Publications

2014

• Sub-ion scale intermittency and the development of filamentary current structures from the Hall effect
  
  • Chapman S. C.
  • Kiyani K. H.
  • Meyrand Romain
  • Sahraoui Fouad
  • Osman K.
  , 2014, 51, pp.SH51D-4184. The distinct quantitative nature of the intermittency seen on fluid and kinetic scales in solar wind plasma turbulence is now well documented from an observational point of view. The classic high-order statistical signature rapidly transitions to a monoscaling signature as one crosses to sub-ion scales. How this scaling depends upon plasma conditions, and the underlying physical implications have yet to be fully explored. We present a study focusing on 28 intervals of solar wind magnetic field data from the Cluster spacecraft sampling a broad range of plasma parameters. We show how the scaling properties vary between these intervals and more importantly, if there are any correlations between the scaling exponents and the plasma parameter variations. We supplement this observational study with a computational investigation where we study spatial samples from an 1024³ EMHD simulation − a model for sub-ion scale magnetic field dynamics consisting solely of the Hall effect. From this, we show that the Hall-term can generate a topological change from current sheets at fluid scales to current filaments at sub-ion scales. We conjecture that this fundamental change in the coherent structures comprising the turbulence is also responsible for the change in the intermittency that we see from our observations; and which could also be responsible for dissipation at these scales.
• Three-Dimensional Iroshnikov-Kraichnan Turbulence in a Mean Magnetic Field
  
  • Muller W. C.
  • Grappin Roland
  • Verdini Andrea
  • Gürcan Özgür D.
  , 2014, 53, pp.SH53C-08. We present a new cascade scenario motivated by the three-dimensional energy spectrum observed in numerical simulations of incompressible MHD turbulence in a strong mean field. It is shown that the energy distribution is not in accord with standard critical balance and the associated scale anisotropy. This is not surprising as the present setup with isotropic large-scale forcing predominantly yields fluctuations in the weak-turbulence regime. In spite of this, measurable anisotropy of structure-function scaling exists independent of taking spatial increments with respect to the mean or local direction of the magnetic field. We, thus, propose a combination of weak Iroshnikov-Kraichnan dynamics governing energy transfer in the field-perpendicular plane and the ricochet process distributing energy quasi-resonantly along all other directions. This turbulence properties are consistent with the main numerical findings, in particular, regarding the energy spectrum: (i) an inertial-range power law exponent independent of direction, (ii) a direction-dependent power-law spectral-range extent brms/B0sim b_rms/B₀. This spectral transfer process asymptotically approaches the 2D IK-cascade as B0B₀ increases. The new transfer mechanism is at variance with the commonly accepted resonant weak-turbulence cascade as well as with the critically balanced strong turbulence cascade, both resulting in strictly perpendicular energy transfer. This is necessary to explain the significant field-parallel extent of the observed energy distribution,The findings also disagree with the small-scale dynamic-alignment phenomenology. The important dynamical roles of (i) pseudo-Alfvén waves and (ii) the correlation time of the turbulence driving are also discussed.
• Turbulent cascade in the solar wind at kinetic scales and quasi-parallel whistler waves
  
  • Alexandrova O.
  • Lacombe C.
  • Mangeney A.
  • Grappin Roland
  • Maksimovic M.
  • Matteini L.
  • Santolík O.
  • Cornilleau-Wehrlin Nicole
  • de Conchy Y.
  , 2014, 51, pp.SH51D-4190. 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 1-400 Hz, during five years (2001-2005) when Cluster was in the free solar wind, i.e. not magnetically connected to the Earth's bow-shock.In most of the analyzed time intervals, the fluctuations are non-polarized and they have a general spectral shape between the ion scales and a fraction of electron scales. The intensity of these spectra is well correlated to the ion thermal pressure. These non-polarized fluctuations seem to have a negligible frequency in the solar wind frame, and a wavevector anisotropy kperp>>k||. In the rest ~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 such waves varies between a few seconds and several hours. We analyze in details the long-lived whistler waves, i.e. with a life time longer than five minutes. We find several conditions for the appearance of such waves: (1) a low level of the background turbulence; (2) a low ion thermal pressure; (3) a slow solar wind speed; (4) an electron heat flux Qe>4muW/m2; (5) an electron mean free path larger than 0.5 AU, i.e., a low collisional frequency; (6) a change in the magnetic field direction. When the level of the background turbulence is high, we cannot affirm that whistler waves do not exist: they can be just masked by the turbulence. The six above conditions for the presence of parallel whistlers in the free solar wind are necessary but are not sufficient. When the electron parallel beta factor betae is larger than 3, the whistler waves are seen along the heat flux threshold of the whistler heat flux instability.
• In-situ observations of magnetic reconnection in the Jovian nightside magnetosphere
  
