Publications

2013

• Analysis of amplitudes of equatorial noise emissions and their variation with L, MLT and magnetic activity
  
  • Hrbackova Z.
  • Santolík O.
  • Cornilleau-Wehrlin Nicole
  , 2013, 15, pp.EGU2013-10281. Wave-particle interactions are an important mechanism of energy exchange in the outer Van Allen radiation belt. These interactions can cause an increase or decrease of relativistic electron flux. The equatorial noise (EN) emissions (also called fast magnetosonic waves) are electromagnetic waves which could be effective in producing MeV electrons. EN emissions propagate predominantly within 10° of the geomagnetic equator at L shells from 1 to 10. Their frequency range is between the local proton cyclotron frequency and the lower hybrid resonance. We use a data set measured by the STAFF-SA instruments onboard four Cluster spacecraft from January 2001 to December 2010. We have compiled the list of the time intervals of the observed EN emissions during the investigated time period. For each interval we have computed an intensity profile of the wave magnetic field as a function of frequency. The frequency band is then determined by an automatic procedure and the measured power spectral densities are reliably transformed into wave amplitudes. The results are shown as a function of the McIlwain's parameter, magnetic local time and magnetic activity - Kp and Dst indexes. This work has received EU support through the FP7-Space grant agreement n 284520 for the MAARBLE collaborative research project.
• Eleven years of Cluster observations of whistler-mode chorus
  
  • Santolík O.
  • Macusova E.
  • Kolmasova Ivana
  • Cornilleau-Wehrlin Nicole
  • Pickett J. S.
  , 2013, 15, pp.EGU2013-10234. Electromagnetic emissions of whistler-mode chorus carry enough power to increase electron fluxes in the outer Van Allen radiation belt at time scales on the order of one day. However, the ability of these waves to efficiently interact with relativistic electrons is controlled by the wave propagation directions and time-frequency structure. Eleven years of measurements of the STAFF-SA and WBD instruments onboard the Cluster spacecraft are systematically analyzed in order to determine the probability density functions of propagation directions of chorus as a function of geomagnetic latitude, magnetic local time, L* parameter, and frequency. A large database of banded whistler-mode emissions and time-frequency structured chorus has been used for this analysis. This work has received EU support through the FP7-Space grant agreement no 284520 for the MAARBLE collaborative research project.
• Formation of the Earth's Ion Foreshock in the quasi-perpendicular collisionless shock region: Full-particle 2D simulation results
  
  • Savoini Philippe
  • Lembège Bertrand
  • Stienlet J.
  , 2013, 15, pp.4978. The ion foreshock located upstream of the Earth's shock front is populated with ions having interacted with the shock and then are reflected back with an high energy gain. In situ spacecrafts measurements have firmly established the existence of two distinct populations in the foreshock usptream of quasi-perpendicular shock region (i.e. for 45° ≤ ΘBn ≤ 90°, where ΘBn is the angle between the shock normal and the upstream magnetostatic field): (i) field-aligned (FAB) ion beams characterized by a gyrotropic distribution, and (ii) gyro-phase bunched (GPB) ions characterized by a NON gyrotropic distribution, which exhibit a non-vanishing perpendicular bulk velocity. Then, the purpose of the present work is to identify the different possible sources of backstreaming ions and is based on the use of 2D PIC simulations of a curved shock, where full curvature effects, time of flight effects and both electrons and ions dynamics are fully described by a self consistent approach. Our analysis evidences that these two populations mentionned above may have different origins identified both in terms of interaction time and distance of penetration. In particular, ours simulations evidence that "GPB" and FAB populations are characterized by a short (ΔTinter = 1 to 2 tci) and much larger (ΔTinter = 1 to 10 tci) interaction time respectively, where tci is the upstream ion gyroperiod. A deeper analysis of both individual and statistical ion trajectories evidences that: (i) both populations can be discriminated in terms of injection angle into the shock front (i.e. defined between the normal to the shock front and the gyration velocity vector when ions reach the shock). Such a behavior explains how reflected ions can be splitted in the observed two populations "FAB" and "GPB". (ii) ion trajectories differ between the "FAB" and "GPB" populations at the shock front. In particular, FAB and GPB ions suffer respectively multi-bounces and one bounce only. (iii) the drift associated to the "FAB" ions allows them to scan a ΘBn range between 10° and 20° (in the quasi-perpendicular domain) which accounts for their gyrotropic distribution (loss of their initial gyro-phase which is not the case for the "GPB" ions). Consequences on parallel energy gain will be illustrated with particles trajectories typical of each population.
• Density Holes, Hot Flow Anomalies and SLAMS Upstream of Earth's Bow Shock
  
