scholarly journals Surface flow structure of the Gulf Stream from composite imagery and satellite-tracked drifters

1994 ◽  
Vol 1 (1) ◽  
pp. 64-71 ◽  
Author(s):  
C. P. Mullen ◽  
A. D. Kirwan, Jr.
Keyword(s):  
Fractal Dimension ◽  
Flow Structure ◽  
Gulf Stream ◽  
Surface Flow ◽  
Geographic Variability ◽  
Data Set ◽  
Study Region ◽  
Physical Conditions ◽  
The North ◽  
Lagrangian Drifter

Abstract. A unique set of coutemporaneous satellite-tracked drifters and five-day composite Advanced Very High Resolution Radionmeter (AVHRR) satellite imagery of the North Atlantic has been analyzed to examine the surface flow structure of the Gulf Stream. The study region was divided into two sections, greater than 37° N and less than 37° N, in order to answer the question of geographic variability. Fractal and spectral analyses methods were applied to the data. Fractal analysis of the Lagrangian trajectories showed a fractal dimension of 1.21 + 0.02 with a scaling range of 83 - 343 km. The fractal dimension of the temperature fronts of the composite imagery is similar for the two regions with D = 1.11 + 0.01 over a scaling range of 4 - 44 km. Spectral analysis also reports a fairly consistent value for the spectral slope and its scaling range. Therefore, we conclude there is no geographic variability in the data set. A suitable scaling range for this contemporaneous data set is 80 - 200 km which is consistent with the expected physical conditions in the region. Finally, we address the idea of using five-day composite imagery to infer the surface flow of the Gulf Stream. Close analyses of the composite thermal fronts and the Lagrangian drifter trajectories show that the former is not a good indicator of the latter.

Thermohaline structure and transport of mesoscale eddies in the Lofoten Basin from in situ and altimetry data

2020 ◽  
Author(s):  
Nikita Sandalyuk
Keyword(s):  
Hot Spot ◽  
Mesoscale Eddy ◽  
Three Dimensional ◽  
Salt Transport ◽  
Set Covering ◽  
Altimetry Data ◽  
Russian Science ◽  
Data Set ◽  
Study Region ◽  
The North

<p>The Lofoten Basin is one of the most dynamically unstable regions of the North Atlantic and represents a ‘hot spot’ of the mesoscale eddy activity in the Nordic Seas.  A quasi-stationary, deep, anticyclonic eddy is located in the central part of the basin. One of the key features of the Lofoten Basin circulation is a separation of eddies from the main branch of Norwegian current and their westward propagation towards the central part of the basin. Because of these processes, warm and saline Atlantic waters are transported to the deeper part of the basin. Understanding the physical processes responsible for the water mass transformations in this area is of particular interest in order to apprehend the climate of the region.</p><p>In this study we obtain three-dimensional structures of cyclonic and anticyclonic eddies for the LB region by combining the observational data set covering the 2000-2017 period with satellite altimetry data. The results reveal that significant eddy-induced anomalies are concentrated within a distance of 1 radius of the composite AE and CE and extend vertically to the depth of 1000 m. The core of the composite AE is located in the 200-400 m while the composite CE has a double-core structure with the maximum anomalies centered in the upper layer above 100 m and a negative peak located at 700 m. The difference in the structure of AE and CE is referred to the upwelling and downwelling processes in the AEs and CEs respectively.</p><p>The study also provides an estimation of the depth-integrated heat and salt transport as well as zonal volume eddy-induced transport. Each AE (CE) generates volume transport of 1.98 Sv (1.87 Sv), heat transport of 2.9*1014 W (-8.3*104 W) and salt transport of 2.3*106 kg/s (-1.6*1013 kg/s).  Zonal eddy-induced transport has a general westward propagation direction reaching maximum of 0.6 Sv in the north-eastern part of the study area. The northward transport takes place predominantly in the southern and eastern parts of the study region and has significantly smaller magnitude. </p><p> </p><p><strong>This work was supported by Russian Science Foundation [project № 18-17-00027];</strong></p>

The tidal and longer-period circulation of Capricornia, Southern Great Barrier Reef