  • Kasahara S.
  • Kronberg E. A.
  • Kimura T.
  • Tao C.
  • Badman S. V.
  • Masters A.
  • Retinò Alessandro
  • Krupp N.
  • Fujimoto M.
  , 2014, 44, pp.SM44B-05. Magnetic reconnection is commonly seen in various planetary magnetospheres. However, morphologies and roles of reconnection in magnetospheric dynamics are not necessarily the same. In a classical view, the Earth's magnetosphere is driven by the solar wind through reconnection, whilst the Jovian magnetosphere has been believed to be centrifugally-driven because of the planetary fast rotation and its internal plasma source. Due to the poor data, however, detailed study of Jovian reconnection has been difficult before the first orbiting spacecraft GALILEO. In-situ observations by GALILEO, equipped with particle detectors and electric/magnetic field sensors, indeed enabled us to refine the above classical view. We show that the plasma structure of Jovian reconnection is similar to the Earth's case despite the existence of heavy ions, whilst the global distribution of transient reconnection events is yet unique to the fast-rotating magnetosphere. Observations also suggest that the solar wind may significantly participate in prominent reconnection events, which was not anticipated in the classical view.
• Twins: A New Mission to Solve the Problem of Turbulence and Energy Dissipation at Electron Scales in the Solar Wind
  
  • Sahraoui Fouad
  , 2014, 51, pp.SH51A-4132. The ESA/Cluster and the NASA/Themis missions have allowed for making a significant progress in understanding the problem of turbulence and energy dissipation at sub-ion and electron scales in the solar wind. Yet, several key questions cannot be addressed by these missions or by the upcoming ones (e.g., MMS, Solar Orbiter) because of instrumental limitations. We will discuss some of these scientific questions and instrumental limitations, then present a new mission concept, TWINS, designed to solve the problem of turbulence and energy dissipation at electron scales in the solar wind. This dual-spacecraft mission is based on the TOR concept, a single spacecraft mission proposed to the ESA/S1-class call in 2012. TWINS is one the mission concepts that is currently being discussed within the community in view of proposing it to the upcoming ESA/M4 call expected in 2014.
• Anisotropy of the cascade in MHD turbulence
  
  • Verdini Andrea
  • Grappin Roland
  • Hellinger P.
  • Landi S.
  • Muller W. C.
  , 2014, 51, pp.SH51A-4153. We use third-order structure functions to compute for the first time the three-dimensional energy cascade rate in simulations of isotropic and anisotropic MHD turbulence. We show how the Politano-Pouquet law can be used to identify the inertial range in decaying and stationary turbulence. In two case-studies we recover the fluxes characteristic of fully isotropic and anisotropic critically-balanced turbulence. We further analyze the case of three-dimensional Iroshnikov-Kraichnan turbulence (see abstract #8406, "Three-Dimensional Iroshnikov-Kraichnan Turbulence in a Mean Magnetic Field") and show how anisotropy develops thanks to an oblique cascade (in real space). We discuss further applications of the method and its relation to the anisotropy of second-order structure functions calculated with respect to the local mean field.
• Langmuir Turbulence in the Solar Wind : Numerical Simulations
  
  • Krafft C.
  • Volokitin A.
  • Krasnoselskikh V.
  , 2014, 31, pp.SH31A-4113. Observations performed in the solar wind by different satellites show that electron beams accelerated in the low corona during solar flares can propagate up to distances around 1 AU, that Langmuir waves' packets can be clumped into spikes with peak amplitudes three orders of magnitude above the mean and that the average level of density fluctuations in the solar wind plasmas can reach several percents. A Hamiltonian model is built describing the properties of Langmuir waves propagating in a plasma with random density fluctuations by the Zakharov's equations and the beam by means of particles moving self-consistently in the fields of the waves. Numerical simulations, performed using parameters relevant to solar type III conditions at 1 AU, show that when the average level of density fluctuations is sufficiently low, the beam relaxation and the wave excitation processes are similar to those in a homogeneous plasma and can be described by the quasilinear equations of the weak turbulence theory. On the contrary, when the average level of density fluctuations overcomes some threshold depending on the ratio of the thermal velocity to the beam velocity, the plasma inhomogeneities crucially influence on the characteristics of the Langmuir turbulence and the beam-plasma interaction. In this case, fluxes of accelerated particles are observed, whose density and kinetic energy can be calculated as a function of the beam and plasma characteristics. Langmuir waveforms are presented in the form they would appear if recorded by a satellite moving in the solar wind. Comparison with recent measurements by the STEREO and WIND satellites shows that their characteristic features are very similar to the observations. Moreover, wave-wave coupling and three wave decay processes are studied as a function of the average level of plasma density fluctuations. References Volokitin, V. V. Krasnoselskikh, C. Krafft, and E. Kuznetsov, Modelling of the beam-plasma interaction in a strongly inhomogeneous plasma. AIP Conf. Proc. 1539, 78 (2013). C. Krafft, A. Volokitin, V. V. Krasnoselskikh, Interaction of energetic particles with waves in strongly inhomogeneous solar wind plasmas, Astrophys. J., 778, 111 (2013).
• Exploring Plasma Turbulence in the Kronian Magnetosheath Using Cassini Data
  
