|Session:||Poster session: Particle Acceleration in the Sun and Heliosphere (10)|
|Date:||Monday, June 13, 2005|
|Time:||00:00 - 00:00|
Statistical Study of Interplanetary Type II Bursts
Aguilar-Rodriguez, Ernesto1; Gopalswamy, N2; MacDowall, R2; Yashiro, S3; Kaiser, M. L.2
1CUA NASA/GSFC, UNITED STATES; 2NASA/GSFC, UNITED STATES; 3The Catholic University of America, UNITED STATES
We present a study of some spectral properties associated with interplanetary Type II radio emission. Type II radio bursts are signatures of violent eruptions from the Sun that result in shock waves propagating through the corona and the interplanetary medium. We investigated the relative bandwidth of all the type II bursts observed by the Radio and Plasma Wave Experiment (WAVES) on board the Wind spacecraft from 1997 up to 2003. We obtained three sets of events, based on the frequency domain of occurrence: 109 events in the low frequency domain (30 KHz to 1000 kHz detected by the RAD1 receiver), 216 events in the high frequency domain (1-14 MHz, observed by the RAD2 receiver), and 73 events that spanned both domains (RAD1 and RAD2). We present statistical results for the bandwidth-to-frequency ratio (BFR) in the three subsets as well as a comparision of our results with the Type II solar radio bursts observed by ISEE-3 radio experiment, which is similar to WAVES/RAD1. We analyzed the bandwidth and BFR evolution with the heliocentric distance as well as an analysis of drift rate magnitude of type II radio bursts and its starting frequency.
Inferring Solar Flare Accelerated Particle Distributions from Asymmetric Hard X-ray Emissions
Alexander, David1; McClements, K. G.2
1Rice University, UNITED STATES; 2UKAEA Culham Division, UNITED KINGDOM
Chromospheric hard X-ray emission in a solar flare generally occurs in two magnetically connected "footpoint" regions. Recent spatially-resolved hard X- ray observations carried out using the RHESSI spacecraft have shown that the ratio of total X-ray fluxes from the two footpoints is time-dependent and demonstrates a weak but detectable photon energy dependence. A Fokker-Planck code is used to identify possible scenarios that could reproduce the observed dependence of footpoint asymmetry on time and energy. The code, which is benchmarked against analytical results in the limit of collisionless precipitation from a symmetric flaring loop, includes collisional friction and pitch angle scattering, asymmetric magnetic mirroring, and a source term that can be prescribed arbitrarily. This model is used to demonstrate that the observed dependence of hard X-ray asymmetry on photon energy can be attributed to an energetic electron source that is isotropic at low energy (presumed due to Coulomb collisions) and at high energy (presumed due to resonant wave-particle scattering), and strongly anisotropic at intermediate energies. The implications of these results for flare particle acceleration are discussed.
Spectra and composition of suprathermal and energetic ions associated with the November 2-6, 2003 interplanetary coronal mass ejection events: SOHO/CELIAS/HSTOF and SOHO/EPHIN data.
Bamert, K.1; Wimmer-Schweingruber, R.F.1; Kallenbach, R.2; Hilchenbach, M.3; Kunow, H.1; Müller-Mellin, R.1; Klassen, A.1; Smith, C.W.4
1University of Kiel, GERMANY; 2International Space Science Institute, SWITZERLAND; 3Max-Planck-Institut für Sonnensystemforschung, GERMANY; 4University of New Hampshire, UNITED STATES
In October/November 2003 the unusually active region 10486 produced several large X-flares and fast coronal mass ejections. We analyze suprathermal and energetic ions associated with the two coronal mass ejection events on Nov. 2 and Nov. 4, 2003. The second event was accompanied by the largest flare (X28) ever observed. In particular, we focus our study on the upstream regions of the interplanetary shocks driven by these CMEs which passed SOHO on Nov. 4 and Nov. 6, 2003, respectively. By combining data of HSTOF and EPHIN we are able to analyze the ions in an extended energy range. HSTOF measures H, He, CNO, and Fe ions in the energy range from 80 keV/e up to 40 MeV/e (for heavy ions). The EPHIN sensor detects protons and the helium isotopes in the energy range 4 to 53 MeV/amu. The temporal evolution of the spectra is resolved in steps of 2 hours (corresponding to a spatial resolution of 0.02 AU). We compare these results to those associated with the Bastille Day event in 2000. Conclusions are drawn on the validity of the quasi-linear theory by Lee (1983).
Sungrazing comets as source of pickup ions at Earth orbit and Ulysses
Bzowski, Maciej; Krolikowska, M
Space Research Centre PAS, POLAND
Most of the sungrazing comets observed by LASCO at SOHO belong to the Kreutz group of comets and follow trajectories that are tigthtly clumped in space. Statistical analysis of 8 years of SOHO observations suggests that the true apparition rate of these comets is as high as one every other day. Practically all these comets break up before perihelion passage. Their material is dissociated and ionized, and subsequently transported away from the Sun as pickup ions in the solar wind. Their mean mass flux is about 3.1E4 g/s. Since the breakup occurs between 40 and 4 solar radii and the ionization is almost immediate, the expected location of these ions in the phase space is close to the location of the inner source of pickup ions. Assuming radial propagation, the cometary pickups should be observable at Earth between August and January, with peak probability at the end of September. At Ulysses, they should be observable approximately between -25 and 40 degrees ecliptic latitude during the fast latitude scans, the first of which occurred in 1995 and the second in 2001. The population of cometary pickup ions should be augmented by about 40% by solar wind protons as a result of charge exchange with the cometary neutral hydrogen and oxygen atoms and subsequent reionizatin of the newly-created Energetic Neutral Atoms, streaming with respect to the solar wind. In total, the average flux of the pickup ions related to the sungrazing comets at 1 AU should be about 1.6E5 g/s/sr within the detection area (and null outside it). This value is comparable to the flux of the inner source-pickup ions and, as we demonstrate, much higher than the expected flux from pickup ions from interstellar neutral gas atoms.
