Publications

2012

Entropy Generation across Earth's Collisionless Bow Shock
- Parks G. K.
- Lee E.
- Mccarthy M.
- Goldstein M. L.
- Fu S. Y.
- Cao J.B.
- Canu Patrick
- Lin N.
- Wilber M.
- Dandouras I.
- Rème H.
- Fazakerley A.
Physical Review Letters, American Physical Society, 2012, 108, pp.061102. Earth's bow shock is a collisionless shock wave but entropy has never been directly measured across it. The plasma experiments on Cluster and Double Star measure 3D plasma distributions upstream and downstream of the bow shock allowing calculation of Boltzmann's entropy function H and his famous H theorem, dH/dt<=0. The collisionless Boltzmann (Vlasov) equation predicts that the total entropy does not change if the distribution function across the shock becomes nonthermal, but it allows changes in the entropy density. Here, we present the first direct measurements of entropy density changes across Earth's bow shock and show that the results generally support the model of the Vlasov analysis. These observations are a starting point for a more sophisticated analysis that includes 3D computer modeling of collisionless shocks with input from observed particles, waves, and turbulences. (10.1103/PhysRevLett.108.061102)
DOI : 10.1103/PhysRevLett.108.061102
Thermodynamics of flow generation Momentum Transport, PV Homogenization and Entropy Production
- Gürcan Özgür D.
, 2012. http://canopus.cnu.ac.kr/lsap2012
Larger Size Planar Wire Arrays with a Modified Central Plane and Their Applications on Zebra with LCM
- Safronova Alla S.
- Esaulov A.
- Kantsyrev Viktor L.
- Chuvatin Alexandre S.
- Coverdale C.
- Jones B.
- Shlyaptseva V. V.
- Weller Michael E.
- Stafford A.
- Shrestha Ishor
- Osborne Glenn C.
- Keim S. F.
, 2012, 57 (12), pp.BO5.00009.
Seasonal TEC Variability in West Africa Equatorial Anomaly Region
- Zoundi Christian
- Ouattara Frédéric
- Fleury Rolland
- Amory-Mazaudier Christine
- Lassudrie-Duchesne Patrick
European Journal of Scientific Research, EuroJournals, 2012, 77 (3), pp.309-319. This paper presented the seasonal variability of TEC/ GPS data recorded at Ouagadougou a West Africa GPS station located near the magnetic equator. Seasonal data TEC time variations are compared to those of TEC derived from IGS GPS network maps. The present study showed that TEC map model predicts well data TEC during equinoctial months and fairly well during solstice months. The best prediction is obtained during spring and the worst during winter. The analysis of seasonal TEC profiles highlighted that model accuracy shows seasonal variations with respect to the complexity of TEC time variations. This work pointed out that model accuracy depends not only on the integration of station data in IGS GPS network data but also on the presence of daytime multi-peaks and/or the presence and the amplitude of night time peak. Solstice and summer data TEC analysis showed that those present F2 layer annual anomaly.
Radiative properties of mixed nested cylindrical wire arrays on Zebra at UNR
- Weller Michael E.
- Safronova Alla S.
- Kantsyrev Viktor L.
- Esaulov A. A.
- Coverdale C. A.
- Chuvatin Alexandre S.
- Ouart N. D.
- Williamson Kenneth M.
- Shrestha Ishor
- Osborne Glenn C.
- Shlyaptseva V. V.
- Keim S. F.
- Stafford A.
High Energy Density Physics, Elsevier, 2012, 8 (2), pp.184-189. The dynamics of mixed nested cylindrical wire arrays were studied at the UNR Zebra generator with our existing theoretical and experimental tools to better understand the contributions of each array to the emitted radiation. In particular, experimental results of mixed brass (70% Cu, 30% Zn) and Al (5056, 5% Mg) nested cylindrical wire arrays are analyzed and compared. The loads used brass in the inner array and Al in the outer array, or alternately, Al in the inner array and brass in the outer array, with a mass ratio of 1:1 (outer to inner). Consequently, radiative properties of K-shell Al and Mg ions and L-shell Cu and Zn ions are compared as functions of the placements of the brass and Al wires on the inner and outer arrays. Results show that the placement of brass and Al, whether on the inner or outer array, dramatically affects the intensity of the X-ray emission. Specifically, the ratio of Cu L-shell to Al K-shell emissions changed from 4 when Al is in the outer array to 40 when brass is in the outer array, and the total radiated yield was highest when the brass was on the outer array (18 kJ, versus 15 kJ when brass is on the inner array). Each load was fielded twice to vary the timing of the time-gated imaging and spectral diagnostics. This provides a more complete understanding of the evolution of the plasma parameters over the X-ray pulse and highlights the importance of the time-gated diagnostics. (10.1016/j.hedp.2012.03.004)
DOI : 10.1016/j.hedp.2012.03.004
Afterglow kinetics in oxygen pulsed discharges
- Guerra V.
