SH43A-1628
Distinguishing physical from pseudo- non time-stationarity in finite interval observations of the scaling exponents of turbulence.
The accurate estimation of scaling exponents is central to the quantitative observational study of scale- invariant phenomena such as turbulence- they allow direct comparison between the data and the predictions of turbulence theories. Stable, time stationary intervals of naturally occurring turbulence, such as that seen in the solar wind, magnetosheath and magnetotail, are unavoidably restricted in space and time. However, methods to quantify the scaling exponents of a stationary stochastic process (time series) can, when applied to finite length intervals of data, also yield apparent time variation in the scaling exponents, suggestive of non-stationarity. This needs to be distinguished from physical non- stationarity that may also be intrinsic to the phenomena under study. We present the results of a study to determine the optimal number of datapoints (length of timeseries) N required to obtain estimates of scaling exponents to a given precision. We focus on structure function estimates but our results are also applicable to power law power spectral estimates. For power law power spectra, the variance in the computed scaling exponents is known for finite variance processes to vary as ~1/N as N goes to infinity, however, the convergence to this behaviour will depend on the details of the process, and may be slow. We study the variation in the scaling of second order moments of the time series increments with N, for a variety of synthetic timeseries and solar wind in- situ observations. We find that in particular for heavy tailed processes, for typical realizable N, one is far from this ~1/N limiting behaviour, and propose a semi-empirical estimate for the minimum N needed to make a meaningful estimate of the scaling exponents. For a given process, once the variance in the computed scaling exponents is known as a function of N, it may be possible for a given dataset to discern 'pseudo' time variation in the exponents due to finite N effects from intrinsic time variation, the prospects for this will also be discussed.
SH43A-1629
Whistler Turbulence: Particle-in-Cell Simulations
Two dimensional electromagnetic particle-in-cell simulations in a magnetized, homogeneous, collisionless
electron-proton plasma demonstrate the forward cascade of whistler turbulence. The simulations represent
decaying turbulence, in which an initial, narrowband spectrum of fluctuations at kc/ωe ~eq 0.1
cascades toward increased damping at kc/ωe ~eq 1.0, where c/ωe is the electron
inertial length. The turbulence displays magnetic energy spectra that are relatively steep functions of
wavenumber and are anisotropic with more energy in directions relatively perpendicular to the background
magnetic field Bo = \hat x Bo than at the same wavenumbers parallel to Bo. In the
weak turbulence regime, the simulations demonstrate that the cascading fluctuations have the following
properties: 1) Magnetic spectra become more anisotropic with increasing fluctuation energy; 2) the
wavevector dependence of the three magnetic energy ratios, |δ Bj|2/|δ B|2 with j = x, y,
z, show good agreement with linear dispersion theory for whistler fluctuations; 3) the magnetic
compressibility summed over the cascading modes satisfies 0.3 ≤sssim|δ Bx|2/|δ B|2
≤sssim 0.6; and 4) the turbulence heats electrons in directions both parallel and perpendicular to
Bo, with stronger heating in the parallel direction. A model to derive basic scaling relations for the
turbulence anisotropy will also be discussed.
http://public.lanl.gov/pgary
SH43A-1630
Quantifying the Anisotropy and Solar Cycle Dependence of the "1/f" Energy Range of Solar Wind Fluctuations Observed by ACE
In-situ observations of the solar wind from satellites such as ACE provide measurements of bulk plasma parameters in the solar wind on timescales spanning seconds to years, enabling exploration of the full solar cycle. At frequencies lower than the inertial range of turbulence, solar wind power spectra typically show a region of "1/f" inverse power law dependence. This "1/f" energy range is believed to be of more direct coronal origin than is the inertial range, so that the "1/f" fluctuations in the solar wind may directly embody aspects of the complex magnetic field structure of the solar corona, and of footpoint stirring in the solar photosphere. Analysis of these fluctuations may thus shed light on intriguing physical questions, such as the extent to which the possibly fractal nature of the coronal magnetic carpet is projected into the solar wind. Here we present statistical analyses that quantify the scaling properties of solar wind fluctuations in the "1/f" energy range, focusing on solar cycle dependence and on anisotropy with respect to the background magnetic field. In particular, we present structure function analysis of magnetic and velocity field fluctuations, in the directions parallel and perpendicular to the mean background magnetic field. It is necessary to go beyond power spectral analysis, which does not uniquely qualify the statistical scaling of the fluctuations, in order to address the question of fractal and multifractal scaling. We find that the magnetic field fluctuations, unlike the velocity fluctuations, show behaviour close to the expected "1/f" scaling exponents. Parallel and perpendicular fluctuations differ from each other in their scaling, which also varies with the solar cycle. These results point to distinct physical processes in the corona, and to their mapping out into the solar wind. The scaling exponents obtained constrain the models for these processes. RN acknowledges the STFC and UKAEA Culham for financial support and R. P. Lepping and the ACE team for data provision.
SH43A-1631
Nonlinear dynamics of mirror instability
It is shown that the main nonlinear mechanism responsible for mirror instability saturation is associated with modification (flattening) of the shape of the background ion distribution function in the resonant region. The nonlinear mode coupling effects at this stage are neglected as corrections of the higher order of smallness. In the nonlinear regime the mirror instability dispersion relation becomes of the second order in frequency. One of its roots is found to be growing. In the course of the nonlinear saturation the mirror mode spatial scales are cascading into the large spatial scales. The results of analytical calculations are compared with particle-in-cell simulations. The relevance of theoretical results to the existing satellite measurements is stressed.
