14th ANNUAL INTERNATIONAL ASTROPHYSICS CONFERENCE ORAL ABSTRACTS
Adhikari, The Transport of Low‐Frequency Turbulence in Astrophysical Flows. II. Solutions for the super‐Alfvenic solar wind Laxman Laxman Adhikari, University of Alabama in Huntsville, USA Gary P. Zank, University of Alabama in Huntsville, USA Roberto Bruno, INAF‐IAPS Instituto di Astrofisica e Planetologia Spaziali, Italy Daniele Telloni, INAF‐Astrophysical Observatory of Torino, Italy Peter Hunana, Center for Space Plasma and Aeronomic Research (CSPAR), USA Alexander Dosch, Center for Space Plasma and Aeronomic Research (CSPAR), USA Raffaele Marino, National Center for Atmospheric Research, USA Qiang Hu, University of Alabama in Huntsville, USA Zank et al. 2012 developed a turbulence transport model for low‐frequency incompressible magnetohydrodynamic (MHD) turbulence in inhomogeneous flows in terms of the energy corresponding to forward and backward propagating modes, the residual energy, the correlation lengths corresponding to forward and backward propagating modes, and the correlation length of the residual energy. We apply the Zank et al. model to the super‐Alfvenic solar wind i.e., |U|>>|V A |and solve the coupled equations for two cases, the first being the heliosphere from 0.29 AU to 5 AU with and without the Alfven velocity, and the second being the “entire” heliosphere from 0.29 AU to 100 AU in the absence of the Alfven velocity. The model shows that (1) shear driving is responsible for the in situ generation of backward propagating modes, (2) the inclusion of the background magnetic field modifies the transport of turbulence in the inner heliosphere, (3) the correlation lengths of forward and backward propagating modes are almost equal beyond ~30 AU, and (4) the fluctuating magnetic and kinetic energies in MHD turbulence are in approximate equipartition beyond~30 AU. A comparison of the model results with observations for the two cases shows that the model reproduces the observations quite well from 0.29 AU to 5 AU. The outer heliosphere (> 1 AU) observations are well described by the model. The temporal and latitudinal dependence of the observations makes a detailed comparison difficult but the overall trends are well captured by the models. We conclude that the results are a reasonable validation of the Zank et al. 2012 model for the super‐Alfvenic solar wind. Antiochos, Spiro The Origin of Impulsive Solar Energetic Particles Spiro K. Antiochos, NASA/GSFC, USA Sophie Masson, LESIA, Paris Observatory, France C. Richard DeVore, NASA/GSFC, USA Among the most important, but least understood forms of space weather are the so‐called Impulsive Solar Energetic Particle (SEP) events, which can be especially hazardous to deep‐space astronauts. These energetic particles are widely believed to be produced by the flare reconnection that is the primary driver of coronal mass ejections (CME) / eruptive flare events. The main difficulty with this idea is that in the standard model for a CME/flare magnetic topology, the particles should remain trapped in the closed flare loops and in the ejected plasmoid, the CME. However, flare‐accelerated particles frequently reach the Earth long before the CME does. In previous 2.5D calculations we showed how the external reconnection that is an essential element of the breakout model for CME initiation could lead to the escape of flare‐accelerated particles. The problem, however, is that in 2.5D this reconnection also tends to destroy the plasmoid, which disagrees with the observation that SEP events are often associated with well‐defined plasmoids at 1 AU, the so‐called magnetic clouds. Consequently, we have extended our calculations to a fully 3D topology that includes a multi‐polar coronal field suitable for a breakout CME/eruptive flare near a coronal hole region. We performed high‐resolution 3D MHD numerical simulations with the Adaptively Refined MHD Solver (ARMS). Our results demonstrate that the model allows for the effective escape of energetic particles from deep within an ejecting well‐defined plasmoid. We show how the complex interactions between the flare and breakout reconnections reproduce all the main observational features of CMEs/flares and impulsive SEPs. We discuss the implications of our calculations for theories of particle acceleration and for observations from the upcoming Solar Orbiter and Solar Probe Plus missions, which will measure impulsive SEPs near the Sun, thereby, mitigating propagation effects. This research was supported, in part, by the NASA SR&T and TR&T Programs. 14th ANNUAL INTERNATIONAL ASTROPHYSICS CONFERENCE ORAL ABSTRACTS
Baring, Matthew Probing Acceleration at Relativistic Shocks in Blazar Jets Markus Böttcher, North‐West University, South Africa Errol J. Summerlin, NASA's Goddard Space Flight Center Acceleration at relativistic shocks is likely to be important in various astrophysical jet sources, including blazars and other radio‐loud active galaxies. An important recent development for blazar science is the ability of Fermi‐LAT data to pin down the power‐law index of the high energy portion of emission in these sources, and therefore also the index of the underlying non‐thermal particle population. This paper highlights how multiwavelength spectra including X‐ray band and Fermi data can be used to probe diffusive acceleration in relativistic, oblique, MHD shocks in blazar jets. The spectral index of the non‐thermal particle distributions resulting from Monte Carlo simulations of shock acceleration, and the fraction of thermal particles accelerated to non‐thermal energies, depend sensitively on the particles' mean free path scale, and also on the mean magnetic field obliquity to the shock normal. We investigate the radiative synchrotron/Compton signatures of the resulting thermal and non‐thermal particle distributions. Important constraints on the frequency of particle scattering and the level of field turbulence are identified for the blazars AO 0235+164 and Mrk 501. The possible interpretation that turbulence levels decline with remoteness from jet shocks, and a significant role for non‐gyroresonant diffusion, are discussed, and analogies to heliospheric conditions are drawn. Bellan, Paul MHD Jets P. M. Bellan, Caltech, USA X. Zhai, Caltech, USA K. B. Chai, Caltech, USA Dynamics relevant to solar and astrophysical plasmas is being investigated using lab experiments governed by the same physics, having the same topology, but much smaller time and space scales. Plasma dynamics is tracked using high speed imaging (movies) that by resolving sub‐Alfven time scales reveal unexpected, new phenomena. In contrast to models which neglect flows and pressure gradients, the movies show that a highly collimated MHD‐driven plasma flow is the outstanding feature of the dynamics. This flow is effectively a lab version of an astrophysical jet. The jet velocity is in good agreement with an MHD acceleration model [1]. Axial stagnation of the jet compresses embedded azimuthal magnetic flux and results in jet self‐collimation. Jets kink when they breach the Kruskal‐Shafranov stability limit. The acceleration of a sufficiently strong kink provides an effective gravity that can provide the environment for a spontaneously developing fine‐scale, extremely fast Rayleigh‐Taylor instability that erodes the current channel to be smaller than the ion skin depth [2]. This cascade from the ideal MHD kink scale to the non‐MHD ion skin depth scale can result in a fast magnetic reconnection whereby the jet breaks off from its source electrode [2] and particles are energized. A 3D numerical MHD code [3] has quantitatively reproduced the acceleration, collimation, and dynamically changing density/pressure/magnetic profile of the jet. Supported by USDOE [1] D. Kumar and P. M. Bellan, Phys. Rev. Letters 103, Art. No. 105003 (2009) [2] A. L. Moser and P. M. Bellan, Nature 482, 379 (2012) [3] X. Zhai, H. Li, P. M. Bellan, and S. T. Li, Astrophys. J. 291, Art. No. 40 (2014) 14th ANNUAL INTERNATIONAL ASTROPHYSICS CONFERENCE ORAL ABSTRACTS
Bucik, Radoslav Long‐Lived Energetic Particle Source Regions on the Sun R. Bucik, MPS, Germany D. E. Innes, MPS, Germany N.‐H. Chen, MPS, Germany G. M. Mason, APL/JHU, USA R. Gomez‐Herrero, SRG/UAH, Spain M. E. Wiedenbeck, JPL/Caltech, USA Discovered more than 40 years ago, impulsive solar energetic particle (SEP) events are still poorly understood. The enormous abundance enhancement of the rare 3He isotope is the most striking feature of these events, though large enhancements in heavy and ultra‐heavy nuclei are also observed. Recurrent 3He‐rich SEPs in impulsive events have only been observed for limited time periods, mostly about one day which is typically the time that a single stationary spacecraft is magnetically connected to the source active regions on the Sun. With the launch of the two STEREO spacecraft we now have the possibility of an uninterrupted view and a longer connection time to solar active regions. We present the first report of source regions with repeated 3He‐rich SEP emissions for relatively long time periods, lasting at least a quarter of a solar rotation. We found that recurrent 3He‐rich SEPs in the long‐lived sources occur after the emergence of magnetic flux. These new observations reveal that physical conditions for particle acceleration and escape from the Sun can persist for a long time, perhaps for the entire lifetime of an active region. Buechner, Joerg Electron Energization in the Solar Corona Joerg Buechner, Max‐Planck‐Institute for Solar System Research Goettingen, Germany Patricio Munoz, Max‐Planck‐Institute for Solar System Research, Goettingen, Germany In the solar corona electrons are accelerated to high energies that cause soft and hard X‐rays by Bremsstrahlung in the chromosphere. Since it is not clear whether slow mode shocks are formed at all in the course of coronal magnetic reconnection we discuss the formation of potential structures (double layers ) in strong coronal current concentrations as well as magnetic reconnection in the strong magnetic (“guide”) field of the corona as two possible ways to reach these energies and demonstrate these mechanisms by means of numerical simulations for the plasma conditions of the solar corona. Burlaga, Leonard Voyager Observations of the Magnetic Field in the Heliosheath and the LISM L. F. Burlaga, NASA GSFC, USA N. F. Ness, Catholic Univ. of America, USA This paper reviews observations of the magnetic field B in the heliosheath by Voyager 1 (V1) and Voyager 2 (V2) and the recent observations of the LISM by V1. The heliosheath is the region between the termination shock (TS) and the heliopause (HP). The TS was identified by both V1 and V2, and the internal structure of the TS was determined by V2. The radial distance of the TS was 94 AU at V1 and 84 AU at V2, suggesting a global asymmetry of the heliosphere. The average direction of B is that of the Parker spiral magnetic field, and non‐periodic magnetic sectors were observed by V1 and V2. The distribution of the magnetic field strength B is typically a Gaussian in unipolard regions an lognormal in the sector zone. The heliosheath is disturbed and turbulent, particularly just behind the termination shock and it is described by the multifractal spectrum and the q‐Gaussian distribution. The multifractal spectrum in the heliosheath also varies with the solar cycle. Voyager 1 has been in the LISM since at least August 25, 2012, but the nature of the HP and the time of the HP crossing not been determined. The magnetic field direction is close to, but distinguishable from the Parker spiral magnetic field and its departure from the Parker spiral magnetic field is slowly increasing with distance from the sun. A large pressure pulse and two shocks or pressure waves have been identified in the LISM, presumably generated inside the heliosphere and transmitted through the heliosheath and heliopause. The interstellar magnetic field lines are draped across the heliopause, and B is approximately 0.5 nT. The fluctuations of B are very small but turbulent on scales 1 day to 468 days, with a Kolmogorov spectrum and an injection scale of approximately 10 pc. 14th ANNUAL INTERNATIONAL ASTROPHYSICS CONFERENCE ORAL ABSTRACTS
Bzowski, Maciej Analysis Ibex‐Lo Observations Of Interstellar Neutral Helium From 2009 To 2014 M. Bzowski, P. Swaczyna, M.A. Kubiak, J.M. Sokół: Space Research Centre PAS, Poland E. Moebius, T. Leonard, D. Heirtzler University of New Hampshire, USA We analyzed measurements of interstellar neutral He (ISN He) performed by the Interstellar Boundary Explorer (IBEX) during the first five years of operation. We elaborated a system of corrections for the instrument interface throughput limitations due to the ambient electrons and refined the determination of the IBEX spin axis positions. We developed a comprehensive system of uncertainties of the data and related correlations and refined the Warsaw Test Particle Model, used to simulate the observed signal. We analyzed the contribution to the signal from the Warm Breeze, which is a newly‐discovered population of neutral He flowing into the heliosphere from the starboard bow of the heliosphere, and from the interstellar neutral H. With this insight, we analyzed the data from the IBEX ISN He observations seasons 2009 through 2014. We will present the ISN He flow vector and temperature based on this analysis. Cairns, Iver Explaining Type II Solar Radio Bursts from the Sun to 1 AU Iver H. Cairns, University of Sydney, Australia J.M. Schmidt, University of Sydney, Australia For over 60 years type II solar radio bursts have defied detailed quantitative explanation, despite their promise for predicting space weather at Earth and their status as the archetype for coherent radio emission stimulated by shocks. Type II bursts are widely accepted to be radio emission produced at the electron plasma frequency and/or twice that frequency upstream from shock waves (usually driven by coronal mass ejections [CMEs]) moving through the corona and solar wind: electrons reflected at the shock develop beam distribution functions, the electron beams drive Langmuir waves, and the Langmuir waves couple linearly and/or nonlinearly to produce the fundamental and harmonic radio emission. We have developed quantitative analytic descriptions for the detailed plasma physics of these steps. We have constructed a state‐of‐the‐art theoretical / simulational model for an arbitrary specified type II burst by combining this kinetic emission theory with a BATS‐R‐US 3D MHD simulation of the CME and associated shock through a realistic, data‐driven, 3D model for the corona and solar wind. Once coronagraph and solar wind data are used to initialize the CME properties/release and 3D solar wind, respectively, there are no free parameters. We demonstrate for the first time impressive quantitative agreement between the predicted and observed properties of both coronal and interplanetary type II bursts. For instance, for an interplanetary type II burst observed by the widely separated spacecraft STEREO A and B, despite the intensities and frequencies of the observed radio emissions varying by factors of a million and thousand, respectively, the theoretical predictions are typically in error by less than a factor of 3 and by 10 percent for both STEREO A and B. Similarly, for the metric type II analyzed the intensities, frequencies, and timing of the split‐band fundamental and harmonic bands are predicted very well. These results suggest that we are very close to having a viable quantitative theory for type II bursts. and so "solving the type II problem". They also suggest that the BATS‐R‐US code, when initialized properly, is impressively accurate. 14th ANNUAL INTERNATIONAL ASTROPHYSICS CONFERENCE ORAL ABSTRACTS
