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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.

We present hybrid simulations of the energy cascade among fast waves in the vicinity of the proton inertial scale. The plasma beta is set to low values typical of the solar corona. The cascade proceeds in the wavenumber space mostly in the direction across the mean magnetic field. The highly oblique fast waves can be efficiently dissipated on the protons by several mechanisms. The resulting proton heating is preferentially perpendicular to the magnetic field. If the wave intensity is constrained by the observed density spectra in the corona, the heating is fast enough to generate the solar wind.

Observations of electron distribution functions with power law at high energies and with elongated tails are common in space plasmas. Since the relativistic electrons, emanating from the solar corona measured at 1 AU are seen generally delayed vs the less energetic type‐III beams, the correlation of their temporal and spatial emergence with other observed processes, the location of the energization sites, and the relation of the observed energetic distributions to acceleration mechanisms are of major importance in solar and heliospheric research. It is conjectured that the delayed electrons are energized along the stretched post‐CME coronal field lines, when the tail of an anisotropic seed population, which is injected in conjunction to the observed radioheliograph bursts interacts with the self—excited whistler waves. The relativistic electron fluxes are not affected directly neither by flares nor by CMEs, but require post CME coronal bursts. The observed particle distributions are determined by the inte...

The Solar Mass Ejection Imager (SMEI) observes the increased brightness from the density enhancements behind interplanetary shocks that are also observed in situ near the Earth. We use the University of California, San Diego (UCSD) time‐dependent three‐dimensional (3D) reconstruction technique to map the extents of these density enhancements. Here, we examine shock‐density enhancements associated with several well‐known interplanetary coronal mass ejections (ICMEs) including those on 30 May 2003 and on 21 January 2005. We compare these densities with reconstructed velocities from the Solar‐Terrestrial Environment Laboratory (STELab) interplanetary scintillation (IPS) observations for the 30 May 2003 ICME, and show the shock is present at the front edge of the reconstructed high speed solar wind. The SMEI analyses certify that the brightness enhancements observed behind shocks identified and measured in situ near Earth are a direct response to the plasma density enhancements that follow the shocked plasma.

Since the work of Burlaga in 1991, various multifractal analyses have been performed to better characterize the intermittency of the fluctuations in the turbulent solar wind. These analyses were based either on the classical structure functions or on the partition function. Recently, two new multifractal analyses have been proposed to better characterize intermittent fluctuations: on one hand, Chang & Wu (2008) proposed a rank‐ordered multifractal analysis based on range‐limited structure functions instead of the classical ones. On the other hand, Macek & Szczepaniak (2008) have developed a generalized two‐scale weighted Cantor set using the partition function technique. Both methods are presented with emphasize on their advantages over the previous multifractal analyses. As an illustration, these new multifractal analyses are applied to a set of magnetic field data measured by Ulysses.

Energetic particle measurements made by Voyager 2 during its crossing of the heliospheric termination shock had distinctive features of a locally shock‐accelerated component in the energy range between 1 and 3.5 MeV. Intensities of energetic ions rose exponentially upstream of the shock and were accompanied by a deceleration of the bulk plasma flow. Our analysis of the Voyager 2 shock precursor shows that the termination shock was in a rare state known as a cosmic‐ray‐mediated shock, where plasma slowdown in the precursor is produced by a positive energetic particle radial pressure gradient. The amount of deceleration in the last 40 days of the precursor was about 13% (by dynamic pressure), which is consistent with earlier model predictions. However, the precursor was narrower than predicted by these models, which assumed dominance of a high‐energy anomalous cosmic‐ray component.

A magnetohydrodynamic model is used to simulate the global steady‐state structure of the solar wind in the region from 0.3 to 100 AU. The model is based on a numerical solution of the combined set of solar wind equations and small‐scale turbulence transport equations and accounts for apparent heating of the solar wind by a turbulence cascade and interstellar pickup protons. We use the model to study the distribution of plasma and magnetic field parameters and the effects of turbulence dissipation and pickup‐proton‐associated‐heating on the variation of plasma temperature in the outer heliosphere. To illuminate the roles of the turbulent cascade and the pickup protons in heating the solar wind with heliocentric distance, we compare the model results with and without turbulence. The variations of plasma temperature in the outer heliosphere are compared with Voyager 2 observations.

