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We present a statistical analysis of more than two thousand bipolar electrostatic solitary waves (ESW) collected from ten quasi-perpendicular Earth's bow shock crossings by Magnetospheric Multiscale spacecraft. We developed and implemented a correction procedure for reconstruction of actual electric fields, velocities, and other properties of ESW from measurements, whose spatial scales are typically comparable with or smaller than spatial distance between voltage-sensitive probes. We determined the optimal ratio between frequency response factors of axial and spin plane antennas to be around 1.65/1.8. We found that more than 95\% of the ESW in the Earth's bow shock are of negative polarity and present an in depth analysis of properties of these ESW. They have spatial scales of about 10--100 m that is within a range of $\lambda_{D}$ to $10\lambda_{D}$, amplitudes typically below a few Volts that is below 0.1 of local electron temperature, and velocities below a few hundreds km/s in spacecraft and plasma rest frames that is on the order of local ion-acoustic speed. The spatial scales of ESW are distinctly correlated with local Debye length $\lambda_{D}$. ESW with amplitudes of 5--30 V or 0.1--0.3 Te have the occurrence rate of a few percent. The ESW have electric fields generally oblique to local magnetic field and propagate highly oblique to shock normal ${\bf N}$; more than 80\% of ESW propagate within 30$^{\circ}$ of the shock plane. In the shock plane, ESW typically propagate within a few tens of degrees of local magnetic field projection ${\bf B}_{\rm LM}$ onto the shock plane and preferentially opposite to ${\bf N}\times {\bf B}_{\rm LM}$. We argue that the ESW of negative polarity are ion phase space holes produced in a nonlinear stage of ion-ion ion-streaming instabilities. We estimated lifetimes of the ion holes to be 10--100 ms, or 1--10 km in terms of spatial distance.

This research shows Part II of the Spacecraft Interaction Plasma Software (SPIS) used to model the Parker Solar Probe (PSP) FIELDS instrument and its interactions with the Solar Wind. Flight data w...

The Spacecraft Interaction Plasma Software package (SPIS), a three-dimension particle in cell (PIC) code, was used to model the Parker Solar Probe (PSP) spacecraft and FIELDS instrument and their i...

The Parker Solar Probe (PSP) spacecraft completed its second Venus gravity assist maneuver (VGA2) on 2019 December 26. For a 20 minute interval surrounding closest approach, the PSP/FIELDS Radio Fr...

We present a statistical analysis of more than 2,400 electrostatic solitary waves interpreted as electron holes (EH) measured aboard at least three Magnetospheric Multiscale (MMS) spacecraft in the Earth's magnetotail. The velocities of EHs are estimated using the multispacecraft interferometry. The EH velocities in the plasma rest frame are in the range from just a few km/s, which is much smaller than ion thermal velocity VTi, up to 20,000 km/s, which is comparable to electron thermal velocity VTe. We argue that fast EHs with velocities larger than about 0.1VTe are produced by bump-on-tail instabilities, while slow EHs with velocities below about 0.05VTe can be produced by warm bistream and, probably, Buneman-type instabilities. We show that typically fast and slow EHs do not coexist, indicating that the instabilities producing EHs of different types operate independently. We have identified a gap in the distribution of EH velocities between VTi and 2VTi, which is considered to be the evidence for self-acceleration (Zhou & Hutchinson, 2018) or ion Landau damping of EHs. Parallel spatial scales and amplitudes of EHs are typically between λD and 10 λD and between 10−3 Te and 0.1 Te, respectively. We show that electrostatic potential amplitudes of EHs are below the threshold of the transverse instability and highly likely restricted by the nonlinear saturation criterion of electron streaming instabilities seeding electron hole formation: (Formula presented.), where ϖ = min(γ, 1.5 ωce), where γ is the increment of instabilities seeding EH formation, while ωce is electron cyclotron frequency. The implications of the presented results are discussed., NASA (Grants 80NSSC18K0155, 80NSSC19K1063)

International audience; The unprecedented detail of measurements by the four Magnetospheric Multiscale (MMS) spacecraft enable deeper investigation of quasi‐perpendicular collisionless shocks. We compare shock normals, planarities, and Normal Incidence Frame (NIF) cross‐shock potentials determined from electric field measurements and proxies, for a subcritical (Fast Magnetosonic Mach number MF = 1.05 ± 0.05) interplanetary shock and a supercritical bow shock (MF = 2.13 ± 0.04). The low‐Mach shock's cross‐shock potential was 26±6V. The shock scale was 33km, too short to allow comparison with proxies from ion moments. Proxies from electron moments provided potential estimates of 40±5V. Shock normals from magnetic field minimum variance analysis were nearly identical, indicating a planar front. The high‐Mach shock's cross‐shock potential was estimated to be from 290 to 440V from the different spacecraft measurements, with shock scale 120km. Reflected ions contaminated the ion‐based proxies upstream, whereas electron‐based proxies yielded reasonable estimates of 250±50V. Shock normals from electric field maximum variance analysis differed, indicating a rippled front.