Cross Helicity and anisotropy in slow and fast solar wind
Dasso, Sergio1; Matthaeus, W.H.2; Milano, L.J.2; Smith, C.W.3
1Instituto de Astronomia y Fisica del Espacio (IAFE) , CONICET-UBA, ARGENTINA; 2Bartol Research Institute, University of Delaware, UNITED STATES; 3Institute for Earth, Oceans and Space, University of New Hampshire, UNITED STATES
MHD scale fluctuations in the solar wind are usually highly anisotropic, and have also been found to exhibit different properties in regions of high and low solar wind speed. These features are often interpreted using different paradigms: waves and turbulence. A key feature in both wave and turbulence pictures is the cross helicity, which measures the correlation between velocity and magnetic field fluctuations. Noninteracting outward propagating Alfven waves are associated with a distinctive correlation between velocity and magnetic fluctuations (high cross-helicity). For an active turbulent medium, there can be an increase of Alfvenic correlation, if the medium is undisturbed and freely decaying, but if the turbulence is driven by large scale shear, which injects zero cross helicity turbulence, the Alfvenic correlation should decrease. Another distinctive feature of MHD turbulence is its tendency to develop anisotropy relative to the direction of the large scale magnetic field. Previous studies show that magnetic correlations present distinct lobes aligned with the parallel and perpendicular axes; this
'Maltese cross' pattern motivates the identification of two idealized populations: a 'slab' population with wave-vectors aligned with the main magnetic field and a 'quasi-2D' population with almost perpendicular
wave-vectors. The fast wind is 'younger', having had a 'more recent' injection of waves near the sun, and is less driven by shear. The slow wind is more evolved at a given heliocentric distance, generally more driven by large scale shear, and therefore its turbulence is 'older'. Thus one might expect to find differences in anisotropy in fast and slow speed streams. We present here an analysis of the cross helicity and magnetic correlations at 1AU, from one-point two-times single spacecraft correlations, employing 5 years of ACE plasma and magnetic field data, as a function of solar wind speed and as a function of the angle between the wave number and the mean magnetic field. We analyse the relative 'slab to quasi-2D' population considering fast/slow solar wind, extending the study done by Milano et al. (2004). We conclude that the fast wind is, relatively speaking, more slab-like, while the slow wind is more 2D-like, while the anisotropy of the cross helicity is similar to that of the energy, implying strong coupling of fluctuations throughout the spectrum.
Solar Electron Bursts Observed Below 1.4 keV by ACE:
Characteristics and Implications for Particle Transport
de Koning, Curt; Gosling, J T; Skoug, R M; Steinberg, J T; Gary, S P
Los Alamos National Laboratory, UNITED STATES
Solar active processes frequently produce electron bursts at energies below 1.4 keV. The characteristics of these solar electron bursts vary considerably from event to event due to the physical processes involved in their acceleration and propagation to Earth. Previous observations have shown that some bursts have a broader pitch-angle distribution than the preceding strahl distribution, suggesting that propagation effects are important for understanding 1 AU observations. We present a study of the pitch-angle distributions of suprathermal electrons observed by ACE before, during, and after solar bursts. We focus on the bursts that have a backscatter population. The presence of backscattered electrons implies a scattering mechanism beyond 1 AU. Of the 67 clearly identifiable bursts observed by ACE in 2002, approximately 50% show no evidence of backscattered electrons, while 30% of the bursts are accompanied by weak and intermittent backscattering, and only 20% show a intense and continuous backscatter population. All the events that have an intense and continuous backscatter population also display a broader beam width during the burst event. Computer simulations based on bi-Maxwellian core and halo distributions suggest that electron-driven instabilities cannot explain the observed beam broadening. We discuss the role of pitch-angle scattering by ambient turbulence as a mechanism for beam broadening and backscattering during a burst.
Simulation of jovian cosmic ray electrons over a solar activity cycle
Fichtner, H1; Lange, D1; Kissmann, R2
1Institut fuer Theoretische Physik IV, Ruhr-Universitaet Bochum, GERMANY; 2Instutut fuer Theoretische Physik, Ruhr-Universitaet Bochum, GERMANY
On the basis of a three-dimensional model for the cosmic ray modulation in the heliosphere we have, for the first time, simulated the Ulysses observations of energetic electron time-dependently over a full solar activity cycle. Within the framework of these simulatons, we have first tested two models for the activity-dependent solar wind velocity field. Second, we test in detail to what extent the electron fluxes can be explained with an activity-dependent fully anisotropic diffusion tensor and arrive at the conclusion that the source of these electrons, i.e. the Jovian magnetosphere is, most probably, significantly variable in time.
Energetic particle scattering in three-dimensional “critical balance” MHD turbulence.
Forman, Miriam1; Horbury, T2; Oughton, S3
1Stony Brook University, UNITED STATES; 2Imperial College, UNITED KINGDOM; 3University of Waikato, NEW ZEALAND
We derived expressions for the quasi-linear coefficient for particle pitch-angle scattering, Dmumu, in 3-dimensional turbulence axi-symmetric about the mean magnetic field. The resulting integrals over the power spectrum tensor of the turbulence are conveniently cast in terms of the scalar functions E, F, C, and H of the wave-vector k, which describe MHD turbulence (Oughton, et al., 1997). The application to a “slab+ 2.5D” model reproduces Bieber, et al.’s (1996) extremely important previous theoretical result that the 2.5D part does not do any pitch-angle scattering. The 2.5D part does increase the perpendicular scattering. The “slab + 2D” is a highly idealized model. The “slab” part of the solar wind turbulence at a given kz, estimated from single-spacecraft measurements, integrates all the turbulence at that kz, at all angles to the mean field. A “slab + 2.5D” model” assigns all of the slab turbulence to exactly zero angle to the mean field. However, our expression for Dmumu in three-dimendional turbulence involves resonance integrals for Rkz and requires Rkr < about 1. Chandran (2000) has pointed out in the context of cosmic-ray scattering in interstellar space, that 3-dimensional “critical balance” turbulence ( Goldreich and Shridar, 1997, Cho, Lazarian, and Vishniac, 2002), has relatively little power at k-vectors at small angles to the mean magnetic field, so would not scatter interstellar cosmic rays effectively.
