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Sunspots are darker areas on the Sun’s photosphere and most of solar eruptions occur in complex sunspot groups. The Mount Wilson classification scheme describes the spatial distribution of magnetic polarities in sunspot groups, which plays an important role in forecasting solar flares. With the rapid accumulation of solar observation data, automatic recognition of magnetic type in sunspot groups is imperative for prompt solar eruption forecast. We present in this study, based on the SDO/HMI SHARP data taken during the time interval 2010-2017, an automatic procedure for the recognition of the predefined magnetic types in sunspot groups utilizing a convolutional neural network (CNN) method. Three different models (A, B, and C) take magnetograms, continuum images, and the two-channel pictures as input, respectively. The results show that CNN has a productive performance in identification of the magnetic types in solar active regions (ARs). The best recognition result emerges when continuum images are used as input data solely, and the total accuracy exceeds 95%, for which the recognition accuracy of Alpha type reaches 98% while the accuracy for Beta type is slightly lower but maintains above 88%.

In space weather forecasting, forecast verification is necessary so that the forecast quality can be assessed. This paper provides an example of how to choose and devise verification methods and techniques according to different space weather forecast products. Solar proton events (SPEs) are hazardous space weather events, and forecasting them is one of the major tasks of the Space Environment Prediction Center (SEPC) at the National Space Science Center of the Chinese Academy of Sciences. Through analyzing SPE occurrence characteristics, SPE forecast properties, and verification requirements at SEPC, verification methods for SPE probability forecasts are identified, and verification results obtained. Overall, SPE probability forecasts at SEPC exhibit good accuracy, reliability, and discrimination. Compared with climatology and persistence forecasts, the SPE forecasts are more accurate. However, the forecasts for SPE onset days are substantially underestimated and need to be considerably improved.

We present in this paper an operational solar wind prediction system. The system is an outcome of the collaborative efforts between scientists in research communities and forecasters at Space Environment Prediction Center (SEPC) in China. This system is mainly composed of three modules: (1) a photospheric magnetic field extrapolation module, along with the Wang-Sheeley-Arge (WSA) empirical method, to obtain the background solar wind speed and the magnetic field strength on the source surface; (2) a modified Hakamada-Akasofu-Fry (HAF) kinematic module for simulating the propagation of solar wind structures in the interplanetary space; and (3) a coronal mass ejection (CME) detection module, which derives CME parameters using the ice-cream cone model based on coronagraph images. By bridging the gap between fundamental science and operational requirements, our system is finally capable of predicting solar wind conditions near Earth, especially the arrival times of the co-rotating interaction regions (CIRs) and CMEs. Our test against historical solar wind data from 2007 to 2016 shows that the hit rate (HR) of the high-speed enhancements (HSEs) is 0.60 and the false alarm rate (FAR) is 0.30. The mean error (ME) and the mean absolute error (MAE) of the maximum speed for the same period are −73.9 km s−1 and 101.2 km s−1, respectively. Meanwhile, the ME and MAE of the arrival time of the maximum speed are 0.15 days and 1.27 days, respectively. There are 25 CMEs simulated and the MAE of the arrival time is 18.0 h.

We extend our earlier Particle Acceleration and Transport in the Heliosphere (PATH) model to study particle acceleration and transport at a coronal mass ejection (CME)-driven shock. We model the propagation of a CME-driven shock in the ecliptic plane using the ZEUS-3D code from 20 solar radii to 2 AU. As in the previous PATH model, the initiation of the CME-driven shock is simplified and modeled as a disturbance at the inner boundary. Different from the earlier PATH model, the disturbance is now longitudinally dependent. Particles are accelerated at the 2-D shock via the diffusive shock acceleration mechanism. The acceleration depends on both the parallel and perpendicular diffusion coefficients κ|| and κ⊥ and is therefore shock-obliquity dependent. Following the procedure used in Li, Shalchi, et al. (2012), we obtain the particle injection energy, the maximum energy, and the accelerated particle spectra at the shock front. Once accelerated, particles diffuse and convect in the shock complex. The diffusion and convection of these particles are treated using a refined 2-D shell model in an approach similar to Zank et al. (2000). When particles escape from the shock, they propagate along and across the interplanetary magnetic field. The propagation is modeled using a focused transport equation with the addition of perpendicular diffusion. We solve the transport equation using a backward stochastic differential equation method where adiabatic cooling, focusing, pitch angle scattering, and cross-field diffusion effects are all included. Time intensity profiles and instantaneous particle spectra as well as particle pitch angle distributions are shown for two example CME shocks.

