SH31B-1667
High time resolution observations of the drivers of Forbush decreases
The drivers of Forbush decreases in galactic cosmic ray (GCR) fluxes are thought to be magnetic turbulence in the sheath of an interplanetary coronal mass ejection (ICME) and the closed magnetic field lines in the ICME itself. This model, however, is the result of studies utilizing hourly or longer time averaging. Such averaging can smooth over important correlations between variabilities in the GCR flux and those in the interplanetary medium. To test the validity of the current model of Forbush decreases, we analyze a number of Forbush decreases using high time resolution GCR data from the High Sensitivity Telescope (HIST) on Polar and the Spectrometer for INTEGRAL (SPI). We seek causal correlations between the onset of the decrease and structures in the solar wind plasma and interplanetary magnetic field, as measured concurrently with ACE and/or Wind. We find evidence that planar magnetic structures in the sheath preceding the ICME may be a factor in driving the decrease in at least one event.
SH31B-1668
Observations of Dispersionless Modulation in the GCR Intensity in Association with Changes in the Suprathermal Electron Heat Flux
Focusing upon the GCR intensity within a three-day interval during an unusually active period in the solar wind from 19 August 2006 to 21 August 2006 reveals many intensity variations in the GCR on a variety of timescales and amplitudes. These intensity variations are greater than the 3ó error in all the datasets used from Wind, ACE, Polar and INTEGRAL. The fine structures in the GCR intensities along with the Forbush decrease are propagated outward from ACE to the Earth with very little change. The solar wind speed stays relatively constant during these periods indicating that parcels of solar wind are transporting the GCR population outward in the heliosphere. This solar wind convection of GCR fine structure is observed for both increases and decreases in GCR intensity and the fine-structure increases and decreases are bracketed by solar wind magnetic field discontinuities associated with ICME magnetosheath regions, clearly seen as discontinuous rotations of the field components at ACE and at Wind. Interestingly, the electron heat flux shows different flux tube connectivity also associated with the different regions of the ICME and magnetosheath. Gosling et al., [2004] first discussed the idea that solar energetic particle intensities commonly undergo dispersionless modulation in direct association with discontinuous changes in the solar wind electron strahl. The observations show that the intensity levels in the GCR flux may undergo a similar partitioning, possibly due to the different magnetic field regions having differing magnetic topologies. This new observation of GCR intensity being modulated by the local magnetic field topology will be compared to previous studies of GCR intensity anti-correlation with the interplanetary magnetic field strength [Burlaga et al., 1993; Burlaga and Ness, 1998] and discussed in more detail. Such comparisons will lead to further understanding of the underlying physics of energetic particle transport though the interplanetary medium.
SH31B-1669
Energetic Particles Measured By COSTEP Experiment During The Last Gnevyshev Gap
We present energetic particle data measured by COSTEP experiment aboard SoHO spacecraft during the last Gnevysev gap (i.e. during the last solar magnetic field polarity reversal). We have focused our attention on the search of anomalous low particle fluxes during that time. Two periods with anomalous (low) energetic particle fluxes have been identified. Those periods show "common" solar/coronal features mainly related with low or very low number of CMEs and X-rays flares. We also describe the interplanetary phenomena that were detected during those periods.
SH31B-1670
Joint Fitting of the Gamma-Ray Spectrum and Neutron-Capture Line Decay Profile and Normalization to Constrain Ion Acceleration in Large Flares
We use the RHESSI (Reuven Ramaty High Energy Solar Spectroscopic Imager) to study solar flare gamma rays that are signatures of the accelerated ions. Specifically, we analyze the prominent 2.2 MeV line due to neutron capture whose time profile depends on the ambient 3He/H ratio, accelerated ion spectral index and incident ion angular distribution. For the first time we fit the 2.2 MeV time profile and overall normalization jointly with a full spectral fit to find a minimum in the total chi-square. This allows for self-consistent constraints on many of the flaring environment parameters, including the energetic particle spectral index, degree of pitch angle scattering, ambient abundances including 3He, accelerated abundances, magnetic field convergence, and the effective angle of the flare. The temporal model consists of a kernel (the response to a delta-function particle injection) convolved with the observed 4-7MeV flux, dominated by prompt nuclear emission. The spectral fitting includes a recently improved model of the nuclear de- excitation continuum. By comparing fits of multiple flares we provide stronger constrains on the flare environment parameters as well as best current constraint to the 3He/H abundance in the sun.
