Small Cyclonic Eddies Research Articles

Very high-resolution modelling of submesoscale turbulent patterns and processes in the Baltic Sea

Abstract. In order to simulate submesoscale turbulent patterns and processes (STPPs) and to analyse their properties and dynamics, the Regional Ocean Modeling System (ROMS) was run for June 2016 in a subregion of the Baltic Sea. To create a realistic mesoscale environment, ROMS with 500 m horizontal resolution (referred to as R500) is one-way nested into an existing operational model, and STPPs with horizontal scales <1 km are resolved with a second nest of 100 m resolution (R100). Both nests use 10 terrain-following layers in the vertical. The comparison of the R500 results with a satellite image shows fair agreement. While R500 is driven by realistic air–sea fluxes, the atmospheric forcing is turned off in R100 because it prevents the generation of STPPs and blurs submesoscale structures. Therefore, R100 provides deep insight into ageostrophic processes and associated quantities under quasi-adiabatic conditions that are approximately met in no-wind or light-wind situations. The validity of the results is furthermore limited to the selected region and the time of the year. STPPs evolve rapidly within a about a day. They are characterized by vertical speeds of 𝒪(10) m d−1 and relative vorticities and divergences reaching multiples of the Coriolis parameter. Typical elements of the secondary circulation of two-dimensional strain-induced frontogenesis are identified at an exemplary front in shallow water, and details of the ageostrophic flow field are revealed. The conditions for inertial and symmetric instability are evaluated for the whole domain, and the components of the tendency equation are computed in a subregion. While anticyclonic eddies are generated solely along coasts, cyclonic eddies are rolled-up streamers and found in the entire domain. A special feature of the cyclones is their ability to absorb internal waves and to sustain patches of continuous upwelling for several days, favouring plankton growth. The kinematic properties show good agreement with observations, while some observed details within a small cyclonic eddy are only partly reproduced, most likely due to a lack of horizontal resolution or nonhydrostatic effects.

OBSERVING SURFACE CIRCULATION OF THE WESTERN MEDITERRANEAN BASIN WITH SATELLITE IMAGERY

Abstract. In this article, the benefits of using satellite imagery of different types (namely thermal infrared, visible-range, and synthetic aperture radar (SAR) images) for observing surface circulation of marine basins are being discussed. As a region of interest, we use the Western Mediterranean Basin. At first, the areas with sharpest thermal and chlorophyll-a gradients within the region of interest were defined on a seasonal base using the data provided by Aqua Moderate Resolution Imaging Spectrometer (MODIS). After that, mesoscale eddies were detected using different sea surface temperature (SST) products and, finally, submesoscale vortices were observed with Envisat Advanced SAR imagery. Thus found locations of eddies were compared with locations of the sharpest fronts discovered in the first part of the study, which showed that the biggest, mostly anticyclonic, eddies tended to correspond to locations of main surface currents; smaller cyclonic eddies were mostly attributed to thermal fronts, while submesoscale eddies were distributed quite homogeneous. The observations performed in that way revealed quite prominent basin-, meso- and submesoscale eddy activity in the region of interest. Additionally, significant seasonal variability in the type of surface water stirring was noted. Thus, the maximum of both meso- and submesoscale eddy activity seems to happen during the warm season, while during winter, presumably due to low Richardson numbers typical for the upper water layer, the turbulent features are still undeveloped and of the smaller spatial scale than during the warm period of year.

Hydrodynamic modeling along the southern tip of India: A special emphasis on Kanyakumari coast

Hydrodynamic models are important to many coastal engineering designs and application, especially addressing sediment and water quality. In this study, MIKE 21 two-dimensional (2D) hydrodynamic model based on the flexible mesh (FM) technique was used to simulate the surface currents forced by tides and winds in Kanyakumari coast. The model results of the tidal level along shore and cross shore currents are agreed well with measured data in Kanyakumari coast. The major components of tides and currents are analyzed by harmonic analysis methods. Root mean square error (RMSE) values for the measured and model tides (0.017 m and 0.079 m) and currents (0.025 m/s and 0.009 m/s) during the northeast (NE) and southwest (SW) monsoon period are calculated. A series of scenario runs for NE and SW monsoon season are used to understand the regional circulation. The model result shows that the Kanyakumari coast is dominated by tides and surface currents flow, which are influenced by the seasonal reversal wind pattern. Flows around this coastal water have been evidenced small scale cyclonic and anti-cyclonic eddies ranged from ∼55 to 120 km in diameter. The cyclonic and anti-cyclonic eddies are mostly appeared in near Kanyakumari and SE coast of Kerala due to local/ remotely generated forces.