International audience; Previous particle-in-cell simulations have evidenced that quasi-perpendicular shocks are non-stationary and suffer a self-reformation on gyro scale of the incoming ions. In this paper, by separating the incoming ions into reflected and directly transmitted parts, we investigate ion acceleration in a non-stationary perpendicular shock. The results show that shock drift acceleration (SDA) is a dominant acceleration mechanism, while shock surfing acceleration (SSA) mechanism becomes more and more important with the increase of the initial particle energy (both their average final energy and percentage increase). The percentage of reflected ions cyclically varies in time with a period equal to the self reformation cycle.

We calculate the power spectra densities of magnetic field fluctuations associated with interplanetary shock waves at 1AU, utilizing in-situ magnetic field measurements from spacecraft ACE and Wind. We derive related quantities both upstream and downstream of a shock as a function of time/distance away from the shock passage. We present results for a few events that exhibit clear upstream enhanced wave activity. We show that mostly they are of Alfvenic nature and confined within certain distance upstream. We also present a preliminary analysis of turbulence-particle interaction based on spectral analysis results. Implications of such analysis to turbulence transport models are also discussed.

We compare the efficiency of proton acceleration at oblique strong CME shocks at radial heliocentric distances from 0.13 to 2.5 AU. We use the PATH code to obtain the diffusion coefficients and maximum achievable particle energies at shocks with 15°, 45° and 75° shock angles. In computing the maximum energy, we use the total diffusion coefficient which is a function of the parallel diffusion coefficient and the perpendicular diffusion coefficient. The parallel diffusion coefficient is calculated from the wave intensity of Alfven waves generated by streaming protons in the shock vicinity [1, 2]. The perpendicular diffusion is described in the NLGC approach and depends on the parallel diffusion coefficient and pre-existing turbulence in the solar wind [3, 4, 6]. It is shown that efficiency of particle acceleration at a fast CME-driven shock depends on the shock angle, injection energy and radial heliocentric distance. Quasi-perpendicular strong shocks are more efficient in accelerating higher-energy seed particles, especially at larger heliocentric distances and close to the Sun. By contrast, quasi-parallel strong shocks can accelerate particles more efficiently at distances about 1 AU.

We calculate the power spectral densities of magnetic field fluctuations associated with interplanetary shock waves, utilizing in-situ magnetic field measurements from spacecraft ACE and Wind at 1AU. We derive related quantities both upstream and downstream of a shock as a function of time/distance away from the shock passage. We present results for a few events that exhibit clear upstream enhanced wave activity. We show that mostly they are of Alfvenic nature and confined within certain distance upstream. We also present a preliminary observational analysis of turbulence-shock interaction based on perturbation analysis.

Relativistic shocks are usually thought to occur in violent astrophysical explosions. These collisionless shocks are mediated by a plasma kinetic streaming instability, often loosely referred to as the Weibel instability, which generates strong magnetic fields "from scratch" very efficiently. In this review paper we discuss the shock micro-physics and present a recent model of "pre-conditioning" of an initially unmagnetized upstream region via the cosmic-ray-driven Weibel-type instability., Subm. to proceedings of the Annual International Astrophysics Conference (AIAC-8), Hawaii, 2009

