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GpsB links peptidoglycan synthases to other proteins that determine the shape of the respiratory pathogenStreptococcus pneumoniae(pneumococcus;Spn) and other low-GC Gram-positive bacteria. GpsB is also required for phosphorylation of proteins by the essential StkP(Spn) Ser/Thr protein kinase. Here we report three classes of frequently arising chromosomal duplications (≈21-176 genes) containingmurZ(MurZ-family homolog of MurA) ormurAthat suppress ΔgpsBor ΔstkP. These duplications arose from three different repeated sequences and demonstrate the facility of pneumococcus to modulate gene dosage of numerous genes. Overproduction of MurZ or MurA alone or overexpression of MurZ caused by ΔkhpABmutations suppressed ΔgpsBor ΔstkPphenotypes to varying extents. ΔgpsBand ΔstkPwere also suppressed by MurZ amino-acid changes distant from the active site, including one in commonly studied laboratory strains, and by truncation or deletion of the homolog of IreB(ReoM). Unlike in other Gram-positive bacteria, MurZ is predominant to MurA in pneumococcal cells. However, ΔgpsBand ΔstkPwere not suppressed by ΔclpCP, which did not alter MurZ or MurA amounts. These results support a model in which regulation of MurZ and MurA activity, likely by IreB(Spn), is the only essential requirement for protein phosphorylation in exponentially growing D39 pneumococcal cells.

The heliopause is a boundary that separates the heliosheath (which contains magnetic fields and plasmas that originate in the Sun) from the interstellar medium (which contains magnetic fields and particles of stellar/interstellar origin). Observations of the heliopause were first made by the particles and fields instruments on the Voyager 1 spacecraft, moving radially in the northern hemisphere, which crossed the heliopause on 25 August 2012 at a distance of 121.6 au. We show using observations of the magnetic field and energetic particles that Voyager 2 crossed the heliopause in the southern hemisphere on 5 November 2018 at a distance of ≈119.0 au. Voyager 2 observed a much thinner and simpler heliopause than Voyager 1 as well as stronger interstellar magnetic fields, and it discovered a ‘magnetic barrier’ in the heliosheath adjacent to the heliopause that strongly influences the entry of cosmic rays into the heliosphere. The magnetic field direction observed by Voyager 2 changed smoothly from the time of arrival at the magnetic barrier, through it, and onwards into the interstellar medium, with a small (a few degrees) or no change across the heliopause. These observations, together with the Voyager 1 observations and existing models, show that the magnetic barrier, the heliopause and the neighbouring very local interstellar medium form a complex interconnected dynamical system. This paper reports measurements of the magnetic fields and energetic particles detected by the Voyager 2 spacecraft as it passed from the heliosphere, through the heliosheath and heliopause, to the interstellar medium. As predicted by models, Voyager 2 encountered a ‘magnetic barrier’ before reaching the heliopause.

The solar wind non-radial velocity components observed beyond the Alfvén point are usually attributed to waves, the interaction of different streams, or other transient phenomena. However, Earth-orbiting spacecraft as well as monitors at L1 indicate systematic deviations of the wind velocity from the radial direction. Since these deviations are of the order of several degrees, the calibration of the instruments is often questioned. This paper investigates for the first time the evolution of non-radial components of the solar wind flow along the path from ≈ 0.17 to 10 AU. A comparison of observations at 1 AU with those closer to or farther from the Sun based on measurements of many spacecraft at different locations in the heliosphere (Parker Solar Probe, Helios 1 and 2, Wind, ACE, Spektr-R, ARTEMIS probes, MAVEN, Voyagers 1and 2) shows that (i) the average values of non-radial components are not zero and vary in a systematic manner with the distance from the Sun, (ii) their values significantly depend on the solar wind radial velocity, (iii) the deviation from radial direction well correlates with the cross-helicity, and (iv) the values of non-radial components peaks at 0.25 AU and gradually decreases toward zero in the outer heliosphere. Our results suggest that the difference in the propagation direction between the faster and slower winds is already established in the solar corona and is connected with the forces emitting solar wind plasma from the coronal magnetic field. The correlation with cross-helicity probably points to outward propagating Alfven waves generated in outer corona as the most probable source of observed deviations.

We present anisotropy results for anomalous cosmic-ray (ACR) protons in the energy range $\sim$0.5-35 MeV from Cosmic Ray Subsytem (CRS) data collected during calibration roll maneuvers for the magnetometer instrument when Voyager 2 (V2) was in the inner heliosheath. We use a new technique to derive for the first time the radial component of the anisotropy vector from CRS data. We find that the CRS-derived radial solar wind speeds, when converted from the radial components of the anisotropy vectors via the Compton-Getting (C-G) effect, generally agree with those similarly-derived speeds from the Low-Energy Charged Particle experiment using 28-43 keV data. However, they often differ significantly from the radial solar wind speeds measured directly by the Plasma Science (PLS) instrument. There are both periods when the C-G-derived radial solar wind speeds are significantly higher than those measured by PLS and times when they are significantly lower. The differences are not expected nor explained, but it appears that after a few years in the heliosheath the V2 radial solar wind speeds derived from the C-G method underestimate the true speeds as the spacecraft approaches the heliopause. We discuss the implications of this observation for the stagnation region reported along the Voyager 1 trajectory as it approached the heliopause inferred using the C-G method.

