Frontal Structure Research Articles

Seek S310‐25: Quasi‐periodic echoes and polarization electric fields

We have reexamined data collected during the flight of the SEEK S310‐25 sounding rocket, together with a second set of radar measurements, to determine whether a more consistent interpretation could be derived, if we allowed for the possibility that sporadic E (Es) was configured as a sequence of elongated strips in the form of a frontal structure. We show that the features found in the plasma density, electric field ( ) and the so‐called quasi‐periodic (QP) echoes are consistent with a polarization process acting on the Es strips that is driven by a Hall and not a Pedersen current. Specifically, we show that three large spikes, measured in situ, appeared at intervals of ground distance that were nearly identical to those of the QP echoes. The vector relationship between the spikes and the background was also consistent with this type of polarization process. We also briefly discuss a counterclockwise rotation of , which could be related with a process responsible for the existence of frontal structures.

Reduced anterior cingulate gyrus volume correlates with executive dysfunction in men with first-episode schizophrenia

Although frontal lobe structural and functional abnormalities have been identified in schizophrenia, their relationship remains elusive. Because the frontal lobes are both structurally and functionally heterogeneous, it is possible that some measures of frontal lobe structure may not have accurately identified relevant frontal lobe subregions. The authors hypothesized that the volumes of two dorsal, ‘archicortical’ subregions (i.e. superior frontal gyrus and anterior cingulate gyrus), but not a ventral, ‘paleocortical’ subregion (i.e. orbital frontal region) would be significantly and selectively correlated with executive and motor dysfunction in patients with schizophrenia as previously reported for the anterior hippocampal region. Volumes of these frontal lobe subregions were measured from magnetic resonance images based on sulcal anatomy in 20 men and 15 women with first-episode schizophrenia. All patients completed a comprehensive neuropsychological test battery while clinically stabilized that encompassed six domains of functioning: attention, executive, motor, visuospatial, memory and language. Findings indicated that reduced anterior cingulate gyrus volume was significantly correlated with worse executive functioning in men; among women, there were no significant correlations. Among men, anterior cingulate gyrus volume was significantly more strongly correlated with executive functioning than with attention, visuospatial, memory, language and general intellectual functioning. Neither executive nor motor functioning was significantly more strongly correlated with the dorsal ‘archicortical’ volumes than with orbital frontal volume. These findings suggest a link between executive deficits and dysfunction of the dorsal ‘archicortical’ system and implicate sex differences in their relationship in first-episode schizophrenia.

Piecewise Frontogenesis from a Potential Vorticity Perspective: Methodology and a Case Study

Output from a numerical simulation by the University of Wisconsin Nonhydrostatic Modeling System is used to investigate the evolution of the surface frontal structure of an intense winter cyclone that occurred off the east coast of North America. Using the model data as input to the piecewise potential vorticity (PV) inversion method developed by Davis and Emanuel, the total surface frontogenesis is partitioned into contributions from discrete PV anomalies. These contributions are calculated using the nondivergent balanced winds associated with PV anomalies in the upper, interior, and surface layers as well as the balanced irrotational winds in what is termed piecewise frontogenesis. The cyclone of interest developed into a nearly stationary, well-occluded storm characterized by a cutoff PV anomaly at the tropopause and near-surface frontogenesis concentrated in the warm frontal zone. During the open wave stage of the cyclone life cycle, this frontogenesis was produced largely by the balanced flow, particularly that portion of it associated with the upper-level PV anomaly. Throughout the remainder of the cyclone life cycle, the upper-level contribution to the frontogenesis retained a distribution similar to that of the total frontogenesis. After the cyclone occluded, however, the frontogenesis forced by the unbalanced portion of the flow became increasingly significant despite the persistent smallness of the unbalanced winds. In fact, a substantial portion of the lower-tropospheric frontogenesis observed in the occluded quadrant, including that along a developing bent-back front, was eventually associated with the unbalanced flow. These results suggest a potentially significant role is played by unbalanced motions in the development and maintenance of lowertropospheric frontal structure in midlatitude cyclones.

