Publications

2015

• Microtearing turbulence: magnetic braiding and disruption limit
  
  • Firpo Marie-Christine
  Physics of Plasmas, American Institute of Physics, 2015, 22, pp.122511. A realistic reduced model involving a large poloidal spectrum of microtearing modes is used to probe the existence of some stochasticity of magnetic field lines. Stochasticity is shown to occur even for the low values of the magnetic perturbation δB/B devoted to magnetic turbulence that have been experimentally measured. Because the diffusion coefficient may strongly depend on the radial (or magnetic-flux) coordinate, being very low near some resonant surfaces, and because its evaluation implicitly makes a normal diffusion hypothesis, one turns to another indicator appropriate to diagnose the confinement: the mean residence time of magnetic field lines. Their computation in the microturbulence frame points to the existence of a disruption limit, namely of a critical order of magnitude of δB/B above which stochasticity is no longer benign yet leads to a macroscopic loss of confinement in some tens to hundred of electron toroidal excursions. Since the level of magnetic turbulence δB/B has been measured to grow with the plasma electron density this would also be a density limit. (10.1063/1.4938273)
  DOI : 10.1063/1.4938273
• Parallel Electric Fields and Wave Phenomena Associated with Magnetic Reconnection: The Merged Magnetic Field Product from MMS
  
  • Argall M. R.
  • Torbert R. B.
  • Le Contel Olivier
  • Russell C. T.
  • Magnes W.
  • Strangeway R. J.
  • Bromund K. R.
  • Lindqvist P. A.
  • Marklund G. T.
  • Ergun R. E.
  • Khotyaintsev Y. V.
  , 2015, 51. Kinetic processes associated with magnetic reconnection current structures are able to be resolved for the first time by the instrument suites and small inter-spacecraft separation of MMS. Measurements of the parallel electric fields responsible for electron acceleration, and wave activity associated with reconnection onset and electron scattering require precise knowledge of the magnetic field amplitude and phase. The fluxgate and searchcoil magnetometers on MMS are sensitive to low- and high-frequency field fluctuations, respectively. In the middle frequency range, we optimize sensitivity by merging the two datasets to create a single magnetic field data product. We analyze frequency-dependent amplitude and phase relationships between the two instruments to determine how they should be joined. The result is a product with the time resolution and Nyquist frequency of the searchcoil, but with the fluxgate's ability to measure the DC magnetic field. This dataset provides improved phase information suitable for determining parallel electric fields during magnetic reconnection events. Its enhanced sensitivity also makes it ideal for resolving thin current layers and uncovering low-amplitude wave activity, such as EMIC waves related to substorm injections and Alfven or lower hybrid waves related to reconnection.
• Transport of Solar Wind Across Earth's Bow Shock
  
  • Parks G. K.
  • Lee E.
  • Yang Z.
  • Liu Y.
  • Fu S. Y.
  • Canu Patrick
  • Goldstein M. L.
  • Dandouras I. S.
  • Rème H.
  • Hong J.
  , 2015, 13. Observations have established that about 20% of the solar wind (SW) is reflected and 80% directly transmitted across Earth's bow shock (Skopke et al, Adv. Space Sci., 15, No. 8/9, 269, 1995). The transmitted SW is not immediately thermalized and the magnetosheath plasma distribution can remain non-Maxwellian for a long time. Cluster observations have further established that most of the magnetosheath bulk flow remains super-Alfvenic except in the polar altitudes near the cusp region (Longmore et al., Anna. Geophysicae, 23, 3351-3364, 2005). We have studied SW ion distributions before and after entering the bow shock to examine the details of the solar wind-bow shock interaction. Preliminary findings indicate that a typical SW H beam with thermal kT ~10 eV drifting at 400 km/s in front of the bow shock appears as ~12 eV beam drifting at 250 km/s after it penetrates the shock barrier. The small kT increase is possibly due to wave-particle interaction at the boundary. While the He ion beam kT behaves similarly as H ions, the drift velocities of He ions do not always slow down as H ions. These observations indicate the physics of SW-bow shock interaction is much more complicated than the models that explain SW slow down as resulting from an electrostatic potential at the shock that decelerates the SW. We have started PIC simulation of SW transport across the bow shock and the results will be presented together with observations.
• An MMS multicase study of magnetotail dipolarization fronts
  