  • Parks G. K.
  • Lee E.
  • Lin N.
  • Canu Patrick
  • Fu Suiyan
  • Cao J.B.
  • Dandouras I.
  • Rème H.
  • Goldstein M. L.
  , 2013, 15, pp.EGU2013-5584. Density holes (DH), Hot Flow Anomalies (HFA) and Short Large Amplitude Magnetic Structures (SLAMS) are transient structures observed in the upstream region of Earth's bow shock. The densities in these structures are depleted and in some cases as much as 99% of the ambient solar wind (SW) density. Moreover, the velocity moments of the SW show slow down and diversion in front of these structures. These structures, which can be as short as 4s (spin period of the spacecraft), are seen only when back-streaming particles are present. But not all backstreaming particles produce upstream structures and the conditions for forming these structures still remain unknown. In 2010 and 2011, the Cluster plasma ion experiment was configured to sample 3D distributions of the SW and the backstreaming particles with spin period time resolution (4s). These results show the SW beam in the hole is persistent and that evolving structures can be produced within existing DHs, HFAs and SLAMS. We present new observations of upstream structures including examples of how the structures can evolve into shocks.
• Heavy ion dynamics at Mercury
  
  • Delcourt Dominique
  , 2013. The MESSENGER spacecraft was inserted into orbit about Mercury on March 18 2011. Particle measurements from the FIPS instrument onboard this spacecraft reveal abundant populations of heavy ions such as O and Na in all magnetospheric regions. These ions appear to significantly contribute to thermal pressure, particularly in the nightside equatorial region where they can account for up to one third of the proton pressure. These heavy ion populations that originate from the planet surface via a variety of processes (e.g., thermal desorption, solar wind sputtering, micro-meteoritic bombardment...) thus have to be considered for a comprehensive investigation of the magnetosphere structure and dynamics at Mercury. We will review some transport features of these heavy ions of planetary origin. These features include : large scale convection from dayside cusp to nightside plasma sheet and subsequent nonadiabatic transport in the magnetotail, impulsive energization during short-lived reconfigurations of the magnetosphere, as well as centrifugally stimulated escape from the exosphere. We will also discuss the fate of planetary ions entering into the magnetosphere from the magnetosheath and their ring-like distribution at low latitudes.
• BV technique for investigating 1D interfaces
  
  • Dorville Nicolas
  • Belmont Gérard
  • Rezeau Laurence
  • Aunai N.
  • Retinò Alessandro
  , 2013.
• Radial evolution of thin current sheets in the Earth's magnetotail
  
  • Malova H. V.
  • Zelenyi L. M.
  • Popov V. Y.
  • Delcourt Dominique
  • Petrukovich A. A.
  , 2013, 15, pp.EGU2013-3116. The model of thin current sheet in the Earth's magnetotail taking into account the radial inhomogeneity of magnetic field is constructed and investigated. It is shown that charge particle dynamics which is different in earthward and tailward regions of current sheet is determined by large-scale changes of the normal component of the magnetic field. At the same time as transient ions support practically 1D structure of current sheet, contributions of electrons and quasi-trapped ions differ dependently on the radial distance from the Earth. Thus quasi-trapped ions should dominate in earthward region of current sheet, in contrast to electrons supporting a narrow strong peak of current density in tailward edge of current sheet. Generally, it is shown that thin current sheets in the Earth's magnetotail might be described as 2D multiscale embedded structure.
• Solar wind plasma turbulence: one or several turbulent regimes?
  