- Marinov Daniil
- Guaitella Olivier
- Rousseau Antoine
, 2012.
Global model of a gridded-ion thruster powered by a radiofrequency inductive coil
- Chabert Pascal
- Arancibia Monreal J.
- Bredin Jérôme
- Popelier Lara
- Aanesland Ane
Physics of Plasmas, American Institute of Physics, 2012, 19, pp.195201. A global (volume-averaged) model of a gridded-ion thruster is proposed. The neutral propellant (xenon gas) is injected into the thruster chamber at a fixed rate and a plasma is generated by circulating a radiofrequency current in an inductive coil. The ions generated in this plasma are accelerated out of the thruster by a pair of DC biased grids. The neutralization downstream is not treated. Xenon atoms also flow out of the thruster across the grids. The model, based on particle and energy balance equations, solves for four global variables in the thruster chamber: the plasma density, the electron temperature, the neutral gas (atom) density, and the neutral gas temperature. The important quantities to evaluate the thruster efficiency and performances are calculated from these variables and from the voltage across the grids. It is found that the mass utilization efficiency rapidly decreases with the gas flow rate. However, the radiofrequency power transfer efficiency increases significantly with the injected gas flow rate. Therefore, there is a compromise to be found between these two quantities. (10.1063/1.4737114)
DOI : 10.1063/1.4737114
Transition from Weak to Strong Cascade in MHD Turbulence
- Verdini Andrea
- Grappin Roland
Physical Review Letters, American Physical Society, 2012, 109, pp.025004. The transition from weak to strong turbulence when passing from large to small scales in magneto-hydrodynamic (MHD) turbulence with guide field is a cornerstone of anisotropic turbulence theory. We present the first check of this transition, using the Shell-RMHD, which combines a shell model of perpendicular nonlinear coupling and linear propagation along the guide field. This model allows us to reach Reynolds numbers around 106. We obtain surprisingly good agreement with the theoretical predictions, with a reduced perpendicular energy spectrum scaling as k^-2 at large scales and as k_⊥^-5/3 at small scales, where critical balance between nonlinear and propagation time is reached. However, even in the strong regime, a high level of excitation is found in the weak coupling region of Fourier space, which is due to the rich frequency spectrum of large eddies. A corollary is that the reduced parallel spectral slope is not a definite test of the spectral anisotropy, contrary to standard belief. (10.1103/PhysRevLett.109.025004)
DOI : 10.1103/PhysRevLett.109.025004
Device convolution effects on the collective scattering signal of the E x B mode from Hall thruster experiments: 2D dispersion relation
- Grésillon D.
- Cavalier J.
- Lemoine N.
- Bonhomme Gildas
- Tsikata Sedina
- Honoré Cyrille
Physics of Plasmas, American Institute of Physics, 2012, 19, pp.082117. The effect of the collective light scattering diagnostic transfer function is considered in the context of the dispersion relation of the unstable E×B mode previously reported. This transfer function is found to have a contribution to the measured frequencies and mode amplitudes which is more or less significant depending on the measurement wavenumbers and angles. After deconvolution, the experimental data are found to be possibly compatible with the idea that the mode frequency in the jet frame (after subtraction of the Doppler effect due to the plasma motion along the thruster axis) is independent of the orientation of the wave vector in the plane orthogonal to the local magnetic field. (10.1063/1.4748286)
DOI : 10.1063/1.4748286
Spatio-temporal evolution of the L -> I -> H transition
- Miki K.
- Diamond P.H.
- Gürcan Özgür D.
- Tynan G.R.
- Estrada T.
- Schlitz L.
- Xu G.S.