  • Schmid D.
  • Nakamura R.
  • Plaschke F.
  • Volwerk M.
  • Narita Y.
  • Baumjohann W.
  • Magnes W.
  • Fischer D.
  • Torbert R. B.
  • Russell C. T.
  • Strangeway R. J.
  • Leinweber H. K.
  • Bromund K. R.
  • Anderson B. J.
  • Le G.
  • Chutter M.
  • Slavin J. A.
  • Kepko L.
  • Moldwin M.
  • Le Contel Olivier
  , 2015, 51, pp.SM51A-2516. Dipolarization fronts (DFs) are characterized by a rapid increase in the northward magnetic field component (Bz) and play a crucial role in the energy and magnetic flux transport in the magnetotail. Multispacecraft observations of DFs in a large portion of the magnetotail by e.g. Geotail, Cluster and THEMIS have been reported for over three decades.During the commissioning phase of MMS we are able to observe DFs at radial distances within 8 Re, which is in a more dipolarized region (well within the flow braking region). We present a statistical study of DFs observed during March-May 2015, using only magnetic field data. First results indicate that the amplitude of the found DFs is greater compared to similar events in the distant tail. Timing analysis yields that many of the DFs propagate tailward, which would suggest a rebound (bouncing) of the DF at the magnetic dipole-dominated near-Earth plasma sheet. Since MMS spacecraft are in a "string-of-pearls" configuration, further analysis is ongoing to evaluate the obtained direction from a simple timing analysis. We compare and contrast the found DFs with that from the DF-eventlist introduced in Schmid et al. [J. Geophys. Res., 2, 120 (2015)], which is based on 9 years (2001-2009) of Cluster magnetotail observations.
• Cold ion heating at the low-latitude magnetopause during magnetic reconnection
  
  • Khotyaintsev Y. V.
  • Lavraud B.
  • Divin A. V.
  • Aunai N.
  • Graham D. B.
  • Toledo-Redondo Sergio
  • Andre M.
  • Vaivads A.
  , 2015, 52, pp.SM52B-02. It has been recently shown that cold ions (energies up to tens of eV) of ionospheric origin are present in the magnetosphere and they can reach the magnetopause, entraining magnetic reconnection. They are of particular importance at low-latitudes where they can dominate over the hot magnetospheric ions (tens of keV). Cold ions have smaller gyroradius, and therefore they remain magnetized down to smaller spatial scales than the hot ions, introducing a new length-scale into the reconnection process. The Cluster orbit crossed the subsolar magnetopause region several times during 2007 and 2008. We observe cold ions ExB drifting with the strong E fields set up during reconnection in many of these crossings. At the same time, the cold ions are heated when convecting towards the exhausts. We investigate the heating mechanisms of the cold ions using two spacecraft, to distinguish spatial and time variations of the E fields.
• First MMS Observations of High Time Resolution 3D Electric and Magnetic fields at the Dayside Magnetopause.
  
  • Torbert R. B.
  • Burch J. L.
  • Russell C. T.
  • Magnes W.
  • Ergun R. E.
  • Lindqvist P. A.
  • Le Contel Olivier
  • Vaith H.
  • Macri J.
  • Myers S.
  • Rau D.
  • Needell J.
  • King B.
  • Granoff M.
  • Chutter M.
  • Dors I.
  • Argall M. R.
  • Shuster J. R.
  • Olsson G.
  • Marklund G. T.
  • Khotyaintsev Y. V.
  • Eriksson A. I.
  • Kletzing C.
  • Bounds S. R.
  • Anderson B. J.
  • Baumjohann W.
  • Steller M.
  • Bromund K. R.
  • Le G.
  • Nakamura R.
  • Strangeway R. J.
  • Leinweber H. K.
  • Tucker S.
  • Westfall J.
  • Fischer D.
  • Plaschke F.
  • Pollock C. J.
  • Giles B. L.
  • Moore T. E.
  • Mauk B.
  • Fuselier S. A.
  , 2015, 41. The electrodynamics at the magnetopause is key to our understanding of ion and electron acceleration within reconnection regions. The Magnetospheric Multiscale (MMS) fleet of four spacecraft was launched into its Phase-1 equatorial orbit of 12 Re apogee specifically to investigate these regions at the Earth's magnetopause. In addition to a comprehensive suite of particle measurements, MMS makes very high time resolution 3D electric and magnetic field measurements of high accuracy using flux-gate, search coil, 3-axis double probe, and electron drift sensors. In September 2015, the MMS fleet will begin to encounter the dusk-side magnetopause in its initial configuration of approximately 160 km separation, allowing investigation of the spatial and temporal characteristics of important electrodynamics during reconnection. Using these field and particle measurements, we present first observations of 3D magnetic and electric fields (including their parallel component), and inferred current sheets, during active magnetopause crossings using the highest time resolution data available on MMS.
• Conversion of electromagnetic energy at plasma jet fronts
  
  • 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.
  , 2015, 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.
• Expert meeting of United Nations 'International Committee of Global Navigation Satellite System
  
  • Amory-Mazaudier Christine
  , 2015. In this paper we presented the evolution of the training in Geophysics and Space Weather, mainly in developing countries (Africa and Asia) from the period 1992 until now. The implementation of GPS in many countries allows the development of Space Weather research. The following points presented are: -The definition of the work (this point changes from one country to another) -The training of students (school and PhD) -The organization of research groups in the various countries -The curricula on Space Weather in the Universities of the different countries -The publications in international scientific journals
• Calibrating MMS Electron Drift Instrument (EDI) Ambient Electron Flux Measurements and Characterizing 3D Electric Field Signatures of Magnetic Reconnection
  
