Baroclinic Rossby Radius Of Deformation Research Articles

Analysis of a Halocline Mesoscale Eddy in the Northwind Basin, Arctic Ocean

Eddies have been observed at all depths and in all regions of the Arctic Ocean. However, given the complex geographic conditions and dynamic environments of this ocean, the synchronized observations of temperature, salinity, and currents, and the detailed analysis of individual eddies are still lacking in the Northwind Basin. Our study aims to address these research gaps. We observed an eddy from a mooring in the Northwind Basin in late October 2017. It is a large anticyclonic cold eddy within the Arctic halocline, with a maximum azimuthal velocity reaching 52.63 cm/s and a horizontal scale (∼56 km) that significantly exceeds the first local baroclinic Rossby radius of deformation, i.e., it is in mesoscale. Its azimuthal velocity and scale are larger compared with those of nearby eddies, suggesting a relatively young state. This eddy possibly originated from the northern Chukchi Sea shelf, converging near Hanna Shoal with the Chukchi Slope Current before being advected northward into the Northwind Basin. Our study outlines detailed steps for extracting and analyzing eddies from mooring data and contributes to improving the understanding of the characteristics of Arctic Ocean eddies, providing a typical case for the investigation of eddies in the Northwind Basin.

Detection and characterization of submesoscale eddies from optical images: a case study in the Argentine continental shelf

ABSTRACT Eddies are structures of recognized physical and biogeochemical relevance. Because of their small space and time scales, submesoscale eddy detection is a challenge, and detection methods for these structures are scarce. In this study, we detect submesoscale eddies (SME) by means of a method implemented on satellite chlorophyll-a (CSAT) and sea surface temperature (SST) data from Visible Infrared Imaging Radiometer Suite (VIIRS) and Moderate Resolution Imaging Spectroradiometer (MODIS) images. The performance of this method is shown through the characterization of the shape and size of the detected eddies. The trajectory and characteristics of one particular eddy could be observed for 6 days over the Argentine continental shelf. The eddy reached the highest CSAT concentration (1.52 mg m−3, decreasing to less than 0.8 mg m−3 in about 3.5 km), and the lowest SST on the same day it developed its largest size. All SME detected within the study period are in agreement with cyclonic eddies and have a radius smaller than the baroclinic Rossby radius of deformation. This paper presents a workflow for the automated recognition of SME that could be applied to other regions with similar characteristics, or different ones with previous changes in the parameters.

Baroclinic instability of spatially-periodic flows in a discrete surface quasi-geostrophic model with two levels

Within the framework of a discrete surface quasi-geostrophic (SQG) model with two levels, the hydrodynamic stability of a spatially periodic flow with sinusoidal velocity profile (Kolmogorov flow) is investigated. Such spatially quasi-periodic flows are often observed in the atmospheres of the giant planets and in the Southern Ocean. To describe the dynamics of perturbations, the Galerkin method with three basis trigonometric functions was used. It provides a tool to study both the linear and nonlinear perturbation dynamics. Analytical expressions are obtained for the growth rates of perturbations in the linear theory of stability, and it is shown that the fastest growing perturbations have a wavelength on the order of the spatial period of the main flow. Using the Galerkin method, it is also shown that the exponential growth of perturbations at the linear stage of development is replaced by the stage of stable nonlinear oscillations. Such oscillations are analogous to the nonlinear fluctuations, or vacillations, found in R. Hide's laboratory experiments. In terms of elliptic integrals, an analytical expression for the period of nonlinear oscillations is obtained, and it is shown that for typical values of the parameters relevant to the Earth’s atmosphere, the period of oscillations is about one month. The paper also proposes a long-wavelength version of the discrete SQG model, which describes the dynamics of perturbations with a horizontal scale much larger than the baroclinic Rossby radius of deformation. It is shown that the use of this version simplifies the study of stability and leads to asymptotically correct results.

