Pair Of Eddies Research Articles

AB-LSTM: a mesoscale eddy feature prediction method based on an improved Conv-LSTM model

Mesoscale eddies are the most important mesoscale phenomena in the oceans, and determining how to predict their spatial and temporal characteristics is a very challenging task. Most previous studies focused on the accuracy of full-domain prediction and ignored the accuracy of single-eddy prediction. To solve this problem, in this paper, we first apply multi-year sea surface height data to produce a spatiotemporal sequence sample dataset with a bidirectional prediction mechanism. Then, we introduce an adversarial generative mechanism through stacked spatiotemporal prediction blocks and rely on the strong generative ability of the generative adversarial network models to construct an adversarial bidirectional long- and short-term memory model (AB-LSTM). Next, the mesoscale eddy mixing algorithm is used to extract the matching eddy pair features from the real and predicted data, and several evaluation metrics are used to conduct error analysis. The experiments yield the following results. Prediction sequence days 1–7: the root mean square error (RMSE) values are 1.97–7.70 cm, the structural similarity index (SSIM) values are >0.61, the accuracy is >54.6%, and the eddy centre distance error is 6.34 km. The result is 11.61 km, which is consistent with many spatiotemporal prediction models and passes the generalisation test in many different sea areas. Finally, we carry out single eddy prediction on the basis of the evaluation of the entire prediction of the sea surface height and also obtain a more satisfactory experimental effect. This method has a better prediction ability than the original spatiotemporal method and has a certain reference significance for mesoscale eddy spatiotemporal feature prediction technology and subsequent underwater reconstruction.

Modulation of Internal Solitary Waves by One Mesoscale Eddy Pair West of the Luzon Strait

Abstract The characteristics of modulated internal solitary waves (ISWs) under the influence of one mesoscale eddy pair in the Luzon Strait, involving one anticyclonic eddy (AE) and one cyclonic eddy (CE) induced by the Kuroshio intrusion, were investigated using a nested high-resolution numerical model in the northeastern South China Sea (SCS). The presence of mesoscale eddies greatly impacts the nonlinear evolution of type-a and type-b ISWs. The eddy pair contributes to distinct wave properties and energy evolutions. Compared to type-b waves, type-a waves display more pronounced modulatory characteristics with a larger spatial scale. CE currents and horizontal inhomogeneous stratification are crucial in modulating the wave behaviors, which induce extremely large-amplitude depression ISWs. The AE thereafter yields retardation effects on the wave energy evolution. The average depth-integrated available potential and kinetic energy showed relative growth rates of −66.12% and −46.07%, respectively, for type-a waves, and −24.26% and −20.15%, respectively, for type-b waves along the propagation path up to the AE core. The deformed and distorted ISW crest lines propagating further northward exhibit a more dramatic shoaling evolution. The maximum total energies of type-a and type-b waves at the north station are approximately 13.5 and 3.5 times, respectively, greater than those at the south station on the continental shelf of the Dongsha Atoll. This work provides essential insights into modulated ISW dynamics under the mesoscale eddy pair within the northeastern SCS deep basin.

An Eddy Pair in the Northwestern Bay of Bengal: Characteristics, Dynamics and Interannual Variability

AbstractMesoscale eddies are active in the Bay of Bengal and have profound effects on the dynamic conditions, the transport of heat and salt, and the primary productivity. We report a pair of periodic eddies in the Bay of Bengal and examine their characteristics, dynamic mechanisms and interannual variability based on satellite observations and a nonlinear 1.5‐layer reduced‐gravity model. The eddy pair mainly occupies the northwestern Bay of Bengal from March to May and consists of a cyclonic eddy in the north and an anticyclonic eddy in the south. The anticyclonic eddy is generated by local wind forcing, whereas the cyclonic eddy is significantly contributed by equatorial and coastal Kelvin waves. On an interannual scale, the eddy pair was exceptionally weak in 1999, 2000 and 2008 due to the extreme La Niña events in these years when the westerly wind anomaly over the equatorial Indian Ocean weakened the local wind forcing and coastal Kelvin waves. This study provides new knowledge on periodic eddies in the Bay of Bengal and advances our understanding of the dynamic connections between this marginal sea and the equator.

