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Recently, Zank et al. 2012 developed a model to describe the transport of low-frequency turbulence in inhomogeneous and magnetized flows, based on the Elsasser description. By taking moments of the small scale Elsasser variables z ±, transport equations for the total energy ET , the cross helicity EC , and the energy difference (residual energy) ED of the turbulence were derived. The set of transport equations was completed by introducing evolution equations for the correlation lengths λ± (corresponding to forward and backward propagating modes of the Elsasser variable), and the correlation length λ D (corresponding to the energy difference ED ). A first simplification was achieved by setting λ+ = λ−. In this paper we show that, based on an integral scale for velocity correlations, the choice of λ+ = λ− has a certain phenomenology with some very specific implications on the set of transport equations. In particular, it is shown that λ D and z ± can no longer be chosen arbitrarily, but must satisfy certain restrictions. These are discussed and a reduced transport model is derived.

Several years of neutral measurements by NASA/IBEX-Lo have yielded detailed observations of direct interstellar neutral helium (primary particles). Prior to IBEX, interstellar helium had been observed through UV backscattering, pickup ions, and directly by Ulysses-GAS. The IBEX measurements now also provide strong indications for the presence of secondary neutral helium that is thought to originate in the outer heliosheath from charge exchange. In order to model both primary and secondary particle populations and characterize them throughout the heliosphere, a detailed calculation method based on Keplerian orbits is used, and some sample results are presented. The helium velocity distribution functions throughout the heliosphere are characterized. In the inner heliosphere they exhibit an intricate structure, in particular downwind of the Sun where the helium focusing cone resides as well.

As the twin Voyager spacecraft approach the boundary of the heliosphere, they continue returning new and unexplained measurements of the solar wind (SW) protons, energetic particles, and magnetic field that often differ markedly between the two spacecraft. Our recent studies show that time-dependent effects play a crucial role in understanding and interpreting the observational data. Since the SW is unsteady on many different time scales, its interaction with the local interstellar medium (LISM) should reflect the solar rotation and cycle, as well as merged interplanetary disturbances. Even a simplified solar cycle model allowed us to predict in 2009 the possibility of a negative radial velocity component in the SWas the heliopause is approached. Further analysis shows a nearly vanishing latitudinal velocity component, while the longitudinal component becomes comparable substantial. Here we discuss the change of the magnetic field and plasma properties across the heliopause, which is important for the identification of its spacecraft crossing. We discuss the effects of heliopause instabilities and corotating interaction regions, and demonstrate that Voyagers are unlikely to see a sharp boundary between the SW and the LISM, but rather a mixing layer of varying width.

We calculate the power spectra densities of magnetic field fluctuations associated with interplanetary shock waves at 1AU, utilizing in-situ magnetic field measurements from spacecraft ACE and Wind. We derive related quantities both upstream and downstream of a shock as a function of time/distance away from the shock passage. We present results for a few events that exhibit clear upstream enhanced wave activity. We show that mostly they are of Alfvenic nature and confined within certain distance upstream. We also present a preliminary analysis of turbulence-particle interaction based on spectral analysis results. Implications of such analysis to turbulence transport models are also discussed.

In this paper we investigate the interaction between the solar wind (SW) and the local interstellar medium (LISM) using spacecraft data and numerical simulations. In particular, we will focus on neutral atom results from NASA’s Interstellar Boundary EXplorer (IBEX) mission, and compare these with implementations of our neutral atom models that look at both the energetic neutral atoms (ENAs) which are created as hydrogen of LISM origin interacts with the heliosphere, as well as the transmission of interstellar Oxygen through the heliospheric interface. The goal of this work is to better understand the global structure of the heliosphere and its interaction with the galaxy.

Although the solar wind, as a collisionless plasma, is properly described by the kinetic Maxwell-Vlasov description, it can be argued that much of our understanding of the solar wind is based on a fluid description of magnetohydrodynamics that derives from interpretation of observational data together with numerical modeling. In recent years, there has been significant interest in better understanding the importance of kinetic effects, i.e., the differences between kinetic and fluid descriptions. Here we concentrate on the physical properties of oblique kinetic Alfven waves (KAWs) that appear to be a key ingredient in the solar wind turbulence cascade. We use three different fluid models with various degrees of complexity and calculate the polarization and magnetic compressibility of KAWs (propagation angle θ = 88°), which we compare to solutions derived from linear kinetic theory. We explore a wide range of possible proton plasma β = [0.1, 10.0] and a wide range of length scales k⊥rL = [0.001, 10.0], whe...