Forecast of drifter trajectories using a Rapid Environmental Assessment based on CTD observations

A high resolution submesoscale resolving ocean model was implemented in a limited area north of Island of Elba where a maritime exercise, named Serious Game 1 (SG1), took place on May 2014 in the framework of the project MEDESS-4MS (Mediterranean Decision Support System for Marine Safety). During the exercise, CTD data have been collected responding to the necessity of a Rapid Environmental Assessment, i.e. to a rapid evaluation of the marine conditions able to provide sensible information for initialisation of modelling tools, in the scenario of possible maritime accidents. The aim of this paper is to evaluate the impact of such mesoscale-resolving CTD observations on short-term forecasts of the surface currents, within the framework of possible oil-spill related emergencies. For this reason, modelling outputs were compared with Lagrangian observations at sea: the high resolution modelled currents, together with the ones of the coarser sub-regional model WMED, are used to force the MEDSLIK-II oil-spill model to simulate drifter trajectories. Both ocean models have been assessed by comparing the prognostic scalar and vector fields as an independent CTD data set and with real drifter trajectories acquired during SG1. The diagnosed and prognosed circulation reveals that the area was characterised by water masses of Atlantic origin influenced by small mesoscale cyclonic and anti-cyclonic eddies, which govern the spatial and temporal evolution of the drifter trajectories and of the water masses distribution. The assimilation of CTD data into the initial conditions of the high resolution model highly improves the accuracy of the short-term forecast in terms of location and structure of the thermocline and positively influence the ability of the model in reproducing the observed paths of the surface drifters.

Cyclonic Eddies in the Gulf of Mexico: Observations by Underwater Gliders and Simulations by Numerical Model

AbstractCirculation in the Gulf of Mexico (GoM) is dominated by the Loop Current (LC) and by Loop Current eddies (LCEs) that form at irregular multimonth intervals by separation from the LC. Comparatively small cyclonic eddies (CEs) are thought to have a controlling influence on the LCE, including its separation from the LC. Because the CEs are so dynamic and short-lived, lasting only a few weeks, they have proved a challenge to observe. This study addresses that challenge using underwater gliders. These gliders’ data and satellite sea surface height (SSH) are used in a four-dimensional variational (4DVAR) assimilation in the Massachusetts Institute of Technology (MIT) general circulation model (MITgcm). The model serves two purposes: first, the model’s estimate of ocean state allows the analysis of four-dimensional fields, and second, the model forecasts are examined to determine the value of glider data. CEs have a Rossby number of about 0.2, implying that the effects of flow curvature, cyclostrophy, to modify the geostrophic momentum balance are slight. The velocity field in CEs is nearly depth independent, while LCEs are more baroclinic, consistent with the CEs origin on the less stratified, dense side of the LCE. CEs are formed from water in the GoM, rather than the Atlantic water that distinguishes the LCE. Model forecasts are improved by glider data, using a quality metric based on satellite SSH, with the best 2-month GoM forecast rivaling the accuracy of a global hindcast.

Mesoscale distribution and community composition of zooplankton in the Mozambique Channel

