Eddy Tracking Research Articles

Census and properties of mesoscale eddies in the Kuril Basin of the Okhotsk Sea

High spatial-resolution satellite images show the presence of numerous eddies in the deep Kuril Basin of the Okhotsk Sea, where in-situ measurements acquired within eddies are relatively rare. We conducted the first altimetry-based systematic census of mesoscale eddies in the Kuril Basin in 1993–2021 using the automatic eddy tracking algorithm AMEDA. The dominance of cyclonic eddies over anticyclonic eddies was observed, which contradicts the common opinion that anticyclonic eddies prevail over cyclonic ones in the Kuril Basin. The paper focuses mainly on the long-lived eddies with the lateral size in the range from several tens of kilometers to some hundreds of kilometers and with the lifetime exceeding 30 days. It was found that these eddies are inhomogeneously distributed over the study area with high values of occurrence frequency in some domains. This is explained by the topographic features and peculiarities of the circulation in the Basin where Soya Warm Current water, Okhotsk Sea water and subarctic Pacific water circulate and mix. The fractions of these water masses and their seasonal and interannual variations within the surface cores of the eddy were estimated using a particle-tracking technique. The kinematic characteristics of these eddies have been computed as well. The vast majority of the anticyclonic and cyclonic eddies have the nonlinearity parameter exceeding one implying that the eddies in the Kuril Basin are coherent features transporting water with its properties. Peculiarities in distribution of formation, occurrence and decay locations have been analyzed. Our results have been compared with shipboard and buoy's observations and numerical simulation of eddies in the Kuril Basin.

Role of Air‐Sea Interaction in the Energy Balance of Anticyclonic and Cyclonic Eddies in the Kuroshio Extension

AbstractUsing eddy‐resolving Community Earth System Model (CESM) simulations, this study investigates mesoscale eddy energetics and the role of air‐sea interaction for both anticyclonic and cyclonic eddies (AEs and CEs) in the Kuroshio Extension (KE) region. Based on energy budget analysis and eddy tracking algorithm, it is found that eddy energy balance depicts similar characteristics for AEs and CEs. The eddy kinetic energy (EKE) is generated through barotropic instability, vertical buoyancy flux, as well as transported from the upper stream Kuroshio. In addition, the temperature variance, which is directly related to eddy potential energy, is maintained by baroclinic instability. Air‐sea heat flux and wind stress act as eddy killers to move energy from oceanic eddies. For both AEs and CEs, heat exchange between atmosphere and oceanic eddies dominates the dissipation of temperature variance and accounts for more than 60% and 72% of the total dissipation, respectively. In comparison, the role of wind power in damping the EKE is relatively small. Only 14% (5%) of EKE dissipation in AEs (CEs) is attributed to eddy wind power.

Vertical Interaction Between NBC Rings and Its Implications for South Atlantic Water Export

AbstractNorthwestward‐propagating North Brazil Current (NBC) Rings are often destroyed upon reaching the Caribbean islands, carrying South Atlantic waters into the North Atlantic gyre and connecting the two branches of the Atlantic Meridional Overturning Circulation. Recent observations of NBC rings reported surface and subsurface cores separated by strong stratification. As independent structures, the subsurface eddies often appeared below—even if not aligned with—the surface rings. Motivated by these findings, this paper investigates the occurrence and consequences of vertical coupling between surface and subsurface NBC rings by applying a simplified theoretical model to a realistic numerical simulation. Eddy tracking in this complex simulation reveals around 1,600 instantaneous observations where eddies overlap. At each observation, we assess the eddies' vertical interaction with a 21/2‐layer quasi‐geostrophic framework. This interaction boils down to either coupling between the layers or a vertical splitting of the system, depending on eddy strength versus background shear. The effects of coupling include long‐lived eddies that can travel longer distances. These effects are particularly important for the lower layer, where differences between coupled and non‐coupled eddies are striking: about 40% of eddies with coupling travel 500 km, with ∼10% carrying South Atlantic Water up to the Caribbean sea. Without coupling, eddies propagate less than 150 km. During coupling, lower‐layer eddies could be driven by their surface counterparts to move offshore and bypass a topographic choke point, thus leaving the NBC retroflection region. Although still speculative, this idea explains the link between coupling and the increase in both lifetime and distance traveled for these eddies.

