Table of contents

Preface

G P Zank

Editor, Proceedings of the 17th Annual International Astrophysics Conference, Center for Space Plasma and Aeronomic Research (CSPAR) and Department of Space Physics, University of Alabama in Huntsville, Huntsville AL 35805, USA

E-mail: garyp.zank@gmail.com

The 17th Annual International Astrophysics Conference was held at the La Posada de Santa Fe hotel, Santa Fe, New Mexico, USA from March 5 to 9, 2018. The meeting entitled, "Dissipative and Heating Processes in Collisionless Plasma: the Solar Corona, the Solar Wind, and the Interstellar Medium," addressed the theme of the transfer of energy from large-scales to small-scales, whether in the solar corona, the solar wind, or the interstellar medium. The topic is of critical importance in our understanding of the energetics and dynamics of collisionless plasma. The transfer of energy can take the form of turbulence in which the energy input at the largest scales is eventually transferred to very small or dissipative scales by some form of cascade mechanism, or from the generation of large compressible structures such as shock waves that dissipate energy on small scales associated with steepened structures, or from the energization of particles via a coupling of large- and small-scale processes, of which diffusive shock acceleration represents the best established example. The 17th AIAC explored these topics via a combination of invited 25 minute talks and a few 40 minute plenary talks. Of particular relevance to the meeting was the just-launched Parker Solar Probe and Solar Orbiter missions.

The 17th AIAC also celebrate Prof. Len Fisk's 75th birthday and his over 50 years engagement in space physics. Len has been one of our most important leaders intellectually, academically, administratively, and politically, and this represented an opportunity to celebrate Len's accomplishments with some selected plenary presentations. Len has written an engaging, entertaining, and informative overview of his life in science, with a good deal of useful advice to young and old alike.

Finally, we would like to thank Adele Corona and ICNS for her continued excellent organization of the AIAC meetings and her help in providing the logistical support for this volume of papers.

All papers published in this volume of Journal of Physics: Conference Series have been peer reviewed through processes administered by the proceedings Editors. Reviews were conducted by expert referees to the professional and scientific standards expected of a proceedings journal published by IOP Publishing.

Adhikari et al [33] recently developed a theoretical model to study anisotropy in magnetic field fluctuations using a dimensional analysis relating the power spectrum of the energy-containing and inertial ranges. We use the Adhikari et al and Zank et al [31] models to study the evolution of the power anisotropy in magnetic field fluctuations in the energy-containing and inertial ranges at different levels of solar activity. We obtain initial conditions at 1 au for the times 2003, 2009, and 2015 from Zhao et al [37] by assuming an 80:20 ratio between the turbulence energies, and a 2:1 ratio between the correlation lengths. The years 2003 and 2015 correspond to solar maxima and the year 2009 to a solar minimum. We find that the anisotropy in magnetic field fluctuations evolves differently during the solar minimum than during the solar maximum throughout the heliosphere.

We present a 3D reduced magnetohydrodynamic (RMHD) model of reflection-driven Alfvén wave turbulence in an open magnetic field at the center of a coronal hole. The non-linear interactions between outward (dominant) and inward (minority) propagating waves generate turbulence. The RMHD equations describing the turbulence include the effects of solar wind outflow velocity on the dissipation of waves. The Alfvén wave turbulence results in the transfer of energy to small perpendicular scales ("direct cascade") or to larger scales ("inverse cascade"). We first show the result of our calculation for a model where there is smooth variation of plasma parameters such as Alfvén speed and density with height along the flux tube. However, this model does not produce the required energy to heat the plasma and accelerate the fast solar wind. Therefore, we introduce our second model, where we include additional density fluctuation along the open field. These density variations simulate the effects of compressive MHD waves in the solar wind. We find that these variations in density enhance the turbulence dissipation rates, and thereby increase the heating rate and the acceleration of the solar wind.

Recent studies have suggested that the tearing instability may play a significant role in magnetic turbulence. In this work we review the theory of the magnetohydrodynamic tearing instability in the general case of an arbitrary tearing parameter, which is relevant for applications in turbulence. We discuss a detailed derivation of the results for the standard Harris profile and accompany it by the derivation of the results for a lesser known sine-shaped profile. We devote special attention to the exact solution of the inner equation, which is the central result in the theory of tearing instability. We also briefly discuss the influence of shear flows on tearing instability in magnetic structures. Our presentation is self-contained; we expect it to be accessible to researchers in plasma turbulence who are not experts in magnetic reconnection.