  • Shuster J. R.
  • Torbert R. B.
  • Vaith H.
  • Argall M. R.
  • Li G.
  • Chen L. J.
  • Ergun R. E.
  • Lindqvist P. A.
  • Marklund G. T.
  • Khotyaintsev Y. V.
  • Russell C. T.
  • Magnes W.
  • Le Contel Olivier
  • Pollock C. J.
  • Giles B. L.
  , 2015, 51, pp.SM51A-2518. The electron drift instruments (EDIs) onboard each MMS spacecraft are designed with large geometric factors (~0.01cm2 str) to facilitate detection of weak (~100 nA) electron beams fired and received by the two gun-detector units (GDUs) when EDI is in its "electric field mode" to determine the local electric and magnetic fields. A consequence of the large geometric factor is that "ambient mode" electron flux measurements (500 eV electrons having 0°, 90°, or 180° pitch angle) can vary depending on the orientation of the EDI instrument with respect to the magnetic field, a nonphysical effect that requires a correction. Here, we present determinations of the theta- and ø-dependent correction factors for the eight EDI GDUs, where theta (ø) is the polar (azimuthal) angle between the GDU symmetry axis and the local magnetic field direction, and compare the corrected fluxes with those measured by the fast plasma instrument (FPI). Using these corrected, high time resolution (~1,000 samples per second) ambient electron fluxes, combined with the unprecedentedly high resolution 3D electric field measurements taken by the spin-plane and axial double probes (SDP and ADP), we are equipped to accurately detect electron-scale current layers and electric field waves associated with the non-Maxwellian (anisotropic and agyrotropic) particle distribution functions predicted to exist in the reconnection diffusion region. We compare initial observations of the diffusion region with distributions and wave analysis from PIC simulations of asymmetric reconnection applicable for modeling reconnection at the Earth's magnetopause, where MMS will begin Science Phase 1 as of September 1, 2015.
• A New Technique for the Investigation of the Energy Cascade Associated with Coherent Structures in Kelvin-Helmoltz Turbulence
  
  • Rossi C.
  • Camporeale E.
  • Califano F.
  • Cerri S. S.
  • Retinò Alessandro
  , 2015, 11, pp.SH11E-2416. The dissipation of turbulent energy at small scales in space plasmas remains an open and challenging problem. Two plausible channels for energy dissipation have been intensively investigated in recent years: linear wave damping and non-linear interactions within coherent structures. However, a general consensus has not yet been reached on what is the relative importance of these two processes. It is now well established that coherent structures in the form of current sheets are associated with localized particle heating, and are generally responsible for the observed intermittent nature of plasma turbulence. Still, the contribution of such structures to the local energy spectrum is not well understood. Here we apply a 'space-filter' technique to a two-fluid plasma simulation of Kelvin-Helmoltz turbulence, in order to obtain a local measure of the inter-scale transfer and to characterize the contribution of coherent structures to the energy spectrum. Despite of being well-known in the hydrodynamics and Large-Eddy-Simulation communities, such technique is applied here for the first time to space plasma turbulence. Specifically, we study in detail the current sheets identified in turbulent Kelvin-Helmoltz vortexes by the Partial Variance of Increments (PVI) technique, and we discuss the correlation between the inter-scale transfer and high values of the PVI index.
• The Hermean bow shock and ion foreshock as seen by three-dimensional global hybrid simulations
  
  • Chanteur Gérard
  • Modolo Ronan
  • Leblanc François
  , 2015, pp.P533A-2085. The thinness of the Hermean magnetosheath evidenced by Mariner 10 and MESSENGER observations results from the small average standoff distance of the Bow Shock equal to 1.45RM and has important consequences especially in the region of the parallel shock. The magnetopause is clearly identified in front of the perpendicular shock meanwhile it is hardly recognized in front of the parallel shock due to a strong interaction between the shock and the magnetospheric boundary mediated by the magnetosheath flow. This interaction is investigated by means of three-dimensional global hybrid simulations for different IMF orientations and by varying the spatial resolution of the simulations between 120 and 40km. Accordingly to MESSENGER observations (Anderson et al, 2012) the planetary magnetic field implemented in the simulations combines a dipole and a quadrupole axisymmetric sources (Richer et al, 2012). 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. 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.
• Bursty Bulk Flow Turbulence as Observed by the Magnetospheric Multiscale Mission
  