Jumbo Flying Squid Distribution within Anticyclonic Eddies under Anomalous Climatic Conditions

Anticyclonic eddies are widely distributed off Peru, producing obvious effects on climate-environment-sensitive jumbo flying squid Dosidicus gigas . However, how the habitat of D. gigas changes within anticyclonic eddies during El Niño events is still unknown. Therefore, this study constructed a habitat model with different weights and screened the optimal performance model using fishery data from September to December during 2015 to 2019, as well as vertical water temperature data (sea surface temperature and 50 m water depth temperature) and surface chlorophyll concentration data (Chl-a). Then, combined with the eddy tracking dataset, the differences in the variation of resource abundance and habitat of D. gigas within the anticyclonic eddy between the 2015 El Niño year and the 2019 normal year were further comparatively analyzed based on the optimal habitat model. Compared with the normal year of 2019, the 2015 El Niño event occurred with a lower intensity of eddy activity, and both temperature in the fishing ground and near-surface sea water temperature within the anticyclonic eddy became warmer, with a small decrease in Chl-a; the percentage of suitable near-surface water temperature within the anticyclonic eddies decreased significantly, and suitable Chl-a decreased slightly; the suitable habitat for D. gigas was reduced dramatically, which was unfavorable to D. gigas survival. Our finding suggested that that anomalous climatic events can have an impact on eddy strength, as well as on the suitable environment and habitat within the anticyclonic eddies, resulting in variations in the abundance of D. gigas .

Vertical distribution of intraseasonal variation signals in the Kuroshio Current source area during 2018–2020

In the Kuroshio Current (KC) source area, intraseasonal variation (ISV) plays a significant role in dynamic oceanic processes. This study used data collected from three moorings (122.7°E, 123°E, 123.3°E) along 18°N from January 2018 to May 2020 to investigate the ISVs of meridional velocities. Notably, our findings reveal that the ISV above 200 m has a period of approximately 56 days and its intensity exhibits a gradual increase toward the west. For the 500–800 m depth interval, the ISV period is 73 days at 122.7°E/18°N and 60 days at 123.3°E/18°N. This discrepancy indicates that the ISVs have different vertical structures and frequencies at 122.7°E and 123.3°E along 18°N. In particular, at 122.7°E/18°N, the distinctiveness of two different periods of ISVs in surface and subsurface layers was more pronounced in 2018 than in 2019. The analyses of eddy kinetic energy distribution and eddy tracking indicate a connection between ISV in stratification and locally generated mesoscale eddies in the KC source area. Specifically, the stronger eddy activity in 2018, in contrast with that in 2019, correlates with a more pronounced ISV. Energy analysis demonstrates a distinct positivity in the baroclinic conversion rate (BC) in the surface layer (upper 200 m) of the KC source region, surpassing the absolute value of the barotropic conversion rate (BT). This finding indicates a notable shift of energy from eddy available potential energy to eddy kinetic energy, strengthening the high-frequency ISV signals in this area. In the subsurface layer, a strong negative BT is observed west of 122.8°E, with its absolute value exceeding the BC. This finding indicates that the energy is converted from eddy kinetic energy into mean kinetic energy, resulting in the appearance of the Luzon Undercurrent (LUC) at mooring station 122.7°E/18°N, characterized by a low frequency of ISV. Contrastingly, a positive BT plays a dominant role at 123.3°E/18°N, leading to the disappearance of the LUC amid an apparent presence of high-frequency ISV.