Magnetic reconnection is a well-known source of electron and ion bulk heating, as well as energetic particles, in the solar system. Several authors have suggested that reconnection occurs at the heliopause. The paper's primary focus is to predict the amount of electron and ion bulk heating for heliopause reconnection, using the empirical relations of T. Phan and colleagues between the changes in electron and ion temperature and an Alfven speed V_A,asym,r. This Alfven speed depends on the strengths of the reconnecting magnetic fields and includes asymmetries in the magnetic fields and densities on the two inflowing sides of the reconnection region. For the undisturbed interstellar flow the predicted V_A,asym,r ≈ 25 km/s and the predicted changes in electron and ion temperature are ΔT_e1000 K and ΔT_i6000 K. These changes are relatively small and likely not important for dynamics at the heliopause. However, a plasma depletion layer (PDL) is predicted beyond the heliopause, analogous to the PDLs observed sunwards of the magnetopauses of Earth, Mercury, Jupiter, and Saturn. In the PDL, the interstellar (ISM) magnetic field lines drape over the heliopause. Plasma ions and electrons with relatively large parallel temperatures escape along the field, increasing the field strength, decreasing the plasma density, and increasing the Alfven speed. In the region of the PDL where these effects are strong, the expected field and density changes are a factor of 4 and 1/4, respectively, increasing V_A,asym,r by a factor close to 3 and the temperature changes by almost a factor of 10. Thus, heliopause reconnection in a strong PDL is predicted to increase the electron and ion temperatures by up to 10⁴ K and 8 × 10⁴ K, respectively, corresponding to changes by factors of order 1.5 and 11 compared to the predicted ISM temperature of ≈ 7500 K. Thus, the effects of bulk heating in heliopause reconnection regions will be most important for plasma inside or magnetically connected to the strong region of the heliopauses PDL. As an aside, Coulomb collisions appear too slow to relax the ion temperature anisotropies in the PDL beyond the heliopause, different than for the electrons.

Observations of the solar corona and the solar wind discover that the solar wind is unsteady and originates from the impulsive events near the surface of the Sun's atmosphere. How solar coronal activities affect the properties of the solar wind is a fundamental issue in heliophysics. We report a simulation and theoretical investigation of how nanoflare accelerated electron beams affect the kinetic-scale properties of the solar wind and generate coherent radio emission. We show that nanoflare-accelerated electron beams can trigger a nonlinear electron two stream instability, which generates kinetic Alfvén and whistler waves, as well as a non-Maxwellian electron velocity distribution function, consistent with observations of the solar wind. The plasma coherent emission produced in our model agrees well with the observations of Type III, J and V solar radio bursts. Open questions in the kinetic solar wind model are also discussed.

Small-scale magnetic flux ropes, which have similar magnetic field configuration as their large-scale counterparts (i.e., magnetic clouds), but with different sizes and origin, constitute an important element of solar wind structures. They are also considered to be associated with local particle energization and other related processes. In this report, we apply the Grad-Shafranov (GS) reconstruction method to detect these small-scale flux ropes with a set of quantitative criteria by utilizing data from the Ulysses spacecraft measurements for the first time. We conduct full range automatic detection for years 1994, 1996, 2004 and 2005 during the solar minimum periods. Based on solar wind speed/helio-latitude ranges, these periods are categorized into two groups: one with high solar wind speeds at high latitudes (1994 and 1996) and the other with low solar wind speeds at low latitudes (2004 and 2005). Through mainly statistical analysis of the results from these four years worth of Ulysses data, we have obtained the following findings: (1) Alfvénic structures occur more frequently at higher latitudes or in high speed solar wind (1994 and 1996). (2) Small-scale flux ropes at lower latitudes tend to align with the nominal Parker spiral direction. (3) The scale sizes of small-scale flux ropes are in the same range for different heliocentric distances. Both scale size and duration distributions seem to obey power laws, similar to the analysis results at 1 astronomical unit (AU). (4) The waiting time distribution (WTD) is fitted well by an exponential function rather than a power law. (5) The power law fitting is applied to the wall-to-wall time distribution with the break point at ∼ 200 min which is 3∼4 times the result at 1 AU.