Coates, Andrew Ion Pickup Observed at Comet 67P with the Rosetta Plasma Consortium (RPC): Similarities and Differences with AMPTE Releases Andrew Coates1,2, Jim Burch3, Ray Goldstein3, Hans Nilsson4, Gabriella Stenberg Wieser4, Etienne Behar4 and the RPC team 1. Mullard Space Science Laboratory, University College London, UK 2. Centre for Planetary Sciences at UCL/Birkbeck, UK 3. Southwest Research Institute, USA 3. Swedish Institute of Space Physics, Sweden Since Rosetta’s arrival at comet 67P in August 2014, the Rosetta Plasma Consortium particle instruments have shown that the low activity cometary environment is dominated by the solar wind and its increasing interaction with the comet ionosphere (Nilsson et al., Science 2015, Goldstein et al., GRL submitted 2015). This was expected in the early stages of the mission (e.g., Trotignon et al., 1999, Coates 2012). In addition to the solar wind and related He+ populations, a low energy pickup ion population is seen intermittently (Nilsson et al., Science 2015, Goldstein et al., GRL submitted 2015). The population is very time dependent, but at times reaches higher energy approaching the solar wind energy. During these intervals, ICA composition data indicate that the ions constitute a ‘spring’ of water group ions (Nilsson et al., 2015). The rising energy signatures of these ions observed at times indicate that they are in the early phases of the pickup process (see Nilsson et al, 2015). Here, we compare these exciting pickup ion measurements with Giotto measurements at the relatively weak (compared to Halley) comet Grigg‐Skjellerup, where early phase pickup was seenn as no ‐gyrotropic cometary ions (Coates et al., 1993) and with the AMPTE lithium and barium releases. We find some striking similarities with the AMPTE releases, particularly the early pickup signature (e.g. during the lithium release, Coates et al., 1986) and a momentum balance between the pickup ions and the deflected solar wind (e.g. during a barium release, Coates et al., 1988). In an AMPTE lithium release there was also evidence for less momentum being given to the solar wind alpha particles than to the protons (Johnstone et al., 1985) – another remarkable feature observed with IES at 67P (Goldstein et al., 2015). Here we summarise the early measurements related to ion pickup from RPC, compare them with the earlier relevant data, and discuss the similarities and differences in the ion pickup physics. Connaughton, Gamma‐Ray Bursts in the era of multi‐messenger astronomy Valerie Valerie Connaughton, University of Alabama in Huntsville, USA Gamma‐Ray Bursts (GRBs) are excellent tools for multi‐messenger science. They provide a clear and impulsive temporal signature that facilitates searches of multiple data sets. Long GRBs are one possiblee sourc of the highest energy cosmic rays, making them likely sources of detectable neutrinos and also of very high energy gamma rays. Short GRBs are favored as the most likely electromagnetic counterpart to the gravitational waves pursued by the next‐generation ground‐based gravitational wave interferometers. With a 50% duty cycle for any point on the sky, and good sensitivity to a wide variety of transient phenomena, the Fermi Gamma‐Ray Burst Monitor is an ideal partner for multi‐ messenger time‐domain astronomy. I will review progress and prospects for breakthroughs with the Fermi gamma‐ray space telescope. Cummings, Alan Voyager 1 Observations of Galactic Cosmic Rays in the Local Interstellar Medium: Ionization Rates and Energy Density A.C. Cummings, Caltech, USA E.C. Stone, Caltech, USA B.C. Heikkila, Goddard Space Flight Center, USA N. Lal, Goddard Space Flight Center, USA W. R. Webber, New Mexico State University, USA Voyager 1 (V1) has been in the local interstellar medium (LISM) since August, 2012. We present the galactic cosmic‐ray (GCR) energy spectra of most elements from H through Ni, and also of electrons, for a period exceeding two years. The V1 energy spectra define the newly‐revealed, low‐energy part of the interstellar spectra of nuclei down to ~1 MeV/nuc and of electrons down to ~8 MeV. We use these observations, along with estimates of the higher‐energy portion of the interstellar electron and nuclei spectra, to estimate the energy density of cosmic rays in the LISM and the cosmic ray ionization rate of atomic H. We find that the total energy density of cosmic rays is ~1.0 eV cm‐3, which includes a contribution of ~0.02 eV cm‐3 from electrons. This energy density is somewhat larger than the energy density of the local interstellar magnetic field (~0.6 eV cm‐3). We find the cosmic ray ionization rate of atomic H to be ~1.5 x 10‐17 s‐1, which is a factor of ~12 below the ionization rates in diffuse interstellar clouds based on astrochemistry methods. The cross section for ionization of H atoms peaks at much lower energies than our observations, so a significant contribution to the total ionization rate of the LISM could be occurring at energies below our detection threshold. In order to match the higher ionization rate, it appears that a high‐intensity, low‐energy population of electrons and/or nuclei might be required. Such a population might originate from a pump mechanism process operating in the LISM, as has been proposed for the source of the suprathermal E‐1.5 energy spectra observed in the heliosphere. This work was supported by NASA under contract NNN12AA012. 14th ANNUAL INTERNATIONAL ASTROPHYSICS CONFERENCE ORAL ABSTRACTS
Dahlin, Joel Electron Acceleration in 2D and 3D Magnetic Reconnection Joel Dahlin, University of Maryland, USA James Drake, University of Maryland, USA Michael Swisdak, University of Maryland, USA Magnetic reconnection is thought to be an important driver of energetic particles in phenomena such as magnetospheric storms, stellar and solar flares, and gamma ray bursts. Using kinetic particle‐in‐cell (PIC) simulations, we show that the stochastic magnetic field structure which develops during 3D guide field reconnection plays a vital role in particle acceleration. Energetic electrons are able to access acceleration sites in a much larger volume and therefore gain energy much more efficiently than in a 2D system. We also examine the relative roles of two important acceleration drivers: parallel electric fields and a Fermi‐type mechanism associated with reflection of charged particles from contracting field lines. We find that parallel electric fields are most important for accelerating low energy electrons, whereasi Ferm reflection dominates energetic electron production. Decker, Rob Energetic Particles in the Heliosheath and Local Interstellar Medium R. B. Decker, Johns Hopkins Applied Physics Lab., USA S. M. Krimigis, Johns Hopkins Applied Physics Lab., USA E. C. Roelof, Johns Hopkins Applied Physics Lab., USA M. E. Hill. Johns Hopkins Applied Physics Lab., USA We discuss angular and spectral variations of energetic ion and electron intensities measured by the Low Energy Charged Particle instruments on Voyager 2 in the heliosheath and Voyager 1 in the very local interstellar medium. Emphasis will be on recent data. At Voyager 2, now roughly 24 AU beyond the termination shock, intensities of ions >30 keV and electrons >20 keV continue to recover in a step‐like fashion from minima reached in early 2013. We reported previously that during the rapid initial recovery from these minima as particle intensities rose at Voyager 2, angular data for ions 30 keV to 30 MeV showed strong and long lasting (about 4 months) net streaming away from the heliospheric nose toward the flank. A similar streaming episode lasting about 2 months occurred in early 2015, again during a period when intensities were rapidly increasing. Energy spectra of 30‐3500 keV heliosheath ions, which have varied little since 2012, steepen in slope with increasing energy as the spectral index varies from about ‐1 to ‐2. At Voyager 1, now roughly 10 AU beyond the heliopause, intensities of low‐energy ions and electrons and of anomalous cosmic rays remain at background levels. Galactic cosmic ray ions continue to show small departures from isotropy, with intensity depletions of ions gyrating nearly perpendicular to the magnetic field. The two episodes in March‐April 2013 and April‐May 2014 when cosmic ray ion intensities showed small increases lasting 10‐20 days indicate small energy boosts, produced possibly by magnetic disturbances from solar activity entering the interstellar medium [Jokipii and Kota, ApJL, 794, 2014]. During these two periods intensities of cosmic rays with pitch angles nearer 90 degrees were increased more than those with pitch angles nearer 0 and 180 degrees. 14th ANNUAL INTERNATIONAL ASTROPHYSICS CONFERENCE ORAL ABSTRACTS
Desai, Mihir Systematic Behavior of Heavy Ion Spectra in Large Solar Energetic Particle Events M. I. Desai, SwRI/UTSA, USA M. A. Dayeh, SwRI, USA R. W. Ebert, SwRI, USA G. M. Mason, JHU/APL, USA D. J. McComas, SwRI/UTSA, USA G. Li, UAH, USA C. M. S. Cohen, Caltech, USA R. A. Mewaldt, Caltech, USA N. A. Schwadron, UNH, USA C. W. Smith, UNH, USA
Our Sun accelerates ions and electrons up to near‐relativistic speeds in at least two ways; magnetic reconnection during solar flares is believed to produce the impulsive or 3He‐ rich solar energetic particles (SEPs), while diffusive shock acceleration at fast coronal mass ejection – or CME–driven shock waves are thought to produce the larger gradual SEPs. Despite recent advances in our understanding of the properties (e.g., time variations, spectral behavior, longitudinal distributions, compositional anomalies etc.) of large SEP events, the relative roles played by many important physical processes remain poorly understood. These effects include variations in the seed populations, the geometry and speed of the shock, the presence or absence of a preceding CME from the same active region, scattering by ambient turbulence or by self‐generated Alfvén waves during acceleration and transport, and the direct presence of flare accelerated material at energies above ~10 MeV/nucleon. Observations and theoretical studies have indicated that many of these effects may manifest in the spectral properties of H and other heavy elements. In this paper, we present results from a survey of the energy spectra of ~0.1‐500 MeV/nucleon H‐Fe nuclei in 46, isolated and well‐connected large gradual SEP events observed by instruments onboard ACE, GOES, SAMPEX, and SoHO and determine how the spectral fit parameters such as the break or roll‐over energies vary with the ion’s Charge‐to‐Mass (Q/M) ratio. In particular, we compare our results with predictions of existing and developing models to understand why some large SEP events exhibit species‐dependent spectral breaks that vary strongly with the ion’s Q/M ratio while others do not. 14th ANNUAL INTERNATIONAL ASTROPHYSICS CONFERENCE ORAL ABSTRACTS
Dialynas, Kostas On the Origin of the 5‐55 keV Heliosheath ENAs: Solar Cycle Dependence of Cassini/INCA Images and Voyager/LECP Ion Measurements Kostas Dialynas, Office of Space Research and Technology, Academy of Athens, Greece Stamatios M. Krimigis, JHU/Applied Physics Laboratory, USA Donald G. Mitchell, JHU/Applied Physics Laboratory, USA Rob B. Decker,d JHU/Applie Physics Laboratory,USA Edmond C. Roelof, JHU/Applied Physics Laboratory, USA Using the Cassini/INCA (Ion and Neutral Camera), we have produced all‐sky ΕΝΑ‐hydrogen maps of the sky from the year 2003 to 2014 in four discrete energy passbands within the energy range of 5.2‐55 keV. We compare the solar cycle variation of the ENAs ‐in both the heliospheric “nose” (upstream) and “anti‐nose” (downstream) directions‐ with the >40 keV ions measured in situ within the heliosheath by the LECP (Low Energy Charged Particle telescope) on VGR1 and VGR2, where we have measurements of protons in the overlapping energy bands ~40‐55 keV. We find that: a) Towards the anti‐nose direction, the ENA‐H intensities tend to decrease during the decline of SC23, i.e. after 2003, ENA intensities decrease to a minimum (by a factor of ~2 lower at all energies) by the end of year 2011, ~1 year after the observed minimum in the solar activity; b) This ENA decrease (5.2‐55 keV) during 2009‐2011 is consistent with the concurrent intensity decrease of the >40 keV ion measurements (by a factor of 2‐3) observed in situ by VGR1 and VGR2 in the heliosheath (Decker et al. 2012); c) Towards the nose direction, minimum intensities in both the INCA ENAs and the VGR2 >40 keV ions (Decker et al. 2015) occur during the year 2013, with a subsequent recovery from 2014 to date (by a factor of ~2 in the >40 keV ion data and a factor of ~1.5 in the >35 keV ENA data). These quantitative correlations between the decreases of INCA ENAs (in both the heliospheric nose and anti‐nose directions) and the in situ Voyager 1 and 2 ion measurements (separated by ~130 AU) during the declining phase of SC23, along with their concurrent jointly shared recoveries at the onset of SC24, imply that: 1) The 5‐55 keV ENAs are produced in the heliosheath (because their transit times over 100 AU are less than a few months at energies >40 keV); 2) The global heliosheath responds promptly (within ~1 year) to outward‐propagating solar wind changes through the solar cycle. 1. Decker, R. B., S. M. Krimigis, E. C. Roelof, and M. E. Hill, 2015, Journal of Physics: Conference Series 577 (2015) 012006, doi:10.1088/1742‐6596/577/1/012006. 2. Decker, R. B., S. M. Krimigis, E. C. Roelof, and M. E. Hill, 2012, Nature, 489, 124. Duffin, Robert Type III‐L Solar Radio Bursts and their Associations with Solar Energetic Proton Events Robert T. Duffin, Laney College, USA. Stephen M. White, Air Force Research Lab, USA. Paul S. Ray, Naval Research Lab, USA Michael L. Kaiser, Lab for Solar Astronomy ‐ NASA, USA Type III‐L bursts ares a sub‐clas of type III solar radio bursts that tend to occur after the impulsive phase of flares; are longer in duration than individual type IIIs and tend to be low‐frequency. There has been a proposal that type III‐Ls are connected to solar energetic proton (SEP) events. Most work on this connection has started from samples of SEP events, but if type III‐Ls are to be useful for prediction of SEP events, then we need to understand the properties of samples of type III‐L bursts. This talk reports preliminary results from such a study. An operating definition based on previous work is used to identify type III‐L events amongst M‐ and X‐class flares from 2001; and then associations with other properties of these events are investigated, including association with SEP events. If there is an association with SEP events, one important factor that these bursts allow us to address is the question of whether acceleration takes place at an associated CME, or closer to the flare site well below the CME. 14th ANNUAL INTERNATIONAL ASTROPHYSICS CONFERENCE ORAL ABSTRACTS
