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Author |
Branger Karine, Drillet Yann, Houssais Marie-Nolle, Testor Pierre, Bourdall-Badie Romain, Alhammoud Bahjat, Bozec Alexandra, Mortier Laurent, Bouruet-Aubertot Pascale, Crpon Michel, |
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Title |
Impact of the spatial distribution of the atmospheric forcing on water mass formation in the Mediterranean Sea
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Type |
Journal Article |
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Year |
2010 |
Publication |
J. Geophys. Res. |
Abbreviated Journal |
J. Geophys. Res. |
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Volume |
115 |
Issue |
C12 |
Pages |
C12041 - |
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Keywords |
Mediterranean Sea, deep water formation, numerical modeling, atmospheric forcing, 4504 Oceanography: Physical: Air/sea interactions, 4215 Oceanography: General: Climate and interannual variability, 4513 Oceanography: Physical: Decadal ocean variability, 4283 Oceanography: General: Water masses, 4520 Oceanography: Physical: Eddies and mesoscale processes, |
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Abstract |
The impact of the atmospheric forcing on the winter ocean convection in the Mediterranean Sea was studied with a high-resolution ocean general circulation model. The major areas of focus are the Levantine basin, the Aegean-Cretan Sea, the Adriatic Sea, and the Gulf of Lion. Two companion simulations differing by the horizontal resolution of the atmospheric forcing were compared. The first simulation (MED16-ERA40) was forced by air-sea fields from ERA40, which is the ECMWF reanalysis. The second simulation (MED16-ECMWF) was forced by the ECMWF-analyzed surface fields that have a horizontal resolution twice as high as those of ERA40. The analysis of the standard deviations of the atmospheric fields shows that increasing the resolution of the atmospheric forcing leads in all regions to a better channeling of the winds by mountains and to the generation of atmospheric mesoscale patterns. Comparing the companion ocean simulation results with available observations in the Adriatic Sea and in the Gulf of Lion shows that MED16-ECMWF is more realistic than MED16-ERA40. In the eastern Mediterranean, although deep water formation occurs in the two experiments, the depth reached by the convection is deeper in MED16-ECMWF. In the Gulf of Lion, deep water formation occurs only in MED16-ECMWF. This larger sensitivity of the western Mediterranean convection to the forcing resolution is investigated by running a set of sensitivity experiments to analyze the impact of different time-space resolutions of the forcing on the intense winter convection event in winter 1998–1999. The sensitivity to the forcing appears to be mainly related to the effect of wind channeling by the land orography, which can only be reproduced in atmospheric models of sufficient resolution. Thus, well-positioned patterns of enhanced wind stress and ocean surface heat loss are able to maintain a vigorous gyre circulation favoring efficient preconditioning of the area at the beginning of winter and to drive realistic buoyancy loss and mixing responsible for strong convection at the end of winter.
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Programme |
452 |
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Bachelor's thesis |
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AGU |
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ISSN |
0148-0227 |
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yes |
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Call Number |
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Serial |
2693 |
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Author |
Chisham G, Freeman M P, Abel G A, Bristow W A, Marchaudon A, Ruohoniemi J M, Sofko G J, |
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Title |
Spatial distribution of average vorticity in the high-latitude ionosphere and its variation with interplanetary magnetic field direction and season
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Type |
Journal Article |
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Year |
2009 |
Publication |
J. Geophys. Res. |
Abbreviated Journal |
J. Geophys. Res. |
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Volume |
114 |
Issue |
A9 |
Pages |
A09301 - |
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Keywords |
ionosphere, vorticity, field-aligned current, 2431 Ionosphere: Ionosphere/magnetosphere interactions, 2409 Ionosphere: Current systems, 2437 Ionosphere: Ionospheric dynamics, 2494 Ionosphere: Instruments and techniques, 2721 Magnetospheric Physics: Field-aligned currents and current systems, |
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Abstract |
We present a technique to measure the magnetic field-aligned vorticity of mesoscale plasma flows in the F region ionosphere using line-of-sight velocity measurements made by the Super Dual Auroral Radar Network (SuperDARN). Vorticity is often used as a proxy for magnetic field-aligned current (FAC) intensity in the ionosphere but also provides information about turbulent processes in the ionosphere and magnetosphere. Using 6 years (2000–2005 inclusive) of vorticity measurements made by six SuperDARN radars in the Northern Hemisphere, we have compiled, for the first time, maps of average vorticity across the northern polar ionosphere. These maps have been subdivided according to different seasonal and interplanetary magnetic field (IMF) conditions. The variations in the morphology of the vorticity maps with IMF direction match very closely those seen in maps of average FAC intensity (determined using different methods and instrumentation), suggesting that vorticity is a good proxy for FAC in an averaged sense. The variations in the morphology of the vorticity maps with season show differences from those seen in the FAC maps, illustrating that ionospheric conductance plays a major role in determining the differences between measurements of vorticity and FAC.
