Publications

2009

• Polar cap boundary and the reconnection electric field
  
  • Aikio A.
  • Pitkänen T.
  • Kozlovsky A.
  • Amm Olaf
  • Fontaine Dominique
  • Hubert B.
  • Fazakerley A.
  • Tscherning C. C.
  , 2009, 11, pp.9311. Magnetic reconnection on the dayside magnetopause and in the nightside magnetotail are the main factors controlling the solar wind energy transfer into the magnetosphere and the ionosphere. Reconnection on the dayside magnetopause creates open magnetic flux and moves the polar cap boundary in the equatorward direction. Reconnection in the magnetotail, either at the distant neutral line or at the near-Earth neutral line during substorm conditions, closes magnetic field lines and moves the polar cap boundary into the poleward direction. The combined effect of dayside and nightside reconnection determines finally the dynamics of the polar cap boundary. A quantity that is related to changes in the amount of open magnetic flux is the reconnection electric field. In this talk, we will review some of the results obtained by using the EISCAT radar facility and supporting instruments (e.g. the MIRACLE magnetometers, the Cluster satellite, and global UVI imagers on Polar and IMAGE satellites) in estimating the motions of the polar cap boundary and the associated reconnection electric field. We have e.g. shown that the nightside reconnection close to substorm onset consists of a series of short-lived reconnection bursts and that isolated reconnection events may occur during the substorm recovery phase. We will also show, quantitatively for the first time to our knowledge, that intensifications in the local reconnection electric field have one-to-one correlation with the appearance of auroral poleward boundary intensifications (PBIs) within the same MLT location. These PBIs are observed by the Polar UVI instrument.
• Europlanet Integrated and Distributed Information Service
  
  • Schmidt Walter
  • Capria Maria Teresa
  • Chanteur Gérard
  • Tscherning C. C.
  , 2009, 11, pp.9366. During the past decades the various disciplines in planetary sciences have developed to a very high international standard. But the collaboration between the different fields should be improved. To overcome the current fragmentation of the EU Planetary Science community and thereby to increase the scientific return of the related investment, the EU commission is funding via its Framework Program 7 the development of the "Europlanet Research Infrastructure -Europlanet RI". The Europlanet RI will consolidate the integration of the European Planetary Science community which started with Europlanet's FP6 project and will integrate major parts of the related distributed European infrastructure to be shared, fed and expanded by all planetary scientists. This infrastructure encompasses as diverse components as space exploration, ground-based observations, laboratory experiments and numerical modeling teams. Europlanet RI aims at bringing scientists from Europe and beyond together who are working in these fields, support the exchange of experts and ideas and make as many resources and data as possible available to the research community. A central part of Europlanet RI is the "Integrated and Distributed Information Service" or Europlanet-IDIS. The task of IDIS as central part of Europlanet is to provide an easy-to-use Web-based platform to locate teams and laboratories with special knowledge needed to support the own research activities, give access to the wealth of already available data, initiate new research activities needed to interpret accumulated data or to solve open questions, and to exploit synergies between space-based missions and capabilities of ground based observatories. It also offers to a wide range of teams and laboratories the possibility to share their data, advertise their capabilities and increase the scientific return by cooperation. IDIS is organized as an EU FP7 Support Activity, consisting of different access nodes which are connected by integrated search facilities, compatible structures and a common management. Each of these nodes concentrates on a special field of planetary sciences, has its own team of related international experts and is responsible for the access to information and data centres related to its area of competence. Integrated keyword-based search-possibilities direct inquiries to those node(s), most likely to return the wanted information. These nodes are hosted by the following organizations: - The Finnish Meteorological Institute (FMI) in Helsinki, Finland, hosts the Technical Node for a wide range of support activities and provides the network management. - The Institute of Planetary Research (IPR) of DLR in Berlin, Germany, hosts the Planetary Surfaces and Interiors Node, concentrating on internal structure, formation and evolution of the planets, their moons, asteroids and comets. - The Institut für Weltraumforschung, IWF (Space Research Institute) of the Austrian Academy of Sciences (OeAW) in Graz hosts the Planetary Plasma Node in close cooperation with the French space plasma data center CDPP in Toulouse. - The Institut Pierre-Simon Laplace in Paris hosts the Planetary Atmospheres Node. - The Paris Observatory hosts the Virtual Observatory Paris Data Center providing among others access to a wide range of atomic and molecular spectral databases. - The Istituto di Fisica dello Spazio Interplanetario (IFSI) in Rome hosts the Small Bodies and Dust Node, in cooperation with the ESA/ESTECs Virtual Meteor Observatory in Noordwijk, The Netherlands, concentrating on research and observations related to solar system asteroids, comets, meteors and interplanetary dust. During the next four years a set of tools for describing, accessing and combining information and data from different sources will be developed, offering finally a Virtual Observatory like access to many data essential for planetary research from European and None-European sources. Web access via any of the mentioned nodes, e.g. the Technical Node at http://www.europlanet-idis.fi
• MHD wave turbulence, numerical results
  