Analysis of baroclinic vertical structures around the Korean marginal seas with a primary focus on the model configuration

Determining the appropriate spatial resolution is crucial for configuring regional ocean models. The first baroclinic Rossby radius of deformation serves as an objective length-scale for ensuring horizontal grid spacing, while little equivalent quantifiable standard exists for the vertical coordinate system. Many models determine vertical grids based on the analysis of baroclinic modes commensurate with the theoretical capabilities of a given horizontal grid. However, under this approach, most of the focus is on the global ocean or ideal cases. Therefore, we analyzed the baroclinic vertical modes around the Korean marginal seas using serial observation data provided by the National Fisheries Research and Development Institute's Korean Oceanographic Data Center. Using the deformation radius-model horizontal grid ratio (Lm/Δ˜) and baroclinic mode analysis, we suggest the optimal level to configure a high-resolution model. The results indicate that a model with a 1/33° horizontal resolution can reproduce up to the first baroclinic mode in the Yellow Sea, the second mode in the East China Sea, and the third mode in the East/Japan Sea. From the zero-crossing depth distribution analysis, we also provided the recommended minimum number of vertical levels to satisfy each baroclinic mode in the sub-regions of the Korean marginal seas. This study clearly highlights that more attention should be paid to configure the vertical coordinate system when designing regional modeling, especially for the sub-areas of the Korean marginal seas, because these values are considerably different from each other with a significant interannual variability.

Observation of submesoscale turbulence in a cyclonic eddy

In this study, we report results from a high-resolution measurement of submesoscale turbulence in a mesoscale eddy. The kinetic energy spectra in the mesoscale eddy are decomposed into mesoscale and submesoscale components using Helmholtz decomposition and wave-vortex decomposition methods. The length scale of transition from mesoscale to submesoscale is quantitatively determined, which is roughly consistent with the first baroclinic Rossby radius of deformation (44 km) and has a relatively weak dependence on depth. Two distinct spectral slopes for the mesoscale and submesoscale turbulence are identified: the kinetic energy spectrum at mesoscale has a vertical average − 2.6 slope, which agrees with the interior QG turbulence theory; at submesoscale, the average slope is −1.5 and weakly dependent on depth, which is consistent with the GM internal wave spectrum.

Cross-spectral analysis of the SST/10-m wind speed coupling resolved by satellite products and climate model simulations

This study aims to determine the spatial–temporal scales where the SST forcing of the near-surface winds takes places, and its relationship with the action of coherent ocean eddies. Here, cross-spectral statistics are used to examine the relationship between satellite-based SST and 10-m wind speed (w) fields at scales between 10 $$^2$$ –10 $$^4$$ km and 10 $$^1$$ –10 $$^3$$ days. It is shown that the transition from negative SST/w correlations at large-scales to positive at oceanic mesoscales occurs at wavelengths coinciding with the atmospheric first baroclinic Rossby radius of deformation; and that the dispersion of positively-correlated signals resembles tropical instability waves near the equator, and Rossby waves in the extratropics. Transfer functions are used to estimate the SST-driven w response in physical space ( $$w_c$$ ), a signal that explains 5–40% of the mesoscale w variance in the equatorial cold tongues, and 2–15% at extratropical SST fronts. The signature of ocean eddies is clearly visible in $$w_c$$ , accounting for 20–60% of its variability in eddy-rich regions. To provide further insight on the role of ocean eddies in the SST-driven coupling, the analysis is repeated for two climate model (CCSM) simulations using ocean grid resolutions of $$1^\circ$$ (eddy-parameterized, LR) and $$0.1^\circ$$ (eddy-resolving, HR). The lack of resolved eddies in LR leads to a significantly underestimated mesoscale w variance relative to HR. Conversely, the $$w_c$$ variability in HR can exceed the satellite estimates by a factor of two at extratropical SST fronts and underestimate it by a factor of almost six near the equator, reflecting shortcomings of the CCSM to be addressed in its future developments.

Mesoscale eddies and baroclinic instability over the eastern Sakhalin shelf of the Sea of Okhotsk: a model-based analysis

Based on an eddy-permitting numerical model, the mesoscale variability in the East-Sakhalin Current is investigated during the winter-spring period. Analysis of necessary conditions for the development of baroclinic instability showed that the nearshore component of the East-Sakhalin Current is potentially baroclinic unstable in the first half-year. The simulated circulation uncovered a generation of anticyclonic eddies on the eastern Sakhalin shelf. It was established that a spatial scale of these eddies and the first baroclinic Rossby radius of deformation are values of the same order; a lifetime of these eddies varies from 4 to 6 weeks, given the Rossby number varies from 0.05 to 0.2. Analysis of the rate of eddy energy conversion on the eastern Sakhalin shelf showed that the generation of the revealed mesoscale eddies results from, mainly, baroclinic instability, whereas barotropic instability can be both favoring and preventing to the generation of these eddies.