Energetic neutral atom (ENA) models typically require post-processing routines to convert the distributions of plasma and H atoms into ENA maps. Here we investigate how two different kinetic-MHD models of the heliosphere (the BU and Moscow models) manifest in modeled ENA maps using the same prescription and how they compare with Interstellar Boundary Explorer (IBEX) observations. Both MHD models treat the solar wind as a single-ion plasma for protons, which include thermal solar wind ions, pick-up ions (PUIs), and electrons. Our ENA prescription partitions the plasma into three distinct ion populations (thermal solar wind, PUIs transmitted and ones energized at the termination shock) and models the populations with Maxwellian distributions. Both kinetic-MHD heliospheric models produce a heliotail with heliosheath plasma organized by the solar magnetic field into two distinct north and south columns that become lobes of high mass flux flowing down the heliotail, though in the BU model the ISM flows between the two lobes at distances in the heliotail larger than 300 AU. While our prescription produces similar ENA maps for the two different plasma and H atom solutions at the IBEX-Hi energy range (0.5 - 6 keV), the modeled ENA maps require a scaling factor of ~2 to be in agreement with the data. This problem is present in other ENA models with the Maxwellian approximation of multiple ion species and indicates that a higher neutral density or some acceleration of PUIs in the heliosheath is required., Comment: 29 pages, 3 tables, 9 figures, accepted to ApJ

Posttranscriptional gene regulation often involves RNA-binding proteins that modulate mRNA translation and/or stability either directly through protein-RNA interactions or indirectly by facilitating the annealing of small regulatory RNAs (sRNAs). The human pathogen Streptococcus pneumoniae D39 (pneumococcus) does not encode homologs to RNA-binding proteins known to be involved in promoting sRNA stability and function, such as Hfq or ProQ, even though it contains genes for at least 112 sRNAs. However, the pneumococcal genome contains genes for other RNA-binding proteins, including at least six S1 domain proteins: ribosomal protein S1 (rpsA), polynucleotide phosphorylase (pnpA), RNase R (rnr), and three proteins with unknown functions. Here, we characterize the function of one of these conserved, yet uncharacterized, S1 domain proteins, SPD_1366, which we have renamed CvfD (conserved virulence factor D), since loss of the protein results in attenuation of virulence in a murine pneumonia model. We report that deletion of cvfD impacts the expression of 144 transcripts, including the pst1 operon, encoding phosphate transport system 1 in S. pneumoniae. We further show that CvfD posttranscriptionally regulates the PhoU2 master regulator of the pneumococcal dual-phosphate transport system by binding phoU2 mRNA and impacting PhoU2 translation. CvfD not only controls expression of phosphate transporter genes but also functions as a pleiotropic regulator that impacts cold sensitivity and the expression of sRNAs and genes involved in diverse cellular functions, including manganese uptake and zinc efflux. Together, our data show that CvfD exerts a broad impact on pneumococcal physiology and virulence, partly by posttranscriptional gene regulation. IMPORTANCE Recent advances have led to the identification of numerous sRNAs in the major human respiratory pathogen S. pneumoniae. However, little is known about the functions of most sRNAs or RNA-binding proteins involved in RNA biology in pneumococcus. In this paper, we characterize the phenotypes and one target of the S1 domain RNA-binding protein CvfD, a homolog of general stress protein 13 identified, but not extensively characterized, in other Firmicutes species. Pneumococcal CvfD is a broadly pleiotropic regulator, whose absence results in misregulation of divalent cation homeostasis, reduced translation of the PhoU2 master regulator of phosphate uptake, altered metabolism and sRNA amounts, cold sensitivity, and attenuation of virulence. These findings underscore the critical roles of RNA biology in pneumococcal physiology and virulence.

Post-transcriptional gene regulation often involves RNA-binding proteins that modulate mRNA translation and/or stability either directly through protein-RNA interactions or indirectly by facilitating the annealing of small regulatory RNAs (sRNAs). The human pathogenStreptococcus pneumoniaeD39 (pneumococcus) does not encode homologs to RNA-binding proteins known to be involved in promoting sRNA stability and function, such as Hfq or ProQ, even though it contains genes for at least 112 sRNAs. However, the pneumococcal genome contains genes for other RNA-binding proteins, including at least six S1-domain proteins; ribosomal protein S1 (rpsA), polynucleotide phosphorylase(pnpA), RNase R (rnr), and three proteins of unknown functions. Here, we characterize the function of one of these conserved, yet uncharacterized S1-domain proteins, SPD_1366, which we have renamed CvfD (ConservedvirulencefactorD), since loss of this protein results in an attenuation of virulence in a murine pneumonia model. We report that deletion ofcvfDimpacts expression of 144 transcripts including thepst1operon, encoding the phosphate transport system 1 inS. pneumoniae. We further show that CvfD post-transcriptionally regulates the PhoU2 master regulator of the pneumococcal dual phosphate transport system by bindingphoU2mRNA and impacting PhoU2 translation. CvfD not only controls expression of phosphate transporter genes, but also functions as a pleiotropic regulator that impacts cold sensitivity and the expression of sRNAs and genes involved in diverse cellular functions, including manganese uptake and zinc efflux. Together, our data show that CvfD exerts a broad impact on pneumococcal physiology and virulence, partly by post-transcriptional gene regulation.SIGNIFICANCERecent advances have led to the identification of numerous sRNAs in the major human respiratory pathogen,S. pneumoniae. However, little is known about the functions of most sRNAs or RNA-binding proteins involved in RNA biology in pneumococcus. In this paper, we characterize the phenotypes and one target of the S1-domain RNA-binding protein CvfD, a homolog of “general-stress protein 13” identified, but not extensively characterized in otherFirmicutespecies. Pneumococcal CvfD is a broadly pleiotropic regulator, whose absence results in misregulation of divalent cation homeostasis, reduced translation of the PhoU2 master regulator of phosphate uptake, altered metabolism and sRNA amounts, cold sensitivity, and attenuation of virulence. These findings underscore the critical roles of RNA biology in pneumococcal physiology and virulence.