During the last half decade, the structure of the heliospheric interface has attracted increasing attention with continual improvements in modelling and observations. The Interstellar Boundary Explore (IBEX) spacecraft is returning important data that require a theoretical model of Heliosphere to ensure proper interpretation. We develop a framework for understanding the measurements of heavier-than-hydrogen atoms by IBEX in terms of a 3D MHD-neutral numerical solution of the sun's interaction with the interstellar medium, combined with a test particle approach for heavy atoms and ions.

We examine ion-acoustic solitons in two-fluid plasmas without the usual simplification of setting electron mass to zero. Assuming one-dimensional, electrostatic and cold protons, the system is treated analytically, resulting in an integral form solution. We present numerical calculations which resolve the ion-acoustic solitary wave signatures. Also, we consider the conditions for which ion-acoustic solitons may exist. The existence conditions set up a Mach number threshold. Our result shows that the Mach number threshold depends on the electron-to-proton mass ratio and the electron adiabatic index; for a special adiabatic index γ = 2, the condition reduces to a cubic equation.

In this paper we describe our group efforts to develop a self-consistent, data-drivenmodel of the solar wind (SW) interaction with the local interstellar medium. The motion of plasma in this model is described with the MHD approach, while the transport of neutral atoms is addressed by either kinetic or multi-fluid equations. The model and its implementation in the Multi-Scale Fluid-Kinetic Simulation Suite (MS-FLUKSS) are continuously tested and validated by comparing our results with other models and spacecraft measurements. In particular, it was successfully applied to explain an unusual SW behavior discovered by the Voyager 1 spacecraft, i.e., the development of a substantial negative radial velocity component, flow turning in the transverse direction, while the latitudinal velocity component goes to very small values. We explain recent SW velocity measurements at Voyager 1 in the context of our 3-D, MHD modeling. We also present a comparison of different turbulence models in their ability to reproduce the SW temperature profile from Voyager 2 measurements. The boundary conditions obtained at 50 solar radii from data-driven numerical simulations are used to model a CME event throughout the heliosphere.

We compare the efficiency of proton acceleration at oblique strong CME shocks at radial heliocentric distances from 0.13 to 2.5 AU. We use the PATH code to obtain the diffusion coefficients and maximum achievable particle energies at shocks with 15°, 45° and 75° shock angles. In computing the maximum energy, we use the total diffusion coefficient which is a function of the parallel diffusion coefficient and the perpendicular diffusion coefficient. The parallel diffusion coefficient is calculated from the wave intensity of Alfven waves generated by streaming protons in the shock vicinity [1, 2]. The perpendicular diffusion is described in the NLGC approach and depends on the parallel diffusion coefficient and pre-existing turbulence in the solar wind [3, 4, 6]. It is shown that efficiency of particle acceleration at a fast CME-driven shock depends on the shock angle, injection energy and radial heliocentric distance. Quasi-perpendicular strong shocks are more efficient in accelerating higher-energy seed particles, especially at larger heliocentric distances and close to the Sun. By contrast, quasi-parallel strong shocks can accelerate particles more efficiently at distances about 1 AU.

In this paper we summarize our group's efforts to develop a self-consistent, data-driven model of the solar wind interaction with the local interstellar medium. In this model, we describe the motion of plasma with the MHD approach, while the transport of neutral atoms is described by either kinetic or multi-fluid equations. The model and its implementation in the Multi-Scale Fluid-Kinetic Simulation Suite (MS-FLUKSS) is thoroughly tested and validated by comparing our results with other models and spacecraft measurements. The model appears to be rather accurate in reproducing the Interstellar Boundary Explorer ribbon and the general features of the plasma flow available from the Voyager 1 and 2 in-situ data. In particular, the timing of the Voyager crossing of the termination shock is reasonably accurately reproduced without involving exotically strong interstellar magnetic field values. We added a turbulence model to our governing equations and started treating pickup ions as a separate fluid, which made it possible to greatly improve our ability to reproduce the proton temperature. We discuss the results of our modeling of corotating interaction regions, global merged interaction regions, and solar cycle effects. A possible explanation is provided for the low radial velocity measurements from Voyager 1.

