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Author |
Thébault, E.; Mandea, M.; Schott, J.J. |
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Title |
Modeling the lithospheric magnetic field over France by means of revised spherical cap harmonic analysis (R-SCHA) |
Type |
Journal Article |
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Year |
2006 |
Publication |
Journal of geophysical research-atmospheres |
Abbreviated Journal |
J. Geophys. Res. |
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Volume  |
111 |
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Keywords |
regional modeling; France; magnetic field; 1517 Geomagnetism and Paleomagnetism: Magnetic anomalies: modeling and interpretation; 1545 Geomagnetism and Paleomagnetism: Spatial variations: all harmonics and anomalies; 0545 Computational Geophysics: Modeling |
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Abstract |
We have recently proposed the revised spherical cap harmonic analysis (R-SCHA) modeling technique. The new mathematical functions represent faithfully the spatial variations of potential fields in a restricted area. In this paper, we tackle the inverse problem and outline the efficiency of the new basis functions with respect to real magnetic data. Processing simultaneously repeat stations, observatory, aeromagnetic, and CHAMP satellite data provides our first vector lithospheric field model over France, which extends from surface to 500 km of altitude. The magnetic field is represented with a minimum horizontal spatial representation of 40 km at the mean Earth radius. The magnetic lithospheric map consistency is confirmed with a comparison to known geological features. The model variation with altitude also suggests that the major French magnetic anomaly, the Paris basin anomaly, is produced by a deep-rooted geological structure. These results demonstrate the superiority of regional modeling over global modeling for delineating small-scale details in the lithospheric field. In view of forthcoming satellite missions, like Swarm, the revised spherical cap harmonic analysis method will help to accurately represent the lithospheric field for more detailed geological interpretations. |
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905;139 |
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American Geophysical Union |
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0148-0227 |
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yes |
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IPEV @ Thierry.Lemaire @ |
Serial |
5617 |
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Author |
Tomasi, C.; Petkov, B.; Benedetti, E.; Vitale, V.; Pellegrini, A.; Dargaud, G.; De Silvestri, L.; Grigioni, P.; Fossat, E.; Roth, W.L.; Valenziano, L. |
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Title |
Characterization of the atmospheric temperature and moisture conditions above Dome C (Antarctica) during austral summer and fall months |
Type |
Journal Article |
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Year |
2006 |
Publication |
Journal of geophysical research-atmospheres |
Abbreviated Journal |
J. Geophys. Res. |
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Volume |
111 |
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Pages |
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Keywords |
radiosounding measurements; precipitable water; Antarctic atmosphere; 3349 Atmospheric Processes: Polar meteorology; 1655 Global Change: Water cycles; 0365 Atmospheric Composition and Structure: Troposphere: composition and chemistry; 7539 Solar Physics, Astrophysics, and Astronomy: Stellar astronomy |
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Abstract |
Two sets of radiosounding measurements were taken at Dome C (Antarctica) in December 2003 and January 2003 and 2004, using RS80-A, RS80-H, and RS90 Vaisala radiosondes, and from March to May 2005, employing the RS92 model. They were examined following accurate correction procedures to remove the main relative humidity dry bias and the temperature and humidity lag errors. The results showed that a strong cooling usually characterizes the thermal conditions of the whole troposphere from December/January to April/May, with an average temperature decrease from 245 to 220 K at the ground, of around 10 K at upper tropospheric levels, and of more than 15 K in the lower stratosphere. The relative humidity data were found to be affected by dry bias of 5–10%, on average, for the RS80-A and RS80-H Humicap sensors and by smaller percentages for the other sensors. The mean monthly vertical profiles of absolute humidity were found to decrease sharply throughout the troposphere, especially within the first 3 km, and to diminish considerably passing from December/January to March/April/May, with average values of precipitable water decreasing from 0.75 to 0.28 mm, median values from 0.69 to 0.25 mm, and first and third quartiles from 0.60 to 0.22 mm and from 0.87 to 0.34 mm, respectively. The results demonstrate that Dome C (where a permanent scientific station has been open for winter operations since austral winter 2005) is a site of comparable quality to the South Pole for both validation of satellite radiance measurements and astronomic observations in the infrared, submillimetric, and millimetric wavelength range, performed with large telescopes that cannot be carried on satellites. |