The solar wind aberration due to non-radial velocity components and the Earth orbital motion is important for the overall magnetosphere geometry because the magnetospheric tail is aligned with the solar wind flow. This paper investigates an evolution of non-radial components of the solar wind flow along the path from the Sun to 6 AU. A comparison of observations at 1 AU and closer to or further from the Sun based on measurements of many spacecraft at different locations in the heliosphere (Wind, ACE, Spektr-R, THEMIS B and C, Helios 1 and 2, Mars-Express, Voyager 1 and 2) shows that (i) the average values of non-radial components vary with the distance from the Sun and (ii) they differ according to solar wind streams.

The heliosheath (HSH) radial speeds at Voyager 2 (V2) derived from the plasma instrument (PLS) and from particle instruments using the Compton–Getting (CG) effect are different. At V2 the CG speeds are more variable than the plasma speeds and decrease about 2 yr before the heliopause. We use magnetic flux conservation to differentiate between these two speed profiles at V2, comparing the magnetic flux observed at 1 au and in the HSH. For V2 the PLS speed profile is significantly more consistent with magnetic flux conservation than the CG speeds. For Voyager 1 (V1), we present new V_R derivations from the Cosmic Ray Subsystem (CRS) using the CG method that agree reasonably well with those previously obtained from the low energy charged particle (LECP) instrument. If we use the V2 PLS speed profile to calculate the magnetic flux at V1, we again find much better agreement than if we use the V1 CG speeds. These results suggest that the radial speeds derived from particle anisotropy observations in the HSH are not reliable.

Voyager 2 observations throughout the heliosheath from the termination shock to the heliopause are used to normalize and constrain model pickup ion (PUI) fluxes. Integrating normalized PUI fluxes along the Voyager 2 trajectory through the heliosheath, and combining these integral fluxes with the energy-dependent charge-exchange cross section and the neutral hydrogen density, produces semi-empirical estimates of the energetic neutral atom (ENA) fluxes from the heliosheath. These estimated ENA fluxes are compared with observed ENA fluxes from the Interstellar Boundary Explorer (IBEX) to determine what percentage of the observed fluxes at each IBEX energy are from the heliosheath. These percentages are a maximum of ∼10% for most energies and depend strongly on termination shock properties, plasma density, bulk plasma flow characteristics, the shape of the heliopause, and turbulent energy diffusion in the heliosheath.

We discuss observations of the journey throughout the Solar System of a large interplanetary coronal mass ejection (ICME) that was ejected at the Sun on 14 October 2014. The ICME hit Mars on 17 October, as observed by the Mars Express, MAVEN, Mars Odyssey and MSL missions, 44 hours before the encounter of the planet with the Siding-Spring comet, for which the space weather context is provided. It reached comet 67P/Churyumov-Gerasimenko, which was perfectly aligned with the Sun and Mars at 3.1 AU, as observed by Rosetta on 22 October. The ICME was also detected by STEREO-A on 16 October at 1 AU, and by Cassini in the solar wind around Saturn on the 12 November at 9.9 AU. Fortuitously, the New Horizons spacecraft was also aligned with the direction of the ICME at 31.6 AU. We investigate whether this ICME has a non-ambiguous signature at New Horizons. A potential detection of this ICME by Voyager-2 at 110-111 AU is also discussed. The multi-spacecraft observations allow the derivation of certain properties of the ICME, such as its large angular extension of at least 116°, its speed as a function of distance, and its magnetic field structure at four locations from 1 to 10 AU. Observations of the speed data allow two different solar wind propagation models to be validated. Finally, we compare the Forbush decreases (transient decreases followed by gradual recoveries in the galactic cosmic ray intensity) due to the passage of this ICME at Mars, comet 67P and Saturn.

The Voyagers 1 and 2 spacecraft flew by Jupiter in March and July of 1979, respectively. The Plasma Science instrument (PLS) acquired detailed measurements of the plasma environment in the equatorial region of the magnetosphere between 4.9 and 4 RJ. While bulk plasma properties such as charge density, ion temperature, and bulk flow were reasonably well determined, the ion composition was only well constrained in occasional regions of cold plasma. The ion data obtained by the PLS instrument have been reanalyzed using physical chemistry models to constrain the composition and reduce the number of free parameters, particularly in regions of hotter plasma. This paper describes the method used for fitting the plasma data and presents the results versus time. Two companion papers describe the composition of heavy ions and present analysis of protons plus other minor ions.