The trajectories of interplanetary CMEs (ICMEs) are modified by their interactions with solar wind streams. These interactions can result in non‐radial deflections of ICME trajectories and changes to their rates of azimuthal expansion. The Solar Mass Ejection Imager (SMEI), launched earlier in 2003 January, has provided heliospheric images of several hundred ICMEs during the declining portion of solar cycle 23. We selected three SMEI ICMEs, each traversing a range of solar elongation angles e>20°, and measured the time changes of their leading‐edge profiles plotted against position angle, PA. The parabolic fits to those profiles yielded the propagation directions of the ICMEs as well as their leading‐edge curvatures and time profiles. The selected ICMEs were associated with LASCO CMEs, so we tracked the PA variations in their propagation over 1 to 3‐day periods. We found good fits for two of the ICMEs, but one yielded generally poor fits.

Ulysses in‐situ measurements have given a new picture on the large‐scale properties of the fast solar wind as well as on the microscopic scales. From the large sample of data obtained during Ulysses fast latitudinal scans in 1994 and 2007 occuring both near solar minima, we will present the spectrum of the electron density fluctuations. The preliminary analysis suggests that a single Kolmogorov‐type power law spectrum does not fit the data at high latitudes in contrast to the ecliptic observations: the spectrum appears to flatten in the high‐frequency range of the inertial domain. We will discuss and compare these results and compute the probability distribution functions (for a timescale spanning from a solar rotation to two minutes), based on the use of Wavelet transforms on Ulysses electron density from the URAP experiment. We show as well an evidence of intermittence nature of the electron density fluctuations.

Mirror mode structures occur in the solar wind either as an isolated magnetic field depression or as trains of magnetic holes (or peaks). Some trains have long durations and have been named mirror mode storms [1]. In this work we investigate mirror mode structures at 1 AU using STEREO A and B high resolution data. Magnetic field data were scanned to search for magnetic holes and peaks in a relatively steady ambient solar wind. We found several examples of mirror mode structures present in the ambient solar wind and also associated with SIRs. In order to study mirror mode origin, we present a case study with mirror mode structures present in the leading edge of a SIR during almost 8 hours corresponding to mirror mode storms. We analyze mirror mode shape and duration as well as plasma and magnetic field conditions that occur in the region surrounding mirror mode storms.

In the last two decades we have assisted at a growing interest in the study of complexity and complex dynamics in space plasmas. This is particularly true in the case of interplanetary and magnetospheric space plasmas which display turbulence, self organization and/or self‐organized critical dynamics. Here, I present some preliminary results on the evolution of order in the radial evolution of solar wind magnetic field. In detail, using the criterion contained in the S‐Theorem by Klimontovich [1], I compute the relative degree of order for the magnetic field intensity fluctuations at different radial distances as observed by interplanetary mission. The preliminary results seems to point toward and increase of order with the radial distance, suggesting the occurrence of structuring (formation of structures) in the course of the evolution.

We utilize STEREO quadrature observations to study two CMEs that both originated from high‐latitude source regions on 2 November 2008. The first CME was associated with a huge polar crown filament eruption and propagated initially clearly northward from the equator. However, the CME was quickly deflected towards the equator while propagating further out. On the other hand, the second CME, originating from an active region, did not deflect from its original northward trajectory. Based on the observations we discuss the role of the size of the erupting structure and the magnetic topology of the surrounding environment in deflecting CMEs and suggest that both a breakout initiation scenario as well as a tether‐cutting initiation scenario can explain the observed deflective dynamics of the filament eruption.

The electron velocity distribution function in the solar wind has often been described as the superposition of an isotropic core, a moderately energetic and slightly anisotropic halo and a high energy field aligned beam. The relative weight of these components depends on the characteristics of the solar wind streams (fast and slow) and on the heliocentric distance. We present kinetic simulations using the model given in [1] to study the effects of electron‐electron and electron‐proton collisions on the electron velocity distribution function in the interplanetary space beyond ∼0.3 AU from the Sun. We show that collisions do naturally generate a two population electron velocity distribution with an isotropic and cold “core” and a hot and collimated “halo.” The temperature profiles and temperature anisotropies observed in our simulations are consistent with spacecraft observations [2, 3, 4]. Since waves are not included in our simulations we suggest that Coulomb collisions are an essential ingredient which should be included in any model of the evolution of the electron velocity distribution function in interplanetary space.

