Cyclonic Ring Research Articles

Optimal Precursor Triggering Kuroshio Large Meander Decay Obtained in a Regional Ocean Model

AbstractThis study investigates the optimal precursor (OPR) triggering Kuroshio large meander (LM) decay using a conditional nonlinear optimal perturbation (CNOP) approach and a regional ocean modeling system (ROMS). The results show that the large amplitudes of the OPR are mainly concentrated at 1,000–2,500 m in the LM upstream region (west of 137°E), and their propagation downstream along the Kuroshio axis contributes to triggering the transition from the LM path to the nonlarge meander (NLM) path. Using the growth of the OPR, it is found that baroclinic instability contributes to the fast vertical development of the perturbations in the early stage of the LM decay, while barotropic processes play a leading role during the cyclonic ring shedding of the LM decay. In particular, the LM decay process is evaluated by the depth‐integrated vorticity equation, implying that the advection term dominates over the beta effect in the LM decay. Furthermore, the vorticity balance associated with the cyclonic eddy indicates that the advection and divergence terms represent a main balance in the spin‐down process of the cyclonic eddy. Under the effects of both, high potential vorticity water flows out from the LM meander tip and then the amplitude of the LM experiences a remarkable decrease. With the detachment of a cyclonic ring, a transition from the LM path to the NLM path occurs. This study further deepens our understanding of the LM decay and provides us some useful hints about designing the observation system of the LM.

Three-dimensional thermohaline anomaly structures of rings in the Kuroshio Extension region

Using AVISO satellite altimeter observations during 1993–2015 and a manual eddy detection method, a total of 276 anticyclonic rings and 242 cyclonic rings shed from the Kuroshio Extension (KE) were identified, and their three-dimensional (3D) anomaly structures were further reconstructd based on the Argo float data and the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) cruise and buoy data through an interpolation method. It is found that the cyclonic (anticyclonic) rings presented consistent negative (positive) anomalies of potential temperature; meanwhile the relevant maximum anomaly center became increasingly shallow for the cyclonic rings whereas it went deeper for the anticyclonic rings as the potential temperature anomaly decreased from the west to the east. The above deepening or shoaling trend is associated with the zonal change of the depth of the main thermocline. Moreover, the composite cold ring between 140° and 150°E was found to exhibit a double-core vertical structure due to the existence of mode water with low potential vorticity. Specifically, a relatively large negative (positive) salinity anomaly and a small positive (negative) one appeared for the composite cyclonic (anticyclonic) ring at the depth above and below 600 m, respectively. The underlying driving force for the temperature and salinity anomaly of the composite rings was also attempted, which varies depending on the intensity of the background current and the temperature and salinity fields in different areas of the KE region, and the rings’ influences on the temperature and salinity could reach deeper than 1 000 m on average.

NPZ response to eddy-induced upwelling in a Brazil Current ring: A theoretical approach

This work explores the effect of a cyclonic mesoscale feature of the Brazil Current (BC) moving northward off SE Brazil (20° S–23° S) in the Nutrients-Phytoplankton-Zooplankton (NPZ) dynamics. We employ the contour dynamics technique in a quasi-geostrophic, inviscid, 1½-layer model set as a meridional jet flowing southward along a rigid western boundary. This hydrodynamical model is coupled to a conventional NPZ model. We evaluate two distinct scenarios: (1) Plankton in a mixed layer (ML) with time-variable depth and no entrainment and; (2) Plankton in an ML held at a fixed depth, which allows entrainment. We perform simulations with different ML depths representing summer (42 m) and winter (86 m) for the region of interest. The presence of the western boundary allows the cyclonic ring to propagate northward due to image effect. The eddy motion produces upwelling (downwelling) in the leading (trailing) edge resulting in different responses in the two scenarios examined. In the variable ML depth simulations, Z is favored relative to P because there is no injection of N. On the other hand, in the fixed ML depth simulations, P is favored relative to Z due to dilution. All simulations show P enrichment within the eddy, but winter simulations show a greater response to the physical forcing. We conclude that the cyclonic eddy shed from BC provides favorable conditions for planktonic growth. Winter-like conditions seem to be more favorable than summer-like ones and, therefore, present more intense blooms associated with the ring.