Starting from the Vlasov or Boltzmann equation for cosmic rays in a random and regular magnetic field, we introduce guiding center coordinates and transform the velocity to a frame moving at the electric field drift velocity. The resultant equation is written in terms of the parallel and perpendicular momentum and gyro-phase of the particle, and describes spatial particle transport in guiding center coordinates. Using the drift ordering in which the gyro-scale and gyro-period are assumed short compared to the background flow length and time scales, and averaging over the gyro-phase gives the drift kinetic equation in which the adiabatic moment and total particle energy in the inertial frame are used to describe the momentum and energy of the particle. If the parallel electric field is small, the adiabatic moment of the particles is conserved to lowest order in the drift ordering. The resultant drift kinetic equation properly takes into account the energy changes of the particles due to drifts along the electric field, and betatron acceleration, but contains only the lowest order approximation for the guiding center drift velocity to describe the spatial advection of the particles. A further transformation of variables, in which the particle momentum and pitch anglemore » are specified in the local fluid frame, gives the focussed transport equation derived by Skilling to describe particle transport in a moving plasma medium, such as the solar wind. The connections to previous derivations of the Skilling's pitch angle focussed transport equation are discussed.« less

An analytic model developed by Ao et al.[1] describes the interaction of turbulence with a thin MHD shock. The interaction is governed by a modified Burgers’ equation. In this paper, we solve the modified Burgers’ equation numerically for arbitrary oblique MHD shocks. Starting with the classical ideal MHD Rankine‐Hugoniot condition, we introduce a perturbed upstream and demonstrate the evolution of the oblique MHD shock structure. We also show the dependence of shock‐turbulence interaction on different oblique angles. Our results show that turbulence plays a very important role in modifying shock front structure for oblique MHD shocks. When turbulence is modifying shock front structure, the oblique angle is another important factor. Larger oblique angle turns out to be able to creat a wider smoothed ramp in some regions and higher compression ratio in other regions.

We present results on two topics: a) The three‐dimensional (3D) Hybrid Heliospheric Modeling System with Pickup Ions (HHMS‐PI) simulations of shock waves and initial comparisons with ACE and Ulysses data for the Halloween 2003 solar events, including the Ulysses SWICS pickup proton densities; and b) Our analyses of Voyager 2 (V2) data near the termination shock (TS). Previously, we used our time‐dependent 3D Hybrid Heliospheric Modeling System (HHMS) for magnetohydrodynamic (MHD) simulations of transient events originating on the Sun. We now have added the physics of “pickup” proton processes to these models. Interstellar neutral hydrogen flows into the heliosphere and becomes ionized by photoionization and by charge exchange with solar wind protons. These “pickup” protons cause a slowing and heating of the solar wind flow in the outer heliosphere. Both HHMS‐PI and HHMS use continuous solar inputs to simulate processes that originate at the Sun. Our V2 analyses identified some elevated readings in the plasma subsystem (PLS) data. It is tempting to interpret these at face value as detections of high energy ions (HEIs) which may interact with the bulk convective plasma through a two stream instability giving rise to the observed enhanced signals in the plasma wave subsystem (PWS).

Comets provide a wonderful laboratory to study the interaction of a fast flowing plasma, the solar wind, with neutral gas from the comet. On ionization, the more massive newly‐born cometary ions are assimilated into the solar wind flow, eventually causing its deceleration via this ‘mass loading’. One of the effects of this is the cometary bow shock. The exploration of comet Halley by an armada of spacecraft in 1986, as well as the in‐situ exploration of comets Giacobini‐Zinner (1985), Grigg‐Skjellerup (1992) and Borrelly (2001), has revealed important results on the behavior of these weak shocks and showed that mass loading plays a key role. In 2014, the Rosetta mission will provide the first observations of the formation of the cometary bow shock as a comet, Churyumov‐Gerasimenko, nears the Sun. Rosetta will also provide the first measurements of the collision‐dominated near‐nucleus region. Here, we briefly review what we know about cometary bow shocks, and we examine the prospects for Rosetta.