Medium-range forecasting of oceanic eddy trajectory

ABSTRACT The capability of continuous eddy tracking has been significantly advanced over the past decades, thanks to the availability of sea surface height measurements routinely collected by satellite altimeters. However, due to the complexity of eddy kinematic mechanisms and underlying oceanic processes, a medium-range forecast of individual eddy trajectories is a challenging task. This study develops an algorithm to effectively achieve a precise prediction of eddy propagation with a ten-day lead time by building a physics-embedded temporal evolution model. The theoretical eddy phase speed, current field, and eddy properties are incorporated as physical constraints. Compared to only considering eddy past/climatological velocities, the forecast accuracy of embedded physics constraints is improved by 21%. Forecasting of 2.3 million altimeter-derived eddy tracks globally shows that trajectory predictions are valid for eddies moving towards any direction, and the forecast error achieves 9.9 km on a ten-day average. After systematically evaluating the global forecast error, we conclude that the forecasting accuracy is geographically correlated and affected by external forcings (topography and wind) and eddy properties (geostrophy and life stage). Achieving accurate eddy trajectory prediction is expected to provide critical guidance for in-situ eddy observations, and bring substantial improvements for understanding oceanic substance transportations and biogeochemical processes.

A census and properties of mesoscale Kuril eddies in the altimetry era

The ocean-side area of the Kuril Islands is a region with high bioproductivity and rich fishing and a convergence of transformed subtropical and subarctic waters with significant impact on weather and climate. Waters of different origin mix in the region including Kuroshio Extention, Japan Sea, Oyashio, Okhotsk Sea and Alaskan Stream waters. Despite the important role of Kuril eddies (KE) in transporting heat, salt, nutrients and their biological activity, there are still major gaps in our knowledge of the properties and dynamics of these energetic and mesoscale features in the northwestern Pacific Ocean. Using altimetry data during 1993–2021, we conducted the first systematic census of KE with the help of the automatic eddy tracking algorithm AMEDA. We separated KE into four groups according to their places of formation in relation to the Kuril-Kamchatka Trench and found a strong inhomogeneous spatial distribution of the Kuril cyclones (KC) and anticyclones (KAC). Different kinematic properties of KE have been studied and analyzed. The Trench has been found to play a role of an eddy guide for long-lived eddies with a comparatively small number of KE being able to cross the Trench. The highest occurrence frequency of KAC was observed along the Trench, especially in the area east off the Bussol Strait, whereas KC occurred more frequently along the ocean side of the Trench. Among the observed long-lived KE, there were more than 90% of eddies with the nonlinearity parameter exceeding 1 implying that the majority of KE are coherent vortices transporting water with its properties. The relative concentrations of waters of different origin inside KAC and KC cores were computed for each group applying the new Lagrangian algorithm. It allowed us to detect transportation of subtropical water in the KE cores to north and subarctic water to south over the distance of the order of 1000 km and more.

Eddy Tracking From In Situ and Satellite Observations

AbstractMesoscale eddies are a dominant source of spatial variability in the surface ocean and play a major role in the biological marine carbon cycle. Satellite altimetry is often used to locate and track eddies, but this approach is rarely validated against in situ observations. Here we compare measurements of a small (under 25 km radius) mode water anticyclonic eddy over the Porcupine Abyssal Plain in the northeastern Atlantic Ocean using CTD and Acoustic Doppler Current Profiler (ADCP) measurements from three ships, two gliders, two profiling floats, and one Lagrangian float with those derived from sea level anomaly (SLA). In situ estimates of the eddy center were estimated from maps of the thickness of its central isopycnal layer, from ADCP velocities at a reference depth, and from the trajectory of the Lagrangian float. These were compared to three methods using altimetric SLA: one based on maximizing geostrophic rotation, one based on a constant SLA contour, and one which maximizes geostrophic velocity speed along the eddy boundary. All algorithms were used to select CTD profiles that were within the eddy. The in‐situ metrics agreed to 97%. The altimetry metrics showed only a small loss of accuracy, giving >90% agreement with the in situ results. This suggests that current satellite altimetry is adequate for understanding the spatial representation of even relatively small mesoscale eddies.

