Estimating the Atlantic overturning at 26N using satellite altimetry [IUGG]Eleanor Frajka-Williams
See http://eleanorfrajka.com/moc-from-space/ Slides from IUGG meeting in Prague: Estimating the Atlantic overturning circulation at 26N from satellite altimetry.
Estimating the Atlantic overturning at 26N using satellite altimetry [IUGG]Eleanor Frajka-Williams
See http://eleanorfrajka.com/moc-from-space/ Slides from IUGG meeting in Prague: Estimating the Atlantic overturning circulation at 26N from satellite altimetry.
Deprem nerede olacak?
Neden OBS Deprem İzleme çalışması?
10 aylık OBS sismisite verisi ile Marmara denizi içinde çok aktif ve az aktif alanların tespiti yapılmış. Aynı süre içerisinde normal deprem istasyonları ile yapılan deprem verisinin 7 misli daha fazla verinin bu şekilde kayıt edildiği belirtiliyor. İlave olarak, deniz tabanında ki faya yakın OBS kayıtçılar ile dış merkez hataları çok minimize ediliyor ve ilave olarak sismik tomografi çalışması fay boyunca yapılabiliyor.
OBS depremler ile deprem tehlikesini doğru anlamak
Aktif olmayan alanların değişimi Marmara denizinin Doğu-Batı yönünde EŞİT değil ve bu farklılık üzerinden ekte verilen çalışmada bir sonuç öneriliyor. Beklenen İstanbul depreminin olacağından şüphe yok fakat esas araştırılan konu fay zonu'nun hangi alanının bu tür büyük bir depremi üretecek enerji birikimi kapasitesini araştırmak.
Aşağıda ki soruları doğal olarak bu paylaşımı okuyan birisi sorabilir.
Nerede olacağını bilmek neden önemli?
İstanbul deprem riski açısından olacak depremin hangi enlem ve boylam (dış merkez) ve derinlikte (iç merkez) olmasının bilinmesi ne yarar sağlar?
Kaynak: Figure 8 of Yamamato et. al., 2016. https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1002/2016JB013608
Deprem nerede olacak?
Neden OBS Deprem İzleme çalışması?
10 aylık OBS sismisite verisi ile Marmara denizi içinde çok aktif ve az aktif alanların tespiti yapılmış. Aynı süre içerisinde normal deprem istasyonları ile yapılan deprem verisinin 7 misli daha fazla verinin bu şekilde kayıt edildiği belirtiliyor. İlave olarak, deniz tabanında ki faya yakın OBS kayıtçılar ile dış merkez hataları çok minimize ediliyor ve ilave olarak sismik tomografi çalışması fay boyunca yapılabiliyor.
OBS depremler ile deprem tehlikesini doğru anlamak
Aktif olmayan alanların değişimi Marmara denizinin Doğu-Batı yönünde EŞİT değil ve bu farklılık üzerinden ekte verilen çalışmada bir sonuç öneriliyor. Beklenen İstanbul depreminin olacağından şüphe yok fakat esas araştırılan konu fay zonu'nun hangi alanının bu tür büyük bir depremi üretecek enerji birikimi kapasitesini araştırmak.
Aşağıda ki soruları doğal olarak bu paylaşımı okuyan birisi sorabilir.
Nerede olacağını bilmek neden önemli?
İstanbul deprem riski açısından olacak depremin hangi enlem ve boylam (dış merkez) ve derinlikte (iç merkez) olmasının bilinmesi ne yarar sağlar?
Kaynak: Figure 8 of Yamamato et. al., 2016. https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1002/2016JB013608
Conclusions
• Studyingthecurrentstateofsub-seapermafrost is of critical importance in order to elucidate the time scale of the ongoing process;
• Giventhatspatialandtemporalvariabilityof methane releases is very high, this underscores importance of establishing monitoring network over the ESAS;
• ConsideringthesignificanceoftheESAS methane reservoir and enhancing mechanism of its destabilization, this region should be considered the most potential in terms of possible climate change caused by abrupt release of methane.
DSD-INT 2018 Characterizing the drivers of coral reef hydrodynamics at the Ro...Deltares
Presentation by Camille Grimaldi, University of Western Australia, Australia, at the Delft3D - User Days (Day 2: Hydrodynamics), during Delft Software Days - Edition 2018. Tuesday, 13 November 2018, Delft.
