Search

Magnetic clouds observed between 1995 and 2003 are fitted using force‐free cylindrical flux rope models. The cloud parameters yielded by a static model are compared with those obtained from a modified model that includes magnetic cloud expansion. The deviations of these fits from measurements are quantified and compared with parameters measured by Wind. The comparison reveals that the model with expansion provides better fits for larger expansion speeds and for magnetic clouds observed close to their axis. We conclude that expansion of magnetic clouds plays an important role in the MC evolution and should be accounted in space weather models.

Previous studies of solar wind proton temperature and speed have found a break in the curve between 400 and 550 km/s. Examining all the OMNI 2 data from 1965 to 2009, we create plots binned in both temperature and speed in order to identify where the majority of the points lie. Using yearly color plots to evaluate the curve shape we find most of the data is well represented by a single linear fit even though the slope varies significantly from year to year. A clear break in the temperature speed curve occurs in 2003 coincident with a large polar coronal hole extension which produced faster wind speeds than expected at low latitudes based on the Ulysses speed‐latitude polar coronal hole relationship. Although the slope does not change in a systematic way for each individual solar cycle, there seems to be an overall decrease in the slope since 1972.

The models of the global heliospheric current sheet are considered with the finite normal dimension and all three components of the magnetic field. The normal to the current sheet magnetic field component is due to the nonstationarity of the radial magnetic field on the source surface of the heliospheric magnetic field. The models are intended for modeling the cosmic ray behavior in the heliosphere and also for studying the small‐scale structure of the magnetic field and solar wind characteristics near the current sheets.

We study the flow in the vicinity of the heliopause stagnation point. The medium is considered as two‐component, with one component being plasma and the other the H atoms. The plasma and H atoms interact through charge exchange. It is assumed that the H atom flow has constant velocity, density and temperature, so that the back reaction of the plasma flow on the H atom flow is neglected. The solution is obtained in the form of power series expansions with respect to the radial distance from the symmetry axis. The main result obtained in our analysis is that the heliopause is not a surface of discontinuity, at least in a vicinity of the stagnation point. Rather it is the surface separating the flows of the solar wind and interstellar medium with all flow parameters continuous at this surface.

Energetic Solar particles and Geomagnetic Indices during the last two cycles were given. The data of the grouped flares and 10.7 cm radio flux were obtained from Solar Geophysical data reports by the US Department of Commerce, during the solar cycle 22 and 23. Power spectrum analyses method were used for the data treatments, to find the intermediate‐term periodicities, 14, 28, 35 are significant. Long‐term periodicities periodicity 154 days appeared, and confirmed with the other results. Halloween storms during Nov. 2003 and its effects on the geomagnetic storms have been studied analytically. The data of amplitude and phase of most common indicators of geomagnetic activities during solar cycle 23 has been analyzed.

For over four decades, low frequency plasma and electromagnetic fluctuations have been observed in the solar wind (SW), making it the most completely studied case of magnetohydrodynamic turbulence in astrophysics, and the only one extensively and directly studied using in situ observations. Magnetohydrodynamic scale fluctuations in the SW are usually anisotropic with respect to the local mean magnetic field (B0). In this work, we present a study of turbulent properties in the inner heliosphere (solar wind between 0.3 and 1 AU) based on modeling in situ plasma and magnetic observations collected by Helios 1 and Helios 2 spacecraft throughout a solar minimum. We present preliminary results on the evolution of the spatial structure of the magnetic self‐correlation function in the inner heliosphere. In particular we focus on the evolution of the integral length scale (λ) for magnetic fluctuations and on its anisotropy in the inertial range. As previously known from different studies, we confirm that near Eart...

We report a study of energetic ion acceleration at shocks bounding co‐rotating interaction regions (CIRs). Archived data obtained by Ulysses magnetic field, solar wind and energetic particle investigations at low latitude CIRs have been assembled and analyzed. The statistical relations between various properties of 22 Forward shocks, energetic particles and upstream heliospheric magnetic field fluctuations are presented. No statistically significant correlations are found between the shock compression ratio, r, or the particle intensity, jp, or the energetic particle spectral index, s, and the shock normal‐upstream field angle, θBn. Furthermore, a theoretical relation between the particle spectral index and shock compression is not consistent with the observed values of s and r. The particle intensities are poorly correlated with the power in upstream heliospheric magnetic field fluctuations contrary to our preliminary study of fewer shocks. We conclude that many of the expectations of Diffusive Shock The...