  • Dong Yue
  • Grappin Roland
  , 2013, 15, pp.3269. The average turbulent spectrum in the solar wind shows non trivial properties. At 1 AU, the average spectral index of the magnetic and kinetic spectra in the inertial range are respectively 5/3 and 3/2, which is not predicted by any turbulence theory. The spectral indices, as well as the amplitude of the fluctuations, actually vary around their average values in a non-random way: they appear to be controled by the average wind parameters, the best control parameter being the ion temperature, as first noted by Grappin Velli Mangeney 1991. We come back on this analysis here using a more refined method that isolates the inertial range from the 1/f range, allowing us to reveal a more reduced variation of the inertial range slope, which is however still controled by the ion temperature. We discuss the possible origin of the variation, and attempt to understand what it reveals on the birth of turbulence close to the Sun.
• Characteristics of banded chorus-like emission measured by the TC-1 Double Star spacecraft
  
  • Macusova E.
  • Santolík O.
  • Cornilleau-Wehrlin Nicole
  • Yearby K. H.
  , 2013, 15, pp.10341. We present a study of the spatio-temporal characteristics of banded whistler-mode emissions. It covers the full operational period of the TC-1 spacecraft, between January 2004 and the end of September 2007. The analyzed data set has been visually selected from the onboard-analyzed time-frequency spectrograms of magnetic field fluctuations below 4 kHz measured by the STAFF/DWP wave instrument situated onboard the TC-1 spacecraft with a low inclination elliptical equatorial orbit. This orbit covers magnetic latitudes between -39o and 39o. The entire data set has been collected between L=2 and L=12. Our results show that almost all intense emissions (above a threshold of 10-5nT2Hz-1) occur at L-shells from 6 to 12 and in the MLT sector from 2 to 11 hours. This is in a good agreement with previous observations. We determine the bandwidth of the observed emission by an automatic procedure based on the measured spectra. This allows us to reliably calculate the integral amplitudes of the measured signals. The majority of the largest amplitudes of chorus-like emissions were found closer to the Earth. The other result is that the upper band chorus-like emissions (above one half of the electron cyclotron frequency) are much less intense than the lower band chorus-like emissions (below one half of the electron cyclotron frequency) and are usually observed closer to the Earth than the lower band. This work has received EU support through the FP7-Space grant agreement n 284520 for the MAARBLE collaborative research project.
• Directions of equatorial noise propagation determined using Cluster and DEMETER spacecraft
  
  • Nemec F.
  • Hrbackova Z.
  • Santolík O.
  • Pickett J. S.
  • Parrot M.
  • Cornilleau-Wehrlin Nicole
  , 2013, 15, pp.EGU2013-2203. Equatorial noise emissions are electromagnetic waves at frequencies between the proton cyclotron frequency and the lower hybrid frequency routinely observed within a few degrees of the geomagnetic equator at radial distances from about 2 to 6 Re. High resolution data reveal that the emissions are formed by a system of spectral lines, being generated by instabilities of proton distribution functions at harmonics of the proton cyclotron frequency in the source region. The waves propagate in the fast magnetosonic mode nearly perpendicularly to the ambient magnetic field, i.e. the corresponding magnetic field fluctuations are almost linearly polarized along the ambient magnetic field and the corresponding electric field fluctuations are elliptically polarized in the equatorial plane, with the major polarization axis having the same direction as wave and Poynting vectors. We conduct a systematic analysis of azimuthal propagation of equatorial noise. Combined WBD and STAFF-SA measurements performed on the Cluster spacecraft are used to determine not only the azimuthal angle of the wave vector direction, but also to estimate the corresponding beaming angle. It is found that the beaming angle is generally rather large, i.e. the detected waves come from a significant range of directions, and a traditionally used approximation of a single plane wave fails. The obtained results are complemented by a raytracing analysis in order to get a comprehensive picture of equatorial noise propagation in the inner magnetosphere. Finally, high resolution multi-component measurements performed by the low-altitude DEMETER spacecraft are used to demonstrate that equatorial noise emissions can reach altitudes as low as 660 km, and that the observed propagation properties are in agreement with the overall propagation picture.
• Electron acceleration to relativistic energies at a strong quasi-parallel shock wave
  