Thermohaline Circulation & Climate ChangeArulalan T
Today I have presented "The Thermohaline Circulation and Climate Change" as Mini-Project for our Science of Climate Change Course ! We can expect THC shutdown around 2050s... OMG ! Yes, we can expect "The Day After Tomorrow" around 2100... All the images credited to the reference papers except one T-S-Sigmat created by me using CDAT5.2.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
Sea Level Changes as recorded in nature itselfIJERA Editor
The science of sea level changes is quite multi-facetted. The level of the oceans is always changing, both vertically and horizontally. We have documented these changes quite carefully. After the last glaciation maximum, sea level has risen in the order of 120 m. This rise has been oscillatory. We can set frames on the maximum rate of a sea level rise; at the most rapid ice-melting after the Last Ice Age, sea level rose at about 10 ±1 mm/yr. The thermal expansion of water is, of course, a function of the water column heated; hence the effect is zero at the shore where there is no water to expand. The claim by the IPCC on a present sea level rise is greatly exaggerated. Coastal tide gauges give relative rates in the order of 0-2 mm/yr. The value of the absolute rise in sea level varies between 0.0 and 1.1 mm/yr. There are firm reasons to downgrade, even neglect, the fear of a disastrous coastal flooding in the present century.
Southern Hemisphere atmospheric circulation: impacts on Antarctic climate and...Andrew Russell
Presentation given at the PAGES symposium in Chile in October 2010. (NB I gave this talk before O'Donnell et al. was published so I'd probably do it differently now.)
diurnal temperature range trend over North Carolina and the associated mechan...Sayem Zaman, Ph.D, PE.
This study seeks to investigate the variability and presence of trends in the diurnal surface air temperature range
(DTR) over North Carolina (NC) for the period 1950–2009. The significance trend test and the magnitude of trends were determined using the non-parametric Mann–Kendall test and the Theil–Sen approach, respectively.
Statewide significant trends (p b 0.05) of decreasing DTR were found in all seasons and annually during the analysis period. The highest (lowest) temporal DTR trends of magnitude −0.19 (−0.031) °C/decade were found in summer (winter). Potential mechanisms for the presence/absence of trends in DTR have been highlighted. Historical
data sets of the three main moisture components (precipitation, total cloud cover (TCC), and soil moisture) and
the two major atmospheric circulation modes (North Atlantic Oscillation and Southern Oscillation) were used for
correlation analysis. The DTRs were found to be negatively correlated with the precipitation, TCC, and soil moisture across the state for all the seasons and annual basis. It appears that the moisture components related better to the DTR than to the atmospheric circulation modes.
Effects of episodic fluid flow on hydrocarbon migration inth.docxtoltonkendal
Effects of episodic fluid flow on hydrocarbon migration in
the Newport-Inglewood Fault Zone, Southern California
B. JUNG1, G. GARVEN 2 AND J. R. BOLES3
1Department of Earth Sciences, Uppsala University, Uppsala, Sweden; 2Department of Earth and Ocean Sciences, Tufts
University, Medford, MA, USA; 3Department of Earth Science, University of California, Santa Barbara, CA, USA
ABSTRACT
Fault permeability may vary through time due to tectonic deformations, transients in pore pressure and effective
stress, and mineralization associated with water-rock reactions. Time-varying permeability will affect subsurface
fluid migration rates and patterns of petroleum accumulation in densely faulted sedimentary basins such as those
associated with the borderland basins of Southern California. This study explores the petroleum fluid dynamics of
this migration. As a multiphase flow and petroleum migration case study on the role of faults, computational
models for both episodic and continuous hydrocarbon migration are constructed to investigate large-scale fluid
flow and petroleum accumulation along a northern section of the Newport-Inglewood fault zone in the Los
Angeles basin, Southern California. The numerical code solves the governing equations for oil, water, and heat
transport in heterogeneous and anisotropic geologic cross sections but neglects flow in the third dimension for
practical applications. Our numerical results suggest that fault permeability and fluid pressure fluctuations are cru-
cial factors for distributing hydrocarbon accumulations associated with fault zones, and they also play important
roles in controlling the geologic timing for reservoir filling. Episodic flow appears to enhance hydrocarbon accu-
mulation more strongly by enabling stepwise build-up in oil saturation in adjacent sedimentary formations due to
temporally high pore pressure and high permeability caused by periodic fault rupture. Under assumptions that
fault permeability fluctuate within the range of 1–1000 millidarcys (10�15–10�12 m2) and fault pressures fluctuate
within 10–80% of overpressure ratio, the estimated oil volume in the Inglewood oil field (approximately 450 mil-
lion barrels oil equivalent) can be accumulated in about 24 000 years, assuming a seismically induced fluid flow
event occurs every 2000 years. This episodic petroleum migration model could be more geologically important
than a continuous-flow model, when considering the observed patterns of hydrocarbons and seismically active
tectonic setting of the Los Angeles basin.
