. gigas abundance throughout the eddy’s different stages. Our research emphasizes that anticyclonic eddies, during their evolution, exerted a more significant impact on the abundance and distribution of D. gigas in the Peruvian waters compared with cyclonic eddies. The eddy-induced changes in water temperature and productivity caused by the eddies may be the primary drivers of this impact.
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Early, Jeffrey J., R. M. Samelson, and Dudley B. Chelton. "The Evolution and Propagation of Quasigeostrophic Ocean Eddies*." Journal of Physical Oceanography 41, no. 8 (August 1, 2011): 1535–55. http://dx.doi.org/10.1175/2011jpo4601.1.
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Abstract The long-term evolution of initially Gaussian eddies is studied in a reduced-gravity shallow-water model using both linear and nonlinear quasigeostrophic theory in an attempt to understand westward-propagating mesoscale eddies observed and tracked by satellite altimetry. By examining both isolated eddies and a large basin seeded with eddies with statistical characteristics consistent with those of observed eddies, it is shown that long-term eddy coherence and the zonal wavenumber–frequency power spectral density are best matched by the nonlinear model. Individual characteristics of the eddies including amplitude decay, horizontal length scale decay, and zonal and meridional propagation speed of a previously unrecognized quasi-stable state are examined. The results show that the meridional deflections from purely westward flow (poleward for cyclones and equatorward for anticyclones) are consistent with satellite observations. Examination of the fluid transport properties of the eddies shows that an inner core of the eddy, defined by the zero relative vorticity contour, contains only fluid from the eddy origin, whereas a surrounding outer ring contains a mixture of ambient fluid from throughout the eddy’s lifetime.
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Liu, Jiaxin, Jue Ning, and Xu Chen. "Evolution of Different Types of Eddies Originating from Different Baroclinic Instability Types." Remote Sensing 15, no. 24 (December 14, 2023): 5730. http://dx.doi.org/10.3390/rs15245730.
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This paper investigates the evolution of global eddies and various types of eddies originating from baroclinic instability (BCI) by utilizing satellite altimetry, Argo profiles, and climatology datasets. The structure of global eddies with regard to potential temperature anomalies experiences downward propagation and spreading from the periods of eddy growth to stabilization. However, from the eddy’s stabilization to the decay period, the process of spreading primarily occurs horizontally, and this process is usually accompanied by weakening. By comparing the evolution of eddies in three typical regions dominated by distinct types of BCI, we found that the basic properties of eddies related to different BCI types evolve similarly; however, there are notable differences in their vertical structures and evolution. Eddies associated with Phillips + Charney_s-type, Charney_s-type, and Eady-type BCIs exhibit dual-core, single-core, and dual-core structures, respectively. In particular, the intrusion of the Okhotsk cold water mass into the Northwest Pacific region forms cold-core anticyclonic eddies, resulting in AEs that are significantly distinct from the rest of the ocean. The evolution of surface-layer cores closely resembles that of the global eddies, while the decay of subsurface and bottom-layer cores is comparably sluggish. Additionally, we examine the impact of local oceanic stratification conditions on eddy decay and determine that stronger vertical gradients result in more vigorous eddy decay, accounting for the concentration of eddies at depths where vertical gradients are weaker during their evolution.
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Avnur, Ron, and Joseph M. Hellerstein. "Eddies." ACM SIGMOD Record 29, no. 2 (June 2000): 261–72. http://dx.doi.org/10.1145/335191.335420.
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Yuan, Quanmu, and Jianyu Hu. "Spatiotemporal Characteristics and Volume Transport of Lagrangian Eddies in the Northwest Pacific." Remote Sensing 15, no. 17 (September 4, 2023): 4355. http://dx.doi.org/10.3390/rs15174355.
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Mesoscale eddies play a crucial role in the transport of mass, heat, salt and nutrients, exerting significant influence on ocean circulation patterns, biogeochemical processes and the global climate system. Based on Lagrangian-Averaged Vorticity Deviation (LAVD) method, this study applies 27 years (1993–2019) of geostrophic current velocity data to detect Rotationally Coherent Lagrangian Vortices (RCLVs) in the Northwest Pacific (NWP; 10°N–30°N, 115°E–155°E), with the spatiotemporal characteristics of Eulerian Sea Surface Height Eddies (SSH eddies) and RCLVs being compared. A higher number of SSH eddies and RCLVs can be observed in spring and winter, and their inter-annual variations are similar. SSH eddies show higher generation number and larger radius in the Subtropical Countercurrent region, while RCLVs occur more favorably in the ocean basin. The propagation speed distributions of both eddy types are nearly identical and decrease with increasing latitude. Due to the material coherent transport maintained by RCLVs within a finite time interval, the coherent cores of RCLVs are considerably smaller in scale as compared to those of SSH eddies. The average zonal transports induced by SSH eddies and RCLVs are estimated to be −0.82 Sv and −0.51 Sv (1 Sv = 106 m3/s), respectively. For non-overlapping SSH eddies with RCLVs, approximately 80% of the water within the eddy leaks out during the eddy’s lifespan. In the case of overlapping SSH eddies, the ratio of coherent water inside the eddy decreases with increasing radius, and the leakage rate is around 58%. Finally, an examination of 36 shedding RCLVs events from the Kuroshio near the Luzon Strait, which induce an average zonal transport of −0.14 Sv, reveals that 54% of the water within the shedding RCLVs originates from the Kuroshio.
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Lai, Yeping, Hao Zhou, Jing Yang, Yuming Zeng, and Biyang Wen. "Submesoscale Eddies in the Taiwan Strait Observed by High-Frequency Radars: Detection Algorithms and Eddy Properties." Journal of Atmospheric and Oceanic Technology 34, no. 4 (April 2017): 939–53. http://dx.doi.org/10.1175/jtech-d-16-0160.1.
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AbstractThis study compared the efficiencies of two widely used automatic eddy detection algorithms—that is, the winding-angle (WA) method and the vector geometry (VG) method—and investigated the submesoscale eddy properties using surface current observations derived from high-frequency radars (HFRs) in the Taiwan Strait. The results showed that the WA method using the streamline and the VG method based on the streamfunction field have almost the same capacity for identifying eddies, but the former is more competent than the latter in capturing the eddy size. The two algorithms simultaneously identified 1080 submesoscale eddies, with the centers and boundaries determined only by the WA method, and they were further used to investigate the eddy properties. In general, no significant difference was observed between the cyclonic and anticyclonic eddies in terms of radius, life span, and kinematics, as well as the evolution during their life cycles. The typical radius of the eddy in this region was 3–18 km. And a strong correlation was observed between the life span and the radius. The spatial distribution of the eddies indicated that topography played a significant role in the generation of the eddies. And the trajectories of the eddies suggested that all the eddies in this area mostly tended to move southeastward. Statistically, three different stages of the eddy’s life span could be identified by the significant growth and decay of the radius and the mean kinetic energy. This study shows the great capability of HFRs in oceanography research and applications, especially for observing the submesocale dynamics.
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Huang, Xiaorong, and Guihua Wang. "Response of a Mesoscale Dipole Eddy to the Passage of a Tropical Cyclone: A Case Study Using Satellite Observations and Numerical Modeling." Remote Sensing 14, no. 12 (June 15, 2022): 2865. http://dx.doi.org/10.3390/rs14122865.
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Mesoscale eddies occurring in the world’s oceans typically exist in pairs known as mesoscale dipole eddies or simply dipole eddies. Tropical cyclones (hereafter TCs) that move over the world’s oceans often encounter and interact with these dipole eddies. Through this interaction, TCs induce significant perturbations in the mesoscale eddies. However, the specific influences that the passage of a TC on a dipole eddy have not been addressed. In this paper, a case study of the dipole eddy’s response to the passage of a TC is conducted by using satellite observations and numerical simulation. The passage of a TC induces a long-duration response in the dipole eddy. First, the cyclonic ocean eddy component (COE) of the dipole is amplified, and the anticyclonic ocean eddy component (AOE) is weakened or even destroyed during the interaction. The amplification of the COE and weakening of the AOE primarily manifests as a change in their amplitudes and radii and as the adjustment of their vertical structure. The dipole eddy’s response to the interaction with a TC manifests as an upwelling anomaly and the injection of positive relative vorticity. Following the passage of the TC, the COE gradually stabilizes, and AOE slowly recovers after the disturbance energy from the interaction dissipates, which facilitates the reestablishment of the dipole eddy. The dipole reaches an equilibrium state through a quasi-geostrophic adjustment process. As a consequence, the overall effect of the interaction of the dipole with the TC leads to an asymmetric signature on the dipole eddy. The eddy–eddy interaction in a dipole may allow it to stabilize in a shorter time relative to that of a solitary eddy.