The soft X‐ray background observed from Earth contains contributions not only from outside the solar system such as the local bubble but also contributions from within the solar system, including contributions from the interplanetary medium, from the terrestrial geocorona, and from the magnetosheath. Great effort was spent on removing non‐cosmic contamination from data collected during the ROSAT all‐sky survey. Some of the contamination is the X‐ray emission produced from charge exchange of solar wind ions with interstellar and geocoronal neutral gas. The time‐varying component of this contamination was removed for the ROSAT survey, but the steady‐state component was not. In this chapter, we present ROSAT 1/4‐keV and 3/4‐keV band all‐sky maps of the cosmic soft X‐ray emission with the steady state heliospheric and geocoronal components removed via modeling procedures. These new determinations of the “true” cosmic background X‐ray emission will allow a re‐interpretation of the nature of the local hot bubble. In particular, the thermal pressure of the bubble gas must be about a factor of two less than the pressures deduced from the original ROSAT all‐sky survey.

We are currently observing the minimum phase of Cycle 23. Magnetic activity during the years 2006–2009 has been very weak with sunspot numbers reaching the lowest values in about 100 years. This long and extended minimum is characterized by weak polar magnetic fields, small polar coronal holes, and a relatively complex coronal morphology. This magnetic configuration at the Sun is remarkably different from the one observed during the previous two solar minima. We review observations made at the Sun and in the solar wind during the recent solar minima and discuss the implications of the observed differences for the heliosphere and geospace.

Recent in‐situ observations by the TDS instrument equipping the STEREO spacecraft revealed that large amplitude spatially localized Langmuir waves are frequent in the solar wind, and correlated with the presence of suprathermal electron beams during type III events or close to the electron foreshock. We briefly present the new theoretical model used to perform the study of these localized electrostatic waves, and show first results of simulations of the destabilization of Langmuir waves by a beam propagating in the inhomogeneous solar wind. The main results are that the destabilized waves are mainly focalized near the minima of the density profiles, and that the nonlinear interaction of the waves with the resonant particles enhances this focalization compared to a situation in which the only propagation effects are taken into account.

Dust grains in the nanometer range bridge the gap between atoms and larger grains made of bulk material. Their small size embodies them with special properties. Due to their high relative surface area, they have a high charge-to-mass ratio, so that the Lorentz force in the solar wind magnetic field exceeds the gravitational force and other forces by a large amount, and they are accelerated to a speed of the order of magnitude of the solar wind speed. When such fast nanoparticles impact a spacecraft, they produce craters whose matter vaporises and ionises, yielding transient voltages as high as do much larger grains of smaller speed. These properties are at the origin of their recent detection at 1 AU in the solar wind. We discuss the detection of fast nanoparticles by wave instruments of different configurations, with applications to the recent detections on STEREO/WAVES and CASSINI/RPWS. Finally we discuss the opportunities for nanoparticle detection by wave instruments on future missions and/or projects in the inner heliosphere such as Bepi-Colombo and Solar Orbiter.

The intensity of the H I Lyα line measured by the UltraViolet Coronagraph Spectrometer (UVCS) onboard the Solar and Heliospheric Observatory (SOHO) is used to investigate the density turbulence within the coronal mass ejection (CME) occurred on 2006 December 24, in the South polar coronal hole. In order to compare the spectral index inside the CME with those found in the undisturbed coronal plasma, we examined the CME data by applying the wavelet technique. This temporal analysis reveals, during the whole observation time, the existence of large‐scale density fluctuations of periods from tens of minutes to a few hours. However, during the CME, the power spectrum becomes less steep with a spectral slope about 5/3, typical of the turbulent regime, whilst prior to the CME and in the recovery phase the spectral slope is about 3. The Kolmogorov‐like spectrum observed within the CME is evidence for the nearly incompressible turbulent character of the CME plasma. This spectrum is significantly different from that of the high‐speed flow from coronal holes and the low‐speed wind originating above closed‐field coronal streamers. This result is particularly important to advance in the understanding of where the main source of CME flux injection resides.

