Publications (80)98.83 Total impact
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Article: Observation of a Complex Solar Wind Reconnection Exhaust from Spacecraft Separated by over 1800 RE
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ABSTRACT: We analyze Wind, ACE, and STEREO (ST-A and ST-B) plasma and magnetic field data in the vicinity of the heliospheric current sheet (HCS) crossed by all spacecraft between 22:15 UT on 31 March and 01:25 UT on 1 April 2007 corresponding to its observation at ST-A and ST-B, which were separated by over 1800 R E (or over 1200 R E across the Sun – Earth line). Although only Wind and ACE provided good ion flow data in accord with a solar wind magnetic reconnection exhaust at the HCS, the magnetic field bifurcation typical of such exhausts was clearly observed at all spacecraft. They also all observed unambiguous strahl mixing within the exhaust, consistent with the sunward flow deflection observed at Wind and ACE and thus with the formation of closed magnetic field lines within the exhaust with both ends attached to the Sun. The strong dawnward flow deflection in the exhaust is consistent with the exhaust and X-line orientations obtained from minimum variance analysis at each spacecraft so that the X-line is almost along the GSE Z-axis and duskward of all the spacecraft. The observation of strahl mixing in extended and intermittent layers outside the exhaust by ST-A and ST-B is consistent with the formation of electron separatrix layers surrounding the exhaust. This event also provides further evidence that balanced parallel and antiparallel suprathermal electron fluxes are not a necessary condition for identification of closed field lines in the solar wind. In the present case the origin of the imbalance simply is the mixing of strahls of substantially different strengths from a different solar source each side of the HCS. The inferred exhaust orientations and distances of each spacecraft relative to the X-line show that the exhaust was likely nonplanar, following the Parker spiral orientation. Finally, the separatrix layers and exhausts properties at each spacecraft suggest that the magnetic reconnection X-line location and/or reconnection rate were variable in both space and time at such large scales.Solar Physics 04/2012; 256(1):379-392. · 2.78 Impact Factor -
Article: The Foreshock
Space Science Reviews 04/2012; 118(1):41-94. · 3.61 Impact Factor -
Article: Reformation of an oblique shock observed by Cluster
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ABSTRACT: On 16 March 2005, the Cluster spacecraft crossed a shock almost at the transition between the quasi-perpendicular and quasi-parallel regimes ($\theta_{Bn}=46^{\circ}$) preceded by an upstream low-frequency ($\sim$ 0.02 Hz in the spacecraft frame) wavetrain observed for more than 10 mn. The wave semi-cycle nearest to the shock was found to grow in time, steepen and reflect an increasing fraction of the incoming ions. This gives strong indication that this pulsation is becoming a new shock front, standing $\sim 5\lambda_p$ upstream of the main front and growing to shock-like amplitude on a time-scale of $\sim 35\Omega_p$. Downstream of the main shock transition, remnants of an older front are found indicating that the reformation is cyclic. This provides a unique example where the dynamics of shock reformation can be sequentially followed. The process shares many characteristics with simulations of reforming quasi-parallel shocks.01/2010; -
Article: Statistics of counter-streaming solar wind suprathermal electrons at solar minimum: STEREO observations
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ABSTRACT: Previous work has shown that solar wind suprathermal electrons can display a number of features in terms of their anisotropy. Of importance is the occurrence of counter-streaming electron patterns, i.e., with "beams" both parallel and anti-parallel to the local magnetic field, which is believed to shed light on the heliospheric magnetic field topology. In the present study, we use STEREO data to obtain the statistical properties of counter-streaming suprathermal electrons (CSEs) in the vicinity of corotating interaction regions (CIRs) during the period March–December 2007. Because this period corresponds to a minimum of solar activity, the results are unrelated to the sampling of large-scale coronal mass ejections, which can lead to CSE owing to their closed magnetic field topology. The present study statistically confirms that CSEs are primarily the result of suprathermal electron leakage from the compressed CIR into the upstream regions with the combined occurrence of halo depletion at 90° pitch angle. The occurrence rate of CSE is found to be about 15–20% on average during the period analyzed (depending on the criteria used), but superposed epoch analysis demonstrates that CSEs are preferentially observed both before and after the passage of the stream interface (with peak occurrence rate >35% in the trailing high speed stream), as well as both inside and outside CIRs. The results quantitatively show that CSEs are common in the solar wind during solar minimum, but yet they suggest that such distributions would be much more common if pitch angle scattering were absent. We further argue that (1) the formation of shocks contributes to the occurrence of enhanced counter-streaming sunward-directed fluxes, but does not appear to be a necessary condition, and (2) that the presence of small-scale transients with closed-field topologies likely also contributes to the occurrence of counter-streaming patterns, but only in the slow solar wind prior to CIRs.01/2010; -