1987 ◽  
Vol 38 (4) ◽  
pp. 461 ◽  
Author(s):  
DA Griffin ◽  
JH Middleton ◽  
L Bode
Keyword(s):  
Continental Shelf ◽  
Great Barrier Reef ◽  
Tidal Flow ◽  
Barrier Reef ◽  
Mean Flow ◽  
Data Set ◽  
Study Region ◽  
North West ◽  
The North ◽  
Hourly Data

Between June and December 1983, nine current meters and three water level recorders were deployed on the continental shelf and slope of the Capricornia Section of the Great Barrier Reef between Fraser Island (25�s.) and the mouth of the Capricorn Channel (23�s.) on the east coast of Australia. Tidal analyses of the hourly data set reveal an amplification of the semi-diurnal tides as they propagate north- westward into the Capricorn Channel. The results of a numerical model of tidal flow show excellent agreement with observations. The daily averaged (non-tidal) currents are highly variable and produce complex circulation patterns, but with a mean flow generally alongshore to the north-west. Comparisons with previous drifter studies and satellite-tracked buoy data suggest that the south-eastward flowing East Australian Current drives a large clockwise eddy, in the lee of the Swain Reefs, located east of the study region. It is postulated that this eddy, in addition to the generally north-westward wind stress, contributes to the north-westward flow within the study region. Temperatures recorded by the deployed instruments and temperature profiles from conductivity-temperature-depth casts confirm that tidal and longer period variablity contribute to upwelling onto the continental shelf.

scholarly journals Anomalous azimuthal variations with 360° periodicity of Rayleigh phase velocities observed in Scandinavia

2020 ◽  
Vol 224 (3) ◽  
pp. 1684-1704
Author(s):  
Alexandra Mauerberger ◽  
Valérie Maupin ◽  
Ólafur Gudmundsson ◽  
Frederik Tilmann
Keyword(s):  
Seismic Anisotropy ◽  
Broad Band ◽  
Shear Velocity ◽  
Velocity Variation ◽  
The South ◽  
Study Region ◽  
Lithospheric Thickness ◽  
Phase Velocities ◽  
The North ◽  
Southern Norway

SUMMARY We use the recently deployed ScanArray network of broad-band stations covering most of Norway and Sweden as well as parts of Finland to analyse the propagation of Rayleigh waves in Scandinavia. Applying an array beamforming technique to teleseismic records from ScanArray and permanent stations in the study region, in total 159 stations with a typical station distance of about 70 km, we obtain phase velocities for three subregions, which collectively cover most of Scandinavia (excluding southern Norway). The average phase dispersion curves are similar for all three subregions. They resemble the dispersion previously observed for the South Baltic craton and are about 1 per cent slower than the North Baltic shield phase velocities for periods between 40 and 80 s. However, a remarkable sin(1θ) phase velocity variation with azimuth is observed for periods >35 s with a 5 per cent deviation between the maximum and minimum velocities, more than the overall lateral variation in average velocity. Such a variation, which is incompatible with seismic anisotropy, occurs in northern Scandinavia and southern Norway/Sweden but not in the central study area. The maximum and minimum velocities were measured for backazimuths of 120° and 300°, respectively. These directions are perpendicular to a step in the lithosphere–asthenosphere boundary (LAB) inferred by previous studies in southern Norway/Sweden, suggesting a relation to large lithospheric heterogeneity. In order to test this hypothesis, we carried out 2-D full-waveform modeling of Rayleigh wave propagation in synthetic models which incorporate a steep gradient in the LAB in combination with a pronounced reduction in the shear velocity below the LAB. This setup reproduces the observations qualitatively, and results in higher phase velocities for propagation in the direction of shallowing LAB, and lower ones for propagation in the direction of deepening LAB, probably due to the interference of forward scattered and reflected surface wave energy with the fundamental mode. Therefore, the reduction in lithospheric thickness towards southern Norway in the south, and towards the Atlantic ocean in the north provide a plausible explanation for the observed azimuthal variations.

scholarly journals Regional differences in the evolution of the merger of /ʃ/ and /ç/ in Luxembourgish

2021 ◽  
pp. 1-18
Author(s):  
François Conrad
Keyword(s):  
Language Contact ◽  
Sound Change ◽  
Young Generation ◽  
The South ◽  
Data Set ◽  
West Germanic ◽  
The North ◽  
Minimal Pairs ◽  
Old Men ◽  
Middle Generation