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Monin, A. S., and G. M. Zhikharev. "Ocean eddies." Uspekhi Fizicheskih Nauk 160, no. 5 (1990): 1. http://dx.doi.org/10.3367/ufnr.0160.199005a.0001.
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Monin, A. S., and G. M. Zhikharev. "Ocean eddies." Soviet Physics Uspekhi 33, no. 5 (May 31, 1990): 313–39. http://dx.doi.org/10.1070/pu1990v033n05abeh002569.
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Eldevik, Tor, and Kristian B. Dysthe. "Spiral Eddies." Journal of Physical Oceanography 32, no. 3 (March 2002): 851–69. http://dx.doi.org/10.1175/1520-0485(2002)032<0851:se>2.0.co;2.
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NOF, DORON. "Orbiting eddies." Tellus A 43, no. 1 (January 1991): 64–67. http://dx.doi.org/10.1034/j.1600-0870.1991.t01-4-00006.x.
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Shang, Longquan, Kaifeng Han, Feng Chen, Ning Wang, and Jiaqing Lu. "Statistical Analysis of Mesoscale Eddy Characteristics in the northwestern Pacific Ocean." Journal of Physics: Conference Series 2718, no. 1 (March 1, 2024): 012005. http://dx.doi.org/10.1088/1742-6596/2718/1/012005.
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Abstract In this paper, the mesoscale eddy data set established by Professor Chelton in Oregon State University is used to analyse the statistical characteristics of mesoscale eddies in the Northwest Pacific Ocean. Mesoscale eddies in this region are divided into short-lived, Mid-lived, and long-lived eddies according to their life cycle with the aim of exploring the characteristics of eddies with different life cycles. Those with a life cycle of less than 6 weeks, 6-9 weeks, and more than 9 weeks are defined as short-lived eddies, mid-lived eddies, and long-lived eddies, respectively. The results show that most of the eddies are short lived eddies with a lifetime of 6 weeks or less. Both short-lived eddies and Mid-lived eddies have more cyclonic eddies than anticyclonic eddies. But long-lived eddies have more anticyclonic eddies than cyclonic eddies. In addition, the number of short-lived eddies in the Subtropical Ocean is more than those in the Kuroshio Extension, while the number of long-lived eddies is the opposite.
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Zheng, Shaojun, Yan Du, Jiaxun Li, and Xuhua Cheng. "Eddy characteristics in the South Indian Ocean as inferred from surface drifter." Ocean Science Discussions 11, no. 6 (December 11, 2014): 2879–905. http://dx.doi.org/10.5194/osd-11-2879-2014.
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Abstract. Using a geometric eddy identification method, cyclonic and anticyclonic eddies from submesoscale to mesoscale in the South Indian Ocean (SIO) have been statistically investigated based on 2082 surface drifters from 1979 to 2013. 19252 eddies are identified with 60% anticyclonic eddies. For the submesoscale eddies (radius r < 10 km), the ratio of cyclonic eddies (3183) to anticyclonic eddies (7182) is 1 to 2. In contrast, number of anticyclonic and cyclonic eddies with radius r ≥ 10 km is almost equal. Mesoscale and submesoscale eddies show different spatial distribution. Eddies with radius r ≥ 100 km mainly appear in a band along 25° S, in Mozambique Channel, and Agulhas Current, characterized by large eddy kinetic energy. The submesoscale anticyclonic eddies are densely distributed in the subtropical basin in the central SIO. The number of mesoscale eddies shows statistically significant seasonal variability, reaching a maximum in October and then minimum in February.
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Zheng, S., Y. Du, J. Li, and X. Cheng. "Eddy characteristics in the South Indian Ocean as inferred from surface drifters." Ocean Science 11, no. 3 (May 12, 2015): 361–71. http://dx.doi.org/10.5194/os-11-361-2015.
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Abstract. Using a geometric eddy identification method, cyclonic and anticyclonic eddies from submesoscale to mesoscale in the South Indian Ocean (SIO) have been statistically investigated based on 2082 surface drifters from 1979 to 2013. A total of 19 252 eddies are identified, 60% of them anticyclonic eddies. For the submesoscale eddies (radius r<10 km), the ratio of cyclonic eddies (3183) to anticyclonic eddies (7182) is 1 to 2. In contrast, the number of anticyclonic and cyclonic eddies with radius r≥10 km is almost equal. Mesoscale and submesoscale eddies show different spatial distributions. Eddies with radius r≥100 km mainly appear in the Leeuwin Current, a band along 25° S, Mozambique Channel, and Agulhas Current, areas characterized by large eddy kinetic energy. The submesoscale anticyclonic eddies are densely distributed in the subtropical basin in the central SIO. The number of mesoscale eddies shows statistically significant seasonal variability, reaching a maximum in October and minimum in February.
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Liu, Qian, Yingjie Liu, and Xiaofeng Li. "Characteristics of surface physical and biogeochemical parameters within mesoscale eddies in the Southern Ocean." Biogeosciences 20, no. 23 (December 7, 2023): 4857–74. http://dx.doi.org/10.5194/bg-20-4857-2023.
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Abstract. Using satellite sea surface temperature (SST) and chlorophyll a (Chl a) as well as observation-based reconstruction of dissolved inorganic carbon (DIC) and partial pressure of CO2 (pCO2) from 1996 to 2015, we investigate the modulation mechanisms of eddies on surface physical and biogeochemical parameters in the Southern Ocean (SO). About one-quarter of eddies are observed to be “abnormal” (cold anticyclonic and warm cyclonic eddies) in the SO, which show opposite SST signatures to “normal” eddies (warm anticyclonic and cold cyclonic eddies). The study finds that the modification of abnormal eddies on physical and biogeochemical parameters is significant and differs from normal eddies due to the combined effects of eddy pumping and eddy-induced Ekman pumping. Normal and abnormal eddies have opposite DIC anomalies, contrary to the SST anomalies. Moreover, the contributions of abnormal eddies to pCO2 are about 2.7 times higher than normal eddies in regions where abnormal eddies dominate. Although Chl a anomalies in normal and abnormal eddies show similar patterns and signals, eddy-induced Ekman pumping attenuates the magnitudes of Chl a anomalies within abnormal eddies. In addition to the variation of the same parameter within different eddies, the dominant eddy-driven mechanisms for different parameters within the same kind of eddies also vary. The strength of the eddy stirring effect on different parameters is the primary factor causing these differences, attributed to variations in the magnitudes of horizontal parameter gradients. Understanding the role of abnormal eddies and the complexity of eddy-driven processes is crucial for accurately estimating the influence of mesoscale eddies on physical and biogeochemical processes in the SO, which is essential for simulating and predicting biogeochemical dynamics and carbon cycling in the region.
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Luo, Dehai. "A Barotropic Envelope Rossby Soliton Model for Block–Eddy Interaction. Part III: Wavenumber Conservation Theorems for Isolated Blocks and Deformed Eddies." Journal of the Atmospheric Sciences 62, no. 11 (November 1, 2005): 3839–59. http://dx.doi.org/10.1175/jas3573.1.