  • Hadid L. Z.
  • Sahraoui Fouad
  • Kiyani Khurom Hussain
  • Modolo Ronan
  • Retinò Alessandro
  • Canu Patrick
  • Masters Adam
  • Dougherty Michele Karen
  , 2014, 51, pp.SH51A-4140. The shocked solar wind plasma upstream of the bowshock forms the magnetosheath. Through this region energy, mass and momentum are transported from the solar wind into the planet's magnetosphere, playing a crucial role in the solar-planet interactions. Hence, the planets' magnetosheath present a high level of turbulence, with a rich variety of wave and stochastic phenomena. While the magnetic turbulence of the terrestrial magnetosheath has been extensively studied, not so much work has been done regarding the planets magnetosheaths. Therefore, and in order to expand our knowledge on plasma turbulence, we investigate here the main properties of the plasma turbulence in the magnetosheath of Saturn using the Cassini spacecraft data and compare it with the well-explored terrestrial solar wind turbulence. These properties include the magnetic field energy spectra, the magnetic compressibility and intermittency, at both MHD and kinetic scales. The analysis is based on in-situ data provided by the Fluxgate Magnetometer of the MAG instrument, which measures the magnetic field data with 32ms time resolution and the plasma data from the CAPS/IMS (Cassini Plasma Spectrometer) and the Electron Spectrometer (ELS), during 39 shock-crossings between 2004 and 2005. Similarities and differences were found between the different media, in particular about the nature of the turbulence and its scaling laws. These finding will be discussed along with theoretical implications on the modeling of space plasma.
• In situ spacecraft observations of suprathermal ion acceleration in the reconnection jet braking region
  
  • Retinò Alessandro
  • Khotyaintsev Y. V.
  • Vaivads A.
  • Le Contel Olivier
  • Fu H.
  • Zieger B.
  • Nakamura R.
  • Artemyev A. V.
  • Kronberg E. A.
  , 2014, 13, pp.SM13A-4154. Reconnection jet fronts and jet braking regions are sites of strong particle energization in space and astrophysical plasmas. Jet fronts are the boundaries separating ambient from reconnection jets while braking regions is where jets are eventually stopped/diverted. Examples are jet fronts and braking regionscan be found in planetary magnetospheres, loop-top regions in the solar corona during flares and astrophysical jets. Jet braking regions have been also recently reproduced in laboratory experiments. A number of recent in situ observations in the Earth's magnetotail have allowed studying in detail electron energization mechanisms at jet fronts/braking regions. Yet, observations of suprathermal ions are scarce. Here we show Cluster spacecraft observations in the near-Earth jet braking region of suprathermal protons and oxygen up to ~ 1 MeV, that is about 10 times their thermal energy. Observations indicate that ions are trapped between large-scale oppositely-directed jets and accelerated therein by strong electric fields. We discuss possible applications of this acceleration mechanism to solar and other astrophysical plasmas.
• Magnetic Reconnection Controls Impacts of Solar Wind Ions at Mercury's Surface : Investigation By Global Hybrid Simulations
  