International audience; We have investigated the dependence of shock parameters (speed vsh, normal (Formula presented.), and angle θBn) on the choice of upstream and downstream regions for 51 bow shock crossings in Magnetospheric Multiscale (MMS) Fast Survey data. We summarize guidelines for selecting stream regions based on the magnetic field and particle moments. Preferred upstream and downstream combinations were identified by minimizing Rankine-Hugoniot conservation errors. Comparing parameters from different upstream/downstream combinations provided a measure of how stream region choices affect the parameters. Shifting from the preferred stream region combination to another would cause

The Radio Frequency Spectrometer (RFS) is a two channel digital receiver and spectrometer, which will make remote sensing observations of radio waves and in situ measurements of electrostatic and electromagnetic fluctuations in the solar wind. A part of the FIELDS suite for Solar Probe Plus (SPP), the RFS is optimized for measurements in the inner heliosphere, where solar radio bursts are more intense and the plasma frequency is higher compared to previous measurements at distances of 1 AU or greater. The inputs to the RFS receiver are the four electric antennas mounted near the front of the SPP spacecraft, and a single axis of the SPP search coil magnetometer (SCM). Each RFS channel selects a monopole or dipole antenna input, or the SCM input, via multiplexers. The primary data products from the RFS are auto and cross spectra from the selected inputs. The spectra are calculated using a polyphase filter bank (PFB), which enables the measurement of low amplitude signals of interest in the presence of high amplitude narrowband noise generated by spacecraft systems. We discuss the science signals of interest driving the RFS measurement objectives, describe the RFS analog design and digital signal processing, and show examples of current performance.

We present a series of electron holes observed simultaneously on four Magnetospheric Multiscale spacecraft in the plasma sheet boundary layer. The multispacecraft probing shows that the electron ho ...

We consider intense electrostatic solitary waves (ESW) observed in a supercritical quasi-perpendicular Earth's bow shock crossing by the Magnetospheric Multiscale Mission. The ESW have spatial scales of a few tens of meters (a few Debye lengths) and propagate oblique to a local quasi-static magnetic field with velocities from a few tens to a few hundred kilometers per second in the spacecraft frame. Because the ESW spatial scales are comparable to the separation between voltage-sensitive probes, correction factors are used to compute the ESW electric fields. The ESW have electric fields with amplitudes exceeding 600 mV/m (oriented oblique to the local magnetic field) and negative electrostatic potentials with amplitudes of a few tenths of the electron temperature. The negative electrostatic potentials indicate that the ESW are not electron phase space holes, while interpretation in terms of ions phase space holes is also questionable. Whatever is their nature, we show that due to the oblique electric field orientation the ESW are capable of efficient pitch-angle scattering and isotropization of thermal electrons. Due to the negative electrostatic potentials the ESW Fermi reflects a significant fraction of the thermal electrons streaming from upstream (downstream) back to upstream (downstream) region, thereby affecting the shock dynamics. The role of the ESW in electron heating is discussed. Plain Language Summary Processes governing electron thermalization across shock waves are not entirely understood. The high resolution particle and 3-D electric field measurements provided by the Magnetospheric Multiscale Mission make it possible to study the Earth's bow shock that is an excellent laboratory for addressing the electron thermalization across supercritical shock waves. Previous observations showed that electron heating across the bow shock is generally governed by macroscopic cross-shock electrostatic field. On the other hand, the role of the turbulence observed across the bow shock in the electron thermalization has remained unclear. In this letter we consider a particular bow shock crossing by the Magnetospheric Multiscale Mission and focus on the role of the high amplitude electrostatic solitary waves in the electron thermalization process. We accurately estimate the electrostatic solitary wave parameters and show that due to electric fields oriented oblique to a local DC magnetic field and negative electrostatic potentials with amplitudes of a few tenths of the electron temperature, these Debye-scale structures are capable of efficient pitch angle scattering, Fermi reflection, and isotropization of thermal electrons.

Using the Three-Dimensional Plasma electron analyzers on the Wind spacecraft, we have analyzed several years of solar wind electron data. We find an anomalous core electron drift of roughly 40 km/s in the sunward xGSEdirection, regardless of the direction of the magnetic field. We interpret this drift as an effect of a spin modulation in the spacecraft floating potential, which can be effectively modeled with the addition of a dipole term to the potential. For typical solar wind conditions, the amplitude of potential modulation is a fraction of a volt. The modulation has negligible effects on the even electron moments (density and temperature) but noticeable effects on the odd moments (bulk velocity and heat flux).

We identify electromagnetic field variations from the Van Allen Probes which have the properties of Doppler shifted kinetic scale Alfvenic field line resonances. These variations are observed during injections of energetic plasmas into the inner magnetosphere. These waves have scale sizes perpendicular to the magnetic field which are determined to be of the order of an ion gyro-radius (ρi) and less. Cross-spectral analysis of the electric and magnetic fields reveals phase transitions at frequencies correlated with enhancements and depressions in the ratio of the electric and magnetic fields. Modeling shows that these observations are consistent with the excitation of field-line resonances over a broad range of wave numbers perpendicular to the magnetic field (k⊥) extending to k⊥ρi ≫ 1. The amplitude of these waves is such that E/Bo ≳ Ωi/k⊥ (E, Bo, and Ωi are the wave amplitude, background field strength, and ion gyro-frequency, respectively) leading to ion demagnetization and acceleration for multiple transitions through the wave potential.