MESI: A Multiparameter Eddy Significance Index

AbstractIn this study, we introduce the Multiparameter Eddy Significance Index (MESI) for use in conjunction with mesoscale eddy tracking to estimate the impact of mesoscale eddies on the upper ocean and marine ecosystems. MESI combines blended satellite observations of sea level anomalies, sea surface temperature, sea surface salinity, and ocean color chlorophyll‐a and is a normalized index. When used in conjunction with mesoscale eddy tracking, MESI can highlight those eddies which extend into the deeper ocean and have a greater effect on nutrient cycling. Preliminary analysis in the Gulf Stream region of the western North Atlantic shows that MESI covaries with model estimates of nitrate, phosphate, iron, and pH with cross‐correlation values between 76% and 95%. These results suggest that when MESI is used in concert with eddy tracking, it can be used as an indicator of eddies and areas that are more likely to impact nutrient cycling in the upper ocean. An additional analysis of MESI values inside eddies during Hurricane Dorian (2019) along the Carolina coast further suggests that MESI is most effective when used to enhance eddy tracking as it provides valuable insight into mesoscale eddy activity and the upper ocean circulation.

A new mesoscale eddy tracking methodology based on fast normalized cross-correlation and its validation in the Northwest Pacific

Most mesoscale eddy tracking methodologies used prior to this study evaluated eddy features using a distance-based proximity relationship, rather than considering similarities between eddies. This study applies a fast normalized cross-correlation methodology in the field of image registration to propose a novel mesoscale eddy tracking methodology that can rapidly and comprehensively calculate the similarities between two eddies and judge their relationship through the correlation coefficient, thus facilitating a more accurate mesoscale eddy trajectory tracking. The sea level anomaly data field is employed to identify the positions of eddies over time. The tracking methodology is then used to track the mesoscale eddy trajectories. After comparing the local nearest neighbor methodology (LNN) with our proposed new methodology in the Northwest Pacific Ocean, we conclude that the proposed methodology can address issues of discontinuity in tracking; especially in cases involving eddies with long lifespans. The tracking trajectories utilized in the proposed methodology achieve superior continuity and integrity and a higher degree of characterization than LNN, with the tracking results showing greater consistency with real eddy motion. The new methodology proposed in this paper has great significance for more widespread use.

Evaluating the impacts of mesoscale eddies on abundance and distribution of neon flying squid in the Northwest Pacific Ocean

Mesoscale eddies are ubiquitous in global oceans yielding significant impacts on marine life. As a short-lived pelagic squid species, the population of neon flying squid (Ommastrephes bartramii) is extremely sensitive to changes in ambient oceanic variables. However, a comprehensive understanding of how mesoscale eddies affect the O. bartramii population in the Northwest Pacific Ocean is still lacking. In this study, a 10-year squid fisheries dataset with eddy tracking and high-resolution reanalysis ocean reanalysis data was used to evaluate the impact of mesoscale eddies and their induced changes in environmental conditions on the abundance and habitat distribution of O. bartramii in the Northwest Pacific Ocean. A weighted-based habitat suitability index (HSI) model was developed with three crucial environmental factors: sea surface temperature (SST), seawater temperature at 50-m depth (T50m), and chlorophyll-a concentration (Chl-a). During years with an unstable Kuroshio Extension (KE) state, the abundance of O. bartramii was significantly higher in anticyclonic eddies (AEs) than that in cyclonic eddies (CEs). This difference was well explained by the distribution pattern of suitable habitats in eddies derived from the HSI model. Enlarged ranges of the preferred SST, T50m, and Chl-a for O. bartramii within AEs were the main causes of more squids occurring inside the warm-core eddies, whereas highly productive CEs matching with unfavorable thermal conditions tended to form unsuitable habitats for O. bartramii. Our findings suggest that with an unstable KE background, suitable thermal conditions combined with favorable foraging conditions within AEs were the main drivers that yielded the high abundance of O. bartramii in the warm eddies.