  • Chanteur Gérard
  • Modolo Ronan
  • Leblanc François
  , 2014, pp.P21C-3925. MESSENGER has revealed the complexity of the Hermean magnetic field which is dominated by dipolar and quadrupolar components (Anderson et al., 2012 and references therein). By contrast to other magnetized planets having large scale dynamo driven magnetic fields Mercury has a quadrupolar field large enough to reinforce the dipolar field at high northern latitudes and to shape the topology of the planetary field in the equatorial region and the southern hemisphere. Magnetic reconnection at Mercury is extremely effective for all IMF orientations [DiBraccio et al., JGR, 2013]. Global hybrid simulations by Richer et al. (2012) have demonstrated the dramatic influence of the quadrupolar field of Mercury on the topology of the Hermean magnetosphere. Then Chanteur et al. (AOGS 2014) have investigated the impacts of solar wind protons and alphas on Mercury’s surface with the same hybrid code and have presented a case study to demonstrate the importance of magnetic reconnection between the IMF and the planetary field in this process. We will present a set of different results corresponding to different configurations depending upon the IMF orientation and solar wind parameters. References Anderson, B. J., C. L. Johnson, H. Korth, R. M. Winslow, J. E. Borovsky, M. E. Purucker, J. A. Slavin, S. C. Solomon, M. T. Zuber, and R. L. McNutt Jr. (2012), Low-degree structure in Mercury’s planetary magnetic field, J. Geophys. Res., 117, E00L12, doi:10.1029/2012JE004159. DiBraccio, G. A., J. A. Slavin, S. A. Boardsen, B. J. Anderson, H. Korth, T. H. Zurbuchen, J. M. Raines, D. N. Baker, R. L. McNutt Jr., and S. C. Solomon (2013), MESSENGER observations of magnetopause structure and dynamics at Mercury, J. Geophys. Res. Space Phys., 118, 997–1008, doi:10.1002/jgra50123. 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. Chanteur, G.M., R. Modolo, and F. Leblanc (2014), Effect of the Hermean Magnetic quadrupole on Magnetic Reconnection and Penetration of the SW Plasma Inside the Magnetosphere, AOGS, 11th annual meeting, Sapporo, Japan, July 28th – August 1st.
• The Alfvén mission concept
  
  • Berthomier Matthieu
  • Fazakerley A.
  , 2014, 11, pp.SM11B-08. The Alfvén mission is a candidate to the 2014 ESA Call for M-class science missions. Its main scientific objective is to elucidate the universal physical processes at work in the Auroral Acceleration Region (AAR). The AAR is a unique laboratory for investigating strongly magnetized plasmas at an interface where ideal magneto-hydrodynamics does not apply. The Alfvén mission will investigate fundamental and multi-scale physical processes that govern what Nobel Prize laureate Hannes Alfvén named the Plasma Universe. The mission concept is designed to teach us where and how the particles that create the aurorae are accelerated, how they emit radiation, and to elucidate the ion heating and outflow processes which are slowly removing the Earth's atmosphere. The only way to distinguish between the models describing acceleration processes at the heart of Magnetosphere-Ionosphere (MI) coupling is to combine high-time resolution in situ measurements (as pioneered by the FAST mission), multi-point measurements (as pioneered by CLUSTER), and auroral arc imaging in one mission. Taking advantage of the existing dense network of ground based observatories the Alfvén mission will also allow a major breakthrough in our understanding of solar terrestrial relationships by providing key experimental measurements to large scale models of MI electrodynamics.
• Properties of Spectral Shapes of Whistler-Mode Emissions
  
  • Macusova E.
  • Santolík O.
  • Pickett J. S.
  • Gurnett D. A.
  • Cornilleau-Wehrlin Nicole
  , 2014, 43, pp.SM43B-4304. Whistler-mode emissions play an important role in wave-particle interactions occurring in the radiation belt region. Whistler mode chorus emissions consist of discrete wave packets which exhibit different spectral shapes. Rising tones (events with positive value of the frequency sweep rate) are frequently observed. Other categories of chorus spectral shapes, such as falling tones, hooks, broadband patterns, are also known. Whistler-mode emissions can additionally occur as hiss or combinations of hiss with discrete patterns. In this study, we have analyzed more than 11 years of high-time resolution measurements provided by the Wideband Data (WBD) instrument onboard four Cluster spacecraft to identify different spectral shapes of whistler mode emissions. We determine the distribution of individual groups of chorus spectral shapes in the Earth's magnetosphere and the effect of the different geomagnetic conditions on their occurrence. We focus on average polarization and propagation properties of the different types of spectral shapes, obtained during visually identified time intervals from multicomponent measurements of the STAFF-SA instrument recorded with a time resolution of 4 seconds.
• Asymmetric Reconnection With a Guide Field: the Saga Continues
  
  • Hesse Michael
  • Aunai N.
  • Liu Y. H.
  • Kuznetsova M. M.
  • Birn Joachim
  , 2014, 12, pp.SM12B-03. Magnetic reconnection at the Earth's magnetopause facilitates the transfer of mass, energy, and momentum from the solar wind into the Earth's magnetosphere. Owing to the variability of the solar wind plasma and magnetic field, the reconnection process typically involves different conditions on both inflow sides, but occasionally more symmetric conditions are encountered as well. Based on prior research we now know that the structure of the reconnection diffusion region depends substantially on the symmetry (or lack thereof) of the inflowing plasmas and magnetic fields. It is therefore of considerable interest to investigate the transition of one scenario to the other - in particular for the purpose of understanding the role of plasma mixing, heating, and of features such as pressure nongyrotropies. This presentation will involve recent theory and modeling results pertaining to these topics, and it will illuminate the means by which these kinetic processes play a role in determining the reconnection rate. Specific emphasis will be on the structure of the reconnection region, when both inflow regions are asymmetric and reconnection occurs at shear angles other than 180 degrees.
• Rebuilding of the Earth's Outer Electron Belts During the 9 October 2012 and 17 March 2013 Geomagnetic Storms
  