Magnetic reconnection is generally accompanied by large and quasi-turbulent spatio-temporal fluctuations from the MHD scales down to the kinetic ones. The study of these turbulent fluctuations is generally based on the investigation of spectral and scaling features. In a recent paper by Consolini et al. [1] it has been shown how the statistics of geometrical invariants of coarse-grained gradient tensor of plasma velocity is able to provide valuable information on the topology of the turbulent structures. Here, we present a preliminary study of the topology of magnetic field structures at kinetic scales in the X-line/dissipation region of a reconnection event observed by MMS constellation [2]. The analysis evidenced vortex sheet Ohmic-dissipation.

Energetic storm particle (ESP) events are enhancements above ∼0.05 MeV/nucleon ions near 1 AU in association with the passage of an interplanetary (IP) coronal mass ejection (ICME). The primary candidate of producing these enhancements is diffusive shock acceleration (DSA). ESPs can produce significant increases in the near-Earth particulate radiation and pose severe hazards to astronauts and hardware in space. Physical parameters thought to affect ESP production include IP shock properties (e.g., speed, strength, obliquity) and conditions upstream of the propagating shock (e.g., seed population, ambient plasma conditions). Several theoretical and observational studies tried to relate ESP production to these drivers; however, reliable prediction of ESP properties (e.g. intensities, spectra, abundances), including their event-to-event variability, has so far proven elusive. This indicates an incomplete understanding of how ICME-driven IP shocks accelerate ESPs.

Using instruments onboard ACE, we investigate the relations between a large set of parameters (28) that characterize (i) ESP properties, (ii) IP shock and ICME properties, and (iii) the upstream and downstream conditions measured across the IP shock. Ee present a comprehensive correlation matrix between all parameters and those of the ESP properties, in an attempt to identify the dominant parameters that influence ESP production and variability. We find that within the selected dataset, (1) spectral and compositional relations strongly indicate a rigidity-dependent acceleration mechanism, (2) correlations between observations and DSA predictions are poor, (iii) ICME sheath temperature appears to play a role in determining the ESP peak intensities.

Magnetic flux ropes (or magnetic islands) are ubiquitous space plasma structures. Recent observations suggest that they are often associated with the acceleration of charged particles, but detailed acceleration mechanisms remain unclear. In this study, we present PIC simulations studying particle acceleration due to magnetic flux ropes. We consider a simple 2D configuration of two-magnetic-island coalescence. Some electrons and protons are found to be accelerated to more than 10 times their initial kinetic energies at the end of the simulation. We use a particle tracing technique on the high-energy particles to clarify the associated acceleration mechanisms. We find that reconnection electric field and Fermi-type acceleration due to magnetic island contraction can explain the particle energy gain, which is consistent with previous simulation studies. Our results also suggest that electrons are more responsive to the island contraction mechanism compared to ions. An effective island contraction rate is derived from the simulation data. Finally we briefly discuss a statistical description of particle acceleration associated with interacting magnetic flux ropes, and how it can be connected to simulations.

This paper is the story of what has motivated my approach to research throughout my career, and a statement of my belief that in order to maintain our scientific discipline as vibrant, dynamic and worth supporting, it is essential that we always seek and welcome new concepts and paradigm shifts.

Light from nearby stars becomes linearly polarized while traversing a dichroic interstellar medium. Polarization data which reveal heliosphere features are summarized. Polarizing dust grains trace a magnetic field direction consistent with the field affecting the warm breeze of secondary interstellar helium found by IBEX. Polarization data also trace the field direction that dominates the configuration of the IBEX ribbon of energetic neutral atoms (ENA). The polarizations that echo heliospheric features appear to arise from magnetically-aligned submicron interstellar dust grains that are excluded from the inner heliosphere by large charge-to-mass ratios, but, due to long collision times, retain their alignment with respect to the interstellar magnetic field draping over the heliosphere.