Chapter: Effect of Shock Normal Orientation Fluctuations on Field-Aligned Beam Distributions
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ABSTRACT: We address the unsolved question of how foreshock field-aligned beam (FAB) parallel temperatures are produced. Studies including numerical simulations and recent observations have indicated that shocks can be nonstationary and include embedded spatial structures with varied scales. As a first step towards assessing the impact of such variability on backstreaming ions, we examine how a randomly distributed shock normal direction will affect FAB parallel velocity (v ∥) distributions. Assuming that the FABs are produced in a quasi-adiabatic reflection process at the shock, we derive a probability distribution function for v ∥. These derived distributions exhibit second, third and fourth order moments that agree well with the observations for a large range of reflection efficiencies δ, and depend strongly upon the average angle between the magnetic field and the shock normal θ Bn0. Best agreement is obtained for fluctuations of the normal orientation of a few degrees about a nominal direction. The derived model predicts a strong correlation between the shock geometry (θ Bn0) and the moments of the parallel velocity distribution, but with stronger tails extending to higher values of θ Bn0, a trend opposite to the observations.12/2009: pages 349-362; -
Article: The loss of ions from Venus through the plasma wake.
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ABSTRACT: Venus, unlike Earth, is an extremely dry planet although both began with similar masses, distances from the Sun, and presumably water inventories. The high deuterium-to-hydrogen ratio in the venusian atmosphere relative to Earth's also indicates that the atmosphere has undergone significantly different evolution over the age of the Solar System. Present-day thermal escape is low for all atmospheric species. However, hydrogen can escape by means of collisions with hot atoms from ionospheric photochemistry, and although the bulk of O and O2 are gravitationally bound, heavy ions have been observed to escape through interaction with the solar wind. Nevertheless, their relative rates of escape, spatial distribution, and composition could not be determined from these previous measurements. Here we report Venus Express measurements showing that the dominant escaping ions are O+, He+ and H+. The escaping ions leave Venus through the plasma sheet (a central portion of the plasma wake) and in a boundary layer of the induced magnetosphere. The escape rate ratios are Q(H+)/Q(O+) = 1.9; Q(He+)/Q(O+) = 0.07. The first of these implies that the escape of H+ and O+, together with the estimated escape of neutral hydrogen and oxygen, currently takes place near the stoichometric ratio corresponding to water.Nature 12/2007; 450(7170):650-3. · 36.28 Impact Factor -
Article: Wave‐particle interaction in the terrestrial ion foreshock: new results from Cluster
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ABSTRACT: Different types of backstreaming ion distributions have been reported in the region upstream from the Earth’s bow shock and magnetically connected to it (ion foreshock): field‐aligned beams (FABs), gyrating ion and diffuse ion distributions. Contrary to the first type, the two others are always associated with ULF waves. Among them, gyrating ions with well‐defined pitch‐angle and gyrophase organization around the local magnetic field have been frequently observed in association with large amplitude quasi‐monochromatic right‐hand mode waves. These waves reveal the existence of coherent wave‐particle interaction which is an efficient process to dissipate the energy of the particles reflected at the collisionless bow shock. It has been shown recently from a large data set from multi‐spacecraft observations by Cluster that the gyrophase‐bunched ion distributions are mainly produced by such a process from cyclotron‐resonant FABs observed just both at the edge of the gyrating ions region and the boundary of ULF waves. © 2007 American Institute of PhysicsAIP Conference Proceedings. 08/2007; 932(1):175-180. -
Article: Ion properties at Earth's foreshock, recent achievements