The interaction between the solar wind (SW) and the local interstellar medium (LISM) has been studied for decades, but has only recently been scrutinized using observational data. One such mission, NASA's Interstellar Boundary EXplorer (IBEX), has provided a wealth of new data that allows for a global picture of the heliospheric interface. While the mysterious “ribbon” seen in the IBEX data has attracted a lot of attention, data from other parts of the sky can still tell us much about the plasma conditions in those directions, and the termination shock conditions that heated the plasma. In this paper we investigate the ENA spectrum seen by IBEX and compare this to various model predictions, both with and without the ribbon.

We present ideas on nonlinear multiple waves in magnetohydrodynamics (MHD). In simple wave solutions, the dependent physical variables (the gas density, fluid velocity, magnetic field induction and gas pressure) depend on one phase variable which can be a function of the space and time variables (x, y, z, t). Double waves are another class of solutions that depend on two independent wave phases. As illustration of these ideas we present examples of double Alfven waves. The solutions possess the usual integrals for Alfven simple waves (the gas density, magnetic pressure, gas pressure and traveling wave velocity or group velocity), and have two independent phases. These waves may well be present in the solar wind. Double wave solutions, involving the other MHD wave modes are also possible.

A set of one-dimensional two-fluid plus Maxwell's equations are solved numerically with very high spatial and temporal resolutions. The simulation captures the formation of the cross-shock potential (CSP) on electron Debye and plasma frequency scales. Test particles are launched towards the shock and their trajectories across the cross-shock electric and magnetic fields indicate the importance of shock surfing acceleration (SSA) at the quasi-perpendicular shock.

A new MHD simulation method for reproducing a realistic and time-varying global heliospheric modelling is developed using solar-wind speed data from interplanetary sintillation (IPS) and photospheric magnetic data from optical observations. The IPS together with the magnetic data provide us inner boundary conditions which include both co-rotating solar-wind speed distribution and magnetic field distributions using a tilted current sheet model. Hence it enables us to reproduce dynamical co-rotating wind-wind interaction and also magnetic field structures such as an oscillating equatorial magnetic neutral sheet in a three-dimensional heliosphere. In our preliminary results of this method, a realistic and oscillating equatorial neutral sheet and wind-wind interactions are shown both in the interplanetary space and the heliosheath.

Alfven wave mixing (interaction) equations used in locally incompressible turbulence transport equations in the solar wind are analyzed from the perspective of linear wave theory. The connection between the wave mixing equations and non-WKB Alfven wave driven wind theories are delineated. We discuss the physical wave energy equation and the canonical wave energy equation for non-WKB Alfven waves and the WKB limit. Variational principles and conservation laws for the linear wave mixing equations for the Heinemann and Olbert non-WKB wind model are obtained. The connection with wave mixing equations used in locally incompressible turbulence transport in the solar wind are discussed.

We calculate the power spectral densities of magnetic field fluctuations associated with interplanetary shock waves, utilizing in-situ magnetic field measurements from spacecraft ACE and Wind at 1AU. We derive related quantities both upstream and downstream of a shock as a function of time/distance away from the shock passage. We present results for a few events that exhibit clear upstream enhanced wave activity. We show that mostly they are of Alfvenic nature and confined within certain distance upstream. We also present a preliminary observational analysis of turbulence-shock interaction based on perturbation analysis.

Terrestrial Gamma‐ray Flashes are short pulses of energetic radiation associated with thunderstorms and lightning. While the Gamma‐ray Burst Monitor (GBM) on Fermi was designed to observe gamma‐ray bursts, its large BGO detectors are excellent for observing TGFs. Using GBM, TGF pulses are seen to either be symmetrical or have faster rise time than fall times. Some TGFs are resolved into double, partially overlapping pulses. Using ground‐based radio observations of lightning from the World Wide Lightning Location Network (WWLLN), TGFs and their associated lightning are found to be simultaneous to ≈40 μ s. The lightning locations are typically within 300 km of the sub‐spacecraft point.