We present an extensive study of identifying small-scale magnetic flux ropes with duration between 9 and 361 minutes from Wind spacecraft in-situ measurements. The approach is based on the well-established Grad-Shafranov (GS) reconstruction method applicable to two-dimensional (2D) magnetohydrostatic structures. An automated computer algorithm is developed to sift through the time-series data covering two solar cycles, from 1996 to 2016. A large number of flux rope events is identified and an online database is built to accommodate the outcome from this detection algorithm. We provide detailed descriptions of the key steps of the GS-based detection algorithm and the general features of the online database. Selected preliminary statistical analyses are shown, which yield the following main results. (1) The occurrence of small-scale flux ropes has strong solar cycle dependency. (2) The small-scale magnetic flux ropes in the ecliptic plane tend to align along the Parker spiral direction. (3) Both the duration and scale size distributions of the small-scale magnetic flux ropes obey power laws. We show the similarities and discrepancies in their properties as compared with their large-scale counterparts, the magnetic clouds. We also discuss the implications on their origination mechanisms.

Voyager 1 crossed the termination shock at the end of 2004, more than a full solar cycle ago. Similarly, Voyager 2 crossed it and entered the heliosheath at the end of August, 2007, which was before the beginning of SC 24. Voyager 1 crossed the heliopause in August, 2012, when solar activity was high. Thus, at each spacecraft changing readings over time in the heliosheath could be due either to the increasing solar distance or to changing solar activity. Comparing energetic particle observations by the two spacecraft at corresponding distances shows cases for which distance is more important. In particular, at both spacecraft the spectral index of protons in the anomalous cosmic ray energy range shows corresponding variations with distance, despite the differing times and the great separation between the spacecraft, and so do ratios of electron count rates in differential energy bands. These comparisons provide insight into the expectation that Voyager 2 will soon cross the heliopause. Consideration of the large-scale spatial structure of moving flare-generated disturbances also provides insight into particle behaviour associated with the plasma wave events observed by Voyager 1 since it crossed the heliopause. We discuss a variety of observations of these phenomena from the heliosheath and the local interstellar medium and suggest a possibility for future simulations.

We present solar energetic particle events observed at 1 AU from the Sun for which the proton energy spectra at energies between ∼50 keV to ∼1 MeV flatten during a period of at least ∼12 hours prior to the passage of the associated interplanetary shock. The flattening of the proton energy spectra occurs when the source of the particles (presumably the traveling interplanetary shock) is still downwind from the spacecraft and particle intensities are still continuously increasing. The arrival of the shock at the spacecraft is then characterized by a steepening of the spectra, where low-energy proton intensities show a more pronounced enhancement than the high-energy proton intensities. We discuss the mechanisms that may result in this flattening of the spectra in terms of current models presented in the literature.

Our previous kinetic transport theoretical development for energetic particle acceleration by and large-scale transport through solar wind regions with numerous dynamic small-scale flux ropes in the strong guide/background field limit is further analyzed and extended. The basic flux-rope acceleration mechanisms and the issue of compressibility are further clarified by applying concepts such as magnetic curvature and shear flow to these structures. A set of new coupled focused-transport-MHD turbulence equations is presented for modeling coherent and stochastic energetic particle acceleration by small-scale flux ropes self-consistently. Furthermore, test particle coherent and stochastic acceleration rates are compared for the different flux-rope acceleration mechanisms, and stochastic acceleration and pitch-angle scattering rates for flux ropes and Alfvén waves are compared, for energetic protons at Earth.

We report on our recent studies of the local interstellar medium (LISM) using high-resolution ultraviolet spectra of nearby stars with the Space Telescope Imaging Spectrograph (STIS) instrument on the Hubble Space Telescope (HST). Our objective is to measure the physical properties, kinematics, and morphology of the LISM near the Sun. After describing our techniques, we call attention to the different direction and speed of the gas in the Local Interstellar Cloud (LIC) surrounding the Sun compared to the infall vector of neutral helium entering the heliosphere as measured by the Interstellar Boundary Explorer (IBEX) and Ulysses spacecraft. We then suggest possible explanations for the differences. We describe the cloud structure and gas properties along the lines of sight to 3 nearby exoplanet host stars. Finally, we determine the cloud structure and properties of the interstellar gas in the directions that the Voyager spacecraft are heading. In the trajectory of Voyager 2, there is no absorption from the LIC or the very close G cloud suggesting that the Sun may lie very close to the outer edge of the LIC or perhaps even outside of the LIC.