As the primary input to coronal and solar wind models, global estimates of the solar photospheric magnetic field distribution are critical to space weather forecasting. These global magnetic maps are essential for accurate modeling of the corona and solar wind, which is vital for gaining the basic understanding necessary to improve forecasting models needed for Air Force operations. In this paper, we describe our efforts and progress toward developing the Air Force Data Assimilative Photospheric flux Transport (ADAPT) model. ADAPT incorporates the various data assimilation techniques, including an ensemble Kalman filter, with a photospheric magnetic flux transport model. The flux transport model evolves the magnetic flux on the Sun using relatively well understood transport processes when observations are not available and then updates the modeled flux with new observations using data assimilation. The data assimilation rigorously takes into account model and observational uncertainties, as well as accounting for regional correlations. The flux transport model and the data assimilation codes have been fully coupled and are now being extensively verified. After verification the model output will then be compared directly with observations (e.g., photospehric field strength and polarity, coronal hole boundaries, polar field strength, and ultimately solar wind). Anticipated outcomes of the ADAPT model include improvement in: 1) the estimation of solar corona and polar fields, 2) understanding the nature and behavior of solar super granular diffusion and meridional flows over the solar cycle, and 3) modeling and forecasting the solar wind near Earth.

It is widely accepted that magnetic disturbances around fast interplanetary magnetic clouds can play an important role in their geo‐effectiveness. An analytical solution for magnetic field in the sheath region of a cylindrical magnetic cloud with an elliptical cross‐section is proposed. Upstream magnetic field can have an arbitrary direction. Normal magnetic field components are conserved through the bow shock with a high accuracy.

Interplanetary scintillation (IPS) allows us to determine solar wind velocity and density structures over a relatively short time by employing computer assisted tomography. This method can be applied to forecast solar wind changes for a few days prior to its reaching Earth. We have been attempting solar wind forecasting by using IPS data observed at Solar‐Terrestrial Environment Laboratory (STELab), Japan. Here we introduce the solar wind forecast using STELab‐IPS and evaluated dependences of the accuracy of the STELab‐IPS forecasts on a number of line‐of‐sight observed with IPS and a solar activity by comparing comparing them with in situ measurements.

We present a model for the transport of solar wind fluctuations, based on the assumption that they can be well‐represented using two distinct components: a quasi‐2D turbulence piece and a wave‐like piece. For each component, coupled transport equations for its energy, cross helicity, and characteristic lengthscale(s) are derived, along with an equation for the proton temperature. This energy‐containing “two‐component” model includes the effects of solar wind expansion and advection, driving by stream shear and pickup ions, and nonlinear cascades. Nonlinear effects are modeled using a recently developed one‐point phenomenology for such a two‐component model of homogeneous MHD turbulence [1]. Heating due to these nonlinear effects is included in the temperature equation. Numerical solutions are discussed and compared with observations.

The electrostatic decay enables energy transfer from a finite amplitude Langmuir to a backscattered daughter Langmuir wave and ion acoustic density fluctuations. This mechanism is thought to be a first step for the generation of type III solar radio emissions at twice the plasma frequency. The electrostatic decay is here investigated through Vlasov-Poisson simulations by considering Langmuir localized wave packets in the case Te = Tp. Simulation results are found to be in good agreement with recently reported observations from the STEREO mission of the electrostatic decay of beam-driven Langmuir waves during a type III burst., 4 pages, 4 figures, Solar Wind 12

Recently it was shown that in resonance regions the antenna effective length can exceed its physical length. Here we show that this happens in reception of Langmuir waves in a streaming solar wind and we discuss the relevant observations of narrow band emissions observed by CLUSTER II.

A short review is given about the self‐consistent MHD model of solar coronal heating recently proposed by Bigot et al. (2008) in which the dynamical effect of the background magnetic field along a coronal structure is taken into account through exact results from Alfven wave turbulence. The main properties of the model are given as well as the heating rate and the microturbulent velocity obtained in the case of coronal loops. The conclusion is that Alfven wave turbulence may produce an efficient background heating for the solar corona.