The transport of angular momentum is one of the most important outstanding problems in astrophysical accretion disk physics. High angular momentum material forms a disk around the accreting object, which can be a forming protostar, a binary companion star, a stellar mass black hole, or even a supermassive black hole. In each of these cases, the magnetorotational instability (MRI) is believed to play a (possibly dominant) role in transporting angular momentum outward, allowing the disk material to fall onto the central object. Previous work has established that the MRI can drive turbulence which in turn can generate by dynamo action the requisite magnetic fields. We report on a series of numerical experiments aimed at understanding the operation of this MRI dynamo over a range of parameters, which while far from realistic, allow some insight into the scaling of the dynamo action.

The first all‐sky maps of Energetic Neutral Atoms (ENAs) from the Interstellar Boundary Explorer (IBEX) exhibited smoothly varying, globally distributed flux and a narrow “ribbon” of enhanced ENA emissions. Since then, IBEX has completed another set of full sky maps, which show that the large‐scale structure was generally stable between the first and second halves of 2009. However, these maps also indicate some very intriguing smaller scale temporal changes in the outer heliospheric emissions. This paper provides an update on the IBEX observations in general and examines their temporal variations in particular. The observed large‐scale stability and the systematic changes at smaller spatial scales provide important new information about the outer heliosphere and its global interaction with the galaxy, as well as illuminating possible mechanisms for producing the IBEX ribbon.

We discuss the relative magnetic helicity of (a) the Parker [1] interplanetary spiral magnetic field, and (b) multi‐dimensional simple Alfven waves in the solar wind. We discuss the different forms of the magnetic vector potential A using either (a) the Coulomb gauge associated with solving a Poisson equation for A, in which the current acts as a source, (b) by using the homotopy form of A or (c) using a poloidal‐toroidal decomposition of the magnetic field B. For the Parker field, we show that the relative helicity for a hemispherical volume north of the current sheet is negative, and the relative helicity for a similar volume south of the current sheet is positive. The relative helicity is also calculated in terms of the linkage of the poloidal and toroidal magnetic flux. These results extend the results of Bieber et al. [2] on the magnetic helicity of the Parker field, and are related to the helicity injection rate into the solar wind determined by Berger and Ruzmaikin [3]. Similar methods are used to ...

In situ observations of the outer heliosphere by the Voyager 1 (V1) and Voyager 2 (V2) spacecrafts show highly variable behavior of the solar wind plasma in deep interplanetary space and the heliosheath (HS). We develop a dynamic and realistic model that satisfies both V1 and V2 observed crossing times and locations of the termination shock (TS) simultaneously, by performing a three‐dimensional (3D) MHD simulation that includes the effects of neutral particles (Washimi et al. (2010)). Daily values of solar‐wind speed and density observed by V2 were used so that short‐term dynamical effects are reproduced in this simulation. Here, we compare the V1 observed high‐energy charged particle flux data in the HS (Webber et al. (2009)) with our MHD simulation results to identify the flux increase/decrease associated with the March 2006 interplanetary shock events.

We present simulation results near the dynamo transition for the Taylor‐Green dynamo for magnetic Prandtl number, PM, of 0.5 and 1. We construct bifurcation diagrams for one of the dominant Fourier mode, B(0,0,1), and the ratio of magnetic and kinetic energy (Eb/Eu) as a function of the forcing amplitude of Taylor‐Green forcing. It is observed that the dynamo transition for PM = 1 is via a supercritical bifurcation, while that for PM = 0.5 is via a subcritical bifurcation. The ratio Eb/Eu varies from 0 to 3 for PM = 1, but it is typically less than 1 for PM = 0.5. Different dynamo states, such as those with constant, time‐periodic, quasiperiodic, and chaotic magnetic fields, have been reported. We also observe coexisting dynamo states.

The heliopause (HP) is the outer edge of the heliosphere that separates the tenuous and hot heliosheath plasma from the relatively dense and cool magnetized plasma of the local interstellar medium (LISM). As a surface of tangential discontinuity, the HP is subject to both Rayleigh‐Taylor (RT) and Kelvin‐Helmholtz (KH) instabilities. The coupling between plasma ions and neutral atoms through charge exchange provides an “effective gravity” for RT, while shear flows due to the velocity difference between the heliosheath and the interstellar flows can drive KH modes. We derive the linearized dispersion relations for waves propagating along the surface of this discontinuity using a fluid picture, to study the possibility for both RT and KH instabilities, including a second population of energetic neutrals produced by charge exchange interactions between the hot solar wind plasma in the heliosheath with interstellar hydrogen. We show that due to charge exchange interactions, the HP is unconditionally unstable t...