EFFECT OF NONLINEAR CIRCULALRY POLARIZED ON LINEAR INSTABILITIES TRIGGERED BY AN ALPHA-PARTICLE BEAM
Universidad de Chile, CHILE
We have shown through a series of papers that large amplitude circularly polarized waves affect the linear properties of right and left â€“hand polarized beam-plasma instabilities [Gomberoff., JGR 2003; Gomberoff et al., JGR 2003; Araneda and Gomberoff , JGR 2004; Gomberoff et al., JGR 2004a,b]. It was also shown that ion-acoustic waves can also be destabilized by nonlinear circularly polarized waves [Hoyos and Gomberoff, JGR 2005]. All these studies considered plasma system involving electrons, core protons and a proton beam. These results have been applied to some long standing problems associated to observations in the fast solar wind, where proton beams are a common feature. These effects have to do with (a) the observation of unstable proton distribution functions in the fast solar wind [Daughton et al., JGR 1999; Araneda and Gomberoff, 2004], (b) enhanced deceleration rates of proton beams in the fast solar wind, [Kaghashvili, JGR 2004], and (c) ion-acoustic waves in solar wind with properties inconsistent with linear theory [Gomberoff et al., 2004a,b; Gomberoff et al., 2005; Hoyos and Gomberoff , JGR (in press) 2005]. However, similar unstable alpha-particle distribution functions have also been observed [Marsch and Livi, JGR 1987], as well as enhanced deceleration of alpha-particle beams Kaghaschvili et al., JGR 2003] . Thus, it is important to study the effect of nonlinear waves on linear alpha particle beam-plasma instabilities. We show here that all the properties found in proton-beams systems apply also to alpha-particle beams. Thus, we show that nonlinear polarized waves can either stabilize or destabilize linear alpha particle beam-plasma interactions depending on the frequency and polarization of the nonlinear waves. It is also shown that these nonlinear waves can destabilize ion-acoustic instabilities supported by the proton core and the alpha-particle
Electrostatic Instabilities Triggered by Finite Amplitude Circularly Polarized Waves
Gomberoff, Luis; Hoyos, J
University of Chile, CHILE
Finite amplitude circularly polarized waves are known to be able to change the properties of linear beam-plasma instabilities (Gomberoff, JGR 2003; Gomberoff et al., JGR 2003). It is also known that electrostatic waves can be destabilized by the presence of large amplitude left-hand polarized waves (Gomberoff et al., JGR 2004). Here, it is shown that electrostatic waves can also be destabilized by right-hand polarized finite amplitude waves, propagating backward relative to the external magnetic field. These results seem to be important for the understanding of a number of situations which are awaiting resolution. In fact, the observation of beam plasma unstable distributions in the solar wind, with beam velocities above the threshold for instability, might be explained by the presence of large amplitude left-handed waves present in the system (Araneda and Gomberoff , JGR 2004). Likewise, the deceleration of streaming alpha-particles and protons relative to the background solar wind protons might also be due to the presence of finite amplitude circularly polarized waves (Kaghashvili et al., JGR 2003 and 2004). The destabilization of ion-acoustic waves due to the presence of finite amplitude polarized waves might also be at the origin of instabilities observed in the solar wind that have been identified as ion-acoustic waves and do not have the properties predicted by the linear theory: they propagate in regions where they should be strongly Landau damped, and their free energy source has not been clearly identified.
Solar Proton and Near-relativistic Electron Events - What is the relationship?
Haggerty, Dennis; Roelof, E. C
JHUAPL, UNITED STATES
We investigate the relationships between the time histories of energetic protons and near-relativistic electrons observed in Solar Energetic Particle (SEP) events through the course of the ACE mission (from Aug 25, 1997). NOAA has cataloged a list of 85 Solar Proton Events (SPE) Affecting the Earth Environment, while the ACE/EPAM instrument has observed 624 near-relativistic electron events with widely varying intensity, fluence, and onset characteristics. We examine the onsets, peak intensity, rise to maximum or “rise-time”, and spectra of the 85 SPE events (E > 10 MeV) observed by GOES and the 624 near-relativistic electron events observed by EPAM (40 < E < 300 keV). This study intends to answer some very specific questions regarding near-relativistic electrons and energetic protons: Is there always an electron event for each identified SPE event? What is the difference between the arrival time of the energetic protons and the electrons? Is there a minimum intensity/energy/spectral-slope for the electron events where over such threshold there is always an SPE event?
ANOMALOUS HYDROGEN AND HELIUM SPECTRA AT THE TERMINATION SHOCK FROM ENERGETIC NEUTRAL ATOMS FLUX INTENSITY MEASUREMENTS
Hilchenbach, Martin1; Czechowski, A.2
1Max-Planck-Institut fuer Sonnensystemforschung, GERMANY; 2Space Research Centre, Polish Academy of Sciences, POLAND
The energetic neutral hydrogen and helium flux intensities measured by CELIAS/HSTOF on SOHO are combined with the high-energy cosmic ray data to estimate the energy spectrum of the anomalous hydrogen and helium cosmic ray ions at the termination shock, assuming that these ions are the source of the neutral atoms observed by HSTOF. The analysis is done separately for the years 1996-97 (the quiet Sun period, which contributed most of the HSTOF energetic neutral atoms data) and for the remaining period of observations.
ENERGETIC NEUTRAL ATOMS IN A TIME-DEPENDENT HELIOSPHERE
Hilchenbach, Martin1; Czechowski, A.2; Scherer, K.3
1Max-Planck-Institut fuer Sonnensystemforschung, GERMANY; 2Space Research Centre, Polish Academy of Sciences, POLAND; 3Institut fuer Astrophysik und Extraterrestrische Forschung der Universitaet Bonn, GERMANY
We calculate the fluxes of the energetic neutral hydrogen atoms of heliospheric origin arriving in the inner solar system in the time-dependent model of the heliosphere based on the gas-dynamical solution of Scherer and Fahr. We concentrate on the case of the energetic neutral atoms originating from the low-energy anomalous cosmic ray protons. The atoms from the shocked solar wind thermal protons and from the pick-up protons are included for comparison. The result cover the period of one solar cycle. We discuss the implications of our results for the possibility of imaging the outer heliosphere and the heliospheric ion populations by means of the energetic neutral atoms.