Climatological mean features and interannual to decadal variability of ring formations in the Kuroshio Extension region

This study examines the climatological mean features of oceanic rings shed from the Kuroshio Extension (KE) jet and their interannual to decadal variability using satellite altimeter observations from October 1992 to December 2010. To objectively capture ring shedding from the KE jet, a new method that consists of the detection of the jet length changes and the tracking of a ring is proposed. Spatial distribution of the ring formations in the KE region indicates that cyclonic (cold-core) rings were most frequently formed in the upstream region between 143° and 147°E around the steady meander of the KE jet. In contrast, most of anticyclonic (warm-core) rings were formed in the downstream region west of the Shatsky Rise. These pinched-off rings in both the upstream and downstream regions generally propagated westward, but about two-thirds of the rings were reabsorbed by the jet. Nevertheless, about one-fourth of the meridional eddy heat transport at the latitude of the KE resulted from the rings that are not reabsorbed by the jet. The number of ring formations showed substantial interannual to decadal variability. In the upstream and downstream KE region, decadal and interannual variability was dominant, respectively. These ring formation fluctuations were negatively correlated with the strength of the KE jet. It is also revealed that the ring formation variations play an important role in sea surface temperature changes north of the KE jet.

Lagrangian study of surface transport in the Kuroshio Extension area based on simulation of propagation of Fukushima-derived radionuclides

Abstract. Lagrangian approach is applied to study near-surface large-scale transport in the Kuroshio Extension area using a simulation with synthetic particles advected by AVISO altimetric velocity field. A material line technique is proposed and applied to find out the origin of water masses in cold-core cyclonic rings pinched off from the jet in summer 2011. Tracking and Lagrangian maps provide the evidence of cross-jet transport. Fukushima-derived caesium isotopes are used as Lagrangian tracers to study transport and mixing in the area a few months after the 11 March 2011 tsunami that caused heavy damage of the Fukushima Nuclear Power Plant (FNPP). Tracking maps are computed to trace the origin of water parcels with measured levels of 134Cs and 137Cs concentrations collected during two research vessel (R/V) cruises in June and July 2011 in the large area of the northwest Pacific (Kaeriyama et al., 2013; Buesseler et al., 2012). It is shown that Lagrangian simulations are useful for finding the surface areas that are potentially dangerous due to the risk of radioactive contamination. The results of simulation are supported by tracks of the surface drifters that were deployed in the area.

The evolving flow of Jupiter’s White Ovals and adjacent cyclones

We present results regarding the dynamical meteorology of Jupiter’s White Ovals at different points in their evolution. Starting from the era with three White Ovals FA, BC, and DE ( Galileo), continuing to the post-merger epoch with only one Oval BA ( Cassini), and finally to Oval BA’s current reddened state ( New Horizons), we demonstrate that the dynamics of their flow have similarly evolved along with their appearance. In the Galileo epoch, Oval DE had an elliptical shape with peak zonal wind speeds of ∼90 m s −1 in both its northern and southern peripheries. During the post-merger epoch, Oval BA’s shape was more triangular and less elliptical than Oval DE; in addition to widening in the north–south direction, its northern periphery was 20 m s −1 slower, and its southern periphery was 20 m s −1 faster than Oval DE’s flow during the Galileo era. Finally, in the New Horizons era, the reddened Oval BA had evolved back to a classical elliptical form. The northern periphery of Oval BA increased in speed by 20 m s −1 from Cassini to New Horizons, ending up at a speed nearly identical to that of the northern periphery of Oval DE during Galileo. However, the peak speeds along the southern rim of the newly formed Oval BA were consistently faster than the corresponding speeds in Oval DE, and they increased still further between Cassini and New Horizons, ending up at ∼140–150 m s −1. Relative vorticity maps of Oval BA reveal a cyclonic ring surrounding its outer periphery, similar to the ring present around the Great Red Spot. The cyclonic ring around Oval BA in 2007 appears to be moderately stronger than observed in 1997 and 2001, suggesting that this may be associated with the coloration of the vortex. The modest strengthening of the winds in Oval BA, the appearance of red aerosols, and the appearance of a turbulent, cyclonic feature to Oval BA’s northwest create a strong resemblance with the Great Red Spot from both a dynamical and morphological perspective. In addition to the White Ovals, we also measure the winds within two compact cyclonic regions, one in the Galileo data set and one in the Cassini data set. In the images, these cyclonic features appear turbulent and filamentary, but our wind field reveals that the flow manifests as a coherent high-speed collar surrounding relatively quiescent interiors. Our relative vorticity maps show that the vorticity likewise concentrates in a collar near the outermost periphery, unlike the White Ovals which have peak relative vorticity magnitudes near the center of the vortex. The cyclones contain several localized bright regions consistent with the characteristics of thunderstorms identified in other studies. Although less studied than their anticyclonic cousins, these cyclones may offer crucial insights into the planet’s cloud-level energetics and dynamical meteorology.