  • Grappin Roland
  , 2009.
• Titan s plasma wake geometry from RPWS and MAG observations
  
  • Modolo Ronan
  • Canu P.
  • Bertucci C.
  • Rosenqvist L.
  • Kurth W. S.
  • Gurnett D.
  • Dougherty M. K.
  , 2009, 11, pp.EGU2009-5912. Up to now, several tens of Titan flybys have been successfully completed by Cassini and have revealed a highly dynamic structure of the near space environment of Titan. The upstream condition of the plasma flow is expected to affect Titan's induced magnetosphere. The Titan's plasma wake has been investigated using observations from the Radio and Plasma Wave Science (RPWS) instruments (Gurnett et al, 2004) and the dual Magnetometer Technique MAG instruments (Dougherty et al, 2004). Electric field emissions were detected by the RPWS antennas during Cassini passes through Titan's wake. These narrow band emissions are identified as upper hybrid resonance emissions and therefore can provide a density estimate of the Titan's cold plasma. Some of Titan's wake flybys show a very strong asymmetry between the inbound and the outbound pass. Good examples are Ta and Tb flybys (Wahlund et al, 2005). Both flybys have a similar trajectory in Titan Interaction coordinate System (TIIS) and have the same illumination condition but the density profiles present major differences. Some of the Cassini flybys have been set back in the DRAP coordinate system (Neubauer et al, 2006) such that the upstream direction of the magnetic field is fixed, in order to determine the geometry of the plasma wake and study asymmetries. Maps of cold plasma in Titan's environment are presented. Information concerning the geometry of the wake is crucial to estimate accurately the plasma escape.
• Nonstationarity of perpendicular shocks
  
  • Hellinger P.
  • Travnicek P.
  • Lembège Bertrand
  • Savoini Philippe
  , 2009.
• Heavy species kinetics in low-pressure dc pulsed discharges in air
  
  • Pintassilgo C.D.
  • Guaitella Olivier
  • Rousseau Antoine
  Plasma Sources Science and Technology, IOP Publishing, 2009, 18, pp.025005. A time-dependent kinetic model is presented to study low-pressure (133 and 210 Pa) pulsed discharges in air for dc currents ranging from 20 to 80mA with a pulse duration from 0.1 up to 1000 ms. The model provides the temporal evolution of the heavy species along the pulse within this range time, where the coupling between vibrational and chemical kinetics is taken into account. This work shows that the predicted values for NO(X) molecules and O(3P) atoms reproduce well previous measured data for these two species. A systematic analysis is carried out on the interpretation of experimental results. It is observed that the N2(X, v 13) + O → NO(X) + N(4S) and the reverse process NO(X) + N(4S) → N2(X, v ∼ 3) + O have practically the same rates for a pulse duration longer than 10 ms, each of them playing a dominant role in the populations of NO(X), N(4S) and, to a lesser extent, in O(3P) kinetics. Our simulations show that for shorter pulse durations, from 0.1 to 10 ms, NO(X) is produced mainly via the processes N2(A) + O → NO(X) + N(2D) and N(2D) + O2 → NO(X) + O, while the oxygen atoms are created mostly from electron impact dissociation of O2 molecules and by dissociative collisions with N2(A) and N2(B) molecules. (10.1088/0963-0252/18/2/025005)
  DOI : 10.1088/0963-0252/18/2/025005
• Etch process control with a deposition-tolerant planar electrostatic probe
  
  • Booth Jean-Paul
  • Keil D.
  • Thorgrimsson C.
  • Nagai M.
  • Albarede L.
  , 2009.
• Physics of multiple-frequency capacitive discharges
  
  • Chabert Pascal
  • Levif P.
  • Raimbault Jean-Luc
  • Turner M.M.
  • Lieberman M.A.
  , 2009.
• Analysis of energetic efficiency and kinetics of intermediates in the problem of plasma assisted ignition (AIAA-2009-692)
  