Physics of Plasmas, American Institute of Physics, 2012, 19, pp.092306. We investigate the dynamics of the low(L) → high(H) transition using a time-dependent, one dimensional (in radius) model which self-consistently describes the time evolution of zonal flows (ZFs), mean flows (MFs), poloidal spin-up, and density and pressure profiles. The model represents the physics of ZF and MF competition, turbulence suppression via E×B shearing, and poloidal flows driven by turbulence. Numerical solutions of this model show that the L→H transition can occur via an intermediate phase (I-phase) which involves oscillations of profiles due to ZF and MF competition. The I-phase appears as a nonlinear transition wave originating at the edge boundary and propagates inward. Locally, I-phase exhibits the characteristics of a limit-cycle oscillation. All these observations are consistent with recent experimental results. We examine the trigger of the L→H transition, by defining a ratio of the rate of energy transfer from the turbulence to the zonal flow to the rate of energy input into the turbulence. When the ratio exceeds order unity, ZF shear gains energy, and a net decay of the turbulence is possible, thus triggering the L→H transition. Numerical calculations indicate that the L→H transition is triggered by this peak of the normalized ZF shearing. Zonal flows act as reservoir, in which to store increasing fluctuation energy without increasing transport, thus allowing the mean flow shear to increase and lock in the transition. A counterpart of the L → I→H transition, i.e., an L→H transition without I-phase, is obtained in a fast power ramp, for which I-phase is compressed into a single burst of ZF, which triggers the transition. Effects of neutral charge exchange on the L→H transition are studied by varying ZF damping and neoclassical viscosity. Results show that the predicted L→H transition power increases when either ZF damping or viscosity increase, suggesting a link between recycling, ZF damping, and the L→H threshold. Studies of fueling effects on the transition and pedestal structure with an emphasis on the particle pinch are reported. (10.1063/1.4753931)
DOI : 10.1063/1.4753931
On the Origin of the 1/f Spectrum in the Solar Wind Magnetic Field
- Verdini Andrea
- Grappin Roland
- Pinto Rui
- Velli Marco
The Astrophysical Journal Letters, Bristol : IOP Publishing, 2012, 750 (2), pp.L33. We present a mechanism for the formation of the low-frequency 1/f magnetic spectrum based on numerical solutions of a shell-reduced MHD model of the turbulent dynamics inside the sub-Alfvénic solar wind. We assign reasonably realistic profiles to the wind speed and the density along the radial direction, and a radial magnetic field. Alfvén waves of short periodicity (600 s) are injected at the base of the chromosphere, penetrate into the corona, and are partially reflected, thus triggering a turbulent cascade. The cascade is strong for the reflected wave while it is weak for the outward propagating waves. Reflection at the transition region recycles the strong turbulent spectrum into the outward weak spectrum, which is advected beyond the Alfvénic critical point without substantial evolution. There, the magnetic field has a perpendicular power-law spectrum with slope close to the Kolmogorov 5/3. The parallel spectrum is inherited from the frequency spectrum of large (perpendicular) eddies. The shape is a double power law with slopes of sime 1 and 2 at low and high frequencies, respectively, with the position of the break depending on the injected spectrum. We suggest that the double power-law spectrum measured by Helios at 0.3 AU, where the average magnetic field is not aligned with the radial (contrary to our assumptions), results from the combination of such different spectral slopes. At low frequency the parallel spectrum dominates with its characteristic 1/f shape, while at higher frequencies its steep spectral slope (2) is masked by the more energetic perpendicular spectrum (slope 5/3). (10.1088/2041-8205/750/2/L33)
DOI : 10.1088/2041-8205/750/2/L33
Upper ionosphere of Mars is not axially symmetrical
- Dubinin E.
- Fraenz M.
- Woch J.
- Modolo Ronan
- Chanteur Gérard
- Duru F.
- Gurnett D. A.
- Barabash S.
- Lundin R.
Earth Planets and Space, Springer / Terra Scientific Publishing Company, 2012, 64 (2), pp.113-120. The measurements carried out by the ASPERA-3 and MARSIS experiments on board the Mars Express (MEX) spacecraft show that the upper Martian ionosphere (h ≥ 400 km) is strongly azimuthally asymmetrical. There are several factors, e.g., the crustal magnetization on Mars and the orientation of the interplanetary magnetic field (IMF) which can give rise to formation of ionospheric swells and valleys. It is shown that expansion of the ionospheric plasma along the magnetic field lines of crustal origin can produce bulges in the plasma density. The absense of a magnetometer on MEX makes the retrieval of an asymmetry caused by the IMF more difficult. However hybrid simulations give a hint that the ionosphere in the hemisphere (E-) to which the motional electric field is pointed occurs more inflated than the ionosphere in the opposite (E+) hemisphere. (10.5047/eps.2011.05.022)
DOI : 10.5047/eps.2011.05.022
Implosions of larger size wire arrays at enhanced current of 1.51.7 MA on Zebra with LCM
- Safronova Alla S.