The paper reviews the new developments on the thermodynamic origin of kappa distributions and their generation in space plasmas. We present the correct formulation of kappa distributions that is consistent with thermodynamics. Then, we present the characterization of mechanisms that generate kappa distributions. There are three fundamental plasma conditions for the kappa distributions to be generated in space plasmas. Several applications of kappa distributions in space plasmas are presented and discussed. Finally, the thermodynamic validity of kappa distributions is presented. According to the zeroth law of thermodynamics, the most generalized form of particle distribution assigned with a temperature, is given by the kappa distributions, where temperature and kappa are two independent parameters spanning the 2-D abstract space of thermodynamics.

Voyager 1 has made in situ measurements of the very local interstellar medium (VLISM) since August 2012 and its magnetometer and plasma wave instrument have detected several VLISM shock waves. Interplanetary shocks propagate through the supersonic solar wind and then through the inner heliosheath after colliding with the heliospheric termination shock (HTS). Interplanetary shock waves are transmitted partially across the heliopause (HP) into the VLISM and partially reflected back into the inner heliosheath. Previous studies showed that the in situ VLISM shocks observed by Voyager 1 were very weak and remarkably broad and had properties different than shocks inside the heliosphere [1, 2]. We model the first VLISM shock observed by Voyager 1 and compare with observations. We calculate the collisionality of the thermal particles and the dissipation terms such as heat conduction and viscosity that are associated with Coulomb collisions in the VLISM. The VLISM is collisional with respect to the thermal plasma and the VLISM shock structure is determined by thermal proton-proton collisions, which is the dominant thermal collisional term. The VLISM shock is controlled by particle collisions and not mediated by PUIs since they do not introduce significant dissipation through the shock transition. As a result, we find that the extremely broadness of the weak VLISM shock is due to the thermal collisionality.

This paper provides the latest data from Voyager 2 on plasma characteristics in the heliosheath including the observations of pressure waves in the plasma and particle data. Models and observations show that solar transients drive pressure waves through the heliosphere. Pressure pulses that could drive heliosheath waves are observed near the previous solar maximum upstream of the termination shock. We show that the most recent data is consistent with the presence of pressure waves and compare the heliosheath waves with the pressure increases in the heliosheath. The magnetic field is better correlated with density and galactic cosmic ray intensities in the supersonic solar wind than in the heliosheath. The galactic cosmic rays are correlated with the plasma and particles with a ∼30-day lag in both the supersonic wind and heliosheath.

The observational implication of braided solar magnetic fields opens a new venue for an interpretation of various solar and interplanetary phenomena. Direct imaging of the coronal fields at frequencies corresponding to atomic transition of hot (∼1MK) plasma pinpoints to their braiding structure, while solar wind measurements of magnetized plasma parcels with distinct orientation, large field deviation and intermittent fading of energetic flare ions suggest that coronal braided field may have been carried by the solar wind to 1AU. The interconnection between the mathematical braids and knots is applied to the topologically non-trivial magnetized structures and their dynamics, from solar corona to the interplanetary medium. The analysis of braided magnetic configurations results in conjectures regarding (i) their stability under large oscillations of magnetic loops, (ii) the structure and stability of the coronal field through successive emergence/decay of heated magnetic braids, and (ii) their evolution into the solar wind. It is anticipated that the resulting conjectures will add to the understanding of the physical processes in the magnetosphere (Van Allen, Cluster satellites) and particularly will attain confirmation with the launch of the Parker Solar Probe.

Observations by the Interstellar Boundary Explorer (IBEX) have revealed the presence of the IBEX Ribbon, an almost circular band of increased ENA emissions that is believed to be centered on the direction of the interstellar magnetic field. IBEX measures a range of interstellar species including H, He, and O. IBEX has been able to distinguish primary He coming directly from the interstellar medium from secondary He that is created through neutralization of He⁺ atoms in the heliosheath. Together with the observations of Lyman-α radiation from SOHO/SWAN, which is resonantly absorbed and re-emitted from interstellar H atoms that move into the heliosphere, the directions of interstellar flow for each of the observed interstellar species (H, primary He, secondary He, and primary O) line-up along a symmetry plane — the interstellar B–V plane — that should contain the interstellar magnetic field direction (B) and the interstellar flow direction (V). The B–V plane also contains the center of the IBEX Ribbon, which supports the concept that the Ribbon center is close to the direction of the interstellar magnetic field. Further, the deflection of the various interstellar species along the B–V plane are consistent with the compression of the heliosheath by the interstellar magnetic field pressure. Lastly, the interstellar magnetic field in the outer heliosheath is directly observed by Voyager 1 (V1). The direction of the interstellar magnetic field observed by V1 is offset from the Ribbon center, consistent with draping around the heliopause, and time variations in the interstellar magnetic field are consistent with the effects of large-scale compression and rarefaction in the outer heliosheath. Thus, we summarize the array of observations that suggest a consistent direction of the interstellar magnetic field, and the effects of the interstellar magnetic field on the structure and time variations in the heliosheath.