Measurements have been made of the resistance of three different electric field sensing antennas on the Wind spacecraft in the solar wind. The measurements have been separated into base resistance and plasma resistance by assuming that the plasma resistance is inversely proportional to the antenna length. Simple formulas for the resistances, as functions of the plasma electron flux, are given and fitted to the data. The results imply that the division of the signal by the base resistance is important and needs to be taken into account in low-frequency measurements of electric fields when the antennas are shorter than a few tens of meters.

Whistler waves propagating along the ambient magnetic field are observed within a coronal mass ejection (on January 10, 1997) associated in time with Langmuir waves and electron distributions of a single loss cone type. In addition, background observations are made on the plasma wave activity in the sheath and foreshock regions that precede the magnetic cloud, on the observed radio emissions (including a type II radio burst) and on the geometry of the cloud. All the data comes from the WIND spacecraft. The whistler waves are identified using full magnetic waveforms while possible evidence of coexisting parallel, and antiparallel propagating Langmuir modes are found in the waveform and spectral wave data from the WAVES experiment. A few hundred low energy electron distributions from the Three-Dimensional Plasma (3DP) experiment are investigated. Finally, we tentatively suggest that this type of plasma wave particle activity is linked to the type II emission observed, i.e., that the emission mechanisms are proceeding and taking place within the magnetic cloud instead of at the shock region as usually thought. The extra suprathermal electrons could source from electrons accelerated at reconnection sites between the magnetic cloud and the ambient interplanetary magnetic field. A linear instability study using observed properties of the electron distributions is to be presented in a following paper.

Using high time resolution particle and wave data from the Wind spacecraft, we examine several crossings of the electron foreshock-solar wind boundary. We show that the most intense electron plasma waves, observed near the foreshock boundary, often occur coincident with a flux of electrons with energies between 1 keV and 27 keV. This corresponds to electron beam speeds of 9vth ≤ vb ≤ 50vth, rather than vb ≈ 5vth, as is inferred from reduced distribution functions obtained by other instruments. Assuming Landau coupling, the resonant index of refraction is then 3 ≤ N0 ≤ 15, which implies that the waves are susceptible to strong scattering by ambient density fluctuations. The most intense electric fields are not well correlated with beam speed, and the distribution of electric field occurrence is broadly aligned with the interplanetary magnetic field direction. We compare the estimated maturity and bandwidth of the instability with those expected of the electrostatic decay instability and nonlinear Landau damping and find that our observations show a narrower bandwidth than expected. We suggest that the observations are consistent with scattering of electrostatic Langmuir waves to small wavenumber. The observed transverse polarization may be explained by the electromagnetic nature of the small-wavenumber z-mode, or as evidence of incident, reflected, and transmitted electrostatic components. The generation of electromagnetic emission at fpe and 2fpe is discussed in the context of the observations.

Two large depressions in the magnitude of the interplanetary magnetic field, lasting ∼10-20 min, have been observed in the solar wind just upstream of the Earth's bow shock by three spacecraft (Active Magnetospheric Particle Tracer Explorer UK Subsatellite (AMPTE UKS), AMPTE Ion Release Module (IRM), and ISEE 1). The multiple satellite observations show that the depressions are convecting with the ambient solar wind. Analysis of the depression boundaries shows that they are tangential discontinuities with normals aligned approximately parallel to the GSE x direction. The electron distributions measured within the structures are remarkably isotropic when compared to the more anisotropic distributions found in the ambient solar wind. There is also a reduction in plasma wave activity during the depressions. The depressions exhibit characteristics similar to those of solar wind magnetic holes but are much larger than has been typically observed. The depressions also display similarities with encounters of the heliospheric plasma sheet and heat flux dropouts, both of which are typically observed near sector boundaries, close to the heliospheric current sheet. The nature of these depressions is discussed in the context of magnetic hole and heliospheric plasma sheet observations. A large magnetic hole structure formed from a conglomeration of small holes appears the more likely scenario for the observed depressions.

On December 6, 1994, during a CIR (Corotating Interaction Region) event, the WIND 3D-Plasma and energetic particle experiment observed a burst (≤ 24 s) of 238-676 keV protons close to the electron foreshock boundary, followed by a 156-236 keV, 101-156 keV and 33-101 keV proton bursts about ∼40 s, 65 s and 85 s later, respectively. Similar dispersed bursts of helium with energies between -50 keV and ∼ 1 MeV followed the proton bursts. During this time, the IMF direction varied slowly with an almost monotonic decrease in θ Bn . The proton energy spectrum is initially peaked at -350 keV, and progresses to lower energies with time. The proton 3D angular distributions are peaked at ∼30° pitch-angle, propagating away from the shock, but they are non-gyrotropic. Finally, we show that the proton energy-spectra as well as the pitch angle distribution agree quantitatively with a model of a single adiabatic reflection of the incident energetic interplanetary ions by the quasi-perpendicular shock.