The existence of shocks driven by Coronal Mass Ejections (CMEs) has always been assumed based on the superalfvenic speeds for some of these events and on indirect evidence such as radio bursts and distant streamer deflections. However, the direct signature of the plasma enhancement at the shock front has escaped detection until recently. Since 2003, work on LASCO observations has shown that CME-driven shocks can be detected by white light coronagraph observations from a few solar radii to at least 20 Rsun. Shock properties, such as the density compression ratio and their direction can be extracted from the data. We review this work here and demonstrate how to recognize the various shock morphologies in the images.We also discuss how the two-viewpoint coronagraph observations from the STEREO mission allow the reconstruction of the 3D envelope of the shock revealing some interesting properties of the shocks (e.g., anisotropic expansion)., Comment: 8 pages, 5 figures, to appear in Shocks Waves in Astrophysical Environments, Proceedings of the 8th Annual International Astrophysics Conference (referred), AIP Conf. Proc

We have surveyed the spectral and compositional properties of suprathermal heavy ions during quiet times from 1995 January 1 to 2008 December 31 using instruments on board ACE and Wind spacecraft in the interplanetary (IP) medium near 1 AU. We find that the composition of the quiet‐time suprathermal heavy ion population (3He and C‐Fe) depends on the level of solar activity: the ions exhibit SEP‐like composition signatures during solar maximum and CIR or solar‐wind like composition during solar minimum. In addition, we find that during quietest times in the IP medium, all ion species exhibit suprathermal tails with power‐law spectral indices ranging from 1.27 to 2.29, i.e., significantly different from recent observations and theoretical predictions of a unique 1.5 index. We discuss the implications of these new observations for the origin of the suprathermal ion population near 1 AU.

Observations by the Voyager 2 spacecraft of the structure of the heliospheric termination shock revealed a quasi‐perpendicular structure that possessed many of the characteristics that are familiar to us from perpendicular shocks observed in the inner heliosphere. However, a surprise was the relative lack of heating experienced by thermal solar wind ions (and electrons), leading to the suggestion that the pickup ions were primarily heated at the heliospheric termination shock. Because the Voyager plasma instrument cannot measure the interstellar pickup ions directly, their behavior at the termination shock could not be gauged directly. Nonetheless, it had already been predicted [16] that the primary dissipation mechanism for the quasi‐perpendicular termination shock would be the reflection of pickup ions rather than solar wind ions; this because of the shell‐like structure of the pickup ion distribution function. We discuss the effect of pickup ions including their trajectories within the structure of the shock observed by Voyager 2. A model for the shock structure is constructed on the basis of preferentially reflected pickup ions, solutions are discussed, and we estimate the degree of heating for the various components.

In nature there are many systems where macroscopic and time varying currents exist. For example, in solar flares, currents in the form of filaments and/or loops have been observed. In a simple asymmetric configuration where steady state currents flow through a straight wire and a loop, a somewhat surprising feature is that the resulting magnetic field can become chaotic depending on the relative size of the currents. This implies that studying particle motion in a time‐dependent chaotic magnetic field is a fundamental problem in space plasma physics and it has profound implications to astrophysical phenomena as the solar flares. Because these currents are time dependent, they induce electric fields. Consequently, electrons and ions moving in the field can experience alternating acceleration and deceleration, leading to a second order Fermi acceleration. We discuss here charged particle motion in a chaotic magnetic fields and the energization process. Particle trajectories are obtained by following single particle motion using the Lorentz equation by a 4‐th order Runge‐Kutta scheme. Implications of our results to particle acceleration and heating at a flare site are discussed.

Voyager 2 has observed the effects of pickup ions since about 20 AU, first in pressure‐balance structures and then in the slowdown and heating of the solar wind. By the time Voyager 2 (V2) reached the termination shock (TS), the speed had decreased by about 17% due to mass‐loading by pickup ions. At the TS, most of the flow energy did not go into the thermal ions but instead heated these pickup ions. ICME‐driven shocks are studied and compared to planetary bow shocks and the TS to see if pickup ions affect the heating at these shocks. The percentage of reflected ions at interplanetary shocks increases to about 35 AU and is similar to the percentage observed in planetary magnetosheaths at the same distance. However, outside 35 AU, no reflected thermal ions are observed downstream of interplanetary shocks or the TS, likely because pickup ions dominate the thermal plasma pressure outside this distance.