Multi-spacecraft Observations of Interplanetary Shock Accelerated Particle Events
Ho, George1; Lario, D.1; Decker, R.B.1; Desai, M.I.2; Hu, Q.3; Vinas, A.F.4
1Johns Hopkins University Applied Physics Laboratory, UNITED STATES; 2University of Maryland, UNITED STATES; 3Institute of Geophysics and Planetary Physics, University of California, UNITED STATES; 4Laboratory for Solar and Space Physics, NASA/GSFC, UNITED STATES
Interplanetary (IP) shocks provide an excellent opportunity to study energetic particle acceleration. During an IP shock related energetic storm particle (ESP) event, both the shock and the accelerated particles can be measured in-situ simultaneously. Thus, a study of in-situ IP shocks and particle distributions in their vicinity provides a meaningful way to test our theoretical understanding of shock acceleration. In addition, with simultaneous multi-point measurements (such as ACE and Wind), we have for the first time enough data to construct a global picture of IP shock propagation and acceleration at Earth vicinity. In this paper, we will combine simultaneous measurements of plasma, magnetic field and energetic particle from ACE and Wind during several ESP events and examine the spatial and temporal variations of these events in the Earth's vicinity. We will also investigate the ion composition and energy spectra for some of these events and investigate their relationship with the locally measured properties of the IP shocks.
BASIC PROPERTIES OF ANISOTROPIC STELLAR WIND EXPANSION IN THE FLUID APPROACH
Hubert, Daniel1; Leblanc, F.2
1Observatoire de Paris and University of British Columbia (Canada), FRANCE; 2Service d'Aeronomie, CNRS, Verrieres le Buisson, FRANCE
The necessary and sufficient conditions for an anisotropic atmosphere to be in an hydrostatic equilibrium are investigated. It is shown that the momentum equation has to be considered for that purpose, contrary to the isotropic case were this property is deduced from the hydrostatic equation. The condition for an hydrostatic equilibrium is that both the parallel and the perpendicular temperature decrease more rapidly than 1/r in the general case and that the perpendicular temperature decreases more rapidly than 1/r in the case were the parallel temperature is constant. The conditions for a supersonic expansion are studied. In an anisotropic one fluid atmosphere the parallel thermal velocity is the critical velocity. The properties of the transonic expansion in an isothermal and anisotropic atmosphere are discussed. The initial velocity, the critical point position, the terminal velocity and the density profile show properties that are significantly different than in the isotropic case. These properties are opposite with respect to the value of the anisotropy larger or lower than 1.0. In particular, for a perpendicular temperature larger than the parallel temperature, to the radial direction of the expansion, (anisotropy larger than 1.0), one obtains that the acceleration starts at a significant large distance from the base of the atmosphere while the critical point is closer to the base of the atmosphere compared to the isotropic case. For an opposite anisotropy, it is obtained that the transonic point moves far away from the base of the atmosphere and that the terminal velocity is significantly decreased for small temperature anisotropy. The mass loss rate is drastically affected for anisotropy larger than 2.0. The extension of this study to multi-moment anisotropic models is direct and can be useful for the interpretation of particle simulation of rarefied stellar atmosphere expansion.
Effects of Waves on Ion Beams Upstream of the Quasiperpendicular Shock
Kaghashvili, Edisher1; Zank, Gary P.2
1University of California, Riverside, UNITED STATES; 2Institute of Geophysics and Planetary Physics, University of Califonria, Riverside, UNITED STATES
We investigate the evolution of ion beams observed upstream of quasiperpendicular shocks, produced typically by reflection at the cross-shock potential. Virtually all calculations of this problem assume a pristine environment into which the reflected beam streams, yet in reality we expect that the beam will propagate into a disturbed, turbulent region. In this study, we investigate the beam evolution in the presence of a pre-existing spectrum of Alfvenic low-frequency fluctuation based on a two and a half dimensional hybrid simulation. We will analyse the effects of waves on ion beams and outline how the obtained picture is related to observations.
An extension of the quasi-linear theory on shock acceleration to low-energy ions
Kallenbach, Reinald1; Bamert, K.2; Hilchenbach, M.3; Smith, C.W.4
1International Space Science Institute, SWITZERLAND; 2University of Kiel, GERMANY; 3Max-Planck-Institut für Sonnensystemforschung, GERMANY; 4University of New Hampshire, UNITED STATES
The quasi-linear theory on self-consistent wave generation and ion acceleration upstream of an interplanetary traveling shock by M.A. Lee (1983) applies for strongly super-Alfvénic ions amplifying pure Alfvén waves in the solar wind. Spacecraft data from the ACE magnetometer and from the CELIAS/HSTOF sensor on board SOHO indicate that weakly super-Alfvénic ions generate ion whistler waves. This is a natural consequence of the dispersion relation of Alfvén waves which enters the ion whistler branch if the wave frequency approaches the proton gyro-frequency. We extend the theory by Lee (1983) to apply for weakly super-Alfvénic ions and for self-generated ion whistler waves.
Self-consistent adjustment of the flux of energetic ions and their injection threshold at heliospheric shocks
Kallenbach, Reinald1; Hilchenbach, M.2; Bamert, K.3
1International Space Science Institute, SWITZERLAND; 2Max-Planck-Institut für Sonnesystemforschung, GERMANY; 3University of Kiel, GERMANY
We present an integrated analytical model on the injection efficiencies of the different ion species of the Anomalous component of the Cosmic Rays (ACRs) at the solar wind termination shock. We find that the injection into diffusive (first-order Fermi) acceleration is dominated by parallel ion diffusion and not by perpendicular diffusion unless the angle α between the shock normal and the heliospheric magnetic field is almost exactly 90°. In steady state the threshold speed for injection into first-order Fermi acceleration at a not exactly perpendicular solar wind termination shock - with the Parker shock angle α ~ 89.3° - adjusts itself self-consistently. Increased anisotropic ACR flux upstream from the termination shock amplifies Alfvénic turbulence which in turn suppresses parallel diffusion upstream and downstream from the shock. It therefore increases the injection threshold and decreases the ACR flux until equilibrium is reached. For this equilibrium situation, we estimate the injection efficiencies of different species of suprathermal ions at the termination shock. Our model results are compared to data from instruments on board the SOHO, ACE, and Ulysses spacecraft associated with interplanetary traveling shocks and to data from the Voyager spacecraft on the flux of ACRs.