Fayock, Brian Lyman‐alpha Radiation Pressure in the Heliosphere: Results from a 3D Monte Carlo Radiative Transfer Simulation Brian Fayock, University of Alabama in Huntsville, USA Gary P Zank, University of Alabama in Huntsville, USA Jacob Heerikhuisen, University of Alabama in Huntsville, USA Chris Gilbert, Georgia Institute of Technology, USA Klaus Scherer, University of Bochum, Germany Models of the heliosphere will always be compared to spacecraft observations for verification of accuracy. Historically, these comparisons have often led to the need for more detail within the model or for certain theoretical assumptions to be lifted. One underutilized avenue of verification is the use of radiative transfer simulations. While there have been a number of insightful studies of absorption profiles of stellar spectra using observations from the Hubble Space Telescope, global radiative transfer simulations and their comparison to ultraviolet observations from deep‐space missions have received little attention with even a smaller amount of success. We show how the results of our 3D Monte Carlo radiative transfer simulation suggest the need for a more accurate description of radiation pressure within heliospheric models. The radiative transfer code used to produce the results shown here is an improved version of our first code that had been compared to ultraviolet data that had been previously reduced in 1992 for Voyager 1, Voyager 2, and Pioneer 10. While comparison to those data sets does not directly involve radiation pressure, it provides validation of the code as well as the heliospheric model in which the code was run. For further verification, the improved code is compared to the complete data sets for Voyager 2, Pioneer 10, and even Pioneer 11. It is also compared to Voyager 1 data out to the beginning of 2011, which is all that we were able to obtain. Among a number of new statistical values ethat ar collected, the radiation pressure is accumulated as the momentum that is transferred to a hydrogen atom during absorption and emission of a photon in the radial direction. The results are then normalized by volume to give the radiative momentum density. While the frequency distribution is interesting, the most important result is the radial trend of the radiative momentum density. The trend is compared to several different rates of exponential decay, and it is shown that the trend does not follow r^{‐2}, which has been a general assumption for most heliospheric models in relation to the balance with gravitational effects on neutral hydrogen atoms. Furthermore, the trend is not isotropic and does not follow a constant exponential decay as a function of heliocentric distance. Fermo, Transient Shocks Beyond the Heliopause Raymond Raymond L. Fermo, University of Alabama in Huntsville, USA Nikolai V. Pogorelov, University of Alabama in Huntsville, USA Leonard F. Burlaga, NASA Goddard Space Flight Center, USA The heliopause is a rich, dynamic surface affected by the time‐dependent solar wind. Stream interactions due to coronal mass ejections (CMEs), corotating interaction regions (CIRs), and other transient phenomena are known to merge producing global merged interaction regions (GMIRs). Numerical simulations of the solar wind interaction with the local interstellar medium (LISM) show that GMIRs, as well other time‐dependent structures in the solar wind, may produce compression/rarefaction waves and shocks in the LISM behind the heliopause. These shocks may initiate wave activity observed by the Voyager spacecraft. The magnetometer onboard Voyager 1 indeed observed a few structures that may be interpreted as shocks. We present numerical simulations of such shocks in the year of 2000, when both Voyager spacecraft were in the supersonic solar wind region, and in 2012, when Voyager 1 observed traveling shocks. In the former case, Voyager observations themselves provide time‐dependent boundary conditions in the solar wind. In the latter case, we use OMNI data at 1 AU to analyze the plasma and magnetic field behavior after Voyager 1 crossed the heliospheric boundary. Numerical results are compared with spacecraft observations. 14th ANNUAL INTERNATIONAL ASTROPHYSICS CONFERENCE ORAL ABSTRACTS
Fisk, Len 50 Year of Research on Particle Acceleration in the Heliosphere L.A. Fisk, University of Michigan, USA In 1965, through the late 1960s, the heliosphere was considered to be a passive place, an impediment to the information on the Galaxy contained in GCR observations, and on the Sun from SEP observations. All this changed in the early 1970s, with the discovery of the ACRs, and the subsequent acceptance that the ACRs are ionized interstellar neutral gas that is accelerated in the heliosphere by four orders of magnitude in energy. In the mid‐1970s, Pioneer 10 and 11 observations provided direct evidence of acceleration. In 1977‐78, diffusive shock acceleration was introduced, and subsequently developed in detail, providing compelling explanations for, e.g., the observed acceleration in CIRs, and a likely explanation for the acceleration of ACRs at the termination shock. In 2004 and 2008, the Voyagers crossed the termination shock, did not observe the acceleration of the ACRs, but did observe that low‐energy particles, up to a few MeV/nucleon, had identical spectra downstream from the termination shock, a distribution function that is a power law in particle speed with a spectral index of ‐5. When Voyager 1 reached about 120 AU, where the high‐energy ACRs are at peak intensity, the ACR spectrum is also a ‐5 spectrum. Moreover, observations of suprathermal tails in the solar wind in the inner solar system have a ‐5 spectrum, often peaking downstream, but not at shocks. These observations led to the development of a new acceleration mechanism, the pump acceleration mechanism of Fisk and Gloeckler, which can account for all the observed ‐5 spectra. Fuselier, Wave‐Particle Interactions and the Heliopause Plasma Depletion Layer Stephen Stephen A. Fuselier, Southwest Research Institute, USA, University of Texas at San Antonio, USA Iver H. Cairns, School of Physics, University of Sydney, Australia Because of draping of the interstellar magnetic field against the heliopause, a plasma depletion layer likely forms at the boundary. In a plasma depletion layer, the magnetic field increases and the plasma density decreases. Other basic properties of the depletion layer and in situ observations from Voyager 1 provide important information on the characteristics of this layer. In this talk, we review these properties with the emphasis on the implications for wave‐particle interactions in the PDL. Giacalone, Joe Hybrid Simulation of Charged Particles Accelerated by a Strong Quasi‐Parallel Interplanetary Shock: Implications for the Injection Problem Joe Giacalone, University of Arizona, USA We present results from a hybrid simulation of a strong quasi‐parallel collisionless shock that accelerates protons from an initially Maxwellian distribution to high energies. The hybrid simulation assumes kinetic protons and massless fluid electrons. Simulation parameters are chosen to match those of the interplanetary shock observed by ACE on DOY 94, 2001. The shock had a shock‐normal angle of about 15 degrees according to two separate analyses, and an Alfven Mach number somewhat larger than 3. The hybrid simulation starts with a drifting Maxwellian distribution of protons that is forced into a rigid wall at one end of the simulation domain resulting in a shock moving back against the flow. Embedded within the plasma is a magnetic field with an average direction of 15 degrees with respect to the wall, and a fluctuating component consisting of a superposition of many Alfven waves with amplitudes based on an assumed power spectrum, also consistent with observations of this interplanetary shock. In the simulation, protons are accelerated by the shock to energies much higher than the kinetic energy of the thermal solar‐wind protons. The resulting simulated spectrum at energies above the thermal energy is a power law up to some characteristic energy and then falls off approximately exponentially at high energies because of losses resulting from the particles escaping the simulation domain. The power‐law part of the simulated spectrum extends near to the lowest energy of the ACE/EPAM instrument at about 50 keV. We find that the intensity of 50keV protons obtained from the simulation agrees very well with the observed intensity. This suggests strongly that the source of the ~50 keV protons at this shock is the thermal solar wind. We will discuss the implications for this with regards to the injection problem. 14th ANNUAL INTERNATIONAL ASTROPHYSICS CONFERENCE ORAL ABSTRACTS
Gloeckler, IBEX Observations provide strong Evidence that Voyager 1 is still in the Heliosheath George George Gloeckler, Department of Atmospheric, Oceanic and Space Sciences, University of Michigan, USA Len Fisk, Department of Atmospheric, Oceanic and Space Sciences, University of Michigan, USA Voyager investigators have concluded and announced that Voyager 1 (V1) had crossed the heliopause and is now exploring the interstellar medium. This conclusion is based primarily on plasma wave observations of Gurnett et al., which reveal a plasma electron density that resembles the density expected in the local interstellar medium. V1 measurements in this presumed interstellar region present numerous puzzles that modelers are attempting to explain. Fisk & Gloeckler have disputed the conclusion that V1 has crossed the heliopause, pointing out that to account for all the V1 observations, particularly the magnetic field direction together with the density, it is necessary to conclude that the higher densities observed by Gurnett et al. are due to compressed solar wind. In this paper we show that the model for the nose region of the heliosheath of Fisk & Gloeckler provides a natural explanation for the both the intensity and spectral shape of 0.006 to 4 keV Energetic Neutral Hydrogen (ENH) observed by Fuselier et al. throughout the nose region of the heliosheath. The source of the ENH observed by IBEX is predominantly the compressed and heated solar wind that must result from the observed decrease of all three components of the solar wind velocity. Moreover, we will show that the spatial distribution in the pressure of interstellar pickup ions inherent in the model of Fisk & Gloeckler provides a natural explanation for the IBEX ribbon of enhanced ENH fluxes observed by McComas et al. Goldstein, Observations of Energetic Ions and Electrons in Earth’s Magnetotail Melvyn Melvyn L. Goldstein, NASA GSFC Kyoung‐Joo Hwang, Univ. of Mary and NASA Goddard Space Flight Center While observations of energetic particles within the magnetosphere are not new, we have collected a few observations of energetic ions and electrons associated with “dipolarization fronts” in the magnetotail. The most common interpretation of such flows is that that arise from magnetic reconnection in the near‐Earth neutral sheet. The observed energization is usually attributed to betatron and/or Fermi acceleration associated with the local magnetic pileup signature of dipolarization fronts and with the large‐ scale reconfiguration (i.e., shortening) of magnetic fields that results from the radial convection of dipolarization fronts as they convect inward. We review some observations of “classical” dipolarization fronts and some unique observations of multiple fronts that appear to be related to multiple reconnecting sites that pass close to the Cluster spacecraft. We also show an event that, rather than convecting Earthward, appears to be convecting tailward. The origin of this event is unclear but it is associated with fluxes of 10’s of keV electrons and ~10 keV protons. That event, which may be associated with some sort of current disruption appears to be unusual in that there is an absence of auroral kilometric radiation and it is not clear that a substorm is connected to that event. Golla, Thejappa Directivity Patterns of Complex Solar Type III Radio Bursts: Stereoscopic Observations Thejappa Golla, UMD, USA R. J. MacDowall, GSFC, NASA, USA Complex solar type III‐like radio bursts are a group of type III bursts that occur in association with slowly drifting type II radio bursts excited by the coronal mass ejection (CME) driven shock waves. We present simultaneous observations of these radio bursts from the STEREO A, B and WIND spacecraft at low frequencies, located from different vantage points in the ecliptic plane. Using these stereoscopic observations, we determine the directivity of these complex radio bursts. We estimate the angles between the directions of the magnetic field at the sources and the lines connecting the source to the spacecraft (viewing angles) by assuming that the sources are located on the Parker spiral magnetic field lines emerging from the associated active regions into the spherically symmetric solar atmosphere. We estimate the normalized peak intensities of these bursts (directivity factors) at each spacecraft using their time profiles at each spacecraft. These observations indicate that the complex type III bursts can be divided into two groups: (1) bursts emitting into a very narrow cone centered around the tangent to the magnetic field, )and (2 bursts emitting into a wider cone. We show that the bursts, which are emitted along the tangent to the spiral magnetic field lines at the source are very intense, and their intensities steadily fall as the viewing angles increase to higher values. We have developed a ray tracing code and computed the distributions of the trajectories of rays emitted at the fundamental and second harmonic of the electron plasma frequency. The comparison of the observed emission patterns with the computed distributions of the ray trajectories indicate that the intense bursts visible in a narrow range of angles around the magnetic field directions probably are emitted in the fundamental mode, whereas the relatively weaker bursts visible to a wide range of angles are probably emitted in the harmonic mode. 14th ANNUAL INTERNATIONAL ASTROPHYSICS CONFERENCE ORAL ABSTRACTS
Gopalswamy, High‐energy Solar Energetic Particle Events in Cycle 24 Nat Nat Gopalswamy NASA Goddard Space Flight Center, USA The Sun is already in the in the declining phase of cycle 24, but the paucity of high‐energy solar energetic particle (SEP) events continues with only two ground level enhancement (GLE) events as of March 31, 2015. In an attempt to understand this, we have identified several factors that seem to be responsible for the very low rate of high‐ energy SEP events in cycle 24: (i) reduced efficiency of shock acceleration (weak Heliospheric magnetic field), (ii) large‐ecliptic distance to solar sources of major eruptions (poor latitudinal connectivity), and (iii) variation in local ambient conditions (e.g. high Alfven speed). There are also other possibilities such as lack of seed particles that can be included in (iii). We examined 55 major frontside eruptions (soft X‐ray flare size ≥M5.0) that occurred during December 1, 2008 to January 31, 2014. These included 16 large SEP events (proton intensity ≥10 pfu in the >10 MeV energy channel) from GOES and 4 from STEREO‐Behind. When the associated CMEs were grouped according to their speeds (V), there were 27 with V <1500 km/s and 28 with V ≥ 1500 km/s). Only three of the <1500 km/s CMEs (or 11%) were associated with large SEP events compared to 17 or (61%) of the ≥ 1500 km/s CMEs. This result confirms the importance of CME speed for SEP association. There were also ten other large SEP events with flare size