We investigate the characteristics of interplanetary (IP) shock waves associated with a stream interaction region (SIR) observed during April 21–24, 2007 by STEREO‐A/B, WIND and ACE spacecraft. During the years 2007–2008 STEREO‐A observed 43 and STEREO‐B crossed 41 shocks. As IP shocks propagate, they encounter solar wind with different characteristics (density, speed) and different orientations of the ambient magnetic field. Hence, it is expected that shock profiles will vary strongly through the space. We use magnetic field and plasma data to study shock structure, strength and orientation. In this example of a SIR we find that the characteristics of the shocks change dramatically from one region to another, the shock structure can be quasi‐perpendicular as observed in one spacecraft and quasi‐parallel when crossed at other point. Low frequency waves with different characteristics appear upstream and downstream of forward and reverse shocks. In this example the region upstream of the forward quasi‐perpe...

In this paper we investigate magnetohydrodynamic (MHD) simple divergence waves in MHD, for models in which ∇⋅B≠0. These models are related to the eight wave Riemann solvers in numerical MHD, in which the eighth wave is the divergence wave associated with ∇⋅B≠0. For simple wave solutions, all physical variables (the gas density, pressure, fluid velocity, entropy, and magnetic field induction in the MHD case) depend on a single phase function φ. We consider the form of the MHD equations used by both Powell et al. [1] and Janhunen [2]. It is shown that the Janhunen version of the equations possesses fully nonlinear, exact simple wave solutions for the divergence wave, but no physically meaningful simple divergence wave solution exists for the Powell et al. system. We suggest that the 1D simple, divergence wave solution for the Janhunen system, may be useful for the testing and validation of numerical MHD codes.

In this work the properties of transport of ions accelerated at the solar wind termination shock are studied. The approach used to investigate the propagation of those particles is probabilistic and is based on the analysis of particle time profiles upstream of the shock front. The data sets come from the Voyager 2 spacecraft and involve 0.22–3.5 MeV ions. At variance with other observations of ion profiles, at such heliocentric distances (≃84 AU) the transport of ions is found to be superdiffusive, their mean square deviation growing as 〈Δx2〉∝tα, with α>1. As already found for electrons, these findings show that also for energetic ions the transport can be intermediate between normal and scatter‐free, an evidence that has implications on the formulation of particle acceleration mechanisms.

Solar Energetic Particle (SEP) measurements from the Ulysses spacecraft have shown that the latitudinal separation between the parent solar flare and the nominal footpoint of the detecting spacecraft is an important parameter in ordering characteristics of the observed time‐intensity profiles during SEP events. In this study, we consider data from the GOES and Wind spacecraft over one solar cycle, to address the question of whether the same trend can be observed from in‐ecliptic SEP measurements at 1 AU. Because of the inclination of the ecliptic plane with respect to the heliographic equatorial plane, the latitudinal separation between the location of the parent flare associated to an SEP event and the footpoint of a near‐Earth detecting spacecraft can vary in latitude between 0 and about 40 degrees. By analyzing a sample of 477 well connected solar events (with source region in W20–W80) and characterized by a magnitude of the associated flare >C8.0, we derive a probability P of observing an SEP event as...

On June 2, 2003, SOHO/LASCO coronagraph observed two CMEs at the West limb of the Sun, at 00.30 and 08:54 UT, respectively, which appeared to originate from the same source region. Both CMEs show the typical three‐part structure. These events have been also observed by SOHO/UVCS, allowing us to infer their physical parameters. We also looked for interplanetary signatures of the CMEs in ACE ‘in situ’ observations but we did not find evidence of the ejected flux rope; however, the solar wind appeared significantly distorted, probably as a consequence of the influence of both CMEs on their surrounding interplanetary plasma.

