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The Quasi-thermal noise (QTN) technique is a reliable tool to yield accurate measurements of the electron parameters in the solar wind. We apply this method on Parker Solar Probe (PSP) observations to derive the total electron temperature ($T_e$) from the linear fit of the high-frequency part of the QTN spectra acquired by the RFS/FIELDS instrument, and present a combination of 12-day period of observations around each perihelion from Encounter One (E01) to Ten (E10) (with E08 not included) with the heliocentric distance varying from about 13 to 60 solar radii ($R_\odot{}$). We find that the total electron temperature decreases with the distance as $\sim$$R^{-0.66}$, which is much slower than adiabatic. The extrapolated $T_e$ based on PSP observations is consistent with the exospheric solar wind model prediction at $\sim$10 $R_\odot{}$, Helios observations at $\sim$0.3 AU and Wind observations at 1 AU. Also, $T_e$, extrapolated back to 10 $R_\odot{}$, is almost the same as the strahl electron temperature $T_s$ (measured by SPAN-E) which is considered to be closely related to or even almost equal to the coronal electron temperature. Furthermore, the radial $T_e$ profiles in the slower solar wind (or flux tube with larger mass flux) are steeper than those in the faster solar wind (or flux tube with smaller mass flux). More pronounced anticorrelated $V_p$-$T_e$ is observed when the solar wind is slower and closer to the Sun., Comment: 10 pages, 7 figures, and Astronomy & Astrophysics Accepted

International audience; Eclipse observations of the W-L corona show linear rays above active regions at times of solar maximum. We show that these linear rays are also observed in the field-of-view of the C2-LASCO coronagraph, in perfect correspondence with the eclipse results. A selected prominent case taken from the 2001 eclipse observation in Angola is analysed with several different methods, including the use of a synoptic map constructed using SoHO/LASCO C2 images. A clear signature of time variations near the eclipse observation is detected, suggesting that at least some parts of the beam are collimated. These observations strongly suggest high speed streams that apparently ignore the potential large scale coronal magnetic field rooted rather low in the corona. A possible origin is the neutral magnetic points located above the active region. Several mechanisms exist to explain how the plasma is accelerated in these regions to large quasi-relativistic velocities, possibly related to the occurrence of type III radio bursts. We point out a curious analogy with phenomena occurring inside coronal holes.

Context. Dust impacts have been observed using radio and wave instruments onboard spacecraft since the 1980s. Voltage waveforms show typical impulsive signals generated by dust grains. Aims. We aim at developing models of how signals are generated to be able to link observed electric signals to the physical properties of the impacting dust. To validate the model, we use the Time Domain Sampler (TDS) subsystem of the STEREO/WAVES instrument which generates high-cadence time series of voltage pulses for each monopole. Methods. We propose a new model that takes impact-ionization-charge collection and electrostatic-influence effects into account. It is an analytical expression for the pulse and allows us to measure the of amount of the total ion charge, Q, the fraction of escaping charge, ϵ, the rise timescale, τi, and the relaxation timescale, τsc. The model is simple and convenient for massive data fitting. To check our model’s accuracy, we collected all the dust events detected by STEREO/WAVES/TDS simultaneously on all three monopoles at 1AU since the beginning of the STEREO mission in 2007. Results. Our study confirms that the rise time largely exceeds the spacecraft’s short timescale of electron collection. Our estimated rise time value allows us to determine the propagation speed of the ion cloud, which is the first time that this information has been derived from space data. Our model also makes it possible to determine properties associated with the electron dynamics, in particular the order of magnitude of the electron escape current. The obtained value gives us an estimate of the cloud’s electron temperature – a result that, as far as we know, has never been obtained before except in laboratory experiments. Furthermore, a strong correlation between the total cloud charge and the escaping charge allows us to estimate the escaping current from the amplitude of the precursor, a result that could be interesting for the study of the pulses recently observed in the magnetic waveforms of Solar Orbiter or Parker Solar Probe, for which the electric waveform is saturated.

A weak continuous line has been recently discovered onboard Voyager 1 in the interstellar medium, whose origin raised two major questions. First, how can this line be produced by plasma quasi-thermal noise on the Voyager short antenna? Second, why does this line emerge at some distance from the heliopause? We provide a simple answer to these questions, which elucidates the origin of this line. First, a minute quantity of supra-thermal electrons, as generally present in plasmas, whence the qualifier quasi-thermal, can produce a small plasma frequency peak on a short antenna, of amplitude independent of the concentration of these electrons; furthermore, the detection required long spectral averages, alleviating the smallness of the peak compared to the background. We therefore attribute the observed line to a minute proportion of fast electrons that contribute negligibly to the pressure. Second, we suggest that, up to some distance from the heliopause, the large compressive fluctuations ubiquitous in this region prevent the line to emerge from the statistical fluctuations of the receiver noise because it is blurred out by the averaging required for detection,especially in the presence of short-wavelength density fluctuations. These results open up novel perspectives for interstellar missions, by showing that a minute proportion of fast electrons may be sufficient to measure the density even with a relatively short antenna, because the quietness of the medium enables a large number of spectra to be averaged., 5 pages, 4 figures, paper accepted for publication in Astronomy & Astrophysics Letters