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908 |
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American Geophysical Union |
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0148-0227 |
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yes |
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Call Number |
IPEV @ Thierry.Lemaire @ |
Serial |
5528 |
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Author |
Priestley, K.; Debayle, E.; McKenzie, D.; Pilidou, S. |
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Title |
Upper mantle structure of eastern Asia from multimode surface waveform tomography |
Type |
Journal Article |
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Year |
2006 |
Publication |
Journal of geophysical research-atmospheres |
Abbreviated Journal |
J. Geophys. Res. |
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Volume |
111 |
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Keywords |
Asian upper mantle; multimode surface waveform; craton; 7208 Seismology: Mantle; 7218 Seismology: Lithosphere; 7255 Seismology: Surface waves and free oscillations; 7270 Seismology: Tomography |
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Abstract |
We present a new three-dimensional Sv wave speed and azimuthal anisotropy model for the upper mantle of eastern Asia constrained by the analysis of more than 17,000 vertical component multimode Rayleigh wave seismograms. This data set allows us to build an upper mantle model for Asia with a horizontal resolution of a few hundred kilometers extending to ?400 km depth. At 75–100 km depth, there is approximately ±9% wave speed perturbation from the “smoothed PREM” reference model used in our analysis, and the pattern of azimuthal anisotropy is complex. Both the amplitude of the Sv wave speed heterogeneity and the complexity and amplitude of the azimuthal anisotropy decrease with depth. Above ?200 km depth the upper mantle structure of the model correlates with surface geology and tectonics; below ?200 km depth the structures primarily reflect the advection of material in the upper mantle. Since shear wave speed is principally controlled by temperature rather than by composition, Vs(z) can be used to calculate the temperature T(z), and hence map the lithospheric thickness. We use the relationship of Priestley and McKenzie to produce a contour map of the lithospheric thickness of eastern Asia from the surface wave tomography. This shows an extensive region of thick lithosphere beneath the Siberian Platform and the West Siberian Basin that extends to the European Platform, forming the stable Eurasian craton or core. The eastern portion of the Eurasian craton has controlled the geometry of continental deformation and the distribution of kimberlites in eastern Asia. |
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133 |
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American Geophysical Union |
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0148-0227 |
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yes |
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IPEV @ Thierry.Lemaire @ |
Serial |
5538 |
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Geirsson, H.; Árnadóttir, T.; Völksen, C.; Jiang, W.; Sturkell, E.; Villemin, T.; Einarsson, P.; Sigmundsson, F.; Stefánsson, R. |
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Title |
Current plate movements across the Mid-Atlantic Ridge determined from 5 years of continuous GPS measurements in Iceland |
Type |
Journal Article |
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Year |
2006 |
Publication |
Journal of geophysical research-atmospheres |
Abbreviated Journal |
J. Geophys. Res. |
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Volume |
111 |
Issue |
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Keywords |
Iceland crustal deformation; continuous GPS; 1240 Geodesy and Gravity: Satellite geodesy: results; 8150 Tectonophysics: Plate boundary: general; 1242 Geodesy and Gravity: Seismic cycle related deformations; 8158 Tectonophysics: Plate motions: present and recent; 7245 Seismology: Mid-ocean ridges |
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Abstract |
We analyze data spanning up to 5 years from 18 continuous GPS stations in Iceland, computing daily positions of the stations with three different high-level geodetic processing software packages. We observe large-scale crustal deformation due to plate spreading across Iceland. The observed plate divergence between the North American and the Eurasian plates is in general agreement with existing models of plate motion. Spreading is taken up within a ?100–150 km wide plate boundary zone that runs through the island. Of the two parallel branches of the plate boundary in south Iceland, the eastern volcanic zone is currently taking up the majority of the spreading and little is left for the western volcanic zone. The plate boundary deformation field has been locally and temporarily affected in south Iceland by two M w = 6.5 earthquakes in June 2000, inflation at Katla volcano during 2000 to 2004, and an eruption of Hekla volcano in February 2000. All stations with significant vertical velocities are moving up relative to the reference station REYK, with the highest velocity exceeding 20 mm/yr in the center of the island. |
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316 |
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American Geophysical Union |