The merger of post-alveolar /ʃ/ and palatal /ç/ into alveolopalatal /ɕ/ has recently gained growing interest in sociophonetic research, especially in the Middle German dialect area. In Luxembourgish, a Continental West Germanic language, the sound change has been linked to age differences, while its origins remain unclear. Two studies with a regional focus are presented in this paper. The first study examines the merger in the Centre and the South of Luxembourg. The acoustic examination of both the spectral peak and the centre of gravity of a spoken data set of five minimal pairs embedded in read and orally translated sentences from 48 speakers (three generations (old generation, 65–91 years; middle generation, 40–64 years; young generation, 20–39 years; each generation, n = 16), men and women) reveals interesting results related to their regional background. In the old generation, the merger is further advanced in the speech of old men from the former mining region in the South compared to their peers in the Centre, the former leading this sound change. On the other hand, young speakers in both regions produce only alveolopalatal /ɕ/, the merger being complete in this generation. The second study presents exploratory data from the East and the North of the country. The analysis of this smaller sample (n = 6 speakers) reveals patterns similar to the central region. Pointing to language contact with Romance in the South as cradle and/or catalyser of the merger, these results not only give further clues as to the development in Luxembourg, but also add to a deeper understanding of sound changes in process in complex sibilant systems.

Stochastic inversion of pressure and saturation changes from time-lapse AVO data

Geophysics ◽  
2006 ◽  
Vol 71 (5) ◽  
pp. C81-C92 ◽  
Author(s):  
Helene Hafslund Veire ◽  
Hilde Grude Borgos ◽  
Martin Landrø
Keyword(s):  
Stochastic Model ◽  
Seismic Data ◽  
Synthetic Data ◽  
Time Lapse ◽  
Bayesian Framework ◽  
Reservoir Modeling ◽  
Data Set ◽  
The North ◽  
Fluid Saturation ◽  
Likelihood Model

Effects of pressure and fluid saturation can have the same degree of impact on seismic amplitudes and differential traveltimes in the reservoir interval; thus, they are often inseparable by analysis of a single stacked seismic data set. In such cases, time-lapse AVO analysis offers an opportunity to discriminate between the two effects. We quantify the uncertainty in estimations to utilize information about pressure- and saturation-related changes in reservoir modeling and simulation. One way of analyzing uncertainties is to formulate the problem in a Bayesian framework. Here, the solution of the problem will be represented by a probability density function (PDF), providing estimations of uncertainties as well as direct estimations of the properties. A stochastic model for estimation of pressure and saturation changes from time-lapse seismic AVO data is investigated within a Bayesian framework. Well-known rock physical relationships are used to set up a prior stochastic model. PP reflection coefficient differences are used to establish a likelihood model for linking reservoir variables and time-lapse seismic data. The methodology incorporates correlation between different variables of the model as well as spatial dependencies for each of the variables. In addition, information about possible bottlenecks causing large uncertainties in the estimations can be identified through sensitivity analysis of the system. The method has been tested on 1D synthetic data and on field time-lapse seismic AVO data from the Gullfaks Field in the North Sea.

scholarly journals On the Relationship between Synoptic Wintertime Atmospheric Variability and Path Shifts in the Gulf Stream and the Kuroshio Extension

2009 ◽  
Vol 22 (12) ◽  
pp. 3177-3192 ◽  
Author(s):  
Terrence M. Joyce ◽  
Young-Oh Kwon ◽  
Lisan Yu
Keyword(s):  
North Atlantic ◽  
North Pacific ◽  
Gulf Stream ◽  
Kuroshio Extension ◽  
Storm Track ◽  
Western Boundary ◽  
Atmospheric Variability ◽  
The North ◽  
The Kuroshio ◽  
The North Pacific