Coupling and de-coupling of the El Niño Southern Oscillation to the supply of larval fishes to benthic populations in the Hawaiian Islands.

Several recent high intensity ENSO events have caused strong negative impacts on the adult phases of foundational species in coral reef ecosystems, but comparatively little is known about how climatic variables related to recent ENSOs are impacting the supply of larvae to benthic populations. In marine fishes and invertebrates, reproductive adults and planktonic larvae are generally more sensitive to environmental variability than older, non-reproductive adults. Further, the transport of larvae in ocean currents may also be strongly ENSO dependent. The interactions between the dynamics of larval survivorship and larval transport could lead to population bottlenecks as stronger ENSO events become more common. We tested the predictions of this hypothesis around the Main Hawaiian Islands (MHI) by constructing a correlation matrix of physical and biological time series variables that spanned 11 years (2007-2017) and multiple ENSO events. Our correlation matrix included four types of variables: i. published ENSO indices, ii. satellite-derived sea surface temperature (SST) and chlorophyll variables, iii. abundance and diversity of larval fishes sampled during the late winter spawning season off Oahu, and iv. abundance and diversity of coral reef fish recruits sampled on the western shore of the Big Island of Hawaii. We found that the abundance and diversity of larval fishes was negatively correlated with the Multivariate El Niño Index (MEI), and that larval variables were positively correlated with measures of fall recruitment (September & November), but not correlated with spring-summer recruitment (May & July). In the MHI, SST variables were not correlated with the MEI, but two successive El Niño events of 2014-15 and 2015-2016 were characterized by SST maxima approaching 30°C. Two large pulses of benthic recruitment occurred in the 2009 and 2014 recruitment seasons, with > 8000 recruits observed by divers over the summer and fall months. Both events were characterized by either neutral or negative MEI indices measured during the preceding winter months. These patterns suggest that La Niña and the neutral phases of the ENSO cycle are generally favorable for adult reproduction and larval development in the spring and summer, while El Niño phases may limit recruitment in the late summer and fall. We hypothesize that episodic recruitment during non-El Niño phases is related to favorable survivorship and transport dynamics that are associated with the formation of pairs of anticyclonic and cyclonic eddies on the leeward sides (western shores) of the Main Hawaiian Islands.

Seasonal–interannual–decadal variations of sea level in the South China Sea and connections with the tropical–subtropical Pacific

AbstractDifferent timescale contributions to the sea‐level variation in the South China Sea (SCS) are evaluated in this paper. On seasonal timescale, the large variance of the sea‐level anomaly (SLA) could account for more than 70% of the monthly sea‐level variation in the western shallow continental shelf and the area of Luzon cold eddy. Besides, the seasonal explained variance percentage (skill) has 2 weak centres (50%–70%) off eastern Vietnam, which is related to the summertime eddy pair in the SCS. On interannual‐to‐decadal (low‐frequency) timescale, the skill has two large‐value regions (Zone A and Zone B). Zone A is characterized by double centres off eastern Vietnam, but the meridional position of the double centres is farther north than that of the eddy pair. The skill in Zone A is in the range of 35%–55%, and about 50%–70% of the low‐frequency variation comes from the steric effect. Zone B is off the west coast of the Philippines. The skill in Zone B increases southward, and it is dominated by the wind‐induced dynamic process which is attributed to the remote Rossby wave from the tropical Pacific. Based on the S‐EOF analysis, the SEOF‐1 mode mainly portrays the decadal variation of the SLA, while the SEOF‐2 mode reflects the interannual variation of the SLA. In Zone B, almost all of the low‐frequency variation could be attributed to ENSO and PDO, especially to PDO which has a larger contribution. However, the double centres in Zone A are governed by the SCS summer monsoon, instead of ENSO and PDO.