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ABSTRACT: Different types of backstreaming ion distributions have been reported in the ion foreshock: field-aligned beams (FABs), gyrating ions and diffuse ions distributions. Contrary to the first type, the two others are always associated with low frequency (ULF) waves. Multi-spacecraft observations by Cluster and the high quality 3-dimensional data obtained by Cluster/CIS has permitted to address specific quantitative questions that could not be resolved previously. Gyrating ions with well-defined pitch-angle and gyrophase organization around the local magnetic field have been frequently observed in association with large amplitude quasi-monochromatic waves. These waves reveal the existence of coherent wave-particle interaction which is an efficient process to dissipate the energy of the particles reflected at the collisionless bow shock. It has been shown recently from a Cluster data set that the gyrophase-bunched ion distributions are mainly produced by such a process from cyclotron-resonant FABs observed just at the edge of both the gyrating ions region and the boundary of ULF waves. New results have also been obtained on the FABs and gyrating ions exhibiting sometimes a high-energy tail likely produced by a local process at the shock which may be micro-turbulence. It has been found that the characteristics of both parallel and perpendicular particle distribution function profiles of field-aligned beams (FABs) are geometry-dependent. Other recent results deal with the properties of ion distributions associated with ULF waves with left-hand polarisation the existence of which has been definitively and unambiguously proven from the four-spacecraft analysis by Cluster. These recent achievements in the properties of ion distributions in the terrestrial ion foreshock will be discussed in the light of theoretical works and recent numerical simulations.AGU Spring Meeting Abstracts. 04/2007; -1:02. -
Article: Rosina – Rosetta Orbiter Spectrometer for Ion and Neutral Analysis
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ABSTRACT: The Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) will answer important questions posed by the mission’s main objectives. After Giotto, this will be the first time the volatile part of a comet will be analyzed in situ. This is a very important investigation, as comets, in contrast to meteorites, have maintained most of the volatiles of the solar nebula. To accomplish the very demanding objectives through all the different phases of the comet’s activity, ROSINA has unprecedented capabilities including very wide mass range (1 to >300 amu), very high mass resolution (m/Δ m > 3000, i.e. the ability to resolve CO from N2 and 13C from 12CH), very wide dynamic range and high sensitivity, as well as the ability to determine cometary gas velocities, and temperature. ROSINA consists of two mass spectrometers for neutrals and primary ions with complementary capabilities and a pressure sensor. To ensure that absolute gas densities can be determined, each mass spectrometer carries a reservoir of a calibrated gas mixture allowing in-flight calibration. Furthermore, identical flight-spares of all three sensors will serve for detailed analysis of all relevant parameters, in particular the sensitivities for complex organic molecules and their fragmentation patterns in our electron bombardment ion sources.Space Science Reviews 01/2007; 128(1):745-801. · 3.61 Impact Factor -
Article: Larmor radius size density holes discovered in the solar wind upstream of Earth’s bow shock
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ABSTRACT: The Cluster and Double Star satellites recently observed plasma density holes upstream of Earth’s collisionless bow shock to apogee distances of ∼ 19 and 13 earth radii, respectively. A survey of 147 isolated density holes using 4 s time resolution data shows they have a mean duration of ∼ 17.9±10.4 s, but holes as short as 4 s are observed. The average fractional density depletion (δn/n) inside the holes is ∼ 0.68±0.14. The upstream edge of density holes can have enhanced densities that are five or more times the solar wind density. Particle distributions show the steepened edge can behave like a shock. Multispacecraft analyses show the density holes move with the solar wind, can have an ion gyroradius scale, and could be expanding. A small normal electric field points outward. Similarly shaped magnetic holes accompany the density holes indicating strong coupling between fields and particles. The density holes are only observed with upstream particles, suggesting that backstreaming particles interacting with the solar wind are important.Physics of Plasmas 05/2006; 13(5):050701-050701-4. · 2.15 Impact Factor -
Article: Low Frequency Waves in the Foreshock of Saturn