Cosmic ray protons accelerated in strong shocks are known to drive various instabilities in the shock precursor. An acoustic instability of the shock precursor driven by the pressure gradient of accelerated particles is studied in the nonlinear regime. After nonlinear steepening of the unstable waves an ensemble of discontinuities, a shocktrain, is created. Traveling wave solutions are obtained analytically and verified dynamically by numerical calculations. By compressing both an ambient and turbulent magnetic fields, and by generating the flow vorticity, the shocktrains not only amplify the magnetic field but also form distinct magnetic structures. These structures change the transport regime of accelerated particles from diffusive (quasi‐linear regime) at lower momenta to fractionally kinetic (Levy flights and traps) over an extended momentum interval below the spectrum cut‐off. As a result, a spectral break should form, typically at sub‐Tev energies and some of the particles of higher energies escape ...

Using analytical theory and data from the Plasma and Suprathermal Ion Composition (PLASTIC) investigation aboard NASA’s Solar Terrestrial Relations Observatory (STEREO), we investigate the thermalization of protons and oxygen ions passing through a shock associated with a corotating interaction region (CIR). The theoretical prediction for the thermalization of protons is based on a simple model of charged particles crossing through an electrostatic shock potential. The oxygen ions just downstream have a different speed relative to the bulk downstream plasma, and the oxygen ions gyrate downstream of the shock. Their thermal speed is the initial gyrospeed immediately after passing through the shock potential; later on part of the initial energy is lost to waves as a result of an Alfven Ion‐Cyclotron instability. We choose time periods when STEREO AHEAD (STEREO‐A) crossed two low‐Mach‐number shocks. These shocks are chosen such that thermalization contributed by reflected protons and the waves generated by the reflected protons are likely negligible. The predicted proton and oxygen thermal speeds match the observations very well.

Collisionless shocks accelerate charged particles throughout heliosphere, from low in the solar corona to the outer edge of the supersonic solar wind. Particles can gain energy while interacting with shocks in different ways, depending on conditions at the shock and on particle species and energy. Different acceleration processes generally produce distinct features in energetic particle anisotropies, energy spectra, and time intensity profiles. Thus, a study of in‐situ interplanetary shocks and particle distributions in their vicinity provides the only meaningful way to test our theoretical understanding of shock acceleration. During solar cycle 23, advanced instrumentation from the ACE spacecraft detected over 300 interplanetary shocks. More than half of these shocks produced signatures (so called energetic storm particle (ESP) events) in the low energy ion intensities. Of these ESP events, only one event did exhibit signatures that agree with steady‐state diffusive shock‐acceleration theory. Generally, ...

The recent Voyager 2 (V2) observations of the termination shock (TS) indicate that it is a plasma shock like no other in the heliosphere with dynamics and structure heavily influenced by the presence of an energized population of pickup ions (PUIs). The ‘unexpected’ finding of a cold plasma in the heliosheath with very little heating of the solar wind suggests that the energy dissipated by the shock could be dominated by the acceleration of PUIs at the TS. We examine the ’shock surfing’ mechanism at the test particle level, where multiply reflected ions (MRIs) gain energy from the motional electric field as a consequence of reflection from the cross‐shockpotential, for a specific model of the TS3 (the third TS crossing measured by V2). The energization of PUI shell distributions at a stationary, perpendicular model of the TS3 indicate that shock surfing can provide substantial PUI acceleration and a dissipation mechanism at the TS. For a strong enough cross‐shock potential and sufficiently narrow shock ra...

We discuss measurements of energetic ions from the LECP instruments on Voyager 1 (V1) and 2 (V2), made primarily in the inner heliosheath (HSH) downstream of the solar wind termination shock. The two features of these data described include: (1) intensity variations of suprathermal HSH ions measured at V1 and V2, and the clear association of these variations with solar wind stream interaction regions, as inferred from coronal hole maps; (2) efforts to separate spatial and temporal variations of HSH oxygen ions at both classical anomalous cosmic ray (ACR) energies >≈3 MeV/nuc and at lower energies

Timing and locating interplanetary (IP) shocks in the heliosphere constitutes a major task in space weather forecasting, as they are source of solar energetic particles and the leading signal of an upcoming magnetic cloud/interplanetary coronal mass ejection (MC/ICME) that causes major geomagnetic and aurora disturbances. Such a task is often complicated by the nonlinear interaction of the shock with its riding solar wind and, in some events, with other IP shocks. Using magnetohydrodynamics numerical simulation, we will discuss following issues. (1) How IP shocks are initiated near the Sun? (2) How IP shocks are evolving in the non‐uniform solar wind medium? (3) How IP shocks are interacting with each other? (4) How IP shocks are accelerating and decelerating? In addition, we will also compare simulation results with in‐situ observations.