Observations of a Filamentous Intrusion and Vigorous Submesoscale Turbulence within a Cyclonic Mesoscale Eddy

Abstract Oceanic submesoscale flows are considered to be a crucial conduit for the downscale transfer of oceanic mesoscale kinetic energy and upper-ocean material exchange, both laterally and vertically, but defining observations revealing submesoscale dynamics and/or transport properties remain sparse. Here, we report on an elaborate observation of a warm and fresh filament intruding into a cyclonic mesoscale eddy. By integrating cruise measurements, satellite observations, particle-tracking simulations, and the trajectory of a surface drifter, we show that the filament originated from an anticyclonic eddy immediately to the west of the cyclonic eddy, and the evolution of the filament was mainly due to the geostrophic flows associated with the eddy pair. Our observations reveal the mass exchange of the eddy pair and suggest that submesoscale flows can degrade the coherence of mesoscale eddies, providing important implications for the transport properties of mesoscale eddies. Vigorous submesoscale turbulence was found within the eddy core region, due to filamentous intrusion and frontogenesis. Our findings have thus offered novel insights into the dynamics and transport properties of oceanic submesoscale flows, which should be taken into account in their simulation and parameterization in ocean and climate models. Significance Statement Mesoscale eddies, with a spatial scale from tens to hundreds of kilometers, are ubiquitous in the global ocean. Carrying the largest proportion of oceanic kinetic energy, mesoscale eddies play a key role in ocean dynamics and have important applications for marine biology. Although mesoscale eddies have been studied extensively over the past decades, there are two major issues that remain inconclusive: (i) How do mesoscale eddies dissipate? (ii) Can eddies coherently trap waters when moving over a long distance? Recent studies, mostly through computer simulations, suggest that oceanic submesoscale processes, with a typical scale of a few kilometers, are highly relevant to the above two issues. This study presents a rare observation of a filament intruding into a cyclonic eddy. Because of this filament intrusion, submesoscale activities are enhanced near the eddy core area, in contrast to previous observations that normally suggest weaker submesoscale activities in the eddy core area than at eddy peripheries. Such dedicated process-oriented observations provide unique opportunities for better understanding the dynamics and transport properties of mesoscale eddies and submesoscale processes.

Flow Structure and Transition to Local Turbulence Downstream of an Asymmetric Narrowing that Imitates Arterial Stenosis

The results of experimental studies and numerical simulation of the flow structure in the separation region downstream of an asymmetric narrowing of smooth canal that simulates 70% one-sided stenosis of the artery are presented. The Reynolds number was equal to 1800. The instantaneous flow velocity vector fields were measured using the SIV technique. The numerical solution was obtained by the large eddy simulation (LES) method. Setting the disturbances in numerical simulation close to the experimental conditions made it possible to obtain a satisfactory agreement between the calculated and experimental velocity fields and the components of the Reynolds stress tensor. The data on formation of the local flow turbulence region behind the constriction and subsequent downstream flow relaminarization are obtained. It is shown that a pair of secondary eddies localized within the region of flow separation is formed near the throat of the constriction.

Flow Structure and Transition to Local Turbulence Downstream of an Asymmetric Narrowing that Imitates Arterial Stenosis

The results of experimental studies and numerical simulation of the flow structure in the separation region downstream of an asymmetric narrowing of smooth canal that simulates 70% onesided stenosis of the artery are presented. The Reynolds number was equal to 1800. The instantaneous flow velocity vector fields were measured using the SIV technique. The numerical solution was obtained by the large eddy simulation (LES) method. Setting the disturbances in numerical simulation close to the experimental conditions made it possible to obtain a satisfactory agreement between the calculated and experimental velocity fields and the components of the Reynolds stress tensor. The data on formation of the local flow turbulence region behind the constriction and subsequent downstream flow relaminarization are obtained. It is shown that a pair of secondary eddies localized within the region of flow separation is formed near the throat of the constriction.