  • Khotyaintsev Y. V.
  • Divin A. V.
  • Graham D. B.
  • Vaivads A.
  • André M.
  • Lindqvist P. A.
  • Retinò Alessandro
  • Le Contel Olivier
  • Ergun R. E.
  • Goodrich K. A.
  • Torbert R. B.
  • Russell C. T.
  • Magnes W.
  • Nakamura R.
  • Pollock C. J.
  • Mauk B.
  • Fuselier S. A.
  , 2014, 22, pp.SM22A-06. We use multi-spacecraft observations by MMS and Cluster in the magnetotail and 3D PIC simulations to investigate conversion of electromagnetic energy at the front of a plasma jet. In PIC simulations the plasma jets (fast localized plasma flows) are produced by magnetic reconnection, while in observations we study bursty bulk flows (BBFs). Jet fronts are known to have a sharp increase of magnetic field (referred to as dipolarization fronts in the magnetospheric physics) as well as sharp gradients in plasma density and temperature. These sharp gradients at the front generate broadband turbulence in the lower-hybrid frequency range, which have amplitudes several times larger than the convective field, wave potential comparable to electron thermal energy, and perpendicular wavelength of the order of several electron gyro-scales. Despite the large wave amplitudes, we find only moderate dissipation due to these waves in the front reference frame, which goes into heating of electrons. We find that the major dissipation is happening in the Earth (laboratory) frame and it is related to reflection and acceleration of ions from the jet front. This dissipation operates at scales of the order several ion inertial lengths, and the primary contribution to E*J is coming from the convective electric field of the front (E=Vfront_x B) and the current flowing at the front.
• Full-particle 2-D Simulations of the Ion Foreshock associated to a Supercritical Quasi-perpendicular Curved Collisionless Shock : Origin of Backstreaming Energetic Particles
  
  • Savoini Philippe
  • Lembège Bertrand
  , 2014, pp.SM41A-4247. The ion foreshock located upstream of the Earth's bow shock is populated with ions reflected back by the shock front. In-situ spacecraft measurements have clearly established the existence of two distinct populations in the upstream of the quasi-perpendicular shock region (i.e. for 45o ≤ ΘBn≤ 90o, where ΘBn is the angle between the shock normal and the upstream magnetostatic field): (i) field-aligned ion beams (or 'FAB') characterized by a gyrotropic distribution, and (ii) gyro-phase bunched ions (or 'GPB') characterized by a NON gyrotropic distribution, which exhibits a non-vanishing perpendicular bulk velocity. The use of 2D PIC simulations where full curvature effects, time of flight effects and both electrons and ions dynamics are fully described, has evidenced that the shock front itself can be the possible source of these two characteristic populations. A recent analysis has evidenced that both populations can be discriminated in terms of interaction time (Δtinter) with the shock front. 'GPB' and 'FAB' populations are characterized by a short (Δtinter ~ 1 τci) and much larger (Δtinter ≥ 2 τci) interaction time respectively, where τci is the ion upstream gyroperiod. In addition, present statistical results evidence that: (i) backstreaming ions are splitted into 'FAB' and 'GPB' populations depending on their injection angle when hitting the shock front (defined between the local normal to the shock front and the gyration velocity vector). (ii) As a consequence, ion trajectories strongly differ between the 'FAB' and 'GPB' populations at the shock front. In particular, 'FAB' ions suffer multi-bounces along the curved front whereas 'GPB' ions make only one bounce. Such differences may explain why the 'FAB' population loses their gyro-phase coherency and become gyrotropic which is not the case for the 'GPB'. Then, the differences observed between 'FAB' and 'GPB' populations do not involve some distinct reflection processes as often claimed in the literature but follow from different particle time histories at the shock front. Both 'FAB' and 'GPB' ions suffer the same reflection process but only 'FAB' population loose their initial phase coherency by suffering several bounces. This important result was not expected and greatly simplifies the question of their origin.
• Current-Driven Instabilities and Energy Dissipation Rates As a Predictive Tool for Solar Probe Plus
  