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0148-0227 |
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yes |
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Call Number |
IPEV @ Thierry.Lemaire @ |
Serial |
5578 |
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Author |
Thébault, E.; Schott, J.J.; Mandea, M. |
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Title |
Revised spherical cap harmonic analysis (R-SCHA): Validation and properties |
Type |
Journal Article |
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Year |
2006 |
Publication |
Journal of geophysical research-atmospheres |
Abbreviated Journal |
J. Geophys. Res. |
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Volume |
111 |
Issue |
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Pages |
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Keywords |
magnetism; regional modeling; Spherical Cap Harmonic Analysis; 1214 Geodesy and Gravity: Geopotential theory and determination; 1517 Geomagnetism and Paleomagnetism: Magnetic anomalies: modeling and interpretation; 1532 Geomagnetism and Paleomagnetism: Reference fields: regional, global; 1541 Geomagnetism and Paleomagnetism: Satellite magnetics: main field, crustal field, external field; 1545 Geomagnetism and Paleomagnetism: Spatial variations: all harmonics and anomalies |
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Abstract |
We recently proposed a technique able to represent the spatial variations of the magnetic field at regional scales. However, we pointed out that these preliminary developments were not suited for the complete representation of the geomagnetic field. In this paper, we propose a complete revision, the revised spherical cap harmonic analysis (R-SCHA), which introduces slight changes in order to rectify the previous shortcomings. In addition, some discussions shed a new light on the former spherical cap harmonic analysis (SCHA) and help us to demonstrate its deficiencies and approximations. We finally show that R-SCHA now fully satisfies the natural properties of potential fields. R-SCHA also yields analytical relationships with the spherical harmonics. Taking advantage of the mathematical equivalence of both representations, we explore the relevance of fundamental concepts like spectrum, minimum wavelength, or internal/external field separation. We conclude that these concepts are misleading and must be handled with care in regional modeling. A prime goal being the ability of R-SCHA to represent real data sets, we also investigate and illustrate the effect of finite series expansions. A norm for the regularization of the inverse problem is proposed as well. The conclusions drawn in this paper allow us to validate the method and to assert that the present proposal is suited for modeling and studying the lithospheric magnetic field from ground to satellite altitudes at regional scales. |
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139;905 |
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American Geophysical Union |
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0148-0227 |
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yes |
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IPEV @ Thierry.Lemaire @ |
Serial |
5626 |
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Author |
Weimerskirch H., Salamolard M., Sarrazin F. & Jouventin P. |
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Title |
Foraging strategy of wandering albatrosses through the breeding season:a study using satellite telemetry. |
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Journal Article |
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Year |
1993 |
Publication |
Auk |
Abbreviated Journal |
Auk |
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Volume |
110 |
Issue |
2 |
Pages |
325-342 |
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109 |
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0004-8038 |
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yes |
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1464 |
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Miyashita, Y.; Ieda, A.; Kamide, Y.; Machida, S.; Mukai, T.; Saito, Y.; Liou, K.; Meng, C.-I.; Parks, G.K.; McEntire, R.W.; Nishitani, N.; Lester, M.; Sofko, G.J.; Villain, J.-P. |
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Title |
Plasmoids observed in the near-Earth magnetotail at X ? ?7 RE |
Type |
Journal Article |
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Year |
2005 |
Publication |
Journal of geophysical research-atmospheres |
Abbreviated Journal |
J. Geophys. Res. |
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Volume |
110 |
Issue |
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Pages |
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Keywords |
plasmoid; Geotail; 2723 Magnetospheric Physics: Magnetic reconnection; 2744 Magnetospheric Physics: Magnetotail; 2790 Magnetospheric Physics: Substorms; 2704 Magnetospheric Physics: Auroral phenomena; 2736 Magnetospheric Physics: Magnetosphere/ionosphere interactions |
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Abstract |
Recent studies have statistically shown that the magnetic reconnection site at substorm expansion onset is located in the magnetotail at X ? ?20 R E on average. For a substorm event that occurred at ?0153 UT on 2 July 1996, however, Geotail observed a series of tailward but slow flows with southward magnetic fields fairly close to the Earth at (X, Y) ? (?7, 9) R E