  • Stawarz J. E.
  • Ergun R.
  • Goodrich K. A.
  • Wilder F. D.
  • Burch J. L.
  • Sturner A. P.
  • Holmes J.
  • Malaspina D.
  • Usanova M.
  • Torbert R. B.
  • Lindqvist P. A.
  • Khotyaintsev Y. V.
  • Russell C. T.
  • Strangeway R. J.
  • Pollock C. J.
  • Magnes W.
  • Chutter M.
  • Needell J.
  • Rau D.
  • Le Contel Olivier
  • Giles B. L.
  • Eriksson S.
  , 2015, 51, pp.SM51A-2524. Bursty Bulk Flows (BBFs), thought to result from reconnection in the near Earth plasma sheet, transfer a significant amount of mass and energy to the inner magnetosphere. The BBF braking region occurs at roughly 10 RE as the flow encounters the dipolar field near Earth and must slow significantly and/or deflect. Previous studies using the THEMIS spacecraft observed electron phase space holes and double-layers in the BBF braking region and speculated that strong field-aligned currents generated by turbulence within the region created these structures. While evidence supporting the existence of turbulence within the region was found, the lack of small-scale spatial information from THEMIS made it difficult to characterize the turbulence and currents within the region. In the present study, BBF braking region observations from the recently launched Magnetospheric Multiscale (MMS) mission are examined. Characteristics of the turbulence are examined through statistical methods such as spatial and temporal correlation functions. Individual structures within the turbulence will also be examined using multi-spacecraft techniques to better characterize the currents, which may contribute to the formation of kinetic structures and dissipation of turbulent energy.
• Energy Dissipation and Transport Associated with Whistler-wave Generation during Plasma Jet Events using MMS Data
  
  • Breuillard Hugo
  • Le Contel Olivier
  • Retinò Alessandro
  • Russell C.
  • Baumjohann W.
  • Mirioni Laurent
  • Khotyaintsev Y. V.
  • Burch J. L.
  • Torbert R. B.
  • Ergun R. E.
  • Anderson B. J.
  • Needell J.
  • Chutter M.
  • Rau D.
  • Dors I.
  • Magnes W.
  • Strangeway R. J.
  • Bromund K. R.
  • Plaschke F.
  • Fischer D.
  • Leinweber H. K.
  • Kepko L.
  • Slavin J. A.
  • Pollock C. J.
  • Lindqvist P. A.
  • Marklund G. T.
  • Mauk B.
  • Fuselier S. A.
  • Le G.
  • Goodrich K. A.
  • Macri J.
  • Vaivads A.
  • Graham D. B.
  • Nakamura R.
  , 2015, 13. Plasma jets aka bursty bulk flows play a crucial role in Earth's magnetosphere dynamics, in particular during substorms where they can penetrate down to the geosynchronous orbit. The energy input from the solar wind is partly dissipated in jet fronts (also called dipolarization fronts) in the form of strong whistler waves that can heat and accelerate energetic electrons. The ratio of the energy transported during jets to the substorm energy consumption can reach one third or more due to kinetic-scale phenomena, that are still under debate due to instrumental limitations. The recently-launched Magnetospheric Multiscale (MMS) mission has already detected numerous plasma jet events, and evolves in a tetrahedral configuration (with an average inter- satellite distance of 160 km and unprecedent resolutions up to 16,000 samples/s) that allows to study in detail the microphysics of these phenomena. Thus in this study we employ MMS data to investigate the energy dissipated in jet fronts related to the generation of whistler waves, and the interaction of such waves with energetic electrons in the vicinity of the flow/jet braking region near the equatorial boundary between tail and inner magnetosphere. We also make use of ray tracing simulations to evaluate their propagation properties, as well as their impact on particles in the off-equatorial magnetosphere.
• Multi-point, multi-scale observation of the near-Earth current sheet reconfiguration during storm-time multi-onset substorms
  
  • Kepko L.
  • Vaith H.
  • Le Contel Olivier
  • Argall M. R.
  • Ergun R. E.
  • Lindqvist P. A.
  • Marklund G. T.
  • Khotyaintsev Y. V.
  • Pollock C. J.
  • Dorelli J. C.
  • Gershman D. J.
  • Fuselier S. A.
  • Mauk B.
  • Baker D. N.
  • Giles B. L.
  • Moore T. E.
  • Singer H. J.
  • Sergeev V. A.
  • Escoubet C. Philippe
  • Nakamura R.
  • Baumjohann W.
  • Plaschke F.
  • Narita Y.
  • Schmid D.
  • Panov E. V.
  • Andriopoulou M.
  • Vörös Z.
  • Magnes W.
  • Fischer D.
  • Steller M.
  • Burch J. L.
  • Torbert R. B.
  • Russell C. T.
  • Strangeway R. J.
  • Leinweber H. K.
  • Le G.
  • Bromund K. R.
  • Anderson B. J.
  • Chutter M.
  • Slavin J. A.
  , 2015, 51, pp.SM51A-2523. On June 23, 2015 between 03 and 06 UT, during the recovery phase of a storm, signatures of two major substorms with multiple-onsets are detected by a fleet of spacecraft in the near-Earth region providing an unique opportunity to study the evolution of the near-Earth current sheet reconfiguration from sub-ion scale to larger scale across the inner magnetosphere. The two onsets around 0315 and 0505 are observed by MMS near the boundary of the premidnight-plasma sheet as a thinning of the current sheet and as dipolarization at GOES 13 and 15 in the dusk to premidnight region, then followed by crossing of an active separatrix region. By using high-resolution magnetic field data onboard MMS, we investigate the detailed propagation properties of the disturbances and structures based on different multi-point analysis techniques (timing, gradient, and wave telescope analysis). By also comparing with current wedge model from ground-based data we identify the 3D evolution of the near-Earth current sheet.
• Electrodynamic Context of Magnetotail and Magnetopause Dynamics Observed by Magnetospheric Multiscal
  