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Abstract In a series of previous papers, an envelope Rossby soliton theory was formulated to investigate the interaction between a preexisting planetary wave and synoptic-scale eddies leading to a typical blocking flow. In this paper, numerical and analytical studies are presented in order to examine the interactive relationship between an isolated vortex pair block and deformed synoptic-scale eddies during their interaction. The deformed blocked flow and eddies are found to satisfy the wavenumber conservation theorem. It is shown that the feedback by a blocked flow on the preexisting synoptic eddies gives rise to two types of eddies: one is the Z-type eddies with a meridional monopole structure that appears at the middle of the channel and the other is the M-type eddies with a meridional tripole structure that have long wavelength and large amplitude. Both the total wavenumber of the blocked flow and M-type eddies and the total wavenumber of the Z- and M-type eddies are conserved. The M- and Z-type eddies are compressed and elongated, respectively, as the blocked flow is elongated zonally during its onset phase, but the reverse is observed during the decay phase. The zonally elongated Z-type eddies are found to counteract the compressed M-type eddies in the blocking region, but strengthen the M-type eddies upstream, causing the split of eddies around the blocking region. In addition, it is also verified theoretically that the blocked flow and synoptic-eddy activity are symbiotically dependent upon one another. The deformed (Z and M type) eddies also display a low-frequency oscillation in amplitude, wavenumber, group velocity, and phase speed, consistent with the blocked flow by the eddy forcing. Thus, it appears that the low-frequency eddy forcing is responsible for the low-frequency variability of the blocked flow and synoptic-eddy activity.
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Jin, Yang, Meibing Jin, Dongxiao Wang, and Changming Dong. "Statistical Analysis of Multi-Year South China Sea Eddies and Exploration of Eddy Classification." Remote Sensing 16, no. 10 (May 20, 2024): 1818. http://dx.doi.org/10.3390/rs16101818.
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Mesoscale eddies are structures of seawater motion with horizontal scales of tens to hundreds of kilometers, impact depths of tens to hundreds of meters, and time scales of days to months. This study presents a statistical analysis of mesoscale eddies in the South China Sea (SCS) from 1993 to 2021 based on eddies extracted from satellite remote sensing data using the vector geometry eddy detection method. On average, about 230 eddies with a wide spatial and temporal distribution are observed each year, and the numbers of CEs (52.2%) and AEs (47.8%) are almost similar, with a significant correlation in spatial distribution. In this article, eddies with a lifetime of at least 28 days (17% of the number of total eddies) are referred to as strong eddies (SEs). The SEs in the SCS that persist for several years in similar months and locations, such as the well-known dipole eddies consisting of CEs and AEs offshore eastern Vietnam, are defined as persistent strong eddies (PSEs). SEs and PSEs affect the thermohaline structure, current field, and material and energy transport in the upper ocean. This paper is important as it names the SEs and PSEs, and the naming of eddies can facilitate research on specific major eddies and improve public understanding of mesoscale eddies as important oceanic phenomena.
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Canuto, V. M., and M. S. Dubovikov. "Modeling mesoscale eddies." Ocean Modelling 8, no. 1-2 (January 2005): 1–30. http://dx.doi.org/10.1016/j.ocemod.2003.11.003.
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Millot, C., I. Taupier-Letage, and M. Benzohra. "The Algerian eddies." Earth-Science Reviews 27, no. 3 (May 1990): 203–19. http://dx.doi.org/10.1016/0012-8252(90)90003-e.
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Drikakis, D., L. G. Margolin, and P. K. Smolarkiewicz. "On ?spurious? eddies." International Journal for Numerical Methods in Fluids 40, no. 1-2 (2002): 313–22. http://dx.doi.org/10.1002/fld.288.
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Arruda, Wilton Z., and Doron Nof. "The Mindanao and Halmahera Eddies—Twin Eddies Induced by Nonlinearities." Journal of Physical Oceanography 33, no. 12 (December 2003): 2815–30. http://dx.doi.org/10.1175/1520-0485(2003)033<2815:tmahee>2.0.co;2.
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Li, J. X., R. Zhang, and B. Jin. "Eddy characteristics in the Northern South China Sea as inferred from Lagrangian drifter data." Ocean Science Discussions 8, no. 4 (July 4, 2011): 1575–99. http://dx.doi.org/10.5194/osd-8-1575-2011.
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Abstract. Cyclones and anticyclones from large scale to submesoscale on the Northern South China Sea (NSCS) have been statistically characterized based on the satellite-tracked Lagrangian drifter data using a geometric eddy identification method. There are totally 1972 eddies identified, 4/5 of which are anticyclonic eddies. If the submesoscale eddies are eliminated, the other eddies in the NSCS will show a 1.1–1 dominance with the number (133) of anticyclones over the number (122) of cyclones. The spatial distribution of all the eddies are: in Zone Z1, the number of anticyclones dominate the number of cyclones, most of which are the submesoscale anticyclonic eddies with small radii; whereas, in Zone Z2, cyclonic eddies are a little more than anticyclonic eddies. The temporal distribution of eddy number in the NSCS has a close relation with monsoon. The number of the large eddies peaks during the winter monsoon, while they tend to decrease quickly in the transition periods of monsoon. In contrast, submesoscale eddies are likely to generate in the summer monsoon, which may be related to the baroclinic instability in the NSCS. The spatial and temporal patterns have a good agreement with the results of SSHA. The maximum and mean tangential velocities of anticyclones (cyclones) are 45 (30) cm s−1 and 30 (15) cm s−1, respectively. Large scale eddies can be considered in geostrophic balance, but ageostrophic dynamics may be important for the submesoscale eddies where centrifugal effects cannot be ignored in the NSCS.
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Shi, Yiyun, Xiaohui Liu, Tongya Liu, and Dake Chen. "Characteristics of Mesoscale Eddies in the Vicinity of the Kuroshio: Statistics from Satellite Altimeter Observations and OFES Model Data." Journal of Marine Science and Engineering 10, no. 12 (December 12, 2022): 1975. http://dx.doi.org/10.3390/jmse10121975.
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Mesoscale eddies propagate westward in the northwestern Pacific Ocean and interact with the Kuroshio in the vicinity of the western boundary of the ocean. However, the processes affecting the eddy properties and the detailed structure of the eddies when they encounter the Kuroshio remain unclear. In this study, we analyze the statistics of the eddy properties around the Kuroshio using 25 years of satellite altimeter data and the eddy-resolving OFES model product. The spatial compositions of the eddies in the northwestern Pacific show that, as the eddies propagate westward, their radius and amplitude decrease sharply when they approach the Kuroshio region. The radius, amplitude, and kinetic energy of the eddies reaching the Kuroshio region decay much faster during their lifespan compared with the eddies in the interior of the Pacific Ocean. Furthermore, the three-dimensional structure of the eddies obtained from the OFES model data shows that the maximum temperature anomalies in the cyclonic and anticyclonic eddies occur at ~300 m, and the maximum depth reduces as a result of the interaction between the eddies and the main Kuroshio current.
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Pilo, G. S., M. M. Mata, and J. L. L. Azevedo. "Eddy Surface properties and propagation at Southern Hemisphere western boundary current systems." Ocean Science Discussions 12, no. 1 (February 9, 2015): 135–60. http://dx.doi.org/10.5194/osd-12-135-2015.
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Abstract. Oceanic eddies occur in all world oceans, but are more energetic when associated to western boundary currents (WBC) systems. In these regions, eddies play an important role on mixing and energy exchange. Therefore, it is important to quantify and qualify eddies occurring within these systems. Previous studies performed eddy censuses in Southern Hemisphere WBC systems. However, important aspects of local eddy population are still unknown. Main questions to be answered relate to eddies' spatial distribution, propagation and lifetime within each system. Here, we use a global eddy dataset to qualify eddies based on their surface characteristics at the Agulhas Current (AC), the Brazil Current (BC) and the East Australian Current (EAC) Systems. We show that eddy propagation within each system is highly forced by the local mean flow and bathymetry. In the AC System, eddy polarity dictates its propagation distance. BC system eddies do not propagate beyond the Argentine Basin, and are advected by the local ocean circulation. EAC System eddies from both polarities cross south of Tasmania, but only anticyclonics reach the Great Australian Bight. Eddies in all systems and from both polarities presented a geographical segregation according to size. Large eddies occur along the Agulhas Retroflection, the Agulhas Return Current, the Brazil-Malvinas Confluence and the Coral Sea. Small eddies occur in the systems southernmost domains. Understanding eddies' propagation helps to establish monitoring programs, and to better understand how these features would affect local mixing.