Abstract Coherent, large-scale shifts in the paths of the Gulf Stream (GS) and the Kuroshio Extension (KE) occur on interannual to decadal time scales. Attention has usually been drawn to causes for these shifts in the overlying atmosphere, with some built-in delay of up to a few years resulting from propagation of wind-forced variability within the ocean. However, these shifts in the latitudes of separated western boundary currents can cause substantial changes in SST, which may influence the synoptic atmospheric variability with little or no time delay. Various measures of wintertime atmospheric variability in the synoptic band (2–8 days) are examined using a relatively new dataset for air–sea exchange [Objectively Analyzed Air–Sea Fluxes (OAFlux)] and subsurface temperature indices of the Gulf Stream and Kuroshio path that are insulated from direct air–sea exchange, and therefore are preferable to SST. Significant changes are found in the atmospheric variability following changes in the paths of these currents, sometimes in a local fashion such as meridional shifts in measures of local storm tracks, and sometimes in nonlocal, broad regions coincident with and downstream of the oceanic forcing. Differences between the North Pacific (KE) and North Atlantic (GS) may be partly related to the more zonal orientation of the KE and the stronger SST signals of the GS, but could also be due to differences in mean storm-track characteristics over the North Pacific and North Atlantic.

Velocity changes across the Ganos segment of the North Anatolian Fault Zone in NW Turkey from systematic variations in body wave arrival times

2021 ◽  
Author(s):  
Esref Yalcinkaya ◽  
Marco Bohnhoff ◽  
Patricia Martinez-Garzon ◽  
Ethem Görgün ◽  
Ali Pınar ◽  
...  
Keyword(s):  
Body Wave ◽  
Waveform Analysis ◽  
Marmara Region ◽  
Rupture Directivity ◽  
Data Set ◽  
High Resolution Data ◽  
Arrival Times ◽  
The North ◽  
Nw Turkey ◽  
Geological Units

<p>Imaging and characterizing transform fault sections that are capable to produce large earthquakes is crucial for evaluating seismic hazard and subsequent risk for nearby population centers. The Marmara Fault near the megacity of Istanbul is one of the best defined seismic gaps in the world and its complexity is captured by seismological, geodetic and geological data. A local dense seismic array (MONGAN) provides a high resolution data set allowing to image the Ganos fault separating two different geological units in the western Marmara region. First results of the waveform analysis from this array present systematic early-phase arrivals at the seismic stations located on the northern block of the Ganos fault which comprises geological units including older and more compact materials than that of the southern block. This difference in the arrival times causes the earthquake epicenters to shift further north than the real locations. In this preliminary results, the early-arrivals will be evaluated according to source azimuths and distances, and possible earth models and wave paths will be discussed. The results have implications for rupture directivity during future earthquakes as input for hazard and risk models for the Marmara region.</p>

Fractal and Convolutional Analysis for Deep Atmospheric Turbulence Using Machine Learning

2021 ◽  
Author(s):  
Nicholas Dudu ◽  
Arturo Rodriguez ◽  
Gael Moran ◽  
Jose Terrazas ◽  
Richard Adansi ◽  
...  
Keyword(s):  
Fractal Dimension ◽  
Atmospheric Turbulence ◽  
Isotropic Turbulence ◽  
Passive Scalar ◽  
Counting Method ◽  
Data Set ◽  
Box Counting ◽  
Box Counting Dimension ◽  
Self Similar ◽  
Box Counting Method

Abstract Atmospheric turbulence studies indicate the presence of self-similar scaling structures over a range of scales from the inertial outer scale to the dissipative inner scale. A measure of this self-similar structure has been obtained by computing the fractal dimension of images visualizing the turbulence using the widely used box-counting method. If applied blindly, the box-counting method can lead to misleading results in which the edges of the scaling range, corresponding to the upper and lower length scales referred to above are incorporated in an incorrect way. Furthermore, certain structures arising in turbulent flows that are not self-similar can deliver spurious contributions to the box-counting dimension. An appropriately trained Convolutional Neural Network can take account of both the above features in an appropriate way, using as inputs more detailed information than just the number of boxes covering the putative fractal set. To give a particular example, how the shape of clusters of covering boxes covering the object changes with box size could be analyzed. We will create a data set of decaying isotropic turbulence scenarios for atmospheric turbulence using Large-Eddy Simulations (LES) and analyze characteristic structures arising from these. These could include contours of velocity magnitude, as well as of levels of a passive scalar introduced into the simulated flows. We will then identify features of the structures that can be used to train the networks to obtain the most appropriate fractal dimension describing the scaling range, even when this range is of limited extent, down to a minimum of one order of magnitude.