Recent studies have shown the Mozambique Channel to exhibit high mesoscale variability, but how mesoscale features influence the zooplankton community in this region is not known. The biovolume, biomass, vertical distribution and community composition of mesozooplankton (>200µm) associated with mesoscale eddies in the Mozambique Channel was investigated during four cruises in September 2007, December 2008, November 2009 and April/May 2010. Stations were categorized according to their location in cyclonic (cold-core) or anticyclonic (warm-core) eddies, frontal, divergence or shelf regions. Mean mesozooplankton biovolume in the upper 200m was 0.33mlm−3, with zooplankton largely concentrated in the upper 100m during all four cruises (weighted mean depth=66.6m). Sampling depth was the most important predictor of biovolume, which was greatest for net samples with a mid-depth of 0–40m, but declined deeper in the water column. Biovolume at the shelf (0.37mlm−3), divergence and cyclonic eddy stations (0.31mlm−3) was significantly greater than at frontal and anticyclonic eddy stations (0.20mlm−3). Mean biovolume was significantly higher during 2008 and 2010 compared to 2007 and 2009, and was also significantly higher for samples collected at night (and twilight) than during the day. The mesozooplankton community in 2007 was strongly dominated by small copepods (~70–80% abundance) followed by appendicularians (10%), ostracods (8%) and chaetognaths (7%). The most abundant copepods were the Paracalanids, Oncaea spp., Oithona spp. and Corycaeus spp. Multivariate analysis showed that the communities in 2007 and 2008 were most strongly structured by depth, but classification (cyclonic/anticyclonic) was also important in 2007 when mesoscale features were more strongly developed. Zooplankton assemblages showed a high degree of homogeneity, with differences between mesoscale features largely due to differing abundances of similar taxa. These observations suggest that mesoscale eddy and shelf interactions play a fundamental role in shaping the Mozambique Channel pelagic ecosystem through the concentration, enhanced growth and redistribution of zooplankton communities. Although frontal areas between eddies were poor in zooplankton biomass, the extensive inter-eddy divergence areas were as rich in biomass as the small cyclonic eddy core regions. These patterns are important for understanding the favorability of observed foraging areas for higher trophic levels.

Shelf edge tide correlated eddies along the southeastern United States

[1] High frequency radar observations in the Southeastern United States have revealed sequences of small short-lived cyclonic eddies along the shoreward edge of the Gulf Stream, that spin up as the local tide turns alongshelf antiparallel to the Stream. Eddies propagate equatorward along the shelf edge, sometimes progressing shoreward before dissipating one to three hours later. They are distinctly different from Gulf Stream meander eddies, which propagate poleward. In this article, radar and mooring data are used to establish three important aspects of these new eddies: they represent an instability process operating at a previously unidentified frequency, scale, and cross-Stream position; they contribute to shoreward momentum fluxes, defining a link between Gulf Stream and outer shelf subtidal variability and illustrating a mechanism to justify locally large horizontal eddy viscosity estimates; and they transport properties across the shelf edge, importing nutrients onto the shelf and transferring heat between the Gulf Stream and the coastal ocean.

Monitoring the greater San Pedro Bay region using autonomous underwater gliders during fall of 2006

Glider surveys of the greater San Pedro Bay region in the Southern California Bight during the fall of 2006 demonstrated the utility of autonomous underwater gliders in a coastal region with complex flow and significant anthropogenic inputs. Three Spray gliders repeatedly surveyed between Santa Catalina Island and the coast of Southern California collecting profiles of temperature, salinity, and chlorophyll fluorescence and estimates of vertically averaged currents. These observations provided context for shelf transport studies during the Huntington Beach 2006 experiment and showed the transition from summer to winter conditions. Vertically averaged currents were predominantly poleward following topography with horizontal scales of approximately 20 km. The gliders surveyed a small cyclonic eddy near Santa Catalina Island and provided a unique view of the structure of the eddy. Nitrate concentration within the euphotic zone was estimated to be 19% greater within the eddy and led to significantly elevated chlorophyll concentrations at the subsurface maximum. Glider observations of salinity reliably detected the distinctly fresh signature of the effluent plume from an ocean outfall near Huntington Beach, California. The salinity anomaly caused by the plume was used to track the spread of the plume as it was advected poleward and away from the coast while remaining subsurface.

Towards the numerical simulation of the summer circulation in Todos Santos Bay, Ensenada, B.C. Mexico

The general circulation of Todos Santos Bay was studied using the ROMS numerical model for the summer season. The model was forced with the California Current System and by synoptic winds, which are mainly towards the equator. The circulation is characterized by two systems: one at the exterior with a strong southward flow that enters to the bay but limited by the ∼35 m isobath and the other at the rest of the bay. The circulation in the interior oscillates between two spatial structures: one in which the general circulation is anticyclonic for two–three days overall the bay producing a large eddy and a small cyclonic eddy in front of Ensenada’s port, then the anticyclonic eddy evolves to produce the second spatial structure by splitting into two counter rotating eddies making the original anticyclonic one to be limited to the northern side of the bay and last three–four days and the small cyclonic eddy reverses its circulation. Such conditions are a consequence of the transport oscillations of the southward flow on the northwestern boundary and the mode with two eddies appears when the associated inflow is more intense. The transition between these two modes takes place in only one–two days. The time average circulation was also analyzed and the circulation with the two eddies dominates as it is of stronger currents and last longer.