The Langmuir waves which are resonant with typical type III solar radio burst electrons have a frequency so little above the ambient plasma frequency that they should be strongly affected by known density fluctuations. Some consequences of this observation are worked out, and the expected consequences are demonstrated in the observations of the Langmuir waves from two quite different bursts, of November 4, 1997, and January 19, 1998.

We present the first observation of the source region of an interplanetary type II radio burst, using instruments on the Wind spacecraft. Type II radio emission tracks the motion of a CME-driven interplanetary (IP) shock which encounters the spacecraft. Upstream of the IP shock backstreaming electrons are observed, first antiparallel to the interplanetary magnetic field (IMF), and then later parallel as well. Langmuir waves are observed concomitant with the shock-accelerated electrons. The electron energy spectrum and Langmuir wave amplitudes are very similar to those observed in the terrestrial electron foreshock. From the connection times to the shock, we infer the existence and characteristic size of large scale structure on the shock front. The type II radio emission seems to be generated in a small bay upstream of the shock, and this may account for some splitting structure observed in the frequency spectrum of many type II bursts.

The Earth's foreshock region, the region which is magnetically connected to the bow shock, is a region of intense Langmuir waves. Some of these waves have an envelope similar to that expected for one-dimensional Langmuir solitons. A computer search for such waveforms has identified a number sufficient for statistical investigation. It is concluded that there is no evidence for stable waveforms like one-dimensional Langmuir solitons.

We present observations of MF/HF ionospheric radio emission observed between 4-7 R e in the terrestrial magnetosphere by the Wind spacecraft. During a perigee pass, and AKR episode, two distinct radio signatures are observed: an intense, sporadic emission near f ≃ 1.8 MHz, and a more steady and weaker emission near f ≃ 4.4 MHz. These emissions show characteristics similar to ground observations of ionospheric 'auroral roar', although to propagate to the spacecraft they must have been generated above the ionospheric F-layer peak. We suggest that the emissions are generated on the topside ionosphere where the condition f uh ≃ nf ce is met. These observations represent a new component of the natural terrestrial radio spectrum as viewed from space.

Previously, the formation of the lunar wake was considered from a magnetohydrodynamic perspective. However, recent Wind particle and field observations suggest the lunar wake may be formed by kinetic processes: those microphysical processes not considered in an MHD formalism. Unfortunately, a full multidimensional and self-consistent kinetic simulation of the lunar wake is beyond current means. However, some elements of the kinetic structure can be simulated via a simple one-dimensional electrostatic particle-in-cell simulation. We present a self-consistent simulation of a cross-sectional element of a plasma void. Essentially, wakeward directed ion beams are formed at the flanks of the simulated void, consistent with the Wind observations of counterstreaming ion beams in the wake region. These wakeward directed beams are generated by ambipolar electric fields formed at the wake edges. Other structures observed by Wind are also seen in the simulation, including an electrostatically turbulent central wake region that causes the wake to fill-in and a rarefaction wave emanating outward from the wake.

A model is proposed for recent ground-based observations of auroral roar emissions, detected at 2Ωe and 3Ωe, where Ωe is the local electron cyclotron frequency in the source region, between 200 and 500 km above the Earth's surface. Electron cyclotron maser emission is a likely mechanism to account for these emissions because it naturally produces coherent radiation at harmonics of Ωe. A theory for auroral roar emissions has already been proposed, whereby maser-generated second (X2) and third (X3) harmonic x mode radiation is amplified in the source region by multiple reflections off the walls of the density cavity in which they are produced. After many reflections the X2 and X3 waves propagate along the density cavity to a ground-based observer. However, it is demonstrated here with ray-tracing calculations that it is highly probable that maser-generated X2 and X3 radiation is reabsorbed at lower altitudes and thus cannot be detected at the ground. An indirect maser mechanism is proposed instead, where maser-generated z mode waves at Ωe grow to high levels in the source region and then undergo repeated nonlinear wave-wave coalescence to produce second- and third-harmonic waves that propagate directly to the ground. The z mode waves must satisfy the necessary kinematic constraints to produce observable second- and third-harmonic radiation. The dependence of the z mode maser on the temperature and functional form of the unstable electron distribution is discussed, along with the conditions required for the coalescence processes to proceed and produce the observed levels of radiation.