Key words: episodic fluid flow, fluid flow in faults, multiphase flow in siliciclastic sedimentary basins, petroleum
migration
Received 21 May 2013; accepted 16 October 2013
Corresponding author: Byeongju Jung, Department of Earth Sciences, Uppsala University, Gl227 Geocentrum,
Villav€agen 16B, 753 36 Uppsala, Sweden.
Email: [email protected] Tel: +46 018 471 2264. Fax: +1 617 627 3584.
Geofluids (2014) 14,.
From the Arctic to the Tropics: The U.S. UNCLOS Bathymetric Mapping ProgramLarry Mayer
Since CHC2006, the University of New Hampshire’s Center for Coastal & Ocean Mapping/Joint Hydrographic Center has mapped with multibeam, the bathymetry of an additional ~220,000 km2 of seafloor in areas as diverse as the Arctic, the Northern Marianas of the western Pacific and the Gulf of Mexico. The mapping supports any potential U.S. submission for of extended continental shelves under Article 76 of the United Nations Convention of the Law of the Sea. Consequently, the mapping has concentrated on capturing the complete extent of the 2500-m isobath and the zone where the Article 76-defined foot of the slope exists. In practice, the complete area between ~1500 and ~4500 m water depths is mapped in each region (with the exception of the Arctic Ocean). The data have been collected in conditions that range from harsh Arctic sea ice to the calms of the Philippine Sea tropics. Although, some of the conditions have limited the quality of some of the data, the data quality is generally quite good and geological surprises have been uncovered on each of the cruises.
Similar to Circulation of the North Atlantic Ocean During the 1990's as Determine by Lagrangian Drifters (20)
Environmentally Adaptive Deployment of Lagrangian Instrumentation Using a Sub...David Fratantoni
Article published in Marine Technology Society Journal: Environmentally Adaptive Deployment of Lagrangian Instrumentation Using a Submerged Autonomous Launch Platform (SALP)
(May 29th, 2024) Advancements in Intravital Microscopy- Insights for Preclini...Scintica Instrumentation
Intravital microscopy (IVM) is a powerful tool utilized to study cellular behavior over time and space in vivo. Much of our understanding of cell biology has been accomplished using various in vitro and ex vivo methods; however, these studies do not necessarily reflect the natural dynamics of biological processes. Unlike traditional cell culture or fixed tissue imaging, IVM allows for the ultra-fast high-resolution imaging of cellular processes over time and space and were studied in its natural environment. Real-time visualization of biological processes in the context of an intact organism helps maintain physiological relevance and provide insights into the progression of disease, response to treatments or developmental processes.
In this webinar we give an overview of advanced applications of the IVM system in preclinical research. IVIM technology is a provider of all-in-one intravital microscopy systems and solutions optimized for in vivo imaging of live animal models at sub-micron resolution. The system’s unique features and user-friendly software enables researchers to probe fast dynamic biological processes such as immune cell tracking, cell-cell interaction as well as vascularization and tumor metastasis with exceptional detail. This webinar will also give an overview of IVM being utilized in drug development, offering a view into the intricate interaction between drugs/nanoparticles and tissues in vivo and allows for the evaluation of therapeutic intervention in a variety of tissues and organs. This interdisciplinary collaboration continues to drive the advancements of novel therapeutic strategies.
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
This pdf is about the Schizophrenia.
For more details visit on YouTube; @SELF-EXPLANATORY;
https://www.youtube.com/channel/UCAiarMZDNhe1A3Rnpr_WkzA/videos
Thanks...!
Richard's entangled aventures in wonderlandRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
Seminar of U.V. Spectroscopy by SAMIR PANDASAMIR PANDA
Spectroscopy is a branch of science dealing the study of interaction of electromagnetic radiation with matter.