Classification and Composite Diagnosis of Extratropical Cyclogenesis Events in the Southwest Pacific

Characteristic patterns of cyclogenesis in the southwest Pacific region are identified from a sample of 40 developing cyclones during 1990–94. Cases were chosen objectively to ensure a realistic sampling of typical rather than “ideal” events. A subjective classification based on synoptic-scale upper-tropospheric flow signatures prior to cyclone intensification suggested four classes into which all but three cases fell. Three categories, each containing about a quarter of the population, involved direct coupling with the upper jet. They represent cyclone formation beneath (i) the poleward exit region of a 300-hPa jet upstream from a diffluent trough (class U), (ii) the confluent equatorward entrance region of the upper wind maximum (E), and (iii) the upper jet exit region where the jet is downstream from the upper trough (class D). These are analogous to previously identified categories for the western North Atlantic region. A fourth class involved cyclones forming beneath a preexisting intense upper-level trough (class T) located poleward of the upper-level jet. Class U cyclones, forming within diffluent airflow, exhibited strong cold fronts, weak warm fronts, and a meridional configuration while class E cyclones forming in confluent flow attained a more zonally elongated structure marked by stronger warm fronts and weak cold fronts. Class U cyclones featured frontal evolution similar to the Norwegian cyclone model while class E and D cyclones exhibited characteristics of the Shapiro–Keyser model. These results provide further observational support for the emerging paradigm of contrasting frontal and cyclone structure resulting from confluent versus diffluent large-scale flow.

336. fMRI activation patterns of attention and working memory in alcoholics

Chronic alcoholics typically exhibit deficits in visual working memory and directed attention and also in frontal lobe structure and function underlying these processes. We used functional MRI (fMRI) to ask whether alcoholics’ residual ability to perform working memory and attentional tasks invoke the same or different brain systems used by healthy subjects. Accordingly, 10 control and 7 alcoholic men served in an fMRI study with three conditions run in a blocked design: a 2-back task assessed visual working memory (subjects viewed a series of 0’s presented in 1 of 9 locations and pressed a button to 0’s appearing in the same spatial location as occurred two items back); a match-to-center task assessed attention (subjects pressed to 0’s appearing in the center); and passive rest (no task). Whole-brain fMRI data were acquired with a T2∗-weighted gradient echo spiral pulse sequence (1.5T, TR = 3000ms, TE = 40ms, flip = 89°, inplane resolution = 3.75mm, thickness = 6mm, 29 slices). For the working memory–rest contrast, the control group showed significantly greater activation than the alcoholic group, most prominent in bilateral dorsolateral and medial frontal cortex. For the attention–rest contrast, activation of controls was greater than that of alcoholics in prefrontal cortex bilaterally, whereas activation of alcoholics was greater than that of controls in right orbital/inferior frontal cortex. To the extent that statistical normalization adequately controls for brain structural differences across individuals and diagnoses, the results suggest a relative inability to normally activate frontal systems required for working memory and functional reorganization of the alcoholics’ approach to the attentional task.

Evolution and mesoscale structure of a polar low outbreak

AbstractAn observational study of an unusual ‘polar low outbreak’ is described in which four lows formed in succession near south‐east Iceland. Because all the lows tracked south‐east, close to Scotland, an unusually dense network of surface observations was available for analysis, including radar. This complemented the geostationary and polar‐orbiting satellite data that are more commonly used in polar low studies.Each of the four polar lows displayed a different structure and evolution. The first was a circular convective low, the second a relatively weak surface signature of an upper‐level feature, while the final two cyclones appeared as a wave train, with one cyclone decaying and the other developing into an intense disturbance.Because of the high resolution of the surface data, it was possible to identify, unambiguously, mesoscale frontal features within the polar lows. These are described in detail. A close examination was made of the final intense low, which showed that its evolution and frontal structure closely matched those found in standard conceptual models of rapidly developing maritime cyclones. This polar low also showed evidence of a warm core, and symmetric instability within an extensive ‘cloud head’.

Continuous monitoring of surface optical properties across a geostrophic front: Biogeochemical inferences

A system was designed for the continuous surface monitoring of hydrological, bio‐optical, and biogeochemical properties in the vicinity of the Almeria‐Oran jet‐front system (Northwestern Mediterranean Sea). This system included a thermosalinograph, a fluorometer, an optical particle counter, and an absorbance‐attenuance meter (AC9), allowing the estimation of the absorption [a(λ), (m−1)] and scattering [b(λ), (m−1)] coefficients at nine wavelengths. More than 500 multivariate records were acquired over a transect crossing the jet‐front system three times and encompassing the diversity of water types encountered in this area. A method is proposed to retrieve relevant biogeochemical or bio‐optical quantities, among which are the chlorophyll a concentration [from a(676)], the particulate carbon concentration [from b(555)], the colored dissolved organic matter [CDOM, from a(412)], and the chlorophyll‐specific scattering coefficient at 555 nm, b*(555) (m2 mg Chl a−1). The analyses of these various quantities with respect to the surface hydrodynamic fields reveal two main features. First, the particle pool displays highly dynamic quantitative variations across the frontal structure. Qualitatively, flagellate‐dominated populations are associated with moderate density waters and maximal jet velocity, while diatoms are recorded at the narrow limit between the jet‐front and the Mediterranean waters, where jet velocity is minimal. Second, the CDOM pool presents remarkable covariations with the surface‐density field. In particular, the lowest aCDOM (412) values are reproducibly associated with the highest density values, which track upwelled flow associated with the frontal circulation; accumulation of CDOM is always observed inside the frontal waters, at a density value of 27.2 kg m−3. These CDOM variations suggest that the frontal system is the place of enhanced biological activity.