Large particulate matter in the Western Mediterranean: I. LPM distribution related to mesoscale hydrodynamics

The relationship between mesoscale hydrodynamics and the distribution of large particulate matter (LPM, particles larger than 200 μm) in the first 1000 m of the Western Mediterranean basin was studied with a microprocessor-driven CTD-video package, the Underwater Video Profiler (UVP). Observations made during the last decade showed that, in late spring and summer, LPM concentration was high in the coastal part of the Western Mediterranean basin at the shelf break and near the continental slope (computed maximum: 149 μg C l −1 between 0 and 100 m near the Spanish coast of the Gibraltar Strait). LPM concentration decreased further offshore into the central Mediterranean Sea where, below 100 m, it remained uniformly low, ranging from 2 to 4 μg C l −1. However, a strong variability was observed in the different mesoscale structures such as the Almeria–Oran jet in the Alboran Sea or the Algerian eddies. LPM concentration was up to one order of magnitude higher in fronts and eddies than in the adjacent oligotrophic Mediterranean waters (i.e. 35 vs. 8 μg C l −1 in the Alboran Sea or 16 vs. 3 μg C l −1 in a small shear cyclonic eddy). Our observations suggest that LPM spatial heterogeneity generated by the upper layer mesoscale hydrodynamics extends into deeper layers. Consequently, the superficial mesoscale dynamics may significantly contribute to the biogeochemical cycling between the upper and meso-pelagic layers.

A Numerical Study on the Coastal Topographic Effect of a Peninsula on the Western Boundary Current

Abstract Coastal topographic effects of a peninsula on the western boundary current are studied numerically with reference to the difference in northern boundary inclination (NBI) from a zonal direction. It is shown from the numerical experiments that the two dominant path patterns of the western boundary current exist: one flow pattern is a large meander path with spinup and spindown of the cyclonic eddy and the other is a nonlarge (straight) path along the northern boundary. If a peninsula is located upstream (west) of the separation point of the mean flow flowing out from the northernmost area of the western boundary region, a large meander path with spinup and spindown of the cyclonic eddy is changed to an irregular oscillation by the topographic effect of the peninsula in the case of no NBI. A nonlarge meander path with a small cyclonic eddy just downstream of the peninsula is formed in the cases with NBI larger than 10°. Formation of the large meander path and the nonlarge meander path agrees with m...

Evolution of the Alboran Sea hydrographic structures during July 1993

During the ICTIOALBORAN-0793 multidisciplinary oceanographic survey carried out in July 1993 by the Instituto Español de Oceanografı́a (IEO) in the Alboran Sea, some anomalous features were detected. One was the presence of a small cyclonic eddy in the western Alboran Basin, close to the African coast. The upper layer of the eddy consisted of Mediterranean Surface Water and was separated from its supposed source (the northern Alboran Sea) by the Atlantic Jet. Another feature was the probable temporary interruption of the flow of fresh Atlantic Water (S≈36.5) into the eastern Alboran Basin and its replacement by a modified (saltier) Atlantic Water. These features can be explained assuming a time evolution of the surface circulation in the Alboran Sea forced by speed variations in the inflowing Atlantic Water through the Strait of Gibraltar. A collection of satellite images covering the survey period and across-strait sea level difference data, indicative of the geostrophic velocity of the inflow through the Strait, were used to check this assumption. Both sets of data supplied independent but compatible information in the sense that they complemented each other and gave support to the proposed evolving model. Finally, some speculative ideas attempting to correlate the inferred variability in the Alboran Sea with the state of the baroclinic water exchange through the Strait of Gibraltar (maximal or submaximal) are discussed.

Generation of ringlets

A mechanism for the generation of ringlets (i.e., small cyclonic eddies (20–40 km) which have recently been observed on the periphery of warm-core rings) is proposed. The suggested process is examined analytically using a reduced gravity one-and-a-half-layer and two-and-a-half-layer model. The underlying hypothesis is that the ringlets are formed by the expulsion of fluid from the outer rim of the warm ring and that this expulsion is the result of an absorption of foreign water into the core of the ring. This nonlinear process is examined using the not-so-frequently used integrated angular momentum constraint as well as the familiar conservation of potential vorticity and mass. These constraints show that when the ring interacts with other bodies of water such as shelf water or the Gulf Stream, the shelf water is sucked into the ring in such a manner that the entire ring is capped. To conserve angular momentum, some other fluid must then be pushed out and it is argued that via instability of the ring's edge, this expulsion forms ringlets.