Direct Observations of the Generation of Seed Populations at Interplanetary Shocks
Kasper, Justin1; Lazarus, A.J.2; Dagen, S.M.2
1Massachusetts Institute of Technology, UNITED STATES; 2MIT, UNITED STATES
In a survey of fast forward interplanetary shocks observed by the Faraday Cup ion instruments on the Wind spacecraft we find a stable suprathermal proton population in the downstream region of approximately 30% of the events. The non-thermal proton distribution extends from the thermal plasma up to several keV before falling rapidly in intensity. Nine events with particularly intense suprathermal particle populations have been analyzed in detail. We find that the particle distributions are well described by a truncated exponential in velocity space that is isotropic in a frame flowing with the respect to the thermal plasma along the local field. These results are significant because they provide an analytic form for the distribution of the seed population which may then be subsequently accelerated to much higher energies. We will describe the characteristics of the ion spectra and the associations we see between the intensity and energy of the suprathermal population and the properties of the interplanetary shocks that have produced them. The orientation of the downstream field relative to the shock is shown to regulate the magnitude of the differential flow of the seed population. The efficiency with which these particles are generated is shown to be a function of fast Mach number and the angle between the upstream field and the shock normal. The maximum energy is compared with the potential of the shock and models for intial acceleration. We will also present an online database of interplanetary shock parameters that is now available for public use at the following address: http://space.mit.edu/home/jck/shockdb/shockdb.html
Sources and Acceleration of Energetic He+ in Interplanetary Space
Kucharek, Harald1; Moebius, E.1; Lu, Y.1; Smith, C.1; Klecker, B.2; Farrugia, C.1; Popecki, M.1; Galvin, A.1; Hilchenbach, M.3; Bochsler, P.4
1University of New Hampshire, UNITED STATES; 2Max-Planck-Institut fuer Extraterrestrische Physik, GERMANY; 3Max-Planck-Institut fuer Sonnensystemforschung, GERMANY; 4University of Bern, SWITZERLAND
Observations with ACE/SEPICA and SOHO CELIAS STOF have shown that energetic He+ is after H+ and He2+ the third most abundant energetic particle population in the heliosphere in the energy range 250keV/n – 800keV/n. The He+/He2+ ratio in the energetic particle population is strongly variable and can reach unusually high values close to unity. The strongest enhancements are found CIR’s, TIR’s, and interplanetary traveling shocks which are known to be major accelerators. Interstellar pickup ions have been identified to be major source of the energetic He+ that are preferentially accelerated at CIR's, TIR's, and interplanetary traveling shocks. Since, compared to solar wind ions pickup ions are already suprathermal, any accelerator can produce an enhancement in the energetic He+/He2+ ratio. Furthermore, because He+ and He2+ differ only in their charge state this pair constitutes an excellent tool to investigate charge state dependent injection and acceleration. We analyzed our survey of energetic helium over three years (1998-2000) from STOF and SEPICA to identify additional discontinuities and magnetic field signatures, such as current sheet crossings, flows, and enhanced magnetic turbulence, which are also associated with major enhancement in energetic He+/He2+ ratio. We found for instance that during current sheet crossings large and prolonged enhancements of the energetic helium ratio are observed. The strongest enhancement is observed simultaneously with the flipping of the Bx polarity. also In addition, we found fast solar wind streams and combinations of such streams with current sheet crossings associated with energetic He+ enhancements, whose time evolution we have studied in detail.
ULYSSES COSPIN/KET Observations of Jovian Electrons During the Distant Ulysses Jupiter Flyby
Kunow, Horst1; Heber, B2; Potgieter, M S3; Ferreira, S E S3; Mueller-Mellin, R1
1Universitaet Kiel, GERMANY; 2Universitaet Osnabrueck, GERMANY; 3North-West University, Potchefstroom, SOUTH AFRICA
Since launch in Oct. 1990 Ulysses sampled the Heliosphere between Earth and Jupiter in three dimensions continuously. With varying heliomagnetic distance to Jupiter and changing solar activity the Jovian electron population varied considerably during this time. In 1992 and 2004 Ulysses had two encounters with Jupiter allowing to study the propagation of Jovian electrons originating from an off-centre point source in the heliosphere. (These observations are crucial for evaluating and testing propagation models.) The closest approach to Jupiter was 0.003 AU in 1992 and 0.803 AU in 2004 (6 RJ and 1682 RJ respectively). Jovian electron observations are presented and compared with propagation models. In addition Jovian electron jets were observed in the vicinity of both encounters in the 3 – 10 MeV range as events with sharp increase and decrease, strong anisotropy, and durations of up to a few hours. Jets were observed as far out as 2.2 AU from the planet after the distant encounter in 2004. The data are presented and discussed with respect to magnetic field connection and structure.
COSMIC RAY MODULATION IN AN ASYMMETRICAL HELIOSPHERE
Langner, Ulrich1; Potgieter, M S2; Borrmann, T3; Fichtner, H3
1Ruhr-Universitaet Bochum, GERMANY; 2Unit for Space Physics, School of Physics, North-West University, 2520 Potchefstroom, South Africa, SOUTH AFRICA; 3Institut für Theoretische Physik IV, Ruhr-Universität Bochum, 44780 Bochum, Germany, GERMANY
The development of realistic and self-consistent global models for the modulation of cosmic rays in the heliosphere has been stimulated the past few years by excellent observations, in particular with the approach of the solar wind termination shock by the Voyager 1 spacecraft and seeing that it will enter the heliosheath in the nearby future. In this light our previous two-dimensional solar wind termination shock model, which was used to simultaneously demonstrate the heliospheric modulation for various galactic and anomalous species, was extended to include an arbitrarily shaped heliospheric outer modulation boundary and this new model is used in this work in accordance with the predictions of a time-dependent three-dimensional hydrodynamic model of the heliosphere, to study the effects of the asymmetry of the heliosphere and the profile of the solar wind in the heliosheath. The modulation model includes the solar wind termination shock, drifts, adiabatic energy changes, diffusion, convection, and a heliosheath, while energetic particles are described kinetically using the Parker transport equation. It was found that significant modulation differences occur between the various solar wind-scenarios in the heliosheath for the symmetrical and the asymmetrical model. The effect of the termination shock is also significantly enhanced and ‘barrier’ modulation significantly different in the heliospheric nose region if these different scenarios were incorporated into an asymmetric model. The solutions are shown for solar minimum and moderate maximum conditions for both heliospheric magnetic field polarity cycles.