  • Aleksandrov N.L.
  • Kindusheva S.V.
  • Kosarev I.N.
  • Starikovskaia Svetlana
  • Starikovskii A.Yu.
  , 2009.
• Auroral evidence for multiple reconnection in the magnetospheric tail plasma sheet
  
  • Treumann R. A.
  • Jaroschek C. H.
  • Pottelette Raymond
  EPL - Europhysics Letters, European Physical Society / EDP Sciences / Società Italiana di Fisica / IOP Publishing, 2009, 85, pp.49001. We present auroral evidence for multiple and, most probably, small-scale reconnection in the near-Earth magnetospheric plasma sheet current layer during auroral activity. Hall currents as the source of upward and downward field-aligned currents require the generation of the corresponding electron fluxes. The auroral spatial ordering in a multiple sequence of these fluxes requires the assumption of the existence of several ―-and possibly―- even many tailward reconnection sites. (10.1209/0295-5075/85/49001)
  DOI : 10.1209/0295-5075/85/49001
• Observations of Double Layers in Earth's Plasma Sheet
  
  • Ergun R. E.
  • Andersson L.
  • Tao J. B.
  • Angelopoulos V.
  • Bonnell J. W.
  • Mcfadden J. P.
  • Larson D. E.
  • Eriksson S.
  • Johansson T.
  • Cully C. M.
  • Newman D. N.
  • Goldman M. V.
  • Roux A.
  • Le Contel Olivier
  • Glassmeier K.-H.
  • Baumjohann W.
  Physical Review Letters, American Physical Society, 2009, 102, pp.155002. We report the first direct observations of parallel electric fields (E<SUB>||</SUB>) carried by double layers (DLs) in the plasma sheet of Earth's magnetosphere. The DL observations, made by the THEMIS spacecraft, have E<SUB>||</SUB> signals that are analogous to those reported in the auroral region. DLs are observed during bursty bulk flow events, in the current sheet, and in plasma sheet boundary layer, all during periods of strong magnetic fluctuations. These observations imply that DLs are a universal process and that strongly nonlinear and kinetic behavior is intrinsic to Earth's plasma sheet. (10.1103/PhysRevLett.102.155002)
  DOI : 10.1103/PhysRevLett.102.155002
• NO production on pyrex under, and after plasma exposure
  
  • Marinov Daniil
  • Guaitella Olivier
  • Rousseau Antoine
  , 2009.
• Mechanisms of filamentary plasma/catalyst coupling for air treatment
  
  • Guaitella Olivier
  • Rousseau Antoine
  • Allegraud Katia
  • Celestin S.
  , 2009.
• Kinetics of ignition of saturated hydrocarbons by nonequilibrium plasma : C<SUB>2</SUB>H<SUB>6</SUB>- to C<SUB>5</SUB>H<SUB>12</SUB>-containing mixtures
  
  • Kosarev I.N.
  • Aleksandrov N.L.
  • Kindysheva S.V.
  • Starikovskaia Svetlana
  • Starikovskii A.Yu.
  Combustion and Flame, Elsevier, 2009, 156 (1), pp.221-233. The kinetics of ignition in CnH2n 2:O2:Ar mixtures for n = 2 to 5 has been studied experimentally and numerically after a high-voltage nanosecond discharge. The ignition delay time behind a reflected shock wave was measured with and without the discharge. It was shown that the initiation of the discharge with a specific deposited energy of 1030 mJ/cm3 leads to an order of magnitude decrease in the ignition delay time. Discharge processes and following chain chemical reactions with energy release were simulated. The generation of atoms, radicals and excited and charged particles was numerically simulated using the measured time-resolved discharge current and electric field in the discharge phase. The calculated densities of the active particles were used as input data to simulate plasma-assisted ignition. The sensitivity of the results to variation in electron cross sections, reaction rates and radical composition was investigated. Good agreement was obtained between the calculated ignition delay times and the experimental data. The analysis of the simulation results showed that the effect of nonequilibrium plasma on the ignition delay is associated with faster development of chain reactions, due to atoms and radicals produced by the electron impact dissociation of molecules in the discharge phase. Finally, we studied the role of various hydrocarbon radicals in the plasma-assisted ignition of the mixtures under consideration. (10.1016/j.combustflame.2008.07.013)
  DOI : 10.1016/j.combustflame.2008.07.013
• Edge-to-center plasma density ratio in high density plasma sources
  