Impacts of dust grains on spacecraft are known to produce typical impulsive signals in the voltage waveform recorded at the terminals of electric antennas. Such signals are routinely detected by the Time Domain Sampler (TDS) system of the Radio and Plasma Waves (RPW) instrument aboard Solar Orbiter. We investigate the capabilities of RPW in terms of interplanetary dust studies and present the first analysis of dust impacts recorded by this instrument. We discuss previously developed models of voltage pulses generation after a dust impact onto a spacecraft and present the relevant technical parameters for Solar Orbiter RPW as a dust detector. Then we present the statistical analysis of the dust impacts recorded by RPW/TDS from April 20th, 2020 to February 27th, 2021 between 0.5 AU and 1 AU. The study shows that the dust population studied presents a radial velocity component directed outward from the Sun, the order of magnitude of which can be roughly estimated as $v_{r, dust} \simeq 50$ km.$s^{-1}$. This is consistent with the flux of impactors being dominated by $\beta$-meteoroids. We estimate the cumulative flux of these grains at 1 AU to be roughly $F_\beta \simeq 8\times 10^{-5} $ m$^{-2}$s$^{-1}$, for particles of radius $r \gtrsim 100$ nm. The power law index $\delta$ of the cumulative mass flux of the impactors is evaluated by two differents methods (direct observations of voltage pulses and indirect effect on the impact rate dependency on the impact speed). Both methods give a result $\delta \simeq 0.3-0.4$. Solar Orbiter RPW proves to be a suitable instrument for interplanetary dust studies. These first results are promising for the continuation of the mission, in particular for the in-situ study of the dust cloud outside the ecliptic plane, which Solar Orbiter will be the first spacecraft to explore., Comment: 13 pages, 8 figures

The solar system contains solids of all sizes, ranging from km-size bodies to nano-sized particles. Nanograins have been detected in situ in the Earth's atmosphere, near cometary and giant planet environments, and more recently in the solar wind at 1 AU. These latter nano grains are thought to be formed in the inner solar system dust cloud, mainly through collisional break-up of larger grains and are then picked-up and accelerated by the magnetized solar wind because of their large charge-to-mass ratio. In the present paper, we analyze the low frequency bursty noise identified in the Cassini radio and plasma wave data during the spacecraft cruise phase inside Jupiter's orbit. The magnitude, spectral shape and waveform of this broadband noise is consistent with the signature of nano particles impinging at nearby the solar wind speed on the spacecraft surface. Nanoparticles were observed whenever the radio instrument was turned on and able to detect them, at different heliocentric distances between Earth and Jupiter, suggesting their ubiquitous presence in the heliosphere. We analyzed the radial dependence of the nano dust flux with heliospheric distance and found that it is consistent with the dynamics of nano dust originating from the inner heliosphere and picked-up by the solar wind. The contribution of the nano dust produced in asteroid belt appears to be negligible compared to the trapping region in the inner heliosphere. In contrast, further out, nano dust are mainly produced by the volcanism of active moons such as Io and Enceladus., Comment: to appear in ApJ

We update two kinds of results obtained with the SWAN instrument on board SOHO. First, we use H cell data recorded in 2001 and derive the H flow direction in the same way we performed the study at solar minimum. We compare with the Helium flow and doing so we correct for the coordinate system change between the Ulysses and SOHO mission. The deflection plane we obtain is compatible with the previous result within error bars, confirming the predominant role of the interstellar magnetic field. Secondly, we extend the derivation of solar wind ionization temporal evolution as a function of heliolatitude. The pattern for the present solar minimum is strikingly different from the previous minimum, with a much wider slow solar wind equatorial belt which persists until at least 2008. Comparing with synoptic LASCO/C2 electron densities we infer from a preliminary study that the acceleration of the high speed solar wind occurs at a higher altitude during this minimum, a change expansion models should be able to explain., 4 pages, Twelfth International Solar Wind Conference, 21-26 June 2009, Saint-Malo, France

International audience; Among several mechanisms issued from simulation and theoretical studies proposed to account for the nonstationarity of quasi-perpendicular supercritical shocks, one process—the so-called self-reformation—driven by the accumulation of reflected ions in the foot has been intensively analyzed with simulations. Present results based on experimental CLUSTER mission clearly evidence signatures of this self-reformation process for the terrestrial bow shock. The study based on magnetic field measurements includes two parts: (i) a detailed analysis of one typical shock crossing for almost perpendicular shock directions where the risk of pollution by other nonstationarity mechanisms is minimal. A special attention is drawn on appropriate treatment of data to avoid any wrong interpretation. One key result is that the ramp width can reach a very narrow value covering a few electron inertial lengths only; (ii) a statistical analysis allows relating the signatures of this nonstationarity with different plasma conditions and shock regimes. Present results are discussed in comparison with previous simulation works.