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Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
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Circulation of the North Atlantic Ocean During the 1990's as Determine by Lagrangian Drifters
1. We have assembled a new North Atlantic climatology of near-surface velocity and eddy kinetic energy (EKE) based exclusively on 15-m
drogued surface drifter trajectories measured between 1990 and 2000. Our objective is to define the state of the North Atlantic surface
circulation during the 1990’s and provide a reference point for both synoptic circulation studies (e.g. theWOCE Atlantic Circulation and
Climate Experiment) and studies of circulation variability associated with inter-decadal climate variability. In this poster we present
decadal-mean circulation statistics computed on a one-degree grid and compare these results with satellite altimetry measurements
and with previous drifter-based studies in the North Atlantic.
The satellite-tracked surface drifters
used in this study are similar in construc-
tion to the WOCE/Tropical Ocean-Global
Atmosphere (TOGA) Lagrangian drifter
described by Sybrandy and Niiler (1991).
All drifters were tracked using ARGOS and
were fitted with a submerged flexible
drogue which hung suspended at a central
depth of 15 m beneath a buoyant surface
float [Figure 1]. Approximately 1500
individual drifter trajectories totaling
nearly 300,000 drifter-days of position and
velocity information were acquired from
the archives of the Global Drifter Data
Assembly Center at NOAA/AOML in
Miami, Florida, U.S.A. Initial processing of
the data at AOML, including quality
control and temporal interpolation, is
described in detail in Hansen and Herman
(1989) and Hansen and Poulain (1996).
Drifter trajectories were truncated when
drogues detached as indicated by an
onboard submergence sensor or strain
gauge. The final data product consists of 6-
hourly interpolated position, velocity, and
surface temperature measurements.
The drifter trajectories used in this
analysis are shown in Figure 2. The
population of drifters in the North Atlantic
increased during the 1990’s and does not
exhibit any particular seasonal bias
[Figure 3]. The regional distribution of drifter trajectories varies signifi-
cantly throughout the decade [Figure 4]. Note the shift in observational
emphasis from the Gulf Stream region (1990-1992) to the eastern subtropi-
cal gyre (1992-1995) to the subpolar gyre (1995-1998) and finally to the
western tropical Atlantic and Caribbean Sea (1997-1999).
A summary of the fastest- and slowest-moving drifters is shown in Figure
5. The fastest drifter motions were found near the equator, along the
western boundary, in the eastward Gulf Stream extension, on the eastern
and western coasts of Greenland, and in a narrow eastward band corre-
sponding to the Azores Current. The greatest number of slow-moving
drifters were found in the eastern subtropical Atlantic.
1000˚W 900˚W 800˚W 700˚W 600˚W 500˚W 400˚W 300˚W 200˚W 100˚W 100˚E
10˚S
10˚N
20˚N
30˚N
40˚N
50˚N
60˚N
70˚N
All Trajectories 1990-2000
0˚
0˚
Fabric Drogue
Surface Float
Subsurface Float
PhotographcourtesyofMarkSwenson,NOAA/AOML
FIGURE 1: AWOCE/TOGA
Lagrangian drifter on the surface
shortly after being deployed. The
fabric drogue is weighted and will
quickly sink to a vertical position
beneath the surface float.
FIGURE 2: A
composite dia-
gram of all
drifter trajecto-
ries used in the
present analy-
sis. All trajec-
tory segments
shown were
measured be-
tween January
1990 and June
1999. Note the
very poorly
sampled region
in the south-
eastern sub-
tropical gyre.
1990 1995 2000
Year
0
50
100
150
200
NumberofObservations(1000's)
J F M A M J J A S O N D
Month
a b
Speed > 40 cm/s
80W 60W 40W 20W 0
Speed < 10 cm/s
80W 60W 40W 20W 0
0
20N
40N
60N
a b
Overview
FIGURE 3: Temporal distribu-
tion of drifter data presented
in histogram form. The verti-
cal axis indicates the number
of 6-hourly measurements of
position and velocity. (a) Dis-
tribution by year from 1990
onwards (through June 1999). (b) Distribution by month.