Magnetic clouds have been defined as special regions in the solar wind with higher magnetic field magnitude, lower proton temperature, and large rotation of the magnetic field vector. In some cases, the rotation exceeds 180° and it is interpreted as a signature that a magnetic cloud/flux rope is curved. It corresponds to common understanding that magnetic clouds are large interplanetary flux ropes, which have loop‐like shapes in the heliosphere. In such cases, magnetic clouds are fitted by approximate linear force‐free toroidal solutions (derived for large aspect ratios). Here an exact constant‐alpha force‐free toroidal solution is compared with approximate ones and it is found a reasonable agreement even for low aspect ratios.

This paper describes recent results from Voyager 2 in the heliosheath (HSh). The speed has been constant across the HSh. The density and temperature have decreased, probably due both to a decrease in solar output and deflection of plasma toward the heliotail. Fluctuations in the speed are smaller than in planetary magnetosheaths, probably because of the large size of the HSh reduces the affect of boundary motions. Density and temperatures variations are similar to those in magnetosheaths, suggesting small scale shock oscillations are the similar at bow shocks and the termination shock. Flows are very different at Voyager 1 and Voyager 2; the Voyager 2 data differ from model predictions.

Helios, Ulysses, and Wind spacecraft have observed the velocity distribution functions (VDFs) of solar wind particles deviating significantly from Maxwellians. We review recent models using different approximations and mechanisms that determine various observed characteristics of the VDFs for the electrons, protons and minor ions. A new generation mechanism is proposed for super‐Alfvenic proton beams and tails that are often observed in the fast solar wind. The mechanism is based on the proton trapping and acceleration by kinetic Alfven waves (KAWs), which carry a field‐aligned potential well propagating with super‐Alfven velocities.

In‐situ data measured by Ulysses—SWOOPS, SWICS and VHM instruments—are used for the study of magnetic field and solar wind plasma parameters for the year 2001, in an attempt of founding new ICMEs based on the combination of classical identification conditions, plasma dynamics signatures, and plasma composition signatures. Three new candidates are determined for the DOY 80.3–81.6, DOY 155.18–156.3, and DOY 161.2–162.8. We track back to the Sun these events and determine their possible solar sources.

The in situ correlation of the proton temperature with the bulk plasma velocity of the solar wind (SW) is a firm result confirmed by several spacecraft, while in interplanetary coronal mass ejections (ICMEs) the proton temperature is both cooler and not correlated with the velocity. For some specific heating mechanism, the internal energy equation alone could provide a temperature increasing with velocity, but the increase remains much weaker than observed in the SW. In fact, it is shown here that the observed correlation is generically obtained from a global energy conservation in thermally driven winds. It results from the conversion of thermal to kinetic energy close to the Sun. The absence (or even anti‐) correlation observed in situ between electron temperature and SW velocity, together with the correlation found for proton temperature, show that protons have a dominant role in the SW acceleration. In contrast, in ICMEs the plasma is contained by the magnetic field since ICMEs have both a closed configuration and a low plasma β. It implies no significant correlation between temperature and velocity, as observed. In conclusion, a different dominating term in the impulsion equation is the main origin of the different relation observed between the proton temperature and the bulk velocity in SW and ICMEs.

Around 350 solar energetic proton events with energies >20 MeV were detected by near‐Earth spacecraft during solar cycle 23. Focusing on the 280 events with ∼25 MeV intensity >2×10−4particles/(cm23 sr s MeV), we examine the early stages (∼first 12 hours) of these events including their intensity and composition and the properties of the related solar phenomena such as CMEs, flares and radio bursts. Although we divide the events into 5 representative groups based on particle profiles and relative abundances, we find no single, or set of variables that divides the particle events into clear cut “classes” for example associated with shock and flare acceleration. In particular, there is a continuum of event properties from the smallest, flare‐accelerated events, to the largest events dominated by shock acceleration. This suggests that both flare and shock acceleration can contribute in individual events.

In this review we summarize our current knowledge regarding the three‐dimensional structure of the quasi‐steady, large‐scale inner heliosphere. This understanding is based on the interpretation of a wide array of remote and in situ measurements, in conjunction with sophisticated numerical models. Observations by the Ulysses spacecraft, in particular, have provided an unprecedented set of measurements for more than 18 years, and observations by the STEREO spacecraft promise no less. Global MHD models of the solar corona and heliosphere have matured to the point that a wide range of measurements can now be reproduced with reasonable fidelity. In the absence of transient effects, this structure is dominated by corotating interaction regions which can be understood—to a large extent—from the consequence of solar rotation on a spatially‐variable velocity profile near the Sun, leading to parcels of plasma with different plasma and magnetic properties becoming radially aligned. This interaction is one of the pri...