Although the priority is not very high, one of the scientific objectives of the Mars Express mission is to study the interaction of the Martian atmosphere with the interplanetary medium. Regarding Mars, the term “atmosphere” must be interpreted in its broadest sense, that is including the exospheric neutral and charged particles of planetary origin, which both extend deeply into the interplanetary medium and strongly interact with it. The antenna impedance measurements (AIM) experiment has been proposed within this framework. The main idea was to take advantage of the presence of a radar antenna onboard the Mars Express Orbiter and to measure its self-impedance in a frequency bandwidth that contains the plasma frequency. Both the real and imaginary parts of the antenna impedance are functions of the total plasma density and electron temperature. Consequently, with about 700 g of electronics, box, cables, and a rather simple interface to the radar antenna it becomes possible to monitor two local aeronomical parameters that play a fundamental role in the interaction between the Martian environment and the solar wind. Due to its lower-frequency bandwidth (8 kHz –2 MHz), which allows a full coverage from the shocked solar wind down to the ionosphere, its capability of measuring the electron temperature, and the reliability of its measurements the AIM experiment perfectly complements the Mars advanced radar for subsurface and ionospheric sounding (MARSIS) ionospheric investigations. In particular, careful computations show that the electron temperature can hardly be derived from the passive electric field measurements planned to be made by MARSIS. Unfortunately, due to a too late decision about the additional payload selection, the proposal of AIM as part of the MARSIS has been rejected.

We have developed a simulation model of particle acceleration in coronal shock waves. The model is based on a Monte Carlo method, where particles are traced in prescribed large-scale electromagnetic fields utilizing the guiding center approximation. The particles are scattered in the turbulence according to quasilinear theory, with the scattering amplitude directly proportional to the intensity of Alfv\'en waves at gyro-resonant wavenumbers. The Alfv\'en waves are traced simultaneously with the particles, so that the wave field is propagated outwards from the Sun using WKB propagation supplemented with a phenomenological wavenumber diffusion term and a growth rate computed from the net flux of the accelerated particles. We consider initial wave amplitudes small enough to allow rapid escape of particles from the shock to the ambient medium. Thus, in our model the Alfv\'en waves responsible for the diffusive acceleration of particles are generated by the accelerated particles themselves. In this work, we study the effects of non-constant shock velocity and non-monotonic Alfv\'en velocity on particle acceleration scenarios. We report in particular how the deceleration of a shock affects particle intensity and turbulence power evolution in the vicinity of the shock., Comment: 5 pages, 8 figures. Copyright (2010) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Twelfth International Solar Wind Conference, AIP Conference Proceedings 2010

Chapman's (1957) conductive model of the solar corona is characterized by a temperature varying as r**(-2/7) with heliocentric distance r. The density distribution in this non-isothermal hydrostatic model has a minimum value at 123 RS, and increases with r above that altitude. It is shown that this hydrostatic model becomes convectively unstable above r = 35 RS, where the temperature lapse rate becomes superadiabatic. Beyond this radial distance heat conduction fails to be efficient enough to keep the temperature gradient smaller than the adiabatic lapse rate. We report the results obtained by Lemaire (1968) who showed that an additional mechanism is then required to transport the energy flux away from the Sun into interplanetary space. He pointed out that this additional mechanism is advection: i.e. the stationary hydrodynamic expansion of the corona. In other words the corona is unable to stay in hydrostatic equilibrium. The hydrodynamic solar wind expansion is thus a physical consequence of the too steep (superadiabatic) temperature gradient beyond the peak of coronal temperature that can be determined from white light brightness distributions observed during solar eclipses. The thermodynamic argument for the existence of a continuous solar wind expansion which is presented here, complements Parker's classical argument based on boundary conditions imposed to the solutions of the hydrodynamic equations for the coronal expansion: i.e. the inability of the mechanical forces to hold the corona in hydrostatic equilibrium. The thermodynamic argument presented here is based on the energy transport equation. It relies on the temperature distribution which becomes super-adiabatic above a certain altitude in the inner corona., Comment: 4 pages, 3 figures, presented at SW12 conference (2009); Copyright 2010 American Institute of Physics 978-0-7354-0759-6/10. This article may be downloaded for personal use only. The following article appeared in CP1216 and may be found at http://proceedings.aip.org

International audience; We describe here a solar wind 1-fluid 1D model which is (1) time-dependent (2) includes transition region down to solar surface (3) uses a moderate number of grid points to enable further generalization to 2D/3D. The present model enables to study the response of the transition region and corona to photospheric pressure perturbations, including the solar wind up to ten solar radii. A simple chromosphere model with uniform temperature is used, in two different forms, either taking into account partial ionization or not. We show here how the amplitude of the response and associated viscous heating vary when attempting to decreasing the dynamical viscosity to approach realistic values.