Estimating the baroclinic Rossby radius of deformation in the Sea of Okhotsk

The first baroclinic Rossby radius of deformation (R 1) in the Sea of Okhotsk is estimated using the hydrological datasets from the World Ocean Atlas (WOA) 2001 and WOA 2013. It is established that the maximum values of R 1 are observed over the Kuril Basin (18–20 km), and its minimum values (1.5–2 km), over the northern shelf of the Sea of Okhotsk. In the central part of the sea R1 varies from 8 to 10 km. The seasonal variability of R1 for both datasets is characterized by the minima in winter and by the maxima in summer. It was found that on the eastern shelf of Sakhalin Island R 1 reaches the maximum both in November (∼6 km) and in April (∼4-5 km). According to the obtained estimates of R 1, the model grid resolution of 3 to 8 km should be used for the eddy-permitting numerical simulation of circulation in the Sea of Okhotsk, and the model grid resolution from 1.5 to 2 km, for the explicit simulation of mesoscale variability.

Extreme N<sub>2</sub>O accumulation in the coastal oxygen minimum zone off Peru

Abstract. Depth profiles of nitrous oxide (N2O) were measured during six cruises to the upwelling area and oxygen minimum zone (OMZ) off Peru in 2009 and 2012/2013, covering both the coastal shelf region and the adjacent open ocean. N2O profiles displayed a strong sensitivity towards oxygen concentrations. Open ocean profiles with distances to the shelf break larger than the first baroclinic Rossby radius of deformation showed a transition from a broad maximum close to the Equator to a double-peak structure south of 5° S where the oxygen minimum was more pronounced. Maximum N2O concentrations in the open ocean were about 80 nM. A linear relationship between ΔN2O and apparent oxygen utilization (AOU) could be found for measurements within the upper oxycline, with a slope similar to studies in other oceanic regions. In contrast, N2O profiles close to the shelf revealed a much higher variability, and N2O concentrations higher than 100 nM were often observed. The highest N2O concentration measured at the shelf was ∼ 850 nM. Due to the extremely sharp oxygen gradients at the shelf, N2O maxima occurred in very shallow water depths of less than 50 m. In the coastal area, a linear relationship between ΔN2O and AOU could not be observed as extremely high ΔN2O values were scattered over the full range of oxygen concentrations. The data points that showed the strongest deviation from a linear ΔN2O ∕ AOU relationship also showed signals of intense nitrogen loss. These results indicate that the coastal upwelling at the Peruvian coast and the subsequent strong remineralization in the water column causes conditions that lead to extreme N2O accumulation, most likely due to the interplay of intense mixing and high rates of remineralization which lead to a rapid switching of the OMZ waters between anoxic and oxic conditions. This, in turn, could trigger incomplete denitrification or pulses of increased nitrification with extreme N2O production.

Interference pattern of the sound field in the presence of an internal Kelvin wave in a stratified lake.

Internal Kelvin waves (IKWs) initiated by rotation of the Earth are one of the main hydrodynamic phenomena in large stratified lakes where baroclinic Rossby radius of deformation is smaller than the horizontal scale of the lake. IKWs can be identified using the spectra of internal waves, where in the presence of IKWs, the inertial frequency is at maximum. IKWs play a rather important role in the lake's dynamics for different processes, both in the water layer and sediment, especially at the periphery of lake. Due to influence of internal waves on the sound propagation, acoustical methods can be used for estimation of behaviour of IKWs. In this paper, the spatiotemporal variability of the mid-frequency (∼1 kHz) sound field in the presence of IKWs in a deep stratified Lake Kinneret is studied using numerical simulations based on normal-mode theory. Due to the specific character of perturbation of the water layer, IKWs can cause specific variations of interference pattern, in particular, a significant shift of the sound interference pattern both in spatial and frequency domain. These shifts can be easily measured and used for reconstruction of IKW parameters.

Vortex dynamics in the southeastern Baltic Sea from satellite radar data

The analysis of radar satellite images shows that vortex dipoles are a typical element of the water circulation in the southeastern part of the Baltic Sea. The wide range of spatial dimensions of observed vortices (from approximately 2 to 25 km) corresponds to mesoscale and submesoscale vortex formations (signifying whether the diameter is respectively larger or smaller than the baroclinic Rossby radius of deformation, equal to 5–6 km). Vortex dipoles typical for different areas and their spatial characteristics are considered. These areas were the Hel Spit, the Taran Cape, the central part of the Gulf of Gdansk and the area northward of the Gulf. It is shown that the mesoscale vortex dipoles and the associated jets condition horizontal water exchange in an area comparable with the size of the considered water area. The differences in the appearance of the cyclonic and anticyclonic components of vortex dipoles revealed in satellite radar images are discussed.