The Local Interstellar Cloud (LIC) is the region of the interstellar medium (ISM) that surrounds and helps to shape the heliosphere. The LIC is part of a collection of nearby low density warm clouds known as the Complex of Local Interstellar Clouds (CLIC), all of which exist inside the hot Local Bubble. Observations of interstellar neutral He atoms flowing into the heliosphere by the IBEX mission and Voyager have constrained the temperature of the LIC to be roughly 7500 K. This temperature is consistent with that derived from absorption line measurements toward nearby stars. Such observations also indicate that the LIC is partially ionized with elemental abundances consistent with a moderate level of depletion onto dust grains as might occur for low density ISM that has been subject to a shock that partially destroyed the dust. The temperature of the cloud is not unusual for the warm ionized medium in the ISM, but it is less ionized than typical. We discuss the various processes that may be important for heating the LIC. We show that the only viable heat source for the ongoing heating of the CLIC is photoionization. Equilibrium models of the ionization and heating of the LIC allow for solutions that match the observations, but the likely origins of the local interstellar medium suggest that the situation is more complex. We propose an evolution scenario in which the clouds were formerly cold and were heated by shocks to reach their current warm state. We present new magneto-hydrodynamical calculations of the evolution of the local ISM. Multiple supernova models can match the parameters of the Local Bubble and heat the cold clouds as desired, though the many constraints on the clouds and bubble have yet to be fully satisfied by the models.

We collect and review the conclusions of several recent papers that address the transport of energy within the inertial range of interplanetary turbulence at 1AU. Techniques have been developed that provide a means of measuring energy transport within the spectrum that do not rely on an assumption of specific dynamics other than the adoption of the complete single-fluid, incompressible magnetohydrodynamic equations. These techniques lead to expressions that do not depend on the form of the power spectrum other than requiring scale separation such that there exists an inertial range where the dynamics are energy conserving. We compute the correlation function for the derived expressions and find that the dynamics of turbulent transport decorrelate on the scale size of interest. We also show that the rate of energy transport at any given scale and any given time or location can be either positive or negative and that the typical rate of energy transport is ∼ 10× the average rate. It is the average rate that agrees well with the computed rate of thermal proton heating in the solar wind. This leads to a model of the turbulence where local transport is stronger than normally considered.

Solar coronal jets have been observed in detail since the early 1990s. While it is clear that these jets are magnetically driven, the details of the driving process has recently been updated. Previously it was suspected that the jets were a consequence of magnetic flux emergence interacting with ambient coronal field. New evidence however indicates that often the direct driver of the jets is erupting field, often carrying cool material (a "minifilament"), that undergoes interchange magnetic reconnection with preexisting field ([1]). More recent work indicates that the trigger for eruption of the minifilament is frequently cancelation of photospheric magnetic fields at the base of the minifilament. These erupting minifilaments are analogous to the better-known larger-scale filament eruptions that produce solar flares and, frequently, coronal mass ejections (CMEs). A subset of coronal jets drive narrow "white-light jets," which are very narrow CME-like features, and apparently a few jets can drive wider, although relatively weak, "streamer-puff" CMEs. Here we summarize these recent findings.

The electron distribution function (eVDF) in the solar wind deviates significantly from an equilibrium Maxwellian distribution, and is comprised of a Maxwellian core, a suprathermal halo, a field-aligned component strahl, and a higher energy superhalo. Charged particle Coulomb collisions are ineffective in relaxing such a velocity distribution beyond a few solar radii. Therefore wave-particle interactions need to be considered. A wave-particle interaction term was introduced into the kinetic equation that describes the interaction of electrons with whistler waves, as well as particle collision terms. The kinetic equation has the form of an advection-diffusion-like equation in which the advection and diffusion coefficients describe the scattering and drag of electrons in whistler turbulence. A reliable numerical method has been developed to solve a full form of the advection-diffusion-like kinetic equation. Preliminary applications of the numerical method to the solar wind electron problem are presented. Comparison and analysis of the electron VDFs in the presence of Coulomb collisons and resonant wave-partcicle interactions are made.