Formulation of a Semi-Geostrophic Model of Frontal Interaction with Isolated Orography

A semi-geostrophic model of frontal passage over topography was developed to examine the effects of the interaction of a well developed front with an isolated mountain, and the subsequent orographically induced flow evolution. The analytic representation of the primary wave and its frontal structure gives us the ability to control the environmental and geometrical constraints and perform an exploration of parameter space. A number of problems appearing because of this approach are discussed. The results shown relate the characteristics of the orographic perturbation to varying amplitude of the primary wave and varying frontal intensity, but suggest that the representation of flow blocking by the mountain,which this model lacks, is crucial for the representation of frontal intensification in the lee of orography.

Idealised Numerical Experiments of Alpine Flow Regimes and Southside Precipitation Events

Heavy precipitation events to the south of the Alps are usually associated with a southerly pre-frontal low-level jet advecting moisture toward the southern slopes of the Alps. Here we use idealised numerical simulations to assess the nature of the associated flow regimes and the mechanisms leading to vertical lifting and precipitation. The idealisations comprise: a simplified arc-shaped barrier-like orographic obstacle of Alpine scale; neglection of the tropopause; a stationary two-dimensional upstream flow configuration that includes a frontal structure and a low-level jet; hydrostatic dynamics with free-slip lower boundary conditions; and a simplified set of parameterizations to address dry, moist absolutely stable, and moist conditionally unstable upstream flow configurations.

Use of the Underwater Video Profiler for the Study of Aggregate Dynamics in the North Mediterranean

The Underwater Video Profiler is a vertically deployed survey system designed for the quantification of particles >280 μm and of large zooplankton in the 0–1000 m water column. Light reflected by undisturbed target objects forms a dark-field image, which is recorded at 25 Hz frequency. The recorded images are automatically digitized and analysed. The results are expressed as abundance or size distributions and they can be converted to volume or mass units. The system can be configured as a multi-instrument array and can simultaneously acquire biological and physical data. From May 1994 to April 1995 a monthly survey was performed across a frontal structure associated to the North Ligurian geostrophic current. In winter and spring 1995 the front, as well as the offshore dispersion limit of particles, were located near to the coast. In contrast, during autumn 1994, its position was open sea and the terrestrial matter was dispersed far from the coast. The continuous presence of intermediate nepheloid layers along the continental slope indicates that different processes may supply and transport the particulate matter to deeper layers, from where it can be diffused into the basin.

A Summertime Antarctic Mesocyclone Event over the Southern Pacific during FROST SOP-3: A Mesoscale Analysis Using AVHRR, SSM/I, ERS, and Numerical Model Data

Abstract The development of three summertime mesoscale cyclones (MCs) over the northern Amundsen and Bellingshausen Seas from 10 to 12 January 1995 (during FROST SOP-3) is studied by means of AVHRR data, ERS and SSM/I retrievals, and mesoscale numerical model data. The most pronounced MC is investigated in detail. It had a diameter of about 800 km, a lifetime of more than 24 h, and reached the intensity of a polar low. The developments take place far away from the sea-ice front or topography. The MCs are detected as cyclonic cloud signatures in the AVHRR imagery, and SSM/I retrievals show a distinct mesoscale signal in the fields of cloud liquid water, wind speed, and integrated water vapor (IWV). The frontal structure of the most intense MC is depicted by high IWV gradients and a large near-surface wind shear. The collocation of ERS- and SSM/I-derived wind speeds shows good agreement (bias, 1.1 m s−1; std dev, 1.2 m s−1). ERS-derived wind vectors give no insight into the structure of the MCs, because of ...