SH31B-1671
Analysis of Suprathermal Events Observed by STEREO/PLASTIC
Since the late 1960's, suprathermal and energetic ion events with energies ranging from just above the solar wind energies up to 2MeV and lasting for several minutes to hours, have been detected upstream of the Earth. Possible sources of these ions include magnetospheric ions, solar wind ions accelerated between the Earth's bow shock and hydromagnetic waves to energies just above the solar wind energies, and remnant ions from heliospheric processes (such as Solar Energetic Particle (SEP) events or Corotating Interaction Regions (CIRs)). The unique orbits of both STEREO spacecraft, STEREO-A (STA) drifting ahead in Earth's orbit and STEREO-B (STB) lagging behind in Earth's orbit, allow for analysis of upstream events in these unexamined regions. Using both the PLASTIC and IMPACT instruments on board STA/B we can examine protons in the energy range of solar wind energies up to 80keV, their spatial distribution, and determine if the spacecraft is magnetically connected to the Earth's bow shock. Suprathermal events observed by STEREO/PLASTIC during solar minimum conditions are examined for possible upstream events using anisotropy measurements, velocity dispersion, magnetic connection to the bow shock, and frequency of events as a function of time and distance.
SH31B-1672
Suprathermal Tails in Solar Wind Oxygen and Iron
High speed suprathermal tails with a fixed energy spectrum have been observed in solar wind H and He2+, as well as in He+ pickup ions (e.g. Gloeckler et al., 2007). These tails appear to have a persistent and constant power law energy spectrum, unchanged in a variety of solar conditions. The presence of the tails have implications for particle injection into the interplanetary shock acceleration process. The suprathermal tails of solar wind Fe and O have been investigated with the STEREO/PLASTIC mass spectrometer. The energy spectra of solar wind O and Fe will be presented for periods of slow and fast solar wind. Variations in energy spectra are observed in both species at speeds up to 1.8 times the solar wind speed.
SH31B-1673
Jovian jets as a probe for the mean free path in the inner heliosphere
Since the pioneer mission, the jovian magnetopshere is known as a dominant source of MeV-electrons in the inner heliosphere. The large scale propagation of these jovian electrons can be described by Parker's transport equation. However, during the first and second Jupiter approach of the Ulysses spacecraft 1992 and 2003, respectively, highly anisotropic jets of MeV-electrons were observed in the vicinity of the planet. It was shown that these electrons are of Jovian origin that propagate along flux tubes connected to Jupiter's magnetosphere. It was found that these electron jets carry an energy spectra that is modulated by Jupiter's rotation period (~10h) into the heliosphere. However, these modulation vanishes at distances of about 0.5 AU. In this contribution we presentate a numerical solution of the Fokker-Planck equation for a periodic source term in order to simulate the modulation of the energy spectra. As a first approach, we consider only pitch-angle diffusion and neglect perpendicular diffusion and adiabatic energy losses. Since the pitch-angle diffusion coefficiant Dμ μ is related to the particle's mean free path, it is possible to derive a mean free path for MeV-electrons in the inner heliosphere when comparing the model calculations with the observations.
SH31B-1674
Perpendicular Diffusion of Solar Energetic Particles
We present new observations which demonstrate an energy dependence in energetic particle diffusion perpendicular to the average magnetic field direction. Dispersionless energetic particle flux "dropouts" represent small scale gradients, and, by examining how particles move off field lines containing particle flux and onto the dropout field lines without particle flux, we can measure the relative diffusion. As expected, the perpendicular energetic particle diffusion coefficient is determined to be larger at higher energies than lower energies.
SH31B-1675
Compound and Perpendicular Diffusion of Cosmic Rays
In this paper we discuss compound and perpendicular diffusion of cosmic rays and field line random walk, based on a Chapman-Kolmogorov equation formulation, in which the probability distribution function (pdf) for cross-field particle transport is given as the convolution of the pdf for particle transport relative to the magnetic field and the pdf for the random walking magnetic field. The pdf for particle transport relative to the field includes the effects of parallel diffusion, local cross-field diffusion, advection and drift. The pdf for cross- field transport, in the case of zero local cross-field diffusion is sharply peaked about the field line where the particles are injected. The effective diffusion of particles across the field due to drifts and field line random walk and the case of compound diffusion are discussed.