Using data from the Active Magnetospheric Particle Tracer Explorers (AMPTE) Charge Composition Explorer (CCE) satellite near local noon, and the AMPTE Ion Release Module (IRM) and United Kingdom Subsatellite (UKS) on the morning flank, we investigate the tailward propagation of a compressional Pc5 wave (380 s period) on October 28, 1984, and suggest that the observation represents a magnetospheric waveguide mode. The observed wave is a transient oscillation lasting about five wave cycles with an observed time of flight from CCE to IRM/UKS of 180 s. The first three or four cycles at the leading edge of the event display a remarkable wave packet coherence between CCE and IRM/UKS despite their large separation in the magnetosphere (∼ 6.2 RE). A time of flight analysis suggests a waveguide mode group speed ∼ 220 km s−1, being much less than the local Alfven speed and comparable to the expected sub-Alfvenic propagation speed of a waveguide mode. The ground-based signature of the event is also observed near local noon by the European Incoherent Scatter magnetometer cross, displaying the same period and lasting for the same number of cycles. The ground-based data show no evidence of a field line resonance; the event is monochromatic, and there is little variation of amplitude and polarization with latitude. An increase in solar wind ram pressure of ∼ 30% is observed by IMP 8 upstream in the solar wind just prior to the event, and this may have provided an impulsive energy source for the waveguide mode. This is the first time the signature of a particular waveguide mode harmonic has been observed by satellites which are widely spaced in the magnetosphere. Moreover, we present the first unambiguous observation of the downtail propagation of a waveguide mode. The observation also provides possible evidence of dispersion in the Earth's outer magnetospheric waveguide.

We examine the phase relation between two orthogonal electric field components for several hundred waveform measurements of intense electron plasma waves in the terrestrial electron foreshock. In general, the phase shift at the carrier frequency is not zero or π as would be expected if the waves were purely electrostatic Langmuir waves, but is a function of the angle between the antennas and the interplanetary magnetic field (IMF). When the antennas are field aligned, the phase shift between the components is large; this value recedes smoothly to zero as the antenna is rotated away from the IMF direction. When solar wind density fluctuations are considered, this is consistent with the dispersion of the electromagnetic z-mode and we assert that the electron foreshock is populated by transverse z-mode waves, not purely longitudinal Langmuir waves. This has implications for conversion to freely propagating modes and large-amplitude saturation mechanisms.

Waveforms of large-amplitude Langmuir oscillations were recorded by the Wind spacecraft in the Earth's upstream electron foreshock region. We present some statistics of the waveforms and discuss them in the context of various saturation mechanisms. In particular, it is found that the value of Epeak/Erms is not large, as previously suggested, and that the largest-amplitude Langmuir waveforms are generally somewhat sinusoidal and lack structure on small spatial scales. The measured probability distribution of electric field amplitude and dimensionless energy suggest that some stochastic process may play a role in wave generation. The values of dimensionless energy needed to arrest Langmuir wave collapse occur with very small probability and the value of Epeak/Erms for large fields suggests that, statistically, Langmuir wave collapse is not an important process in the terrestrial foreshock.

We report observations of electrostatic ion acoustic waves and Langmuir waves during a recent lunar encounter by the Wind spacecraft. These waves are observed when Wind is magnetically connected to the nominal wake and at distances greater than 8 lunar radii from the wake. When interpreted in the context of a simple time-of-flight model, these observations imply the existence of a system of currents and disturbed particle distributions that extends far into solar wind.

Some theories of the generation of 2ωpe radiation, in the upstream solar wind, invoke the notion of nonlinear wave-wave interactions. We present observations, from the WIND spacecraft, of an event in the upstream solar wind with first and second harmonic emissions. The bicoherence spectrum of this event shows coherence amongst components that suggest three-wave interactions of the type described in (Cairns and Melrose, 1985). We discuss this result and its theoretical context.

[1] Intense localized Langmuir waves in the solar wind are often associated with type III solar radio bursts. Wave packets with a Gaussian fall-off of electric field with distance are shown to be consistent with strong turbulence simulations. The collapse threshold for these Gaussian wave packets is calculated analytically and shown to be consistent with previous estimates and simulations. We then assess whether intense Langmuir events detected by the SWAVES instrument on the twin STEREO spacecraft during type III bursts are consistent with known conditions for wave packet collapse. Eight different type III events are selected and a total of 167 wave packets analyzed. An approximate analysis of the observed spatial scales and electric fields shows that none of the wave packets are consistent with collapse. The electric field structures predicted for collapsing wave packets, based on the nucleation mechanism and extensive three-dimensional electrostatic and electromagnetic Zakharov simulations, are also fitted to the observed data: about a third of the packets are well fitted by a potential with a Gaussian radial function. Where good fits can be found, the wave packets do not meet the requirements for collapse. Good eigenmode fits are found for wave packets with waveforms well fitted by the structural form of collapsing wave packets. This is because the electric field envelopes of collapsing wave packets and trapped Langmuir eigenmodes are both Hermite-Gauss functions. This rules out the possibility of wave packet collapse and strong turbulence being important processes in type III source regions.