  • Anderson B. J.
  • Korth H.
  • Waters C. L.
  • Barnes R. J.
  • Samara M.
  • Russell C. T.
  • Strangeway R. J.
  • Plaschke F.
  • Magnes W.
  • Fischer D.
  • Merkin V. G.
  • Nakamura R.
  • Baumjohann W.
  • Torbert R. B.
  • Leinweber H. K.
  • Le G.
  • Bromund K. R.
  • Chutter M.
  • Slavin J. A.
  • Kepko L.
  • Le Contel Olivier
  • Mauk B.
  • Westlake J. H.
  • Gjerloev J. W.
  • Ruohoniemi J. M.
  , 2015, 51, pp.SM51D-2587. After successful launch and deployment on 14 March 2015, the four Magnetosphere Multiscale (MMS) spacecraft were commissioned during the first local time precession of the orbit line of apsides across the magnetotail from dawn to dusk. Prime science observations began in September 2015 when orbit apogee had moved to the dusk sector at magnetopause distances. Signatures of magnetotail dynamics were observed during payload and fleet commissioning. The electrodynamic context of the magnetotail events at MMS as well as observations at the dusk and afternoon magnetopause is assessed using correlative observations from low Earth orbit and ground-based instruments including the Active Magnetosphere and Polar Electrodynamics Response Experiment (AMPERE), SuperMAG, and SuperDARN. Substorm current onsets are prevalent in AMPERE data and are highly correlated with magnetotail injections and dipolarizations observed by MMS. To better constrain how the MMS magnetotail observations are related to global processes, we also examine the occurrence and prevalence of similar ionospheric onset signatures when MMS was at high altitudes in the magnetotail but observed no local signatures of injections or dipolarizations. For MMS magnetopause observations, we explore the relationship of magnetic reconnection signatures at MMS with the convection patterns derived from AMPERE and ionosphere observations to establish the relationship of the local MMS observations and global magnetospheric convective state.
• A Statistical Study of the Magnetic Structure of Magnetic Clouds Downstream of the Earth's Bow Shock
  
  • Turc Lucile
  • Fontaine Dominique
  • Kilpua E. K. J.
  • Escoubet C. Philippe
  , 2015, 12. Magnetic clouds (MCs) are large-scale solar wind transients characterized primarily by an enhanced and smoothly-rotating magnetic field over periods of the order of one day. They are the drivers of the most intense geomagnetic storms, therefore understanding their interaction with the Earth's environment is of major interest for space weather forecasting. The first steps of this complex chain of processes are their interaction with the terrestrial bow shock and the ensuing propagation in the magnetosheath. Recent studies have shown that under certain conditions the distinctive magnetic structure of MCs can be significantly altered downstream of the bow shock. In such case, the magnetic field impinging on the magnetosphere strongly differs from that in the upstream solar wind and could lead to a reconnection pattern very different from that expected from the solar wind observations. The aim of the present work is to substantiate and generalize these results, obtained from a few MC events, in performing a statistical study. For this purpose, a comprehensive database of MC events, covering about 15 years of data, from 2000 to 2014, has been compiled. It lists presently 151 MCs observed in L1 by either Wind or ACE. Using the events during which spacecraft observations in the magnetosheath are simultaneously available, we investigate the evolution of the magnetic structure of MCs from the solar wind to the magnetosheath. The influence of the upstream solar wind parameters, such as the plasma beta, the Alfven Mach number or the magnetic field strength, is examined. Using a semi-analytical model, we estimate the local shock properties encountered upon entering the magnetosheath and find that the alteration of the magnetic structure of MCs strongly depend on the shock geometry. The large dataset allows us to assess the limitations of the magnetosheath model. The consequences of our results in terms of the geoeffectivity of MCs are discussed.
• Equatorial Noise Emissions and Their Quasi-Periodic Modulation
  