Intensification of “river in the sea” along the western Bay of Bengal Coast during two consecutive La Niña events of 2020 and 2021 based on SMAP satellite observations

A narrow strip of low salinity water that hugs the western Bay of Bengal (BoB) is known as a “river in the sea” (RIS). During the autumns of 2020 and 2021, Soil Moisture Active Passive (SMAP) identified an intensification of the RIS that was characterized by a continuous, uniform strip of low salinity water (<31 psu) that was 100 km wide extending along the western BoB coast to south of Sri Lanka. The analysis shows that the La Niña events in 2020–2021 were responsible for this intensification. During the La Niña events of 2020 and 2021, cyclonic circulation anomalies were generated along the BoB coast, causing a stronger Eastern Indian Coastal Current (EICC). Meanwhile, the northern BoB received increased river discharge during the summer monsoons of the two years. The stronger EICC and increased river discharge together led to anomalous freshwater transport that contributed to the intensification of the RIS. Notably, the RIS extended far southward during La Niña events of 2016 and 2017. However, the spatial structure of the RIS differed sharply between 2016–2017 and 2020–2021. The results indicate that pairs of eddies in the western BoB steered the freshwater offshore by several hundred kilometers. As a result, offshore extending tongue-shaped freshwater plumes were formed that inhibited the formation of an organized RIS structure along the western BoB coast during 2016–2017. This study highlights that the year-to-year variability of the RIS was significantly influenced by the La Niña events and modulated by mesoscale processes.

Phytoplankton Blooms Triggered by Anticyclonic Eddy and Cyclonic Eddy during Tropical Cyclone Nada

Tropical cyclone (TC) Nada occurred in the southwestern Bay of Bengal (BOB) in the winter of 2016. With high photosynthetically available radiation (PAR) and minimal precipitation, phytoplankton blooms occurred from offshore to nearshore respectively. In this study, there was an pre-existed ocean eddy pair on the left and right sides of Nada’s path before its passage, we studied the different mechanisms of phytoplankton blooms caused by TC Nada and the ocean eddy pair with satellite observation, multisource reanalysis products, and Argo float data. An anticyclonic eddy near Sri Lanka was weakened during Nada and horizontal transport of chlorophyll-a (Chl-a) balanced the inhibition effect of anticyclone on Chl-a. Near the anticyclonic eddy’s periphery, an upwelling above the thermocline was enhanced by Nada which promoted the uplift of nutrient-rich deep-water. Meanwhile, the large cyclonic eddy in the northern Bay of Bengal was strengthened by Nada, with the vorticity increasing from 0.19 s^–1 to 0.28 s^–1. Significant inertial oscillation (~2 days period) happened in the subsurface layer, leading to strong vertical mixing and upwelling and subsequently causing the offshore surface Chl-a bloom. This study provides new insights to evaluate typhoons and ocean eddies that induce biological responses in the future.

Impact of Horizontal Resolution (Submesoscale Permitting vs. Mesoscale Resolving) on Ocean Dynamic Features in the South China Sea

AbstractModel resolution is a key factor that impacts the model bias in simulating ocean dynamics. How would model resolution influence model bias is an important question. In this study, we set up two sets of experiments with identical settings except the grid resolution, one with a minimum spacing of 2 km, referred to as the submesoscale permitting (SP) model, and the other with a minimum spacing of 6 km, referred to as the mesoscale resolving (MR) model, to investigate the impact of horizontal resolution on simulated dynamic features in the South China Sea. Results show that the SP outperforms the MR model in simulating both barotropic and baroclinic tides, upper ocean circulation, sea surface height, and temperature in the South China Sea, and in simulating the evolution of the eddy pair east of Indo‐China Peninsula in summer and the Kuroshio loop current in the Luzon Strait in winter. The SP model also performs better in simulating thermal structure within the ocean and the winter mixed layer depth. Additionally, the SP model can capture more vertical motion features. The superiority of the SP model lies in its ability to better resolve terrain features that have a significant impact on ocean dynamical processes, and to resolve more physical processes. As a result, the SP model relies less on the uncertain parameterized processes. Our study has important implications for studies on the modeling of physical oceanography in the South China Sea, as well as for the reduction of climate model biases.