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Kuang, Xiaodi, Zhiyuan Zhang, Jingshi Li, and chengyi Yuan. "An interpretation experiment on eddies’ role in sound propagation in the ocean using ray model." Journal of Physics: Conference Series 2718, no. 1 (March 1, 2024): 012081. http://dx.doi.org/10.1088/1742-6596/2718/1/012081.
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Abstract The relationship between mesoscale eddies and ambient acoustic propagation under different conditions were studied using high resolution ocean reanalysis products in South China Sea, which was summarized by a linear-equation representing the convergence zone change with respect to eddy signatures and source positions. Beyond the experiments scales, warm eddies “dragged” the sound propagation and cold eddies “squeezed” that in contrast, and the acoustic amplifying mechanism can be summarized as stronger(eddies), nearer(eddies) and deeper(source).
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Karstensen, J., B. Fiedler, F. Schütte, P. Brandt, A. Körtzinger, G. Fischer, R. Zantopp, J. Hahn, M. Visbeck, and D. Wallace. "Open ocean dead zones in the tropical North Atlantic Ocean." Biogeosciences 12, no. 8 (April 30, 2015): 2597–605. http://dx.doi.org/10.5194/bg-12-2597-2015.
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Abstract. Here we present first observations, from instrumentation installed on moorings and a float, of unexpectedly low (<2 μmol kg−1) oxygen environments in the open waters of the tropical North Atlantic, a region where oxygen concentration does normally not fall much below 40 μmol kg−1. The low-oxygen zones are created at shallow depth, just below the mixed layer, in the euphotic zone of cyclonic eddies and anticyclonic-modewater eddies. Both types of eddies are prone to high surface productivity. Net respiration rates for the eddies are found to be 3 to 5 times higher when compared with surrounding waters. Oxygen is lowest in the centre of the eddies, in a depth range where the swirl velocity, defining the transition between eddy and surroundings, has its maximum. It is assumed that the strong velocity at the outer rim of the eddies hampers the transport of properties across the eddies boundary and as such isolates their cores. This is supported by a remarkably stable hydrographic structure of the eddies core over periods of several months. The eddies propagate westward, at about 4 to 5 km day−1, from their generation region off the West African coast into the open ocean. High productivity and accompanying respiration, paired with sluggish exchange across the eddy boundary, create the "dead zone" inside the eddies, so far only reported for coastal areas or lakes. We observe a direct impact of the open ocean dead zones on the marine ecosystem as such that the diurnal vertical migration of zooplankton is suppressed inside the eddies.
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Cui, Wei, Jungang Yang, Yongjun Jia, and Jie Zhang. "Oceanic Eddy Detection and Analysis from Satellite-Derived SSH and SST Fields in the Kuroshio Extension." Remote Sensing 14, no. 22 (November 16, 2022): 5776. http://dx.doi.org/10.3390/rs14225776.
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Vigorous mesoscale eddies are broadly distributed in the Kuroshio Extension and can generally be identified from sea surface height (SSH) and sea surface temperature (SST) fields. Nevertheless, the changes in SSH and SST caused by mesoscale eddies and their seasonal correlation in the Kuroshio Extension are not clear, as well as the difference between identified eddy results from the two data. Combining in situ Argo float profiles data, the correlation between SSH anomaly (SSHA) and SST anomaly (SSTA) signals in mesoscale eddies are analyzed. The result shows that SSTA–SSHA signals inside eddies are generally more correlated in winter than in summer. Argo subsurface temperature anomalies θ′ and SSHA signals inside eddies show a high correlation, with a regression coefficient θ′/SSHA of about 7 °C·m−1, while correlations of Argo θ′–SSTA inside eddies are low. Generally, the lifetime and propagation distance of SSTA-based eddies are shorter and smaller than those of SSHA-based eddies, which may be related to the rapid changes in SSTA field and the interference of small-scale oceanic signal in the SST field. Comparing with SSHA-based eddies, which exist primarily around the region of the Kuroshio mainstream (33°–36°N), SSTA-based eddies are concentrated in the Oyashio Extension (39°–42°N), where SST gradient is large, and changes in SST fields caused by mesoscale eddies are more obvious and more likely to be captured by satellites there. In addition, the geographical distributions of SSHA- and SSTA-based eddy amplitudes are consistent with the absolute dynamic topography and SST gradient.
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Yang, Shengmu, Jiuxing Xing, Daoyi Chen, and Shengli Chen. "A modelling study of eddy-splitting by an island/seamount." Ocean Science 13, no. 5 (October 25, 2017): 837–49. http://dx.doi.org/10.5194/os-13-837-2017.
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Abstract. A mesoscale eddy's trajectory and its interaction with topography under the planetary β and nonlinear effects in the South China Sea are examined using the MIT General Circulation Model (MITgcm). Warm eddies propagate to the southwest while cold eddies propagate to the northwest. The propagation speed of both warm and cold eddies is about 2.4 km day−1 in the model. The eddy trajectory and its structure are affected by an island or a seamount, in particular, under certain conditions, the eddy may split during the interaction with an island/seamount. We focus this research on two parameters R and S (where R and S are two dimensionless parameters of the island size and submergence depth; R is the ratio of the island radius to the eddy radius, and S is the ratio of the seamount submergence depth to the eddy vertical length). The results of sensitivity experiments with varying island or seamount geometry indicate that the eddy would split in the qualitative range of 1∕4 < R < 2 and S < 1∕5. The scale of the secondary eddy split-off decreases as the island diameter or the seamount submergence depth increases. In the splitting process, besides the off-spring eddy, there are also some filaments or eddies with opposite vorticity appearing around the eddy. Eddy-splitting, therefore, is an important way to transform energy from the mesoscale to sub-mesoscale in the ocean.
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Aguedjou, Habib Micaël A., Alexis Chaigneau, Isabelle Dadou, Yves Morel, Ezinvi Baloïtcha, and Casimir Y. Da-Allada. "Imprint of Mesoscale Eddies on Air-Sea Interaction in the Tropical Atlantic Ocean." Remote Sensing 15, no. 12 (June 13, 2023): 3087. http://dx.doi.org/10.3390/rs15123087.
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This study investigates the effect of mesoscale eddies on air–sea heat and fresh water exchange in the tropical Atlantic Ocean (TAO) using 8 years of satellite altimetry data, combined with sea surface temperature (SST), latent and sensible heat fluxes (LHF and SHF), infrared fluxes (IRF) and precipitation (PR) data. Results indicate that approximately ∼40% of cyclonic eddies contribute to warm SST anomalies, and ∼40% of anticyclonic eddies contribute to cold SST anomalies. Eddies were found to play a role in the variability in LHF, SHF and IRF, contributing 10–35% of their total variability, with the largest contributions observed beneath the intertropical convergence zone (ITCZ) and frontal SST areas. Composite analysis of SST and heat flux anomalies over eddies suggested that the anomalies created through horizontal advection processes may not significantly impact the overall LHF, SHF and IRF over eddies, contrary to vertical processes. Despite a lack of clear correlation between heat flux and PR anomalies over eddies in the TAO, significant correlations were found beneath the ITCZ, suggesting that eddies may impact both heat fluxes and PR in the ITCZ region. This study provides an original contribution to the understanding of the impact of ocean mesoscale eddies on the atmosphere in the TAO.
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Liu, F., S. Tang, and C. Chen. "Satellite observations of the small-scale cyclonic eddies in the western South China Sea." Biogeosciences 12, no. 2 (January 16, 2015): 299–305. http://dx.doi.org/10.5194/bg-12-299-2015.
