N. Cornilleau-Wehrlin

École Polytechnique, Paliseau, Île-de-France, France

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Publications (253)355.86 Total impact

  • Source
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    ABSTRACT: The nature of the magnetic field fluctuations in the solar wind between the ion and electron scales is still under debate. Using the Cluster/STAFF instrument, we make a survey of the power spectral density and of the polarization of these fluctuations at frequencies $f\in[1,400]$ Hz, during five years (2001-2005), when Cluster was in the free solar wind. In $\sim 10\%$ of the selected data, we observe narrow-band, right-handed, circularly polarized fluctuations, with wave vectors quasi-parallel to the mean magnetic field, superimposed on the spectrum of the permanent background turbulence. We interpret these coherent fluctuations as whistler mode waves. The life time of these waves varies between a few seconds and several hours. Here we present, for the first time, an analysis of long-lived whistler waves, i.e. lasting more than five minutes. We find several necessary (but not sufficient) conditions for the observation of whistler waves, mainly a low level of the background turbulence, a slow wind, a relatively large electron heat flux and a low electron collision frequency. When the electron parallel beta factor $\beta_{e\parallel}$ is larger than 3, the whistler waves are seen along the heat flux threshold of the whistler heat flux instability. The presence of such whistler waves confirms that the whistler heat flux instability contributes to the regulation of the solar wind heat flux, at least for $\beta_{e\parallel} \ge$ 3, in the slow wind, at 1 AU.
    The Astrophysical Journal 10/2014; 796(1). · 6.73 Impact Factor
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    ABSTRACT: [1] Equatorial noise (EN) 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. They propagate in the extraordinary (fast magnetosonic) mode nearly perpendicularly to the ambient magnetic field. We conduct a systematic analysis of azimuthal directions of wave propagation, using all available Cluster data from 2001 to 2010. Altogether, combined measurements of the Wide-Band Data and Spectrum Analyzer of the Spatio-Temporal Analysis of Field Fluctuations instruments allowed us to determine azimuthal angle of wave propagation for more than 100 EN events. It is found that the observed propagation pattern is mostly related to the plasmapause location. While principally isotropic azimuthal directions of EN propagation were detected inside the plasmasphere, wave propagation in the plasma trough was predominantly found directed to the West or East, perpendicular to the radial direction. The observed propagation pattern can be explained using a simple propagation analysis, assuming that the emissions are generated close to the plasmapause.
    Journal of Geophysical Research: Space Physics 11/2013; 118(11). · 3.44 Impact Factor
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    ABSTRACT: We provide evidence of the simultaneous occurrence of large-amplitude, quasi-parallel whistler mode waves and ion-scale magnetic structures, which have been observed by the Cluster spacecraft in the plasma sheet at 17 Earth radii, during a substorm event. It is shown that the magnetic structures are characterized by both a magnetic field strength minimum and a density hump and that they propagate in a direction quasi-perpendicular to the average magnetic field. The observed whistler mode waves are efficiently ducted by the inhomogeneity associated with such ion-scale magnetic structures. The large amplitude of the confined whistler waves suggests that electron precipitations could be enhanced locally via strong pitch angle scattering. Furthermore, electron distribution functions indicate that a strong parallel heating of electrons occurs within these ion-scale structures. This study provides new insights on the possible multiscale coupling of plasma dynamics during the substorm expansion, on the basis of the whistler mode wave trapping by coherent ion-scale structures.