In coronal outflows and solar winds, the presence of the interplanetary magnetic field and heat fluxes combined with jets and shock waves give rise to important thermal anisotropies and energetic counterstreaming motions of plasma shells. Such anisotropic structures of plasma quickly lead to the onset of the kinetic electromagnetic instabilities which are dependent solely on bulk properties of the plasma and not on resonant interaction with charged particles. Here the interplay between the Weibel and firehose instabilities, both driven by an excess of kinetic energy in the direction of the ambient magnetic field, is considered. Their growth rates and thresholds are evaluated and compared for the electron temperature anisotropies in the solar wind. It is shown that the instability of the Weibel-type, which is improperly known as the “oblique firehose” instability, is the most efficient mechanism of isotropisation limiting the increase of particle velocity anisotropy and thus confirming the observations. These instabilities can explain the origin of interplanetary magnetic field fluctuations, which are expected to enhance along the temperature anisotropy thresholds. ispartof: pages:280-283 ispartof: AIP Conference Proceedings vol:1216 issue:1 pages:280-283 ispartof: International Solar Wind Conference location:Saint-Malo, France date:21 Jun - 26 Jun 2009 status: published

Suprathermal electron heat flux dropouts (HFD) serve as a sensitive test of the magnetic topology of the inner heliosphere. Since the heat flux electron strahl always flows away from the Sun, a heat flux dropout should indicate either that the magnetic field line is completely disconnected from the Sun or that the heat flux strahl is scattered into other pitch angles. We present observations of two suprathermal electron heat flux dropout events observed by the Advanced Composition Explorer (ACE) spacecraft which occur simultaneously with impulsive energetic ion events. Since suprathermal electrons encompass the same velocity range as ions with energies of a few MeV/nucleon, the similarities and differences between them as observed at 1 AU probes the sources and transport of these two species. We compare the two events to show the difference between the signatures of a simple disconnection and a more complicated reconnection scenario. Comparing suprathermal electron modulations with energetic ion modulations is a powerful technique for determining the magnetic topology between particle injection at the Sun and observation at 1 AU.

Observations of energetic ions and electrons from STEREO and ACE have been used to investigate the longitudinal extent of particle emissions from 3He ‐rich solar energetic particle (SEP) events. In the event of 3–4 Nov 2008, ions and electrons were detected 20° ahead and behind the nominal connection from the source region to 1 AU, and electrons were also detected 60° ahead. The results are consistent with those of earlier studies that correlated data from near‐Earth spacecraft with Helios data or with observations of source regions on the Sun.

Since early 2007, significant particle enhancements due to corotating interaction regions (CIRs) have regularly appeared at 1 AU without any appreciable contamination from solar energetic particles (SEPs). In 2009 the prevalence of CIRs diminished as the maximum speed of the high speed solar wind streams in the ecliptic decreased along with the tilt of the heliospheric current sheet. Observations of CIR time profiles at different longitudes from STEREO show delays between the Behind and Ahead spacecraft that are often roughly as expected from the corotation time lag, although small differences in the spacecraft latitudes introduce significant scatter in the time delays. In some cases different features seen at Ahead and Behind suggest that transient disturbances in the solar wind may alter connection to or transport from the shock, or that temporal changes occur in the CIR shock itself. H and He data from STEREO/LET at 1.8–6 MeV/nucleon show that 1) the CIR spectral index at these energies is ~−4, independent of intensity but with considerable variability, 2) the He/H ratio is ~0.03 for larger CIRs but varies systematically with energy and event intensity, and 3) although the correlation between the CIR MeV particle increases and solar wind speed is generally good, many times a high-speed stream is not associated with MeV particles, while at other times a recurring series of CIR particle increases appears only at higher energies and may be associated with current sheet crossings and low speed solar wind.

Whistler waves are present in solar wind plasma. These waves possess characteristic turbulent fluctuations that are characterized typically by the frequency and length scales that are respectively bigger than ion gyro frequency and smaller than ion gyro radius. The electron inertial length is an intrinsic length scale in whistler wave turbulence that distinguishably divides the high frequency solar wind turbulent spectra into scales smaller and bigger than the electron inertial length. We present nonlinear three dimensional, time dependent, fluid simulations of whistler wave turbulence to investigate their role in solar wind plasma. Our simulations find that the dispersive whistler modes evolve entirely differently in the two regimes. While the dispersive whistler wave effects are stronger in the large scale regime, they do not influence the spectral cascades which are describable by a Kolmogorov-like $k^{-7/3}$ spectrum. By contrast, the small scale turbulent fluctuations exhibit a Navier-Stokes like evolution where characteristic turbulent eddies exhibit a typical $k^{-5/3}$ hydrodynamic turbulent spectrum. By virtue of equipartition between the wave velocity and magnetic fields, we quantify the role of whistler waves in the solar wind plasma fluctuations., Comment: To appear in the Proceedings of Solar Wind 12

We have surveyed the spectral and compositional properties of suprathermal (∼40–320 keV nucleon−1) heavy ions during quiet times from 1995 January 1 to 2008 December 31 using instruments on board ACE and Wind spacecraft in the interplanetary (IP) medium near 1 AU. We find that the composition of the quiet‐time suprathermal heavy ion population (3He and C‐Fe) depends on the level of solar activity: the ions exhibit SEP‐like composition signatures during solar maximum and CIR or solar‐wind like composition during solar minimum. In addition, we find that during quietest times in the IP medium, all ion species exhibit suprathermal tails with power‐law spectral indices ranging from 1.27 to 2.29, i.e., significantly different from recent observations and theoretical predictions of a unique 1.5 index. We discuss the implications of these new observations for the origin of the suprathermal ion population near 1 AU.