The prediction of a supersonic solar wind1 was first confirmed by spacecraft near Earth2,3 and later by spacecraft at heliocentric distances as small as 62 solar radii4. These missions showed that plasma accelerates as it emerges from the corona, aided by unidentified processes that transport energy outwards from the Sun before depositing it in the wind. Alfvenic fluctuations are a promising candidate for such a process because they are seen in the corona and solar wind and contain considerable energy5–7. Magnetic tension forces the corona to co-rotate with the Sun, but any residual rotation far from the Sun reported until now has been much smaller than the amplitude of waves and deflections from interacting wind streams8. Here we report observations of solar-wind plasma at heliocentric distances of about 35 solar radii9–11, well within the distance at which stream interactions become important. We find that Alfven waves organize into structured velocity spikes with duration of up to minutes, which are associated with propagating S-like bends in the magnetic-field lines. We detect an increasing rotational component to the flow velocity of the solar wind around the Sun, peaking at 35 to 50 kilometres per second—considerably above the amplitude of the waves. These flows exceed classical velocity predictions of a few kilometres per second, challenging models of circulation in the corona and calling into question our understanding of how stars lose angular momentum and spin down as they age12–14. Data collected by the Parker Solar Probe in the solar corona are used to determine the organization of Alfven waves, revealing an increasing flow velocity peaking at 35–50 km s−1.

In mid-2012, a GMIR observed by Voyager 2 crossed through the heliosheath and collided with the heliopause, generating a pressure pulse that propagated into the very local interstellar medium. The effects of the transmitted wave were seen by Voyager 1 just 93 days after its own heliopause crossing. The passage of the transient was accompanied by long-lasting decreases in galactic cosmic ray intensities that occurred from ~2012.55 to ~2013.35 and ~2012.91 to ~2013.70 at Voyager 2 and Voyager 1, respectively. Omnidirectional (>20 MeV) proton-dominated measurements from each spacecraft's Cosmic Ray Subsystem reveal a remarkable similarity between these causally-related events, with a correlation coefficient of 91.2% and a time-lag of 130 days. Knowing the locations of the two spacecraft, we use the observed time-delay to calculate the GMIR's average speed through the heliosheath (inside the heliopause) as a function of temperature in the very local interstellar medium. This, combined with particle, field, and plasma observations enables us to infer previously unmeasured properties of the heliosheath, including a range of sound speeds and total effective pressures. For a nominal temperature of ~20,000 K just outside the heliopause, we find a sound speed of 314 (+/-) 32 km/s and total effective pressure of 267 (+/-) 55 fPa inside the heliopause. We compare these results with the Interstellar Boundary Explorer's data-driven models of heliosheath pressures derived from energetic neutral atom fluxes (the globally distributed flux) and present them as additional evidence that the heliosheath's dynamics are driven by suprathermal energetic processes.

We have analyzed data collected from the Cosmic Ray Subsystem instrument (Stone et al., 1977) on the Voyager 2 (V2) spacecraft during calibration manuevers for the magnetic field instrument while the spacecraft was located in the inner heliosheath of the heliosphere. We find that there is a diffusive anisotropy in the intensity of ~0.5-35 MeV particles (mostly protons) that indicates that there exists a diffusive flow of these particles from the flank or tail of the heliosphere towards the nose and is slightly equatorward as well. This work is consistent with the findings of an earlier, similar, but more restricted study (Stone et al., 2017). Depending on which part of the energy range is the main contributor to the observed diffusive anisotropy, these results may indicate that the acceleration site of anomalous cosmic rays is back towards the flank or tail of the solar wind termination shock.

The understanding of inertial-scale dynamics in the heliosheath is not yet thorough. Magnetic field fluctuations across the inner heliosheath (IHS) and the local interstellar medium (LISM) are here considered to provide accurate and highly resolved statistics over different plasma conditions between 88 and 136 au. By using the unique in situ 48 s measurements from the Voyager Interstellar Mission, we investigate different fluctuation regimes at the magnetohydrodynamic (MHD) scales, down to the MHD-to-kinetic transition. We focus on a range of scales exceeding five frequency decades (5 x 10-8 < f < 10-2 Hz), which is unprecedented in literature analysis. A set of magnetic field data for eight intervals in the IHS, in both unipolar and sector regions, and four intervals in the LISM is used for the analysis. Results are set forth in terms of the power spectral density, spectral compressibility, structure functions, and intermittency of magnetic field increments. In the heliosheath, we identify the energy-injection regime displaying a ~1/f energy decay, and the inertial-cascade regime. Here, the power spectrum is anisotropic and dominated by compressive modes, with intermittency that can reach kurtosis values of up to 10. In the interstellar medium the structure of turbulence is anisotropic as well, with transverse fluctuations clearly prevailing after 2015 May. Here, we show that intermittent features occur only at scales smaller than 10-6 Hz., 32 pages, 12 figures