    Journal of Geophysical Research Atmospheres 10/2013; 118(10):6072-6089. · 3.44 Impact Factor
  • F. Němec, O. Santolík, J. S. Pickett, M. Parrot, N. Cornilleau-Wehrlin
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    ABSTRACT: Quasiperiodic (QP) emissions are electromagnetic waves at frequencies of about 0.5-4 kHz characterized by a periodic time modulation of the wave intensity, with a typical modulation period on the order of minutes. We present results of a survey of QP emissions observed by the Wide-Band Data (WBD) instruments on board the Cluster spacecraft. All WBD data measured in the appropriate frequency range during the first 10 years of operation (2001-2010) at radial distances lower than 10 RE were visually inspected for the presence of QP emissions, resulting in 21 positively identified events. These are systematically analyzed, and their frequency ranges and modulation periods are determined. Moreover, a detailed wave analysis has been done for the events that were strong enough to be seen in low-resolution Spatio-Temporal Analysis of Field Fluctuations-Spectrum Analyzer data. Wave vectors are found to be nearly field-aligned in the equatorial region, but they become oblique at larger geomagnetic latitudes. This is consistent with a hypothesis of unducted propagation. ULF magnetic field pulsations were detected at the same time as QP emissions in 4 out of the 21 events. They were polarized in the plane perpendicular to the ambient magnetic field, and their frequencies roughly corresponded to the modulation period of the QP events.
    Journal of Geophysical Research Atmospheres 07/2013; 118(7):4210-4220. · 3.44 Impact Factor
  • Zuzana Hrbáčková, Ondřej Santolík, Nicole Cornilleau-Wehrlin
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    ABSTRACT: 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.
    04/2013;
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    ABSTRACT: 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.
    04/2013;
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    ABSTRACT: 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.
    04/2013;
  • Eva Macúšová, Ondřej Santolík, Nicole Cornilleau-Wehrlin, Keith Yearby
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    ABSTRACT: 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.
    04/2013;
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    ABSTRACT: Electron scale solar wind turbulence has attracted great interest in recent years. Clear evidences have been given from the Cluster data that turbulence is not fully dissipated near the proton scale but continues cascading down to the electron scales. However, the scaling of the energy spectra as well as the nature of the plasma modes involved at those small scales are still not fully determined. Here we survey 10 years of the Cluster search-coil magnetometer (SCM) waveforms measured in the solar wind and perform a statistical study of the magnetic energy spectra in the frequency range [$1, 180$]Hz. We show that a large fraction of the spectra exhibit clear breakpoints near the electon gyroscale $\rho_e$, followed by steeper power-law like spectra. We show that the scaling below the electron breakpoint cannot be determined unambiguously due to instrumental limitations that will be discussed in detail. We compare our results to recent ones reported in other studies and discuss their implication on the physical mechanisms and the theoretical modeling of energy dissipation in the SW.
    The Astrophysical Journal 03/2013; 777(1). · 6.73 Impact Factor
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    ABSTRACT: Quasi‐periodic (QP) emissions are electromagnetic emissions at frequencies of about 0.5–4 kHz that are characterized by a periodic time modulation of the wave intensity. Typical periods of this modulation are on the order of minutes. We present a case study of a large‐scale long‐lasting QP event observed simultaneously on board the DEMETER (Detection of Electro‐Magnetic Emissions Transmitted from Earthquake Regions) and the Cluster spacecraft. The measurements by the Wide‐Band Data instrument on board the Cluster spacecraft enabled us to obtain high‐resolution frequency‐time spectrograms of the event close to the equatorial region over a large range of radial distances, while the measurements by the STAFF‐SA instrument allowed us to perform a detailed wave analysis. Conjugate observations by the DEMETER spacecraft have been used to estimate the spatial and temporal extent of the emissions. The analyzed QP event lasted as long as 5 h and it spanned over the L‐shells from about 1.5 to 5.5. Simultaneous observations of the same event by DEMETER and Cluster show that the same QP modulation of the wave intensity is observed at the same time at very different locations in the inner magnetosphere. ULF magnetic field fluctuations with a period roughly comparable to, but somewhat larger than the period of the QP modulation were detected by the fluxgate magnetometers instrument on board the Cluster spacecraft near the equatorial region, suggesting these are likely to be related to the QP generation. Results of a detailed wave analysis show that the QP emissions detected by Cluster propagate unducted, with oblique wave normal angles at higher geomagnetic latitudes.