Frontogenesis and frontal motion due to confluent deformation with a translating dilatation axis

AbstractA two‐dimensional model of primitive‐equation frontogenesis is formulated in which the forcing is due to a basic‐state field of confluent deformation with a dilatation axis that translates in the cross‐front direction. Although the translation speed and direction of motion of the basic‐state dilatation axis have no effect on frontal structure when the total deformation is spatially uniform, they can influence considerably the motion of the front. At the surface, this motion may be separated into two components: (i) internal motion, directed towards the warm air, which is associated with the secondary ageostrophic circulation of the front itself; and (ii) external motion, either towards cold or warm air, which is associated with the initial location and translation speed of the basicstate dilatation axis. the latter component ultimately dominates, and thus the motion of a mature front may be thought of as being controlled by the large‐scale flow. However, the former may dominate early on in the frontal evolution, resulting in significantly different frontal trajectories depending on the initial location of the basic‐state dilatation axis and on whether this axis is moving towards the cold or the warm air. the relative locations of various conventional frontal measures are examined in the special case of a uniformly translating dilatation axis. of these measures the axes of maximum baroclinicity and vorticity become collocated at the surface as the front intensifies. However, the basic‐state dilatation axis and the confluence axis, the latter being defined as the location of zero total wind in the cross‐front direction, may be displaced considerably from this merger point, with this displacement depending on the initial location and subsequent motion of the basic‐state dilatation axis. Potential extensions of the model are discussed with regard to improved understanding of the difference in structure and motion between cold and warm fronts.

Interaction of Orographic Disturbance with Front

The interaction of orographic disturbance with front is investigated with a nonhydrostatic fully compressible mesoscale model (ARPS). It is shown that the front is dominated mainly by the orographic disturbance if the front is weak. Firstly, because the stratified airstream is forced to flow along the topographic surface, the topographic surface almost coincides with the lowest isentrope for the barotropic flow. The potential temperature gradients are opposite on upwind slope and downwind slope. As the cold front moves across the mountain, its intensity decreases on the upwind side and increases on the downwind side due to the thermal superposition. Conversely, the warm front is strengthened on the upwind slope and weakened on the downwind slope. This is the thermal superposition effect. Secondly, the mountain-forced circulation and orographic waves, which depend on the shape and size of topography and characteristics of airflow, contribute to frontogenesis and / or frontolysis. This is referred as dynamical action. For the mesoscale mountain ridge of gentle slope, the dynamical action weakens the cold front on the upwind slope, and strengthens the cold front on the lee side. While for the mesoscale mountain of steep slope, the dynamical effect weakens the cold front on the upwind side and strengthens the cold front on the mountain top, the frontal intensity is decreased when front moves downslope rapidly. As front moves into the convergent zone near the mountain base, its intensity is enhanced severely. If the front is intensive, there is strong interaction between the orographic disturbance and the front. The cold front dramatically increases downslope wind and lee side gravity wave activity. And these in turn act upon the frontal intensity and frontal structure. For the baroclinic basic flow, the southerly warm advection on the upwind side makes the cold front less frontolysis; the northerly on the lee side violently intensifies the clod front.

Schizophrenia and the frontal brain: a quantitative review.

Structural and physiological frontal brain system deficits in patients with schizophrenia are reviewed quantitatively. We report effect sizes from studies since 1980 that used structural (CT, MRI), and functional (PET) neuroimaging methods. We found both literatures to be distinguished by heterogeneity whereby most patients show normative frontal function and structure, a minority shows diminished values and some patients demonstrate augmented function and structure rather than deficit. The average magnitude of difference between patients and controls is generally too modest to support the idea that frontal brain dysfunction is a necessary component of schizophrenia. This modesty is most apparent in average effects obtained for frontal brain volume (M = -.36), left frontal brain volume (M = -.16), frontal resting metabolism, and blood flow (M = -.64). Effect sizes of this magnitude imply that schizophrenia and control distributions overlap by as much as 88% and no less than about 60% on frontal brain measures. It is only when behavioral measures are employed as activation tasks during frontal blood flow and metabolism studies, that average effect sizes rise in magnitude to indicate patient-control distribution overlaps that are less than 50%. Overall, the findings are hard to incorporate within single disease models that propose major involvement of the frontal system, at least at the degree of resolution obtained with current imaging technology.