  • Nemec F.
  • Santolik O.
  • Hrbackova Z.
  • Pickett J. S.
  • Cornilleau-Wehrlin Nicole
  • Parrot M.
  • Hayosh M.
  , 2015, 51, pp.SM51F-03. Equatorial noise (EN) emissions are electromagnetic waves at frequencies between the proton cyclotron frequency and the lower hybrid frequency routinely observed in the equatorial region of the inner magnetosphere. They propagate in the extraordinary mode nearly perpendicular to the ambient magnetic field, and they exhibit a harmonic structure related to the ion cyclotron frequency in the source region. We analyze more than 2000 EN events observed by the wave instruments on board the Cluster spacecraft, and we find that about 5% of EN events are not continuous in time, but exhibit a quasi-periodic (QP) modulation of the wave intensity. Typical modulation periods are on the order of minutes. The events predominantly occur in the noon-to-dawn local time sector, and their occurrence is related to the periods of increased geomagnetic activity and higher solar wind speeds. We suggest that the QP modulation of EN events may be due to compressional ULF pulsations, which periodically modulate the wave growth in the source region. These compressional ULF pulsations were identified in about half of the events. Finally, we demonstrate that EN emissions with QP modulation of the wave intensity can propagate down to altitudes as low as 700 km.
• Low-frequency wave activity related to dipolarization fronts detected by MMS in the magnetotail
  
  • Le Contel Olivier
  • Retinò Alessandro
  • Breuillard Hugo
  • Mirioni Laurent
  • Roux A.
  • Chust Thomas
  • Chasapis A.
  • Lavraud B.
  • Lindqvist P. A.
  • Khotyaintsev Y. V.
  • Vaivads A.
  • Fu H.
  • Marklund G. T.
  • Nakamura R.
  • Burch J. L.
  • Torbert R. B.
  • Moore T. E.
  • Ergun R.
  • Goodrich K. A.
  • Needell J.
  • Chutter M.
  • Rau D.
  • Dors I.
  • Russell C. T.
  • Magnes W.
  • Strangeway R. J.
  • Le G.
  • Bromund K. R.
  • Plaschke F.
  • Fischer D.
  • Leinweber H. K.
  • Anderson B. J.
  • Argall M. R.
  • Slavin J. A.
  • Kepko L.
  • Baumjohann W.
  • Pollock C. J.
  • Mauk B.
  • Fuselier S. A.
  , 2015, 41, pp.SM41I-05. Dipolarization fronts are often associated to reconnection jets in the magnetotail current sheet and are sites of important energy dissipation and particle energization. Since the launch on March 12th and until the 9th of July 2015, the MMS constellation has been moving from dawn to dusk in a string of pearls formation. Although particle instruments were rarely operating and only FIELDS instrument suite was often gathering data, the MMS spacecraft have detected numerous dipolarization fronts, in particular on May 15th. Since 9th of July, the MMS evolved into a tetrahedral configuration with an average inter-satellite distance of 160 km and was still able to detect dipolarization fronts in the dusk magnetotail. As the Larmor radius of thermal protons is about 500 km in this region and dipolarization fronts have a typical thickness of the order of the Larmor radius, such a separation allows us to investigate in detail the microphysics of dipolarization fronts. In this study, we focus in particular on low-frequency electromagnetic wave activity related to the fronts and discuss possible mechanisms of particle heating and acceleration both at large scales (string of pearls configuration) and at kinetic scales (tetrahedral configuration).
• Low-Frequency Wave Activity Detected by MMS during Dusk Magnetopause Crossings and its Relation to Heating and Acceleration of Particles
  
  • Le Contel Olivier
  • Roux A.
  • Retinò Alessandro
  • Mirioni Laurent
  • Sahraoui Fouad
  • Chust Thomas
  • Berthomier Matthieu
  • Chasapis A.
  • Aunai N.
  • Leroy Paul
  • Alison Dominique
  • Lavraud B.
  • Lindqvist P. A.
  • Khotyaintsev Y. V.
  • Vaivads A.
  • Marklund G. T.
  • Burch J. L.
  • Torbert R. B.
  • Moore T. E.
  • Ergun R. E.
  • Needell J.
  • Chutter M.
  • Rau D.
  • Dors I.
  • Macri J.
  • Russell C. T.
  • Magnes W.
  • Strangeway R. J.
  • Bromund K. R.
  • Plaschke F.
  • Fischer D.
  • Leinweber H. K.
  • Anderson B. J.
  • Nakamura R.
  • Argall M. R.
  • Le G.
  • Slavin J. A.
  • Kepko L.
  • Baumjohann W.
  • Pollock C. J.
  • Mauk B.
  • Fuselier S. A.
  • Goodrich K. A.
  • Wilder F. D.
  , 2015, 12, pp.SM12A-09. Since the 9th of July, the MMS fleet of four satellites have evolved into a tetrahedral configuration with an average inter-satellite distance of 160 km and an apogee of 12 earth radii on the dusk side. In this study we report on ultra-low (1 mHz to ~10 Hz) and very-low (10 Hz to ~ 4 kHz) frequency wave activity measured by the four satellites during several crossings of the dusk equatorial magnetopause. Since the Larmor radius of magnetosheath protons is of the order of 50 km, this inter-satellite distance allows us to investigate in detail the physics of the magnetopause at proton scales including current structures related to Kelvin-Helmholtz instability as well as other energy transfer processes. From wave polarization analysis, we characterize the different types of emissions and discuss different mechanisms of heating and acceleration of particles. In particular, we focus on the electron heating by kinetic Alfvén waves and lower hybrid waves and the electron acceleration by oblique whistler mode waves, which have been suggested as possible mechanisms from previous Cluster and THEMIS measurements.
• MMS Observations of Kinetic Features in the Earth's Bursty Bulk Flow Braking Region
  