Deep-Current Intraseasonal Variability Interpreted as Topographic Rossby Waves and Deep Eddies in the Xisha Islands of the South China Sea

Abstract Strong subinertial variability near a seamount at the Xisha Islands in the South China Sea was revealed by mooring observations from January 2017 to January 2018. The intraseasonal deep flows presented two significant frequency bands, with periods of 9–20 and 30–120 days, corresponding to topographic Rossby waves (TRWs) and deep eddies, respectively. The TRW and deep eddy signals explained approximately 60% of the kinetic energy of the deep subinertial currents. The TRWs at the Ma, Mb, and Mc moorings had 297, 262, and 274 m vertical trapping lengths, and ∼43, 38, and 55 km wavelengths, respectively. Deep eddies were independent from the upper layer, with the largest temperature anomaly being >0.4°C. The generation of the TRWs was induced by mesoscale perturbations in the upper layer. The interaction between the cyclonic–anticyclonic eddy pair and the seamount topography contributed to the generation of deep eddies. Owing to the potential vorticity conservation, the westward-propagating tilted interface across the eddy pair squeezed the deep-water column, thereby giving rise to negative vorticity west of the seamount. The strong front between the eddy pair induced a northward deep flow, thereby generating a strong horizontal velocity shear because of lateral friction and enhanced negative vorticity. Approximately 4 years of observations further confirmed the high occurrence of TRWs and deep eddies. TRWs and deep eddies might be crucial for deep mixing near rough topographies by transferring mesoscale energy to small scales.

Submesoscale processes-induced vertical heat transport modulated by oceanic mesoscale eddies

Oceanic submesoscale processes mainly arise from phenomena such as jets, density fronts, and mesoscale eddies. Previous studies suggest that the overall submesoscale processes transport heat vertically upgradient, i.e. from cold to warm. However, it is not clear whether the submesoscale processes-induced vertical heat transport (VHT) in mesoscale eddies remains upgradient. Therefore, the present study focuses on submesoscale-induced VHT modulated by mesoscale eddies. A high-resolution oceanic numerical model product is applied to examine the VHT induced by submesoscale processes associated with a pair of cyclonic and anticyclonic mesoscale eddies in the Kuroshio Extension (KE) region. Eddies at different time steps are collocated in terms of the eddy centers to reconstruct a time series of a new eddy dataset that presents eddy-modulated submesoscale processes. The frequency-wavenumber spectra, Rossby numbers, and strain rates in the pair of eddies reveal the existence of submesoscale motions surrounding mesoscale eddies. The variables are decomposed into monthly mean mesoscale and submesoscale components to calculate submesoscale VHT at low-frequency (LF) and high-frequency (HF). The results indicate that submesoscale VHT is modulated by mesoscale eddies mainly along the eddy boundaries. The LF submesoscale VHT (upward in both cyclonic and anticyclonic eddies) dominates the monthly-averaged submesoscale VHT. The magnitude of the hourly HF submesoscale VHT is larger than the LF component, while its monthly average becomes negligible because it is caused by periodical internal waves. The submesoscale VHT along the eddy edges is related to strong frontogenesis which develops the vertical flux.

A Case Study on the Dynamics of Phytoplankton Blooms Caused by Tropical Cyclones in the Southeastern Arabian Sea

A phytoplankton bloom was observed in the southeastern Arabian Sea after the passage of the anti-S-type track Tropical cyclone ARB 06 in 1998, which lasted for 22 days. The dynamic mechanism of the phytoplankton bloom was investigated with high-resolution satellite remote sensing data, reanalysis data and buoy data. The results show that the double thermocline structure hindered the uplift of deep nutrients to the surface before the tropical cyclone arrival. During and after the passage of the cyclone, the shallower thermocline disappeared, the deeper thermocline changed from 45.7 m to 76.5 m, the mixed layer deepened, and the upper oceanic stratification weakened. Additionally, a weak ocean eddy pair was enhanced gradually after the passage of cyclone. The relative vorticity of the ocean eddy pair was calculated. In the oscillation with a period of two days, the vorticity of the cyclonic eddy was stronger than that of the anticyclonic eddy, which enhanced a strong upwelling at a depth of more than 55 m for more than 10 days. The vertical current shear generated by the oscillation not only enhanced the vertical mixing, but also plays an important role in the distribution of phytoplankton blooms. The phytoplankton bloom was triggered by the nutrient below the thermocline into the sea surface, where a strong upwelling and weakened oceanic stratification occurred after the passage of cyclone. This study offers new insights on the mechanism of phytoplankton bloom induced by tropical cyclones and will be helpful for evaluating tropical cyclone-induced biological responses in future.