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ABSTRACT: The study of the physical phenomena in the region upstream from the outer planets provides important information on how key processes in terrestrial space plasma physics such as the formation of quasi-parallel shocks, ion reflection at quasi-perpendicular shocks, particle leakage, etc., operate in plasma environments with high magnetosonic Mach numbers. In this work we study the properties of low frequency electromagnetic waves as seen by the magnetometer onboard Cassini upstream from the bow shock of Saturn with periods between tens of seconds and several minutes. During these events, the prolongation of the local mean magnetic field intersects the mean position of the bow shock suggesting that these waves are generated in the Kronian foreshock. We analyze the polarization and propagation of these waves and also their spatial distribution with respect to the orientation of the interplanetary magnetic field. In addition, we use measurements from other Cassini instruments to try to determine which type of ion distribution is associated with these waves and to infer the instabilities responsible for their generationAGU Fall Meeting Abstracts. 11/2005; -1:1211. -
Article: Morphology of Langmuir wave active sites in the Earth's foreshock observed from the four points CLUSTER constellation : analysis of a case event at small separation
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ABSTRACT: High frequency fluctuating electric field upstream from the Earth bowshock, at frequencies near the local electron plasma frequency Fpe, but varying within a considerable range (~ 0.1 to 1.1 Fpe), have been observed in situ by several plasma wave instruments. Referred to as `Langmuir waves' when found near the plasma frequency, as `upshifted'or `downshifted' oscillations when found above or below Fpe, they are associated with the flux of electrons which move upstream from the bowshock. The Cluster constellation offers a unique opportunity to perform a spatio-temporal analysis of the active sites of such electrostatic emissions when at small (~ 100 km) average separation. We present a case event taken in this context, over a few minutes time interval. The presence of so called 30 s (period) ULF waves in DC magnetic field and plasma density indicates a position in the ion foreshock. The HF electrostatic fluctuations are measured in the 2 - 80 kHz band with a good time resolution: the instrument performs signal acquisitions in snapshots of 6.3 ms duration at a recurrence of 13.3 ms, transmitting to ground a survey of large band signal variations at resolution 13.3 ms, and, at 107 ms recurrence, the accumulation of frequency spectra (at 160 Hz resolution) derived on board for all the snapshots. The HF fluctuations, as observed from the accumulated spectra, can be sorted in several classes: (a) thermal noise above the plasma frequency, the position of which is precisely measured by the sounder at regular intervals,(b)Langmuir waves in the close vicinity of Fpe, sometimes associated with emissions at 2 Fpe, (c) downshifted waves, (c)broadband noise at the low frequency end of the Whisper range.In many instances, more than one class (excluding thermal noise, always present) are associated in the same accumulated spectrum. Although the emissions are quite sporadic in term of amplitude variations, the global characteristics, in term of frequency signatures, can persist over a few seconds, the changes being seen on all spacecraft at nearby time boundaries. We can thus define regions, or active sites, of a given class (simple or composite) of frequency signatures. We shall present and discuss an analysis of a) the size and velocity of given regions (from simple boundary time analysis), b) occurrence of a given site as compared to global plasma parameters, such as DC magnetic field configuration, solar wind velocity, or global features in the ion and electron populations, c) directivity properties (in the antenna spin plane) of the spectral signatures, compared to DC magnetic field and solar wind velocity orientation.AGU Fall Meeting Abstracts. 11/2005; -1:1210. -
Article: Upstream gyrating ion events: Cluster observations and simulations
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ABSTRACT: Localized events of low‐frequency quasi‐monochromatic waves in the 30s range observed by Cluster in the upstream region of Earth are analyzed. They are associated with a gyro‐motion of the two ion populations consisting of the incoming solar wind protons and the back‐streaming ions from the shock. A coordinate system is chosen in which one axis is parallel to the ambient magnetic field B0 and the other one is in the vsw×B0 direction. The variation of the plasma parameters is compared with the result of two‐fluid Hall‐MHD simulations using different beam densities and velocities. Keeping a fixed (relative) beam density (e.g. α=0.005), non‐stationary ‘shock‐like’ structures are generated if the beam velocity exceeds a certain threshold of about ten times the Alfven velocity. Below the threshold, the localized events represent stationary, nonlinear waves (oscillitons) in a beam‐plasma system in which the Reynold’s stresses of the plasma and beam ions are balanced by the magnetic field stress. © 2005 American Institute of PhysicsAIP Conference Proceedings. 07/2005; 781(1):146-150. -
Article: A review of field‐aligned beams observed upstream of the bow shock