    Journal of Geophysical Research Atmospheres 01/2013; 118(1):198-208. · 3.44 Impact Factor
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    ABSTRACT: We summarize the outcome of the scientific and technical study conducted in the past 3 years for the definition and prototyping of a LOFAR Super Station (LSS) in Nançay. We first present the LSS concept, then the steps addressed by the design study and the conclusions reached. We give an overview of the science case for the LSS, with special emphasis on the interest of a dedicated backend for standalone use. We compare the expected LSS characteristics to those of large low-frequency radio instruments, existing or in project. The main advantage of the LSS in standalone mode will be its very high instantaneous sensitivity, enabling or significantly improving a broad range of scientific studies. It will be a SKA precursor for the French community, both scientific and technical.
    SF2A-2012: Proceedings of the Annual meeting of the French Society of Astronomy and Astrophysics. Eds.: S. Boissier, P. de Laverny, N. Nardetto, R. Samadi, D. Valls-Gabaud and H. Wozniak, pp.687-694; 12/2012
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    ABSTRACT: We present a new model of self-consistent coupling between low frequency, ion-scale coherent structures with high frequency whistler waves in order to interpret Cluster data. The idea relies on the possibility of trapping whistler waves by inhomogeneous external fields where they can be spatially confined and propagate for times much longer than their characteristic electronic time scale. Here we take the example of a slow magnetosonic soliton acting as a wave guide in analogy with the ducting properties of an inhomogeneous plasma. The soliton is characterized by a magnetic dip and density hump that traps and advects high frequency waves over many ion times. The model represents a new possible way of explaining space measurements often detecting the presence of whistler waves in correspondence to magnetic depressions and density humps. This approach, here given by means of slow solitons, but more general than that, is alternative to the standard approach of considering whistler wave packets as associated with nonpropagating magnetic holes resulting from a mirror-type instability.
    Physical Review Letters 10/2012; 109(15):155005. · 7.73 Impact Factor
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    ABSTRACT: Acceleration and dynamics of energetic electrons in the outer Van Allen radiation belt can be influenced by cross-energy coupling among the particle populations in the radiation belts, ring current and plasmasphere. Waves of different frequencies have been shown to play a significant role in these interactions. We analyze more than 10 years of measurements of the four Cluster spacecraft to investigate propagation properties of whistler-mode waves in the crucial regions of the Earth's magnetosphere. We use this unprecedented database to determine the distribution of the wave energy density in the space of the wave vector directions, which is a crucial parameter for modeling of both the wave-particle interactions and wave propagation in the inner magnetosphere. We show implications for radiation belt studies and upcoming inner magnetosphere spacecraft missions, and we also show similarities of the observed whistler-mode waves with results from the magnetosphere of Saturn collected by the Cassini mission.
    07/2012;
  • Z. Hrbackova, O. Santolik, F. Nemec, N. Cornilleau-Wehrlin
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    ABSTRACT: We report results of a statistical analysis of equatorial noise (EN) emissions based on the data set collected by the four Cluster spacecraft between January 2001 and December 2010. We have investigated a large range of the McIlwain's parameter from L≈1 to L≈12 thanks to the change of orbital parameters of the Cluster mission. We have processed data from the STAFF-SA instruments which analyze measurements of electric and magnetic field fluctuations onboard and provide us with hermitian spectral matrices. We have used linear polarization of magnetic field fluctuations as a selection criterion. Propagation in the vicinity of the geomagnetic equator has been used as an additional criterion for recognition of EN. We have identified more than 2000 events during the investigated time period. We demonstrate that EN can occur at all the analyzed L-shells. However, the occurrence rate at L-shells below 2.5 and above 7.0 is very low. We show that EN occurs in the plasmasphere as well as outside of the plasmasphere but with a lower occurrence rate.