  • Goodrich K. A.
  • Ergun R.
  • Wilder F. D.
  • Sturner A. P.
  • Holmes J.
  • Stawarz J. E.
  • Malaspina D.
  • Usanova M.
  • Torbert R. B.
  • Lindqvist P. A.
  • Khotyaintsev Y. V.
  • Burch J. L.
  • Russell C. T.
  • Strangeway R. J.
  • Pollock C. J.
  • Magnes W.
  • Le Contel Olivier
  • Giles B. L.
  • Chutter M.
  • Needell J.
  • Rau D.
  • Gershman D. J.
  , 2015, 44, pp.SM44A-08. We present MMS observations of particle and wave activity in the Earth's Bursty Bulk Flow (BBF) Braking region (6 - 12 Earth radii tailward). This region, previously examined by the THEMIS spacecraft, has shown evidence of bursty, high velocity, Earthward particle flows, turbulent magnetic fields, and large amplitude electric field signatures (amplitudes can, at times, exceed 100 mV/m). Kinetic features such as double layers, electron phase-space holes, and magnetic holes have been observed frequently throughout this region. The Magnetospheric Multi-scale (MMS) spacecraft, launched March 2015, are currently orbiting the Earth with the objective of observing the microphysics of magnetic reconnection. During its commissioning phase (March 2015 - August 2015), all four spacecraft apogees were primarily in the BBF Braking region. The presence of MMS in this region can offer higher spatial and temporal resolution of the BBF Braking region than ever before. We examine MMS observations kinetic structures (double layers, electron phase-space and magnetic holes) to further characterize the BBF braking region and its overall effects on the Earth space environment.
• Scaling of compressible magnetohydrodynamic turbulence in the fast solar wind
  
  • Sahraoui Fouad
  • Banerjee Supratik
  • Galtier Sébastien
  • Hadid L. Z.
  , 2015, 33, pp.SH33A-2456. The role of compressible uctuations in the energy cascade of fast solar wind turbulence is studiedusing an exact law derived recently for compressible isothermal magnetohydrodynamics and in-situobservations of the THEMIS spacecraft. For the first time, a direct turbulent energy cascade isevidenced over three decades of scales which is signicantly broader than the previous estimatesmade from an exact incompressible law or from a compressible heuristic model. Unlike previousworks, our evaluation gives an energy ux which keeps a constant sign over the inertial range. Aterm-by-term analysis reveals that the dominant contribution to the energy ux comes from purecompressible uctuations. Furthermore, the compressible turbulent cascade rate is shown to providethe adequate energy dissipation required to account for the local heating of the non-adiabatic solarwind.
• How to Find Magnetic Nulls and Reconstruct Field Topology with MMS Data?
  
  • Fu H.
  • Vaivads A.
  • Khotyaintsev Y. V.
  • Olshevsky V.
  • André M.
  • Cao J.B.
  • Huang S. Y.
  • Retinò Alessandro
  • Lapenta G.
  , 2015, 51, pp.SM51A-2517. In this study, we apply a new method−-the first-order Taylor expansion (FOTE)−-to find magnetic nulls and reconstruct magnetic field topology, in order to use it with the data from the forth-coming MMS mission. We compare this method with the previously used Poincare index (PI), and find that they are generally consistent, except that the PI method can only find a null inside the spacecraft (SC) tetrahedron, while the FOTE method can find a null both inside and outside the tetrahedron and also deduce its drift velocity. In addition, the FOTE method can (1) avoid limitations of the PI method such as data resolution, instrument uncertainty (Bz offset), and SC separation; (2) identify 3D null types (A, B, As, and Bs) and determine whether these types can degenerate into 2D (X and O); (3) reconstruct the magnetic field topology. We quantitively test the accuracy of FOTE in positioning magnetic nulls and reconstructing field topology, by using the data from 3D kinetic simulations. The influences of SC separation (0.05~1 di) and null-SC distance (0~1 di) on the accuracy are both considered. We find that: (1) for an isolated null, the method is accurate when the SC separation is smaller than 1 di, and the null-SC distance is smaller than 0.25~0.5 di; (2) for a null pair, the accuracy is same as in the isolated-null situation, except at the separator line, where the field is nonlinear. We define a parameter in terms of the eigenvalues of the null to quantify the quality of our method−-the smaller this parameter the better the results. Comparing to the previously used one, this parameter is more relevant for null identification. Using the new method, we reconstruct the magnetic field topology around a radial-type null and a spiral-type null, and find that the topologies are well consistent with those predicted in theory. We therefore suggest using this method to find magnetic nulls and reconstruct field topology with four-point measurements, particularly from Cluster and the forth-coming MMS mission. For the MMS mission, this null-finding algorithm can be used to trigger its burst-mode measurements.
• MMS Spacecraft Observation of Near Tail Thin Current Sheets: Their Locations, Conditions for Formation and Relation to Geomagnetic Activity
  