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ABSTRACT: For more than two decades the Earth’s bow shock and traveling interplanetary shocks have attracted much attention as researchers have attempted to understand the collisionless mechanisms that thermalize transmitted particles and accelerate those that are observed propagating away from the shock into the upstream. We are concerned here with the class of particles emerging from the shock that are field‐aligned and have energies of a few to several keV, and base our results on observations primarily from the Earth’s foreshock. While the basic empirical picture has been known for some time, fundamental questions about the underlying mechanisms producing them have resisted a comprehensive explanation. This review talk will begin with an overview of the observational framework, along with selected new results. The latter include recent refinements in the characterizations of upstream field‐aligned beams as a function of the shock geometry parameter θBn. Other observations from the Cluster spacecraft have shown the occurence of a very sharp boundary separating FABs and gyrating ion populations in the foreshock. The Wind spacecraft has seen FABs at distances in excess of ∼100 RE from the Earth, indicating lifetimes greater than expected from linear theory of the ion‐ion streaming instability. These observations prompt new questions. Some analytic calculations will be reviewed briefly. Models based upon the guiding center approximation and those which introduce diffusion as a means of enhancing the fluxes of upstream beams fail to produce the properties observed. © 2005 American Institute of PhysicsAIP Conference Proceedings. 07/2005; 781(1):116-122. -
Article: Bow Shock and Upstream Waves at Jupiter and Saturn: Cassini Magnetometer Observations
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ABSTRACT: The measurements obtained by the Cassini magnetometer investigation (MAG) during the first orbits of its mission around Saturn yielded a rich set of observations of the bow shock and the upstream region at that planet. In this work we comment on the properties of the Kronian bow shock as implied by MAG data. We also study the properties of non‐linear, low frequency waves observed in the foreshock of Saturn and we discuss their origin and their role in the formation of the quasi parallel shock. Finally, we compare these recent results with similar observations at Jupiter obtained by Cassini MAG during the 2000–2001 Jupiter flyby. © 2005 American Institute of PhysicsAIP Conference Proceedings. 07/2005; 781(1):109-115. -
Article: Structure of the magnetic pileup boundary at Mars and Venus
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ABSTRACT: 1] The magnetic pileup boundary (MPB) is a sharp, thin, and well-defined plasma boundary located between the bow shock and the inner ionospheric boundary at comets, Mars, and Venus. This boundary separates the magnetosheath, a region of low magnetic fields with a conspicuous wave activity, from the magnetic pileup region dominated by strong, highly organized magnetic fields as a result of the pileup and draping of the interplanetary magnetic field. In the present paper we study the magnetic structure of the magnetic pileup boundary at Mars and Venus by means of the technique of minimum variance of the magnetic field. For each one of the crossings analyzed, we obtain a very well defined minimum variance vector. At Mars the direction of this vector agrees with the normal to the MPB fit obtained from Mars Global Surveyor crossings. The results confirm that the MPB is a well-defined plasma boundary. According to empirical criteria based on minimum variance analysis results, the Martian and Venusian MPB crossings would resemble an MHD tangential discontinuity rather than a rotational discontinuity. However, spacecraft observations suggest that the nature of the MPB could be far more complex. We compare our results with similar studies at the MPB of comets and the magnetic tail boundary of Titan, and we discuss the nature of the boundary from a general perspective.J. Geophys. Res. 01/2005; 110. -
Article: Size and shape of ULF waves in the terrestrial foreshock
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ABSTRACT: 1] Using simultaneous four spacecraft data, estimates of the size and shape of ULF waves in the terrestrial foreshock are presented. Estimates of the size of the waves in different directions are obtained by calculating the spatial autocorrelation function of the magnetic field in the wave frame using cross-correlations of magnetic field measurements between the four Cluster spacecraft. The correlation length along the wave vector, its wavelength, is typically 1–3 R E , consistent with previous estimates. The correlation length perpendicular to the wave vector, however, is typically 3–8 times the wavelength, between 8 and 18 R E . The shape of the waves can be approximated as an oblate spheroid, symmetric around the wave vector. However, the wave front tends to be significantly more planar than a spheroid, implying planarity of the waves over several R E and hence a coherent periodic variation of the magnetic field at the bow shock on these scales. There is some evidence that at least during one extended interval of ULF waves, their finite perpendicular extent results in an additional quasi-periodic enhancement and modulation of the waves, with a period of several minutes, at the spacecraft.J. Geophys. Res. 01/2005; 110. -