Supernova Remnant shocks have long been identified as the major site of cosmic ray acceleration. At the shock front, cosmic rays traverse upstream and downstream multiple times and gain energies up to 1013–14 eV and perhaps even reach 1018 eV. The maximum achievable energy at a SNR shock is decided by many factors. Among these, shock geometry is an important one. Using a simple quasi‐linear theory, Jokipii [1] showed that the acceleration rate at a perpendicular shock can be orders of magnitude faster than that at a quasi‐parallel shock. Consequently, high energy cosmic rays are produced at quasi‐perpendicular portion of a SNR shock. The perpendicular diffusion coefficient used in Jokipii [1], however, do not agree with careful numerical calculations. In this paper, we discuss cosmic ray acceleration at SNR shock using the Non Linear Guiding Center (NLGC) Theory for κ⊥. We show that at an oblique shock, the generation of Alfven waves along the upstream magnetic field direction will reduce κ‖, which is cou...

In the years 2004 and 2007, the instruments onboard the Voyager 1&2 spacecraft delivered unprecedented data on the structure of the solar wind termination shock. This shock has been assumed to be responsible for the acceleration of the anomalous component of cosmic rays (ACRs) from a pick‐up ion seed population derived from the interstellar neutral gas penetrating the heliosphere. In this article, we present model results on the evolution of solar wind turbulence and suprathermal tails with heliocentric distance to support the hypothesis that stochastic acceleration all over the heliosphere but in particular in the heliosheath is an important process to energize the ACRs if not the most important one.

Planetary bow shocks, interplanetary shocks, and other heliospheric shocks are remotely observable at radio frequencies due to plasma emission. In this process, shocks are a source of energetic electron beams which excite electrostatic plasma oscillations (Langmuir waves) near the shock. Langmuir waves are then converted into electromagnetic emission at the local plasma frequency (fp) and its harmonic (2fp). While the production of electron beams by shocks and the subsequent generation of Langmuir waves are well understood, the mechanism which converts electrostatic Langmuir waves into electromagnetic radiation at fp and 2fp remains a subject of debate. A conversion mechanism is presented based on the idea that a substantial fraction of Langmuir waves are localized as eigenmodes of ambient plasma density fluctuations. Thus localized, the fp and 2fp currents associated with Langmuir waves radiate as antennas. Evidence, in the form of observations from the STEREO and WIND spacecraft, is presented for the lo...

We have surveyed the sky for residual energetic neutral atom (ENA) signals in the energy range of 0.2–3.0 keV. Approximately three years of data obtained by the Neutral Particle Detector (NPD) on board Venus Express (VEX) from May 2006 through August 2009 have been analyzed. After applying strict viewing criteria to minimize all known signals and subtracting the UV background from the Milky Way, we find a residual energy spectral shape with a ledge/bump at around 0.5 keV and a break in the spectral slope at about 1.0 keV. When the ENA spectrum is divided by the energy dependent charge exchange cross section its slope above 1 keV has a spectral power‐law index of 1.5, which is consistent with that measured in‐situ in the inner heliosheath (HS) by the Low‐Energy Charged Particle (LECP) instrument (>40 keV) on board Voyager‐1 (V1). The ledge/bump at about 0.5 keV appears consistent with twice the plasma flow velocity obtained by the V1 measurements in the inner HS.