Counter-rotating eddy pair in the Luzon Strait

Abstract. Based on satellite remote-sensing observation data and Hybrid Coordinate Ocean Model (HYCOM) re-analysis data, we studied the counter-rotating eddy pair in the Luzon Strait (LS). Statistical analysis reveals that when an anti-cyclonic mesoscale eddy (AE) (cyclonic mesoscale eddy [CE]) in the Northwest Pacific (NWP) gradually approaches the east side of the LS, a CE (an AE) gradually forms on the west side of the LS, and it is defined as the AE (CE) mode of the counter-rotating eddy pair in the LS. The counter-rotating eddy pair exhibits obvious seasonal variation: the AE mode mainly occurs in the summer half of the year, while the CE mode mainly occurs in the winter half of the year. The mean durations of the AE and CE modes are both approximately 70 d. Based on the vorticity budget equation and energy analysis, the dynamic mechanism of counter-rotating eddy-pair occurrence is determined to be as follows: the AE (CE) on the east side of the LS causes a positive (negative) vorticity anomaly through horizontal velocity shear on the west side of the LS, and the positive (negative) vorticity anomaly is transported westward by the zonal advection of the vorticity, finally leading to the formation of the CE (AE) on the west side of the LS.

Reviews and syntheses: Physical and biogeochemical processes associated with upwelling in the Indian Ocean

Reviews and syntheses: Physical and biogeochemical processes associated with upwelling in the Indian Ocean

Characteristic Analysis of Sea Surface Currents around Taiwan Island from CODAR Observations

Sea surface currents observed by high-frequency (HF) radars have been widely used in ocean circulation research. In this study, hourly sea surface currents observed by the Taiwan Coastal Ocean Dynamics Applications Radar (CODAR) system from 2015 to 2019 were analyzed by the empirical orthogonal function (EOF) analysis to reveal the characteristics of the sea surface currents around Taiwan Island. The study area is divided into two regions, the Kuroshio region east of Taiwan Island and the Taiwan Strait west of Taiwan Island. In the Kuroshio region, the first EOF mode shows that the Kuroshio is characterized by higher current speeds with greater variability in summer. The second and third EOF modes present a dipole eddy pair and single eddy impingement on the Kuroshio during different periods. The seasonal variation of the dipole eddy pair indicates that the cyclonic/anticyclonic eddy on the north/south side appears more frequently in summer. Single eddy impingement occurs at multiple periods, including daily, intraseasonal, interseasonal, and annual periods. For the Taiwan Strait, the first EOF mode displays the tide signals. The tides enter the Taiwan Strait from the north and south, forming strong sea surface currents around the northern tip of Taiwan Island and the Penghu Archipelago. The second EOF mode exhibits the seasonal changes of the sea surface currents driven by the monsoon winds. The sea surface currents in the northern Taiwan Strait are relatively strong, possibly due to the narrow and shallow terrain there. The high spatiotemporal resolution of sea surface currents derived from CODAR observations provide more detailed characteristics of sea surface circulation around Taiwan Island.