Heavy Ion Acceleration and transport at CME-driven Shocks
Li, Gang1; Zank, GZ2
1IGPP, Uviersity of California, UNITED STATES; 2IGPP, University of California at Riverside, UNITED STATES
Large SEP events are now believed to be results of particle acceleration at CME-driven shocks. As a CME-driven shock propagates out, particles are accelerated at the shock front as they undergo many back and forth traversals at the shock front. It is believed, at least at quasi-parallel shocks, the upstream waves that driven by streaming protons serve the role of scattering centers. Heavy ions, having smaller number densities, can be treated as ideal test particles. Thus, studying the acceleration and transport of heavy ions can provide an excellent test of the underlying first order Fermi acceleration mechanism. In this work, we study the acceleration of heavy ions at CME-driven shocks and their subsequent transport in inner heliosphere. The propagation of the shock is followed using a 2D MHD ZEUS code, and particle acceleration are model using a shell model. The propagation of energetic particles leaking out of the shock is followed using a Monte-Carlo approach. Particle spectra and time intensity profiles are obtained and these results are compared with observations made by spacecraft such as ACE and WIND.
A Survey of H, He, and Electron Spectra in Large Solar Particle Events
Mewaldt, R. A.1; Mason, G. M.2; Haggerty, D. K.3; Looper, M. D.4; Selesnick, R. S.4; Cohen, C. M. S.1; Desai, M. I.2; Labrador, A. W.1; Leske, R. A.1; Mazur, J. E.4
1Caltech, UNITED STATES; 2University of Maryland, UNITED STATES; 3JHU/APL, UNITED STATES; 4Aerospace Corporation, UNITED STATES
We present the results of a new survey of the energy spectra and relative composition of H, He, O, and electrons in large solar energetic particle (SEP) events during the period from late 1997 to early 2005. Included are most of the largest events from the last solar maximum, including the Halloween 2003 events and the Jan. 20, 2005 event. For each SEP event fluence spectra for H, He, and O were measured over the energy range from ~0.1 to >100 MeV/nuc by combining data from the EPAM, ULEIS, and SIS instruments on ACE, the PET instrument on SAMPEX, and from GOES. Electron spectra were measured from ~0.04 to 8 MeV. Both the ion and electron spectra commonly exhibit spectral breaks that vary in energy from event to event. Measured fluences from more than 20 events have been fit with Ellison-Ramaty and double-power-law spectra to determine the location of these breaks, and to investigate how they scale from one species to another. We report on correlations of these data with flare and CME properties for these events, and with composition data for heavier species up through Fe.
The radial dependence of solar energetic particle fluxes and fluences
Ruzmaikin, Alexander1; Feynman, J.1; Jun, I.1; Li, G.2; Zank, G.2
1Jet Propulsion Laboratory, California Institute of Technology, UNITED STATES; 2Institute of Geophysics and Planetary Physics, University of California Riverside, UNITED STATES
A knowledge of radial dependence of the particle fluxes and fluences is required to estimate the expected solar energetic particle (SEP) impact on space systems unshielded by the Earth’s magnetic field. This radial dependence has not been obtained from existing observations because the large events, which dominate particle event hazards are rare. The measured radial dependencies (such as a few measurements by Helios I, II in the range 0.3-1 AU) are scarce and do not support the simple 1/r^2 or 1/r^3 dependencies, which are commonly used in many engineering applications. We evaluate the radial dependence of SEP derived from a model of particle acceleration in gradual events. These particles are accelerated at shock waves driven from the Sun by coronal mass ejections (CME). The acceleration and transport of particles at the propagating and evolving interplanetary shock is calculated using the dynamical model developed by Li, Zank, and Rice (2003). As the CME-driven shock propagates, expands and weakens particles accelerated diffusively at the shock escape upstream and downstream into the solar wind. We found that the resulting radial profiles of the fluxes and fluences depend on energy and the location of the spacecraft.
Semi-Empirical Model of Electron Heat Flux: SOHO and Ulysses Data
Sittler, Edward1; Skoug, R M2; Ofman, L3; Fludra, A4
1NASA/Goddard Space Flight Center, UNITED STATES; 2Los Alamos National Laboratory, UNITED STATES; 3Catholic University of America, UNITED STATES; 4Rutherford Appleton Laboratory, UNITED KINGDOM
We have developed a semi-empirical model of the electron heat conduction which is based on both theoretical and observational considerations. The model is applied to the polar regions of the Sun during solar minimum where suprathermal tails may form. This model is a 'local model' which uses the Krook's anzatz in the Boltzmann equation using the collision term (δf*/δt)coll=-(f* - f*0)/Tcoll where Tcoll = (Lwave/WC)(U3/(U4 + Lwave/Lcoul)) is the collision time, Lwave is a characteristic 'local' scattering length due to waves, Lcoul is a characteristic collision length 'local' due to coulomb collisions, U = (W/WC), WC is the thermal speed of the core electrons, W is the electron speed in the electron proper frame, and f* = f*0 + f*1 where f* is the proper frame electron distribution function, f*0 is the unpertured electron distribution function and f*1 is the perturbed correction term due to plasma gradients and collisions. Assuming a kappa distribution function for f*0 we can compute an expansion of the Boltzmann equation and derive an expression for f*1 with some undetermined parameters. Then by imposing constraint of particle conservation ∑f*e1d3W = 0 and the zero current condition J*ll = -e∑f*e1Wlld3W = 0 to give us a relationship for the interplanetary potential, we can reduce the number of free parameters in our model. Then by specifying the logarithmic derivative of the electron density, core electron temperature and the magnetic field from the base of the corona to 1 AU using SOHO and Ulysses data we can, in principle, derive a relationship for kappa and thus f*1 with Lwave as a free parameter. We then used the relationship Q*ell=1/2Me∑f*e1W2Wlld3W to give us the electron heat flux along B and set it equal to Qeff from the semi-empirical MHD model of Sittler and Guhathakurta [1999, 2002] to constrain Lwave as a function of radial distance. This analysis allows us to solve for the interplanetary potential, Pint = 2-3 kV, which is large enough to accelerate the protons to speeds of 700 km/s. We estimate that Lwave/Lcoul tends to be small for r around 2 RS over a polar coronal hole and r > 1 AU at high latitudes, while at other radial distances Coulomb collisions are more important. In regions where Lwave/Lcoul is small wave scattering will be important (i.e., whistler mode waves) and the plasma must become unstable to wave growth within these regions. Finally, we will use Ulysses plasma electron observations to constrain kappa as a function of radial distance and provide a further constraint to our model. We will compare our derived electron distribution functions with interplanetary observations.