We estimate the intensity of interstellar pickup protons accelerated to ∼50 keV at various locations along the solar-wind termination shock, using two-dimensional hybrid simulations. Parameters for the solar wind, interstellar pickup ions (PUIs), and magnetic field just upstream of the termination shock at one flank of the heliosphere, and at the location in the downwind (or tail-ward) direction are based on a solar-wind/pickup-ion/turbulence model. The parameters upstream of the shock where Voyager 2 crossed are based on observations. The simulation is limited in size, and therefore cannot accurately model the distribution to energies much beyond ∼50 keV. This is sufficient to study the origin of the high-energy tail of the distribution, which is the low-energy portion of the anomalous cosmic-ray spectrum. We also extrapolate our results to other locations along the termination shock, such as the other flank, and the poles of the heliosphere. We find that the intensity of ∼10–50 keV accelerated pickup protons is remarkably similar at all three locations we simulated, suggesting that particles in this energy range are relatively uniformly distributed along the termination shock, and are likely quite uniform throughout the entire heliosheath. In addition, we find significant differences in the distribution in the 0.5–1 keV energy range for energetic neutral atoms coming from the tail region of the heliosphere compared to that at the nose or flank look directions. This is because the peak in the PUI distribution is at a higher energy there.

We present observations of the magnetic field in the outermost region of the heliosheath made by Voyager 2 (V2) from 2016 to 2018.6, just before V2 entered the magnetic barrier inside of the heliopause. The average magnetic field strength (B) during this interval was relatively large, 0.135 nT, mainly due to numerous merged interaction regions. Sector structure was observed, and the direction of azimuthal angle λ was primarily close to the Parker spiral magnetic field directions 90° and 270°. Thus, the heliospheric current sheet extended to relatively high southern latitudes poleward of V2 (>30°). On smaller scales, distributions of daily increments in B and the components of from 2016 to 2018.6 were accurately described by q-Gaussian distributions. The average values of the nonextensivity parameter q for one-day increments of the components decreased from q = 1.7 ± 0.01 during 2016 (near solar maximum) to q = 1.3 ± 0.1 during 2017 and 2018, as solar activity declined. The BT direction was close to the average magnetic field direction, and V2 measured primarily compressible fluctuations. These new results are also presented in the context of an overview of the observations of the magnetic field in the heliosheath from the termination shock crossing to the heliopause.

We report a unique combination of ~10 eV to ~344 MeV in situ ion measurements from the Plasma Science (PLS), Low Energy Charged Particle (LECP), and Cosmic Ray Subsystem (CRS) experiments on the Voyager 2 (V2) spacecraft, and remotely sensed ~110 eV to ~55 keV energetic neutral atom (ENA) measurements from the Interstellar Boundary Explorer (IBEX) mission and Ion and Neutral Camera (INCA) on the Cassini mission. This combination is done over the time period from 2009 to the end of 2016, along the V2 trajectory, toward assessing the properties of the ion energy spectra inside the heliosheath. The combined energy spectra exhibit a series of softening and hardening breaks, providing important insights on the various ion acceleration processes inside the heliosheath. Ions in the 5.2 keV) provide a significant contribution to the total pressure. With the assumption that all ENAs (~110 eV to 55 keV) are created by charge-exchange interactions inside the heliosheath, we estimate that the magnetic field upstream at the heliopause required to balance the pressure from the heliosheath in the direction of V2 is ~0.67 nT. This number is consistent with the measured magnetic field at V2 from 2018 November, when the spacecraft entered interstellar space.

We augment the heliospheric network of galactic cosmic ray (GCR) monitors using 2012–2017 penetrating radiation measurements from the New Horizons (NH) Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI), obtaining intensities of ≳75 MeV particles. The new, predominantly GCR observations provide critical links between the Sun and Voyager 2 and Voyager 1 (V2 and V1), in the heliosheath and local interstellar medium (LISM), respectively. We provide NH, Advanced Composition Explorer (ACE), V2, and V1 GCR observations, using them to track solar cycle variations and short-term Forbush decreases from the Sun to the LISM, and to examine the interaction that results in the surprising, previously reported V1 LISM anisotropy episodes. To investigate these episodes and the hitherto unexplained lagging of associated in situ shock features at V1, propagating disturbances seen at ACE, NH, and V2 were compared to V1. We conclude that the region where LISM magnetic field lines drape around the heliopause is likely critical for communicating solar disturbance signals upstream of the heliosheath to V1. We propose that the anisotropy-causing physical process that suppresses intensities at ∼90° pitch angles relies on GCRs escaping from a single compression in the draping region, not on GCRs trapped between two compressions. We also show that NH suprathermal and energetic particle data from PEPSSI are consistent with the interpretation that traveling shocks and corotating interaction region (CIR) remnants can be distinguished by the existence or lack of Forbush decreases, respectively, because turbulent magnetic fields at local shocks inhibit GCR transport while older CIR structures reaching the outer heliosphere do not.