We investigated the injection of ions into the inner magnetosphere during the sudden storm commencement (SSC) of the 28 October 2001 geomagnetic storm by carrying out a large‐scale kinetic particle tracing study of the event. We launched H+ ions from the solar wind and O+ ions from the ionosphere in global time‐dependent electric and magnetic fields obtained from a global magnetohydrodynamic (MHD) simulation of the storm, and compared our results to those from IMAGE/HENA and the LANL geosynchronous spacecraft 1995‐095. We show that the SSC resulted in a dramatic increase in the density and energy density of both ion species. In addition, our results show an injection of solar wind ions from the dawn flank that is consistent with observations and with previously published results.

In an observational overview of ionized Hydrogen in our Galaxy, I summarize its large scale structure and the plasma physics scales that are relevant to turbulence. My emphasis is on the very small scale turbulence revealed by radio interstellar scintillation (ISS), which probes inhomo‐geneity in the electron density. A standard picture has emerged of an isotropic 3‐D Kolmogorov spectrum of electron density from ISS observations of many pulsars since the 1970s. This suggests a turbulent cascade even though the observations do not probe the velocity or magnetic fields. However, recent ISS measurements using “scintillation arcs” show the plasma turbulence on some lines of sight to be both anisotropic and highly intermittent on AU scales. I speculate on their possible origin as remnant turbulence from long past supernovae.

The most thoroughly observed region of the interstellar medium (ISM) is that which immediately surrounds the heliosphere. Evidence that this gas is partially ionized (about 20% for H, 40% for He) comes from a variety of sources including absorption lines toward nearby stars, and in situ detection of interstellar neutral atoms and pickup ions in the solar system. The ionization in the Local Interstellar Cloud (LIC) is dominated by photoionization and requires more ionizing flux than is available stellar sources. Diffuse radiation from nearby hot gas can provide the necessary hard yet low intensity interstellar radiation field. To put the local ISM in a Galactic context, one can compare it to the warm ionized medium (WIM), but the H ionization level of the LIC is apparently substantially lower than that in the WIM. We discuss the nature and source of ionization of the LIC and compare it with evidence on more distant regions of the warm, diffuse ISM.

The Fermi Gamma‐ray Burst Monitor (GBM) monitors the entire unocculted sky for transient activity in the energy range from 8 keV to 40 MeV. Now in operation for more than two years, GBM triggers not only on gamma‐ray bursts and other cosmic events such as bursts from magnetars but also on solar flares and terrestrial gamma‐ray flashes. GBM’s continuous data collection over the entire sky also allows continual hard X‐ray monitoring of persistent and transient sources using Earth occultation and pulsed source analysis techniques. In this paper I describe the GBM instrument and present some science highlights from GBM observations.

Interactions between ions and neutrals in a partially ionized plasma are important throughout heliophysics, including near the solar surface in prominences. Understanding how ion-neutral coupling affects formation, support, structure, and dynamics of prominences will advance our physical understanding of magnetized systems involving a transition from a weakly ionized dense gas to a fully ionized tenuous plasma. We address the fundamental physics of prominence support, which is normally described in terms of a magnetic force on the prominence plasma that balances the solar gravitational force, and the implications for observations. Because the prominence plasma is only partially ionized, it is necessary to consider the support of the both the ionized and neutral components. Support of the neutrals is accomplished through a frictional interaction between the neutral and ionized components of the plasma, and its efficacy depends strongly on the degree of ionization of the plasma. More specifically, the frictional force is proportional to the relative flow of neutral and ion species, and for a sufficiently weakly ionized plasma, this flow must be relatively large to produce a frictional force that balances gravity. A large relative flow, of course, implies significant draining of neutral particles from the prominence. We evaluate the importance of this draining effect for a hydrogen-helium plasma, and consider the observational evidence for cross-field diffusion of neutral prominence material.