[1] We analyze dust impacts recorded by the S/WAVES radio instrument onboard the two STEREO spacecraft near 1 A.U. during the period 2007–2010. The impact of a dust particle on a spacecraft produces a plasma cloud whose associated electric field can be detected by on-board electric antennas. For this study we use the electric potential time series recorded by the waveform sampler of the instrument. The high time resolution and long sampling times of this measurement enable us to deduce considerably more information than in previous studies based on the dynamic power spectra provided by the same instrument or by radio instruments onboard other spacecraft. The large detection area compared to conventional dust detectors provides flux data with a better statistics. We show that the dust-generated signals are of two kinds, corresponding to impacts of dust from distinctly different mass ranges. We propose calibration formulas for these signals and show that we are able to use S/WAVES as a dust detector with convincing results both in the nanometer and micrometer size ranges. In the latter, the orbital motion of the spacecraft enables us to distinguish between interstellar and interplanetary dust components. Our measurements cover the mass intervals ∼10−22–10−20 kg and ∼10−17 − 5 × 10−16 kg. The flux of the larger dust agrees with measurements of other instruments on different spacecraft.

[1] The cross-shock electrostatic potential at the front of collision-less shocks plays a key role in the distribution of energy at the shock front. Multipoint measurements such as those provided by the Cluster II mission provide an ideal framework for the study of the cross-shock potential because of their ability to distinguish between temporal and spacial variations at the shock front. We present a statistical study of the cross-shock potential calculated for around 50 crossings of the terrestrial bow shock. The statistical dependency of the normalized (with resect to upstream ion kinetic energy) cross-shock potential (ΦK) on the upstream Alfven Mach number is in good agreement with analytical results that predict decrease of Φk with increasing Mach number.

[1] We investigate statistically the dependence of electron foreshock Langmuir wave activity on the properties of the upstream electron distribution function, using wave and electron measurements from the Wind spacecraft. We find that the presence of a strong strahl beam in the upstream solar wind leads to a significant increase in the occurrence of Langmuir wave activity in the sunward wing of the electron foreshock, generating an asymmetry in the foreshock between the sunward and anti-sunward wings. This asymmetry of electrostatic wave occurrence is likely to be reflected in the radio emission properties of the two foreshock wings. The mechanism behind the asymmetry was first postulated in the context of the Venus foreshock, and may be relevant to recent observations of Langmuir wave activity in solar wind magnetic holes. Furthermore, the likely absence of a strahl-related enhancement at fast forward interplanetary shocks points out a key difference between the physics of electron acceleration at interplanetary shocks and bow shocks.

[1] We present general formulas to calibrate the antennas of a space-based radio instrument using as a reference source the galactic background radiation (or any isotropic source). We apply these formulas to determine the effective length of the STEREO/WAVES antennas. The results for the monopoles are in agreement with the measurements performed on ground, and we provide new results for the XY and YZ dipoles used by the instrument. Our method also allows us to accurately determine the internal noise background of the radio receiver.

[1] It is known from in situ observations that large-amplitude spatially localized Langmuir waves are frequent in the solar wind, and usually correlated with the presence of suprathermal electron beams, during type III events or close to the electron foreshock. It seems that the influence of the solar wind density fluctuations on the propagation effects of the Langmuir waves play an important role in the formation of these wave packets. In this article, we focus on the mechanism of generation of localized wave packets by electron beams propagating in an inhomogeneous medium. To this purpose, we present a theoretical model based on the resolution of the high-frequency component of the Zakharov's equation in which a source term describing the electron beam has been introduced, and show that this model is able to reproduce classical results about beam plasma instability and wave trapping in density cavities. Then we present simulation results of the generation of Langmuir wave packets in typical solar wind conditions at 1 A.U., and discuss the origin and nature of their localization.

[1] We have examined 178 interplanetary shocks observed by the Wind spacecraft to establish which shock and plasma parameters are favorable for the production of upstream Langmuir waves and therefore to determine which shocks are likely to generate interplanetary Type II radio bursts. Of the 178 shocks included in this study, 43 produced upstream Langmuir waves, as evinced by enhancements in wave power near the plasma frequency. The large number of observed shocks permits the use of statistical tests to determine which parameters control the upstream activity. The best predictor of activity is the de Hoffmann-Teller speed, a result consistent with the fast Fermi model of electron acceleration. Several other parameters, including the magnetic field strength and the level of solar activity (but not the Mach number), are also correlated with upstream activity. These additional parameters may be associated with an increased level of shock front curvature or upstream structure, leading to the formation of upstream foreshock regions, or with the generation of an upstream electron population favorable for shock reflection.

[1] We report on the finding of a new periodicity in the Jovian decametric radio emission (DAM). Periodic bursts of non-Io component of DAM which recur with a period 1.5% longer than the Jupiter rotation (System III) have been found in the dynamic radio spectra acquired by STEREO/WAVES, Wind/WAVES and Cassini/RPWS during the years 2002–2008. Typically, the bursts appear very periodically over several Jovian days with a decreasing intensity and they display a negative frequency drift. All the bursts were detected within the same sector of Jovian Central Meridian Longitude (III), between 300° and 60° (via 360°) of CML (III), close to the region of the non-Io-C source. No correlation has been found with the position of Io. Considering the simultaneous stereoscopic observations onboard STEREO-A and STEREO-B, as well as Wind and Cassini we can conclude that the sources of the periodic bursts most probably sub-corotate with Jupiter.