  • Wilson Iii L. B.
  • Breneman A. W.
  • Malaspina D.
  • Le Contel Olivier
  • Cully C. M.
  , 2014, 41, pp.SM41A-4232. We present recent observational evidence of current-driven instabilities in the terrestrial bow shock. We use an observed positive correlation between |deltaE| and |jo| to extrapolate the results to currently inaccessible regions of space (e.g., the solar corona). Magnitudes of energy dissipation per unit volume in the solar corona due to current-driven instabilities can be estimated using electric and magnetic fields values extrapolated to coronal values. The energy dissipation values estimated this way represent an upper bound on the true energy dissipation in these regions. For instance, previous studies have estimated current densities in the solar corona to range from 104 to 107 muA m-2, which correspond to extrapolated deltaE magnitudes in excess of 12,000 mV/m and thus, energy dissipation rates in excess of 108 muW m-3. These rates are six orders of magnitude higher than is necessary to explain the temperature of the corona. Similar extrapolations can be made for astrophysical phenomena such as the surface of a neutron star. The results are of particular importance for future missions like Solar Probe Plus and Solar Orbiter.
• Connection between high-latitude arcs and the low-latitude boundary layer during periods of northward IMF
  
  • Maggiolo R.
  • Fontaine Dominique
  • Hosokawa K.
  • Maes Lukas
  • Zhang Y.
  • Fear R. C.
  • Cumnock J. A.
  • Kozlovsky A.
  • Kullen A.
  • Milan S. E.
  • Shiokawa K.
  • Echim M.
  , 2014, 13, pp.SM13F-4229. High-latitude auroral arcs are a typical feature of periods of northward IMF. They consist in thin and elongated optical emission similar to discrete auroral arcs but located in the polar ionosphere. Their formation mechanism and the magnetospheric regions to which they are connected are still not well understood. On November 10, 2005, high-latitude arcs were detected by an all-sky camera at Resolute Bay in Canada and by the TIMED/GUVI and DMSP/SUSIE space-based imagers. These observations indicate that they were detaching from the duskside auroral oval and then drifting poleward while pointing in the cusp direction. The same day, the Cluster spacecraft were flying in the dawn-dusk direction from the lobe region at altitudes ~5 RE to the magnetospheric equatorial plane at geocentric distances ~19 RE. Cluster observations reveal the presence of field-aligned acceleration regions above the polar ionosphere associated with the high-latitude arcs detected by the imagers. We analyze Cluster particle observations from the lobe region to the duskside magnetopause. In the high-latitude arcs region, Cluster detects upgoing ions and precipitating electrons accelerated by a quasi-static electric field. These accelerated particles coexist with plasmasheet-like plasma embedded in the lobe region. A comparison between the 4 Cluster spacecraft electron measurements for the most poleward arc reveals that the plasmasheet-like electron population is vanishing on a time scale of a few minutes while the plasmasheet-like ion population doesn't display any temporal evolution. The most equatorward arc is separated from the auroral oval by a "transition" region where weak fluxes of ions with plasmasheet like temperatures are detected. Then the Cluster spacecraft cross the plasmasheet until they reach the low-latitude boundary layer (LLBL) characterized by a mixture of plasmasheet and magnetosheath plasma. The "transition" region and the LLBL are magnetically connected. Using Cluster observations we show that these two regions display many similar features which suggest that the origin of high-latitude auroral arcs may be related to processes occurring in the LLBL during periods of northward IMF. We'll discuss the implication of these observations on the formation mechanisms of high-latitude auroral arcs.
• Violation of the Taylor hypothesis at electron scales in the solar wind and its effects on the energy spectra measured onboard spacecraft
  
  • Huang S. Y.
  • Sahraoui Fouad
  , 2014, 51, pp.SH51D-4189. The solar wind is a natural laboratory for the study of turbulent plasma. In-situ observations from different spacecraft such as STEREO, Wind, ACE or Cluster allow us to investigate turbulence from magnetohydrodynamic (MHD) to kinetic scales (sub-ion and electron scales) of solar wind turbulence. With single spacecraft observations the Taylor frozen-in-flow assumption (Vf<<Vsw, Vf is the phase speed of the fluctuations) is usually used to infer spatial (i.e., wavenumber) spectra from the temporal (i.e., frequency) ones measured onboard the spacecraft. While this assumption is generally valid at MHD scales, its validity at electron scales is questionable because of the possible presence of fluctuations having high phase speeds (e.g., whistler or parallel Alfvén waves). In this study we use a simple method to test the validity of Taylor hypothesis in solar wind turbulence at electron scales using the FGM and the STAFF data of the Cluster mission. We show that a significant fraction of the observed spectra violates the Taylor hypothesis. Furthermore, we introduce a toy model to investigate the effects of violating of the Taylor hypothesis on the slopes of the turbulent spectra. From different possible propagation angles and solar wind speeds we show that the slopes vary only slightly in the inertial range, while they vary significantly in the dispersive range. These simulations results can explain the narrow (resp. broader) distribution of the slopes in the inertial (resp. dispersive) range observed in the solar wind.
• Ground and satellite observations of multiple sun-aligned auroral arcs on the duskside
  