Global coarse-grained mesoscale eddy statistics based on integrated kinetic energy and enstrophy correlations

Abstract. Recently, Jánosi et al. (2019) introduced the concept of a “vortex proxy” based on an observation of strong correlations between integrated kinetic energy and integrated enstrophy over a large enough surface area. When mesoscale vortices are assumed to exhibit a Gaussian shape, the two spatial integrals have particularly simple functional forms, and a ratio of them defines an effective radius of a “proxy vortex”. In the original work, the idea was tested over a restricted area in the Californian Current System. Here we extend the analysis to global scale by means of 25 years of AVISO altimetry data covering the (ice-free) global ocean. The results are compared with a global vortex database containing over 64 million mesoscale eddies. We demonstrate that the proxy vortex representation of surface flow fields also works globally and provides a quick and reliable way to obtain coarse-grained vortex statistics. Estimated mean eddy sizes (effective radii) are extracted in very good agreement with the data from the vortex census. Recorded eddy amplitudes are directly used to infer the kinetic energy transported by the mesoscale vortices. The ratio of total and eddy kinetic energies is somewhat higher than found in previous studies. The characteristic westward drift velocities are evaluated by a time-lagged cross-correlation analysis of the kinetic energy fields. While zonal mean drift speeds are in good agreement with vortex trajectory evaluation in the latitude bands 30–5∘ S and 5–30∘ N, discrepancies are exhibited mostly at higher latitudes on both hemispheres. A plausible reason for somewhat different drift velocities obtained by eddy tracking and cross-correlation analysis is the fact that the drift of mesoscale eddies is only one component of the surface flow fields. Rossby wave activities, coherent currents, and other propagating features on the ocean surface apparently contribute to the zonal transport of kinetic energy.

Characterizing Mesoscale Eddies of Eastern Upwelling Origins in the Atlantic Ocean and Their Role in Offshore Transport

Motivated by the recurrent formation of eddies in the eastern upwelling areas, we examine cross-basin connectivity that is promoted by coherent, long-lived and long-propagating mesoscale eddies in the Atlantic Ocean. By applying the TOEddies detection and tracking algorithm to daily satellite observations (AVISO/DUACS) of Absolute Dynamic Topography (ADT), we characterize mesoscale eddy activity and variability in the North and South Atlantic. This method provides a robust eddy-network reconstruction, enabling the tracking of eddies formed in the Atlantic eastern upwelling systems together with any merging and splitting events they undergo during their lifetime as long as they remain detectable in the altimetry field. We show that during the years of observations, mesoscale eddies are long-lived coherent structures that can ensure oceanic connectivity between the eastern and the western boundaries, as a result of complex inter-eddy interactions. Moreover, alignment of South Atlantic eddies of eastern boundary origins with available Argo floats achieves a mean cross-basin connectivity signal from both anticyclonic and cyc5lonic eddies which is particularly evident at depth, along thermocline isopycnal layers of γn = 26 - 27 kg m–3. We explore two individual cyclonic eddy trajectories from in-situ measurements gathered by different Argo profiling floats trapped inside the eddy cores. Our results support the hypothesis that mesoscale eddies sustain and transport water masses while subducting during their westward propagation.