A Drag-Induced Barotropic Instability in Air–Sea Interaction

Abstract A new mechanism that induces barotropic instability in the ocean is discussed. It is due to the air–sea interaction with a quadratic drag law and horizontal viscous dissipation in the atmosphere. The authors show that the instability spreads to the atmosphere. The preferred spatial scale of the instability is that of the oceanic baroclinic Rossby radius of deformation. It can only be represented in numerical models, when the dynamics at this scale is resolved in the atmosphere and ocean. The dynamics are studied using two superposed shallow water layers: one for the ocean and one for the atmosphere. The interaction is due to the shear between the two layers. The shear applied to the ocean is calculated using the velocity difference between the ocean and the atmosphere and the quadratic drag law. In one-way interaction, the shear applied to the atmosphere neglects the ocean dynamics; it is calculated using the atmospheric wind only. In two-way interaction, it is opposite to the shear applied to the ocean. In one-way interaction, the atmospheric shear leads to a barotropic instability in the ocean. The instability in the ocean is amplified, in amplitude and scale, in two-way interaction and also triggers an instability in the atmosphere.

Eddy properties in the Mozambique Channel: A comparison between observations and two numerical ocean circulation models

Analysis of satellite altimetry observations, transports estimates from a mooring array, as well as output from two different numerical ocean circulation models (ROMS and HYCOM), have been used to investigate the mesoscale eddy properties and transport variability in the Mozambique Channel. The power spectral density of model transports at 17°S indicates the models ability to represent the transport variability at mesoscale frequencies (range between 3yr−1 and 10yr−1). The models have shown an exaggerated representation of the lower frequencies (~ <3yr−1), while underestimating the higher frequency signals (~ >10yr−1). The overestimation of the seasonal cycle appears in our case not to be related to a misrepresentation of the mesoscale variability. The eddies were identified using an automatic eddy tracking scheme. Both anticyclonic and cyclonic eddies appeared to have a preferred site of formation within the channel. The density distribution showed that the anticyclones exhibited a bi-modal distribution: the first mode was associated with the typical scale for the oceanic mesoscale turbulence, while the second mode was related to the passage of large rings at a frequency of about 4–7 per year. On the other hand, cyclonic eddies had a single mode distribution that follows the first baroclinic Rossby radius of deformation, which is a typical scale for the oceanic mesoscale surface eddy variability, suggesting that their formation is associated with baroclinic instability. Eddy mean amplitudes per class of radius (<100km), increase linearly with increasing radius, while no linear relationship exists for the rings. Different from the rings, the increase in the amplitude of the eddies was consistent with the increase of their life expectancy and travelling distances.

Downwelling in Basins Subject to Buoyancy Loss

Abstract Recent observational, theoretical, and modeling studies all suggest that the upper part of the downwelling limb of the thermohaline circulation is concentrated in strong currents subject to buoyancy loss near lateral boundaries. This is fundamentally different from the traditional view that downwelling takes place in regions of deep convection. Even when resolving the buoyant boundary currents, coarse-resolution global circulation and climate models rely on parameterizations of poorly known turbulent mixing processes. In this study, the first direct measurements of downwelling occurring within a basin subject to buoyancy loss are obtained. Downwelling is observed near the basin’s vertical wall within the buoyant boundary current flowing cyclonically around the basin. Although the entire basin is cooled, large-scale mean downwelling is absent in the basin interior. Laboratory rotating experiments are conducted to explicitly resolve the turbulent mixing due to convective plumes and the baroclinic eddies generated by the boundary current, and to identify where downwelling takes place. Small vertical velocities can be measured more reliably in the laboratory than in many numerical calculations, whereas the measurement of these small vertical velocities is still a challenge for field experiments. Downwelling is observed near the vertical wall within a boundary layer with a thickness that scales with the baroclinic Rossby radius of deformation, consistent with the dynamical balance proposed by a previous numerical study. Hence, downwelling in the Labrador Sea and Lofoten Basin cyclonic boundary currents may be concentrated in a baroclinic Rossby radius of deformation thick boundary layer in regions with large eddy generation.