A familiar feature of turbulence in a low collisionality turbulence is an increase in the electric field spectrum, relative to the magnetic field spectrum, at wavenumbers near the reciprocal of the ion inertial scale. This effect is commonly observed in the solar wind. Here we examine this feature numerically, using a variety of simulations, including compressible Hall MHD, incompressible Hall MHD, and one‐, two‐, and three‐dimensional cases. A feature of this type is even found in a statistical Hall MHD model with no dissipation. This leads to the conclusion that the only requirement for obtaining this dispersive effect is the Hall term in the generalized Ohm’s law. Therefore this observation does not distinguish between whistler and kinetic Alfven waves, between waves and turbulence, nor even between fluid and kinetic plasma models.

In addition to the high temperatures, SOHO/UVCS observations have shown that heavy ions in the polar corona are heated more than protons, and that heavy ion heating is more than mass proportional; further, the perpendicular temperatures are much larger than parallel temperatures. Here, we propose that the more than mass proportional heating of heavy ions in coronal holes is due to the ion reflection at supercritical quasi‐perpendicular shocks and to the ion acceleration by the motional electric field in the shock frame. We also discuss the formation of collisionless shock in the polar corona.

The heliospheric current sheet (HCS) is a permanent solar wind feature, with well predicted Earth passages, but it can be structured and its main orientation can be highly distorted. We report new observations from 2 spacecraft in the solar wind (supported by observations from 3 spacecraft in the nightside magnetosheath), showing an evolution across the Sun‐Earth line of large field reversals adjacent to the HCS. Contrary to a previously reported multi‐spacecraft event, this case shows that the field inversion structure cannot be assumed to be well preserved and close to planar on the scale of the magnetospheric cross‐section. However, both cases indicate the presence of field reversals in an away sector that is connected to the southern solar magnetic hemisphere but lies unexpectedly above a toward sector. Following the interpretation of the reversals as transient outflowing loops, associated initial flow deviations can be envisaged to account for the HCS deformations.

The elemental and ionic composition of the slow (∼400 km/s) solar wind (SW) differs from that of the fast (>600 km/s) SW streams. In particular, the first ionization potential (FIP) effect and the O7/O6 ratios are higher in the slow SW than in the fast SW. While this fundamental difference between fast and slow SW has long been appreciated, there has been no reason to expect or effort to search for systematic variations within given fast or slow SW streams. If present, however, such systematic variations could be diagnostic of the solar processes at the sources of the SW. We suggest two reasons to expect compositional differences between leading and trailing edges of slow SW streams. After selecting two long‐lived fast SW streams from 2005 and 2006 and determining their slow‐fast (SF) and fast‐slow (FS) stream interfaces (SIs), ACE SWICS (version 3) compositional data were obtained for the 1‐day periods of the preceding SF and following FS slow SW streams. The statistics were limited, but no compositional...

Spectral analysis of the high‐quality dual‐frequency data obtained with the radio sounding experiment MaRS on the ESA spacecraft Mars Express has revealed a quasi‐periodic component (QPC) at heliocentric distances from 4 to 10 solar radii. The QPC typically appears as a broad maximum in the temporal frequency fluctuation spectrum centered at a frequency in the range 3.7 mHz

The May and November 2007 ICMEs were observed by both STEREO spacecraft as well as the ACE spacecraft. Simultaneous magnetic cloud fits using a multispacecraft model indicate that the axis of the May 2007 flux rope was perpendicular to the plane of the sky, while axis of the November 2007 event was in the ecliptic plane. A new spatial mapping tool has been developed to understand in‐situ composition in terms of the overall magnetic structure of the ICME. The charges states are low for both of these events; though for the May 2007 event there were enhancements beyond the magnetic cloud, but within the ICME. The tools that have been developed in this effort have been proven useful for gaining insight into ICME structures.

The present study concerns a comparison between the slow solar wind plasma parameters obtained in the extended corona by the UV spectroscopic data from the Ultraviolet Coronagraph Spectrometer (UVCS) onboard SOHO during the minimum of solar activity (1996) and the results of a time‐dependent 2.5 D three‐fluid MHD model of coronal streamer belt. The aim of the study is to improve the knowledge of the slow solar wind acceleration mechanism and the origin of its variability.