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312;911 |
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Bachelor's thesis |
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AGU |
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0148-0227 |
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yes |
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Call Number |
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Serial |
2084 |
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Author |
Zhang Yang, Ritsema Jeroen, Thorne Michael S, |
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Title |
Modeling the ratios of SKKS and SKS amplitudes with ultra-low velocity zones at the core-mantle boundary
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Type |
Journal Article |
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Year |
2009 |
Publication |
Geophys. Res. Lett. |
Abbreviated Journal |
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Volume |
36 |
Issue |
19 |
Pages |
L19303- |
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Keywords |
core-mantle boundary, SKS waves, amplitudes, 7203 Seismology: Body waves, 7208 Seismology: Mantle, 0545 Computational Geophysics: Modeling, |
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Programme |
133 |
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Bachelor's thesis |
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AGU |
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ISSN |
0094-8276 |
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yes |
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Call Number |
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Serial |
2966 |
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Author |
Herbaut C. and M.-N. Houssais |
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Title |
Response of the eastern North Atlantic subpolar gyre to the North Atlantic Oscillation |
Type |
Journal Article |
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Year |
2009 |
Publication |
GEOPHYSICAL RESEARCH LETTERS |
Abbreviated Journal |
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Volume |
36 |
Issue |
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Pages |
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Abstract |
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Programme |
452 |
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0094-8276 |
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Notes |
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Approved |
yes |
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Call Number |
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Serial |
6016 |
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Author |
Homberg, C.; Bergerat, F.; Angelier, J.; Garcia, S. |
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Title |
Fault interaction and stresses along broad oceanic transform zone: Tjrnes Fracture Zone, north Iceland |
Type |
Journal Article |
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Year |
2010 |
Publication |
Tectonics |
Abbreviated Journal |
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Volume |
29 |
Issue |
1 |
Pages |
TC1002 |
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Keywords |
oceanic transform; fault interaction; stresses; Iceland; slip transfer; 8150 Tectonophysics: Plate boundary: general; 8164 Tectonophysics: Stresses: crust and lithosphere; 8020 Structural Geology: Mechanics, theory, and modeling |
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Abstract |
Transform motion along oceanic transforms generally occurs along narrow faults zones. Another class of oceanic transforms exists where the plate boundary is quite large (∼100 km) and includes several subparallel faults. Using a 2-D numerical modeling, we simulate the slip distribution and the crustal stress field geometry within such broad oceanic transforms (BOTs). We examine the possible configurations and evolution of such BOTs, where the plate boundary includes one, two, or three faults. Our experiments show that at any time during the development of the plate boundary, the plate motion is not distributed along each of the plate boundary faults but mainly occurs along a single master fault. The finite width of a BOT results from slip transfer through time with locking of early faults, not from a permanent distribution of deformation over a wide area. Because of fault interaction, the stress field geometry within the BOTs is more complex than that along classical oceanic transforms and includes stress deflections close to but also away from the major faults. Application of this modeling to the 100 km wide Tjrnes Fracture Zone (TFZ) in North Iceland, a major BOT of the Mid-Atlantic Ridge that includes three main faults, suggests that the Dalvik Fault and the Husavik-Flatey Fault developed first, the Grismsey Fault being the latest active structure. Since initiation of the TFZ, the Husavik-Flatey Fault accommodated most of the plate motion and probably persists until now as the main plate structure. |
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Programme |
316 |
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AGU |
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ISSN |
0278-7407 |
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yes |
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Call Number |
IPEV @ Thierry.Lemaire @ |
Serial |
6062 |
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Author |
Legrand M, Preunkert S, Jourdain B, Galle H, Goutail F, Weller R, Savarino J, |
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Title |
Year-round record of surface ozone at coastal (Dumont d'Urville) and inland (Concordia) sites in East Antarctica
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Type |
Journal Article |
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Year |
2009 |
Publication |
J. Geophys. Res. |
Abbreviated Journal |
J. Geophys. Res. |
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Volume |
114 |
Issue |
D20 |
Pages |
D20306 - |
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Keywords |
Ozone, Antarctica, 0365 Atmospheric Composition and Structure: Troposphere: composition and chemistry, 0368 Atmospheric Composition and Structure: Troposphere: constituent transport and chemistry, 0330 Atmospheric Composition and Structure: Geochemical cycles, |
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Abstract |
Surface ozone is measured since 2004 at the coastal East Antarctic station of Dumont d'Urville (DDU) and since 2007 at the Concordia station located on the high East Antarctic plateau. Ozone levels at Concordia reach a maximum of 35 ppbv in July and a minimum of 21 ppbv in February. From November to January, sudden increases of the ozone level, up to 15–20 ppbv above average, often take place. They are attributed to local photochemical ozone production as previously seen at the South Pole. The detailed examination of the diurnal ozone record in summer at Concordia suggests a local photochemical ozone production of around 0.2 ppbv h-1 during the morning. The ozone record at DDU exhibits a maximum of 35 ppbv in July and a minimum of 18 ppbv in January. Mixing ratios at DDU are always higher than those at Neumayer (NM), another coastal Antarctic station. A noticeable difference in the ozone records at the two coastal sites lies in the larger ozone depletion events occurring from July to September at NM compared to DDU, likely due to stronger BrO episodes in relation with a larger sea ice coverage offshore that site. A second difference is the large day-to-day fluctuations which are observed from November to January at DDU but not at NM. That is attributed to a stronger impact at DDU than at NM of air masses coming from the Antarctic plateau. The consequences of such a high oxidizing property of the atmosphere over East Antarctica are discussed with regard to the dimethylsulfide (DMS) chemistry.