A Geostrophic Adjustment Model of Two Buoyant Fluids

Abstract A combination of analytical calculations and laboratory experiments has been used to investigate the geostrophic adjustment of two buoyant fluids having different densities in a third denser ambient fluid. The frontal position, the depth profile, and the horizontal and vertical alignments of the two buoyant fluids at the final equilibrium state are determined by the ratio of the baroclinic Rossby radii of deformation Γ1 = λ31/λ21 and Γ2 = λ32/λ21 and the Burger numbers B1 = λ31/L1 and B2 = λ32/L2 of the two buoyant fluids, where is the baroclinic Rossby radius of deformation between fluids i and j. The buoyant fluids 1 and 2 have densities ρ1 and ρ2 (ρ1 &amp;lt; ρ2), respectively; the ambient denser fluid has density ρ3; g′ is the reduced gravity; H and L are the buoyant fluids’ initial depth and width, respectively; and f is the Coriolis parameter. Laboratory rotating experiments confirmed the analytical prediction of the location of the two fronts. After reaching geostrophic equilibrium, the two buoyant currents align mainly horizontally when the extent of the fronts between fluids 1 and 3 and between fluids 2 and 3 is large compared to the extent of the front between fluids 1 and 2: that is, large values of λ31 and λ32 compared to λ21 or equivalently Γ1 ≫ 1 and Γ2 ≫ 1. Alternatively, if the extent of the fronts between the three fluids is similar (i.e., Γ1 ≈ Γ2 ≈ 1), the buoyant currents align mainly vertically. Furthermore, the Burger number of the lightest fluid B1 controls the distance of the inner front from the coast, while B2 controls the offshore extent of the outer front.

Baroclinic Rossby radius of deformation in the southern Baltic Sea

ThefirstbaroclinicRossbyradiusofdeformation(R1)isafundamentalhorizontal scale of mesoscaleprocesses. This scale is important for planning both numerical modellingandstudyareas. R1 was computed on the basis of an 11-year series of high resolution CTD measurements collected during r/v ‘Oceania’ cruises. The data set covered the three main basins of the Baltic Proper: the Bornholm Basin (BB), the Slupsk Furrow (SF) and the Gdansk Basin (GB). The smallest mean value of R1 was foundintheGdanskBasin(5.2km),thelargestoneintheBornholmDeep(7.3km). TheseasonalvariabilityofR1islowerinthewesternbasinthanintheeastern one. The seasonal cycle of R1 may be broken by extreme events, e.g. main Baltic inflows (MBI) of saline water. The inflowing water rebuilds the vertical stratification in the southern Baltic Sea and dramatically changes the R1values. ThedifferenceofR1betweenastagnationperiodandaninflowsituationisshown * ThisworkwassupportedbythePolishStateCommitteeofScientificResearchunder grantNo. N N305 111636. Thecomplete textof thepaperis available athttp://www.iopan.gda.pl/oceanologia/

Geographical and monthly variability of the first baroclinic Rossby radius of deformation in the South China Sea

In this paper, based on the 1-degree grided data of the monthly mean temperature and salinity data at standard levels in the South China Sea(SCS), we solve the linearized vertical eigenvalue problem for horizontal large-scale waves, the first baroclinic phase speed c 1 and the first baroclinic Rossby radius of deformation R 1 are obtained. Due to the regional variations of the water depth, stratification and latitude, R 1 varies largely. In most months of a year, in the deep sea area, the effect of temporal variation of the stratification on R 1 can be neglected, however, in November and December, R 1 in the central SCS changes largely due to a large stratification variation of the local water mass; in the wide continental shelf, the effect of temporal variation of the stratification on R 1 is very important. The westward phase speed of the first baroclinic Rossby wave C R 1 derived from observations and numerical models give an independent estimation which is consistent with solving the vertical eigenvalue problem, which shows that the estimated C R 1 could be used to distinguish and trace the propagation signal of baroclinic Rossby waves in the SCS.