Velocity and vorticity measurements of Jupiter's Great Red Spot using automated cloud feature tracking

We have produced mosaics of the Great Red Spot (GRS) using images taken by the Galileo spacecraft in May 2000, and have measured the winds of the GRS using an automated algorithm that does not require manual cloud tracking. Our technique yields a high-density, regular grid of wind velocity vectors that is advantageous over a limited number of scattered wind vectors that result from manual cloud tracking. The high-velocity collar of the GRS is clearly seen from our velocity vector map, and highest wind velocities are measured to be around 170 m/s. The high resolution of the mosaics have also enabled us to map turbulent eddies inside the chaotic central region of the GRS, similar to those mapped by Sada et al. (1996) and Vasavada et al. (1998). Using the wind velocity measurements, we computed particle trajectories around the GRS as well as maps of relative and absolute vorticities. We have discovered a narrow ring of cyclonic vorticity that surrounds the main anti-cyclonic high-velocity collar. This narrow ring appears to correspond to a ring surrounding the GRS that is bright in 5-microns (Terrile and Beebe 1979). It appears that this cyclonic ring is not a transient feature of the GRS, as we have discovered it in a re-analysis of Galileo data taken in 1996 first analyzed by Vasavada et al. (1998). We also calculate how absolute vorticity changes as a function of latitude along a trajectory around the GRS and compare these measurements to similar ones performed by Dowling and Ingersoll (1988) using Voyager data. We show no dramatic evolution in the structure of the GRS since the Voyager era except for additional evidence for a counterrotating GRS core, an increase in velocity in the main velocity collar, and an overall decrease in the length of the GRS.

Kuroshio intrusion into the South China Sea

In this article, the circulation of the South China Sea (SCS), which is idealized as the rectangular basin with constant depth, is studied under Kuroshio boundary forces. Starting from the linearly quasi-geostrophic vorticity equation, the solution of the SCS circulation is given in the form of corrected Fourier series under proper boundary conditions. The results show that the intruded current flows westward and separates into the northward branch and the southward branch before arriving at the western boundary. The southward branch flows out of the SCS through the southwestern passage, at the same time, the induced cyclonic (anti-clockwise) ring almost occupies the middle and southern parts, and concomitant anti-cyclonic (clockwise) vortex appears between the cyclone and the western boundary. While the northward branch outflows through the northeastern passage, the anti-cyclonic (clockwise) ring is triggered at the northern part of the SCS. The above two vortexes are both intensified if the south-entering and the north-leaving current loop intrusion are superposed. The outer flow of the northern vortex flows westward, then northward, and then eastward, and it is very similar to the configuration of the SCS Warm Current (SCSWC) at the northern part of the SCS, thus, a kind of generating mechanism of the SCSWC is presented.