FIGURE 5: A summary of the fastest and slowest drifters in the present database. Only
trajectory segments meeting the specified speed criterion for a contiguous 36-hour period
are plotted. (a) Fast drifters, with speeds exceeding 40 cm/s. The fastest drifters were found
near the equator, along the western boundary, in the eastward Gulf Stream extension, on
the eastern and western coasts of Greenland, and in a narrow eastward band correspond-
ing to the Azores Current. (b) Slow drifters, with speeds less than 10 cm/s. The greatest
number of slow-moving drifters were found in the eastern subtropical Atlantic.
Using historical hydrographic observations Curry and McCartney (2000)
describe a relationship between baroclinic ocean transport in the
subtropical gyre and the phase of the atmospheric North Atlantic Oscilla-
tion (NAO). We now consider whether the present drifter data, in combina-
tion with previous drifter observations, can be used to directly measure
interdecadal changes in surface circulation strength or character.
Richardson (1983) synthesized North Atlantic surface drifter measure-
ments during the period 1977-1980. This time interval coincides with a
period during which the NAO index (Hurrell, 1995) was relatively low
[Figure 10]. In contrast, the first half of the 1990’s were characterized by
particularly large values of the NAO index. Large values of the NAO index
correspond to stronger westerly winds and tend to result in a more
northerly Gulf Stream position (Taylor and Stephens, 1998).We hypoth-
esize that variations in the baroclinic transport of the subtropical gyre/Gulf
Stream system associated with these NAO index extrema should result in
observable changes in the near surface circulation.
1998
Gulf Stream
1
Newfoundland
Basin
3
Gulf Stream
Extension
2
North Atlantic
Current
4
70W 50W 30W
40N
50N
0
500
1000
1500
2000
2500
Gulf Stream Gulf Stream
Extension
Newfoundland
Basin
North Atlantic
Current
1990-2000 (This study)
1977-1980 (Richardson, 1983)
EKE(cm2/s2)
1 32 4
Acknowledgements
Eddy kinetic energy derived fromTOPEX and ERS altimeters was provided by Nicolas Ducet of
CLS Space Oceanography Division, France. Processing of the raw drifter data was performed at the
Global Drifter Data Assembly Center at NOAA/AOML under the direction of Mark Swenson and
Mayra Pazos.This work was supported by the National Oceanic and Atmospheric Administration as
part of a cooperative project with Dr. Robert Cheney of the NOAA Laboratory for Satellite Altimetry.
References
Hansen, D.V. and A. Herman, Temporal sampling requirements surface drifter buoys in the tropical Pacific, J. Atmos.
Ocean. Tech., 6, 599-607, 1989.
Hansen, D.V. and P.-M. Poulain, Quality control and interpolations of WOCE/TOGA drifter data, J. Atmos. Ocean.
Tech., 13, 900-909, 1996.
Hurrell, J. W., Decadal trends in the North Atlantic Oscillation: Regional temperatures and precipitation. Science,
269, 676-679, 1995.
Curry, R.G. and M.S. McCartney, Ocean Gyre Circulation Changes Associated with the North Atlantic Oscillation,
submitted to J. Phys. Oceanogr., 2000.
Richardson, P. L., Eddy kinetic energy in the North Atlantic from surface drifters, J. Geophys. Res., 88, 4355-4367, 1983.
Sybrandy, A. L. and P. P. Niiler, WOCE/TOGA Lagrangian drifter construction manual, SIO Ref. 91/6, WOCE Rep. 63,
58 pp., Scripps Institution of Oceanography, La Jolla, Calif., 1991.
Taylor, A. H., and J. A. Stephens,The North Atlantic Oscillation and the latitude of the Gulf Stream,Tellus, 50A, 134-142, 1998.
As additional drifter data from the 1990’s become available (or are made
known to us by others) we will continue to update and improve this
climatology. We are presently extending our study of the drifter-derived
quasi-Eulerian velocity and EKE fields to include joint analysis of contem-
porary hydrographic data, TOPEX and ERS altimetry, and surface wind
products. Drifter-derived surface velocity and EKE data on one- and two-
degree grids are available for general use by the oceanographic commu-
nity. Please contact the lead author for details (dfratantoni@whoi.edu).
FIGURE 4: Temporal and spatial distribution of drifter
trajectories for each year from 1990-1999. Note the shift
in observational emphasis from the Gulf Stream region
(1990-1992) to the eastern subtropical gyre (1992-1995)
to the subpolar gyre (1995-1998) and finally to the west-
ern tropical Atlantic and Caribbean Sea (1997-1999).