Influence of Global Warming on Baroclinic Rossby Radius in the Ocean: A Model Intercomparison

Abstract Results from eight ocean–atmosphere general circulation models are used to evaluate the influence of the projected changes in the oceanic stratification on the first baroclinic Rossby radius of deformation in the ocean, associated with atmospheric CO2 increase. For each of the models, an oceanic state corresponding to the A1B stabilization experiment (with atmospheric CO2 concentration of 720 ppm) is compared to a state corresponding to the preindustrial control experiment (with atmospheric CO2 concentration of 280 ppm). In all of the models, the first baroclinic Rossby radius increases with increasing oceanic stratification in the warmer climate. There is, however, a considerable range among the models in the magnitude of the increase. At the latitudes of intense eddy activity associated with instability of western boundary currents (around 35°–40°), the increase reaches 4 km on average, or about 15% of the local baroclinic Rossby radius. Some of the models predict an increase of the baroclinic Rossby radius by more than 20% at these latitudes under the applied forcing. It is therefore suggested that in a plausible future warmer climate, the characteristic length scale of mesoscale eddies, as well as boundary currents and fronts, may increase. In addition, since the speed of long baroclinic Rossby waves is proportional to the squared baroclinic Rossby radius of deformation, the results suggest that the time scale for large-scale dynamical oceanic adjustment may decrease in the warmer climate, thereby increasing the frequency of long-term climate variability where the oceanic Rossby wave dynamics set the dominant period. Finally, the speed of equatorial Kelvin waves and Rossby waves, carrying signals along the equator, including those related to ENSO, is projected to increase.

Global autocorrelation scales of the partial pressure of oceanic CO2

A global database of approximately 1.7 million observations of the partial pressure of carbon dioxide in surface ocean waters (pCO2) collected between 1970 and 2003 is used to estimate its spatial autocorrelation structure. The patterns of the lag distance where the autocorrelation exceeds 0.8 is similar to patterns in the spatial distribution of the first baroclinic Rossby radius of deformation indicating that ocean circulation processes play a significant role in determining the spatial variability of pCO2. Separate calculations for times when the Sun is north and south of the equator revealed no obvious seasonal dependence of the spatial autocorrelation scales. The pCO2 measurements at Ocean Weather Station (OWS) “P” in the eastern subarctic Pacific (50°N, 145°W) is the only fixed location where an uninterrupted time series of sufficient length exists to calculate a meaningful temporal autocorrelation function for lags greater than a few days. The estimated temporal autocorrelation function at OWS “P” is highly variable. A spectral analysis of the longest four pCO2 time series indicates a high level of variability occurring over periods from the atmospheric synoptic to the maximum length of the time series, in this case 42 days. It is likely that a relative peak in variability with a period of 3–6 days is related to atmospheric synoptic period variability and ocean mixing events due to wind stirring. However, the short length of available time series makes identifying temporal relationships between pCO2 and atmospheric or ocean processes problematic.

The temporal evolution of a geostrophic flow in a rotating stratified basin

A laboratory study in a rotating stratified basin examines the instability and long time evolution of the geostrophic double gyre introduced by the baroclinic adjustment to an initial basin-scale step height discontinuity Δ H in the density interface of a two-layer fluid. The dimensionless parameters that are important in determining the observed response are the Burger number S = R / R 0 (where R is the baroclinic Rossby radius of deformation and R 0 is the basin radius) and the initial forcing amplitude ɛ = Δ H / H 1 ( H 1 is the upper layer depth). Experimental observations and a numerical approach, using contour dynamics, are used to identify the mechanisms that result in the dominance of nonlinear behaviour in the long time evolution, τ > 2 ɛ − 1 (where τ is time scaled by the inertial period T I = 2 π / f ). When the influence of rotation is moderate ( 0.25 ≤ S ≤ 1 ), the instability mechanism is associated with the finite amplitude potential vorticity (PV) perturbation introduced when the double gyre is established. On the other hand, when the influence of rotation is strong ( S ≤ 0.1 ), baroclinic instability contributes to the nonlinear behaviour. Regardless of the mechanism, nonlinearity acts to transfer energy from the geostrophic double gyre to smaller scales associated with an eddy field. In the lower layer, Ekman damping is pronounced, resulting in the dissipation of the eddy field after only 40 T I . In the upper layer, where dissipative effects are weak, the eddy field evolves until it reaches a symmetric distribution of potential vorticity within the domain consisting of cyclonic and anticyclonic eddy pairs, after approximately 100 T I . The functional dependence of the characteristic eddy lengthscale L E on S is consistent with previous laboratory studies on continuously forced geostrophic turbulence. The cyclonic and anticyclonic eddy pairs are maintained until viscous effects eventually dissipate all motion in the upper layer after approximately 800 T I . The outcomes of this study are considered in terms of their contribution to the understanding of the energy pathways and transport processes associated with basin-scale motions in large stratified lakes.