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Abstract. High-resolution ocean color observations offer an opportunity to investigate the oceanic small-scale processes. In this study, the Medium Resolution Imaging Spectrometer (MERIS) daily 300 m data were used to study small-scale processes in the western South China Sea. It is indicated that the cyclonic eddies with horizontal scales of 10 km are frequently observed during the upwelling season of each year over the 2004–2009 period. These small-scale eddies were generated in the vicinity of the southern front of the cold tongue, and then propagated eastward with a speed of approximately 12 cm s−1. This propagation speed was consistent with the velocity of the western boundary current. As a result, the small-scale eddies kept the high levels of phytoplankton rotating away from the coastal areas, resulting in the accumulation of phytoplankton in the interior of the eddies. The generation of the small-scale eddies may be associated with strengthening of the relative movement between the rotation speed of the anticyclonic mesoscale eddies and the offshore transport. With the increases of the normalized rotation speed of the anticyclonic mesoscale eddies relative to the offshore transport, the offshore current became a meander under the impacts of the anticyclonic mesoscale eddies. The meandered cold tongue and instability front may stimulate the generation of the small-scale eddies. Unidirectional uniform wind along the cold tongue may also contribute to the formation of the small-scale eddies.
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Ueno, Hiromichi, Kanako Sato, Howard J. Freeland, William R. Crawford, Hiroji Onishi, Eitarou Oka, and Toshio Suga. "Anticyclonic Eddies in the Alaskan Stream." Journal of Physical Oceanography 39, no. 4 (April 1, 2009): 934–51. http://dx.doi.org/10.1175/2008jpo3948.1.
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Abstract Anticyclonic eddies propagating southwestward in the Alaskan Stream (AS) were investigated through analysis of altimetry data from satellite observations during 1992–2006 and hydrographic data from profiling float observations during 2001–06. Fifteen long-lived eddies were identified and categorized based on their area of first appearance. Three eddies were present at the beginning of the satellite observations; another three formed in the eastern Gulf of Alaska off Sitka, Alaska; and four were first detected at the head of the Gulf of Alaska near Yakutat, Alaska. The other five eddies formed along the AS between 157° and 169°W, and were named AS eddies. While the eddies that formed in the Gulf of Alaska mainly decayed before exiting the Gulf of Alaska, the AS eddies mostly crossed the 180° meridian and reached the western subarctic gyre. Four of five AS eddies formed under negative or weakly positive wind stress curls, which possibly caused AS separation from the coast. Comparison of eddy propagation speeds in the AS with the bottom slope showed that eddies propagated faster over steeper slopes, although eddy speeds were slower than those predicted by the topographic planetary wave dispersion relation. An AS eddy was observed by profiling floats in the western subarctic gyre after it detached from the AS. Intermediate-layer water near the eddy center had low potential vorticity compared with the surrounding water, suggesting that AS eddies provided the western subarctic gyre with water just south of the Aleutian Islands.
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Liu, F., S. Tang, and C. Chen. "Satellite observations of the small-scale cyclonic eddies in the western South China Sea." Biogeosciences Discussions 11, no. 9 (September 19, 2014): 13515–32. http://dx.doi.org/10.5194/bgd-11-13515-2014.
Full textAbstract:
Abstract. High-resolution ocean color observation offers an opportunity to investigate the oceanic small-scale processes. In this study, The Medium Resolution Imaging Spectrometer (MERIS) daily 300 m data are used to study small-scale processes in the western South China Sea. It is indicated that the cyclonic eddies with horizontal scales of the order of 10 km are frequently observed during upwelling season of each year over 2004–2009. These small-scale eddies are generated in the vicinity of the southern front of the cold tongue, and then propagate eastward with a speed of approximately 12 cm s−1. This propagation speed is consistent with the velocity of the western boundary current. As a result, the small-scale eddies keep rotating high levels of the phytoplankton away from the coastal areas, resulting in the accumulation of phytoplankton in the interior of the eddies. The generation of the small-scale eddies may be associated with strengthening of the relative movement between the rotation speed of the anticylconic mesoscale eddies and the offshore transport. With the increases of the normalized rotation speed of the anticyclonic mesoscale eddies relative to the offshore transport, the offshore current become meander under the impacts of the anticyclonic mesoscale eddies. The meandered cold tongue and instability front may stimulate the generation of the small-scale eddies. Unidirectional uniform wind along cold tongue may also contribute to the formation of the small-scale eddies.
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Ni, Qinbiao, Xiaoming Zhai, Zhibin Yang, and Dake Chen. "Generation of Cold Anticyclonic Eddies and Warm Cyclonic Eddies in the Tropical Oceans." Journal of Physical Oceanography 53, no. 6 (June 2023): 1485–98. http://dx.doi.org/10.1175/jpo-d-22-0197.1.
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Abstract Mesoscale eddies are ubiquitous features of the global ocean circulation. Traditionally, anticyclonic eddies are thought to be associated with positive temperature anomalies while cyclonic eddies are associated with negative temperature anomalies. However, our recent study found that about one-fifth of the eddies identified from global satellite observations are cold-core anticyclonic eddies (CAEs) and warm-core cyclonic eddies (WCEs). Here we show that in the tropical oceans where the probabilities of CAEs and WCEs are high, there are significantly more CAEs and WCEs in summer than in winter. We conduct a suite of idealized numerical model experiments initialized with composite eddy structures obtained from Argo profiles as well as a heat budget analysis. The results highlight the key role of relative wind-stress-induced Ekman pumping, surface mixed layer depth, and vertical entrainment in the formation and seasonal cycle of these unconventional eddies. The relative wind stress is found to be particularly effective in converting conventional eddies into CAEs or WCEs when the surface mixed layer is shallow. The abundance of CAEs and WCEs in the global ocean calls for further research on this topic.
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Hao, Zhanjiu, Zhenhua Xu, Ming Feng, Qun Li, and Baoshu Yin. "Spatiotemporal Variability of Mesoscale Eddies in the Indonesian Seas." Remote Sensing 13, no. 5 (March 8, 2021): 1017. http://dx.doi.org/10.3390/rs13051017.
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Mesoscale eddies are ubiquitous in the world ocean and well researched both globally and regionally, while their properties and distributions across the whole Indonesian Seas are not yet fully understood. This study investigates for the first time the spatiotemporal variations and generation mechanisms of mesoscale eddies across the whole Indonesian Seas. Eddies are detected from altimetry sea level anomalies by an automatic identification algorithm. The Sulu Sea, Sulawesi Sea, Maluku Sea and Banda Sea are the main eddy generation regions. More than 80% of eddies are short-lived with a lifetime below 30 days. The properties of eddies exhibit high spatial inhomogeneity, with the typical amplitudes and radiuses of 2–6 cm and 50–160 km, respectively. The most energetic eddies are observed in the Sulawesi Sea and Seram Sea. Eddies feature different seasonal cycles between anticyclonic and cyclonic eddies in each basin, especially given that the average latitude of the eddy centroid has inverse seasonal variations. About 48% of eddies in the Sulawesi Sea are highly nonlinear, which is the case for less than 30% in the Sulu Sea and Banda Sea. Instability analysis is performed using high-resolution model outputs from Bluelink Reanalysis to assess mechanisms of eddy generation. Barotropic instability of the mean flow dominates eddy generation in the Sulu Sea and Sulawesi Sea, while baroclinic instability is slightly more in the Maluku Sea and Banda Sea.
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Liu, Tongya, and Ryan Abernathey. "A global Lagrangian eddy dataset based on satellite altimetry." Earth System Science Data 15, no. 4 (April 19, 2023): 1765–78. http://dx.doi.org/10.5194/essd-15-1765-2023.
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Abstract. The methods used to identify coherent ocean eddies are either Eulerian or Lagrangian in nature, and nearly all existing eddy datasets are based on the Eulerian method. In this study, millions of Lagrangian particles are advected by satellite-derived surface geostrophic velocities over the period of 1993–2019. Using the method of Lagrangian-averaged vorticity deviation (LAVD), we present a global Lagrangian eddy dataset (GLED v1.0, Liu and Abernathey, 2022, https://doi.org/10.5281/zenodo.7349753). This open-source dataset contains not only the general features (eddy center position, equivalent radius, rotation property, etc.) of eddies with lifetimes of 30, 90, and 180 d, but also the trajectories of particles trapped by coherent eddies over the lifetime. We present the statistical features of Lagrangian eddies and compare them with those of the most widely used sea surface height (SSH) eddies, focusing on generation sites, size, and propagation speed. A remarkable feature is that Lagrangian eddies are generally smaller than SSH eddies, with a radius ratio of about 0.5. Also, the validation using Argo floats indicates that coherent eddies from GLED v1.0 exist in the real ocean and have the ability to transport water parcels. Our eddy dataset provides an additional option for oceanographers to understand the interaction between coherent eddies and other physical or biochemical processes in the Earth system.