Spatial Structure of Solar Electron Bursts: Two-Point Observations using Genesis and ACE
Steinberg, John T; de Koning, C. A.; Gosling, J. T.; Skoug, R. M.; Wiens, R.C.
Los Alamos National Laboratory, UNITED STATES
ACE studies have found that transient solar electron bursts associated with solar type III radio bursts are commonly observed at energies below 1.4 keV. At these energies the bursts appear as anti-sunward-directed electron beams superimposed on the suprathermal electron strahl and halo. Solar electron bursts are typified by their characteristic energy-time and pitch angle-time dispersion. Durations of burst events from onset to decay can vary from less than 1 hour to more than 30 hours, implying that the interplanetary magnetic filaments occupied by solar burst electrons are spatially broad. However, the true spatial extent and uniformity of a burst-carrying filament cannot be established from single spacecraft measurements. In order to explore the spatial characteristics of solar electron bursts, we have examined bursts detected at two spatially separated spacecraft: Genesis and ACE. Genesis and ACE provided simultaneous observations at spatial separations up to 1 million km for more than 2 years. We compared measurements from the nearly identical electron spectrometers on the two spacecraft. To date we have surveyed data from November 2001 to May 2003, and found 136 solar electron bursts simultaneously detected by both spacecraft. More than two thirds of the burst events are strikingly similar at the two spacecraft, indicating that bursts are most often spatially uniform across ACE-Genesis separation distances. However, a number of burst events exhibit notable differences in the simultaneous Genesis and ACE observations, consistent with a non-uniform burst structure. Such structure indicates that the two spacecraft, though relatively near one another, are nonetheless found on interplanetary magnetic field lines mapping back to different solar source regions. We conclude that braided intermixing of interplanetary filaments is evident at 1 AU on separation scales of approximately one million km.
Multi-Spacecraft Observations of Interplanetary Shocks
NASA Goddard Space Flight Center, UNITED STATES
Interplanetary shocks are thought to be one of the primary accelerators of particles in in the heliosphere. However, the exact mechanism of acceleration is unclear. The local characteristics of IP shocks appear to determine efficiency of local acceleration. In this paper, multi-spacecraft solar wind observations will be presented to substantiate that many interplanetary shocks deviate significantly from exact planarity on scale length of the magnetospheric cross section. A number of different IP shock observations with four spacecraft will be presented to demonstrate quantitatively the angular deviations between shock normals obtained from 4-spacecraft methods, using only the time and position information of shock observations but assuming a exactly planar geometry, and those obtained from a non-linear least squares fitting of the “Rankine-Hugoniot” conservation equations at each spacecraft. Moreover, the local shock type can vary from quasi-parallel to quasi-perpendicular within a few tens of Re. High resolution magnetic field data from multiple satellites demonstrate this variation suggesting that even in the inner heliosphere the acceleration sites might be patchy.
Electron acceleration by coronal shocks and solar type II bursts
Vandas, Marek1; Karlicky, M.2
1Astronomical Institute, CZECH REPUBLIC; 2Astronomical Institute, Ondrejov Observatory, CZECH REPUBLIC
Type II bursts are supposed to be generated by accelerated electrons at a shock front, presumably with a shock drift mechanism in action. Sometimes type II bursts exhibit a fine structure (herringbones). Zlobec et al. (1993) suggested to explain it by a qualitative model where electrons are accelerated by a nearly perpendicular weavy shock front. We examine this possibility quantitatively. Our calculations, combining analytical and numerical approaches, will show how electron acceleration efficiency depends on geometric parameters on the shock and namely on a global angle between the shock front and ambient magnetic field.
A heliospheric hybrid model: hydrodynamic plasma flow and kinetic cosmic ray transport
Scherer, K.1; Ferreira, S.E.S.2
1University of Bonn, GERMANY; 2Unit for Space Physics, School of Physics, North-West University, 2520 Potchefstroom, SOUTH AFRICA
We present a new five particle species hybrid model for calculating cosmic ray particle transport and acceleration in a dynamic heliospheric environment. In particular the effects of solar cycle related changes in the solar wind speed on the heliospheric geometry, solar wind flow and cosmic ray distribution are discussed, when a polar-ecliptic asymmetry at the inner boundary is modeled. It is shown that the disappearance of the fast solar wind over the solar poles toward solar maximum influences the geometry of the termination shock which is an important structure for cosmic ray acceleration. For solar maximum conditions, the shock radius is smaller in the polar regions and in the heliospheric tail compared to solar minimum. These changes influence cosmic ray transport and acceleration in these regions, especially for the polarity cycle where positive particles drift in along the heliospheric current sheet. For this polarity cycle, and for both the anomalous and galactic cosmic ray protons, an increase in particle intensities at the shock in the heliospheric tail is computed as the shock moves inward toward the Sun. For the heliospheric nose, it is also shown that both the plasma speed and cosmic ray intensities are relative insensitive to changes in the latitudinal profile of the solar wind speed. Therefore toward solar maximum conditions there is a decrease in the nose-tail asymmetry of the computed cosmic ray distribution compared to solar minimum conditions.