. The flows had enhancements of the total pressure and the total magnetic field as well as bidirectional field-aligned low-energy electrons in their central part. We interpret these as signatures for tailward moving small plasmoids with scales of ?0.5–3 R E
. Considering that GOES-8 observed a dipolarization at (X, Y) ? (?4, 5) R E after the expansion onset, we estimate that the magnetic reconnection occurred between the Geotail and GOES-8 positions. UVI auroral images from Polar and ground magnetic field data show that this substorm, initiated at ?20 hours MLT and ?64° magnetic latitude, was not very intense, and the period examined was not during an intense storm. The southward interplanetary magnetic field (IMF) was not very large, while the large duskward IMF persisted for more than 12 hours before the onset as well as the somewhat large solar wind dynamic pressure. It seems likely that the global ionospheric convection was not very strong. Locally enhanced convection and auroral oval expansion due to the large IMF B y and the solar wind dynamic pressure might lead to the initiation of the magnetic reconnection much closer to the Earth than usual. |
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312;911 |
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Publisher |
American Geophysical Union |
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ISSN |
0148-0227 |
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Approved |
yes |
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Call Number |
IPEV @ Thierry.Lemaire @ |
Serial |
5619 |
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Author |
Thuillier, G.; Perrin, J.-M.; Lathuillère, C.; Hersé, M.; Fuller-Rowell, T.; Codrescu, M.; Huppert, F.; Fehrenbach, M. |
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Title |
Dynamics in the polar thermosphere after the coronal mass ejection of 28 October 2003 observed with the EPIS interferometer at Svalbard |
Type |
Journal Article |
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Year |
2005 |
Publication |
Journal of geophysical research-atmospheres |
Abbreviated Journal |
J. Geophys. Res. |
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Volume |
110 |
Issue |
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Pages |
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Keywords |
thermosphere; CME; neutral winds; EPIS; ESR; 0310 Atmospheric Composition and Structure: Airglow and aurora; 0358 Atmospheric Composition and Structure: Thermosphere: energy deposition; 7513 Solar Physics, Astrophysics, and Astronomy: Coronal mass ejections |
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Abstract |
The upper atmosphere dynamics in the polar cap is mainly driven by ion-drag momentum sources imposed by the mapping of magnetosphere convection into the thermosphere/ionosphere and by Joule and auroral particle heating. Auroral particles also enhance conductivity particularly in the middle and lower ionosphere. Changes in the magnetospheric energy and momentum sources can significantly modify the wind circulation during geomagnetic storms. To observe these effects, a Michelson interferometer has been installed in Svalbard to measure winds in the thermosphere. Prior to 30 October 2003, cloud cover over Svalbard rendered the conditions unfavorable for optical observation. However, meteorological conditions improved after this date to enable the thermospheric response to the 28 October coronal mass ejection to be made. During quiet geomagnetic conditions measured wind velocities were in good agreement with those predicted by the Horizontal Wind Model (HWM). During disturbed geomagnetic conditions, HWM tended to underestimate the observed velocities. Comparison of the wind observations with a physical model tended to show reasonable agreement during both the strongly driven and recovery phase of the storm. Although the physical model did not always capture the timing of the rapid changes in the wind response in the early phase of the storm, the amplitudes of the fluctuations were in good agreement. After the initial phase the physical model agreed well with both the timing and amplitude of the meridional and zonal wind fluctuations. The meridional wind component was also derived from the EISCAT Svalbard Radar ion velocity and was found to be in close agreement with the optical winds observations. |
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384 |
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Publisher |
American Geophysical Union |
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0148-0227 |
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yes |
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Call Number |
IPEV @ Thierry.Lemaire @ |
Serial |
5585 |
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Author |
Bouruet-Aubertot, P.; Mercier, H.; Gaillard, F.; Lherminier, P. |
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Title |
Evidence of strong inertia-gravity wave activity during the POMME experiment |
Type |
Journal Article |
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Year |
2005 |
Publication |
Journal of geophysical research-atmospheres |
Abbreviated Journal |
J. Geophys. Res. |
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Volume |
110 |
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Keywords |