Local and remote forcing effects of oceanic eddies in the subtropical front zone on the mid-latitude atmosphere in Winter

Multiple oceanic eddies coexist in the North Pacific subtropical front zone (STFZ) in winter, which can be classified into the isolated single eddies, the combined double isotropic eddies and pairs of anisotropic eddies. The forcings of these eddies on the mid-latitude atmosphere are investigated using Climate Forecast System Reanalysis (CFSR) data from year 1979 to 2009, which are divided into the remote and local effects in this research. In the years with a stronger subtropical front, there are more cyclonic isolated and double eddies to the north, more anticyclonic isolated and double eddies to the south of the STFZ, and more eddy pairs with cold to the north and warm to the south concentrated around the main axis of the STFZ. These eddy distributions enhance the strength of the subtropical front, intensify the propagation of upwards baroclinic waves in the lower atmosphere, and finally enhance the zonal wind at upper atmosphere, which is defined as the remote effects of the eddies. However, distinct from this basin-scale remote forcings, three types of oceanic eddies also have different local forcings on the marine atmospheric boundary layer (MABL) above and on the middle atmosphere as expressed in local precipitation difference. The local effects of the isolated single eddies and combined double isotropic eddies take place near the eddy center, whereas that of the pairs of anisotropic eddies at the boundary of the two eddies.

Influence of Two Eddy Pairs on High‐Salinity Water Intrusion in the Northern South China Sea During Fall‐Winter 2015/2016

AbstractTwo processes of high‐salinity water (≥34.7 psu; HSW) intrusion were recorded by an Argo float in the northeastern South China Sea (SCS) during fall‐winter of 2015/2016. Combined with the satellite altimetry and reanalysis data, the influence of related eddy pairs on HSW transport was investigated. The results show that apart from the Kuroshio‐originated anticyclonic eddy (AE), the localized cyclonic eddy (CE), and the westward jet between the eddy pair all contributed to the HSW transport. In the first process, the effect of eddy trapping accounted for 74% of the HSW transport, while the associated jet accounted for the residual 26%. The contribution of the southern CE was stronger than that of the northern AE. In the second process, the Kuroshio‐originated AE and its southern jet dominated the HSW transport. The westward jet conveyed abundant HSW to the interior SCS before the eddy pair propagated westward, accounting for 52% of HSW transport, while AE accounted for 43% and CE for 5%. Energy analysis showed that barotropic and baroclinic instabilities were important for the generation and growth of the AE in both processes, and CE in the first process was produced by baroclinic instability and wind stress work, while CE in the second process was predominantly triggered by barotropic instability. The development of eddy pairs combined with the SCS interior circulation jointly affected the HSW transport. This study identified the important contributions from two eddy pairs and discussed the effect of interior circulation‐Kuroshio interaction on HSW intrusion in the northern SCS.

A Study on an Anticyclonic-Cyclonic Eddy Pair Off Fraser Island, Australia

This research examines a cyclonic-anticyclonic eddy (AE) pair off Fraser Island next to the eastern Australian coast in 2009 using the Bluelink Reanalysis data, where the local eddies are poorly understood. This eddy pair formed in July and dissipated in November. We detailed the horizontal and vertical structures of the eddy pair in terms of three-dimensional variations in relative vorticity, hydrographic properties, velocity, and dynamic structures, which presented notable scales of the eddy pair. The AE formed beside the meandering of the East Australian Current (EAC) at 24°S and had a tilting structure in the upper 1,000 m toward the EAC. A cyclonic eddy (CE) formed a month later and interacted with the AE, which had a tilting structure toward the AE in the upper 1,000 m. Heterogeneity in the AE and CE composing this eddy pair was observed in the horizontal and vertical planes. The AE had a stronger and more coherent dynamic structure than the CE. The AE and the EAC interacted in the generation stage when the EAC path shifted eastward, away from the coast. As the EAC subsequently swung back to the coastal area, the AE and the EAC separated. The AE then interacted with the surrounding eddy fields, propagated westward, before finally merging again with the EAC. The energy transfer during this process also indicated the interactions among the eddy pair, the surrounding eddy fields and the EAC. Baroclinic instability (BCI) was a main contributor to the AE in the generation stage. Barotropic instability (BTI) also contributed energy to the AE when it interacted with the EAC but accounted for a much smaller proportion. Both BCI and BTI contributed to the CE for most of its life cycle but to a much less extend than to the AE. The zonal heat and salt mass transported by the AE and CE were calculated based on a Lagrangian framework method, and these amounts were considerable compared with global zonal averaged heat and salt mass transported by other mesoscale eddies.