The dispersion relation for internal acoustic-gravity waves in a baroclinic fluid

The dispersion relation for internal waves in a fluid is generalized from the barotropic approximation to the baroclinic case to allow for the inclination of surfaces of constant density to surfaces of constant pressure. This generalization allows the barotropic approximation to be tested in a variety of situations. The dispersion relation applies to both acoustic waves and internal gravity waves propagating in either the ocean or the atmosphere. Imaginary terms in the dispersion relation proportional to the baroclinic vector indicate energy exchange between the wave and the mean flow, a result of buoyancy being a nonconservative force in a baroclinic fluid. A buoyancy calculation shows that the baroclinic generalization of the Brunt–Väisälä frequency N is given by N2=∇ρθ⋅∇p/ρ2, where ρ is density, ρθ is potential density, and p is pressure. The baroclinicity in a weather front or cyclonic ring can sometimes have as large an effect as the Earth’s rotation on the propagation of internal gravity waves.

Ring‐slope interactions and the formation of the western boundary current in the Gulf of Mexico

Hydrographic data from the Gulf of Mexico (gulf) provide evidence that a western boundary current was set up by the interaction of an anticyclonic Loop Current (LC) ring with the continental margin of the western gulf during March‐August 1985. The March 1985 geostrophic circulation reveals a remnant anticyclonic ring colliding with the slope. During this collision, two cyclonic rings were shed as the anticyclone transferred vorticity to the surrounding slope water. During July‐August 1985, the ring triad weakened and evolved into a ∼900‐km‐long, north flowing, along‐slope, western boundary current and cyclonic‐anticyclonic ring pairs distributed throughout the central and western gulf. This western boundary current attained maximum northward flow speeds of 25 cm s−1 and an 8.3‐Sv mass transport between 94°–96°W at 25°N. Our March‐August 1985 observations reveal that the residence time and decay period of LC anticyclones in the western gulf may exceed 150 days. Within this time period the western gulf's cyclonic‐anticyclonic vorticity field decayed ∼50%. Thus the western boundary current's evolutionary period, from its gestation to its absolute decay, is estimated to be of the order of 300 days. Although the presence of a western boundary current in the gulf has been attributed to the annual wind stress curl cycle [Sturges, 1993], our analyses of the western gulf March and July‐August 1985 ring‐driven geostrophic circulation and corresponding (January, February and May, June 1985) monthly mean synoptic wind stress curl distributions reveal that these constitute competing forcing mechanisms for the gulf's regional circulation. However, when very strong local forcing such as large eddies are present, the wind‐driven background circulation is overwhelmed by such eddy forcing.

Detecting "dipole ring" separatrices with zebra palettes

Two new analysis methods applicable to remote sensing of the sea surface are described. The first is a zebra false-color palette that combines a slowly varying rainbow with a rapid gray-scale sinusoid, and the other is a routine that tracks the thermal separatrix, or dividing line, between two (of more) circulation regimes. Used together, a significant increase in data retention is achieved compared to traditional algorithms based on frontal digitizations. These two methods are applied to historical infrared data of Gulf Stream rings from the western North Atlantic. The ring data indicate anticyclonic rings usually have at least one cyclonic companion and are more appropriately modeled as dipoles. Several examples of cyclonic rings in the Sargasso Sea are seen with anticyclonic companions and are also believed to be dipoles. The separatrix method is shown to provide reliable rotation rates for these vortex systems.

Life history of a cyclonic ring detached from the Kuroshio Extension as seen by the Geosat altimeter

The sea surface dynamic topography (SSDT; sea surface height relative to the geoid) is approximately estimated by combining the temporal fluctuation of SSDT determined from altimetry data with the climatological mean SSDT calculated from hydrographic data. This approximated SSDT, or composite SSDT, is obtained in the area southeast of Japan for the first year (1986–1987) of the Geosat Exact Repeat Mission. Variations in the Kuroshio Current System are well described by the composite SSDT. In particular, a complete life history of a cyclonic ring is observed for the first time in this region, namely, westward propagation of a southward meander of the Kuroshio Extension, its pinching‐off to form a cyclonic ring, the ring's westward movement, its coalescence with the Kuroshio, and its eastward advection. All available hydrographic data and cloud‐free satellite infrared images support the existence of this series of phenomena.