Processes in the solar corona are prodigious accelerators of near‐relativistic electrons. Only a small fraction of these electrons escape the low corona, yet they are by far the most abundant species observed in Solar Energetic Particle events. These beam‐like energetic electron events are sometimes time‐associated with coronal mass ejections from the western solar hemisphere. However, a significant number of events are observed without any apparent association with a transient event. The relationship between solar energetic particle events, coronal mass ejections, and near‐relativistic electron events are better ordered when we classify the intensity time profiles during the duration of the beam‐like anisotropies into three broad categories: 1) Spikes (rapid and equal rise and decay); 2) Pulses (rapid rise, slower decay); and 3) Ramps (rapid rise followed by a plateau). We report on the results of a study that is based on our catalog (covering nearly the complete Solar Cycle 23) of 216 near‐relativistic ...

Diffusive shock acceleration (DSA) at relativistic shocks is expected to be an important acceleration mechanism in a variety of astrophysical objects including extragalactic jets in active galactic nuclei and gamma ray bursts. These sources remain strong and interesting candidate sites for the generation of ultra-high energy cosmic rays. In this paper, key predictions of DSA at relativistic shocks that are salient to the issue of cosmic ray ion and electron production are outlined. Results from a Monte Carlo simulation of such diffusive acceleration in test-particle, relativistic, oblique, MHD shocks are presented. Simulation output is described for both large angle and small angle scattering scenarios, and a variety of shock obliquities including superluminal regimes when the de Hoffman-Teller frame does not exist. The distribution function power-law indices compare favorably with results from other techniques. They are found to depend sensitively on the mean magnetic field orientation in the shock, and the nature of MHD turbulence that propagates along fields in shock environs. An interesting regime of flat spectrum generation is addressed, providing evidence for its origin being due to shock drift acceleration. The impact of these theoretical results on gamma-ray burst and blazar science is outlined. Specifically, Fermi gamma-ray observations of these cosmic sources are already providing significant constraints on important environmental quantities for relativistic shocks, namely the frequency of scattering and the level of field turbulence., Comment: 11 pages, 6 figures, to appear in Proc. of the 8th International Astrophysics Conference "Shock Waves in Space and Astrophysical Environments" (2010), eds. X. Ao, R. Burrows and G. P. Zank (AIP Conf. Proc., New York)

Although it has been long that spacecraft observed the anisotropy of velocity protons in the solar wind, there is still not a reasonable explanation. In this paper we try to give an explanation from the diffusion plateau of proton cyclotron resonance predicted by the quasi-linear theory for the resonance between the protons and the parallel propagating waves. We consider the effect of dispersion relation on diffusion plateau and notice that the diffusion plateau we have got by using cold plasma dispersion relation accords with the density contours in the velocity phase space detected at 0.3 AU in fast solar wind. For explaining proton distributions obtained in the fast solar wind from 0.7 AU to 1 AU hot plasma dispersion relation should be considered. We also give a theoretical relation of proton thermal anisotropyA and plasma parameter β.

International audience; The Voyager 2 (V2) plasma observations of the proton temperature downstream of the quasi-perpendicular heliospheric termination shock (TS) showed that upstream thermal solar wind ions played little role in the shock dissipation mechanism and their downstream temperature is an order of magnitude smaller than predicted by MHD Rankine-Hugoniot conditions. While pickup ions (PUI) are generally expected to play an important role in energy dissipation at the shock, the details remain unclear. Here, one-dimensional (1-D) Particle-in-cell (PIC) code is used to examine kinetic properties and downstream velocity distribution functions of pickup ions (the hot supra-thermal component) and solar wind protons (SWs, the cold component) at the perpendicular heliospheric termination shock. The code treats the pickup ions self-consistently as a third component. Present results show that: (1) both of the incident SWs and PUIs can be separated into two parts: reflected (R) ions and directly transmitted (DT) ions, the energy gain of the R ions at the shock front is much larger than that of the DT ions; (2) the fraction of reflected SWs and their downstream temperature decrease with the relative percentage PUI%; (3) no matter how large the PUI% is, the downstream ion velocity distribution function always can be separated into three parts: 1. a high energy tail (i.e. the wings) dominated by the reflected PUIs, 2. a low energy core mainly contributed by the directly transmitted SWs, and 3. a middle energy part which is a complicated superposition of reflected SWs and directly transmitted PUIs. The significance of the presence of pickup ions on shock front micro-structure and nonstationarity is also discussed.