[1] One of the most accurate techniques for in situ measuring the electron density and temperature in space plasmas is the quasi-thermal noise spectroscopy, which uses the voltage fluctuation spectrum on an electric antenna. This technique has been used successfully on the WIND and ULYSSES spacecraft; however, on STEREO this technique may only work in high-density filamentary structures, where the Debye length is small, because the STEREO/WAVES antennas have a large surface area, so that the resulting shot noise spectrum in the solar wind dominates the power at lower frequencies. In the unperturbed solar wind, we can use instead the electron shot noise to infer the plasma density. For doing so, we use well calibrated WIND particle data to deduce the stray capacitance of the STEREO/WAVES antenna system in a special configuration when the STEREO-B spacecraft was just downstream of WIND. This stray capacitance is also compared to ground experiments done on the flight spare equipment and independent calibrations performed using the galactic radio background.

[1] The STEREO/WAVES instrument is designed to measure interplanetary radio emission and in situ plasma waves in the solar wind. The instrument uses three orthogonal monopole electric antennas as its sensor system in both a pseudodipole and monopole mode. At high radio frequencies, the capacitance of the antennas determines the system gain. Here we estimate the stray capacitance in the antenna system by comparing the measured voltage spectrum with a model of the galactic continuum spectrum, which is the instrument background at high frequencies. Together with the antenna free-space capacitance, these measurements provide an absolute calibration of the STEREO/WAVES experiment at radio frequencies, a prerequisite for quantitative studies of solar and astrophysical radio emission.

International audience; Daily variations of terrestrial auroral kilometric radiation (AKR) are considered; an effect that is detected in STEREO/WAVES data. It has been found that the intensities of the AKR emitted from Northern and Southern sources are modulated with a period of ~24 hours. The occurrence frequency of the AKR has been shown to be strongly dependent on the orientation of the rotating oblique magnetic dipole of the Earth relative to the Sun. AKR is found to occur more often and emit in a broader frequency range when the axis of the terrestrial magnetic dipole in the given hemisphere is oriented toward the nightside. We suggest that the observed ~24 h variations of AKR are connected with diurnal changes of the ambient plasma density in the auroral region.

[1] Using new capabilities of waveform analyses provided by the S/WAVES instruments onboard the two STEREO spacecraft, we present for the first time a complete set of direct evidence for three-wave coupling occurring during a type III emission and involving two Langmuir waves and an ion acoustic wave. Information on the Doppler-shifted frequencies and especially the phases of the waves are used in order to check first the conservation of momentum and energy, through Fourier analyses, and second the phase locking between the waves, through bicoherence analyses. Wavelet analyses allow us to resolve for the first time the coupling regions, in which spatial length is estimated to be 18 ± 5 km. The wave packets travel at comparable speed, and the characteristic available interaction time is about 1 s. Interpretations of the phase coupling and evaluation of the growth rate of the waves tend to favor the parametric decay, at least in the observational events considered in this work.

[1] The S/WAVES experiments on the two STEREO spacecraft measure waves, both in situ plasma waves and remotely generated waves such as Type II and Type III solar bursts. A part of the experiment is aimed at understanding the generation of electromagnetic waves from electrostatic Langmuir waves. For this, rapid measurements of plasma density, sufficiently rapid to be on the time scale of Langmuir wave fluctuations, are deemed necessary. Measurements of the potential of the antennas relative to the spacecraft can supply these rapid measurements. The antennas were not provided with a bias current, and so this unbiased technique has not been used previously. However, the cylindrical antennas of S/WAVES respond to temperature as well as the density of the ambient plasma, giving five quantities, ne, Te, and 3 components of E, to be determined from the three measurements of antenna potential. The work presented here discusses the analysis and interpretation of these measurements from the early part of the mission, when there were frequent observations of foreshock Langmuir waves to use for calibration. A model of the photoemission-plasma equilibrium has been constructed, using these and other measurements. It is shown that the response to one or a few of the five quantities may be negligible, depending on the phenomenon observed, so that useful measurements are obtained of the others. Application to observation and analysis of various plasma wave phenomena will be discussed.

We examine the upstream meridional deflection flows of interplanetary coronal mass ejections (ICMEs) in an effort to investigate their cross-sectional shape and the magnetic field orientation in their sheath regions. Eight out of 11 magnetic clouds (MCs) near solar minimum identified for the curvature study are concave outward as indicated by the elevation angle of the MC normal with respect to the solar equatorial plane; an inverse correlation is observed between the meridional deflection flow and the spacecraft latitude for these concave-outward MCs, which suggests that the upstream plasma is deflected toward the equatorial plane. MHD simulations, however, show that the meridional deflection flow moves poleward for a concave-outward CME. The poleward flow deflection is observed only ahead of convex-outward MCs. Possibilities leading to this discrepancy are discussed. The deflection flow speed in sheath regions of ICMEs increases with the ICME speed relative to the ambient solar wind, which together with the coupling between the meridional magnetic field and deflection flow yields a positive linear correlation between the sheath meridional field and the ICME relative speed. This empirical relationship could predict the sheath meridional field based on the observed CME speed, which may be useful for space weather forecasting as ICME sheaths are often geoeffective. Implications of the deflection flows and ICME curvature are also discussed in terms of magnetic reconnection and particle acceleration in ICME sheaths.