Solar type III radio bursts are the fast drifting radio emissions excited by the flare accelerated electron beams in the corona and interplanetary medium. In this paper, we report the observations of several nonlinear processes, obtained by the time domain sampler (TDS) of the WAVES experiment of the STEREO spacecraft in the source region of one of these bursts. These include: (1) a four wave-wave interaction process called the oscillating two stream instability (OTSI) $L+L\mathop{\to }\limits^{S}{L}_{U}+{L}_{D}$, where L is the beam excited Langmuir wave, S is the ion sound wave, and L_U and L_D are the up- and down-shifted Langmuir waves, respectively, and (2) two wave-wave merging processes L_U + L_D → T_2fpe and L + T_2fpe → T_3fpe, where T_2fpe and T_3fpe are the electromagnetic waves at the second and third harmonic of the electron plasma frequency, f_pe and L can be either a beam-excited Langmuir wave, or an up- or down-shifted sideband. The newly developed higher order spectral (HOS) techniques have been used to identify the signatures of these wave-wave interactions in the waveform data. The implication of these findings is that strong Langmuir turbulence processes play key roles in excitation of solar type III radio bursts, especially, in the beam stabilization and conversion of Langmuir waves into electromagnetic waves at the fundamental and higher harmonics of the electron plasma frequency, f_pe.

The active region corona is believed to be heated by magnetic disturbances that propagate into the corona from the convection zone below. A reduced magnetohydrodynamic (MHD) model of Alfvén waves in a coronal loop is presented. The waves are launched in the photosphere from a collection of kilogauss flux tubes, and they reflect at various positions along the loop, leading to counter-propagating waves and turbulence. It is found that turbulent Alfvén waves can produce only enough heat to maintain a peak temperature of about 2.5 MK, less than the temperatures typically observed in active regions (∼ 4 MK). We consider an alternative model in which the flux tubes are subject to slow random footpoint motions, but we find that such braiding motions produce less heating than the waves inside the flux tubes. Therefore, models of coronal heating based on small-scale random footpoint motions cannot readily explain the observed high temperatures loops; more energetic "nanoflare" heating events are required. We suggest that such strong heating events may be produced by disturbances associated with flux emergence and large-scale non-potential fields.

Very recent measurements of stellar winds are used to update relations between winds and coronal activity. New wind constraints include an upper limit of < 0.1 _⊙ for τ Ceti (G8 V), derived from a nondetection of astrospheric H I Lyman-α absorption. This upper limit is reported here for the first time, and represents the weakest wind constrained using the astrospheric absorption technique. A high mass loss rate measurement of = 10 _⊙ for δ Pav (G8 IV) from astrospheric Lyman-α absorption suggests stronger winds for subgiants than for main sequence stars of equivalent activity. A very low mass-loss rate of ≈ 0.06 _⊙ recently estimated for GJ 436 (M3 V) from Lyman-α absorption from an evaporating exoplanetary atmosphere implies inactive M dwarfs may have weak winds compared with GK dwarfs of similar activity.

We use OMNI 1-minute resolution data sets from 1995 through 2017, covering about two consecutive solar cycles, to investigate the solar cycle dependence of various turbulence quantities and cosmic ray (CR) mean free paths. We employ quasi-linear theory (QLT) and nonlinear guiding center theory (NLGC) to evaluate the CR parallel and perpendicular diffusion. We find that in the ecliptic plane at 1 au (1) the fluctuating magnetic energy density ⟨z^±2⟩, residual energy E_D, and corresponding correlation functions all have an obvious solar cycle dependence. The residual energy E_D is always negative, which indicates that the energy in magnetic fluctuations is larger than the energy in kinetic fluctuations, especially at solar maximum; (2) the correlation length λ for magnetic fluctuations does not show significant solar cycle variation; (3) the temporally varying shear source of turbulence, which is most important in the inner heliosphere, depends on the solar cycle; and (4) high level turbulence will increase CR perpendicular diffusion and decrease CR parallel diffusion, but this trend can be masked if the background interplanetary magnetic field (IMF) changes in concert with turbulence in response to solar activity. These results provide quantitative inputs for both turbulence transport models and CR diffusion coefficient models.