  • Hosokawa K.
  • Maggiolo R.
  • Zhang Y.
  • Fear R. C.
  • Fontaine Dominique
  • Cumnock J. A.
  • Kullen A.
  • Milan S. E.
  • Kozlovsky A.
  • Echim M.
  • Shiokawa K.
  , 2014, 13, pp.SM13F-4230. Sun-aligned auroral arcs (SAAs) are one of the outstanding phenomena in the high-latitude region during periods of northward interplanetary magnetic field (IMF). Smaller scale SAAs tend to occur either in the duskside or dawnside of the polar cap and are known to drift in the dawn-dusk direction depending on the sign of the IMF By. Studies of SAAs are of particular importance because they represent dynamical characteristics of their source plasma in the magnetosphere, for example in the interaction region between the solar wind and magnetosphere or in the boundary between the plasma sheet and tail lobe. To date, however, very little has been known about the spatial structure and/or temporal evolution of the magnetospheric counterpart of SAAs. In order to gain more comprehensive understanding of the field-aligned plasma transport in the vicinity of SAAs, we have investigated an event of SAAs on November 10, 2005, during which multiple SAAs were detected by a ground-based all-sky camera at Resolute Bay, Canada. During this interval, several SAAs were detached from the duskside oval and moved poleward. The large-scale structure of these arcs was visualized by space-based imagers of TIMED/GUVI and DMSP/SSUSI. In addition to these optical observations, we employ the Cluster satellites to reveal the high-altitude particle signature corresponding to the small-scale SAAs. The ionospheric footprints of the 4 Cluster satellites encountered the SAAs sequentially and observed well correlated enhancements of electron fluxes at weak energies (< 1 keV). The Cluster satellites also detected signatures of upflowing beams of ions and electrons in the vicinity of the SAAs. This implies that these ions and electrons were accelerated upward by a quasi-stationary electric field existing in the vicinity of the SAAs and constitute a current system in the magnetosphere-ionosphere coupling system. Ionospheric convection measurement from one of the SuperDARN radars shows an indication that the SAAs are embedded in the lobe cell during northward IMF conditions. In the presentation, we will show the results of detailed comparison between the ground-based radio and optical signatures of the SAAs and those obtained by the Cluster spacecraft at magnetospheric altitudes.
• Kinetic equilibrium for an asymmetric tangential layer with rotation of the magnetic field
  
  • Dorville Nicolas
  • Belmont Gérard
  • Aunai N.
  • Rezeau Laurence
  , 2014. Finding kinetic equilibria for tangential current layers is a key issue for the modeling of plasma phenomena such as magnetic reconnection, for which theoretical and numerical studies usually aim in starting from steady state current layers. The famous Harris equilibrium is known to be limited to symmetric layers surrounded by vacuum, with constant temperature, and constant ion and electron flow velocities, and with a current variation depending only on the density variation. It is clearly not suited for the modeling of ``magnetopause-like'' layers, which separate two plasmas of different densities and temperatures. In order to understand this kind of boundaries, Belmont et al (2012) presented a new asymmetric equilibrium which was validated in a hybrid simulation by Aunai et al (2013), and more recently in a fully kinetic simulation as well. For this equilibrium to be computed, the magnetic field had to stay coplanar inside the layer. We present here an important generalization, where the magnetic field rotates inside the layer (restricted to a 180° rotation hitherto). The tangential layers so obtained are thus closer to those encountered at the magnetopause. This will be necessary, in the future, for comparing directly the theoretical profiles with the experimental ones for the various physical parameters. As it was done previously, the equilibrium is tested with a hybrid simulation.
• Response of the Martian environment to solar wind dynamic pressure change
  
  • Modolo Ronan
  • Leblanc François
  • Chaufray Jean-Yves
  • Curry Shannon
  • Leclercq Ludivine
  • Chanteur Gérard
  • Savoini Philippe
  , 2014, pp.P51B-3951. The main structures of the solar wind plasma interaction with the upper atmosphere can be usually described using a steady state picture, however time-dependent effects play important roles. In the last couple of years sophisticated 3D simulation try to address the response of the induced magnetosphere and its escape to different time-dependent drivers. Modolo et al (2012) discussed about timescales required for the induced magnetosphere to recover from an IMF rotation. Ma et al (2013) used time-varying solar wind conditions (density and velocity enhancement) and concluded that the ionospheric/atmospheric system reach a new equilibrium in few hours. We use a 3D parallel multi-species hybrid simulation model to study the response of the induced magnetosphere to a time-varying solar wind dynamic pressure. The hybrid model (Modolo et al, 2014, in prep) includes crustal fields, a ionospheric chemistry scheme and uses a 3D description of the Martian thermosphere (Chaufray et al, 2014) and exosphere (Yagi et al, 2012). The impact of a solar wind dynamic pressure change on plasma boundaries is discussed. A special attention is focused on the time-varying energy deposition in the upper atmosphere by O+ ions precipitation as well as the escape flux of planetary ions.
• In Situ Observations of Ion Scale Current Sheets and Associated Electron Heating in Turbulent Space Plasmas
  