Guo, Xiaocheng Investigation of Galactic Cosmic Rays Modulation by the Corotating Interaction Regions Xiaocheng Guo, The University of Alabama in Huntsville, USA Vladimir, Florinski, The University of Alabama in Huntsville, USA Corotating interaction regions (CIRs) are produced as a result of the interaction between fast and slow solar‐wind streams, and quite ubiquitous in every region of the heliosphere. Observations shown that the stream interfaces of CIRs between fast and slow solar wind streams and the leading edges of CIRs are responsible for the depressions of galactic cosmic rays (GCRs) intensity. Based on the well known local‐scale expansion of the ideal MHD conservation law and the developed global MHD model of CIRs in the heliosphere, we perform the numerical investigation of the transport and turbulence of the solar wind fluctuation in CIRs. Turbulent energy density and correlation length distribution throughout the heliosphere are presented, and further in turn used to compute the mean free path and perpendicular diffusion coefficient of energetic particles. We attempt to use the plasma background from the global MHD simulations and the transport coefficients in our existing stochastic cosmic‐ray transport code to numerically solve the Parker transport equation for GCRs. The modulated GCR spectrum from Voyager 2 observations near the termination shock was used at the external boundary condition. The computed GCR spectral features and temporal profiles at any given location was directly compared with observations by spacecraft based cosmic‐ray detectors and neutron monitors on the ground, which will greatly enhance our understanding of the physics of GCR modulation by the CIRs in heliosphere. Gurnett, Don Precursors to Interstellar Shocks of Solar Origin D.A. Gurnett, University of Iowa, USA W.S. Kurth, University of Iowa, USA E.C. Stone, California Inst. Technology, USA A.C. Cummings, California Inst. Technology, USA S.M. Krimigis, Applied Physics Lab./JHU, USA R.B Decker, Applied Physics Lab./JHU, USA N.F. Ness, Catholic Univ. of America, USA L.F. Burlaga, NASA/Goddard Space Flight Center, USA On or about August 25, 2012, the Voyager 1 spacecraft crossed the heliopause into the nearby interstellar plasma. In the roughly two and a half years that the spacecraft has been in interstellar space, three notable plasma oscillation events have been observed, each apparently associated with a shock wave propagating outward from an energetic solar event. Here, we present a detailed analysis of the third and most impressive of these events. The shock responsible for this event was first detected on February 17, 2014, by the onset of narrowband radio emissions from the approaching shock, followed on May 16 by the abrupt appearance of intense electron plasma oscillations at the electron plasma frequency generated by electrons streaming outward ahead of the shock. The radio emissions first detected on February 17 are believed to be produced by these plasma oscillations via nonlinear interactions. Finally, kthe shoc arrived on August 23, followed by a gradual increase in the plasma density, probably due to the pressure pulse driving the shock. Small but significant disturbances in the intensity and anisotropy of galactic cosmic rays were also observed ahead of the shock. Comparisons to the two previous weaker events show somewhat similar precursor effects, although not in as much detail. It is notable that many of these upstream effects are very similar to those observed ahead of planetary bow shocks and interplanetary shocks, only on a vastly larger spatial scale. Ho, George Composition Variations of Low Energy Heavy Ions during Solar Energetic Particle Events George C. Ho, Johns Hopkins University Applied Physics Laboratory, USA The time‐intensity profile of large solar energetic particle (SEP) event is well organized by solar longitude as observed at Earth orbit. This is mostly due to different magnetic connection to the shock that is associated with large SEP event propagates out from the Sun to the heliosphere. Recent studies have shown event averaged heavy ion abundance ratios can also vary as a function of solar longitude. It was found that the Fe/O ratio for high energy particle (>10 MeV/nucleon) is higher for those western magnetically well connected events compare to the eastern events as observed at L1 by ACE. In this paper, we have examined the low energy (~ 1 MeV/nucleon) heavy ions in large SEP events from 2009 to the end of 2014 using ULEIS instruments on ACE spacecraft. We selected only isolated events that show clear onset at 1 AU. The optical and radio signatures for all of our events are identified and when data are available we also located the associated CME data. We will investigate the event average and temporal variation of the heavy ion abundances in these large SEP events as a function of their solar origins and intensity levels. 14th ANNUAL INTERNATIONAL ASTROPHYSICS CONFERENCE ORAL ABSTRACTS
Hunana, Peter Fluid models with kinetic effects Hunana P., University of Alabama in Huntsville, USA Zank G. P., University of Alabama in Huntsville, USA Goldstein M. L., NASA Goddard Space Flight Center, USA In recent years there has been an increased interest in so‐called kinetic effects in the turbulent evolution of the solar wind, i.e. the differences between a fluid and kinetic descriptions. We will explore differences between traditional fluid models (Hall‐MHD, CGL), advanced fluid models that incorporate proton and electron Landau damping and finite Larmor radius corrections (Landau fluids) and compare them with linear kinetic theory. We will show that many effects that appear purely kinetic in nature can be reproduced and understood in a fluid framework. We will also discuss a three fluid model (protons, electrons, pickup protons), where rapid pitch‐angle scattering of hot pickup protons by turbulence introduces additional damping to the usual two fluid model, (protons electrons) that is typically used to describe the solar wind and the interstellar medium. Jeffrey, Natasha The collisional relaxation of electrons in a finite temperature plasma and its effect upon the diagnostics of solar flare accelerated electrons from X‐ray spectra and imaging Natasha Jeffrey, University of Glasgow, UK Eduard Kontar, University of Glasgow, UK Gordon Emslie, University of Western Kentucky, USA Nicolas Bian, University of Glasgow, UK During a solar flare, a large number of electrons are accelerated, and their properties deduced by X‐ray observations with instruments such as the Ramaty High Energy Solar Spectroscopic Imager (RHESSI). The properties of accelerated electrons are changed when they encounter a dense atmosphere, either in the corona or the chromosphere, where they lose energy collisionally, mainly to other electrons. Therefore, the properties of the accelerated electron distribution must be deduced via the application of a chosen model, which is frequently where electrons lose energy frictionally in a 'cold’ (where the electron energy is much greater than the background temperature) high density region. However, such a model does not realistically account for the behaviour of accelerated electrons in a finite temperature ambient plasma (at 10s of megaKelvin in the corona) and the subsequent collisional diffusion and thermalization of accelerated electrons during a flare. Firstly, I will discuss how the inferred properties of the accelerated electron distribution from solar flare X‐ray spectra, such as the injection rate and total energy content can be dramatically changed by accounting for the effects of collisional diffusion and thermalization. Particularly, I will discuss how such a model must be used to describe the observation of hot 20 MK, high density coronal X‐ray sources, observed during a number of flares. The spatial changes of such coronal X‐ray sources have been used to infer, and deduce, the properties of an electron acceleration region from X‐ray imaging, and I will also discuss how the inferred properties of the acceleration region itself, such as its size and number density, are altered by properly accounting for the collisional relaxation of electrons in a finite temperature plasma. 14th ANNUAL INTERNATIONAL ASTROPHYSICS CONFERENCE ORAL ABSTRACTS
Khabarova, Olga Dynamical small‐scale magnetic islands as a source of local acceleration of particles to suprathermal energies in the solar wind Olga Khabarova, Heliophysical Laboratory, IZMIRAN, Russia Gary P. Zank, Center for Space Plasma and Aeronomic Research (CSPAR), University of Alabama in Huntsville, USA Gang Li, CSPAR, University of Alabama in Huntsville, USA Jakobus A. le Roux, CSPAR, University of Alabama in Huntsville, USA Gary M. Webb, CSPAR, University of Alabama in Huntsville, USA Alexander Dosch, CSPAR, University of Alabama in Huntsville, USA Olga E. Malandraki, IAASARS, National Observatory of Athens, Greece Valentina V. Zharkova, Department of Mathematics and Information Sciences, Northumbria University, UK We present evidence for significant role of magnetic islands (MIs) in particle acceleration in the solar wind plasma. Usually, the occurrence of suprathermal particles possessing keV‐MeV energies at 1 AU is supposed to be related to acceleration either at the Sun or at the ICME bow shock/interplanetary shocks. The obtained results give a possibility to explain the presence of energetic particles near the Earth’s orbit alternatively: through their local acceleration directly at 1 AU. Multi‐spacecraft observations show that numerous cases of unusual energetic particle flux increases (so‐called local SEP‐events) correspond to passages of spacecraft through areas filled with MIs that experience dynamical merging or/and contraction. Small‐scale MIs with a typical size of l <0.1 AU are commonly observed in the solar wind plasma. These structures are characterized by a rotating magnetic field in combination with an anti‐correlated “density – magnetic field” pair; and they are often regarded to magnetic reconnection. As places where magnetic reconnection re‐currently occurs, interplanetary current sheets represent the main source of the small‐scale magnetic islands in the solar wind at 1 AU. The probability of MI observation increases with approaching to the heliospheric current sheet ‐ HCS (Cartwright & Moldwin, JGR, 2010). Plasma confinement of any kind leads to formation of such structures as well. Recent theoretical investigations have shown that dynamically changing magnetic islands in radially expanding solar wind may serve as a source of particle acceleration (Zank et al., ApJ, 2014; Le Roux et al., ApJ, 2015). We provide here support for theory and simulations, showing signatures of particle energization related to magnetic islands both near the reconnecting HCS and far from it, inside specifically confined regions of expanding solar wind observed by several spacecraft. An application of the idea to interpretation of CIR‐associated energetic particle events is discussed as well. Kontar, Eduard Turbulent electron pitch angle scattering in solar flares: diagnostics and models Kontar, Eduard P., Glasgow University, UK Bian, Nicolas H., Glasgow University, UK Emslie, A. Gordon, Western Kentucky University, USA Vilmer, Nicole, Observatoire de Paris, France We consider turbulent (non‐collisional) pitch‐angle scattering of fast electrons off low‐frequency magnetic fluctuations as a pitch angle scattering mechanism leading to a spatial diffusion parallel to the mean magnetic field. Comparing the predictions of the model with RHESSI observations, we find the typical mean free paths required by observations for deka‐keV electrons. Some non‐collisional pitch angle scattering is found to be consistent with the observations, at the same time strong pitch‐angle scattering is inconsistent with RHESSI observations. Implications for acceleration and transport models in solar flares will be discussed. 14th ANNUAL INTERNATIONAL ASTROPHYSICS CONFERENCE ORAL ABSTRACTS
Kota, Jozsef Compressive and Non‐compressive Particle Acceleration: Illustrative Numerical Simulations Jozsef Kota, The University of Arizona, USA
We discuss compressive and non‐compressive particle acceleration due to random fluctuation in plasma density and magnetic field strength. For diagnostic purposes, we consider simple cases with single sinusoidal variations in density and/or magnetic field strength. Analytical expressions are derived for the rate of energy diffusion Compressive acceleration is described by the diffusive Parker equation cast in a Lagrangian form. We present a simple toy‐model including the back‐reaction of accelerated energetic particles on the core fluid. Non‐compressive particle acceleration can occur without net compression in the fluid due to variations in the magnetic field strength resulting from random contraction or dilatation of magnetic field lines. Analytical estimates and numerical simulations will be presented employing the focused transport equation written in Lagrangian form. Krimigis, Overview of Voyager 1, 2 Energetic Particle Measurements 2013‐2015 Stamatios Stamatios Krimigis, Johns Hopkins University Applied Physics Laboratory, USA, and Academy of Athens, Greece Robert B Decker, Johns Hopkins University Applied Physics Laboratory, USA M. E. Hill, Johns Hopkins University Applied Physics Laboratory, USA E. C. Roelof, Johns Hopkins University Applied Physics Laboratory, USA The two Voyager spacecraft currently at 131 AU (V1) and 108 AU (V2), are exploring the near interstellar medium and the southern heliosheath, respectively. The anisotropy in galactic cosmic rays (GCR) at E greater than 211 Mev seen upon crossing the heliopause at 121.6 AU on August 25, 2012 (Krimigis et al, 2013) reached a maximum of 8.5% in March 2013 between the magnetic field‐aligned and normal components but then decreased rapidly to zero by mid‐August 2013, suggesting that V1 entered an apparently undisturbed region of nearby local interstellar medium (LISM) some 4 AU after the crossing. The GCR anisotropy, however, returned in mid‐May 2014 but isotropy was again restored by mid‐August. There is now some evidence that a third cycle of anisotropic activity may be in progress, suggesting that such disturbances are rather common within the LISM to distances at least about 10 AU upstream of the heliopause. Much as the first disturbance was associated with solar activity (Krimigis et al, 2013), so the other events may also have their origin on the Sun. The anomalous cosmic ray intensities (ACR) characteristic of heliosheath matter (H, He, O) at les than about 20 Mev/nucleon continue to be absent from the region upstream of the heliopause to this date. Intensities of ACR at V2 are currently about the same as those at V1 just prior to crossing the heliopause. Examination of intensity and spectral signatures suggests that a crossing of the heliopause at V2 is not imminent. Krimigis, S. M., R. B. Decker, E. C. Roelof, M. E. Hill, T. P. Armstrong, G. Gloeckler, D. C. Hamilton, and L. J. Lanzerotti (2013), Search for the Exit: Voyager 1 at Heliosphere’s Border with the Galaxy, Science 341, pp. 144‐147, doi:10.1126/science.1235721. Kucharek, Wave‐Particle Interactions and Ion Acceleration in the Outer Heliosphere: A 3D Hybrid Simulation Study. Harald Konstantin Gamayunov, Florida Institute of Technology, Melbourne, FL, USA Nikolai Pogorelov, University of Alabama in Huntsville, Huntsville, AL, USA Voyager data and IBEX observations provided outstanding new insights in the global structure of our heliopshere. The detection of a ribbon structure in the light of energetic neutral atoms, the possible absence of a heliospheric bow shock, and the strong indication that Voyager 1 has left our solar system raised many questions about the physical processes that may happen at the heliospheric boundaries to the interstellar space. Most of the physical processes, such as charge exchange, and small‐ to medium‐scale turbulence initiated by wave‐particle interactions, happen on the ion scale. To understand physical processes in the outer heliosheath is in particular important because this region is considered to be a source location of the ribbon, and it is the next‐to‐outermost boundary of our solar system: the heliopause. At this boundary the interstellar plasma flow is deflected and turbulence is created. Currently we are far from understanding the turbulence and the associated physical processes at these boundaries. Hybrid simulations, which include all kinetic processes self‐consistently on the ion level, are proven to be a very powerful tool to investigate wave‐particle interaction, turbulence, and phase‐space evolution of pickup and solar wind ions (such as H+, He+ and He2+). We performed 3D multi‐species hybrid simulations for an ion/ion beam instability to study the temporal evolution of ion distributions, their stability, and the associated ENA production under the influence of self‐generated, self‐consistent waves and the ion energetization in the heliosheath. Therefore, these investigations are critical to understand and interpret Voyager and IBEX observations. 14th ANNUAL INTERNATIONAL ASTROPHYSICS CONFERENCE ORAL ABSTRACTS