scholarly journals Transport and storage of anthropogenic C in the North Atlantic Subpolar Ocean

2018 ◽  
Vol 15 (14) ◽  
pp. 4661-4682 ◽  
Author(s):  
Virginie Racapé ◽  
Patricia Zunino ◽  
Herlé Mercier ◽  
Pascale Lherminier ◽  
Laurent Bopp ◽  
...  
Keyword(s):  
Interannual Variability ◽  
North Atlantic ◽  
General Circulation ◽  
Meridional Overturning Circulation ◽  
Intermediate Water ◽  
Data Set ◽  
The North ◽  
Storage Rate ◽  
The North Atlantic ◽  
And Storage

Abstract. The North Atlantic Ocean is a major sink region for atmospheric CO2 and contributes to the storage of anthropogenic carbon (Cant). While there is general agreement that the intensity of the meridional overturning circulation (MOC) modulates uptake, transport and storage of Cant in the North Atlantic Subpolar Ocean, processes controlling their recent variability and evolution over the 21st century remain uncertain. This study investigates the relationship between transport, air–sea flux and storage rate of Cant in the North Atlantic Subpolar Ocean over the past 53 years. Its relies on the combined analysis of a multiannual in situ data set and outputs from a global biogeochemical ocean general circulation model (NEMO–PISCES) at 1∕2∘ spatial resolution forced by an atmospheric reanalysis. Despite an underestimation of Cant transport and an overestimation of anthropogenic air–sea CO2 flux in the model, the interannual variability of the regional Cant storage rate and its driving processes were well simulated by the model. Analysis of the multi-decadal simulation revealed that the MOC intensity variability was the major driver of the Cant transport variability at 25 and 36∘ N, but not at OVIDE. At the subpolar OVIDE section, the interannual variability of Cant transport was controlled by the accumulation of Cant in the MOC upper limb. At multi-decadal timescales, long-term changes in the North Atlantic storage rate of Cant were driven by the increase in air–sea fluxes of anthropogenic CO2. North Atlantic Central Water played a key role for storing Cant in the upper layer of the subtropical region and for supplying Cant to Intermediate Water and North Atlantic Deep Water. The transfer of Cant from surface to deep waters occurred mainly north of the OVIDE section. Most of the Cant transferred to the deep ocean was stored in the subpolar region, while the remainder was exported to the subtropical gyre within the lower MOC.

scholarly journals Monitoring compliance with sulfur content regulations of shipping fuel by in situ measurements of ship emissions

2015 ◽  
Vol 15 (17) ◽  
pp. 10087-10092 ◽  
Author(s):  
L. Kattner ◽  
B. Mathieu-Üffing ◽  
J. P. Burrows ◽  
A. Richter ◽  
S. Schmolke ◽  
...  
Keyword(s):  
Sulfur Content ◽  
Air Pollutant ◽  
Monitoring Site ◽  
Data Set ◽  
The North ◽  
Position Data ◽  
Gas Measurements ◽  
Set Up ◽  
Carbon Dioxide Co2

Abstract. In 1997 the International Maritime Organisation (IMO) adopted MARPOL Annex VI to prevent air pollution by shipping emissions. It regulates, among other issues, the sulfur content in shipping fuels, which is transformed into the air pollutant sulfur dioxide (SO2) during combustion. Within designated Sulfur Emission Control Areas (SECA), the sulfur content was limited to 1 %, and on 1 January 2015, this limit was further reduced to 0.1 %. Here we present the set-up and measurement results of a permanent ship emission monitoring site near Hamburg harbour in the North Sea SECA. Trace gas measurements are conducted with in situ instruments and a data set from September 2014 to January 2015 is presented. By combining measurements of carbon dioxide (CO2) and SO2 with ship position data, it is possible to deduce the sulfur fuel content of individual ships passing the measurement station, thus facilitating the monitoring of compliance of ships with the IMO regulations. While compliance is almost 100 % for the 2014 data, it decreases only very little in 2015 to 95.4 % despite the much stricter limit. We analysed more than 1400 ship plumes in total and for months with favourable conditions, up to 40 % of all ships entering and leaving Hamburg harbour could be checked for their sulfur fuel content.

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