  • Zhao C.
  • Russell C. T.
  • Strangeway R. J.
  • Anderson B. J.
  • Baumjohann W.
  • Bromund K. R.
  • Chutter M.
  • Fischer D.
  • Kepko L.
  • Le Contel Olivier
  • Leinweber H. K.
  • Magnes W.
  • Nakamura R.
  • Plaschke F.
  • Slavin J. A.
  • Torbert R. B.
  , 2015, 13. During the commissioning phase of the MMS mission, when the apogee (~12Re) of MMS orbit swept from the pre-midnight to the dusk section of the magnetosphere, the four spacecraft probed the dynamic region of the near-Earth magnetotail. The MMS fleet encountered many structures with unambiguously small-scale spatial gradient in magnetic field (comparable to the separation of the fleet), indicating the existence of very thin current sheets in this near-tail region. During this commissioning phase, the MMS spacecraft were in a string of pearls configuration, not ideally suitable for "curlometer" determination of the current density. Thus the current density and thickness of the sheets are only roughly determined using reasonable assumptions. In this study we correlate the current sheet's location and thickness with solar wind conditions and the ground magnetic field records.
• MMS observations of waves and instabilities in the separatrices and diffusion region of magnetopause reconnection
  
  • Graham D. B.
  • Khotyaintsev Y. V.
  • Vaivads A.
  • André M.
  • Lindqvist P. A.
  • Le Contel Olivier
  • Ergun R. E.
  • Goodrich K. A.
  • Torbert R. B.
  • Russell C.
  • Magnes W.
  • Pollock C. J.
  • Mauk B.
  • Fuselier S. A.
  , 2015, 51, pp.SM51A-2556. One of the major challenges in understanding magnetic reconnection is determining the role of processes operating at electron spatial scales within the diffusion region and separatrices. Currently, the processes operating at these scales are difficult to identify and characterize, but are crucial for enabling magnetic fields to reconnect. However, the recently launched Magnetospheric Multiscale (MMS) mission is specifically designed to investigate these electron scale processes. We use MMS data to investigate the type of electrostatic and electromagnetic instabilities present in the diffusion region and separatrices of asymmetric reconnection at the magnetopause. The waves are characterized using polarization analyses and interferometry techniques. Of particular interest are whistler waves and electrostatic solitary waves, which have a large range of observed properties. We investigate the generation mechanisms of the waves as well as their role in plasma heating and anomalous resistivity, using high time resolution wave and particle measurements.
• MMS observations of small magnetic flux ropes in the near-tail (X > -11 Re)
  
  • Slavin J. A.
  • Poh G.
  • Le G.
  • Strangeway R. J.
  • Russell C. T.
  • Anderson B. J.
  • Fischer D.
  • Plaschke F.
  • Bromund K. R.
  • Leinweber H. K.
  • Kepko L.
  • Chutter M.
  • Le Contel Olivier
  • Torbert R. B.
  • Nakamura R.
  • Magnes W.
  • Baumjohann W.
  , 2015, 51, pp.SM51A-2536. Magnetic reconnection is the most important energy conversion process in the Earth's magnetotail. Flux ropes are helical magnetic structures created by multiple X-line reconnection in the tail current sheet in the presence of a guide field in the east - west direction. Many numerical simulations predict that the formation of small flux ropes, referred to as secondary islands, takes place as reconnection transitions from the slow Sweet-Parker mode to fast reconnection with inertial scale neutral points. High time resolution MMS magnetic and electric fields measurements are near ideal for the investigation of secondary island - type flux ropes carried Earthward from downstream reconnnection sites, as well as their interaction with the strong dipolar magnetic fields of the inner magnetosphere. We present and analyze initial MMS magnetic field measurements of small flux ropes in the near-tail during the commissioning phase while the spacecraft were in a "string-­of-­pearls" configuration.