  • Raimbault Jean-Luc
  • Chabert Pascal
  Plasma Sources Science and Technology, IOP Publishing, 2009, 18, pp.014017. The flux of positive ions leaving a classical low-temperature plasma discharge is proportional to the plasma density at the plasmasheath edge, and the edge-to-center plasma density ratio, the so-called hl factor, normally depends only on the discharge size and the neutral gas pressure. The ion flux leaving the discharge is therefore linearly proportional to the central plasma density. The hl factor has been previously derived by solving the plasma transport equations over a large pressure range, with the assumption of constant neutral gas density within the discharge. Tonks and Langmuir derived the low pressure (collisionless) solution of this problem in 1929. More recent works have shown that the neutral gas density is no longer constant when the plasma pressure becomes comparable to the neutral gas pressure. In this paper, we solve the plasma transport equations in this new situation and we propose a new expression for the hl factor. It is shown that hl becomes a function of the central plasma density which implies that the ion flux leaving the discharge is no longer proportional to this density. This effect has to be included in particle and energy balance equations used in global models of high density plasma sources. (10.1088/0963-0252/18/1/014017)
  DOI : 10.1088/0963-0252/18/1/014017
• Study of hydrogen plasma in the negative-ion extraction region
  
  • Svarnas P.
  • Annaratone B.M.
  • Béchu Stéphane
  • Pelletier J.
  • Bacal M.
  Plasma Sources Science and Technology, IOP Publishing, 2009, 18, pp.045010. (10.1088/0963-0252/18/4/045010)
  DOI : 10.1088/0963-0252/18/4/045010
• Plasma sheet circulation pathways
  
  • Moore T. E.
  • Fok M.-C. H.
  • Delcourt Dominique
  • Slinker Steve P.
  • Damiano P.
  , 2009.
• Plasma discharge inside water
  
  • Ceccato P H
  • Guaitella Olivier
  • Rousseau Antoine
  , 2009.
• Shape, size, velocity and field-aligned currents of dayside plasma injections: a multi-altitude study
  
  • Marchaudon Aurelie
  • Cerisier Jean-Claude
  • Dunlop M.W.
  • Pitout Frederic
  • Bosqued Jean-Michel
  • Fazakerley A. N.
  Annales Geophysicae, European Geosciences Union, 2009, 27 (3), pp.1251-1266. On 20 February 2005, Cluster in the outer magnetosphere and Double Star-2 (TC-2) at mid-altitude are situated in the vicinity of the northern cusp/mantle, with Cluster moving sunward and TC-2 anti-sunward. Their magnetic footprints come very close together at about 15:28 UT, over the common field-of-view of SuperDARN radars. Thanks to this conjunction, we determine the velocity, the transverse sizes, perpendicular and parallel to this velocity, and the shape of three magnetic flux tubes of magnetosheath plasma injection. The velocity of the structures determined from the Cluster four-spacecraft timing analysis is almost purely antisunward, in contrast with the antisunward and duskward convection velocity inside the flux tubes. The transverse sizes are defined from the Cluster-TC-2 separation perpendicular to the magnetic field, and from the time spent by a Cluster spacecraft in one structure; they are comprised between 0.6 and 2 RE in agreement with previous studies. Finally, using a comparison between the eigenvectors deduced from a variance analysis of the magnetic perturbation at the four Cluster and at TC-2, we show that the upstream side of the injection flux tubes is magnetically well defined, with even a concave front for the third one giving a bean-like shape, whereas the downstream side is far more turbulent. We also realise the first quantitative comparison between field-aligned currents at Cluster calculated with the curlometer technique and with the single-spacecraft method, assuming infinite parallel current sheets and taking into account the velocity of the injection flux tubes. The results agree nicely, confirming the validity of both methods. Finally, we compare the field-aligned current distribution of the three injection flux tubes at the altitudes of Cluster and TC-2. Both profiles are fairly similar, with mainly a pair of opposite field-aligned currents, upward at low-latitude and downward at high-latitude. In terms of intensity, the field-aligned currents at Cluster are two to three times less intense than at TC-2 for the first two flux tubes, in agreement with magnetic field line convergence. For the third flux tube, the intensity is equal, which is explained by the fact that TC-2 crosses the tube on its edge. Finally, the analysis of the ion and electron moments at Cluster shows that the field-aligned currents result from a small difference between upward ion and electron fluxes. (10.5194/angeo-27-1251-2009)
  DOI : 10.5194/angeo-27-1251-2009
• Magnetic island formation between large-scale flow vortices at an undulating postnoon magnetopause for northward interplanetary magnetic field
  