The Voyager 2 (V2) observations of the heliospheric termination shock indicate that it is heavily influenced by the presence of interstellar pickup ions (PUIs). The V2 instrument measured less solar wind heating than expected and a downstream flow speed that remained supersonic. While PUIs are expected to play a role in energy dissipation at the shock, the details remain unclear. Here, we use particle‐in‐cell (PIC) simulations and show that PUIs indeed play an important role and that the downstream flow speed remains supersonic if the magnetosonic speed were measured without the contribution of PUIs.

It has been suggested that intermittent regions of strong slab turbulence in the solar wind might be responsible for dropout events observed in solar energetic particle fluxes on small spatial scales. In this paper the large‐scale transport of cosmic rays in three‐dimensional magneto‐hydrodynamic turbulence dominated by uniform two‐dimensional turbulence, but including a minor intermittent slab turbulence component, is investigated theoretically. The main finding is that at late times both cosmic‐ray transport parallel and perpendicular to the mean magnetic field are the net effect of an interplay between diffusive and nondiffusive (super or subdiffusive) transport effects as a consequence of this intermittency. In the case of subdiffusion diffusion dominates. When superdiffusion occurs, it dominates diffusive transport.

NASA’s Chandra X‐Ray Observatory was launched in July of 1999. Featuring a 1000 cm2‐class X‐ray telescope with sub‐arcsecond angular resolution, the Observatory has observed targets from the solar system including the Earth’s moon, comets, and planets to the most distant galaxy clusters and active galactic nuclei. Capable of performing moderate energy resolution image‐resolved spectroscopy using its CCD detectors, and high‐resolution grating spectroscopy, the Observatory has produced, and continues to produce, valuable data and insights into the emission mechanisms of the ionized plasmas in which the X‐rays originate. We present an overview admittedly brief of the Observatory to provide insight as to how to use it for your investigations. We also present an, admittedly brief and biased, of some of the results of investigations performed with Chandra that may be of interest to this audience.

Particle scattering in pure magnetic turbulence is investigated by combining the Newton‐Lorentz equation with the well‐established nonlinear guiding center theory. Cross field diffusion coefficients are calculated as well as certain limits in particle energy and turbulence strength. In addition to the well‐known nonlinear results we find a new contribution which describes particle scattering away from a single field line. In particular, perpendicular diffusion can be described as a superposition of scattering due to wandering magnetic field lines and scattering away from a single field line. As an example, the new results are used to calculate the maximum energy of protons accelerated at perpendicular interplanetary shock waves driven by a coronal mass ejection.

The dynamical equations for a partially ionized plasma are a matter of some recent controversy. Understanding this problem is important in understanding the interaction of the interstellar medium with the heliosphere and for understanding the spectrum of interstellar turbulence. If collision scales are much smaller than the internal interaction scales such as the ion gyroradius, the fluid approximation may be used. The analysis then must deal with at least three fluids (protons, electrons, and neutrals) which are coupled to each other by collisions and/or electromagnetic fields. Often, the proton and electron gyro‐radii are much smaller than the collision length scales, so the electric and magnetic fields dominate the motions of the electrons and protons. In this case, the only important particle‐particle collisions are those of the electrons and protons with the neutral atoms. Since the three species have, in general, different velocities, it is not immediately clear which fluid velocity to use. This ambiguity in the choice of fluid velocity has led to recent confusion regarding the physics of partially ionized plasmas. If the neutrals have a significant fraction of the mass, working in the center‐of‐mass coordinate frame can result in dynamical equations that differ greatly from those of ideal MHD. This is because the magnetic field is not frozen into the frame moving at the center‐of‐mass velocity, which leads to additional effects on the magnetic field that can be difficult to understand intuitively. To the extent that the electron mass is negligible, the magnetic field is actually found to be frozen into the frame moving with the electron bulk velocity. If we then take U to be the bulk velocity of the proton fluid the resulting dynamical equations closely resemble those of ideal MHD with the exception of the Hall term in the induction equation. Similarly, the frequently used Cowling conductivity also depends on the choice of coordinate frame. These conclusions address directly the recent controversy regarding the interaction of the interstellar medium with the heliosphere and also impact our understanding of interstellar turbulence.