We compared the Richardson (1983) quasi-Eulerian circulation statistics
with those resulting from our 1990-2000 analysis. There are significant
differences in both data volume and spatial distribution between the two
climatologies (the 1990-2000 climatology contains almost an order of
magnitude more data than the 1977-1980 analysis). We tried to minimize
the importance of these differences by concentrating our comparisons in a
region encompassing the Gulf Stream and the North Atlantic Current,
features that are reasonable well sampled in both analyses. In addition, we
focused our comparisons on EKE rather than on the mean velocity field. As
found by Richardson (1983), EKE exceeds the energy of the mean circula-
tion over most of the North Atlantic by a factor of about 10-20. This strong
variability makes it difficult to accurately resolve the mean circulation
without enormous quantities of data. The present 1990-2000 climatology is
sufficiently data-dense to compute meaningful means over large areas —
the 1977-1980 dataset is not.
-10
0
10
20
30
40
50
U(cm/s)
0
500
1000
1500
2000
2500
3000
EKE(cm2/s2)
30354045
Latitude
30354045
Latitude
1990-2000
1977-1980
55W65W
55W65W
1990-2000
1977-1980
1990-2000
1977-1980
Gulf Stream Sections at 65W and 55W
We computed EKE within four spatial subregions [Figure 11] using both
climatologies. In the Gulf Stream, Gulf Stream Extension, and Newfound-
land Basin subregions we find an increase in EKE in the 1990-2000
climatology relative to the 1977-1980 measurements [Figure 12]. However,
within the computed 90% confidence limits there has been no significant
change in the regionally-averaged EKE over the last 20 years. Note that the
Richardson (1983) climatology includes both drogued and undrogued
drifter trajectories. This suggests that the 1977-1980 EKE values could be
overestimates of the actual EKE, particularly in the Gulf Stream region
where large wind stress and strong synoptic atmospheric variability may
account for much of the motion of an undrogued drifter.
We compared sections of zonal velocity and EKE across the Gulf Stream at
55W and 65W [Figure 13] and found little difference in the structure of the
zonal Gulf Stream jet. There is a slight northward shift in the location of the
mean jet and the associated EKE maximum at 55W in the 1990-2000
climatology relative to the 1977-1980 realization.While the sense of this shift is
consistent with our expectations based on the phase of the NAO (e.g.Taylor
and Stephens, 1998), the magnitude of the shift is not statistically significant.
To summarize, we find that Lagrangian observations of surface velocity
and EKE in the vicinity of the Gulf Stream do not show a significant change
in circulation strength or character from the late 1970’s to the 1990’s.
Although the differences we observed in regional eddy variability and in
the structure of the Gulf Stream jet are suggestive, the available data are
insufficient to prove or disprove our initial hypothesis.
-6
-4
-2
0
2
4
6
1960 1970 1980 1990 2000
Year
NAOIndex
North Atlantic Oscillation Index
This study
Richardson (1983)
5-year mean
FIGURE 10: The North At-
lantic Oscillation (NAO)
index for the past 40 years.
The black curve corre-
sponds to a 5-year running
mean. Intervals corre-
sponding to the Richardson
(1983) surface drifter
analysis (1977-1980) and
the present analysis (1990-
2000) are shaded.
FIGURE 13: A comparison of the meridional structure of zonal velocity (upper panels)
and eddy kinetic energy (EKE; lower panels) between the present surface drifter clima-
tology (1990-2000; red) and the previous 1977-1980 (blue) climatology of Richardson
(1983). There is a slight (but statistically insignificant) northward shift of the Gulf
Stream and its associated EKE maximum at 55W.
FIGURE 11: Eddy kinetic energy (EKE)
was computed within four rectangular
subregions corresponding
to areas of relatively dis-
tinct circulation character.
(1) the Gulf Stream; (2)
the eastward
Gulf Stream
Extension; (3)
the Newfound-
land Basin, and (4) the
North Atlantic Current. Tra-
jectories from a single year
of the 1990-2000 drifter cli-
matology are shown.
FIGURE 12: A compari-
son of eddy kinetic en-
ergy (EKE) between the
present surface drifter
climatology (1990-
2000; red) and the pre-
vious 1977-1980 (blue)
climatology of
Richardson (1983). EKE
was computed in four
subregions (see Figure
11). The vertical black
bars denote the 90%
confidence interval.