This paper discusses plasma characteristics in the heliosheath region before the heliopause (HP), at the HP, and in the very local interstellar medium (VLISM). The Voyager 2 (V2) HP was a sharp boundary where the radial plasma currents went to background levels. The radial flow speeds derived from 53-85 keV (V1) and 28-43 keV (V2) ion data decreased about 2 years (8 AU) before the HP at V1 and V2. A speed decrease was not observed by the V2 plasma instrument until 160 days (1.5 AU) before the HP crossing when V2 entered the plasma boundary layer where the plasma density and 28-43 keV ion intensity increased. We determine the HP orientation based on the plasma flow and magnetic field data and show these observations are consistent with models predicting a blunt HP. Variations are observed in the currents observed in the VLISM; roll data from this region clearly show the plasma instrument observes the interstellar plasma and may be consistent with larger than expected VLISM temperatures near the HP.

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 Interstellar Mapping and Acceleration Probe (IMAP) is a revolutionary mission that simultaneously investigates two of the most important overarching issues in Heliophysics today: the acceleration of energetic particles and interaction of the solar wind with the local interstellar medium. While seemingly disparate, these are intimately coupled because particles accelerated in the inner heliosphere play critical roles in the outer heliospheric interaction. Selected by NASA in 2018, IMAP is planned to launch in 2024. The IMAP spacecraft is a simple sun-pointed spinner in orbit about the Sun-Earth L1 point. IMAP’s ten instruments provide a complete and synergistic set of observations to simultaneously dissect the particle injection and acceleration processes at 1 AU while remotely probing the global heliospheric interaction and its response to particle populations generated by these processes. In situ at 1 AU, IMAP provides detailed observations of solar wind electrons and ions; suprathermal, pickup, and energetic ions; and the interplanetary magnetic field. For the outer heliosphere interaction, IMAP provides advanced global observations of the remote plasma and energetic ions over a broad energy range via energetic neutral atom imaging, and precise observations of interstellar neutral atoms penetrating the heliosphere. Complementary observations of interstellar dust and the ultraviolet glow of interstellar neutrals further deepen the physical understanding from IMAP. IMAP also continuously broadcasts vital real-time space weather observations. Finally, IMAP engages the broader Heliophysics community through a variety of innovative opportunities. This paper summarizes the IMAP mission at the start of Phase A development. Keywords: Heliosphere, Interstellar medium, IBEX, IMAP, ENA, Energetic particle

The NASA New Horizons spacecraft flies past Pluto on July 14, 2015, carrying two instruments that detect charged particles. Pluto has a tenuous, extended atmosphere that is escaping the weak gravity of the planet. The interaction of the solar wind with the escaping atmosphere of Pluto depends on solar wind conditions as well as the vertical structure of the atmosphere. We have analyzed Voyager 2 particles and fields measurements between 25 and 39 AU and present their statistical variations. We have adjusted these predictions to allow for the declining activity of the Sun and solar wind output. We summarize the range of SW conditions that can be expected at 33 AU and survey the range of scales of interaction that New Horizons might experience. Model estimates for the solar wind stand-off distance vary from approximately 7 to 1000 RP with our best estimate being around 40 RP (where we take the radius of Pluto to be RP=1184 km).

Voyager 2 observations revealed that the hot solar wind ions (the so-called pickup ions) play a dominant role in the thermodynamics of the termination shock and the heliosheath. The number density and temperature of this hot population, however, have remained unknown, since the plasma instrument on board Voyager 2 can only detect the colder thermal ion component. Here we show that due to the multifluid nature of the plasma, the fast magnetosonic mode splits into a low-frequency fast mode and a high-frequency fast mode. The coupling between the two fast modes results in a quasi-stationary nonlinear wave mode, the “oscilliton,” which creates a large-amplitude trailing wave train downstream of the thermal ion shock. By fitting multifluid shock wave solutions to the shock structure observed by Voyager 2, we are able to constrain both the abundance and the temperature of the undetected pickup ions. In our three-fluid model, we take into account the nonnegligible partial pressure of suprathermal energetic electrons (0.022–1.5 MeV) observed by the Low-Energy Charged Particle Experiment instrument on board Voyager 2. The best fitting simulation suggests a pickup ion abundance of 20 ± 3%, an upstream pickup ion temperature of 13.4 ± 2 MK, and a hot electron population with an apparent temperature of ~0.83 MK. We conclude that the actual shock transition is a subcritical dispersive shock wave with low Mach number and high plasma β.

Undergraduates (N = 135) evaluated 1 of 4 simulated 1st counseling sessions. Two international counselors (Canadian and Korean) alternated between making or not making broaching statements about their language and cultural differences. Significant main effects for counselor nationality and interaction effects between counselor nationality and broaching were found. Participants perceived the Canadian counselor more positively and the Korean counselor less positively in the broaching condition. Participants' cognitive flexibility was a significant covariate of their perceptions. Un grupo de estudiantes universitarios (N = 135) evaluo 1 de 4 sesiones iniciales de consejeria simuladas. Dos consejeros internacionales (canadiense y coreano) alternaron entre hacer comentarios o no para abordar las diferencias entre sus idiomas y culturas. Se encontraron efectos principales significativos en relacion a la nacionalidad del consejero y una interaccion entre la nacionalidad y el abordamiento. Los participantes percibieron al consejero canadiense de forma mas positiva y al consejero coreano de forma menos positiva en la situacion de abordamiento. La flexibilidad cognitiva de los participantes fue una covariable significativa en su percepcion.