Laming, Martin Wave Propagation at Oblique Shocks: How Did Tycho Get Its Stripes? Martin Laming, Naval Research Laboratory, USA We describe a new model for the ``stripes'' of synchrotron radiation seen in the remnant of Tycho's supernova. In our picture, cosmic rays streaming ahead of the forward shock generate parallel (with respect to the local magnetic field direction) circularly polarized Alfven waves that are almost free of dissipation, and due to being circularly polarized exhibit no spatial variation of magnetic field strength. Following interaction with the SNR shock with nonzero obliquity, these parallel waves become obliquely propagating, due the the wave refraction (different in principle for the different plane wave components), and dissipation sets in. The magnetosonic polarization decays faster, due to transit time damping, leaving only the Alfven mode. This surviving mode now exhibits a spatial variation of the magnetic field, leading to local maxima and minima in the synchrotron emission,. i.e the stripes. We attribute the initial wave generation to the Bell instability, which in contrast to the resonant generation of upstream Alfven waves, gives rise to a preferred wavelength, and hence the single wave period at which the stripes are seen. Based on estimates for damping rates due to turbulent cascade and transit time damping, we estimate the dependence of the visibility of the stripes on the shock obliquity, and determine a maximum cosmic ray energy in Tycho's SNR in the range 6e14 ‐ 1e15 eV Lario, David Energetic Particle Pressure at Interplanetary Shocks D. Lario, JHU/APL, USA R.B. Decker, JHU/APL, USA E.C. Roelof, JHU/APL, USA A.‐F. Viñas, NASA/GSFC, USA We study periods of elevated energetic particle intensities observed by STEREO‐A when the partial energy density associated with energetic (≥80 keV) particles dominates that of the magnetic field and thermal plasma populations. These periods are frequently observed and commonly associated with the passage of interplanetary shocks. In the foreshock region of the most intense events the pressure exerted by the energetic particles may exceed by more than one order of magnitude both the magnetic field and the thermal solar wind pressures, as depressed magnetic field and decreased solar wind densities coincide with the increase of energetic particle intensities. Prolonged periods dominated by the energetic particle pressure are also observed when the injection of particles by an approaching shock occurs in a region characterized by low magnetic field and tenuous solar wind density. We emphasize the need to consider the energetic particle effects when studying the properties of shocks running into these regions and discuss whether these shocks show the properties typically associated with the so‐called “cosmic‐ray‐modified” shocks. This research is partially supported by the NASA LWS program. le Roux, Jakobus A Kinetic Transport Theory for Energetic Particle Acceleration in Solar Wind Regions with Multiple Contracting and Reconnecting Small‐scale Flux Ropes Jakobus A. le Roux, University of Alabama in Huntsville, USA Gary P. Zank, University of Alabama in Huntsville, USA Gary M. Webb, University of Alabama in Huntsville, USA Olga Khabarova, IZMIRAN, Russia Simulations of particle acceleration in turbulent plasma regions with multiple contracting and merging (reconnecting) magnetic islands emphasize the key role of temporary particle trapping in island structures for the efficient acceleration of particles to form hard power‐law spectra. A comprehensive statistical kinetic transport theory has recently been developed by Zank et al. that unifies the essential physics of particle acceleration in multi‐island regions. This theory is further developed by considering not only the acceleration effects of the mean electric fields induced by the dynamics of multiple small‐scale scale flux ropes, but also their variance. A focused transport equation is derived that includes new Fokker–Planck terms for particle scattering and stochastic acceleration due to the variance in multiple flux‐rope magnetic fields, electric fields induced by the plasma flows associated with flux‐rope dynamics, and reconnection electric fields produced by merging flux ropes. A Parker transport equation is also derived in which an expression for momentum diffusion appears, combining stochastic acceleration by particle scattering in the mean multi‐flux‐rope electric fields with acceleration by the variance in these electric fields. Test particle acceleration is modeled analytically considering drift acceleration by the variance in the induced electric fields of flux ropes in the slow supersonic, radially expanding solar wind. It was found that hard power‐law spectra occur for sufficiently strong inertial‐scale flux ropes with an index modified by adiabatic cooling, solar wind advection, and diffusive escape from flux ropes. It is speculated that flux ropes might potentially be sufficiently strong behind interplanetary shocks to reproduce the index of suprathermal ion power‐law spectra observed in the supersonic solar wind. Preliminary results will be discussed to illustrate how particle acceleration might be affected when both diffusive shock acceleration and drift acceleration by small‐scale flux rope induced electric fields occur simultaneously at interplanetary shocks. 14th ANNUAL INTERNATIONAL ASTROPHYSICS CONFERENCE ORAL ABSTRACTS
Li, Gang Particle acceleration at CIRs L. Zhao, Department of Space Science, UAH, USA G. Li, Department of Space Science and CSPAR, UAH, USA R. W. Ebert, Southwest Research Institute, USA M. A. Dayeh, Southwest Research Institute, USA M. I. Desai, University of Texas at San Antonio and Southwest Research Institute, USA G. M. Mason, Applied Physics Laboratory, Johns Hopkins University, USA Z. Wu, Insitute of Space Sciences and School of Space Science and Physics, Shandong University at Weihai, China Y. Chen, Insitute of Space Sciences and School of Space Science and Physics, Shandong University at Weihai, China During solar minimum, energetic particles up to a few to $10$'s MeV/nucleon are often observed with Corotating Interaction Regions (CIRs). In the model proposed by \citet{Fisk1980}, these energetic particles are accelerated at the CIR reverse shock formed $\sim 3$ to $5$ Astronomical Units (AUs) and then propagate back to $1$ AU. Later observations, however, showed that in many CIR events there are signs of local acceleration near $1$ AU. In this study, we examine one CIR event, which occurred on $2008$ Feburary $08$ and was observed by both the Advanced Composition Explorer (ACE) and the Solar TErrestrial RElations Observatory (STEREO)‐B spacecraft. A reverse shock was observed by STEREO‐B ($1.0$ AU) but not by ACE ($0.98$ AU), suggesting that the CIR shock was formed at a heliocentric distance very close to 1 AU. Using STEREO‐B observations and assuming the CIR structure does not vary significantly in the corotating frame, we can estimate the shock location for both the STEREO‐B and ACE observations at later times. Further assuming the accelerated particle spectral shape at the shock does not vary with shock location, we calculate the particle differential intensities as observed by ACE and STEREO‐B at different times using the focused transport equation. We assume that particles move along Parker's field and do not consider perpendicular diffusion in this work. %The solar wind turbulence strength is assumed to vary as $\delta_B^2 \sim r^{‐3.5}$ % radial dependent solar wind turbulence strength and a radial dependent acceleration efficiency, Reasonable comparisons between the simulations and the observations by both ACE and STEREO‐B can be obtained, provided that the shock can accelerate particles more efficiently at a larger distance. Implication of our simulation on the source location of CIR energetic particles is discussed. Livadiotis, Rankine–Hugoniot conditions for shocks in plasmas described by kappa distributions George George Livadiotis, Southwest Research Institute, USA The present paper examines the Rankine–Hugoniot (R‐H) jump conditions for shocks in space plasmas described by kappa distributions. The R‐H conditions constitute the relationship between thermodynamic variables of the flow on both sides of a shock wave. Using this relationship, each of the thermodynamic variables upstream the shock can be expressed in terms of thermodynamic variables downstream the shock. Here we discuss the effect of kappa distributions, explaining the presence of kappa indices in jump conditions. The challenge is to find the connection between the kappa values of the plasmas upstream and downstream the shock. Several past attempts to connect the upstream/downstream kappa indices were based on ill‐defined first physical principles, such as the dependence of the mean kinetic energy, or the thermal pressure, on the kappa index. However, the conservation, of mass momentum, and energy equations are independent of the kappa index, and thus, all the states of different kappa are equivalent for describing the known R‐H conditions. The upstream/downstream kappa values must be connected through a new R‐H condition yet to be discovered. In order to reveal this relationship is necessary to shed light on the physical concepts behind the statistical origin of kappa distributions and their governing parameter, the kappa index. Lu, Quanming Electron acceleration in the dipolarization front driven by magnetic reconnection Quanming Lu, Can Huang, Mingyu Wu, RongSheng Wang University of Science and Technology of China, China A large scale two‐dimensional (2‐D) particle‐in‐cell (PIC) simulation is performed in this paper to investigate electron acceleration in the dipolarization front (DF) region during magnetic reconnection. It is found that the DF is mainly driven by an ion outflow which also generates a positive potential region behind the DF. The DF propagates with an almost constant speed and gets growing, while the electrons in the DF region can be highly energized in the perpendicular direction due to betatron acceleration. For the first time, we reveal that there exists a velocity threshold, only the electrons below the threshold can be trapped by the parallel electric potential in the DF region and then energetized by betatron acceleration. 14th ANNUAL INTERNATIONAL ASTROPHYSICS CONFERENCE ORAL ABSTRACTS
Manchester, Simulating Alfven Wave Enhancements at Stream Interaction Regions Ward Ward Manchester IV, University of Michigan Xiangyun Zhang, University of Michigan Doga Can Su Ozturk, University of Michigan Bart van der Holst, University of Michigan We use the Alfven Wave Solar Model (AWSoM): a global model for the corona and inner heliosphere to study Alfven wave turbulence at stream interaction regions (SIRs). With this advanced model, coronal heating and solar wind acceleration are addressed with low‐frequency Alfven wave turbulence including the following physical processes: wave reflection due to Alfven speed gradients, counter‐propagating waves, which lead to nonlinear wave dissipation, and two temperatures: electron temperature and proton temperatures with field aligned heat conduction, In this way, the propagation, dissipation and energy deposition of Alfven waves is self‐consistently captured in the corona and heliosphere. Here, we study the formation of SIRs during solar minimum and the interaction of low‐frequency Alfven waves with the SIR compressions in the solar wind near 1 AU. We compare our model predictions to in situ observations of Alfven wave turbulence, and find the model reproduces the observed levels of enhanced turbulence at the SIR compressions. Mann, Gottfried Generation of energetic electrons during solar flares Gottfried Mann, Leibniz‐Institut fuer Astrophysik Potsdam, Germany A flare is defined as an sudden enhancement of the emission of electromagnetic radiation of the Sun covering a broad range of the spectrum from the radio up to the gamma‐ ray range. That indicates the generation of energetic electrons during flares, which are considered as the manifestation of magnetic reconnection in the solar corona. In which way 10^36 electrons are accelerated up to an energy > 30 keV within a second during solar flares, is still an open question in solar physics. The flare is considered as a manifestation of magnetic reconnection in the corona. According to the standard flare model, the inflow region of the reconnection region is separated from the outflow one by pairs of slow mode shocks. At them, the magnetic field energy is efficiently annihilated and transfered into a strong heating of the outflow plasma leading to the generation of energetic electrons as required for the hard X‐ray radiation at large flares. The slow mode shocks are studied in terms of the Rankine‐Hugoniot relationships. Especially, the jump of the temperature and the magnetic field across the shock is evaluated to study the heating of the plasma in the outflow region. The resulting fluxes of energetic electrons in the outflow region are calculated in a fully relativistic manner. Due to the strong heating of the plasma at the slow mode shocks, enough electrons with energies > 30 keV are generated in the outflow region as required for the hard X‐ray radiation. The theoretically obtained fluxes of energetic electrons agree well with those as measured by RHESSI during large flares. Mason, Glenn Longitudinal Properties of Low Energy SEP Heavy Ions C. M. S. Cohen, Caltech, USA R. A. Mewaldt, Caltech, USA We have surveyed the properties of SEP heavy ions viewed by multiple spacecraft using the ACE and STEREO SEP instruments during the period 2011‐2014 in order to test scenarios of SEP acceleration and transport. Studies to date have been primarily at multi‐MeV/nucleon energies, and have revealed events with surprisingly broad longitudinal extent with sometimes fast initial rises seen from widely separated spacecraft. Within the picture of particle acceleration by CME‐driven shocks, it could be expected that the higher energy particles were energized primarily near the shock nose and so might have a smaller longitudinal extent than lower energy particles. On the other hand, if the wide longitudinal extent is primarily a transport effect, then the higher energy particles might be seen over a broader range since their mobility is higher. We focus on larger SEP events so that the low and high energy particle behavior can be compared on a case by case basis, with emphasis on longitudinal extent, Fe/O ratio, and spectral indices. 14th ANNUAL INTERNATIONAL ASTROPHYSICS CONFERENCE ORAL ABSTRACTS