SH31B-1676
Transport Equation for MHD Turbulence: Application to Particle Production at Interplanetary Shocks
The aim of the present paper is to unify the various transport equations for turbulent waves that are used in different areas of space physics. Here, we mostly focus on the magnetohydrodynamic (MHD) turbulence, in particular the Alfvénic turbulence. The applied methods, however, are general and can be extended to other forms of turbulence, for example the acoustic turbulence, or Langmuir plasma waves. With minor modifications, the derivations followed here can be extended for relativistic motions, thus making it possible to apply them to the wave transport in astrophysical objects with high plasma speeds (radio-jets), or strong gravity (black hole surroundings). The transport equation is incorporated into the numerical model of the solar energetic particle acceleration at the front of interplanetary shock wave. The resulting turbulence spectra upstream and downstream the shock are presented and their contribution to the particle acceleration is evaluated.
SH31B-1677
Non-linear Evolution of Self-Generated Kolmogorov Turbulence in SEP-Accelerating Coronal Shocks
Acceleration in coronal and interplanetary CME-driven shocks is currently considered the primary source of large solar energetic particle intensities. A requirement for rapid acceleration and escape is strong turbulence trapping in front of the shock and weaker trapping further out. Such a turbulent structure can, in large events, be maintained by streaming of the accelerated particles themselves. While a steady-state description for this process has been known for decades, current research has focused on time-dependent modeling. In a recent study, Vainio and Laitinen reported on an approach including particle acceleration by self-generated waves but no non-linear evolution of the turbulent wave spectrum. Instead, an ad-hoc linear diffusion of the wave spectrum was employed. While this simplification was sufficient for the first study, the non-linear nature of turbulence must be taken into account. To that end, we employ the phenomenological Kolmogorov turbulence evolution description for non-linear diffusion in frequency. Our study presents the effects on the obtained particle and turbulence spectra, followed by discussion on the challenges associated with turbulence modeling and the work needed for improving the consistency of particle acceleration by self-generated waves.
SH31B-1678
Seedless Particle Acceleration by Quasi-Parallel Shocks
The theoretical study of proton acceleration at a quasi-parallel shock due to interaction with Alfven waves self-consistently excited in both upstream and downstream regions was conducted using a scale-separation model [1]. The model uses conservation laws and resonance conditions to find where waves will be generated or dumped and hence particles will be pitch angle scattered as well as the change of the wave energy due to instability or damping. It includes in consideration the total distribution function (the bulk plasma and high energy tail), so no any assumptions (e.g. seed populations, or some ad-hoc escape rate of accelerated particles) are required. The dynamics of ion acceleration by the November 11-12, 1978 interplanetary traveling shock was investigated and compared with the observations [2] as well as with solution obtained using the so-called convection-diffusion equation for distribution function of accelerated particles [3]. [1] Galinsky, V.L., and V.I. Shevchenko, Astrophys. J., 669, L109, 2007. [2] Kennel, C.F., F.W. Coroniti, F.L. Scarf, W.A. Livesey, C.T. Russell, E.J. Smith, K.P. Wenzel, and M. Scholer, J. Geophys. Res. 91, 11,917, 1986. [3] Gordon B.E., M.A. Lee, E. Mobius, and K.J. Trattner, J. Geophys. Res., 104, 28,263, 1990.
SH31B-1679
Injection of Heavy Ions Into Diffusive Shock Acceleration
Solar energetic particle events are commonly divided into gradual and impulsive events, with diffusive shock acceleration (DSA) and acceleration in resonant wave processes in solar flares as the main acceleration mechanisms, respectively. The gradual events typically have much larger particle intensities and coronal elemental abundances, while impulsive events typically show higher mean ionic charges, enhanced 3He/4He ratio, and enhanced heavy ion abundances. However, gradual events have been shown to be highly variable in their heavy ion statistics at the highest energies, with some events showing characteristics typical to impulsive events. One proposed solution to this variability is a selective acceleration at shock waves driven by coronal mass ejections, and a compound seed population consisting of coronal / solar wind plasma and ions preaccelerated by flares. The idea of selective shock acceleration is sensitive to the injection threshold, i.e., to the factors that determine whether or not a given incident ion is picked up by the DSA mechanism. Such factors are, for example, speed of the incident ion, shock obliquity angle, and the level of turbulence in the electromagnetic field. We have previously studied the injection of heavy ions using Monte Carlo simulations, which confirm the idea of selective ion injection. However, in these simulations, self-consistent modeling of particle transport perpendicular to the mean magnetic field is not included. In the present work, we use a self-consistent quasi- neutral hybrid simulation to study the injection problem. Results from the two numerical approaches are compared and their similarities and differences discussed.