Inner‐source pickup ions have been investigated by several workers who all assumed an initial velocity distribution function which is dominated by high velocities in the solar wind velocity frame. This non‐thermal velocity distribution is supposed to be due to the Lorentz force which acts on the freshly ionized particles. However, the location where inner‐source pickup ions are ionized lies close to the Sun (probably between 5 and 25 r⊙). The magnetic field and solar wind velocity are near radial there and the Lorentz force acting on freshly created ions is small. Particles sputtered or ejected with small relative velocities (E

We summarize the properties of the ∼320 interplanetary coronal mass ejections (ICMEs) identified in the near‐Earth solar wind during solar cycle 23 up to mid‐2009 and note a recent increase in the ICME rate that may be associated with the new solar cycle. We also discuss how recent revisions in the ACE/SWICS solar wind composition data require the ICME identification methods described in [1] based on these data to be modified.

The angle between the normal to an interplanetary shock front and the upstream magnetic field (θBn), though often considered to be a property “of the shock,” also depends on the direction of the interplanetary magnetic field through which the shock is traveling. We examine the solar wind context of 105 near‐Earth quasi‐perpendicular fast forward shocks in 1996–2005 identified by θBn⩾80° and/or by evidence of shock drift particle acceleration. These shocks (87% driven by interplanetary coronal mass ejections; ICMEs) were propagating through a variety of solar wind structures including unrelated ICMEs, slow solar wind, high‐speed streams, the heliospheric plasma sheet, and shock sheaths. Magnetic field orientations upstream of the shocks were more likely to be highly inclined to the radial direction than in the solar wind as a whole. We also compare the Fe/O ratio in solar wind and energetic particles (∼1 MeV/n) in the vicinity of these shocks. Average values are similar (∼0.14), but occasionally both are e...

Coronal radio sounding observations were carried out with the radio science experiment MaRS on the ESA spacecraft Mars Express during the period from 25 August to 22 October 2004. Differential frequency and log‐amplitude fluctuations of the dual‐frequency signals were recorded during a period of low solar activity. The data are applicable to low heliographic latitudes, i.e. to slow solar wind. The mean frequency fluctuation and power law index of the frequency fluctuation temporal spectra are determined as a function of heliocentric distance. The radial dependence of the frequency fluctuation spectral index α reflects the previously documented flattening of the scintillation power spectra in the solar wind acceleration region. Temporal spectra of S‐band and X‐band normalized log‐amplitude fluctuations were investigated over the range of fluctuation frequencies 0.01 Hz

Cavitons have been recently discovered in the Earth’s foreshock. Foreshock cavitons have first been predicted by global hybrid simulations and later structures with similar properties were discovered in observational data from the Cluster mission. Cavitons are observed as simultaneous depressions of the magnitude of the magnetic field and plasma density (δB/B, δn/n⩾0.2) that commonly last ⩽30 s and are surrounded by a rim of enhanced values of B and n. They are always immersed in a sea of compressive low frequency waves. Numerical simulations results suggest that the cavitons are produced by the interaction of foreshock sinusoidal plasma waves with perpendicularly propagating compressive fast mode waves. Here we present a study of the waves that were observed in the immediate neighborhood or inside two foreshock cavitons detected by the Cluster I spacecraft. We analyze the frequency, polarization, direction of propagation and compressibility of the waves.

Recent studies have compared properties of the magnetic field in simulations of Hall MHD turbulence with spacecraft data, focusing on methods used to identify classical discontinuities and intermittency statistics. Comparison of ACE solar wind data and simulations of 2D and 3D turbulence shows good agreement in waiting‐time analysis of magnetic discontinuities, and in the related distribution of magnetic field increments. This supports the idea that the magnetic structures in the solar wind may emerge fast and locally from nonlinear dynamics that can be understood in the framework of nonlinear MHD theory. The analysis suggests that small scale current sheets form spontaneously and rapidly enough that some of the observed solar wind discontinuities may be locally generated, representing boundaries between interacting flux tubes.

The scaling laws of mixed third‐order structure functions for isotropic, homogeneous, and incompressible magnetohydrodynamic (MHD) turbulence have been recently applied in solar wind studies, even though there is recognition that isotropy is not well satisfied. Other studies have taken account of the anisotropy induced by a constant mean magnetic field. However, large‐scale shear can also cause departures from isotropy. Here we examine shear effects in the simplest case, and derive the third‐order laws for MHD turbulence with constant shear, where homogeneity is still assumed. This generalized scaling law has been checked by data from direct numerical simulations (DNS) of two‐dimensional (2D) MHD and is found to hold across the inertial range. These results suggest that third‐order structure function analysis and interpretation in the solar wind should be undertaken with some caution, since, when present, shear can change the meaning of the third‐order relations.