Linking Coherent Anticyclonic Eddies in the Iceland Basin to Decadal Oceanic Variability in the Subpolar North Atlantic

AbstractThe Iceland Basin in the eastern Subpolar North Atlantic is an eddy‐rich region characterized by intense anticyclonic eddy activity. Our study present the variability of coherent Anticyclonic Eddies (AEs) generated in this region, using satellite altimetry and two ocean eddy tracking algorithms. The yearly count of AEs in the Iceland Basin reveals a decadal variability similar to that of ocean heat content change in the eastern subpolar gyre. Periods with higher number of AEs coincide with periods of increased ocean heat content, and vice versa. However, both algorithms agree that more than 50% of the detected AEs are confined to the central Iceland Basin. The annual number of AEs also tracks zonal shifts of the subpolar front, a variable that can explain about 53 (77)% of the interannual (decadal) variability of AEs in the Iceland Basin. Finally, a Lagrangian approach is used to demonstrate that the amount of subtropical versus subpolar water masses reaching the Iceland Basin appears to influence, via baroclinic instability, the generation of AEs.

Shelf Water Export at the Brazil-Malvinas Confluence Evidenced From Combined in situ and Satellite Observations

The Brazil-Malvinas Confluence (BMC) is the region where opposing and intense western boundary currents meet along the Southwestern Atlantic slope at about 38°S, generating one of the most energetic mesoscale regions of the global ocean. Based on shipborne observations acquired within the Uruguayan Economic Exclusive Zone (EEZ), combined with satellite data and an eddy tracking algorithm, we analyze the cross-shelf exchanges during May 2016, when the BMC was in an anomalous northern position. Two types of shelf water export were observed triggered by mesoscale dynamics: one was the export of shallow Rio de la Plata Plume waters driven off-shelf by the retroflection of the Brazil Current. This export formed a 70 km wide, 20 m deep filament that propagated offshore at 0.3 m s–1, with a transport of 0.42 Sv. It lasted about 10 days before being mixed with ambient Confluence waters by strong winds. An additional type of off-shelf transport consisted of a subsurface layer of Subantarctic Shelf Waters (SASW) about 60 m thick that subducted at the BMC reaching 130 m deep and transporting 0.91 ± 0.91 Sv. We show that geostrophic currents derived from satellite altimetry over the slope can be useful to track this subsurface off-shelf export as they are significantly correlated with absolute velocity measurements at this depth. Argo temperature and salinity profiles show evidence of these two types of shelf water export occurring between the BMC front and the separation of the Brazil Current from the shelf-break, suggesting this is a relatively frequent phenomenon, in agreement with previous observations.

Verification of eddy properties in operational oceanographic analysis systems

Mesoscale eddy features are found ubiquitously throughout the world’s oceans. Many needs exist for numerical products from operational oceanographic systems to provide information on eddy properties. While numerous eddy identification and tracking methods have been developed for oceanic eddies, specific methods and metrics tailored to verify the skill of ocean analyses and forecasts in capturing these features are lacking. Here we introduce a novel feature-based verification methodology for operational oceanographic systems. This methodology builds on previous efforts at eddy tracking and applies open-source software to provide a robust method to evaluate the skill of operational oceanographic systems in terms of representing observed eddies. We demonstrate that an eddy tracking methodology can discern clear improvements in analyses produced using a regional analysis system (RIOPS; 1/12° grid-resolution) over a global system (GIOPS; 1/4° grid resolution). For eddies with amplitudes greater than 10 cm, RIOPS has a probability of detection 10%–30% higher than GIOPS with a false alarm ratio 5%–10% lower. A significant improvement in the spatial properties of simulated eddies in RIOPS is also found. In particular, results show a marked improvement in radius and separation distance errors (by 25% and 21% respectively), with fewer occurrences of errors above 20 km in radius and 40 km in separation distance. This basic demonstration opens the door for a more detailed examination of eddy features in ocean prediction systems.