Drifter velocity was computed using a cubic spline
function at each 6-hourly interpolated position. The
resulting velocities were grouped into spatial and temporal
bins to construct quasi-Eulerian fields of velocity and eddy
kinetic energy (EKE). EKE was defined as one-half the sum
of the zonal and meridional velocity variances within each
grid box. The number of individual velocity observations in
each one-degree square is shown in Figure 6.
The decadal-mean surface velocity field for the North
Atlantic constructed at one-degree resolution for the period
January 1990 – June 1999 is shown in Figure 7a. The
corresponding EKE field is shown in Figure 7b. Note the
enhanced EKE in the vicinity of the Gulf Stream down-
stream of the New England Seamounts (40N), and in the
Labrador Sea near theWest Greenland Current (60N). There
is also a zonal band of elevated EKE near 34N associated
with the Azores Current. More detailed views of the surface
circulation in the subpolar gyre, the Gulf Stream region,
and the Caribbean Sea are shown in Figure 8.
In Figure 9 we compare EKE computed from our surface
drifter climatology with EKE derived from TOPEX and ERS
altimetry during the period 1992-1998. The general spatial
distributions of EKE are similar with highest values
located within the Gulf Stream downstream of the New
England Seamounts. The enhanced EKE in the Labrador
Sea seen in Figure 9a is absent in the altimeter-derived
EKE field. This is probably due to the choice of a constant
(rather than latitude-dependent) horizontal lengthscale in
the altimeter EKE calculations. RMS sea level anomalies
from ERS and TOPEX confirm the region of enhanced
variability in the vicinity of the West Greenland Current as
seen in the drifter-based EKE field.
70W 60W 50W 40W 30W 20W 10W
30N
40N
50N
60N
Surface Drifter Climatology
1990-2000
Eddy Kinetic Energy (cm2/s2)
TOPEX and ERS Altimetry
1992-1997
Variance Axes
1000 cm2/s2
a
Data Source: Saskia Esselborn, Institut fur Meereskunde, Hamburg, Germany
300 400 500 750 1000 1500 2000 2500 3000
70W 60W 50W 40W 30W 20W 10W
30N
40N
50N
60N
b
FIGURE 8: Detailed view of mean velocity field in three regions. (a) The Labrador Sea and Subpolar
Gyre. (b) The Gulf Stream and its eastward extension.(c) The Caribbean Sea.
60W 50W 40W 30W 20W 10W 0 10E
50N
60N
70N
50 cm/s
10 cm/s
80W
30N
40N
50N
70W 60W 50W 40W 30W
50 cm/s
10 cm/s
90W 80W 70W 60W
10N
20N
30N
0 15 30 100
50 cm/s
10 cm/s
FIGURE 6: Number of individual 6-hourly velocity observations per one-degree square.
FIGURE 7: (a) A decadal-mean surface velocity field for the North Atlantic computed by aver-
aging northward and eastward drifter velocities into one-degree square bins over the period
January 1990 – June 1999.Vectors are only shown for bins containing more than 100 individual
observations. Error ellipses correspond to one standard error in the zonal and meridional di-
rections.We assumed a 10-day Lagrangian integral timescale in the error computations.
FIGURE 7: (b) The corresponding field of eddy kinetic energy (EKE). Regions with insufficient
data (less than 100 observations per one-degree square) are shaded gray. Note the enhanced
EKE in the vicinity of the Gulf Stream downstream of the New England Seamounts (40N), and
in the Labrador Sea near the West Greenland Current (60N).
90W 80W 70W 60W 50W 40W 30W 20W 10W 0
0
10N
20N
30N
40N
50N
60N
70N
<100
100-200
200-500
>500
80W 70W 60W 50W 40W 30W 20W 10W 0 10E
20N
30N
40N
50N
60N
70N
0 15 30 100
50 cm/s
10 cm/s
Mean Surface Velocity (cm/s)
80W 70W 60W 50W 40W 30W 20W 10W 0 10E
20N
30N
40N
50N
60N
70N
0 100 200 300 400 500 750 1000 1500 2000 2500 3000
Eddy Kinetic Energy (cm2/s2) FIGURE 9: Eddy kinetic energy (EKE) in the subtropical and
subpolar gyres computed from (a) the present surface drifter
climatology, and (b) a blend of ERS and TOPEX satellite altim-
etry for an overlapping time period. The contour intervals and
shading are identical.