The edge of a solar active region (AR) is considered as a possible source region of the slow solar wind. Winebarger et al. (2001) observed outflows from an AR with velocities between 5 and 20 km/s. Recently, Sakao et al. (2007) reported the outflow of X‐ray‐emitting plasma from the edge of an AR. This outflow was inferred from the observation of outward traveling intensity enhancements. However, in Robbrecht et al. (2001), propagation of slow magnetoacoustic waves along the strand was considered as the possible cause for the longitudinal extension of the strand. Whether this phenomenon relates to a slow‐mode wave or the outflow of plasma or a heating process of different parts of the strand is still an open question. Here we try to identify the nature of such a traveling event through studying the longitudinal motions of certain intensity level fronts in the strand. We find that the intensity front is oscillating like a sinusoidal signal along the strand with a period of 11 minutes. This result suggests that the oscillation might be partly related with the 5‐minute p‐mode oscillation in the photosphere. Moreover, we find that such oscillation of intensity‐level fronts can be described by a model in which the strand has periodic extension. Yet, the relation between the extending strand and slow solar wind needs to be further studied.

Quasi‐thermal noise spectroscopy has been intensively used to measure in situ the solar wind electron density and core temperature in space with various spacecraft. This method allowed study of the large‐scale properties of the solar wind. This paper reminds theoretical tools to compute the quasi‐thermal noise spectroscopy using a superposition of two Maxwellian distributions to describe the electrons, and the ones using a kappa distribution, which has been recently extended to non integer values of kappa. This paper presents an example of Ulysses data fitted with quasi‐thermal noise using a kappa and the sum of two Maxwellians. We make a preliminary comparison of the two results.

Observed properties of the strahl using high resolution 3D electron velocity distribution data obtained from the Cluster/PEACE experiment are used to investigate its linear stability. An automated method to isolate the strahl is used to allow its moments to be computed independent of the solar wind core+halo. Results show that the strahl can have a high temperature anisotropy (T(perpindicular)/T(parallell) approximately > 2). This anisotropy is shown to be an important free energy source for the excitation of high frequency whistler waves. The analysis suggests that the resultant whistler waves are strong enough to regulate the electron velocity distributions in the solar wind through pitch-angle scattering

The different models of the infinitely thin global heliospheric current sheet with small (

This paper summarizes some of the recent rebirth of interest in interplanetary discontinuities. Vasquez et al. have developed a new method of searching for discontinuities that allows the study of structures with small angles of rotation. Those discontinuities are consistent with the in situ generation of discontinuities by Alfvenic turbulence. Borovsky has proposed that discontinuities with large rotation angles are the boundaries of flux tubes originating at the Sun. We conclude that both the Sun and turbulence are important sources of interplanetary discontinuities. We also argue that, at least in the slow solar wind, Tsurutani’s in‐situ generation by phase‐steepened Alfven waves may be a manifestation of exhaust fan reconnection. We furthermore suggest that such reconnection may be responsible for the Walen ratio ([4πρ]1/2|Δv|/|ΔB|) across rotational discontinuities being less than the theoretically predicted value of unity. Whether or not the wind consists of discrete flux tubes rather than being sim...

We examine the effects of including effects of both protons and electrons on the heating of the fast solar wind through two different approaches. In the first approach, we incorporate the electron temperature in an MHD turbulence transport model for the solar wind. In the second approach, we adopt more empirically based methods by analyzing the measured proton and electron temperatures to calculate the heat deposition rates. Overall, we conclude that incorporating separate proton and electron temperatures and heat conduction effects provides an improved and more complete model of the heating of the solar wind.

We present fully self consistent 3D simulations of compressible Hall MHD plasma that describe spectral features relevant to the solar wind plasma. We find that a $k^{-7/3}$ spectrum sets in for the fluctuations that are smaller than ion gyro radius. We further investigate scale dependent anisotropy led by nonlinear processes relevant to the solar wind plasma. Our work is important particularly in understanding the role of wave and nonlinear cascades in the evolution of the solar wind, structure formation at the largest scales., Comment: To appear in the Proceedings of Solar Wind 12

The first Indian lunar mission Chandrayaan-1 was launched on 22 October 2008. The Sub-keV Atom Reflecting Analyzer (SARA) instrument onboard Chandrayaan-1 consists of an energetic neutral atom (ENA) imaging mass analyzer called CENA (Chandrayaan-1 Energetic Neutrals Analyzer), and an ion-mass analyzer called SWIM (Solar wind Monitor). CENA performed the first ever experiment to study the solar wind-planetary surface interaction via detection of sputtered neutral atoms and neutralized backscattered solar wind protons in the energy range ~0.01-3.0 keV. SWIM measures solar wind ions, magnetosheath and magnetotail ions, as well as ions scattered from lunar surface in the ~0.01-15 keV energy range. The neutral atom sensor uses conversion of the incoming neutrals to positive ions, which are then analyzed via surface interaction technique. The ion mass analyzer is based on similar principle. This paper presents the SARA instrument and the first results obtained by the SWIM and CENA sensors. SARA observations suggest that about 20% of the incident solar wind protons are backscattered as neutral hydrogen and ~1% as protons from the lunar surface. These findings have important implications for other airless bodies in the solar system., Comment: 4 pages, 6 figures