Article: Magnetic Flux Ropes in the Martian Atmosphere: Global Characteristics
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ABSTRACT: We report observations of magnetic fields amplitude, which consist of a series of individual spikes in the Martian atmosphere. A minimum variance analysis shows that these spikes form twisted cylindrical filaments. These small diameter magnetic filaments are commonly called magnetic flux ropes. We examine the global characteristics of magnetic flux ropes, which are observed on 5% of the elliptical orbits of Mars Global Surveyor. Flux ropes are more often observed in Venus' atmosphere (70% of the orbits). In this paper we report some of the global characteristics of the flux ropes identified in the Martian atmosphere. No flux ropes are observed in the southern hemisphere of Mars. Most of them occur at high solar zenith angles, close to the terminator plane, and at high latitude with altitudes below 400 km. The orientation of the flux ropes appears random while in the case of Venus the orientation is more horizontal near the terminator for altitudes greater than 200 km. We have identified fewer flux ropes for SZA between 40 to 60 deg and for SZA lower than 20 deg, like in the case of Venus (Elphic and Russell, 1983b). Statistically, Mars' ionosphere with SZA range between 40circ to 60circ is less magnetized than near the subsolar point. As the Martian ionosphere is quite often magnetized by the magnetic components of the crustal field, this crustal magnetic field seems to inhibit the flux ropes formation in the southern hemisphere. However, some orbits without crustal magnetic field, called magnetic cavities, were observed without flux ropes. So the flux ropes formation process seems to be uppressed by another factor, like the solar wind dynamic pressure for Venus (Krymskii and Breus, 1988).Space Science Reviews 01/2004; 111(1):223-231. · 3.61 Impact Factor -
Article: Bow Shock and Upstream Phenomena at Mars
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ABSTRACT: Mars Global Surveyor is the sixth spacecraft to return measurements of the Martian bow shock. The earlier missions were Mariner 4 (1964), Mars 2 and 3 (1972), Mars 5 (1975) and Phobos 2 (1989) (see reviews by Gringauz, 1981; Slavin and Holzer, 1982; Russell, 1985; Vaisberg, 1992a,b; Zakharov, 1992). Previous investigations of planetary bow shocks have established that their position, shape and jump conditions are functions of the upstream flow parameters and the nature of the solar wind — planet interaction (Spreiter and Stahara, 1980; Slavin et al., 1983; Russell, 1985). At Mars, however, the exact nature of the solar wind interaction was elusive due to the lack of low altitude plasma and magnetic field measurements (e.g., Axford, 1991). In fact our knowledge of the nature of the interaction of Mars with the solar wind was incomplete until the arrival of MGS and the acquisition of close-in magnetic field data (Acuña et al., 1998). As detailed by a series of review papers in this monograph, the Mars Global Surveyor (MGS) mission has now shown that the Mars environment is very complex with strong, highly structured crustal magnetic remnants in the southern hemisphere, while the northern hemisphere experiences the direct impingement of solar wind plasma. This review paper first presents a survey of the observations on the Martian bow shock and the upstream phenomena in the light of results from all the missions to date. It also discusses the kinetic properties of the Martian bow shock compared to the predictions of simulations studies. Then it examines the current status of understanding of these phenomena, including the possible sources of upstream low-frequency waves and the interpretations of localized disturbances in the upstream solar wind around Mars. Finally, it briefly discusses the open issues and questions that require further study.Space Science Reviews 01/2004; 111(1):115-181. · 3.61 Impact Factor -
Article: The plasma Environment of Mars
Space Science Reviews 01/2004; 111(1):33-114. · 3.61 Impact Factor
Top co-authors
Top Journals
Institutions
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2009
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Centre National d’Etudes Spatiales
Paris, Ile-de-France, France
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2007
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Swedish Institute of Space Physics
Kiruna, Norrbotten, Sweden
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2006
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Université Paul Sabatier - Toulouse 3
Toulouse, Midi-Pyrenees, France
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