To explain the unexpected discovery of C+, the existence of an inner source of pickup ions close to the Sun was proposed. We report on detailed analyses of the composition and the radial and latitudinal variations of inner source pickup ions measured with the Solar Wind Ion Composition Spectrometer on Ulysses from 1991 to 1998, approaching and during solar minimum. We find that the C+ intensity drops off with radial distance R as R−1.53, peaks at mid latitudes and drops to its lowest value in the ecliptic. In addition to C+, N+, O+, Ne+, Na+, Mg+, Ar+, S+, K+, CH+, NH+, OH+, H2O+, H3O+, MgH+, HCN+, C2H4+, SO+ and many other heavy ions and molecular ions are observed. Possible causes for the unexpected latitudinal variations and the neutral source(s) producing the inner source pickup ions are discussed.

We have examined the burst lifetime distribution functions of various solar wind parameters for 1998 and 2003 and compared them with the same for contemporaneous SYM‐H. The analysis yields clear power‐law exponents of the lifetime probability distributions. The power laws are consistently observed for different activity thresholds showing that these features are robust and repeatable, although scaling can vary depending on solar cycle.

Intermittency is one of the main features of the solar wind turbulence. We investigate the intermittency of ion flux and magnetic field scalar fluctuations under large statistics of the high time resolution measurements onboard Interball‐1 spacecraft. A large degree of intermittency is observed in the solar wind, and it grows significantly from a large (more than 10000 s) to a small (less than 100 s) scales. We give a special attention to a comparison of intermittency for the solar wind observation intervals containing SCIF (Sudden Changes of Ion Flux) to ones for intervals without SCIF. Such a comparison allows us to reveal the fundamental turbulent properties of the solar wind regions in which SCIF is observed more frequently. Especially it is important that the intermittency of the high frequency (up to 1 Hz) plasma variations is investigated for the first time. So we significantly extend the range of intermittency observations for solar wind plasma.

The past three years have been characterized by very weak sunspot and CME activity making this a long and deep solar minimum. In spite of the lack of magnetic activity at the Sun, white light and EUV images have shown that a relatively complex corona with multiple streamers and low latitude coronal holes persisted during most of this extended minimum. At the same time, solar wind observations indicated that the heliospheric current sheet was more warped during the declining and minimum phase of this cycle. This morphology of the corona and heliosphere differs from the one observed during the previous solar minimum when coronal streamers were confined to low heliolatitudes and the heliospheric current sheet was nearly flat. Interestingly, the polar magnetic fields observed at the solar photosphere during the present minimum are about 40% weaker than during the previous minimum. We use a potential field model to test if the weaker polar fields (and associated weaker dipole moment) can explain the differences observed in the corona and heliosphere during the past two minima.

Our prediction for the development of sunspot cycle 23 activity came true; one of the very few to have attained this status. We use the 3‐cycle quasi‐periodicity observed in the planetary index Ap. We improve our method by including data for 150 years and draw inferences as to what to expect for the development phase of cycle 24. Our forecast for the smoothed sunspot number at cycle 24 peak 78±5 in June 2013; the possibility that next three cycles may be progressively less active cannot be ruled out; the trend may possibly continue for the rest of the 21st century.

Interplanetary electron beams, produced by CMEs and flares, are unstable in the solar wind and generate Langmuir waves at the local plasma frequency or its harmonic. Radio observations of those waves in the range 4 kHz–256 kHz from the WAVES experiment onboard the WIND spacecraft have been statistically analyzed. A subset of 10 events has been selected for this study. The background consisting of thermal noise, type III bursts and Galactic background has been removed and the histogram of the remaining power spectral density has been fitted by Pearson’s system of distributions.

We perform 1 D hybrid simulations to investigate the nonlinear kinetic behavior of the tenuous collisionless magnetized plasma in coronal holes and fast solar wind. Initially isotropic ion distributions are reshaped via wave‐particle interactions with resonant daughter waves that are born by parametrically unstable large‐amplitude Alfven‐cyclotron waves. Decay processes lead to the formation of both acoustic and electromagnetic micro‐turbulence, which further influence the motion of the ions via Landau damping and pitch‐angle scattering. This leads to a depletion of the pump and destroys the fluid coherence of the medium. Parametric instabilities act to randomize the ion distributions, causing anisotropic heating and resulting in differential streaming and formation of ion beams. Due to their low mass densities and charge‐to‐mass ratios heavy ions are preferentially heated and obtain higher anisotropies than protons.