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Zhang, Yang, Xiu-Qun Yang, Yu Nie, and Gang Chen. "Annular Mode–Like Variation in a Multilayer Quasigeostrophic Model." Journal of the Atmospheric Sciences 69, no. 10 (May 31, 2012): 2940–58. http://dx.doi.org/10.1175/jas-d-11-0214.1.
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Abstract Eddy–zonal flow interactions in the annular modes are investigated in this study using a modified beta-plane multilayer quasigeostrophic (QG) channel model. This study shows the different response of high- and low-phase-speed (frequency) eddies to the zonal wind anomalies and suggests a baroclinic mechanism through which the two eddies work symbiotically maintaining the positive eddy feedback in the annular modes. Analysis also indicates that the different roles played by these two eddies in the annular modes are related to the differences in their critical line distributions. Eddies with higher phase speeds experience a low-level critical layer at the center of the jet. They drive the zonal wind anomalies associated with the annular mode but weaken the baroclinicity of the jet in the process. Lower-phase-speed eddies encounter low-level critical lines on the jet flanks. While their momentum fluxes are not as important for the jet shift, they play an important role by restoring the lower-level baroclinicity at the jet center, creating a positive feedback loop with the fast eddies that extends the persistence of the jet shift. The importance of the lower-level baroclinicity restoration by the low-phase-speed eddies in the annular modes is further demonstrated in sensitivity runs, in which surface friction on eddies is increased to selectively damp the low-phase-speed eddies. For simulations in which the low-phase-speed eddies become inactive, the leading mode of the zonal wind variability shifts from the position fluctuation to a pulsing of the jet intensity. Further studies indicate that the response of the lower-level baroclinicity to the zonal wind anomalies caused by the low-phase-speed eddies can be crucial in maintaining the annular mode–like variations.
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Sun, Wen Zheng, Jian Cheng Kang, Guo Qi Han, Guo Dong Wang, Jiong Zhu, Qin Chen Han, Chao Liu, et al. "Temporal and Spatial Variation of Vortex at Northeast Taiwan from 1992 to 2009." Advanced Materials Research 518-523 (May 2012): 4278–82. http://dx.doi.org/10.4028/www.scientific.net/amr.518-523.4278.
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Using the satellite altimetric sea level data during 1992 to 2009 from AVISO, analyzed seasonal, annual variations of vortexes in northeast Taiwan (24°N ~ 27°N, 120°E ~ 124°E). The result shows that: (1) Cyclonic and anti-cyclonic eddies are found in research area and had significant seasonal variation; (2) Cyclonic eddies had five-years cycle in winter; (3) Cyclonic eddies and anti-cyclonic eddies often appeared in pairs and swing in the east-west direction simultaneously; (4) Changes in spatial distribution of the eddies are the result from the Kuroshio’s period oscillation and the topography at northeast of Taiwan.
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van Westen, René M., and Henk A. Dijkstra. "Ocean eddies strongly affect global mean sea-level projections." Science Advances 7, no. 15 (April 2021): eabf1674. http://dx.doi.org/10.1126/sciadv.abf1674.
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Current sea-level projections are based on climate models in which the effects of ocean eddies are parameterized. Here, we investigate the effect of ocean eddies on global mean sea-level rise (GMSLR) projections, using climate model simulations. Explicitly resolving ocean eddies leads to a more realistic Southern Ocean temperature distribution and volume transport. These quantities control the rate of basal melt, which eventually results in Antarctic mass loss. In a model with resolved ocean eddies, the Southern Ocean temperature changes lead to a smaller Antarctic GMSLR contribution compared to the same model in which eddies are parameterized. As a result, the projected GMSLR is about 25% lower at the end of this century in the eddying model. Relatively small-scale ocean eddies can hence have profound large-scale effects and consequently affect GMSLR projections.
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Ni, Qinbiao, Xiaoming Zhai, Xuemin Jiang, and Dake Chen. "Abundant Cold Anticyclonic Eddies and Warm Cyclonic Eddies in the Global Ocean." Journal of Physical Oceanography 51, no. 9 (September 2021): 2793–806. http://dx.doi.org/10.1175/jpo-d-21-0010.1.
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AbstractMesoscale eddies are ubiquitous features of the global ocean circulation and play a key role in transporting ocean properties and modulating air–sea exchanges. Anticyclonic and cyclonic eddies are traditionally thought to be associated with anomalous warm and cold surface waters, respectively. Using satellite altimeter and microwave data, here we show that surface cold-core anticyclonic eddies (CAEs) and warm-core cyclonic eddies (WCEs) are surprisingly abundant in the global ocean—about 20% of the eddies inferred from altimeter data are CAEs and WCEs. Composite analysis using Argo float profiles reveals that the cold cores of CAEs and warm cores of WCEs are generally confined in the upper 50 m. Interestingly, CAEs and WCEs alter air–sea momentum and heat fluxes and modulate mixed layer depth and surface chlorophyll concentration in a way markedly different from the traditional warm-core anticyclonic and cold-core cyclonic eddies. Given their abundance, CAEs and WCEs need to be properly accounted for when assessing and parameterizing the role of ocean eddies in Earth’s climate system.
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Jones-Kellett, Alexandra E., and Michael J. Follows. "A Lagrangian coherent eddy atlas for biogeochemical applications in the North Pacific Subtropical Gyre." Earth System Science Data 16, no. 3 (March 15, 2024): 1475–501. http://dx.doi.org/10.5194/essd-16-1475-2024.
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Abstract. Mesoscale eddies affect phytoplankton in several ways, including the horizontal dispersal and mixing of populations. Coherent eddies trap and contain fluid masses, whereas other eddies mix more freely with surrounding waters. To evaluate the role of lateral dispersal and trapping on the biogeochemical properties of eddies, we must accurately characterize their coherency. We employed a Lagrangian approach to identify materially coherent structures in remote sensing observations and developed a methodology to track them over their entire individual lifetimes. We provide an atlas of two decades of coherent eddies with an 8 d resolution in an intensely studied region of the North Pacific Subtropical Gyre (Jones-Kellett, 2023a, https://doi.org/10.5281/zenodo.8139149). The atlas was specifically designed to facilitate biogeochemical applications and was synchronized with available ocean color products. We identified coherent features using backward Lagrangian trajectories because the recent history of coherency (rather than the future coherency) will be most valuable for interpreting associated biogeochemical signatures. We compared the atlas of Lagrangian coherent eddies with an atlas of Eulerian eddies identified using the more conventionally used Sea Level Anomaly method. Although 65 % of tracked Sea Level Anomaly eddies are classified as coherent at some point in their lifetime, only 54 % contain a Lagrangian coherent structure at any given time. We found similar variations in the temporal and spatial distributions of coherent and Sea Level Anomaly eddies. However, strictly coherent eddies have a clearer relationship between size and longevity and form distinct regional regimes based on polarity. We illustrate the potential of the coherent eddy atlas for biogeochemical applications by examining the relationship between bloom development and eddy evolution in a case study of a Hawaiian Lee cyclone.
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Callendar, W., J. M. Klymak, and M. G. G. Foreman. "Tidal generation of large sub-mesoscale eddy dipoles." Ocean Science 7, no. 4 (August 3, 2011): 487–502. http://dx.doi.org/10.5194/os-7-487-2011.
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Abstract. Numerical simulations of tidal flow past Cape St. James on the south tip of Haida Gwaii (Queen Charlotte Islands) are presented that indicate mesoscale dipoles are formed from coalescing tidal eddies. Observations in this region demonstrate robust eddy generation at the Cape, with the primary process being flow separation of buoyant or wind driven outflows forming large anti-cyclonic, negative potential vorticity, Haida Eddies. However, there are other times where dipoles are observed in satellites, indicating a source of positive potential vorticity must also be present. The simulations here build on previous work that implicates oscillating tidal flow past the cape in creating the positive vorticity. Small headland eddies of alternating vorticity are created each tide. During certain tidal cycles, the headland eddies coalesce and self organize in such a way as to create large >20-km diameter eddies that then self-advect into deep water. The self advection speed is faster than the beta drift of anti-cyclones, and the propagation direction appears to be more southerly than typical Haida Eddies, though the model contains no mean wind-driven flows. These eddies are smaller than Haida Eddies, but given their tidal origin, may represent a more consistent source of coastal water that is injected into the interior of the subpolar gyre.