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Programme |
414;903;904;1011 |
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Address |
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Corporate Author |
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Thesis |
Bachelor's thesis |
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Publisher |
AGU |
Place of Publication |
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Editor |
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Language |
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Summary Language |
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Original Title |
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Series Title |
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Abbreviated Series Title |
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Series Volume |
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Series Issue |
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Edition |
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ISSN |
0148-0227 |
ISBN |
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Notes |
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Approved |
yes |
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Call Number |
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Serial |
2180 |
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Author |
Baroni, Mlanie; Savarino, Jol; Cole-Dai, J.; Rai, V.K.; Thiemens, M.H. |
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Title |
Anomalous sulfur isotope compositions of volcanic sulfate over the last millennium in Antarctic ice cores |
Type |
Journal Article |
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Year |
2008 |
Publication |
J. Geophys. Res. |
Abbreviated Journal |
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Volume |
113 |
Issue |
D20 |
Pages |
D20112 |
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Keywords |
sulfur isotope anomaly; volcanic eruption; ice cores; 0370 Atmospheric Composition and Structure: Volcanic effects; 0454 Biogeosciences: Isotopic composition and chemistry; 0473 Biogeosciences: Paleoclimatology and paleoceanography; 0724 Cryosphere: Ice cores; 1041 Geochemistry: Stable isotope geochemistry |
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Abstract |
The reconstruction of past volcanism from glaciological archives is based on the measurement of sulfate concentrations in ice. This method does not allow a proper evaluation of the climatic impact of an eruption owing to the uncertainty in classifying an event between stratospheric or tropospheric. This work develops a new method, using anomalous sulfur isotope composition of volcanic sulfate in order to identify stratospheric eruptions over the last millennium. The advantages and limits of this new method are established with the examination of the 10 largest volcanic signals in ice cores from Dome C and South Pole, Antarctica. Of the 10, seven are identified as stratospheric eruptions. Among them, three have been known to be stratospheric (Tambora, Kuwae, the 1259 Unknown Event) and they exhibit anomalous sulfur isotope compositions. Three unknown events (circa 1277, 1230, 1170 A.D.) and the Serua eruption have been identified as stratospheric eruptions, which suggests for the first time that they could have had significant climatic impact. However, the Kuwae and the 1259 Unknown Event stratospheric eruptions exhibit different anomalous sulfur isotope compositions between South Pole and Dome C samples. Differences in sulfate deposition and preservation patterns between the two sites can help explain these discrepancies. This study shows that the presence of an anomalous sulfur isotope composition of volcanic sulfate in ice core indicates a stratospheric eruption, but the absence of such composition does not necessarily lead to the conclusion of a tropospheric process because of differences in the sulfate deposition on the ice sheet. |
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Programme |
1011 |
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Publisher |
AGU |
Place of Publication |
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Edition |
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ISSN |
0148-0227 |
ISBN |
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Medium |
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Notes |
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Approved |
yes |
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Call Number |
IPEV @ Thierry.Lemaire @ |
Serial |
6048 |
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Author |
Melanie Baroni, Joel Savarino, Jihong Cole-Dai, Vinai K. Rai and Mark H. Thiemens |
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Title |
Anomalous sulfur isotope compositions of volcanic sulfate over the last millennium in Antarctic ice cores |
Type |
Journal Article |
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Year |
2008 |
Publication |
JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES |
Abbreviated Journal |
J. Geophys. Res. |
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Volume |
113 |
Issue |
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Pages |
D20112 |
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Keywords |
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Abstract |
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Programme |
1011 |
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ISSN |
0148-0227 |
ISBN |
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Notes |
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Approved |
yes |
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Call Number |
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Serial |
5827 |
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Author |
Preunkert, S.; Jourdain, B.; Legrand, M.; Udisti, R.; Becagli, S.; Cerri, O. |
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Title |
Seasonality of sulfur species (dimethyl sulfide, sulfate, and methanesulfonate) in Antarctica: Inland versus coastal regions |
Type |
Journal Article |
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Year |
2008 |
Publication |
Journal of geophysical research-atmospheres |
Abbreviated Journal |
J. Geophys. Res. |
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Volume |
113 |
Issue |
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Pages |
D15302 |
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Keywords |