The combination of the Interstellar Boundary Explorer (IBEX) all‐sky maps of the energetic neutral atom fluxes with the Voyager in situ measurements gives us a unique opportunity to learn more about the physics governing the solar wind (SW) interaction with the local interstellar medium (LISM). Moreover, since the position of the ribbon of an enhanced ENA flux in the sky strongly depends on the LISM properties, we are able to constrain those by comparing numerical simulations with the IBEX observations. In this paper, we discuss the current status of the Huntsville model of the SW‐LISM interaction, compare numerical results with the IBEX and Voyager observations, and discuss the importance of taking into account time‐dependent phenomena, particularly the solar cycle effects.

Comets provide a wonderful laboratory for studying the ion pickup process. As a comet nears the Sun, neutral atoms and molecules sublime from the nucleus and from ice grains in the coma, providing an extended water‐rich region. Photoionisation and charge exchange provide a source of new pickup ions, which immediately interact with the electric and magnetic field in the surrounding plasma. The missions to comets Halley, Giacobini‐Zinner, Grigg‐Skjellerup and Borrelly provided a wealth of data on pickup ions and their interaction with plasma waves, including observations of ring and bispherical shell distributions and mass loading over significant regions of space. At comet Grigg‐Skjellerup, non‐gyrotropic pickup ions were also seen. Here, we review the observations and interpretation of pickup ions at comets, illustrating what was learned from the cometary missions and following the evolution of the ion distribution. We also discuss the international Rosetta mission which will orbit rendezvous with and the...

The relative motion of the Sun through the Local Interstellar Cloud (LIC) leads to a neutral wind through the heliosphere. Because of its high ionization potential, He remains neutral to well within 1 AU, where it is deflected by the Sun’s gravity and forms a focusing cone on the downwind side. This flow pattern has been studied with UV backscattering, through pickup ions (PUI), and atom imaging. A consolidated set of the physical parameters of He in the LIC has been derived combining all three methods. However, it is still poorly understood why PUI fluxes and velocity distributions vary substantially on temporal scales from hours to many days, which leads among other phenomena to apparent changes in the appearance of the focusing cone, even after averaging over several days. With the combination of PLASTIC on STEREO A and B as well as SWICS on ACE, simultaneous PUI observations over an increasing range of heliospheric longitudes have become possible, for which we have initiated a cross‐calibration effort...

A short survey of work done on the interaction of the interstellar medium with the solar wind in view of the Voyagers data and observations of the Interstellar Boundary Explorer (IBEX) is made. The paper reviews several heliospheric numerical models presented in the last decades. Some philosophical questions concerning current possibilities of modeling are raised, in particular, to what extent it is necessary to complicate models to reproduce the nature.

This paper outlines the present status of the kinetic theory of turbulence in magnetized plasmas as being developed by the present author. The systematic program to formulate the theory of turbulence starting from the Vlasov‐Klimontovich formalism began with the works by pioneers of modern plasma physics in the 1960s and 1970s. However, early efforts adopted the heuristic semi‐classical method instead of the statistical mechanical formulation, which is necessary for a quantitative analysis. Recently, the present author picked up where the early pioneers left, and began to reformulate the kinetic turbulence theory of turbulence in magnetized plasmas from statistical mechanical formalism. This paper is a brief outline of the progress to date.

The particle instrument CELIAS/HSTOF onboard SOHO is observing the energetic neutral atom (ENA) flux in the ecliptic plane since 1996. During quiet time periods, the ENA flux is well separated from the energetic ion flux, originating in the solar corona and/ or heliosphere. The instrument is capable to measure the energetic neutral hydrogen (ENH) and helium (ENHe) fluxes along the line‐of‐sight of the instrument field‐of‐view. We will discuss the neutral energetic flux measurements of hydrogen and helium in the 28 to 88 keV/n energy/mass range of CELIAS/HSTOF, focusing on the frequently increased fluxes from the tail direction of the heliosphere. Potential source regions might be co‐rotating interaction regions (CIRs) and the helium cone in the inner heliosphere, solar energetic particle events, accelerated pick‐up ions in the outer heliosphere and energetic neutral particles originating from the heliosheath region and beyond.

Ions created from the neutral comae of active comets are picked up by the solar wind and carried downstream to form induced magnetotails. These are observed remotely as comets’ ion or plasma tails. Here, we review the magnetic field structure of these tails, and summarize remote and in situ observations that have helped our understanding of them. Magnetometer measurements by spacecraft have confirmed the predicted two‐lobe magnetic field structure, but this is complicated by variations in the heliospheric magnetic field, HMF, local to the comet. The tails formed at comets close to the Sun appear to be surrounded by a region of the solar wind where the HMF has draped around the magnetotail structure itself. Candidate weakened shock structures on either side of magnetotail traversals indicate that the regions affected by an active comet’s presence often occupies a significant portion of the inner heliosphere.