We study the near‐relativistic (NR; >30 keV) electron event observed on 2000 February 18 by the Advanced Composition Explorer spacecraft. Highly collimated pitch‐angle distributions were observed during the first ∼2 h of the event. Roel of (2008) explained this event by assuming that the propagation of NR electrons is essentially “scatter‐free” in the inner heliosphere and that beyond 1 AU, particles are “back‐scattered” by magnetic field compressions and irregularities. We use Monte Carlo simulations to explore this approach. We fit observational sectored intensities to assure that the directional information contained in the data is used in full. We conclude that the event cannot be explained without assuming a back‐scatter region beyond 1 AU and that NR electrons propagated under weak‐scattering conditions in the inner heliosphere.

A turbulent energy cascade has been recently identified in high‐latitude solar wind data samples by using a Yaglom‐like relation. However, analogous scaling law, suitably modified to take into account compressible fluctuations, has been observed in a much more extended fraction of the same data set recorded by the Ulysses spacecraft. Thus, it seems that large scale density fluctuations, despite their low amplitude, play a major role in the basic scaling properties of turbulence. The compressive turbulent cascade, moreover, seems to be able to supply the energy needed to account for the local heating of the non‐adiabatic solar wind.

Magnetic reconnection in the solar wind commonly occurs in a quasi‐stationary mode. It produces extensive Petschek‐like exhausts of roughly Alfvenic jetting plasma typically bounded by back‐to‐back rotational discontinuities that bifurcate a reconnecting current sheet. It occurs most frequently at current sheets associated with relatively small (

The transition from fast to slow solar wind has not been studied to the same extent as the transition from slow to fast streams: the stream interface. The fast‐to‐slow transition has been reported as a smaller‐scale mirror image of a stream interface. It is characterized by changes in speed, density, temperature, and composition (Geiss et al. 1995; Zurbuchen et al. 1999; Burlaga, Mish, and Whang 1990; Siscoe and Intriligator 1993; Burton et al. 1999). In this study we use solar wind ion data from STEREO/PLASTIC to further investigate the fast‐to‐slow wind interface, with particular emphasis on possible correlations between changes in the proton specific entropy argument and the solar wind’s flow direction. The data were obtained during solar minimum near 1 AU and in the ecliptic plane. We find the fast‐to‐slow transition derived from the change in flow angle is neither as extended as the change in compositional signatures near 1 AU, nor as abrupt as that based on entropy at 4.5 to 5 AU.

Sunspot cycle 23 is turning out to be longer than cycle 20. Magnetic field measurements at Wilcox Solar Observatory indicate that solar polar field strength for cycle 23 is ∼50% lower than for previous three sunspot cycles; the flux of the open magnetic field lines at earth orbit is at its lowest level since in situ measurements began in 1963. During the recovery phase of cycle 23 the structure of the heliosphere is significantly different from that observed for cycles 21 and 22; heliospheric current sheet has not flattened yet. Not surprisingly, we find that galactic cosmic ray recovery at earth orbit has reached the highest level ever observed, since continuous monitoring began by global network of neutron monitors in 1951. We show that neutron monitor rate increases for 2006–2009 are linearly correlated with the monotonic decrease in magnetic intensity at earth orbit. We conclude that normal physical processes are operative in the heliosphere during this time period.

The kinetic properties of the solar wind are a result of complex interactions in the solar corona and interplanetary space. So far, observations of Velocity Distribution Functions (VDFs) of solar wind heavy ions have been solely 1D. They are known to exhibit non‐thermal features, but because they are 1D projections of the 3D velocity phase space it is difficult to interpret them properly. Based on 3D observations of protons and alpha particles from Helios, we have set up a model for heavy‐ion VDFs. In it, the magnetic field vector plays a crucial role by defining the symmetry axis of the VDFs. A thermal anisotropy T‖/T⊥ ≠1 and a beam drifting along the magnetic field vector at a relative speed of approximately the Alfven speed are included. The modeled VDFs are analysed using a virtual detector and then compared with data from the Solar Wind Ion Composition Spectrometer (SWICS) on the Advanced Composition Explorer (ACE). Our observations give evidence for the existence of heavy‐ion beams. The projection o...