- Esaulov A. A.
- Kantsyrev Viktor L.
- Stafford A.
- Weller Michael E.
- Shlyaptseva V. V.
- Zunino H. A.
- Shrestha Ishor
- Osborne Glenn C.
- Keim S. F.
- Chuvatin Alexandre S.
- Coverdale C. A.
, 2012, pp.6C7. Experiments on Zebra with a Load Current Multiplier (LCM, which provides an enhanced current of 1.5-1.7 MA) allow the implosion of larger wire array loads than possible with the standard current of 1 MA. Advantages of the larger wire arrays include enhanced energy coupling to plasmas and better diagnostic access to observable plasma regions. Diagnostics, fielded on 10 beam lines, included PCD, XRD, and EUV detectors, X-ray/EUV spectrometers and X-ray pinhole cameras, and laser shadowgraphy. For this work, we collected and analyzed the experimental results from standard and modified triple planar wire arrays (TPWA), as well as cylindrical wire arrays (CWA). The anode-cathode gap in these experiments with LCM was 1 cm, which is half the gap used in the standard mode. For TPWAs, two outer wire planes were made out of mid-atomic-number wire material (Ni or Cu) with the inter-row gap increased from 1.5 or 3 mm (usually used at 1 MA current) up to 4.5 mm. The different designs of a central wire plane from Al were implemented to investigate its role as a magnetic field extruder to prevent the formation of closed magnetic configurations around each wire plane. Previous work has shown that larger double planar wire arrays (at a standard current) can block the inward motion of ablated plasma jets. Therefore, multi-planar wire arrays provide a new test bed to study jet formations in larger wire arrays for laboratory astrophysics. In addition, we measured higher linear radiation yield and the high-temperature precursor Al plasmas, not previously observable in experiments on Zebra at 1 Ma current. However, the observation of high-temperature precursor plasmas from Cu CWAs at enhanced current was consistent with previous findings at a standard current of 1 MA. (10.1109/PLASMA.2012.6384037)
DOI : 10.1109/PLASMA.2012.6384037
VOC elimination using plasma enhanced catalysis in a post situ configuration
- Barakat Christelle
- Gravejat Paul
- Guaitella Olivier
- Rousseau Antoine
, 2012.
Adsorption and reactivity of nitrogen atoms on dielectric surfaces under
- Marinov Daniil
- Guaitella Olivier
- Rousseau Antoine
, 2012.
A load current multiplier of the MIG terawatt generator
- Chaikovsky S. A.
- Chuvatin Alexandre S.
- Oreshkin V. I.
Instruments and Experimental Techniques, MAIK Nauka/Interperiodica, 2012, 55 (2), pp.209-217. The design of the load current multiplier with a 1.75-current enlargement factor, when the pulse amplitude of the current through a 3-MA load of the MIG terawatt pulse generator (multifunction pulse generator), is described, and its operation is demonstrated. The design of the multiplier is sufficiently simple, and it is easily demounted, allowing one to use the MIG generator in other operation modes with different-impedance loads. It is shown that it is expedient to use the multiplier for operation with static low-inductance loads, e.g., in studies of the skin electric explosion or nonlinear diffusion of megagauss magnetic fields. In this case, the multiplier application is intended to ensure a one-and-one-half increase in the current through the load as compared to the standard operation mode of the МИГ generator.
Analytical-numerical global model of atmospheric-pressure radio-frequency capacitive discharges
- Lazzaroni Claudia
- Chabert Pascal
- Lieberman M.A.
- Lichtenberg A.J.
- Leblanc A.
Plasma Sources Science and Technology, IOP Publishing, 2012, 21, pp.035013. A one-dimensional hybrid analyticalnumerical global model of atmospheric-pressure, radio-frequency (rf) driven capacitive discharges is developed. The feed gas is assumed to be helium with small admixtures of oxygen or nitrogen. The electrical characteristics are modeled analytically as a current-driven homogeneous discharge. The electron power balance is solved analytically to determine a time-varying Maxwellian electron temperature, which oscillates on the rf timescale. Averaging over the rf period yields effective rate coefficients for gas phase activated processes. The particle balance relations for all species are then integrated numerically to determine the equilibrium discharge parameters. The coupling of analytical solutions of the time-varying discharge and electron temperature dynamics, and numerical solutions of the discharge chemistry, allows for a fast solution of the discharge equilibrium. Variations of discharge parameters with discharge composition and rf power are determined. Comparisons are made to more accurate but numerically costly fluid models, with space and time variations, but with the range of parameters limited by computational time. (10.1088/0963-0252/21/3/035013)
DOI : 10.1088/0963-0252/21/3/035013
Microcrystalline silicon solar cells deposited using a plasma process excited by tailored voltage waveforms
- Johnson E.V.