Matsukiyo, Electron acceleration at a high beta shock Shuichi Shuichi Matsukiyo, Kyushu Univ., Japan Yosuke Matsumoto, Chiba Univ., Japan A high beta shock has not been paid much attention from the aspect of particle acceleration, since it is a relatively weak shock so that its structure is more or less laminar and steady where the activities of waves are generally thought to be low. In space, on the other hand, a number of high beta shocks are observed and some of them indicate the evidence of particle acceleration. For instance, radio synchrotron emissions from relics of galaxy cluster mergers imply the presence of relativistic electrons accelerated in the merger shocks. Voyager spacecraft revealed that the heliospheric termination shock, which has high effective beta due to the presence of pickup ions, is also an accelerator of non‐thermal ions and electrons. Recently, it is shown by Matsukiyo et al.(2011) and Matsukiyo and Scholer (2014) that high beta shocks such as the above mentioned circumstances can efficiently accelerate electrons through shock drift mechanism by using 1D full PIC simulations. However, the one dimensionality may be too strong constraint in the sense that possible wave propagation near the shock is allowed only along the shock normal direction. In this study we perform 2D full PIC simulation of a high beta shock with realistic ion‐to‐electron mass ratio. It is shown that microstructure of the shock is unexpectedly complex due to the excitation of a variety of waves. Furthermore, acceleration mechanism of electrons drastically changes from the one‐dimensional case for the particular parameters examined. McComas, David Remote Observations of Particle Distributions from the Outer Heliosphere by IBEX David McComas, Southwest Research Institute, USA The Interstellar Boundary Explorer (IBEX) has now returned five full years of global observations of the outer heliosphere. The data include 10 sets of energy resolved all‐sky maps of Energetic Neutral Atoms (ENAs) emanating in from both the inner heliosheath (between the termination shock and heliopause) and the outer heliosheath (beyond the heliopause). With these data, we observe significant time dependence as the outer heliosphere responds, with an appropriate time delay, to the combined effects of the 11‐year solar cycle and longer term evolution of the three dimensional solar wind. IBEX observations have underlined the absolutely critical role of suprathermal ions in dominating the internal pressure and thus plasma processes in the inner heliosheath plasma. For example, most recently, IBEX‐measured particle pressures were used to explain the observed plasma flows at Voyager 2, which are inconsistent with expectations from prior modeling techniques that largely treat the inner heliosheath plasma distributions as Maxwellian. Instead, IBEX observations have shown that outer heliospheric plasmas are actually far from equilibrium, with kappa values approaching 1.5 (“anti‐equilibrium” – the furthest stationary state away from it). Such distributions arise naturally from the continued injection of pickup ions into the solar wind, which add order to the distributions and drive down their entropy. In this study we examine recent discoveries driven by IBEX observations and discuss their implications for our rapidly evolving understanding of the physics of the outer heliosphere – our home in the galaxy. McIntosh, Scott Modified Rossby Waves in the Solar Interior: The Need For A Solar Meteorology Mission Scott W. McIntosh, High Altitude Observatory, NCAR, USA. Using a combination of STEREO/SECCHI/EUVI and SDO/AIA imaging we reveal patterns in the imaging data that are consistent in appearance with global scale rotationally driven waves on the activity bands of the solar magnetic polarity cycle. These observations point to new insight into the root causes of space weather and motivate a new multi‐ viewpoint study of the entire solar atmosphere. Medvedev, Particle acceleration in astrophysical relativistic jets Mikhail M.V. Medvedev, U. Kansas, USA Relativistic jets (e.g., in AGN) are often thought to be accelerators of high‐energy cosmic rays. This is a lore but no justification of it exists. We investigate this problem from the first principle and argue that "no‐jets" are better accelerators than the jets themselves. 14th ANNUAL INTERNATIONAL ASTROPHYSICS CONFERENCE ORAL ABSTRACTS
Morlino, Particle acceleration at shocks propagating in partially ionized plasmas Giovanni Giovanni Morlino, INFN/GSSI, L'Aquila, ITALY The shocks of several young supernova remnants (SNR) are often associated with very thin optical filaments dominated by Balmer emission resulting from charge‐exchange and collisional excitation between neutral Hydrogen from the interstellar medium and shocked protons and electrons. Optical lines are a direct probe of the conditions at the shock, in particular the width of the narrow and broad components reflect the temperature upstream and downstream of the shock, respectively. When the shock accelerate efficiently non‐thermal particles, the shock structure changes producing anomalous sBalmer line and it is possible to use their line shape and their spatial profile to check the efficiency of SNR shocks in accelerating cosmic rays. Here we illustrate the kinetic theory of shock acceleration in presence of neutrals with some applications to young SNRs. We show that in some cases anomalous Balmer lines can be explained assuming that a fraction of ~10% of the total shock kinetic energy is converted into not thermal particles. Olmi, Barbara Particle acceleration and non‐thermal emission in Pulsar Wind Nebulae from relativistic MHD simulations Barbara Olmi, Università degli Studi di Firenze, Italy Luca Del Zanna, Università degli Studi di Firenze, Italy Elena Amato, Osservatorio Astrofisico di Arcetri INAF, Italy Niccolò Bucciantini, Osservatorio Astrofisico di Arcetri INAF, Italy Pulsar wind nebulae (PWNe) are among the most powerful particle accelerators in the Galaxy. In recent years relativistic axisymmetric MHD models have proven to be excellent tools for describing the physics of such objects. In particular they result very successful at explaining the X‐ray emission morphology of PWNe, down to very fine details. Nevertheless two important aspects are still obscure in PWNe physics: the nature of the low energy emitting particles (namely the radio ones) and the mechanism responsible for the particle acceleration. The correct interpretation of the radio emission is of fundamental importance, as it holds information about pulsar properties and their role as antimatter factories. Particle acceleration, at least for high energetic particles, is commonly thought to occur at the pulsar wind termination shock. Since the upstream flow is thought to have non‐uniform properties along the shock surface, important constraints on the acceleration mechanism could come from the exact knowledge of the location where particles are being accelerated. By means of 2D numerical MHD simulations both these topics are investigated in details. The perfect object to compare with is certainly the Crab Nebula, the PWN prototype, since it is one of the most studied objects in the sky and, of course, it is know with great and fine details. Different assumptions for the origin of the radio particles and for the particle injection sites at the termination shock surface are considered, and the corresponding emission properties are computed. I will discuss which constraints can result from the comparison of these synthetic emission properties and the available data. 14th ANNUAL INTERNATIONAL ASTROPHYSICS CONFERENCE ORAL ABSTRACTS
Parks, George New Clues on the Formation of Nonlinear Structures observed Upstream of Earth’s bow shock Z. W. Yang 2, Y. Liu2, E. S. Lee3, S. Y. Fu4, N. Lin1, I. Dandouras5, H. Rème5, P. Canu6, and M. L. Goldstein7 1Space Sciences Laboratory, University of California Berkeley, USA 2Space Weather, Chinese Academy of Sciences, China 3School of Space Research, Kyung Hee University, Korea 4School of Earth and Space Sciences, Peking University, China 5CNRS, IRAP, CNRS and Toulouse University, France 6 LPP, Ecole Polytechnique, France 7 Goddard Space Flight Center, NASA, USA In the region upstream of Earth’s bow shock, a single magnetic pulsation can grow mysteriously out of the ambient wave train and evolves into a transient nonlinear structure1. A well‐known example of a nonlinear wave growth is a SLAMS event that can grow out of low frequency (~0.05 Hz) pulsations1 and which sometimes evolves into a nonlinear structure. The known upstream nonlinear structures include hot flow anomalies (HFA)6, hot diamagnetic cavities (HDC)7, Short Large Amplitude Magnetic Structures (SLAMS)8, foreshock cavities (FC)9, and density holes (DH)10. A nonlinear structure in the upstream is formed by a combination of the interplanetary current sheet interacting with the bow shock and reflected solar wind particles1 that are channeled back into the upstream region where they can interact with the incident SW2. However, what processes can select a particular pulsation to grow and how that pulsation can evolve into a nonlinear structure remain unexplained. On 2 April 2002 the four Cluster spacecraft (SC) were operating in “burst mode” and soon after the SC crossed the bow shock, two steepened magnetic pulsations were detected in succession but only one developed into a nonlinear structure. We have studied the high‐time resolution magnetic field data sampled 67 times s‐1 together with waves and 3D particle distributions obtained on spin period time scale (4s). Here we show that the magnetic pulsation that evolved into a nonlinear structure resulted from spontaneous generation of a field‐aligned current (FAC) produced by the incident SW strahl electrons drifting through back streaming SW ions. The FAC was unstable and we detected intense electrostatic (ES) waves generated very possibly by the Buneman instability. We then saw plasma heated to more than ten million degrees and the high temperature plasma expanded at super‐Alfvenic speeds steepening the edges into shock waves. Perri, Silvia Evidence for Superdiffusive Shock Acceleration at Interplanetary Shock Waves Silvia Perri, Dipartimento di Fisica, Universita della Calabria, Rende, Italy Gaetano Zimbardo, Dipartimento di Fisica, Universita della Calabria, Rende, Italy Recent analysis of time profiles of energetic particles accelerated at interplanetary shocks have shown evidences for superdiffusive transport upstream of the shock fronts, namely for a transport characterized by a particle mean square displacement that grows faster than linearly in time. While for normal, diffusive transport exponential particle time profiles are predicted, a large number of interplanetary shock events, included the termination shock of the solar wind, exhibits energetic particle time profiles that upstream decay as power laws. This power law trend has been analytically derived in the framework of particle superdiffusion, where the propagator of the process has power law tails. Further, the standard theory of diffusive shock acceleration has been extended to the case of particle superdiffusive transport (superdiffusivek shoc acceleration), allowing to derive harder energy spectral indices both for relativistic and non relativistic particles and the acceleration times. Here we present new results after testing the theory for a number of interplanetary shock waves, observed by the Ulysses and the ACE spacecraft, that accelerate both protons and electrons. We show that: power law particle time profiles upstream of the shocks are very frequent and clearly indicate a superdiffusive transport (since the variance of the magnetic field fluctuations, which is related to the particle diffusion coefficient, does not vary from the shock front); from the data it is possible to determine all the parameters that characterize the particle transport, as the anomalous diffusion coefficient; the particle energy spectra in some events are in a very good agreement with the superdiffusive shock acceleration prediction; the estimated acceleration times are shorter or comparable with the ones obtained from the diffusive shock acceleration theory, although this new acceleration mechanism seems to be more efficient for protons than for energetic electrons. 14th ANNUAL INTERNATIONAL ASTROPHYSICS CONFERENCE ORAL ABSTRACTS
Pierrard, Viviane Influence of Suprathermal Electrons on the Acceleration of Solar Wind Particles Viviane Pierrard, Belgian Institute for Space Aeronomy and University Catholique de Louvain, Belgium Sofia Moschou, Belgian Institute for Space Aeronomy and Katholieke University Leuven, Belgium Space plasmas are essentially collisionless systems out of thermal equilibrium, where enhanced populations of suprathermal particles are observed. The velocity distribution functions of their particles are not fully described by Maxwellian distributions. They generally have more suprathermal particles in the tail of the distribution. The presence of non‐thermal electrons in many space plasmas suggests a universal mechanism for which whistler turbulence can contribute. The Kappa distribution provides a generalization for the successful description of such plasmas with tails decreasing as a power law of the velocity. Suprathermal electrons play a crucial role in the heating and the acceleration of plasmas in several important space and astrophysical contexts. They affect the temperature and the generation of the ambipolar electric field, contributing to the collisionless electron heat flux processes. In the solar corona, such electrons make the dominant contribution to the electron heat flux and, thus, play an important role in the coronal heating energy budget. They also support large ambipolar electric fields along open magnetic flux tubes in stellar coronae and thus contribute significantly to solar and stellar wind acceleration. The distributions observed in situ in the solar wind have clear halo populations. The solar wind model developed on the basis of such kappa distributions has been improved by incorporating azimuthally varying boundary conditions to produce a spatially structured view of the solar wind expansion. By starting from the top of the chromosphere to the heliosphere and by applying relevant boundary conditions in the ecliptic plane, a global model of the corona and the solar wind is developed for each particle species. The model includes the natural heating of the solar corona automatically appearing when an enhanced population of suprathermal particles is present at low altitude in the solar (or stellar) atmosphere. This applies not only for electrons and protons, but also for the minor ions. The presence of suprathermal electrons contributes to the acceleration of the solar wind to high bulk velocities when Coulomb collisions are neglected. The results of the model are illustrated in the solar corona and in the solar wind for the different particles species and can now be directly compared in two dimensions with spacecraft observations in the ecliptic plane. Pinto, Rui X‐ray Emission in Simulations of Flaring Coronal Loops R. Pinto, IRAP, France N. Vilmer, LESIA, France M. Gordovskyy, U. Manchester, UK P. Browning, U. Manchester, UK Solar flares are associated with intense X‐ray emission generated by hot flaring plasma and by energetic particles in coronal magnetic loops. We investigate the temporal, spectral and spatial evolution of the properties of the X‐ray emission produced in simulated kink‐unstable magnetic flux‐ropes (using MHD and test‐particle methods). The numerical setup used consists of a highly twisted loop embedded in a region of uniform and untwisted background coronal magnetic field. The magnetic flux‐rope reconnects with the background flux after the triggering of the kink instability and is then allowed to relax to a lower energy state. Strong ohmic heating leads to strong and quick heating (up to more than 15 MK), to a strong peak of soft X‐ray emission and to the hardening of the thermal X‐ray spectrum. Particles are accelerated in all the flaring loop volume, but the associated synthetic hard X‐ray emission is concentrated near the footpoints. The amount of twist deduced from the thermal X‐ray emission alone is considerably lower than the maximum twist in the simulated flux‐ropes. The flux‐rope plasma becomes strongly multi‐thermal during the flaring episode, and the emission measure evolves into a bi‐ modal distribution as a function of temperature during the saturation phase, and later converges to the power‐law distribution during the relaxation/cooling phase. 14th ANNUAL INTERNATIONAL ASTROPHYSICS CONFERENCE ORAL ABSTRACTS
Poedts, Stefaan Coronal heating and solar wind acceleration by drift waves S. Poedts KU Leuven, Dept. of Mathematics, Center for mathematical Plasma Astrophysics (CmPA), and Leuven Computational Modeling Center (LCMC), Belgium An alternative approach to the coronal heating problem, based on the theory of drift waves, has been proposed. The drift mode is the only mode that is able to survive the drastically different (collisional–collisionless) extremes in the different layers of the solar atmosphere. As a matter of fact, this mode is overstable, i.e. able to grow, in both of these extreme situations, and has been called the ‘universally growing mode’ in the literature. In collisional plasma of the lower layers of the solar atmosphere, the drift mode grows due to the electron collisions and this can be described within the two‐fluid model. In the collisionless coronal plasma, however, the mode grows due to a pure kinetic effect, viz. the electron resonance effect in the presence of a density gradient.