[1] The normal electric field structure of a supercritical (Mms = 5.2), quasiperpendicular (θBn = 70°) collisionless shock is examined using Cluster four-spacecraft observations of the terrestrial bow shock. Comparing the observed electric field with magnetic field and plasma observations, two different techniques find that the J × B/ne term in the generalized Ohm's law accounts for a majority of the large-scale normal electric field and potential drop encountered by the ions - the solar wind ion deceleration is in good empirical agreement with the observed potential drop, confirming earlier work. Large amplitude electric field fluctuations on shorter timescales, corresponding to fine scale structure, are not observed to contribute to the ion energization.

[1] This paper studies high-frequency plasma waves during 28 encounters of the Wind spacecraft with solar wind reconnection exhausts. We use measurements by the Thermal Noise Receiver (TNR) and Time Domain Sampler (TDS) experiments on Wind/WAVES to survey characteristics of electron plasma waves and the most common regions where they are found. TNR spectrograms showed intense emission bursts ∼4 kHz (corresponding to the ion acoustic range) during 79% of the events while around the local electron plasma frequency intense emission bursts were recorded for 39% of the events. The TDS instrument, operating at 120,000 samples per second, detected three kinds of electric waveforms: Langmuir waves, electron solitary waves (ESW), and wave packets with frequencies between ion and electron plasma frequencies typically interpreted as Doppler-shifted ion acoustic waves. Except for one very intense ESW event, the average amplitudes for all these three waveform types were similar, below 1 mV/m. We found an increased probability to observe intense plasma wave activity when the reconnection X-line region was approached. Wave activity may be present anywhere in the reconnection exhaust, although the boundary region of the exhaust appears to be the most dynamic region for wave activity. In particular, the majority of the captured ESW occurred near the exhaust boundaries.

[1] During January, 2005, there were several large X-class solar flares and associated solar energetic particle (SEP) events. Coincidentally, the MINIS balloon campaign had multiple payloads aloft in the stratosphere above Antarctica measuring dc electric fields, conductivity and x-ray flux. One-to-one increases in the electrical conductivity and decreases to near zero of both the vertical and horizontal electric field components were observed in conjunction with an increase in particle flux at SEP onset. Combined with an atmospheric electric field mapping model, these data are consistent with a shorting out of the global electric circuit and point toward substantial ionospheric convection modifications. Additionally, two subsequent, rapid changes were detected in the vertical electric field component several hours after SEP onset. These changes result in similar fluctuations in the calculated vertical current density. We will describe how rigidity cut-off dynamics may be crucial in understanding these sudden jumps in the vertical electric field.

[1] Formation of inhomogeneous electromagnetic structures with gradients in magnetic field and intrinsic electric fields is commonly observed in magnetized plasmas. Heliospheric plasmas are susceptible to formation of localized, supersonically propagating electromagnetic inhomogeneities. Coronal relaxation may result in an emergence close to solar surface of a shock wave which traverses significant parts of the heliosphere. Shocks of solar origin may accelerate ions to high energies, and some of these ions can be trapped in quasi-stable orbits of planetary magnetospheres. The observationally deduced ion acceleration close to the Sun, at low Mach numbers and low turbulence levels, poses a dilemma regarding the energization mechanism. When the magnetic ramp of an obliquely propagating electromagnetic substructure narrows to a size of a fraction of ion skin depth, as conjectured during merging of successively propagating shocks, the trajectories of some ions exhibit strongly nonadiabatic characteristics. Subset of ions is energized while surfing along the shock due to the combined forces of magnetic fields and cross-shock electric potential gradient, forming a high-energy tail. This tail may be additionally accelerated after traversing the shock multiple times as a result of scattering and reflection due to Alfvenic wave diffusion. We follow the orbits of seed ions in a presence of a stationary, fluid-based, self-consistent model, and investigate their behavior for a variety of plasma parameters and geometries. The results indicate that (1) the energization of ions for low Mach numbers, as observed for emerging shocks close to the Sun, depends crucially on the narrowness of the electromagnetic structures, (2) the sufficiently narrow heliospheric structure can energize thermal protons and a subset of rare ions which were enriched due to impulsive coronal processes, (3) the energization is sensitive to the pitch angle of the seed population, indicating dependence on the geometry of the shock-plasma flow system, and (4) the preacceleration by surfing mechanism is a prerequisite for an additional energization due to diffusive shock acceleration. We conclude that the best configuration for an effective acceleration due to an emerging shock at small heliocentric distances and low Mach number consists of a narrow electromagnetic substructure which energizes heliospheric thermal protons directly from their thermal level, as well as trace elements which enrich the seed population due to previous coronal processes. The narrowness of the shock or its substructure and the surfing mechanism may help in explaining the observed energization when other mechanisms become inefficient due to an insufficient level of the turbulence. The energetic ion populations may have a direct profound impact on human space exploration.