The difference in the heliocentric distances at which the Voyager 1 and Voyager 2 spacecraft crossed the termination shock (TS) is likely due to a combination of the heliospheric asymmetry caused by the interstellar magnetic field (ISMF) and time‐dependent boundary conditions at the Sun. We analyze both effects numerically. It is shown that an increase in the ISMF makes the termination shock more asymmetric, but results in an increasingly large discrepancy between the calculated and observed distributions of the solar wind (SW) velocity in the inner heliosheath. We analyze possible effects of the solar cycle on the SW properties in the inner heliosheath. The possibility is explored of the SW velocity to have a rather small gradient as V2 penetrates deeper into the heliosheath. To analyze the effect of the solar cycle we also perform the calculations of the SW—interstellar medium interaction with the inner boundary conditions extracted from the Ulysses data obtained during its first and third pole‐to‐pole ...

we present a statistical theory of self‐organisation of shear flows, modeled by a nonlinear diffusion equation driven by a stochastic forcing. A non‐perturbative method based on a coherent structure is utilized for the prediction of the PDFs, showing strong intermittency with exponential tails. We confirm these results by numerical simulations. Furthermore, the results reveal a significant probability of supercritical states due to stochastic perturbation, which could have crucial implications in a variety of systems. To elucidate a crucial role of relative time scales of relaxation and disturbance in the determination of the PDFs, we present numerical simulation results obtained in a threshold model where the diffusion is given by discontinuous values. Our results highlight the importance of the statistical description of gradients, rather than their average value as has conventionally been done.

Coronal mass ejections (CMEs) often appear in coronagraph images as three‐part structures composed of a leading bright front, a dark cavity and a bright core, which are believed to be associated with the sheath of compressed solar wind, the erupting magnetic flux rope and the cool and dense prominence plasma, respectively. However, a convincing identification of this three‐part structure in the in‐situ solar wind is extremely rare. Therefore, there still remains an open question as to what kind of signatures these three CME parts will reveal in the in situ data ([5]). Our work presents a clear identification of prominence material from in situ observations of the solar wind magnetic field and plasma parameters. The Helios 2 solar probe detected a magnetic cloud at 0.5 AU on 30 March 1976. In this event, we found a region with lower proton temperature and higher proton number density than outside, which is consistent with key features of a prominence as cold and dense solar material. During the same time w...

The Kelvin-Helmholtz (KH) instability can operate in various situations in the solar wind, but at the boundaries of planetary obstacles, for example the Earth's magnetopause, it is most amenable to investigation. Reliable estimates of wave characteristics are essential for comparison with theoretical and numerical models and for understanding the non-linear development of KH waves and their role in the plasma entry into the magnetosphere. After discussing their typical conditions of appearance in KH unstable domains at the magnetopause, both theoretically and observationally, we outline recent results of multi-spacecraft analysis with Cluster giving accurate, albeit spatially limited, determination of surface wave characteristics. Those characteristics (wavelength and propagation direction), close to the terminator on the nightside, are likely to be prescribed by the 3-D geometry and the bending of field lines developed by the KH waves, rather than by the magnitude and the direction of the magnetosheath or background flow. An unprecedented number of satellites provides now the opportunity to extend the analysis of source regions of KH waves and their domains of development.

The energy balance at large scales in a coronal loop is studied, using an analytical model. We generalize a previous model by including a longitudinal inhomonegeity in the background density. The dynamics is regulated by the resonance between motions at the loop basis and eigenmodes, giving rise to energy storage within the loop, and by nonlinear effects that move this energy to smaller scales. We derive a scaling law for the input energy flux, the properties of eigenmodes and of their nonlinear coupling, and estimations for the nonlinear flux and for the velocity perturbation. For typical loop conditions, the resulting values are in accordance with the energy flux required for the quiet‐Sun corona and with measured nonthermal velocities.