Solar wind electron halo and strahl formation by resonant interaction with whistler waves
Vocks, Christian1; Salem, C.2
1Astrophysical Institute Potsdam, GERMANY; 2Space Sciences Laboratory of UC Berkeley, UNITED STATES
Observations of solar wind electron velocity distribution functions (VDFs) show significant deviations from a simple Maxwellian VDF. A thermal core, a suprathermal halo and an anti-sunward, magnetic field-aligned beam or "strahl" can be distinguished. At higher energies above 2 keV, a superhalo can even be observed. A kinetic description of the electrons in the solar corona and wind that includes resonant interaction with whistler waves can reproduce the enhancement of suprathermal electron fluxes over the core flux. These whistlers are assumed to be generated below the coronal base and propagate through the corona into interplanetary space. However, the resonance condition between electrons and whistlers precludes an interaction between these waves and anti-sunward moving electrons. Thus, this simple model lacks an diffusion mechanism for those electrons. As a consequence, the mirror force due to the opening magnetic field geometry of a coronal hole and in the solar wind focusses the anti-sunward moving electrons into an extremeley narrow beam in interplanetary space. Since solar wind observations show a "strahl" with finite width and a quasi-isotropic superhalo, some diffusion mechanism for the anti-sunward moving electrons must exist. It is shown that the introduction of sunward propagating whistler waves into the model can provide this diffusion. Their wave power is estimated as a small fraction of the total wave power that is measured in interplanetary space. The kinetic results show that the whistler waves are capable of influencing the solar wind electron VDFs significantly, leading to the formation of both the halo and strahl populations, and a more isotropic distribution at higher energies, in good agreement with solar wind observations.
Comparison between impulsive 3He-rich events and energetic electron events
Wang, Linghua1; Lin, R. P.2; Krucker, S.3; Mason, G. M.4
1University of California, Berkeley, UNITED STATES; 2Space Sciences Laboratory & Physics Department, UCB, UNITED STATES; 3Space Sciences Laboratory, UCB, UNITED STATES; 4Physics Department, University of Maryland, UNITED STATES
Impulsive solar energetic particle events with large enrichments of 3He ions are associated with ~2-100 keV impulsive electrons. Electron observations with the energy range of ~3 eV - 500 keV by the WIND 3-D Plasma and Energetic Particle experiment (3DP) and ion measurements with the energy range of ~0.02 - 10 MeV/nucleon by the ACE Ultra-Low Energy Isotopic Spectrometer (ULEIS) provide the first possibility of an accurate timing comparison between impulsive 3He-rich events and energetic electron events. We select eleven solar impulsive events with a clear velocity dispersion of both 3He-rich ion events (with 3He / 4He ~0.1-1.5) and scatter-free electron events over a wide energy range. We remove the contaminations of higher energy electrons at energies above 25 keV in 3DP, determine the interplanetary path length from the solar wind speed (Parker spiral length) and the linear fit to peak times of in situ electron data with energies above 25 keV, and obtain the electron injection profiles at the Sun from triangular fits to in situ observations. The onsets and peaks of the injection of 3He-rich ion events at the Sun are estimated from those of ACE ion data observed in situ by taking into account the travel time along the same path length of the electron events. The comparison study shows a systematic delay of the injection of 3He-rich ions events with respect to the injection of electron events. Nine of ten events with available SOHO/LASCO observations have a fast (> 570km/s) west limb CME with the onset of electron injection close to the origin of the CME, and with the onset of ion injection corresponding to a median CME height of ~ 5 Rs.
Effects of Coronal Holes on Gradual Solar Energetic Particle Events
Wang, Yuming; Shen, C; Ye, P; Wang, S
University of Science and Technology of China, CHINA
Shock acceleration is considered the main mechanism of gradual solar energetic particle (SEP) events. The intensity of a SEP event is certainly related to the shock strength as well as the configuration of magnetic field near the shock. Coronal holes (CHs) are the sources of fast solar wind, in which the speed of fast mode wave is high and the magnetic field is opened. The two properties are both unfavorable for the formation of gradual SEP events. On the other hand, the shock drivers, coronal mass ejections (CMEs), originate from the outside of CHs. Whether does a CH affect a near CME in production of energetic particles? To answer this question, we investigate all the definite frontside fast halo CMEs from 1997 through 2003 as well as the CHs close to them. It is found that there is an effective range, within which a CH affects the gradual SEP events significantly. For a CH-proximity CME, a major SEP event will difficult to be produced. More details are still being studied.
ACE Observations of 3He from Impulsive Solar Energetic Particle Events
Wiedenbeck, M. E.1; Mason, G. M.2; Cohen, C. M. S.3; Cummings, A. C.3; Dwyer, J. R.4; Gold, R. E.5; Krimigis, S. M.5; Leske, R. A.3; Mazur, J. E.6; Mewaldt, R. A.3; Stone, E. C.3; von Rosenvinge, T. T.7
1Jet Propulsion Laboratory / Caltech, UNITED STATES; 2University of Maryland, UNITED STATES; 3California Institute of Technology, UNITED STATES; 4Florida Institute of Technology, UNITED STATES; 5Applied Physics Laboratory, Johns Hopkins University, UNITED STATES; 6Aerospace Corporation, UNITED STATES; 7NASA / Goddard Space Flight Center, UNITED STATES
ACE observations of helium isotopes in solar energetic particles have shown that 3He was present in the interplanetary medium at 1 AU more than half of the time during the early portion of solar cycle 23 (specifically from August 1997 to April 2002). The observed 3He particles, with energies in the range 0.2 to 16 MeV/nuc, are believed to be accelerated in numerous small impulsive solar flare events. The suprathermal ions resulting from such events have been shown to provide a seed population which can be further accelerated by shocks in the solar corona or interplanetary medium. We have extended our previous investigation to include the time interval from early 2002 to early 2005, a period during which solar activity declined significantly. In addition to presenting the time dependence of 3He in the interplanetary medium over a 7-year period, we examine correlations between this energetic particle population and various measures of solar flare activity in order to assess, on a statistical basis, the characteristics of the sources of these particles and to determine the extent to which flare activity can provide a useful indication of the presence of flare suprathermals in the interplanetary medium.