Water circulation and a cyclonic ring in the Gulf Stream splitting region in May–June 1990

Results of two hydrographical surveys of the area southeast of Newfoundland, where the Gulf Stream branches into the North Atlantic Current and the Azores Current, are presented. The surveys were carried out by the R/Vs Vityaz and Professor Shtokman in May–June, 1990, as a part of the Atlantex‐90 experiment. The process of detachment of a cyclonic meander and the appearance of a new, extremely strong cyclonic ring are described. Thermohaline structure and local dynamics of the ring and the origin of its water mass are explored. Integral parameters describing the heat and salt content of the ring are defined, and fluxes of heat and salt transferred across the Subarctic Front by such rings are estimated. Volume transport variations of the Gulf Stream are coupled with the appearance of the ring. Structure and variability of individual jets of the Azores Current and the North Atlantic Current and their interaction with the synoptic scale cyclones and anticyclones are described. From the analysis of the thermohaline structure and parameters of these eddies their origin can be determined. The hydrological structure of the Subarctic, Labrador Current, and Azores Fronts is described.

Baroclinic flows, transports, and kinematic properties in a cyclonic‐anticyclonic‐cyclonic ring triad in the Gulf of Mexico

During October‐November 1986 the baroclinic circulation of the central and western Gulf of Mexico was dominated by an anticyclonic ring that was being bisected by two north and south flanking cyclonic rings. The baroclinic circulation revealed a well‐defined cyclonic‐anticyclonic‐cyclonic triad system. The anticyclone's collision against the western gulf continental slope at 22.5°N, 97°W originated the north and south flanking cyclonic rings. The weakening of the anticyclone's relative vorticity, during the collision, was compensated by along‐shelf north (26 cm s−1) and south (58 cm s−1) jet currents and by the anticyclone's flanking water mass's gain of cyclonic vorticity from lateral shear contributed by east (56 cm s−1) and west (42 cm s−1) current jets with individual mass transports of ∼18 Sv. Within the 0–1000 and 0–500 dbar layers and across 96°W the magnitudes of the colliding westward transports were 17.80 and 8.59 Sv, respectively. These corresponding transports were 85 and 94% balanced by along‐shelf jet currents north and south of the anticyclone's collision zone. This indicates that only minor amounts (<15%) of the anticyclone's colliding westward transports might have flowed into the western gulf's continental shelf water mass or else they sank into deeper water along the continental slope during the anticyclone's collision event. The resultant effect of the coupled interaction between the anticyclone and the cyclonic pair was the surging of the water mass in the cyclones and its sinking in the anticyclone. This mechanism controlled the magnitude, direction, location of vertical advection, and transfer of kinetic energy from the upper to the deeper water layers. Our vertical transport estimates through the 1000‐m‐depth surface revealed a net vertical descending transport of 0.4 Sv for the ring triad system. This mass flux occurred primordially within the south central gulf region and most likely constituted a principal mechanism that propelled the gulf's deep horizontal circulation. The volume renewal time is ∼5 years for the ring triad system within 0–1000 dbar. The volume renewal time for the gulf's deep water layer (2000–3000 dbar), estimated as a function of its horizontal outflowing mass flux (1.96 Sv), is of the same order of magnitude and reveals that the deeper layer of the Gulf of Mexico is as well ventilated as its upper layer (0–1000 dbar). The ring triad's surface kinematic properties were derived from the sea surface baroclinic circulation field referenced to 500 dbar. Within this layer, individual ring geometries were conserved. Maximum tangential ring velocities were 60 and 58 cm s−1, for the north and south cyclones respectively, and 30 cm s−1 for the anticyclone. The corresponding periods of revolution were 16, 19, and 26 days, and vertical velocities calculated at the rings' peripheries, where maximum horizontal divergence was encountered, were 1.5, 1.0, and −1.0 m d−1.