Low‐latitude boundary layer (LLBL) can be considered as an interface between magnetosheath and plasma sheet and it mediates the transfer of plasma between these regions. Its spatial profile thus can bring important information on the processes involved. The paper presents a case study of five‐point LLBL observations. We have used simultaneous observations of five Themis spacecraft and found smooth and monotonous changes of the ion density and temperature over a distance of about 1 RE under quiet upstream conditions and northward pointing magnetosheath magnetic field. We propose that the observations suggesting a non‐monotonous profile of the parameters during disturbed conditions would be interpreted in terms of distorted magnetopause surface and that the monotonous profiles are kept even under such conditions.

Using our kinetic Particle‐in‐Cell simulation code, we have examined the behavior of different plasma modes in the environment close to a CME shock front, with special focus on the modes that may contribute to the formation of type II radio bursts. Apart from electron velocity spectra, numerical dispersion plots obtained from simulation data allow for analysis of wave modes in the simulated plasma, especially showing growth and damping of these modes over time. These plots reveal features at 2ωp which are not predicted by linear wave theory, that may be results of nonlinear three wave interaction processes as theoretically predicted for type II emission processes.

The basic conservation laws for mass, momentum and energy along flow tubes from the sun to the Earth, together with observational constraints coming from remote sensing observations of the corona and in‐situ measurements of the wind may be used to derive scaling laws relating the asymptotic solar wind properties to the source regions on the sun. This paper reviews and compares theories of solar wind acceleration based on such conservation principles, stressing the different approximations involved.

Observational data of neutral atoms provides us with a 1 AU picture of the neutral atom flux in the heliosphere. The large mean free paths of neutrals allow us to infer properties of their distant source, as well as the properties of the intermediary medium. Energetic neutral hydrogen, for example, travels on almost straight trajectories, so that the particles observed coming from a particular direction were created from energetic protons along that line of sight. Similarly, low energy interstellar atoms are attenuated and deflected as they enter the heliosphere, and this deflection tells us something about the structure of the heliospheric interface. Of course, to infer quantitative features of the global heliosphere from neutral atom observations at 1 AU, we need accurate models that capture the 3D structure of the heliosphere. In this paper we present our MHD‐plasma/kinetic‐neutral model of the heliospheric interface that uses a Lorentzian distribution function to approximate a suprathermal tail on the...

Resonant interactions between ions and Alfv\'en/ion-cyclotron (A/IC) waves may play an important role in the heating and acceleration of the fast solar wind. Although such interactions have been studied extensively for "parallel" waves, whose wave vectors ${\bf k}$ are aligned with the background magnetic field ${\bf B}_0$, much less is known about interactions between ions and oblique A/IC waves, for which the angle $\theta$ between ${\bf k}$ and ${\bf B}_0$ is nonzero. In this paper, we present new numerical results on resonant cyclotron interactions between protons and oblique A/IC waves in collisionless low-beta plasmas such as the solar corona. We find that if some mechanism generates oblique high-frequency A/IC waves, then these waves initially modify the proton distribution function in such a way that it becomes unstable to parallel waves. Parallel waves are then amplified to the point that they dominate the wave energy at the large parallel wave numbers at which the waves resonate with the particles. Pitch-angle scattering by these waves then causes the plasma to evolve towards a state in which the proton distribution is constant along a particular set of nested "scattering surfaces" in velocity space, whose shapes have been calculated previously. As the distribution function approaches this state, the imaginary part of the frequency of parallel A/IC waves drops continuously towards zero, but oblique waves continue to undergo cyclotron damping while simultaneously causing protons to diffuse across these kinetic shells to higher energies. We conclude that oblique A/IC waves can be more effective at heating protons than parallel A/IC waves, because for oblique waves the plasma does not relax towards a state in which proton damping of oblique A/IC waves ceases.