  • Masters A.
  • Stawarz L.
  • Fujimoto M.
  • Schwartz S. J.
  • Sergis N.
  • Thomsen M. F.
  • Retinò Alessandro
  • Hasegawa H.
  • Zieger B.
  • Lewis G. R.
  • Coates A. J.
  • Canu Patrick
  • Dougherty M.
  , 2013, 15, pp.EGU2013-6522. Electrons can be accelerated to ultrarelativistic energies at strong (high-Mach number) collisionless shock waves that form when stellar debris rapidly expands after a supernova. Collisionless shock waves also form in the flow of particles from the Sun (the solar wind), and extensive spacecraft observations have established that electron acceleration at these shocks is effectively absent whenever the upstream magnetic field is roughly parallel to the shock surface normal (quasi-parallel conditions). However, it is unclear whether this magnetic dependence of electron acceleration also applies to the far stronger shocks around young supernova remnants, where local magnetic conditions are poorly understood. Here we present Cassini spacecraft observations of an unusually strong solar system shock wave (Saturn's bow shock) where significant local electron acceleration has been confirmed under quasi-parallel magnetic conditions for the first time, contradicting the established magnetic dependence of electron acceleration at solar system shocks. Furthermore, the acceleration led to electrons at relativistic energies (~MeV), comparable to the highest energies ever attributed to shock-acceleration in the solar wind. These observations suggest that at high-Mach numbers, like those of young supernova remnant shocks, quasi-parallel shocks become considerably more effective electron accelerators.
• A single spacecraft method to study the spatial profiles inside the magnetopause
  
  • Dorville Nicolas
  • Belmont Gérard
  • Rezeau Laurence
  • Aunai N.
  • Retinò Alessandro
  , 2013, 15, pp.EGU2013-2282. Previous magnetopause observations have revealed that the tangential magnetic field often rotates over C-shaped hodograms during the boundary crossing. Using observations of magnetopause crossings by the ESA Cluster mission and a simulation developed at LPP by Nicolas Aunai, we developed a single spacecraft method using the temporal information on the magnetic field in such crossings, complemented by the ion data. We can so obtain a 1D spatial parameter to characterize the depth in the layer and study the structure of the magnetopause as a function of this parameter. This allows using one single spacecraft magnetic data, completed by ion data at large temporal scales, to study the spatial structure of the boundary, and access scales that the particle temporal measurements of the four spacecraft do not permit. To obtain the normal direction and position, we first initialize our computations thanks to the standard MVABC method. Then we use the magnetic field data in the current layer, and suppose it is 1D, rotating in the tangential plane along an ellipse, with an angle variation essentially linear in space, with small sinusoidal perturbations. Making the assumption that the normal velocity of ions is dominated by the motion of the boundary and that the internal structure of the magnetopause is stationary over the duration of a crossing, we can compute the best normal direction and parameters of the model with CIS velocity and FGM magnetic field data, and so derive the spatial position of the spacecraft in the boundary. This method, which has been tested on the simulation data, could be applied successfully on several magnetopause crossings observed by Cluster. It directly gives a thickness and a normal direction, and permits to establish spatial profiles of all the physical quantities inside the boundary. It can be used to better understand the internal structure of the boundary, its physical properties and behavior regarding the flux conservation equations. The obtained results are compared with the results of other methods.
• Mercury intrinsic magnetic field : Limits of the offset-dipole representation
  