The stream particles are nanometer‐size dust particles ejected from the jovian and the saturnian systems with velocities greater than 100 kms−1. Due to their small size, stream particles are more sensitive to the electromagnetic force than to gravity. It has been shown by the simulations that the stream—particle dynamics in interplanetary space should be dominated by the interplanetary magnetic field (IMF) [15]. Based on the measurements by the dust detector on board the Cassini spacecraft, we found that the detection patterns of the stream particles are well correlated with the IMF structures. As the spacecraft crosses the compression regions of the Co—rotation Interaction Regions (CIRs), not only the directionality of the impacts changes with the field direction, but also the impact signal and rate vary with an increase of field strength. By understanding the interaction of stream particles and the solar wind, the data provide important insight to the formation environments of the stream particles and i...

Collisionless shocks are an important component of the heliosphere and are ubiquituos in astrophysical environments. Across them the solar wind is heated, deviated and compressed. Collisionless shocks are able to accelerate a fraction of particles to very high energies. In this work we discuss the earth’s bow shock region and relate processes occuring at this shock and foreshock to phenomena associated to shocks propagating in the solar wind. Our understanding of the bow shock microphysics can serve as a tool to understand stream interaction and transient shocks structure, their evolution, and the kinetic phenomena that take place in regions associated with these shocks.

Today the field of planetary X‐rays is very dynamic and in the forefront of new research. Apart from the Sun, the known X‐ray emitters now include planets (Venus, Earth, Mars, Jupiter, and Saturn), planetary satellites (Moon, Io, Europa, and Ganymede), all active comets, the Io plasma torus, the rings of Saturn, the coronae (exospheres) of Earth, Mars and Venus, and the heliosphere. Scattering of solar X‐rays mainly produces the non‐auroral X‐ray emissions from Jupiter, Saturn, and Earth, those from the disk of Mars and Venus, from the surface of the Moon, and from the rings of Saturn. The X‐ray emission from comets, the heliosphere, the geocorona, and the Martian and Venusian exospheres are all largely produced in charge exchange collision between highly ionized minor heavy ions in the solar wind and gaseous neutral species in the bodies’ atmosphere—a process known as solar wind charge exchange (SWCX). Thus, both, the solar radiation and out‐flowing plasma from the Sun (solar wind) power the production of X‐ray emission from solar system bodies. A brief overview on X‐rays from the solar system bodies and their connection with solar X‐rays and solar wind is presented in this paper.Today the field of planetary X‐rays is very dynamic and in the forefront of new research. Apart from the Sun, the known X‐ray emitters now include planets (Venus, Earth, Mars, Jupiter, and Saturn), planetary satellites (Moon, Io, Europa, and Ganymede), all active comets, the Io plasma torus, the rings of Saturn, the coronae (exospheres) of Earth, Mars and Venus, and the heliosphere. Scattering of solar X‐rays mainly produces the non‐auroral X‐ray emissions from Jupiter, Saturn, and Earth, those from the disk of Mars and Venus, from the surface of the Moon, and from the rings of Saturn. The X‐ray emission from comets, the heliosphere, the geocorona, and the Martian and Venusian exospheres are all largely produced in charge exchange collision between highly ionized minor heavy ions in the solar wind and gaseous neutral species in the bodies’ atmosphere—a process known as solar wind charge exchange (SWCX). Thus, both, the solar radiation and out‐flowing plasma from the Sun (solar wind) power the production o...

We present generalized structure function (GSF) analysis of magnetic and velocity field fluctuations measured in situ in the solar wind at ∼ 1 AU with the ACE spacecraft. We decompose the fluctuations into directions parallel and perpendicular to the mean local background magnetic field. GSF plots based on these quantities are shown to provide a clear indicator of the spectral break between the inertial range and “1/f“ range of scaling. In GSF plots, the projected velocity and magnetic field fluctuations track each other closely in the inertial range in both fast and slow solar wind and at solar maximum and minimum. At longer timescales the “1/f” range is easily identified, because the magnetic field fluctuations display a flattening of the GSFs (exponents become zero) consistent with a ∼1/f PSD. The velocity fluctuations on the other hand have GSFs which steepen, consistent with a PSD of ∼1/fα where α as determined by GSF varies with solar wind speed and solar cycle but is closer to two. The extent of th...

STEREO/PLASTIC provides detailed information on the three‐dimensional velocity distributions of solar wind iron ions with a time resolution of 5 minutes. In general the distributions at 1 AU contain complicated structures showing persistence over several records, i.e., over intervals of up to 30 minutes, but no clear correlation of the properties of these distributions with the direction of the ambient magnetic field is evident. We have performed a statistical analysis using nearly 9000 observations. Iron ions follow the same trends as protons, alpha particles, and electrons: The ratio T⊥/T‖ seems to be limited by the ion cyclotron instability, whereas T‖/T⊥ is bounded by the firehose instability.