New study confirms conclusions made in [M. Eselevich, and V. Eselevich, 2008]; according to it, there is a disturbed region expended along the CME propagation direction in front of a coronal mass ejection whose velocity $u$ is lower than the critical $u_C$ relative to the surrounding coronal plasma. The time difference brightness (plasma density) in the disturbed region smoothly decreases to larger distances in front of CME. A shock wave forms at u higher than $u_C$ in the front part of the disturbed region manifested as a discontinuity in radial distributions of the difference brightness., Comment: 3 figures

I outline the development of four generations of kinetic models, starting with Chamberlain's solar breeze exospheric model. It is shown why this first kinetic model did not give apposite supersonic evaporation velocities, like early hydrodynamic models of the solar wind. When a self-consistent polarization electric potential distribution is used in the coronal plasma, instead of the Pannekoek-Rosseland's one, supersonic bulk velocities are readily obtained in the second generation of kinetic models. It is outlined how the third and fourth generations of these models have improved the agreement with observations of slow and fast speed solar wind streams., Comment: 10 pages, 3 figures, presented at SW12 conf. ; Copyright (2010 AIP 978-0-7354-0759-6/10) 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 (CP1216) and may be found at (http://proceedings.aip.org)

The onset of a Solar Energetic Particle (SEP) event has been traditionally determined by using the velocity dispersion analysis (VDA), where the event onset at the Sun is determined by fitting the solar onset time and the particles’ path length to match the observed event onset at 1 AU for several SEP energy channels. This approach has been studied by using energetic particle simulations, in order to understand the effect of the interplanetary scattering on the arrival time of the first particles to 1 AU. In these studies, the SEP event onset at 1 AU has been defined as the time when the intensities reach certain percentage of the maximum of the event. This is often not feasible for practical work, as a real event may be complex in its structure, and the pre‐event background may mask the SEP onset to differing degrees in different energies. In order to estimate the usability of the VDA method, we study the simulated SEP onset on a pre‐existing particle background by varying the pre‐event background level, the difference of the pre‐event background and the simulated event maximum spectral indices, the interplanetary mean free path and the injection profile. As in the previous studies, we find that large path length variation can be explained as an artifact resulting from the use of the VDA method. More importantly, the error in the obtained solar onset time depends strongly on the properties of the pre‐event background.

Large‐scale phenomena in the solar wind are important elements of heliospheric physics and space weather. On the basis of the OMNI database of interplanetary measurements we identified large‐scale structures of solar wind (SW types) for all time intervals during 1976–2000. Our classification includes quasi—steady types: (1) Heliospheric current sheet (HCS), (2) Slow and (3) Fast SW streams, respectively, from closed and open magnetic field structures in the solar corona, and disturbed types: (4) Corotating interaction regions (CIR—compressed regions between slow and fast SW streams), (5) SHEATH (compressed regions ahead of MC/EJECTA) and (6) Magnetic cloud (MC) and (7) EJECTA as well as (8) direct and (9) reverse interplanetary shocks (see catalog on site ftp://ftp.iki.rssi.ru/pub/omni/ and paper [1] ). We discuss several preliminary results obtained with our catalog (see more details in http://www.iki.rssi.ru./people/yyermol_inf.html) including effects on the Space Weather.

The interplanetary medium provides a vast natural laboratory for studying many fundamental questions about astrophysical plasmas. In this paper I make a short review on what we know about turbulent fluctuations which behave differently at low (f Hz) frequencies. Particular attention is made about anisotropy at low frequency and its MHD modeling as well as the origin of a second inertial range at high frequencies characterized by steep power law spectra which cannot be associated with MHD fluctuations.

We have recently presented a mechanism for preferential acceleration and heating of coronal hole minor ions [1, 2]. The energization is due to the effect of multiple cyclotron resonances in the presence of sunward and anti‐sunward dispersive ion cyclotron waves, providing a second‐order Fermi interaction. The mechanism is preferential because coronal hole protons do not experience such multiple resonances. The detailed model results depend on many parameters, including poorly‐known quantities such as the wave intensities, spectral shapes and radial profiles. In this paper, we show that reasonable choices for these quantities can yield excellent agreement with the observations. We find that only a small fraction of the extrapolated wave power is needed to provide the observed heating, and there is an indication that the resonant wave levels are increasing with radial position between r = 2 Rs and 4 Rs.

We consider the Lemaire‐Scherer construction of the supersonic solar wind as the kinetic escape of a collisionless (scatter‐free) plasma from an exosphere near the Sun. The radial electric field enforces equality of the electron and ion densities and also equality of the electron and ion fluxes. Consequently, the electrons form an electrostatically confined atmosphere with the temperature declining outward only slowly from the exosphere and becoming the work horse that lifts and accelerates the ions to supersonic velocity.