A model for the structure of anticyclonic and cyclonic rings with uniform dynamical energy density

This paper derives a model for interface depth and velocity profiles of anticyclonic and cyclonic rings under the assumption of uniform distribution of the sum of each density of kinetic and available potential energies. This assumption really means that the sum of each energy per unit area of a column of upper water of 1½-layer rings in cyclogeostrophic and hydrostatic balances is proportional to the vertical thickness of the column. The width of rotating annular warm water for an anticyclonic ring is between values of double and triple the radius of deformation, that for a cyclonic ring is less than double the radius, and both approach double the radius with increasing size of the anticyclonic and cyclonic rings. The core of an anticyclonic ring either can be at rest or in solid-body rotation, like the one studied by Kawai (1978, Preprint for 1978 Autumn Meeting of Oceanographical Society of Japan, pp. 16–17) with vorticity − ƒ/3, where ƒ is the Coriolis frequency. On the other hand, a cyclonic ring always must have a static core. Despite the possibility of anticyclonic rings with static cores, hardly any measurements have supported continuous existence of such rings. The coreless anticyclonic ring model of Kawai (1978), with uniform distribution of the sum of each density of kinetic and available potential energies, predicts velocity and other quantities greater than directly or indirectly observed ones. Discrepancy in magnitude between the predicted and observed quantities is partly accounted for by assuming that the sum of each energy density contains not only kinetic energy density from azimuthal velocity but also that from radial, vertical, turbulent and oscillating velocities. The greater, the ratio of kinetic energy density from these residual velocities to that from azimuthal velocity, the smaller the predicted quantities such as velocity become. For certain values of the vertical thickness at center and the radius of deformation, this model shows a minimum of the sum of kinetic and available potential energies contained in the ring, compared to other coreless anticyclonic rings, and hence might be optional. Adjustment of any type of anticyclonic ring in solid-body rotation to winter-cooling is briefly discussed.

Collision of a loop current anticyclonic ring against the continental shelf slope of the western Gulf of Mexico

A Loop Current anticyclonic ring ∼330 km in diameter and extending to a depth of >1500 m was observed to collide in January of 1984 against the continental shelf slope of the western Gulf of Mexico between 21.5° and 23°N. The collision occurred precisely at the time we conducted our Argos 84−1 hydrographic cruise in the western gulf (26°00′ to 19°20′N) aboard the R/V Justo Sierra. The Caribbean Subtropical Underwater (SUW) was used as a tracer to identify the Loop Current anticyclonic ring within the western gulf. The collision was identified from temperature and salinity distributions and from the dynamic topography distribution relative to 500 m. The ring's collision zone was identified by the presence of a horizontal baroclinic flow divergence, to the east of Tamiahua, that divides the surface circulation into northward and southward baroclinic currents parallel to the western gulf's continental shelf break, with speeds of 85 and 32 cm s−1, respectively. Horizontal divergence and vertical convergence (ring asymmetries) resulted at the focus of the anticyclonic ring's collision and originated the alongshore self advection and northward translation of the colliding anticyclone. Upon colliding the anticyclonic ring shed approximately one third of its volume (∼2 × 104 km3), mass, and transferred angular momentum to the south flanking water mass, thus generating a cyclonic ring to the south of the collision zone. The observed alongshelf southward current results from mass conservation and volume continuity requirements associated with the anticyclonic ring's volume shedding and most probably constitutes the colliding ring's potential vorticity conservation mechanism. The weakening of the anticyclonic ring's relative vorticity due to the collision is most likely made up by gain of vorticity from lateral shear in the northward and southward current jets parallel to the continental shelf break. The core of both the anticyclonic and cyclonic rings had typical SUW salinity (>36.5‰) and temperature (∼22.5°C) values. The rings were separated by a 5 × 104 km2 divergence zone occupied by Gulf Common Water (GCW). The SUW was absent within the collision zone to the east of Tampico (22.3°N, 97.8°W). The GCW within this divergence zone resulted from the convective mixing and dilution of the SUW with less saline (36.1 ≤ S ≤ 36.3‰) water from the uppermost layer of the thermocline. Hence the collision of Loop Current anticyclones against the western continental shelf slope of the gulf constitutes a primary mechanism by which 30 Sv of SUW are converted to GCW in the Gulf of Mexico. On the other hand, the coastal and continental shelf water temperature and salinity distributions that resulted from the ring's collision indicate that the offshore GCW mass intrudes the continental shelf to the east of Tamiahua and is diluted by low‐salinity coastal water within the western continental shelf. This GCW mass intrusion most probably constitutes a principal and efficient exchange mechanism between the western gulf's continental shelf and offshore waters.