Lower continental slope cyclonic eddies in the central Gulf of Mexico

Current meters, an inverted echo sounder, hydrography, drifters, and satellite imagery are used to characterize relatively small (100‐ to 150‐km diameter) cold cyclonic eddies in the central basin and on the lower Louisiana slope of the Gulf of Mexico. These cyclones are shown to be long‐lived (6 months or more), have limited movements when compared with Loop Current anticyclones, and be fairly vigorous, with upper layer currents of 30–50 cm s−1. They usually have only small temperature differences with surrounding water masses in the upper 50 to 100 m of the water column and are therefore not readily apparent in satellite thermal imagery. The largest isotherm displacements occur over depths of 200–800 m. In one case, a cyclone was traced from the deep basin near 92°W to the northern slope as a major anticyclone propagated southwestward through the gulf. The presence of cyclones and anticyclones on the Louisiana slope is consistent with observed current meter measurements in the upper half of the water column that have long (several months) periods and approximately equal variances in the cross‐slope and along‐slope directions.

Hydrography and microstructure of an Arctic cyclonic eddy

Hydrographic and velocity profiles were made through a small baroclinic cyclonic eddy during the Arctic Internal Wave Experiment in the Canada Basin in April 1985. The maximum measured azimuthal velocity was 0.38 m s−1 at a depth of 115 m, with velocities decaying to near zero at 30 and 270 m. Maximum isopycnal displacements at the closest approach to the eddy's axis were about 40 m. The deduced radius of maximum velocity is r0 = 7±2 km, and the total radius is about 13 km. Kinetic energy dissipation rate, ε, was enhanced within 70 m of the surface throughout the transect, and for radius r < r0 near 60 m and 180m. The subsurface maxima in ε do not correspond to regions of low Richardson number, but are colocated with locally reduced shear, consistent with the observed dissipation rates being merely the remnants of recent, more energetic mixing events. The time scale for the decay of the eddy, based on its total energy and the measured dissipation rates, is O(10) years. Given this large dissipation time scale, critical layer absorption of vertically propagating internal wave momentum may be dynamically significant to the eddy's evolution.

Currents off south-eastern Australia: results from the Australian coastal experiment

The Australian Coastal Experiment was conducted off the east coast of New South Wales between September 1983 and March 1984. The experiment was conducted with arrays of current meters spanning the continental margin at three latitudes (37.5�, 34.5�, and 33.0�S.), additional shelf moorings at 29� and 42�S. coastal wind and sea-level measurements, monthly conductivity-temperature-depth probe/expendable bathythermograph (CTD/XBT) surveys, and two satellite-tracked buoys. Over the continental shelf and slope, the alongshore component of the current generally exceeded the onshore component, and the subtidal (<0.6 cpd, cycles per day) current variability greatly exceeded the mean flow. Part of the current variability was associated with two separate warm-core eddies that approached the coast, causing strong (>50 cm sec-1), persistent (>8 days), southward currents over the continental slope and outer shelf. Temperature and geostrophic velocity sections through the eddies, maps of ship's drift vectors and temperature contours at 250 m, and the satellite-tracked drifter trajectories showed that these eddies were similar in structure to those observed previously in the East Australian Current region. Both eddies migrated generally southward. Eddy currents over the shelf and slope were rare at Cape Howe (37.5�S.), more common near Sydney (34.5�S.), and frequent at Newcastle (33.0�S.), where strong northward currents were also observed. Near Sydney, the eddy currents over the slope turned clockwise with depth between 280 and 740 m, suggesting net downwelling there. Repeated CTD sections also indicated onshore transport and downwelling at shallower levels; presumably, upwelling occurred farther south where the eddy currents turned offshore. Periodic rotary currents over the continental slope near Sydney and Newcastle indicated the presence of small cyclonic eddies on the flank of a much larger anticyclonic eddy. Between early October and late January, no strong southward currents were observed over the continental margin near Sydney. Data from this 'eddy-free' period were analysed further to examine the structure and variability of the coastal currents. Much of this variability was correlated with fluctuations in coastal sea-level (at zero lag) and with the wind stress (at various lags). The coherence and phase relationships among current, wind-stress, and sea-level records at different latitudes (determined from spectral analysis and frequency-domain empirical orthogonal functions) were consistent with the equatorward propagation of coastal-trapped waves generated by winds in phase with those near Cape Howe. Time-domain empirical orthogonal functions show that the current fluctuations decayed with distance from shore and with depth, as expected of coastal-trapped waves.