sulfur cycle; DMS; 0365 Atmospheric Composition and Structure: Troposphere: composition and chemistry; 0315 Atmospheric Composition and Structure: Biosphere/atmosphere interactions; 0305 Atmospheric Composition and Structure: Aerosols and particles |
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Abstract |
To gain a better understanding of sulfate and methanesulfonate (MS?) signals recorded in central Antarctic ice cores in terms of past atmospheric changes, an atmospheric year-round study of these aerosols was performed in 2006 at the Concordia station (75°S, 123°E) located on the high Antarctic plateau. In addition, a year-round study of dimethyl sulfide (DMS), the gaseous precursor of sulfur aerosol, was conducted in 2007. The DMS mixing ratio remains below 1 pptv from October to January and exhibits a maximum of 10 pptv during the first half of winter (from April to July). Surprisingly, the well-marked maximum of sulfur aerosol recorded in January at coastal Antarctic sites is observed at Concordia for sulfate but not for MS? which peaks before and after sulfate in November and March, respectively. This first study of DMS and of its by-oxidation aerosol species conducted at inland Antarctica points out the complex coupling between transport and photochemistry of sulfur species over Antarctica. The findings highlight the complexity of the link between MS? ice core records extracted at high Antarctic plateau sites and DMS emissions from the Southern ocean. |
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Programme |
414;903;1181 |
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Publisher |
American Geophysical Union |
Place of Publication |
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Series Editor |
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Abbreviated Series Title |
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Series Issue |
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Edition |
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ISSN |
0148-0227 |
ISBN |
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Medium |
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Area |
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Expedition |
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Notes |
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Approved |
yes |
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Call Number |
IPEV @ Thierry.Lemaire @ |
Serial |
5518 |
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Author |
Bosqued J M, Ashour-Abdalla M, Umeda T, El Alaoui M, Peroomian V, Frey H U, Marchaudon A, Laakso H, |
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Title |
Cluster observations and numerical modeling of energy-dispersed ionospheric H+ ions bouncing at the plasma sheet boundary layer
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Type |
Journal Article |
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Year |
2009 |
Publication |
J. Geophys. Res. |
Abbreviated Journal |
J. Geophys. Res. |
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Volume |
114 |
Issue |
A4 |
Pages |
A04216- |
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Keywords |
dispersed structures, 2704 Magnetospheric Physics: Auroral phenomena, 2736 Magnetospheric Physics: Magnetosphere/ionosphere interactions, 2455 Ionosphere: Particle precipitation, 2463 Ionosphere: Plasma convection, 2753 Magnetospheric Physics: Numerical modeling, |
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Abstract |
The Cluster mission offers a unique opportunity to investigate the origin of the energy-dispersed ion structures frequently observed at 4.5–5 R E altitude in the auroral region. We present a detailed study of the 14 February 2001 northern pass, characterized by the successive observation by three spacecraft of a series of energy-dispersed structures at ~72–75 ILAT in a region of poleward convection. Equatorward, the satellites also observed a localized, steady, and intense source of outflowing energetic (3–10 keV) H+ and O+ ions. These substructures were modeled by launching millions of H+ ions from this ionospheric source and following them through time-dependent electric and magnetic fields obtained from a global MHD simulation of this event. Despite the complexity of ion orbits, the simulations showed that a large number of ions returned to the Cluster location, poleward of their source, in a number of adjacent or overlapping energy-latitude substructures with the correct dispersion. The first dispersed echo was unexpectedly generated by “half-bouncing” ions that interacted with the current sheet to return to the same hemisphere. The time-shifted observations made by two Cluster (SC1 and SC3) spacecrafts were correctly reproduced. Almost all the ions returning to the spacecraft underwent a ~2–5 keV nonadiabatic acceleration at each interaction with the current sheet in a very confined resonant region. This acceleration explains the overall energy increase from one structure to the next. This event confirms the importance of the ionospheric source in populating bouncing ion clusters within the magnetosphere, even at high latitudes.
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Programme |
312;911 |
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Campaign |
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Address |
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Corporate Author |
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Thesis |
Bachelor's thesis |
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Publisher |
AGU |
Place of Publication |
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Editor |
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Language |
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Summary Language |
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Original Title |
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Series Issue |
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Edition |
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ISSN |
0148-0227 |
ISBN |
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Medium |
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Conference |
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Notes |
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Approved |
yes |
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Call Number |
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Serial |
2893 |
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| Permanent link to this record |