    04/2012;
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    ABSTRACT: Intense whistler-mode waves can be generated by cyclotron interactions with anisotropic electrons at energies between a few and tens of keV. It has been shown that whistler-mode waves propagating in the Earth's magnetosphere can influence relativistic electrons in the outer Van Allen radiation belt. These electromagnetic wave emissions are therefore receiving increased attention for their possible role in coupling electron populations at lower energies to the electron radiation belt. Whistler-mode chorus emissions are known for their predominant occurrence in the dawnside and dayside magnetosphere. While it is generally accepted that dawnside chorus is excited by injected anisotropic plasma sheet electrons, the details of this process are still debated. Especially, possible mechanisms describing the origin of the dayside chorus are a subject of active research, including the role of the plasma density variations, and the role of a particular dayside configuration of the compressed Earth's magnetic field. We use data collected by the Cluster mission during the last few years, when the orbit of the Cluster spacecraft reached to larger radial distances from the Earth in the dayside low-latitude region. We analyze multipoint measurements of the WBD and STAFF-SA instruments. We investigate propagation and spectral properties of the observed whistler-mode waves. We concentrate our analysis on the properties of the chorus source and we show that the dayside magnetic field topology can lead to a displacement of the source region from the dipole equator to higher latitudes.
    04/2012;
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    ABSTRACT: Strong ULF wave activity has been observed at magnetopause crossings since a long time. Those turbulent-like waves are possible contributors to particle penetration from the Solar Wind to the Magnetosphere through the magnetopause. Statistical studies have been performed to understand under which conditions the ULF wave power is the most intense and thus the waves can be the most efficient for particle transport from one region to the other. Clearly the solar wind pressure organizes the data, the stronger the pressure, the higher the ULF power (Attié et al 2008). Double STAR-Cluster comparison has shown that ULF wave power is stronger at low latitude than at high latitude (Cornilleau-Wehrlin et al, 2008). The different studies performed have not, up to now, shown a stronger power in the vicinity of local noon. Nevertheless under identical activity conditions, the variability of this power, even at a given location in latitude and local time is very high. The present work intends at understanding this variability by means of the multi spacecraft mission Cluster. The data used are from spring 2008, while Cluster was crossing the magnetopause at low latitude, in particularly quite Solar Wind conditions. The first region of interest of this study is the sub-solar point vicinity where the long wavelength surface wave effects are most unlikely.
    04/2012;
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    ABSTRACT: EMIC triggered emissions are observed close to the equatorial plane of the magnetosphere at locations where EMIC waves are commonly observed: close to the plasmapause region and in the dayside magnetosphere close to the magnetopause. Their overall characteristics (frequency with time dispersion, generation mechanism) make those waves the EMIC analogue of rising frequency whistler-mode chorus emissions. In our observations the Poynting flux of these emissions is usually clearly arriving from the equatorial region direction, especially when observations take place at more than 5 degrees of magnetic latitude. Simulations have also confirmed that the conditions of generation by interaction with energetic ions are at a maximum at the magnetic equator (lowest value of the background magnetic field along the field line). However in the Cluster case study presented here the Poynting flux of EMIC triggered emissions is propagating toward the equatorial region. The large angle between the wave vector and the background magnetic field is also unusual for this kind of emission. The rising tone starts just above half of the He+ gyrofrequency (Fhe+) and it disappears close to Fhe+. At the time of detection, the spacecraft magnetic latitude is larger than 10 degrees and L shell is about 4. The propagation sense of the emissions has been established using two independent methods: 1) sense of the parallel component of the Poynting flux for a single spacecraft and 2) timing of the emission detections at each of the four Cluster spacecraft which were in a relatively close configuration. We propose here to discuss this unexpected result considering a reflection of this emission at higher latitude.
    AGU Fall Meeting Abstracts. 12/2011;
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    ABSTRACT: Whistler-mode chorus emissions are known for their capacity to interact with energetic electrons. We use data collected by the Cluster mission after 2005, when the orbit of the four Cluster spacecraft changed, thus facilitating the analysis of chorus in a large range of different radial distances from the Earth. We concentrate our analysis on the equatorial source region of chorus. We use multipoint measurements of the WBD and STAFF-SA instruments to characterize propagation and spectral properties of the observed waves. We show that intense whistler-mode emissions are found at large radial distances up to the dayside magnetopause. These emissions either have the form of hiss or they contain the typical structure of chorus wave packets. This result is supported by case studies as well as by statistical results, using the unprecedented database of Cluster measurements.