  • Cully C. M.
  • Larson D. E.
  • Ergun R. E.
  • Roux A.
  • Carlson C. W.
  • Eriksson S.
  • Hasegawa H.
  • Teh W.-L.
  • Sonnerup B. U. Ö.
  • Mcfadden J. P.
  • Glassmeier K.-H.
  • Le Contel Olivier
  • Angelopoulos V.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2009, 114. Time History of Events and Macroscale Interactions during Substorms multispacecraft observations are presented for a ~2-h-long postnoon magnetopause event on 8 June 2007 that for the first time indicate that the trailing (sunward) edges of Kelvin-Helmholtz (KH) waves are commonly related to small-scale <0.56 R <SUB> E </SUB> magnetic islands or flux transfer events (FTE) during the growth phase of these surface waves. The FTEs typically show a characteristic bipolar B <SUB> N </SUB> structure with enhanced total pressure at their center. Most of the small-scale FTEs are not related to any major plasma acceleration. TH-A observations of one small FTE at a transition from the low-latitude boundary layer (LLBL) into a magnetosheath plasma depletion layer were reconstructed using separate techniques that together confirm the presence of a magnetic island within the LLBL adjacent to the magnetopause. The island was associated with a small plasma vortex and both features appeared between two large-scale (~1 R <SUB> E </SUB> long and 2000 km wide) plasma vortices. We propose that the observed magnetic islands may have been generated from a time-varying reconnection process in a low ion plasma beta (beta <SUB> i </SUB> < 0.2) and low 8.3° field shear environment at the sunward edge of the growing KH waves where the local magnetopause current sheet may be compressed by the converging flow of the large-scale plasma vortices as suggested by numerical simulations of the KH instability. (10.1029/2008JA013505)
  DOI : 10.1029/2008JA013505
• An Observation Linking the Origin of Plasmaspheric Hiss to Discrete Chorus Emissions
  
  • Bortnik J.
  • Li W.
  • Thorne R. M.
  • Angelopoulos V.
  • Cully C. M.
  • Bonnell J. W.
  • Le Contel Olivier
  • Roux A.
  Science, American Association for the Advancement of Science (AAAS), 2009, 324 (5928), pp.775-778. A long-standing problem in the field of space physics has been the origin of plasmaspheric hiss, a naturally occurring electromagnetic wave in the high-density plasmasphere (roughly within 20,000 kilometers of Earth) that is known to remove the high-energy Van Allen Belt electrons that pose a threat to satellites and astronauts. A recent theory tied the origin of plasmaspheric hiss to a seemingly different wave in the outer magnetosphere, but this theory was difficult to test because of a challenging set of observational requirements. Here we report on the experimental verification of the theory, made with a five-satellite NASA mission. This confirmation will allow modeling of plasmaspheric hiss and its effects on the high-energy radiation environment. (10.1126/science.1171273)
  DOI : 10.1126/science.1171273
• Evaluation of whistler-mode chorus intensification on the nightside during an injection event observed on the THEMIS spacecraft
  
  • Li W.
  • Thorne R. M.
  • Angelopoulos V.
  • Bonnell J. W.
  • Mcfadden J. P.
  • Carlson C. W.
  • Le Contel Olivier
  • Roux A.
  • Glassmeier K.-H.
  • Auster H.-U.
  Journal of Geophysical Research Space Physics, American Geophysical Union/Wiley, 2009, 114. The intensification of the nightside whistler-mode chorus emissions is observed in the low-density region outside the plasmapause during the injection of anisotropic plasma sheet electrons into the inner magnetosphere. Time History of Events and Macroscale Interactions During Substorms data of the electron phase space density over the energy range between 0.1 keV and 30 keV are used to develop an analytical model for the distribution of injected suprathermal electrons. The path-integrated gain of chorus waves is then evaluated with the HOTRAY code by tracing whistler-mode chorus waves in a hot magnetized plasma. The simulated wave gain is compared to the observed wave electric field and magnetic field, respectively. The results indicate that lower-energy (<1 keV) plasma sheet electrons can penetrate deeper toward the Earth but cause little chorus intensification, while higher-energy (1 keV to tens of kiloelectron volts) electrons can be injected at relatively higher L-shells and are responsible for the intensification of lower-band and upper-band whistler-mode chorus. Compared to the lower-band chorus, a relatively higher electron anisotropy is required to generate upper-band chorus. In addition, higher plasma density results in stronger wave intensity and a broader frequency band of chorus waves. (10.1029/2008JA013554)
  DOI : 10.1029/2008JA013554
• Electric propulsion using ion-ion plasmas
  