The global structure of the heliosphere predicted from our 3D MHD time dependent code for several sets of boundary conditions is discussed. Time variations of the solar wind caused by the 11‐year solar cycle are simulated, and the effect on the termination shock and heliopause is analyzed. The results from different models, assuming either spherical or anisotropic solar wind, with or without the interplanetary magnetic field, are compared. The interaction with neutral hydrogen via charge exchange is included. The role of the interstellar magnetic field is discussed.

Magnetic isolated large amplitude depressions in the interplanetary magnetic field are commonly observed in the solar wind. Some of these magnetic structures are accompanied by bursts of electrostatic waves close to electron plasma frequency. Combining STEREO/WAVES and IMPACT data we are able to accurately localize the waves emission. We show that they also appear inside kinetic holes, themselves situated inside larger holes. We provide, for the first time, the detailed waveform of the waves that reveal their very bursty nature. These results are complemented by CLUSTER data, which allow to resolve the electron distribution and obtain a better description of spatio‐temporal variations in Langmuir wave activity. Such observations are confronted to different emission mechanisms.

Numerical simulations of two-dimensional Magnetohydrodynamic (2D MHD) turbulence reveal the presence of a huge number of sites where magnetic reconnection locally occurs. The properties of this ensemble of reconnection events, that are spontaneously generated by turbulence, have been studied. The associated reconnection rates, computed as the electric field at the neutral points, are broadly distributed and the statistics of these events are presented. This new description of reconnection is relevant for space and laboratory plasmas, where generally turbulence is present. © 2010 American Institute of Physics. Fil: Servidio, S.. Bartol Research Institute; Estados Unidos Fil: Shay, M.A.. Bartol Research Institute; Estados Unidos Fil: Matthaeus, W. H.. Bartol Research Institute; Estados Unidos Fil: Dmitruk, Pablo Ariel. Universidad de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentina Fil: Cassak, P.A.. West Virginia University; Estados Unidos Fil: Wan, M.. Bartol Research Institute; Estados Unidos

Heliospheric energetic particle reservoirs are usually observed in the decay phase of large solar energetic particle (SEP) events when particle intensities measured by widely separated spacecraft (in longitude, latitude and radial distance) present comparable intensities (within a factor of 2–3) that evolve similarly in time. We use near‐relativistic electron observations from both the ACE and Ulysses spacecraft throughout solar cycle 23 to determine when and where these reservoirs were observed by these two spacecraft. Particle reservoirs were more prominently observed during the intense active periods of November 2000 and November 2001 when Ulysses was at high (>70 deg) latitudes and at heliocentric radial distances 2.15

Properties of multiple ion beams in the solar wind beyond 1 AU as observed by the SWOOPS experiment on Ulysses are discussed. The solar wind proton distributions are approximated by a two beam bi‐Maxwellian model. The slower outward traveling beam typically comprises the majority of the solar wind density. Differential streaming between the slower and faster proton beams decreases with distance from the Sun. The greatest difference between the beams in their evolution with distance from the Sun is that the parallel temperature component of the faster beam decreases more rapidly, r−1.22, than that of the slower beam, r−0.39. The difference in behavior for the perpendicular components (r−0.46 for the faster beam and r−0.73 for the slower beam) is real but less marked. The indication that relative perpendicular cooling is less for the faster beam while relative parallel cooling is greater and differential beam speed decreases is generally consistent with expectations from a streaming instability between the ...

Interplanetary Field Enhancements are rare but very distinct increases in the magnetic field strength, reaching a nearly symmetric cusp‐shaped peak. These increases are usually accompanied by a thin central current sheet. Their associations with the perihelion passages of the asteroid 2201 Oljato and with the comet De Vico have led to the hypothesis that these events are associated with the interaction of the solar wind with dust particles. In this paper we examine observations of these events with the Helios 1/2 spacecraft that flew as close to the Sun as 0.29 AU. These events are observed over the entire range of distances studied by Helios 1 and 2. The ponderomotive force exerted by the magnetic field strength decreases with radial distance roughly inversely proportional to the distance squared.