Directly tracking an interplanetary coronal mass ejection (ICME) by widely separated spacecrafts is a great challenge. However, such an event could provide us a good opportunity to study the evolution of embedded Alfv\'enic fluctuations (AFs) inside ICME and their contributions to local plasma heating directly. In this study, an ICME observed by Wind at 1.0 au on March 4-6 1998 is tracked to the location of Ulysess at 5.4 au. AFs are commonly found inside the ICME at 1.0 au, with an occurrence rate of 21.7% and at broadband frequencies from 4$\times 10^{-4}$ to 5$\times 10^{-2}$ Hz. When the ICME propagates to 5.4 au, the Aflv\'enicity decreases significantly, and AFs are rare and only found at few localized frequencies with the occurrence rate decreasing to 3.0%. At the same time, the magnetic field intensity at the AF-rich region has an extra magnetic dissipation except ICME expansion effect. The energetics of the ICME at different radial distance is also investigated here. Under similar magnetic field intensity situations at 1.0 au, the turbulence cascade rate at the AF-rich region is much larger than the value at the AF-lack region. Moreover, it can maintain as the decrease of magnetic field intensity if there is lack of AFs. However, when there exists many AFs, it reduces significantly as the AFs disappear. The turbulence cascade dissipation rate within the ICME is inferred to be 1622.3 $J\cdot kg^{-1}\cdot s^{-1}$, which satisfies the requirement of local ICME plasma heating rate, 1653.2 $J\cdot kg^{-1}\cdot s^{-1}$. We suggest that AF dissipation is responsible for extra magnetic dissipation and local plasma heating inside ICME., Comment: 15 pages, 3 figures, 1 table

The misalignment of the solar rotation axis and the magnetic axis of the Sun produces a periodic reversal of the Parker spiral magnetic field and the sectored solar wind. The compression of the sectors is expected to lead to reconnection in the heliosheath (HS). We present particle-in-cell simulations of the sectored HS that reflect the plasma environment along the Voyager 1 and 2 trajectories, specifically including unequal positive and negative azimuthal magnetic flux as seen in the Voyager data \citep{Burlaga03}. Reconnection proceeds on individual current sheets until islands on adjacent current layers merge. At late time bands of the dominant flux survive, separated by bands of deep magnetic field depletion. The ambient plasma pressure supports the strong magnetic pressure variation so that pressure is anti-correlated with magnetic field strength. There is little variation in the magnetic field direction across the boundaries of the magnetic depressions. At irregular intervals within the magnetic depressions are long-lived pairs of magnetic islands where the magnetic field direction reverses so that spacecraft data would reveal sharp magnetic field depressions with only occasional crossings with jumps in magnetic field direction. This is typical of the magnetic field data from the Voyager spacecraft \citep{Burlaga11,Burlaga16}. Voyager 2 data reveals that fluctuations in the density and magnetic field strength are anti-correlated in the sector zone as expected from reconnection but not in unipolar regions. The consequence of the annihilation of subdominant flux is a sharp reduction in the "number of sectors" and a loss in magnetic flux as documented from the Voyager 1 magnetic field and flow data \citep{Richardson13}.

Quantitatively estimating the energy input from the solar wind into the magnetosphere on a global scale is still an observational challenge. We perform three- dimensional magnetohydrodynamic (MHD) simulations to derive the energy coupling function. Based on 240 numerical test runs, the energy coupling function is given by E-in = 3.78 x 10(7)n(sw)(0.24)V(sw)(1.47)B(T)(0.86) [sin(2.70)(theta/2) + 0.25]. We study the correlations between the energy coupling function and a wide variety of magnetospheric activity, such as the indices of Dst, Kp, ap, AE, AU, AL, the polar cap index, and the hemispheric auroral power. The results indicate that this energy coupling function gives better correlations than the epsilon function. This result is also applied to a storm event under northward interplanetary magnetic field conditions. About 13% of the solar wind kinetic energy is transferred into the magnetosphere and about 35% of the input energy is dissipated in the ionosphere, consistent with previous studies.

We discuss magnetic field and plasma observations from Voyager 2 (V2) during 2011, when V2 was beginning to see the effects of increasing solar activity following the solar minimum in 2009. The magnetic field strength (B) profile showed large amplitude fluctuations that can be resolved into a linear increase of B with time and a sinusoidal variation of the period of 86.2 ± 0.8 days. Voyager 2 was in a unipolar region in which the magnetic polarity was directed away from the Sun along the Parker spiral 96% of the time, indicating that V2 was poleward of the heliospheric current sheet throughout most of 2011. The distribution of B was lognormal, but a Gaussian distribution was observed when the linear variation of B was subtracted from the data. The distribution of daily increments of B was a q-Gaussian distribution with q = 1.1 ± 0.1, which is less intermittent than normally observed in the heliosheath. However, the distribution of hourly increments of B was a q-Gaussian distribution with q = 1.5 ± 0.03. The density, temperature, and velocity increased linearly from the beginning of 2011 to approximately day 254. The magnetic and thermal pressure tended to increase throughout the year, but the magnetic pressure dominated most of the time. The counting rate of >70 MeV/nucleon particles increased rapidly during the first 250 days, but it leveled out during the rest of the year when B was stronger. The empirical CR-B relationship describes this behavior.