Interstellar pickup ions, in scattering to isotropy, should generate waves in particular frequency ranges, but observations of such waves are very rare. To date, only proton‐generated waves at Ulysses have been reported, and only sporadically during times of quasi‐radial field. Here, we present two sets of wave observations. The first set are waves due to pickup H+ seen by the Ulysses spacecraft as part of a new study to gather and build a data base of observations that can better be questioned regarding the fundamental physics of wave generation by interstellar pickup ions. There we demonstrate that the waves may have small signatures in the power spectrum while showing strong evidence of wave‐particle dynamics in the polarization spectra. The second set is a spectral enhancement measured at the Voyager 2 spacecraft during 4.5 hours on DOY 7, 1979 at a heliocentric radial position of 4.5 AU. The large‐scale IMF was nearly radial, and the frequency range and polarization of the enhanced fluctuations are c...

Two of the most recent outer heliospheric kHz emissions detected by the University of Iowa plasma wave detector on Voyager 1 started at about 2004.64 and 2006.39, respectively. Large interplanetary shocks reached V1 and V2, which are near the heliospheric termination shock, at almost the same time that the two kHz radio emissions turned‐on. So, in fact, the arrivals of these large shocks near the heliospheric termination shock were coincident with the onset of these kHz emissions. These two large shocks were unusual in that they were the two strongest shocks in solar cycle 23 seen in the outer heliosphere at V2. They had developed maximum dynamic pressures ∼4–6 times the average solar wind dynamic pressure for periods >26 days by the time they reached V2.

We show realistic and time‐varying 3D MHD models of the outer heliosphere which satisfy both Voyager 1 (V1) and Voyager 2 (V2) observed crossing times of the termination shock (TS) simultaneously. The short‐term variations found are a) the TS position increases whenever a solar‐wind high‐ram pressure pulse collides with the TS, b) a large amplitude magneto‐sonic pulse is generated downstream of the TS when a solar‐wind high ram pressure pulse collides with the TS, c) the generated pulse propagates outward in the heliosheath and is reflected at the plasma sheet, and d) when the reflected pulse collides with the TS, the TS position decreases. We also present preliminary results of galactic cosmic rays (GCRs) trajectories as they respond to three‐dimensional global electric and magnetic fields in the outer heliosphere. This allows us to investigate (1) how GCRs cross the heliosphere and enter the inner heliosphere, and (2) their long‐term variation. Preliminary GCR distributions in the outer heliosphere are ...

In this paper we focus on hybrid simulations, which were performed in order to support data analysis and interpretation of Voyager data and most recent IBEX observations. Two‐dimensional multi‐species hybrid simulations for the termination shock have been performed in which we used almost realistic plasma parameters. In these simulations we included self‐consistently solar wind protons and pickup protons. We investigated the change of the turbulence around and at the shock front as well as spatial and temporal evolution of the solar wind proton distribution under the impact of pickup protons. The results of this study show that pickup ions have a significant impact. Pickup ions mediate the shock turbulence, ion reflection, thermalization, and also slow down incoming solar wind. Furthermore, these simulations also show that gyrating solar wind and pickup ions may be a significant source for Energetic Neutral Atoms (ENAs).

Studies of reconnection in the solar wind led by Gosling and collaborators have revealed surprising results that are posing serious challenges to current theoretical understanding of the reconnection process. These include presence of prolonged quasi‐steady reconnection, low magnetic shear angles, and no substantial particle acceleration. Here we put forth the conjecture that many of the solar wind exhaust events may be fossil sites. We explore the viability of this possibility using full particle simulations.

Through ejection from its southern hemisphere, Enceladus is a dominant source of neutral gas and dust in Saturn’s inner magnetosphere. The interaction of the corotating plasma with the gas and dust modifies the plasma environment around Enceladus. We use 3‐D hybrid (kinetic ions, fluid electrons) simulations to examine the effects of gas and dust on the nature of the interaction region and use Cassini observations to constrain their properties.