  • Chasapis A.
  • Retinò Alessandro
  • Sahraoui Fouad
  • Greco A.
  • Vaivads A.
  • Khotyaintsev Y. V.
  • Sundkvist D. J.
  • Canu Patrick
  , 2014, 53, pp.SH53C-06. We present a statistical study of ion-scale current sheets in turbulent space plasma. The study was performed using in situ measurements from the Earth's magnetosheath downstream of the quasi-parallel shock. Intermittent structures were identified using the Partial Variance of Increments method. We studied the distribution of the identified structures as a function of their magnetic shear angle, the PVI index and the electron heating. The properties of the observed current sheets were different for high (>3) and low (<3) values of the PVI index. We observed a distinct population of high PVI (>3) structures that accounted for ~20% of the total. Those current sheets have high magnetic shear (>90 degrees) and were observed mostly in close proximity to the bow shock with their numbers reducing towards the magnetopause. Enhancement of the estimated electron temperature within these current sheets suggest that they are important for local electron heating and energy dissipation.
• Mercury's Plasma Mantle during Solar Wind Dynamical Pressure Enhancements
  
  • Delcourt Dominique
  • Seki K.
  • Terada N.
  • Moore T. E.
  , 2014, 44, pp.SM44B-08. Because of the weak planetary magnetic field as well as proximity to the Sun, the magnetosphere of Mercury is very dynamical and at times subjected to prominent compression. Recent observations from MESSENGER reveal that during events of enhanced solar wind dynamical pressure, the subsolar magnetopause may actually be pushed until the immediate vicinity of the planet surface. Using three-dimensional single-particle simulations, we examine the dynamics of solar wind originating protons during such events. We show that these impulsive events can lead to substantial (several hundreds of eVs or a few keVs) H energization in the plasma mantle. Unlike ions with large mass-to-charge ratios (e.g., Na of planetary origin), H are transported adiabatically during these events, their energization being due to the ExB convection surge. MESSENGER observations of the plasma mantle show repeated evidences of such a transient H energization which may follow from the variable character of Mercury's magnetosphere.
• Interaction of magnetic clouds with the Earth's environment: effects due to the terrestrial bow shock
  
  • Fontaine Dominique
  • Turc Lucile
  • Savoini Philippe
  , 2014, 43, pp.SH43A-4173. Magnetic clouds represent a sub-class of coronal mass ejection (CME) well identified in the solar wind by ACE or WIND with a magnetic structure described as a flux rope. They are known as very geoeffective events, capable to trigger strong storms in the terrestrial environment. Statistical studies that address their geoeffectiveness show dependence on their orientation in the interplanetary medium, on preceding or trailing events, ... Before interacting with the magnetosphere, they cross the terrestrial bow shock and the magnetosheath. From CLUSTER observations in the magnetosheath, we show that their magnetic structure can be similar or modified downstream of the bow shock, and in some cases it presents a large rotation relative to upstream direction. The orientation of the magnetic field and in particular the orientation of the Bz component is crucial for the development of geomagnetic activity inside the magnetosphere. From observations and from simple modeling, we examine the configurations where the terrestrial bow shock is responsible for a modification of the clouds' magnetic field orientation and even for its reversal. We show that this depends on the configuration quasi-parallel/quasi-perpendicular at the shock and discuss the possible consequences for the geomagnetic activity.
• M<SUP>4</SUP> - a mission candidate for ESA M4
  
  • Retinò Alessandro
  • Vaivads A.
  , 2014, 51, pp.SH51A-4133. We present a mission concept that will be proposed in the response to the upcoming ESA M4 Call. The working name of the mission is M&#8308;. The scientific theme of the M&#8308; mission is turbulent energy dissipation and particle energization. The main focus is on turbulence and shock processes, however areas where the different fundamental processes interact, such as reconnection in turbulence or shock generated turbulence, is also of high importance. The M&#8308; mission aims to address such fundamental questions as how energy is dissipated at kinetic scales, how energy is partitioned among different plasma components, what is the relative importance of waves and coherent structures in the dissipation processes. To reach the goal a careful design work of the M&#8308; mission and its payload has been done and it is based on the earlier mission concepts of Tor, EIDOSCOPE and Cross-Scale. We present the basic concepts of the M&#8308; mission and its payload as well as illustrate how it will help to address the science questions posed.