It has been shown, with qualitative and quantitative arguments, that the drift waves have the potential to satisfy all coronal heating requirements. The basic ingredient required for the heating is the presence of density gradients in the direction perpendicular to the magnetic flux surfaces. The drift wave theory is well‐established and has been explicitly verified experimentally in laboratory (fusion) plasmas, similar (hot, low‐beta, highly conductive) to those in the solar atmosphere. In these circumstances, two mechanisms of the energy exchange and heating take place simultaneously: Landau damping in the direction parallel to the magnetic field, and stochastic heating in the perpendicular direction. The latter, in fact, is more effective on ions than on electrons, acts predominantly in the perpendicular direction, and heats heavy ions more efficiently than lighter ions. Moreover, for plasmas at a temperature of 1MK and beyond, thel paralle wave field resulting from the drift waves exceeds the Dreicer field so that the bulk plasma species (primarily electrons) can be accelerated/decelerated by the wave in the parallel direction. In addition, this acceleration is more effective on the particles that are already more energetic, resulting in a distribution function considerably different from a Maxwellian, similar to the observed kappa‐distribution in the outer solar atmosphere and in the solar wind. Pogorelov, Magnetic Field in the Heliosphere and Beyond Nikolai Nikolai Pogorelov, UAH, USA Jacob Heerikhuisen, UAH, USA Ming Zhang, FIT, USA Particle energization and transport throughout the heliosphere are strongly dependent on the magnetic field distributions. We present the results of our numerical simulation of the heliospheric magnetic field and ins coupling with the interstellar magnetic field (ISMF) at the heliopause. The effects of the ISMF draping are discussed together with the heliopause instability. Special attention is paid to the magnetic field distribution in the heliotail and the displacement of the latter due to the action of the ISMF. Possibilities are discussed of constraining the interstellar medium properties using IBEX, SOHO, and TeV cosmic ray anisotropy data. Qin, Gang Numerical test particle simulations of the Voyager 1 GCR increase beyond the heliopause caused by moving magnetic disturbance Gang Qin, and Lihua Zhang State Key Laboratory of Space Weather, Center for Space Science and Applied Research, Chinese Academy of Sciences, China There is transient increase of the Voyager 1 (V1) observation of galactic cosmic ray flux beyond the heliopause in 2013 March, which Jokipii and Kota suggested is caused by a propagating magnetic disturbance from heliosphere. In this work, we model a magnetic disturbance moving radially from heliosphere towards V1 as a background field superposed by magnetic turbulence, and we numerically solve GCR particles' Newton equation of motion with Lorentz force and induced electric field. From the numerical results we can get increase of GCR flux compatible to the V1 observation. 14th ANNUAL INTERNATIONAL ASTROPHYSICS CONFERENCE ORAL ABSTRACTS
Randol, Brent Numerical simulations of kappa distributions generated self‐consistently via Coulomb’s law Goddard Space Flight Center, USA In a previous study (Randol and Christian, JGR, 2014), numerical simulations of protons and anti‐protons obeying Coulomb’s law provided insight into the self‐consistent generation of kappa distributions from first principles physics. In that study, the velocity distribution function (VDF) first formed a tail with the common spectral index of ‐5 and then gradually became a kappa‐r distribution, with kappa = 1.5, corresponding to the “common” spectrum of solar wind ions. However, the results were for extremely cold, dense plasma. In this talk, we will discuss extending the range of density and temperature to include those of the solar wind at 1 AU. Having explored an extremely large parameter space of initial temperature and density, we find that a single parameter, N_D, the number of particles in a Debye sphere, controls the shape of the final VDF. For N_D<<1, our previous result of a kappa = 1.5 is recovered; for N_D>>1, there is no deviation from the initial Gaussian. Between the two extremes, there is a smooth transition in the shape of the final VDF. The results are instructive for understanding kappa distributed plasmas in many different applications. Richardson, Voyager Observations of Plasma in the Heliosheath John John Richardson, MIT, USA Voyager 2 is now 25 AU deep into the heliosheath; if the width is similar to that in the Voyager 1 direction it is 3/4 of the way to the heliopause. We present recent observations, compare with observationsm fro Voyager 1, and compare with model predictions. The speed of the flows observed by Voyager 2 in the heliosheath have been, on average, remarkably constant at 150 km/s. The flow angle has changed dramatically, however, and is now 75 degrees from radial, with more of the turning occurring in the RT than RN planes. After 2011, the average density and temperature of the plasma have also not changed. These flows are very different than at V1, where the speed was always below 100 km/s and decreased across the heliosheath. Models predict VR at Voyager 2 well, but the flow angle predictions differ from the observations. Roelof, Edmond Charged Particle Energization and Transport in Reservoirs Throughout the Heliosphere Edmond C. Roelof, Johns Hopkins University/APL, USA “Reservoirs” of energetic charged particles are regions where the particle population is quasi‐trapped in large‐scale (relative to the gyroradii) magnetic field structures. Reservoirs are found throughout the heliosphere: the huge heliosheath (90 Rouillard, Alexis Probing the origin of SEPs using multipoint imagery and in‐situ measurements Rouillard, A.P., Pinto, R., Plotnikov, I., Tirole, M., Research Institute in Astrophysics and Planetology, France, Tylka, A.J., Goddard Space Flight Center, USA Vourlidas, A., John Hopkins Applied Physics Laboratory, USA The origin of the most energetic solar particles released during solar storms is still debated. In this study, combined observations and modelling techniques are used to test the hypothesis that the most energetic solar energetic particles (SEPs) are accelerated by coronal shock waves. Combined STEREO SOHO and SDO observations allow us to reconstruct the 3‐D extent of pressure waves formed during the eruption of coronal mass ejections. We concentrate on the proton‐rich events detected by the near‐Earth spacecraft and the STEREOs between 2011 to 2014. The SEPs measured in situ during these episodes of propagating coronal waves propagate along coronal and interplanetary magnetic field lines between the Sun and 1 AU. We use a combination of observations and modelling to reconstruct the 3‐D location of magnetic field lines and thereby establish the magnetic connectivity between the shock near the Sun and the points of in‐situ measurements near 1AU. This 3‐D localisation allows us to determine the (1) determine the height and spatial extent of the pressure waves at the SEP release times near the Sun, (2) compare the longitudinal extent of SEP events with the extent of the pressure waves. We combine a 1D Solar Wind hydrodynamical code (VP code) with a potential model of the solar corona to compute the density, bulk speed, ion and electron temperatures and pressures along the relevant magnetic flux tubes. This allows us to compute the characteristic speeds of the medium and the fast and slow‐mode speeds at the potential shock transition. We compare the properties of the inferred shocks with those of the SEPs measured in situ. Salem, Chadi Thermodynamics of Solar Wind Electrons and their role in the evolution of the solar wind Chadi Salem, Space Sciences Laboratory, University of California Berkeley, USA Marc Pulupa, Space Sciences Laboratory, University of California Berkeley, USA Stuart Bale, Space Sciences Laboratory, University of California Berkeley, USA Daniel Verscharen, Space Science Center, University of New Hampshire, USA We present a statistical analysis of solar wind electrons at 1AU using several years of accurate core, halo and strahl electron parameters to investigate the properties of these different populations and the physical processe(s) that likely act to control and regulate them. We discuss new results obtained on (1) the electron temperature anisotropies and their variation with collisions and/or solar wind fluctuations and instabilities, (2) the properties of core and halo drifts in the solar wind proton frame, (3) the electron heat flux, and (4) the electron strahl. These new observations emphasize the non‐negligible role of Coulomb collisions in shaping the electron distribution function and regulating of the thermal and supra thermal electrons, but that the solar wind electron expansion and compression are limited fundamentally by some instabilities under certain conditions. Schwadron, Particle Acceleration at Low Coronal Expansion Shocks Nathan N. A. Schwadron, M. A. Lee, M. Gorby, N. Lugaz, H. E. Spence University of New Hampshire. USA M. Desai Southwest Research Institute, USA T. Torok, C. Downs, J. Linker, R. Lionello, Z. Mikic and P. Riley Predictive Science Inc., USA J. Giacalone, J. R. Jokipii and J. Kota University of Arizona, USA We present a study of particle acceleration in the low corona associated with the expansion and acceleration of coronal mass ejections (CMEs). Because CME expansion regions low in the corona are effective accelerators over a finite spatial region, we show that there is a rigidity regime where particles effectively diffuse away and escape from the acceleration sites. This leads to the formation of broken power‐law distributions. We find a natural ordering of the break energy and second power‐law slope (above the break energy) as a function of the scattering characteristics. These relations provide testable predictions for the particle acceleration from low in the corona. Analysis of solar energetic particle observations suggests a range of shock compression ratios and rigidity dependencies that give rise to the SEP events studied. The wide range of characteristics inferred suggests competing mechanisms at work in SEP acceleration. Thus, CME expansion and acceleration in the low corona may naturally give rise to rapid particle acceleration and broken power‐law distributions in large SEP events. 14th ANNUAL INTERNATIONAL ASTROPHYSICS CONFERENCE ORAL ABSTRACTS Shiota, Daikou Turbulent transport model in three‐dimensional solar wind Shiota, Daikou1, Zank, G.P.2, Adhikari, L.2, Hunana, P.2 1. Nagoya University, Japan 2. The University of Alabama in Huntsville, USA Turbulence in solar wind plasma can play essential roles in the heating of coronal and solar wind plasma and the acceleratione of th solar wind, as well as acceleration of energetic particles associated with interplanetary shocks. On the other hand, turbulence can be produced by energetic particles and shocks and is also due to the radial and lateral inhomogeneity of global magnetic field and solar wind plasma distribution. Because of the close coupling of turbulence, plasma heating, solar wind, and energetic particles, a comprehensive model describing not only turbulence but also the large‐scale inhomogeneity of the solar wind and the interplanetary magnetic field is necessary to understand the physics of these phenomena. Recently we have developed a solar wind MHD modelr in the inne heliosphere based on synoptic observations of the photospheric magnetic field (Shiota et al. 2014). The numerical results show reasonable agreement with in situ measurements of the solar wind at the orbits of Earth, Venus, and Mars. This MHD model is now used as part of the real‐etime spac weather forecast system SUSANOO (http://st4a.stelab.nagoya‐u.ac.jp/susanoo/). We have extended our 3D MHD model to include the transport and dissipation of turbulence using the theoretical model developed by Zank et al. (2012). We solve for the temporal and spatial evolution of three moments or variables that describe turbulent fluctuations and their three corresponding correlation lengths coupled to our 3D model of the inhomogeneous solar wind. We report the results of this solar wind ‐ turbulence model under the assumption of a simple magnetic configuration of a tilted dipole to mimic solar minimum conditions, and we compare the results with in situ measurements made around the last solar minimum of 2008. Based on this comparison, we discuss the connection between turbulence generation and the bimodal solar wind structure. Stasiewicz, Assessing the Role of Electric Field Gradients in Ion Acceleration on Electromagnetic Structures at Parallel Foreshocks Krzysztof Krzysztof Stasiewicz, Space Research Center, Poland Marek Strumik, Space Research Center, Poland Recent observations by Cluster of solar wind ions accelerated to 1MeV in front of quasi‐parallel bowshocks (Stasiewicz et al., EPL, 102, 4901, doi:10.1209/0295‐ 5075/102/49001, 2014) indicate that electric field gradients of electromagnetic structures may play important role for ion acceleration in space plasmas. We apply a gradient method to four‐point Cluster measurements to determine geometrical and spatial properties of nonlinear electromagnetic structures observed in the vicinity of the Earth bowshock. We perform also test particle simulations of the ion heating on model electromagnetic structures and on structures produced from global hybrid numerical simulations. We discuss our results and compare them with standard models of diffusive shock acceleration and other mechanisms found in the literature. Strauss, Du Toit Cosmic Ray Transport near the Heliopause Du Toit Strauss, Center for Space Research, NWU, South Africa Marius Potgieter, Center for Space Research, NWU, South Africa Horst Fichtner, Ruhr University Bochum, Germany Xi Luo, National Space Science Center CAS, China It is by now generally accepted that the Voyager 1 (V1) spacecraft crossed the heliopause (HP) in late 2012 and has, since then, been sampling the (very) interstellar medium (ISM) in situ. Cosmic ray (CR) intensities showed a clear and anticipated signal when the HP was crossed – galactic (anomalous) CRs increased (decreased) abruptly across the HP. The CR intensities in the ISM however displayed unexpected anisotropies. We discuss the CR transport conditions that must be in place in order to explain these CR observations and show that: (i) Reduced perpendicular diffusion in the ISM can lead to the observed intensity jumps beyond the HP. (ii) This in turn will lead to little or no modulation of galactic CRs occurring beyond the HP. (iii) By implementing an appropriate form for this suppressed perpendicular diffusion coefficient, the seemingly incongruous observed CR anisotropies can be explained very easily. 