    AGU Fall Meeting Abstracts. 12/2011;
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    ABSTRACT: Investigating space plasma turbulence from single-point measurements is known to be characterized by unavoidable ambiguities in disentangling temporal and spatial variations. Solving this problem has been one of the major goals of the Cluster mission. For that purpose multipoint measurements techniques, such as the k-filtering, have been developed. Such techniques combine several time series recorded simultaneously at different points in space to estimate the corresponding energy density in the wavenumber space. Here we apply the technique to both simulated and Cluster magnetometer data in the solar wind (SW) and investigate the errors and limitations that arise due to the separation of the spacecraft and the quality of the tetrahedral configuration. Specifically, we provide an estimation of the minimum and maximum scales that can be accurately measured given a specific distance between the satellites and show the importance of the geometry of the tetrahedron and the relationship of that geometry to spatial aliasing. We also present recent results on characterizing small scale SW turbulence and provide scientific arguments supporting the need of new magnetometers having better sensitivity than the existing ones. Throughout the paper we emphasize technical challenges and their solutions that can be considered for a better preparation of the Cross-Scale mission.
    Planetary and Space Science 01/2011; 59(7):585-591. · 2.11 Impact Factor
  • O. Santolik, J. S. Pickett, M. Parrot, D. A. Gurnett, N. Cornilleau-Wehrlin
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    ABSTRACT: Whistler-mode waves, especially chorus, can influence energetic electrons in the Van Allen radiation belts. These electromagnetic waves propagate over long distances in the magnetosphere. It has been previously shown that chorus can propagate from its equatorial source down to the subauroral ionosphere. We investigate cases where whistler-mode waves were simultaneously measured by the Cluster spacecraft in the magnetosphere and by the low-orbiting Demeter spacecraft. Multicomponent measurements of both these spacecraft missions allow us to investigate the wave-vector directions and Poynting flux. We can therefore show conjugate propagation properties of the waves in two different magnetospheric regions.
    01/2011;

Publication Stats

2k Citations
355.86 Total Impact Points

Institutions

  • 2012–2013
    • École Polytechnique
      Paliseau, Île-de-France, France
    • Università di Pisa
      • Department of Physics "E.Fermi"
      Pisa, Tuscany, Italy
  • 2011–2013
    • Laboratory of Plasma Physics
      Paliseau, Île-de-France, France
  • 2010
    • La Station de Radioastronomie de Nançay
      Orléans, Centre, France
  • 2005–2009
    • French National Centre for Scientific Research
      • Laboratoire de physique et chimie de l'environnement et de l'Espace (LPC2E)
      Lutetia Parisorum, Île-de-France, France
    • University of Iowa
      • Department of Physics and Astronomy
      Iowa City, IA, United States
  • 2007
    • University of California, Berkeley
      • Space Sciences Laboratory
      Berkeley, MO, United States
  • 2005–2006
    • Charles University in Prague
      • Matematicko-fyzikální fakulta
      Praha, Hlavni mesto Praha, Czech Republic
  • 2004–2006
    • Institut Pierre Simon Laplace
      Lutetia Parisorum, Île-de-France, France
  • 1997
    • Université de Versailles Saint-Quentin
      Versailles, Île-de-France, France
    • West Virginia University
      • Department of Physics
      Morgantown, West Virginia, United States
    • Université Paris-Sud 11
      • Institut d'Astrophysique Spatiale
      Orsay, Île-de-France, France
  • 1995
    • Imperial Valley College
      Los Alamos, New Mexico, United States
  • 1993
    • Observatoire de Paris
      Lutetia Parisorum, Île-de-France, France
  • 1978
    • The University of Sheffield
      Sheffield, England, United Kingdom