  • Aanesland Ane
  • Meige A.
  • Chabert Pascal
  Journal of Physics: Conference Series, IOP Science, 2009, 162, pp.012009. Recently, we have proposed to use both positive and negative ions for thrust in an electromagnetic space propulsion system. This concept is called PEGASES for Plasma Propulsion with Electronegative GASES and has been patented by the Ecole Polytechnique in France in 2007. The basic idea is to create a stratified plasma with an electron free (ion-ion plasma) region at the periphery of a highly ionized plasma core such that both positive and negative ions can be extracted and accelerated to provide thrust. As the extracted beam is globally neutral there is no need for a downstream neutralizer. The recombination of positive and negative ions is very efficient and will result in a fast recombination downstream of the thruster and hence there is no creation of a plasma plume downstream. The first PEGASES prototype, designed in 2007, has recently been installed in a small vacuum chamber for preliminary tests in our laboratory and the first results have been presented in several conferences. This paper reviews important work that has been used in the process of designing the first PEGASES prototype. (10.1088/1742-6596/162/1/012009)
  DOI : 10.1088/1742-6596/162/1/012009
• A novel mechanism for exciting intrinsic toroidal rotation
  
  • Mcdevitt C.J.
  • Diamond P.H.
  • Gürcan Özgür D.
  • Hahm T.S.
  Physics of Plasmas, American Institute of Physics, 2009, 16, pp.052302. Beginning from a phase space conserving gyrokinetic formulation, a systematic derivation of parallel momentum conservation uncovers two physically distinct mechanisms by which microturbulence may drive intrinsic rotation. The first mechanism, which emanates from E×B convection of parallel momentum, has already been analyzed [ O. D. Gurcan et al., Phys. Plasmas 14, 042306 (2007) ; R. R. Dominguez and G. M. Staebler, Phys. Fluids B 5, 3876 (1993) ] and was shown to follow from radial electric field shear induced symmetry breaking of the spectrally averaged parallel wave number. Thus, this mechanism is most likely active in regions with steep pressure gradients or strong poloidal flow shear. The second mechanism uncovered, which appears in the gyrokinetic formulation through the parallel nonlinearity, emerges due to charge separation induced by the polarization drift. This novel means of driving intrinsic rotation, while nominally higher order in an expansion of the mode frequency divided by the ion cyclotron frequency, does not depend on radial electric field shear. Thus, while the magnitude of the former mechanism is strongly reduced in regions of weak radial electric field shear, this mechanism remains unabated and is thus likely relevant in complementary regimes. (10.1063/1.3122048)
  DOI : 10.1063/1.3122048
• Titan's ionosphere in the magnetosheath : Cassini RPWS results during the T32 flyby
  
  • Garnier P.
  • Wahlund J.-E.
  • Rosenqvist L.
  • Modolo Ronan
  • Agren K.
  • Sergis N.
  • Canu Patrick
  • Andre M.
  • Gurnett D.A.
  • Kurth W.S.
  • Krimigis S.M.
  • Coates A.
  • Dougherty M.
  • Waite J.H
  Annales Geophysicae, European Geosciences Union, 2009, 27 (11), pp.4257-4272. The Cassini mission has provided much information about the Titan environment, with numerous low altitude encounters with the moon being always inside the magnetosphere. The only encounter taking place outside the magnetopause, in the magnetosheath, occurred the 13 June 2007 (T32 flyby). This paper is dedicated to the analysis of the Radio and Plasma Wave investigation data during this specific encounter, in particular with the Langmuir probe, providing a detailed picture of the cold plasma environment and of Titan's ionosphere with these unique plasma conditions. The various pressure terms were also calculated during the flyby. The comparison with the T30 flyby, whose geometry was very similar to the T32 encounter but where Titan was immersed in the kronian magnetosphere, reveals that the evolution of the incident plasma has a significant influence on the structure of the ionosphere, with in particular a change of the exo-ionospheric shape. The electrical conductivities are given along the trajectory of the spacecraft and the discovery of a polar plasma cavity is reported. (10.5194/angeo-27-4257-2009)
  DOI : 10.5194/angeo-27-4257-2009