14th ANNUAL INTERNATIONAL ASTROPHYSICS CONFERENCE ORAL ABSTRACTS Strumik, Marek Particle transport and energization processes in the vicinity of the heliopause Marek Strumik, Space Research Centre, Polish Academy of Sciences, Poland Andrzej Czechowski, Space Research Centre, Polish Academy of Sciences, Poland Stanislaw Grzedzielski, Space Research Centre, Polish Academy of Sciences, Poland Krzysztof Stasiewicz, Space Research Centre, Polish Academy of Sciences, Poland Results of magnetohydrodynamic (MHD) simulations of magnetic‐reconnection‐driven dynamical processes in the vicinity of the heliopause are shown to match the magnetic field variations observed by Voyager 1 in August 2012, when the spacecraft presumably crossed the heliopause and entered the interstellar medium. Using the MHD solutions as a background electromagnetic field, we investigate the transport of energetic particles (including both ACRs and GCRs) in this region. Besides of a modulation of CR fluxes, electromagnetic structures produced at this boundary are shown to accelerate particles (e.g. by contracting‐magnetic‐islands mechanisms). The question whether the modeled dynamics is a relevant description of processes in real plasmas is discussed in the context of correspondence between the simulations and Voyager spacecraft observations. Suzuki, Takeru Response of Solar Wind on Extreme Solar Activity. Takeru K. Suzuki, Department of Physics, Nagoya University, Japan We investigate how the mass loss by the solar wind depends on the solar activity levels, particularly focusing on the solar wind during extremely high activity.We perform forward‐type magnetohydrodynamical numerical experimentsr fo Alfven wave‐driven solar winds with a wide range of the input Poynting flux from the photosphere.Increasing the magnetic field strength and the turbulent velocity at the solar photosphere from the current solar level, the mass loss rate rapidly increases at first owing to the suppression of the reflection of the Alfven waves. The surface materials are lifted up by the magnetic pressure associated with the Alfven waves, and the cool dense chromosphere is intermittently extended to 10 ‐ 20 % of the solar radius. The dense atmospheres enhance the radiative losses and eventually most of the input Poynting energy frome the surfac escapes by the radiation. As a result, there is no more sufficient energy remained for the kinetic energy of the wind; the solar wind saturates for the extreme activity level, as observed in Wood et al. The saturation level is positively correlated with the average magnetic field strength contributed from open flux tubes. If the field strength is a few times larger than the present level, the mass loss rate could be as high as 1000 times. Wang, Linghua Solar Wind Superhalo Electrons at Quiet Times Linghua Wang1, Liu Yang1, Jiansen He1, Chuanyi Tu1, Zhongtian Pei1, Robert F.Wimmer‐Schweingruber2, and Stuart Bale3 1 Institute of Space Physics and Applied Technology, Peking University, China 2 Institute for Experimental and Applied Physics,University of Kiel, Germany 3 Department of Physics and Space Sciences Laboratory, University of California Berkeley, USA High‐energy superhalo electrons are present in the interplanetary medium even in the absence of any solar activity, carrying important information on electron acceleration in the solar wind. We present a statistical survey of ~20 ‐ 200 keV superhalo electrons measured at 1 AU by the WIND 3DP instrument during quiet‐time periods from January 1995 through December 2013. The observed omnidirectional flux of these quiet‐time superhalo electrons generally fits to a power‐law spectrum, J = A × ( E/mc^2 )^−β, with β ranging from ～1.1 to ～3.7 and the integrated density nsup ranging from 10^−9 cm^−3 to from 10^−5 cm^−3. Both β and the logarithm of nsup correlate with the sunspot number, with larger density and softer spectrum (β ～2.0 − 2.6) at solar maximum but smaller density and harder spectrum (β ～1.2 − 1.8) at solar minimum. β and A also show different correlations at solar minimum and maximum. These results suggest the presence of two populations of superhalo electrons in the solar wind. Population I has a soft power‐law spectrum with the electron intensity increasing with solar activity, dominating at solar maximum. It may originate from nonthermal processes related to the acceleration of the solar wind such as nanoflares. Population II has a hard spectrum and low electron intensity, mainly dominating at ～20 ‐200 keV at solar minimum. It could be produced by further acceleration and/or long‐distance propagation of population I superhalo electrons, solar energetic electrons, and solar wind halo/strahl electrons in the interplanetary medium. 14th ANNUAL INTERNATIONAL ASTROPHYSICS CONFERENCE ORAL ABSTRACTS Washimi, North‐South Asymmetric Structure of the Outer Heliosphere and Recent Voyagers Observations Haruichi H. Washimi(1), G.P. Zank(1), Q. Hu(1), T. Tanaka(2) & K. Munakata(3) (1) CSPAR, University of Alabama in Huntsville, USA (2) Faculty of Sciences, Kyushu University, Japan (3)Faculty of Sciences, Shinshu University, Japan The north‐south (N‐S) asymmetric structure of the outer heliosphere is studied in some detail using a 3D MHD simulation that includes the charge‐exchange process between protons and neutral hydrogen as modeled by Pauls et al., 1995. The solar wind in the vicinity of the heliopause in the northern hemisphere is found to come from the solar corona of the southern hemisphere. This means that the heliopause of the northern hemisphere is populated by the toroidal magnetic field from the southern solar magnetic field, for which the magnetic polarity is opposite to that in the solar corona of the northern hemisphere. Thus the N ‐S asymmetry of the heliosphere leads to the development of a complicated magnetic field structure in the northern hemisphere near the heliopause. This complicated magnetic field structure together with the possibility of magnetic reconnection may explain the first step increase of the galactic cosmic ray intensity profile very near the heliopause observed by Voyager 1 (V1) a few months prior to the V1 crossing of the heliopause during July‐Autumn 2012. Wood, Brian Ulysses and IBEX Constraints on the ISM Helium Distribution Brian E. Wood, Naval Research Laboratory, USA Hans‐Reinhard Mueller, Dartmouth College, USA Interstellar neutral helium flowing through the solar system provides the best local diagnostic of properties of the undisturbed ISM surrounding the Sun. The Ulysses and IBEX missions both provide measurements of the interstellar He. Analysis of these data require a forward modeling of the ISM particle distribution to the spacecraft in the inner heliosphere, under the influence of the Sun's gravity and photoionization. These forward models almost always assume that the He distribution in the ISM is Maxwellian. Stimulated in part by inconsistencies that seem to exist between the Ulysses and IBEX measurements, we investigate how potential non‐Maxwellian ISM distributions could affect these analyses. For Ulysses, we investigate the potential effect of contamination by heavy neutrals, in effect a contamination of the dominant Maxwellian distribution with a narrower one. Such an effect could help resolve the discrepancies between Ulysses and IBEX, but the required amount of contamination is about an order of magnitude higher than one would expect. For IBEX, we take advantage of the particularly high signal‐to‐noise of its data to explore whether relaxing the Maxwellian assumption can improve the quality of fit. Wu, Yihong Pickup Ion Production in the Global Heliosphere and Heliosheath and Their Diagnostics by Fluxes of Energetic Neutral Atoms Yihong Wu, The University of Alabama in Huntsville, USA Vladimir Florinski, The University of Alabama in Huntsville, USA Xiaocheng Guo, The University of Alabama in Huntsville, USA In this study, we perform simulations of the production and transport of pickup ions (PUIs) in the global heliosphere and heliosheath. We examine the distributions of two PUI populations: (1) core PUIs and (2) tail PUIs. Both of the two populations experience a convection with the solar wind and adiabatic cooling or heating, but only tail PUIs experience second‐order Fermi process, i.e. velocity diffusion. The isotropic PUI distributions are modeled using numerical solutions to the transport equation. The intensity of the simulated tail PUIs has a power law dependence on energy with a spectral index ‐1.5. Our results are roughly consistent with the observations made by New Horizons, Ulysses and Voyager. Also, spectra of energetic neutral atoms (ENA) fluxes with energies of about 0.2‐6 keV based on our current PUI model nearly match IBEX‐Hi spectra of distributed ENA fluxes. We conclude that only a fraction of PUIs participate in the second‐order Fermi acceleration process. 14th ANNUAL INTERNATIONAL ASTROPHYSICS CONFERENCE ORAL ABSTRACTS Yoon, Peter Solar Wind Electron Energization by Plasma Turbulence Peter H. Yoon, IPST, University of Maryland, USA The solar wind electrons are made of low‐energy Maxwellian core component with tens of eV energy range, the intermediate (approximately 100s eV to keV) energy halo electrons, highly field‐aligned anti‐Sunward streaming component called the strahl, which occupy the similar energy range as the halo electrons, and the highly‐energetic (keV to 100 keV) super‐halo electrons. The present paper will discuss the local acceleration model for the halo electrons based upon the wave‐particle interaction between these electrons and the whistler turbulence in the solar wind, and a similar local acceleration/heating theory of super‐halo electrons that interact with the Langmuir turbulence in the solar wind. The whistler turbulence in the solar wind is not always easy to distinguish from the Doppler‐shifted permanent magnetic field fluctuations, but recent work by Lacombe et al. [2014] show that quasi‐parallel right‐hand circularly‐polarized whistler waves can be identified under certain conditions. These fluctuations occupy the frequency range of 100 Hz, and it is assumed that halo electrons resonate with these waves. Langmuir type of high‐frequency quasi‐longitudinal fluctuations, known as the quasi‐thermal noise with frequency range of 100 kHz, are a persistent feature in the solar wind. It is assumed that these fluctuations can effectively interact with the super‐halo electrons. Particle kinetic equation and nonlinear wave kinetic equations for the whistler and Langmuir turbulence are self‐consistently solved for their asymptotic steady‐state solution, and it is shown that the resulting solutions compare reasonably with STEREO and WIND observations made near 1 A.U. The strahl component is not considered in the present discussion since it requires inhomogeneity, which is a global (or nonlocal) effect, but a brief mention will be made on future work that will encompass the strahl and the important problem of strahl‐to‐halo pitch‐angle scattering the radial dependence of strahl‐to‐halo evolution. Zank, Gary Particle Acceleration via Reconnection Processes in the Supersonic Solar Wind G.P. Zank, University of Alabama in Huntsville, USA P. Hunana, University of Alabama in Huntsville, USA P. Mostafavi, University of Alabama in Huntsville, USA J.A. le Roux, University of Alabama in Huntsville, USA Gang Li, University of Alabama in, Huntsville USA O. Khabarova, IZMIRAN, Russia An emerging paradigm for the dissipation of magnetic turbulence in the supersonic solar wind is via localized small‐scale reconnection processes, essentially between quasi‐2D interacting magnetic islands. Charged particles trapped in merging magnetic islands can be accelerated by the electric field generated by magnetic island merging and the contraction of magnetic islands. We derive a gyrophase‐averaged transport equation for particles experiencing pitch‐angle scattering and energization in a super‐Alfvenic flowing plasma experiencing multiple small‐scale reconnection events. A simpler advection‐diffusion transport equation for a nearly isotropic particle distribution is derived. The dominant charged particle energization processes are 1) the electric field induced by quasi‐2D magnetic island merging, and 2) magnetic island contraction. The magnetic island topology ensures that charged particles are trapped in regions where they experience repeated interactions with the induced electric field or contracting magnetic islands. Steady‐state solutions of the isotropic transport equation with only the induced electric field and a fixed source yields a power law spectrum for the accelerated particles with index q = ‐(3 + M_A)/2, where M_A is the Alfven Mach number. Considering only magnetic island contraction yields power‐law‐like solutions with index ‐3(1 + T_c/(8 T_d)), where T_c/T_d is the ratio of time scales between magnetic island contraction and charged particle diffusion. The general solution is a power law‐like solution with an index that depends on the Alfven Mach number and the time scale ratio T_c/T_d. Observed power law distributions of energetic particles observed in the quiet supersonic solar wind at 1 AU may be a consequence of particle acceleration associated with dissipative small‐scale reconnection processes in a turbulent plasma, including the widely reported v^(‐5) (v particle speed) spectra observed by Fisk and Gloeckler 2006 and Mewaldt et al 2001. We report on extensions to include diffusive shock acceleration. 14th ANNUAL INTERNATIONAL ASTROPHYSICS CONFERENCE ORAL ABSTRACTS Zhang, Ming Acceleration of Pickup Ions by Compressive Plasma Waves Ming Zhang, Florida Institute of Technology, USA Pick up ions are suprathermal particles constantly loaded to the solar wind plasma through charge exchanges with the interstellar neutrals. When these particles propagating through regions of plasma compression or rarefaction in compressive plasma waves, they may experience repeated acceleration or cooling. If the size of compression or rarefaction is smaller than the particle diffusion scale, the acceleration of particles behaves very much like stochastic acceleration with a momentum diffusion coefficient proportional to momentum p square. Without any particle loss mechanism, its particle distribution function asymptotically approaches to a power‐law of momentum with a slope of ‐3 at high energies and a flat distribution at low energies. This distribution is independent of detailed structures of plasma compression and it is valid for a large range of particle mean free path. The acceleration process can be very rapid, resulting in an exponential increase of pressure from the accelerated particles. This pressure can in turn moderate the wave amplitude so that the system of particles and waves eventually establishes an equilibrium. At that point, a power‐law of momentum with a slope of ‐5 distribution is automatically fulfilled by balancing the rate of particle acceleration with any particle loss mechanisms. This situation is more easily achieved with intensive intermittent compressive waves that only occupy a limited volume of space. Zharkova, Particle acceleration in 3D reconnecting current sheets with Particle‐in‐cell approach in applications to the solar corona and the heliosphere Valentina V. Zharkova, Northumbria University, UK T. Siversky, National University of Kiev, Ukraine R. Dobranskis, Northumria University, UK In this talk we present the key points of particle acceleration during their passage through a reconnecting current sheet from the ambient plasma particles using combined Particle‐in‐cell (PIC) and test particle approach. This will include evaluation of particle trajectories and their volume parameters such as: densities, energies and pitch angles at ejection from a current sheet. We will argue ethat a larg number or particle can be accelerated in this process by a reconnection electric field. And the energies particle gain are strongly dependent on magnetic field topologies, e.g. the longer particle spends in a current sheet, the higher the energy it gains. We show that motion of electrons and protons in 3D magnetic field topologies reveals strong asymmetry (or charge separation) towards the midplane leading to a full or partial separation of HXR and gamma‐ray sources in the corona and other effects in the heliosphere. In addition, we will explore a role of polarisation (Hall) electric field induced by accelerated particles in the ambient plasma in defining the particle motion about current sheet midplanes leading to velocity profiles skewed either to positive or negative semiplanes of a current sheet and three peaked plasma density profiles with respect to the midplane (for the heliosphere) or formation of electron clouds about the midplane (in the corona). We also show that the particle motion in 3D magnetic field topologies leads to formation of two beams of the same charge with different energies that results in formation of plasma turbulence by these beams before their ejection from a current sheet. The theoretical parameters will be probed by the observational properties of charged particles in the corona and the heliosphere. We also discuss some consequences on the parameters of accelerated particles of the current sheet stability and formation of multiple current sheets (or magnetic islands). Zirnstein, Eric The Effects of Slow, Intermediate, and Fast Solar Wind Speeds on the IBEX Ribbon Eric Zirnstein, Southwest Research Institute, USA Herbert Funsten, Los Alamos National Laboratory, USA Jacob Heerikhuisen, University of Alabama in Huntsville, USA David McComas, Southwest Research Institute, USA The Interstellar Boundary Explorer (IBEX) ribbon is an intense feature of energetic neutral atoms (ENAs) encircling the sky, exhibiting spectral characteristics that appear to be related to the characteristics of the solar wind. A strong candidate for the origin of the ribbon is the secondary ENA mechanism, where primary ENAs generated by charge‐ exchange between solar wind ions and interstellar neutral atoms propagate outside the heliosphere, undergo two charge‐exchange events, and become secondary ENAs that may be preferentially directed back toward Earth in directions perpendicular to the interstellar magnetic field. According to this mechanism, the IBEX ribbon is sensitive to ENAs generated in the solar wind, and thus sensitive to the global solar wind properties. The acceleration of the solar wind plasma results in speeds ranging between ~350‐500 km/s (slow) at low latitudes and >700 km/s (fast) at high latitudes during solar minimum, and highly variable speeds over all latitudes during solar maximum. We present results from the simulation and analysis of the influence of different solar wind parameters, uniform in latitude, on the global structure and spectral properties of the IBEX ribbon, finding a strong dependence of ribbon intensity and structure on solar wind speed. We will also present an analysis of the ribbon’s center, radius, eccentricity, and rotation angle as a function of ENA energy and solar wind speed.