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Callendar, W., J. M. Klymak, and M. G. G. Foreman. "Tidal generation of large sub-mesoscale eddy dipoles." Ocean Science Discussions 8, no. 2 (April 7, 2011): 723–60. http://dx.doi.org/10.5194/osd-8-723-2011.
Full textAbstract:
Abstract. Numerical simulations of tidal flow past Cape St. James on the south tip of Haida Gwai (Queen Charlotte Islands) are presented that indicate mesoscale dipoles are formed from coalescing tidal eddies. Observations in this region demonstrate robust eddy generation at the Cape, with the primary process being flow separation of buoyant or wind driven outflows forming large anti-cyclonic, negative potential vorticity, Haida Eddies. However, there are other times where dipoles are observed in satellites, indicating a source of positive potential vorticity must also be present. The simulations here build on previous work that implicates oscillating tidal flow past the cape in creating the positive vorticity. Small headland eddies of alternating vorticity are created each tide. During certain tidal cycles, the headland eddies coalesce and self organize in such a way as to create large >20-km diameter eddies that then self-advect into deep water. The self advection speed is faster than the beta drift of anti-cyclones, and the propagation direction appears to be more southerly than typical Haida Eddies, though the model contains no mean wind-driven flows. These eddies are smaller than Haida Eddies, but given their tidal origin, may represent a more consistent source of coastal water that is injected into to the interior of the subpolar gyre.
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Rocha, Cesar B., and Iury T. Simoes-Sousa. "Compact Mesoscale Eddies in the South Brazil Bight." Remote Sensing 14, no. 22 (November 16, 2022): 5781. http://dx.doi.org/10.3390/rs14225781.
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Recent studies suggest that the South Brazil Bight (SBB) hosts strong westward propagating mesoscale eddies. We use 28 years of satellite altimetry data and a new Eddy Atlas to estimate how much of the eddy kinetic energy (EKE) observed in the SBB is accounted for by local eddies, generated in the Brazil Current (BC) region, versus remote eddies generated eastward of the BC region. First, we estimate a BC frontal density to obtain a robust definition of BC region. The BC front is well-defined throughout the SBB, occupying the region between the 200-m and 1000-m isobath, except in eddy hotspots downstream of sharp inflections of the continental slope, where the EKE far exceeds the mean kinetic energy (MKE). Compact, closed-contour mesoscale eddies account for 30–50% of the total EKE observed in the SBB, with local eddies accounting for most of the compact EKE in the BC region, defined as the area within 200 km of the 28-year mean BC front. Remote compact eddies account for less than 10% of the EKE observed in the BC region; compact eddies generated at long distances from the SBB, including eddies generated in the Southeastern Atlantic, contribute an insignificant fraction of EKE in the BC region.
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Ma, Chunyong, Siqing Li, Yang Yang, Jie Yang, and Ge Chen. "Extraction of Revolving Channels of Drifters around Mesoscale Eddy Centers Based on Spatiotemporal Trajectory Clustering." Journal of Atmospheric and Oceanic Technology 36, no. 9 (September 2019): 1903–16. http://dx.doi.org/10.1175/jtech-d-19-0007.1.
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The global oceanic transports of energy, plankton, and other tracers by mesoscale eddies can be estimated by combining satellite altimetry and in situ data. However, the revolving channels of particles entrained by mesoscale eddies, which could help explain the dynamic process of eddies entraining materials, are still unknown. In this study, satellite altimeter and drifter data from 1993 to 2016 are adopted, and the normalized trajectory clustering algorithm (N-TRACLUS) is proposed to extract the revolving channels of drifters. First, the trajectories of drifters are normalized and clustered by using the density-based spatial clustering of applications with noise (DBSCAN) algorithm. Next, the revolving channels of drifters around the eddy center are extracted. The ring or arc pattern in the middle of a normalized eddy appears when drifters are uninterruptedly entrained by eddies for more than 30 days. Moreover, the revolving channels of drifters in cyclonic eddies are relatively closer to the eddy center than those in anticyclonic eddies. These revolving channels suggest the principal mode of materials’ continuous motion processes that are inside eddies.
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Li, Gang, Yijun He, Jinghan Wen, Guoqiang Liu, Vladimir Kudryavtsev, Xiaojie Lu, and William Perrie. "The Characteristics of Submesoscale Eddies Near the Coastal Regions of Eastern Japan: Insights from Sentinel-1 Imagery." Journal of Marine Science and Engineering 12, no. 5 (April 30, 2024): 761. http://dx.doi.org/10.3390/jmse12050761.
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A long-term time series of 319 Sentinel-1 SAR Imagery with Interferometric Wide Swath (IW) mode was used to study the characteristics of submesoscale eddies over Japanese coastal regions from 2015 to 2021, including spatiotemporal eddy properties and possible mechanisms of their formation. The results showed that around 98% of the 1499 eddies identified from the SAR snapshots were submesoscale eddies (horizontal scales of O1–20 km) with a ratio of around 78% cyclones to around 22% anticyclones. Around 8% of the submesoscale eddies were found in these SAR images in winter since the submesoscale current-induced signals are masked by the stronger wind speed, compared with other seasons. Typical features of submesoscale eddies are summarized, providing a preliminary qualitative analysis of potential generation mechanisms specific to the eddy characteristics in this region. This study suggests that Sentinel-1 images are capable of providing insights into the observed submesoscale eddies near the coastal regions of eastern Japan, thereby contributing to the improved understanding of the generation of submesoscale eddies.
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Moutin, T., and L. Prieur. "Influence of anticyclonic eddies on the Biogeochemistry from the Oligotrophic to the Ultraoligotrophic Mediterranean (BOUM cruise)." Biogeosciences 9, no. 10 (October 8, 2012): 3827–55. http://dx.doi.org/10.5194/bg-9-3827-2012.
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Abstract. We studied a longitudinal transect in the Mediterranean Sea (MS) and along this transect, the influence of anticyclonic eddies at three long duration (LD) stations. The deep chlorophyll maximum depth, the euphotic layer depth and the top of the nitracline depth are clearly correlated outside of the eddies, and deepen from the oligotrophic western to the ultraoligotrophic eastern MS. We provide evidence that the locations of the three LD stations studied were near the axis of the eddies. Their diameters were close to 100 km and the studied areas were less than 10 km from the centre of the eddies. The positions of the LD stations are marked by an increase in the flux function and a decrease in apparent oxygen utilization (AOU) and in excess density σ), as expected for anticyclonic eddies. Integrated mean primary production measured in situ inside the three studied eddies confirms the previous conclusion that integrated primary production (IPP) about 150 mgC m−2 d−1 may appear as a lower limit for IPP during strong oligotrophic conditions. The mesoscale activity is strong enough to locally modify the very well-documented western-to-eastern gradient of trophic conditions in the MS. We proposed a new calculation for mixed layer depths (MLDs) enabling the determination of MLD to take into consideration processes occurring with time scales ranging from a few hours to several days, and also the winter MLD. Studying the main physical, chemical and dynamical characteristics of the three eddies enables us to consider that the vorticity barrier prevents any strong mixing and advection of outer water inside the eddy and explains why the depth range of eddies starts from the surface. As a first approximation, the anticyclonic eddies could be considered as closed systems dating back to the previous winter, making possible to draw first-order budgets. The daily new N-input in the photic zone is virtually identical to the N-export measured at 230 m by drifting traps. This means that the eddies are close to an equilibrium state where input is equal to loss. The annual N-input by winter convection, which is a fundamental criterion for new nutrient availability, may be extremely variable inside eddies, with W-MLD varying from 90.5 m at the western station to 396.5 m at the eastern station. W-MLDs are always deeper inside the eddies than outside where they are in keeping with climatological averages. AOU was low inside the eddies; this together with the near-identical export measured at 230 and 460 m seems to indicate that eddy cores are areas where low mineralisation of particulate organic matter occurs. "In" and "out" AOU comparisons indicate lower mineralisation inside the eddies suggesting a higher efficiency for CO2 sequestration via sedimentation of particulate organic matter. The three eddies are enriched in dissolved organic carbon (DOC). Sequestration of CO2 by vertical export of accumulated DOC therefore seems to be higher inside eddies. The relative importance of DOC transport in the biological pump is probably one of the main characteristics of low-P low chlorophyll (LPLC) areas, and it is likely to be reinforced inside anticyclonic eddies. The numerous anticyclonic eddies in the MS are likely to influence the water masses and their dispersion, and therefore have a strong impact on the biogeochemical properties at the scale of the MS.