inertia-gravity waves, turbulent mixing; 4544 Oceanography: Physical: Internal and inertial waves; 4568 Oceanography: Physical: Turbulence, diffusion, and mixing processes; 4572 Oceanography: Physical: Upper ocean and mixed layer processes |
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Abstract |
The purpose of this paper is to characterize inertia-gravity waves (IGW) activity and to investigate the variability of these waves in relationship to atmospheric forcing and larger-scale motions. To this aim, we analyzed Eulerian measurements of horizontal currents and temperature collected over 1 year during the Programme Océan Multidisciplinaire Méso Echelle (POMME). We focused on the main frequency components of the IGW spectrum, namely the inertial frequency f and the semidiurnal frequency M2. Time evolution of the relative energy of these two components gave evidence of isolated events of high intensity. We performed a detailed analysis of these events and identified mechanisms of generation of these waves. Localized spots of intense, near-inertial IGW were observed in winter. During the mixed layer deepening, one event was correlated with plume-like structures resulting from peaks of intense surface cooling. This suggests a local generation process driven by strong downward vertical motions. Instead, other events of strong IGW could be related to submesoscale features, characteristic of a frontal region, in particular, wave trapping within anticyclonic eddies. In contrast, a downward energy propagation down to about 500 m below the mixed layer was isolated after a stormy period. Eventually, internal tidal beams, possibly generated at a nearby seamount, intermittently crossed the mooring, though less energetically than the previous events. Last, we estimated the eddy diffusivity from the velocity vertical shear. Large variations were obtained, from 10?6 m2/s up to 10?3 m2/s, consistent with the intense events previously isolated. |
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417 |
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American Geophysical Union |
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0148-0227 |
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yes |
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Call Number |
IPEV @ Thierry.Lemaire @ |
Serial |
5590 |
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Author |
Legagneux, L.; Domine, F. |
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Title |
A mean field model of the decrease of the specific surface area of dry snow during isothermal metamorphism |
Type |
Journal Article |
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Year |
2005 |
Publication |
Journal of geophysical research-atmospheres |
Abbreviated Journal |
J. Geophys. Res. |
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Volume |
110 |
Issue |
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Pages |
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Keywords |
model; isothermal snow metamorphism; Ostwald ripening; 0736 Cryosphere: Snow; 3947 Mineral Physics: Surfaces and interfaces; 1847 Hydrology: Modeling; 5112 Physical Properties of Rocks: Microstructure |
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Abstract |
The surface area of snow that is accessible to gases is an essential parameter for quantifying the exchange of trace gases between the snowpack and the atmosphere and is called the specific surface area (SSA). Snow SSA decreases during metamorphism, but this is not described in current snow models owing to the complexity of the physics and geometry of snow. In this paper, we test whether it is possible to model snow SSA changes during isothermal metamorphism without accounting for all the complexity of the three-dimensional (3-D) structure of real snow. We have developed a mean field model of snow metamorphism under isothermal conditions, grounded in the theoretical framework of transient Ostwald ripening and representing snow as a distribution of spherical particles. Analytical expressions of the growth rates of these spheres are obtained, and the evolution of two measurable parameters that characterize snow geometry, the SSA and the distribution of radii of curvature (DRC), are simulated and compared to experimental data obtained by X-ray tomography. The qualitative effects of temperature, snow density, and the condensation coefficient on the rate of SSA decrease are examined. The model predicts very well the rate of evolution of the particle size distribution, which validates our physical description of isothermal metamorphism. In particular, we find that vapor phase diffusion is rate limiting. However, the calculation of the SSA from the DRC appears delicate and evidences too crude approximations in our description of the 3-D geometry of snow. Finally, it is stressed that the initial DRC can greatly influence the rate of SSA decrease, while experimental measurements of the rate of SSA decrease suggest that all snow types evolve in a similar way. It is thus proposed that most natural fresh snows have similar DRCs. |
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American Geophysical Union |
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0148-0227 |
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yes |
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Call Number |
IPEV @ Thierry.Lemaire @ |
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5650 |
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