Rings in the Ocean

Certain robust, long-lived eddy features in t he world's ocean have come to be k nown as rings. The nomenclature stems from Fuglister 1 (1972), who c oined t he name based on the c ircle or ring of Gulf Stream waters t hat surrounded a class of eddies formed from t he G ulf Stream through the pinch-off of meanders . Here it s uffices to define rings as intense eddies or vortices that represent a wrapped-up piece of a major ocean c urrent. They t ranslate over space scales of hundreds to thousands of k ilometers and exist for periods lasting from months to years . Rings move t hrough the ocean carrying anomalies s imilar to the contrasts in physical, biological, and chemical properties observed across the major ocean c urrents . While the term ring is t ied to Fuglister, t he existence ofthese features was evident at least as early as t he 1930s , when Iselin 2 (1936, 1940) encountered strong cold anomalies in the region south of the Gulf Stream that we would identify as c old-corc , cyclonic rings today. Iselin fully rec ognized these features as part of the highly time-dependent eddy motion in the ocean. Later, Iselin & Fuglister (1948) were the first to survey what is now k nown as a warm-core, anticyc lonic ring. There are tw o types of rings: cold-core rings are made up of w aters from the poleward s ide of c urrents like the Gulf Stream that are introduced to

The behavior of isolated free eddies in a rotating fluid: Laboratory experiment

It is demonstated that an isolated free eddy similar to a Gulf Stream cyclonic ring can be generated in a rotating laboratory basin by applying local cooling to the free surface of the working fluid (water). Visual observations show that the resulting stratified eddy is inherently stable and preserves its monopolar structure even in the presence of bottom slope. On a sloping bottom, the eddy cuurent along with the eddy's water mass migrates away from the formation region. Characteristics of the eddy migration due to bottom slope are also presented.

A unified geostrophic equation with application to a cold core ring

The present paper considers a possible extension of previous work on intermediate geostrophic (IG) dynamics and an application to the Gulf Stream cyclonic ring. We generalize the IG equation to the degree at which either total energy or potential enstrophy of a reduced-gravity shallow water fluid system is conserved in time. Some progress is made in this respect and an evolution equation is derived via a perturbation approach using a high-order expansion in the Rossby number. The energy integral expression contains an ageostrophic term which is cubic in the geopotential function and suggests an asymmetric evolution of positive and negative IG vortices. We attempt to model the satellite-observed motions of a cyclonic Gulf Stream ring by using our approximate equation. The result for this example shows the present model to be superior to the quasi-geostrophic model. DOI: 10.1111/j.1600-0870.1988.tb00358.x

Shelf water entrainment by Gulf Stream warm‐core rings

Examination of 7 years of satellite advanced very high resolution radiometer imagery demonstrates that shelf water removal by entrainment adjacent to warm‐core rings is a common phenomenon, representing an important process for shelf water budgets. South of Georges Bank, streamer entrainment occurred 69 ± 20% of the time. In addition, 9 ± 6% of the time more than one streamer was active. The data show little mean seasonal variability but large interannual variability in streamer occurrence. Most of the variability is related to the passage of warm‐core rings south of Georges Bank. An instantaneous streamer transport value of 2.5 × 105 m3 s−1 was determined from ship‐tracked drogues and hydrographic data. Reducing this value to 70% gives an estimated mean annual shelf water removal by streamer entrainment of 1.8 × 105 m3 s−1 (5700 km3 yr−1) for this segment of the shelf. A balanced Gulf of Main transport budget can not be obtained when this value is compiled with transports across the other boundaries of the gulf; instead a net export of 16 × 104 m3 s−1 of water results. This lack of a balance emphasizes the uncertainty of the existing transport measurements. The fate of streamers includes incorporation into the warm‐core ring and detrainment from the ring with either the formation of cold cyclonic rings in the slope water or entrainment into the northern edge of the Gulf Stream. In addition to streamer entrainment, the satellite imagery reveals that a number of different phenomena are occurring which move shelf water across the shelf‐slope front. In 86 ± 13% of the images, some type of offshore transport is observed.