Lakshadweep High Propagation and Impacts on the Somali Current and Eddies During the Southwest Monsoon

AbstractClimatological eddies in the Arabian Sea (AS), including the Lakshadweep High (LH) and the Great Whirl (GW), play major roles in the regional fluxes of upper ocean properties. For the first time, we apply an eddy tracking algorithm to the LH using altimetric sea surface height observations from 1993 through 2019. We additionally analyze the LH's water mass composition throughout its life cycle using the 1/12° Global eddy resolving physical ocean and sea ice reanalysis (GLORYS12). We observe that the second annual downwelling coastal Kelvin wave's (CKW) arrival during the winter monsoon is primarily responsible for generating the LH. In March, Rossby waves propagate along 8°N at the same speed of that of the LH. In 17 of 27 years, the LH maintains coherence across the AS. The LH sustains a shallow lens of lower salinity Bay of Bengal water up to 68°E in these years. In the remaining 10 years, the LH dissipates between 60°E and 70°E or fails to propagate beyond the southwest Indian coast. We attribute the differences between propagation types to fluctuations in the CKW strength, differences in wind stress between the southern tip of India and Sri Lanka, and the variable distribution of wind stress curl around the LH. We also find that longer propagating LH types negatively correlate with the eddy kinetic energy of the Somali Current region during the summer monsoon. We conclude that, upon its arrival in late July, the LH either merges with or replaces the GW, disrupting the cyclone that normally orbits the GW.

From 1/4° to 1/8°: Influence of Spatial Resolution on Eddy Detection Using Altimeter Data

A substantial portion of ocean eddies, especially small ones, may be missed due to insufficient spatial or temporal sampling by satellite altimetry. In order to illustrate the influence of spatial resolution on eddy detection, this study provides a comparison of eddy identification, tracking, and analysis between two sets of merged altimeter data with spatial resolutions of 1/4° and 1/8°. One main study area (the Mediterranean Sea), and three confirmatory areas (the South-China Sea, the North-West Pacific, and the South-East Pacific) are chosen. The results show that the number and density of eddies captured by the 1/8° data are about twice as much as those captured by the 1/4° data, while the ratios of corresponding eddy parameters, i.e., radius, amplitude, (eddy kinetic energy (EKE)) are about 0.6–0.8 (1.3) for the two datasets (1/8° ÷ 1/4°). Long-term eddy tracking (1993–2018) is conducted in the Mediterranean Sea, indicating that the improvement in spatial resolution will increase the observed values of both the lifetime and the propagation distance of robust eddies. The number of eddies identified using the 1/4° data only accounts for ~30% to 60% of those identified using the 1/8° data. However, for eddies that can be detected using the two datasets, ~5% to 10% present errors (i.e., confusion). In comparison between the four regions, we find that for the enclosed seas with complex conditions, the increase in spatial resolution may lead to more significant improvements in the efficiency and accuracy of eddy detection.

Large River Plumes Detection by Satellite Altimetry: Case Study of the Ob–Yenisei Plume

Satellite altimetry is an efficient instrument for detection dynamical processes in the World Ocean, including reconstruction of geostrophic currents and tracking of mesoscale eddies. Satellite altimetry has the potential to detect large river plumes, which have reduced salinity and, therefore, elevated surface level as compared to surrounding saline sea. In this study, we analyze applicability of satellite altimetry for detection of the Ob–Yenisei plume in the Kara Sea, which is among the largest river plumes in the World Ocean. Based on the extensive in situ data collected at the study area during oceanographic surveys in 2007–2019, we analyze the accuracy and efficiency of satellite altimetry in reproducing, first, the outer boundary of the plume and, second, the internal structure of the plume. We reveal that the value of positive level anomaly within the Ob–Yenisei plume strongly depends on the vertical plume structure and is prone to significant synoptic and seasonal variability due to wind forcing and mixing of the plume with subjacent sea. As a result, despite generally high statistical correlation between the ADT and surface salinity, straightforward usage of ADT for detection of the river plume is incorrect and produces misleading results. Satellite altimetry could provide correct information about spatial extents and shape of the Ob–Yenisei plume only if it is validated by synchronous in situ measurements.

Automatic identification and tracking of meso-scale eddies in the Persian Gulf using the pattern mining approach

Automatic identification and tracking of meso-scale eddies in the Persian Gulf using the pattern mining approach