- Delattre Pierre-Alexandre
- Booth Jean-Paul
Applied Physics Letters, American Institute of Physics, 2012, 100, pp.133504. Thin film solar cells in a p-i-n structure with an absorbing layer of intrinsic hydrogenated microcrystalline silicon (μc-Si:H) deposited through plasma enhanced chemical vapour deposition excited by tailored voltage waveforms have been prepared. The use of an asymmetric voltage waveform decouples the ion-bombardment energy at the growth surface from the injected power and allows the growth of good quality μc-Si:H at reasonable deposition rates (3 Å/s) using low pressure, powder-free conditions. Unoptimized photovoltaic devices with an efficiency of 6.1% are demonstrated using an i-layer deposited at 1.3 Å/s and a process pressure of 500 mTorr. (10.1063/1.3699222)
DOI : 10.1063/1.3699222
Multiple scattering of electromagnetic waves by an array of parallel gyrotropic rods
- Es'Kin V. A.
- Kudrin A. V.
- Zaboronkova T. M.
- Krafft C.
Physical Review E, American Physical Society (APS), 2012, 86, pp.067601. We study multiple scattering of electromagnetic waves by an array of parallel gyrotropic circular rods and show that such an array can exhibit fairly unusual scattering properties and provide, under certain conditions, a giant enhancement of the scattered field. Among the scattering patterns of such an array at its resonant frequencies, the most interesting is the distribution of the total field in the form of a perfect self-similar structure of chessboard type. The scattering characteristics of the array are found to be essentially determined by the resonant properties of its gyrotropic elements and cannot be realized for arrays of nongyrotropic rods. It is expected that the results obtained can lead to a wide variety of practical applications. (10.1103/PhysRevE.86.067601)
DOI : 10.1103/PhysRevE.86.067601
Electron acceleration in the reconnection diffusion region: Cluster observations
- Huang S. Y.
- Vaivads A.
- Khotyaintsev Y. V.
- Zhou M.
- Fu H.S.
- Retinò Alessandro
- Deng X. H.
- André M.
- Cully C. M.
- He J. S.
- Sahraoui Fouad
- Yuan Z. G.
- Pang Y.
Geophysical Research Letters, American Geophysical Union, 2012, 39, pp.11103. We present one case study of magnetic islands and energetic electrons in the reconnection diffusion region observed by the Cluster spacecraft. The cores of the islands are characterized by strong core magnetic fields and density depletion. Intense currents, with the dominant component parallel to the ambient magnetic field, are detected inside the magnetic islands. A thin current sheet is observed in the close vicinity of one magnetic island. Energetic electron fluxes increase at the location of the thin current sheet, and further increase inside the magnetic island, with the highest fluxes located at the core region of the island. We suggest that these energetic electrons are firstly accelerated in the thin current sheet, and then trapped and further accelerated in the magnetic island by betatron and Fermi acceleration. (10.1029/2012GL051946)
DOI : 10.1029/2012GL051946
Producing Kiloelectronvolt L-Shell Plasmas on Zebra at UNR
- Safronova Alla S.
- Kantsyrev Viktor L.
- Esaulov A. A.
- Shrestha Ishor
- Shlyapstseva V. V.
- Weller Michael E.
- Ouart N. D.
- Osborne Glenn C.
- Stafford A.
- Keim S. F.
- Velikovich A. L.
- Giuliani J. L.
- Chuvatin Alexandre S.