East Australian current adjacent to the Great Barrier Reef

Hydrographic data from a series of cruises during 1980-1981 are used to determine the circulation in the western Coral Sea region immediately adjacent to the Great Barrier Reef. The data show flow westward towards the Great Barrier Reef, bifurcating just north of 18�S. During the monsoon season (December to February), the bifurcation point moves north to at least 14�s. The geostrophic westward flow has a subsurface maximum at a depth of about 150 m. South of the bifurcation point, the flow is south-eastward on the upper continental slope and north-eastward offshore. North of the bifurcation point, the surface flow and transport (relative to 900 dbar) are northward. However, there is sometimes a south-eastwards near-surface shear. Near the bifurcation point, the surface currents are weak and variable. All of these features of the surface flow are reflected in the paths followed by satellite-tracked drifters. Although the drifters were fixed infrequently, the drifter data indicate the possible presence of small cyclonic eddies in the region of the bifurcation. All of the satellite-tracked drifters went aground in the Great Barrier Reef within 30 days of entering the region offshore from the Reef. The data are consistent with recent models of the wind-driven circulation in the South Pacific that propose that the westward flow bifurcates at about 20�S., with 17 x 106 m3 s-1 flowing through the Indonesian Archipelago from the Pacific Ocean to the Indian Ocean.

Low‐frequency propagation across an East Greenland ice‐edge eddy: Winter conditions

A series of small cyclonic eddies have been observed along the ice edge adjacent to the East Greenland current in the vicinity of the Fram Strait. These eddies arc characterized by a unique spiral surface pattern as pack ice is drawn into the circulation. Melt water from this ice contributes to a complicated temperature‐salinity structure. An analysis of low‐frequency (50 Hz) propagation is presented using environmental range‐dependent acoustic prediction models: parabolic equation (PE) and ray model [GRASS]. The environmental data are for winter conditions based on a longitudinal oceanographic transect. Results are compared to previous analyses of a similar eddy in the Fram Strait under summer conditions and the directional dependence of acoustic modes across the East Greenland current frontal zone. [Work supported by NUSC and ONR.]

Structure and Origin of a Small Cyclonic Eddy Observed during the POLYMODE Local Dynamics Experiment

In the POLYMODE Local Dynamics Experiment (31°N; 69.5°W) a small cyclonic eddy was discovered and mapped. The eddy was characterized by an upward doming of isotherms in the upper part of the main thermocline. The dynamical signal extended from the surface downward to a pressure of 800 db and outwards to a radius of 25–30 km. There was no deep-water property signal associated with the eddy, but a layer (∼10m thick) of very low salinity water was observed at the sea surface immediately above the feature. The salinities in the surface layer were lower than any reported in the historical hydrographic data for the region. Rainfall is discounted as a possible source of this signal because of the layer's thickness and horizontal scale. Alternatively the closest source for the low salinity is in the Slope Water, some 500 km away. The eddy may have originated by the splitting near several Gulf Stream rings. This mechanism could also account for the unusually low surface salinities since rings may trap Slope Water and transport it into the Sargasso Sea.

Upper‐ocean velocity structure of Gulf Stream warm‐core ring 82B

Acoustio Doppler current profiling of warm‐core ring (WCR) 82B revealed changes in the velocity structure over much of the ring's 7‐month lifespan. As ring diameter decreased, peak speeds in the high‐velocity region decreased from 0.8 m s−1 in April 1982 to 0.5 m s−1 in August 1982. Azimuthally averaged velocities revealed the core of WCR 82B to be in near solid‐body rotation, with little measurable horizontal divergence at 100 m. In addition, potential vorticity was conserved in the ring core despite interactions with the Gulf Stream and large changes in ring size. Deviations from symmetry in WCR 82B were caused by superposition with the shelf‐slope front, small cyclonic eddies, and upper‐layer mean flow.