  • Chanteur Gérard
  • Modolo Ronan
  • Richer Emilie
  • Hess Sebastien
  • Leblanc François
  , 2013, 15, pp.EGU2013-6483. The interaction of the solar wind (SW) with the magnetic field of The analysis of MESSENGER orbital observations led Anderson et al (2011) to propose a dipole centered on the spin axis of the planet with a northward offset equal to 484±11 km to represent the intrinsic magnetic field of Mercury at northern latitudes higher than 30°. The magnetic moment has a magnitude of 195±10nT, points southward and is tilted by less than 3° with respect to the spin axis. The restriction to northern latitude comes from the lack of low altitude measurements of the magnetic field at southern latitudes due to MESSENGER orbit. Hence for the moment being there is no observation to constrain the representation of the southern planetary field. The suggested offset is equal to about 20% of the planetary radius which is quite a large value by comparison to 8.5% in the terrestrial case although with a lateral offset. This representation of the intrinsic field by an offset dipole suggests that the southern polar cap should be much wider than the northern one, leading to important consequences for magnetospheric dynamics. Nevertheless the offset dipole is just a convenient representation that can be fitted by the first terms of the multipolar development. The surface field of the planet produced by the offset dipole (OD) proposed by Anderson et al (2011) is thus fitted by the sum of a dipolar and a quadrupolar field (DQ) for northern latitudes higher than 50°. The resulting field differs slightly from the offset dipole field at northern latitudes but a separatrix exists at southern latitudes between dipolar-like and quadrupolar like field lines. This separatrix begins on the polar axis at an altitude RS equal to three times the ratio of the quadrupolar to the dipolar moment. When the relative axial offset of the dipole becomes larger than 16% then RS becomes larger than the planetary radius leading to important topological changes of the southern field. Global hybrid simulations of the Hermean magnetosphere for the two models OD and DQ demonstrate that the southern magnetosphere produced by the DQ model differs greatly from what is expected using the OD model (Richer et al 2012). Reference: Anderson et al., Science, 333 , 1859, (2011) Richer, E., R. Modolo, G. M. Chanteur, S. Hess, and F. Leblanc (2012), A global hybrid model for Mercury's interaction with the solar wind: Case study of the dipole representation, J. Geophys. Res., 117, A10228, doi:10.1029/2012JA017898.
• Detection of thin current sheets and associated reconnection in the Earth's turbulent magnetosheath using cluster multi-point measurements
  
  • Chasapis A.
  • Retinò Alessandro
  • Sahraoui Fouad
  • Greco A.
  • Vaivads A.
  • Sundkvist D.
  • Canu Patrick
  , 2013, 15, pp.EGU2013-5796.
• Suprathermal electron acceleration at reconnection jet fronts and braking regions in the Earth's magnetotail
  
  • Retinò Alessandro
  • Vaivads A.
  • Zieger B.
  • Fujimoto M.
  • Kasahara S.
  • Nakamura R.
  • Chasapis A.
  • Fu H.S.
  , 2013, 15, pp.EGU2013-5627. Magnetic reconnection is an efficient mechanisms for accelerating charged particles to energies much higher than their thermal energy. Important examples are the solar corona and planetary magnetospheres. A number of recent numerical simulations as well as in situ observations in Earth's magnetotail indicate that strong acceleration occurs at reconnection jet fronts, the boundary separating jetting from ambient plasma, and in jet braking regions, where jets eventually stop/dissipate. Yet the details of the acceleration mechanisms are not fully understood. Here we present a few examples of jet fronts/braking regions and associated suprathermal electron acceleration in the Earth's magnetotail, by using Cluster spacecraft data. We discuss the properties of accelerated electrons and electromagnetic fields for both jet front and jet braking regions.
• A 3D parallel model of Ganymede's exosphere
  
  • Leclercq Ludivine
  • Turc Lucile
  • Leblanc François
  • Modolo Ronan
  , 2013, pp.EGU2013-9679. Ganymede is a unique object : it is the biggest moon of our solar system, and the only satellite which has its own intrinsic magnetic field. Its surface is covered by water ice and by regolith. Some previous observations suggest that below its surface may exist an ocean of liquid water. The atmosphere of the planet is poorly known but should be composed essentially of water, hydrogen and oxygen (Marconi et al., Icarus, 2007). These atmospheric particles mainly originate from the surface thanks to sublimation of water-ice and sputtering, a process driven by the magnetospheric Jovian particles impacting Ganymede surface and leading to ejection of atoms and molecules into Ganymede atmosphere. We developed a model of Ganymede's atmosphere based on a 3D Monte Carlo description of the fate of the ejected particles from the surface. This model has been parallelized allowing a much better statistical, spatial and temporal description of Ganymede's environment. This model includes the main sources of the neutral atmosphere and is able to calculate all its characteristics. It was successfully compared to the few known observations as well as to previous modeling. In this presentation, we will present the main characteristics of this model and what it tells us on Ganymede's atmosphere, in terms of spatial structure, composition, temporal variability and relations with both magnetosphere and surface.
• Review of Recent Mid-Z Precursor Wire Array Experiments on the Zebra Generator at UNR
  
  • Stafford A.
  • Safronova Alla S.
  • Kantsyrev Viktor L.
  • Esaulov A. A.
  • Weller Michael E.
  • Osborne Glenn C.
  • Shrestha Ishor
  • Keim S. F.
  • Shlyaptseva V. V.
  • Coverdale C.
  • Chuvatin Alexandre S.
  , 2013.
• Radiation Sources with Planar Wire Arrays for ICF and High Energy Density Physics Research
  