In this work, we analyze the long-term cosmic-ray modulation observed by the Hermanus neutron monitor, which is the detector with the longest cosmic-ray record, from 1957 July. For our study we use the force-field approximation to the cosmic-ray transport equation, and the newest results on the mean free paths from the scattering theory. We compare the modulation parameter (phgr) with different rigidity (P) dependences: P, P 2, and P 2/3. We correlate them with solar and interplanetary parameters. We found that (1) these rigidity dependences properly describe the modulation, (2) long-term cosmic-ray variations are better correlated with the magnitude of the heliospheric magnetic field (HMF) than the sunspot number, solar wind speed, and tilt angle of the HMF, and (3) the theoretical dependence of the parallel mean free path on the magnetic field variance is in agreement with the modulation parameter and therefore with the neutron monitor record. We also found that the force-field approximation is not able to take into account the effects of three-dimensional particle transport, showing a poor correlation with the perpendicular mean free path

The mixture/interaction of anti-sunward-propagating Alfvenic fluctuations (AFs) and sunward-propagating Alfvenic fluctuations (SAFs) is believed to result in the decrease of the Alfvenicity of solar wind fluctuations with increasing heliocentric distance. However, SAFs are rarely observed at 1 au and solar wind AFs are found to be generally outward. Using the measurements from Voyager 2 and Wind , we perform a statistical survey of SAFs in the heliosphere inside 6 au. We first report two SAF events observed by Voyager 2 . One is in the anti-sunward magnetic sector with a strong positive correlation between the fluctuations of magnetic field and solar wind velocity. The other one is in the sunward magnetic sector with a strong negative magnetic field—velocity correlation. Statistically, the percentage of SAFs increases gradually with heliocentric distance, from about 2.7% at 1.0 au to about 8.7% at 5.5 au. These results provide new clues for understanding the generation mechanism of SAFs.

The Voyager spacecraft are making the first direct plasma measurements of the heliosheath and interstellar medium. This paper discusses the differences in the heliosheath observations of Voyager 1 (V1) and Voyager 2 (V2), the V1 heliopause crossing, and observations of transient structures in the local interstellar medium (LISM). The heliosheath velocities at V1 are smaller than expected throughout the heliosheath and are zero in the stagnation region, which persists for 8 AU before the heliopause crossing. The V2 flow profile is very different from that at V1; the average speed stays constant at 145 km/s but the flow has turned over 60° from radial. The heliopause crossing region has numerous structures in cosmic rays, termination shock particles, and magnetic field so that the exact heliopause crossing point is still controversial. Solar transients drive shocks which propagate through the LISM, generate anisotropies and intensity changes in the galactic cosmic rays (GCRs) and excite plasma and radio waves.

The solar wind environment has a large influence on the transport of cosmic rays. This chapter discusses the observations of the solar wind plasma and magnetic field in the outer heliosphere and the heliosheath. In the supersonic solar wind, interaction regions with large magnetic fields form barriers to cosmic ray transport. This effect, the "CR-B" relationship, has been quantified and is shown to be valid everywhere inside the termination shock (TS). In the heliosheath, this relationship breaks down, perhaps because of a change in the nature of the turbulence. Turbulence is compressive in the heliosheath, whereas it was non-compressive in the solar wind. The plasma pressure in the outer heliosphere is dominated by the pickup ions which gain most of the flow energy at the TS. The heliosheath plasma and magnetic field are highly variable on scales as small as ten minutes. The plasma flow turns away from the nose roughly as predicted, but the radial speeds at Voyager 1 are much less than those at Voyager 2, which is not understood. Despite predictions to the contrary, magnetic reconnection is not an important process in the inner heliosheath with only one observed occurrence to date.

Interplanetary coronal mass ejections (ICMEs) and their subset, magnetic clouds (MCs), are important manifestations of solar activity which have substantial impact on the geomagnetic field. We re-analyze events already identified in Wind and Voyager 2 data and estimate changes of their geometry along the path from the Sun. The analysis is based on the thickness of the sheath between a shock and a particular ICME or MC which is proportional to the apparent curvature radius of ICMEs/MCs. We have found that this apparent radius of curvature increases with the Mach number and this effect is attributed to the larger deformation of the fast ICME/MC. Further, the relative sheath thickness that is proportional to the flux rope oblateness decreases with the magnetic field intensity inside the ICME/MC and increases with the heliospheric distance.

This paper compares three kinds of shocks and sheaths; the bow shock and magnetosheaths of planets, interplanetary coronal mass ejection (ICME) shocks and sheaths, and the termination shock and heliosheath. We compare the energy balance across these shocks, fluctuations in the sheaths, asymmetries, and shock evolution. All three shocks and sheaths display asymmetries imposed by outside magnetic fields. Energy balance is often achieved through reflection of ions of the shocks, but in some cases no reflected ions are observed. The shocks may have similar small scale fluctuations which drive density changes in the sheaths.