A robust multiscale analysis of high‐frequency magnetic field measurements from the Cluster spacecraft is presented using complimentary measurements from the magnetometer and search‐coil instruments; in a stationary interval of fast ambient solar wind. We show a surprising and novel result: that for time‐scales smaller than the ion‐gyro period the magnetic field fluctuations exhibit non‐Gaussian monoscaling i.e. are globally scale invariant and can be characterized by a single scaling exponent and thus a single universal scaling function for the probability density. This presents new questions, as well as theoretical constraints, for determining how magnetic turbulent energy is dissipated in collisionless plasmas.

We examine the distribution of directions of the heliospheric magnetic field (HMF) measured by the Ulysses spacecraft during its mid‐latitude transits of the heliosphere when it observed solar wind shears from the incursions of high‐latitude fast solar wind toward the low‐latitude slow solar wind. We look for nearly radial field orientations commonly observed in rarefaction regions (i.e. where the solar wind velocity decreases monotonically over several days). In contrast to CMEs where the HMF tends to be enhanced, the rarefaction regions with nearly radial magnetic fields tend to have extremely low magnetic field magnitude values. Within these rarefaction regions, there are “dwells” in the coronal source longitude of the measured solar wind in which the time dependence of the solar wind velocity is given to a very good approximation by V(t) = R/(t‐t0), where R is the heliocentric radial distance of the spacecraft. We have therefore compiled distributions within the dwells of the parameter |Br|/B which is...

We discuss cosmic dust in the interplanetary medium focusing on its interaction with the solar wind and recent observational results related to such interactions. The dust contributes to pick‐up ions in the solar wind and dust collisional vaporization can explain the observed heavy inner source pick‐up ions, as well as the presence of molecular ions. We predict that ions generated by dust destruction inside 0.1 AU are multiply charged in the solar wind near 1 AU. The mass loading of the solar wind during passage of cometary dust trails appears too small to explain the interplanetary field enhancements that are observed in solar wind magnetic field measurements. Nano dust in the interplanetary medium can be efficiently accelerated in the solar wind and hypervelocity impacts of nano dust onto the spacecraft can explain frequent events measured with the plasma instrument onboard STEREO.

Fluctuations in the solar wind parameters and in the heliospheric magnetic field have been studied extensively. The nature of fluctuations has been shown to depend on the origin of the solar wind. However, the regions of transition between the high‐speed and the slow speed streams have not been investigated with high resolution. In this work we use high resolution magnetic field measurements on the Ulysses spacecraft to calculate the variances of the fluctuations in the magnetic field components and its magnitude over several timescales, concentrating on intervals of rapid change in the solar wind parameters. At the same time, we computed the cross helicity to assess the Alfvenicity of the fluctuations and changes in it during transitions. The strong variability of all those parameters seems to indicate a filamentary nature of the heliospheric medium.

Wavelet analysis is a tool that can simultaneously analyze spacecraft data in both time and frequency. This enables the magnetic energy spectrum (trace spectrum) to be measured for different angles between the local mean magnetic field B0 and the direction of the mean flow within a single data set. Examples obtained around solar minimum using Ulysses data at high latitudes and Stereo data for high‐speed streams in the ecliptic plane show that the spectral exponent in the inertial range varies nearly monotonically from approximately 1.6 when B0 is perpendicular to the flow to 2.0 when B0 is parallel to the flow, roughly consistent with anisotropic theories of incompressible MHD turbulence. This and other new information about the 3D wavector spectrum of solar wind fluctuations in the inertial range and the dissipation range are briefly discussed.

Solar rotational tomography is applied to almost eleven years of LASCO C2/SOHO data, revealing for the first time the structural behavior of streamers over almost a full solar activity cycle. Streamers are most often shaped as extended, narrow plasma sheets. The sheets can be extremely narrow at times (⩽0.14×106 km at 4R⊙). This is over twice their heliocentric angular thickness at 1 AU. For most of the activity cycle, streamers share the same latitudinal extent as filaments on the disk, showing that large‐scale stable streamers are closely linked to the same large‐scale photospheric magnetic configuration which give rise to large filaments. There is considerable differential rotation of streamers at high latitudes, which makes comparison between disk and coronal structure complicated. The presence of differential rotation has implications for many areas of coronal and heliospheric research.