A Nonclassical Cold Front Observed during COPS-91: Frontal Structure and the Process of Severe Storm Initiation

Abstract This case study addresses the issue of gravity current and bore development at surface cold fronts, and the role of these phenomena in the generation of severe frontal convection. The event investigated occurred on 27 April 1991 during the Cooperative Oklahoma Profiler Studies 1991 field project. The development of a bore from a gravity current–like structure along a cold front, the subsequent propagation of the bore ahead of the front on a low-level inversion, and the process of severe thunderstorm development along the front are revealed by a dense network of remote sensing and other special observations. Evidence for the gravity current and bore is strengthened by comparisons made between the synthesized observations and theory. The bore developed after a nocturnal inversion, which acted as a waveguide, had become established. The bore and gravity current were both evident as “fine lines” in the radar reflectivity displays. A microscale envelope of enhanced water vapor with an embedded roll cl...

Aircraft observations of sea‐breeze frontal structure

AbstractDetailed aircraft observations of sea‐breeze frontal structure and dynamics are presented for two cases of well defined sea‐breeze fronts near the east coast of England. In the first case the sea‐breeze was advancing into a well mixed convective boundary layer with strong turbulence and an offshore breeze of around 3 m s‐1. In the second case the sea‐breeze was penetrating into a convective boundary layer characterized by weaker turbulence and an offshore wind speed of 2‐3 m s‐1. Indeed, during the course of the measurements a stable internal boundary layer was forming in the early evening. Cross‐sections of the frontal structure are derived from aircraft traverses at a range of heights along a fixed line normal to the coast. A typical head‐like structure is observed in both cases, with a region of strong mixing immediately seawards of the head. an approximately exponential fall‐off in dissipation rate with distance seaward of the leading edge of the front is found. Heat and momentum fluxes are used to derive turbulent kinetic energy (TKE) budgets for the mixing region and indicate that turbulence in this mixing region is maintained by TKE generated by strong shear at the top of the cold‐air inflow. In the first case the shear production of TKE is almost twice that of the second case, suggesting that the presence of ambient turbulence in the convective boundary layer has a significant effect upon the frontal dynamics. In the second case, as the turbulence decayed, a curious wave‐like structure appeared behind the leading edge of the front. the waves have wavelengths of 1‐3 km and it is unlikely that they were caused by Kelvin‐Helmholtz instability. It is suggested that the waves might be a solitary wave‐train emerging as the sea‐breeze interacts with a low‐level stable layer forming in the early evening.

Frontal structure and Antarctic Bottom Water flow through the Princess Elizabeth Trough, Antarctica

Hydrographic, current meter and ADCP data collected during two recent cruises in the South Indian Ocean ( RRS Discovery cruise 200 in February 1993 and RRS Discovery cruise 207 in February 1994) are used to investigate the current structure within the Princess Elizabeth Trough (PET), near the Antarctic continent at 85°E, 63–66°S. This gap in topography between the Kerguelen Plateau and the Antarctic continent, with sill depth 3750 m, provides a route for the exchange of Antarctic Bottom Water between the Australian–Antarctic Basin and the Weddell–Enderby Basin. Shears derived from ADCP and hydrographic data are used to deduce the barotropic component of the velocity field, and thus the volume transports of the water masses. Both the Southern Antarctic Circumpolar Current Front (SACCF) and the Southern Boundary of the Antarctic Circumpolar Current (SB) pass through the northern PET (latitudes 63 to 64.5°S) associated with eastward transports. These are deep-reaching fronts with associated bottom velocities of several cm s -1. Antarctic Bottom water (AABW) from the Weddell–Enderby Basin is transported eastwards in the jets associated with these fronts. The transport of water with potential temperatures less than 0°C is 3 (±1) Sv. The SB is shown to meander in the PET, caused by the cyclonic gyre immediately west of the PET in Prydz Bay. The AABW therefore also meanders before continuing eastwards. In the southern PET (latitudes 64.5 to 66°S) a bottom intensified flow of AABW is observed flowing west. This AABW has most likely formed not far from the PET, along the Antarctic continental shelf and slope to the east. Current meters show that speeds in this flow have an annual scalar mean of 10 cm s -1. The transport of water with potential temperatures less than 0°C is 20 (±3) Sv. The southern PET features westward flow throughout the water column, since the shallower depths are dominated by the flow associated with the Antarctic Slope Front. Including the westward flow of bottom water, the total westward transport of the whole water column in the southern PET is 45 (±6) Sv.