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Rouault, M., P. Verley, and B. Backeberg. "Wind changes above warm Agulhas Current eddies." Ocean Science 12, no. 2 (April 5, 2016): 495–506. http://dx.doi.org/10.5194/os-12-495-2016.
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Abstract. Sea surface temperature (SST) estimated from the Advanced Microwave Scanning Radiometer E onboard the Aqua satellite and altimetry-derived sea level anomalies are used south of the Agulhas Current to identify warm-core mesoscale eddies presenting a distinct SST perturbation greater than to 1 °C to the surrounding ocean. The analysis of twice daily instantaneous charts of equivalent stability-neutral wind speed estimates from the SeaWinds scatterometer onboard the QuikScat satellite collocated with SST for six identified eddies shows stronger wind speed above the warm eddies than the surrounding water in all wind directions, if averaged over the lifespan of the eddies, as was found in previous studies. However, only half of the cases showed higher wind speeds above the eddies at the instantaneous scale; 20 % of cases had incomplete data due to partial global coverage by the scatterometer for one path. For cases where the wind is stronger above warm eddies, there is no relationship between the increase in surface wind speed and the SST perturbation, but we do find a linear relationship between the decrease in wind speed from the centre to the border of the eddy downstream and the SST perturbation. SST perturbations range from 1 to 6 °C for a mean eddy SST of 15.9 °C and mean SST perturbation of 2.65 °C. The diameter of the eddies range from 100 to 250 km. Mean background wind speed is about 12 m s−1 (mostly southwesterly to northwesterly) and ranging mainly from 4 to 16 m s−1. The mean wind increase is about 15 %, which corresponds to 1.8 m s−1. A wind speed increase of 4 to 7 m s−1 above warm eddies is not uncommon. Cases where the wind did not increase above the eddies or did not decrease downstream had higher wind speeds and occurred during a cold front associated with intense cyclonic low-pressure systems, suggesting certain synoptic conditions need to be met to allow for the development of wind speed anomalies over warm-core ocean eddies. In many cases, change in wind speed above eddies was masked by a large-scale synoptic wind speed deceleration/acceleration affecting parts of the eddies.
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You, Zhiwei, Lingxiao Liu, Brandon J. Bethel, and Changming Dong. "Feature Comparison of Two Mesoscale Eddy Datasets Based on Satellite Altimeter Data." Remote Sensing 14, no. 1 (December 28, 2021): 116. http://dx.doi.org/10.3390/rs14010116.
Full textAbstract:
Although a variety of ocean mesoscale eddy datasets are available for researchers to study eddy properties throughout the global ocean, subtle differences in how these datasets are produced often lead to large differences between one another. This study compares the Global Ocean Mesoscale Eddy Atmospheric-Oceanic-Biological interaction Observational Dataset (GOMEAD) with the well-recognized Mesoscale Eddy Trajectory Atlas in four regions with strong eddy activity: the Northwest Pacific Subtropical Front (SF), Kuroshio Extension (KE), South China Sea (SCS), and California Coastal Current (CC), and assesses the relative advantages and disadvantages of each. It was identified that while there is a slight difference in the total number of eddies detected in each dataset, the frequency distribution of eddy radii presents a right-skewed normal distribution, tending towards larger radii eddies, and there are more short- than long-lived eddies. Interestingly, the total number of GOMEAD eddies is 8% smaller than in the META dataset and this is most likely caused by the GOMEAD dataset’s underestimation of total eddy numbers and lifespans due to their presence near islands, and the tendency to eliminate eddies from its database if their radii are too small to be adequately detected. By contrast, the META dataset, due to tracking jumps in detecting eddies, may misidentify two eddies as a single eddy, reducing total number of eddies detected. Additionally, because the META dataset is reliant on satellite observations of sea surface level anomalies (SLAs), when SLAs are weak, the META dataset struggles to detect eddies. The GOMEAD dataset, by contrast, is reliant on applying vector geometry to detect and track eddies, and thus, is largely insulated from this problem. Thus, although both datasets are excellent in detecting and characterizing eddies, users should use the GOMEAD dataset when the region of interest is far from islands or when SLAs are weak but use the META dataset if the region of interest is populated by islands, or if SLAs are intense.
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Bibby, T. S., and C. M. Moore. "Silicate:nitrate ratios of upwelled waters control the phytoplankton community sustained by mesoscale eddies in sub-tropical North Atlantic and Pacific." Biogeosciences Discussions 7, no. 5 (October 14, 2010): 7505–25. http://dx.doi.org/10.5194/bgd-7-7505-2010.
Full textAbstract:
Abstract. Mesoscale eddies in sub-tropical gyres physically perturb the water column and can introduce macronutrients to the euphotic zone, stimulating a biological response by which phytoplankton communities can become dominated by large phytoplankton. Mesoscale eddies are therefore important in driving export in oligotrophic regions of the modern ocean. The character and magnitude of the biological response sustained by eddies are, however, variable. Here we present data from mesoscale eddies in the Sargasso Sea (Atlantic) and the waters off Hawai'i (Pacific), alongside mesoscale events that affected the Bermuda Atlantic Time Series (BATS) over the past decade. From this analysis, we suggest that the phytoplankton community structure sustained by mesoscale eddies is predetermined by the relative abundance of silicate over nitrate (Si*) in the upwelled waters. We present data that demonstrate that mode-water eddies (MWE) in the Sargasso Sea upwell locally formed waters with high Si* to the euphotic zone, and that cyclonic eddies in the Sargasso Sea introduce waters with low Si*, a signature that originated in the iron-limited Southern Ocean. We propose that this phenomenon can explain the observed abundance of large-diatom species in MWE and small prokaryotic phytoplankton in cyclonic features. In contrast to the Atlantic, cyclonic eddies in waters off Hawai'i induce North Pacific Intermediate Water (NPIW) that has high Si* and therefore also appears capable of establishing diatom populations. These observations suggest that the structure of phytoplankton communities sustained by eddies may not be directly related to the physical nature of the eddy but rather to the chemical composition of the upwelled waters. This paper links the biological production and export efficiency of mesoscale eddies to events in spatially and temporally disparate locations.
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Li, Ce, Yunyan Du, Fuyuan Liang, Jiawei Yi, and V. Chris Lakhan. "A GIS-based method for depicting the characteristics of mesoscale eddies: a case study in the Northern South China Sea." Canadian Journal of Earth Sciences 52, no. 9 (September 2015): 746–56. http://dx.doi.org/10.1139/cjes-2014-0177.
Full textAbstract:
The paper presents a geographical information system (GIS)-based method for depicting the characteristics, particularly the internal structures and evolutionary processes, of mesoscale eddies. This was done by examining topologic relations among closed sea surface height (SSH) contours that were reconstructed from the Naval Research Laboratory Navy layered ocean model (NLOM). Different scenarios of the topological relations among the contour lines permitted the identification of the outermost outline of eddies and the depiction of the number of cores in each mesoscale oceanic eddy. With full consideration of the internal structure of the eddies, we then reconstructed the evolutionary processes of these eddies, and the results were compared with empirical observations on three long-lived mesoscale eddies in the northern South China Sea (SCS). Tracking results were similar, thereby validating our method as being efficient and robust in reconstructing mesoscale ocean eddies, especially their evolutionary processes based on their internal structures.