IEEE Transactions on Plasma Science, Institute of Electrical and Electronics Engineers, 2012, 40 (12), pp.3347-3353. Experiments with various wire loads from mid-atomic-number wires, which were performed on the university-scale 1-MA Zebra generator at the University of Nevada, Reno, during the last few years, are analyzed to assess the highest electron temperature reached. In particular, the results from experiments with planar wire arrays (PWAs) were considered. Load materials from mid-atomic-number such as stainless steel, Alumel, Cu, brass, Mo, and up to Ag were used to generate L-shell plasmas and to study plasma parameters. Though the full diagnostic set was utilized, the main focus was on X-ray spectroscopic data and on the non-local thermodynamic equilibrium kinetic modeling. As a result, the scaling of the maximum Te with the load material atomic number is presented for the first time in the range from Fe to Ag for L-shell plasmas from PWAs. The highest values of the electron temperature in L-shell plasmas, which are estimated from the modeling, were from both Ag PWAs and X-pinches. This work is important for the development of efficient X-ray radiators on university-scale Z-pinch generators. (10.1109/TPS.2012.2222451)
DOI : 10.1109/TPS.2012.2222451
New probing techniques of radiative shocks
- Stehlé Chantal
- Kozlova Michaela
- Larour Jean
- Nejdl Jaroslav
- Champion Norbert
- Barroso Patrice
- Suzuki-Vidal Francisco
- Acef Ouali
- Delattre Pierre-Alexandre
- Dostal Jan
- Krus Miroslav
- Chièze Jean-Pierre
Optics Communications, Elsevier, 2012, 285, pp.64-69. Radiative shock waves propagating in xenon at a low pressure have been produced using 60 joules of iodine laser (λ = 1.315 μm) at PALS center. The shocks have been probed by XUV imaging using a Zn X-raylaser (λ = 21 nm) generated with a 20-ns delay after the shock creating pulse. Auxiliary high-speed silicon diodes allowed performing space- and time-resolved measurement of plasma self-emission in the visible and XUV. The results show the generation of a shock wave propagating at 60 km/s preceded by a radiative precursor. This demonstrates the feasibility of radiative shock generation using high power infrared lasers and the use of XRL backlighting as a suitable diagnostic for shock imaging. (10.1016/j.optcom.2011.09.008)
DOI : 10.1016/j.optcom.2011.09.008
Electron-cylotron maser radiation from electron holes: downward current region
- Treumann R. A.
- Baumjohann W.
- Pottelette Raymond
Annales Geophysicae, European Geosciences Union, 2012, 30, pp.119-130. The electron-cyclotron maser emission theory from electron holes is applied to holes generated in the downward current region of the aurora. It is argued that the main background auroral kilometric radiation source may still be located in the upward current region electron-ring (horseshoe) distribution while the fine structure is caused by electron holes predominantly in the downward current region. There the existence of electron holes is well established and electron densities are high enough for substantial maser growth rates. Trapping of radiation by the holes provides strong amplification. Upward motion of holes favours the escape of radiation both, from the holes and from the downward current region, into the upward current region. Since upward and downward current regions always exist simultaneously, they are acting in tandem in generating auroral kilometric radiation and its fine structure by the same mechanism though in different ways. This mechanism solves the long-standing problem of auroral kilometric radiation fine structure. (10.5194/angeo-30-119-2012)
DOI : 10.5194/angeo-30-119-2012
On the reactivity of C2H2 on plasma pretreated TiO2 surface
- Marinov Daniil
- Lopatik D.
- Hübner M.
- Guaitella Olivier
- Roepcke J.
- Rousseau Antoine
, 2012.
La science au service du développement
- Amory-Mazaudier Christine
, 2012. Dans cet ouvrage est présentée une expérience humaine d'un réseau de scientifiques, GIRGEA, qui a réuni, et qui réunit toujours plusieurs centaines d'étudiants, ingénieurs, techniciens, chercheurs, enseignants, etc. autour d'un objectif central : développer la recherche en sciences de l'espace en Afrique en installant des instruments, en formant des chercheurs de niveau international qui pourront constituer des équipes de recherche dans leur pays et assurer ainsi la pérennité du réseau. Il semble impensable, et pourtant, qu'au XXIe siècle un scientifique puisse prétendre développer des études planétaires des phénomènes physiques de l'environnement terrestre sans mesures sur l'ensemble du globe. Le Nord est indispensable au Sud et le Sud est indispensable au Nord. L'éruption du volcan Eyjafjöll en 2010 a révélé la fragilité des pays du Nord techniquement avancés. Le tsunami du 26 décembre 2004 a mis en évidence la grande vulnérabilité des habitants de certaines régions du Sud ayant des réseaux d'alerte au tsunami défaillants ou inexistants. Mais ces événements ont aussi surtout démontré nos liens, nous vivons tous sur la même planète : la Terre est un petit village et nous dépendons les uns des autres. Le GIRGEA propose donc une méthode pour allier science de l'espace au niveau international et règles éthiques afin de favoriser une recherche à l'échelle planétaire indispensable à l'avancée des connaissances et profitable à tous.

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