  • Kantsyrev Viktor L.
  • Chuvatin Alexandre S.
  • Safronova Alla S.
  • Rudakov Leonid I.
  • Esaulov A. A.
  • Velikovich A. L.
  • Shrestha Ishor
  • Astanovitsky A.
  • Obsorne G. C.
  • Shlyaptseva V. V.
  • Weller S. F.
  • Keim S.
  • Stafford A.
  , 2013.
• RADIATION FROM MULTI-PLANAR WIRE ARRAYS AND APPLICATIONS
  
  • Safronova Alla S.
  • Kantsyrev Viktor L.
  • Esaulov A. A.
  • Weller Michael E.
  • Shlyaptseva V. V.
  • Shrestha Ishor
  • Osborne Glenn C.
  • Keim S. F.
  • Stafford A.
  • Chuvatin Alexandre S.
  • Apruzese J. P.
  • Giuliani J. L.
  • Coverdale C. A.
  • Jones Brent M.
  , 2013. as a Sandia report, number SAND2013-2638C
• Etudes de l'Ionosphère Equatoriale dans le cadre du réseau GIRGEA (Groupe International de Recherche en Géophysique Europe Afrique)
  
  • Amory-Mazaudier Christine
  • Fleury Rolland
  • Ouattara Frédéric Martial
  • Zerbo J.-L.
  • Pham Thi Thu Hong
  • Shimeis Amira
  • Zoundi C.
  • Fathy Ibrahim
  • Le Huy Minh
  • Mahrous A. M.
  , 2013, http://ursi-france.institut-telecom.fr/index.php?id=67. Résumé: Durant la dernière décennie dans le cadre des projets CAWSES (Climate and Weather in the Sun Earth System), AHI (Année Héliophysique Internationale) 2006-2009 et ISWI (International Space Weather Initiative) 2010-2012, la connaissance du soleil et de son impact sur les couches ionisées a considérablement avancé suivant différents canaux : - synthèse connectant la physique du soleil à celle de lionosphère - analyse de longues séries de données ionosphériques sur plusieurs cycles solaires - déploiement dinstruments (GPS et magnétomètres) sur le continent africain dans des régions où les mesures étaient inexistantes, ce fait entrainant la révision de certains modèles. Le réseau de recherche GIRGEA a profité de ces projets et développé des études des zones équatoriales en Afrique et en Asie. Cet article présente les résultats obtenus concernant principalement les variations long terme de lIonosphère équatoriale, limpact des éjections de masse coronale et des jets de vents rapides issus des trous coronaux sur les couches ionisés, et linadéquation de certains modèles à représenter les récentes observations en Afrique.
• Spectral dynamics and Predator-Prey oscillations in turbulence in fusion plasmas
  
  • Gürcan Özgür D.
  • Morel Pierre
  • Berionni Vincent
  , 2013.
• Cluster-STAFF sensitivity
  
  • Piberne Rodrigue
  • Robert Patrick
  , 2013. This software was developped in order to produce figure 8 and 9 of the article: Patrick Robert, Nicole Cornilleau-Wehrlin, Rodrigue Piberne, Y. de Conchy, C. Lacombe, et al.. CLUSTER-STAFF search coil magnetometer calibration - comparisons with FGM. Geoscientific Instrumentation, Methods and Data Systems, 2014, 3, pp.153-177. ⟨10.5194/gi-3-153-2014⟩.
• Wave emissions at ion scales close to Ganymede
  
  • Grison B.
  • Santolík O.
  • Pickett J. S.
  • Chust Thomas
  • Zouganelis I.
  , 2013.
• Goniopolarimetry with Coupled Electric and Magnetic Measurements
  
  • Cecconi Baptiste
  • Gautier Anne-Lise
  • Bergman J. E. S.
  • Chust Thomas
  • Marchaudon Aurélie
  • Cavoit C.
  • Santolýk Ondrej
  , 2013.
• Cascade and dissipation from MHD to electron scale turbulence in the solar wind
  
  • Sahraoui Fouad
  , 2013.