Volumetric analysis of frontal lobe regions in schizophrenia: relation to cognitive function and symptomatology

Background: The purpose of this study was to examine the structure of dorsolateral, medial, and orbital regions of the frontal lobe in schizophrenia, and to determine whether their volumetric measurements were related to cognitive function and symptomatology.Methods: High resolution magnetic resonance imaging scans of the brains of 14 schizophrenic patients and 14 closely matched healthy controls were acquired. Volumes of gray and white matter of the left and right dorsolateral, medial, and orbital prefrontal brain regions were measured. Tests of verbal and visual memory and executive functions were used to assess cognitive function. The SANS and SAPS were used to obtain symptom ratings in patients.Results: Data of 13 schizophrenic patients were analyzed. Patients showed a general, though not significant, decrease in volumes of frontal regions as compared to controls. In patients, but not in controls, smaller left and right prefrontal gray matter volumes were significantly correlated with impaired performance on immediate recall in verbal and visual memory and semantic fluency. Furthermore, in patients, smaller total orbitofrontal gray matter volume was significantly correlated with more severe negative symptomatology (rs = −.76, p = .006).Conclusions: These findings suggest that in schizophrenia, deficits in verbal and visual memory and semantic fluency and negative symptoms may be related to (subtle) abnormalities in frontal lobe structure.

Structure and Motion of the Southwestern Taiwan Fold and Thrust Belt

Surface and limited seismic data have been used to construct new cross sections across the southwestern Taiwan Fold and Thrust Belt. South of Chiayi, the best fit to the data is achieved if the detachment lies at a depth of 10 to 12km, stepping up to about 6km to the west. The Chukou fault and its extension to the south (Lunhou fault) are not the frontal structures in this area. Available data indicate the frontal structure may be composed of incipient reactivated normal faults in the north and triangle zones in the south. Published leveling data show that, whatever the structure, it is growing. From north of Chiayi to the south the salient nature of the structures of the Foothills province include: 1) a considerable amount of pre-Miocene strata are involved in the deformation. The involvement of pre-Miocene decreases to the south, but the depth of the basal detachment does not change due to the thickening of the Miocene and younger section;2)the involvement of pre-existing normal faults and consequent 'basement' highs affecting the trajectory of thrust ramps abruptly ends south of Chiayi, separated by buried transverse faults from, 3) the thick foreland synorogenic stratigraphic sequence rides passively above the duplex wedge. Current seismicity appears to have no correlation to the interpreted locations of faults, whether thrust, normal or strike-slip. Preliminary GPS data from this portion of the fold and thrust belt indicates, as first shown by Yu and Chen (1994), that structures are generally moving westward with respect to the Chinese craton. However, our data show abrupt changes in horizontal velocity, not all of which are associated with mapped faults. There is a region of high horizontal velocity and strain rate to the east of the Chukou-Lunhou fault. On a finer scale, the velocities can vary greatly over distances of as little as 10km.Some thrust sheets appear to be rotating counterclockwise around a vertical axis whereas others appear to be moving uniformly westward. Horizontal velocities are uniformly low in the Coastal Plain although they increase from west to east into the region of folding and blind thrusting in the footwall of the Chukou-Lunhou fault. The eastward increasing of shortening velocity in the Foothills Belt implies that a common detachment exists at depth or thrusts in the east of the Chukou-Lunhou fault are also active or both.

Krill transport in the Scotia Sea and environs

Historical observations of the large-scale flow and frontal structure of the Antarctic Circumpolar Current in the Scotia Sea region were combined with the wind-induced surface Ekman transport to produce a composite flow field. This was used with a Lagrangian model to investigate transport of Antarctic krill. Particle displacements from known krill spawning areas that result from surface Ekman drift, a composite large-scale flow, and the combination of the two were calculated. Surface Ekman drift alone only transports particles a few kilometres over the 150-day krill larval development time. The large-scale composite flow moves particles several hundreds of kilometres over the same time, suggesting this is the primary transport mechanism. An important contribution of the surface Ekman drift on particles released along the continental shelf break west of the Antarctic Peninsula is moving them north-northeast into the high-speed core of the southern Antarctic Circumpolar Current Front, which then transports the particles to South Georgia in about 140–160 days. Similar particle displacement calculations using surface flow fields obtained from the Fine Resolution Antarctic Model do not show overall transport from the Antarctic Peninsula to South Georgia due to the inaccurate position of the southern Antarctic Circumpolar Current Front in the simulated circulation fields. The particle transit times obtained with the composite large-scale flow field are consistent with regional abundances of larval krill developmental stages collected in the Scotia Sea. These results strongly suggest that krill populations west of the Antarctic Peninsula provide the source for the krill populations found around South Georgia.