SH43A-1632
Cross-scale effects in solar wind turbulence
The effects of kinetic particle dynamics on 1D slab turbulence in solar wind plasmas is numerically investigated in the range of wavenumbers around and beyond the Hall wavenumber ki, through a recently developed hybrid-Vlasov code (F. Valentini, P. Trávníček, F. Califano, P. Hellinger, and A. Mangeney, J. Comput. Phys. 225, 753-770, 2007), where ions are considered as kinetic particles, while electrons as a massless fluid. This zero-noise Vlasov algorithm is particularly efficient in the analysis of the short-scale termination of turbulence, where the energy level of the fluctuations is typically very low. In our simulations, nonlinear three-wave coupling processes at large wavelengths produce a MHD turbulent cascade that transfers energy towards scales of the order of the ion skin depth. In this range of wavenumbers, proton cyclotron resonance with left-handed cyclotron waves self-consistently generates perpendicular temperature anisotropy in the ion distribution function. For hot electrons, a significant level of electrostatic activity is observed at short wavelengths. The careful analysis of the numerical k-ω spectra showed that ion-acoustic waves, propagating parallel to the ambient magnetic field, are produced as the result of the nonlinear cascade of energy. Besides these ion-acoustic waves, detected ubiquitous in solar wind plasmas, new short-wavelength fluctuations of the acoustic form, and with phase velocity close to the ion thermal speed, were recovered in the simulations. These waves are driven by particle trapping kinetic effects and are usually associated with the generation of double-beam proton velocity distributions (F. Valentini, P. Veltri, F. Califano, and A. Mangeney, Phys. Rev. Lett. 101, 025006, 2008). The presence of fast beams in the proton velocity distributions is a feature frequently observed in solar wind plasmas, usually in presence of short-scale electrostatic activity (D. A. Gurnett et al., J. Geophys. Res. 84, 2029, 1979).
SH43A-1633
Stochastic Modeling of Fluctuations in Large-scale Properties of the Solar Wind or the Magnetosphere-ionosphere System
It has recently been shown that fluctuations of global quantities (let us name it X) in certain avalanching and turbulent systems can be described by stochastic differential equations (SDEs) driven by a colored noise term with a diffusion coefficient depending on X. The equation also contains a deterministic drift term, which keeps X within certain limits. This SDE has been determined for the Bak-Tang-Wiesenfeld sandpile model in [1], and for the Zhang-sandpile and a simulated two-dimensional (2D) Navier-Stokes turbulence in [2] (see the poster by M. Rypdal in this session), and may provide criteria for distinguishing between sandpile avalanching and 2D turbulence from observational time-series data. In this contribution we employ this modeling technique to observational time-series data which are believed to reflect large-scale properties of the solar wind or the magnetosphere-ionosphere system. However, time-series analysis of quantities like the interplanetary magnetic field, disturbed storm-time index, and auroral electrojet index , reveal a multifractal structure. Thus, stochastic modeling of these signals requires that we replace the colored noise with a multifractal source term in the SDE. We demonstrate how this kind of analysis and modeling can be employed to characterize the dynamics of different elements in the Sun-Earth interaction. [1] M. Rypdal and K. Rypdal, arXiv: 0710.4010 [2] M. Rypdal and K. Rypdal, arXiv: 0807.3416
SH43A-1634
On the Formation of Short-Wavelength Nonlinear Alfvenic Disturbances in the Solar Wind
Short-wavelength Alfvenic disturbances are commonly observed in the leading edge and the trailing edge of the high-speed solar wind (e.g., Belcher and Davis, 1971; Mavromichalaki et al., 1988; Neugebauer and Buti, 1990). Due to the incompressible nature of the shear-Alfven mode in the MHD plasma, the short-wavelength shear-Alfven wave cannot be developed directly from the long-wavelength shear-Alfven wave via nonlinear steepening. Thus, the formation of the short-wavelength nonlinear Alfven waves in the solar wind must rely on either kinetic processes or a more complicated nonlinear process in the fluid plasma. In this study, we use simulation to show that the short-wavelength nonlinear Alfven waves can be developed from the fast- mode Mach-cone-like nonlinear waves. It has been shown that the fast-mode Mach-cone-like nonlinear waves can be generated by velocity shear instability when the propagation speed of the surface wave is greater than the fast-mode speed in the ambient plasma (e.g., Lai and Lyu, 2006; 2008). The constructive interference and the nonlinear steepening of the fast-mode waves make the Mach-cone-like nonlinear wave a short-wavelength solitary wave. Wave-mode conversion can take place when the fast-mode Mach-cone-like nonlinear waves propagate into a medium in which the magnetic field slowly changes its direction. The Alfven waves that were converted from the short-wavelength fast-mode solitary waves are also of short wavelength. Our results not only solve the non-evolutionary problem of the short-wavelength nonlinear Alfven waves, but also provide a good explanation on why the short-wavelength Alfvenic disturbances commonly occur near the velocity shear regions in the solar wind.
SH43A-1635
Diagnosis of Magnetic Structures and Intermittency in Space Plasma Turbulence Using the Method of Surrogate Data
Several observations in space plasmas have reported the presence of coherent structures at different plasma scales. Structure formation is believed to be a direct consequence of nonlinear interactions between plasma modes that depend strongly on the phase synchronization of those modes. Despite this important role of phases in turbulence, very limited work has been devoted to study the phases as potential tracers of nonlinearities in comparison with the wealth of literature on power spectra of turbulence, where phases are generally ignored. The reason why the phases are seldom used is probably because they usually appear to be completely mixed (due to their dependence on an arbitrary time origin and to their 2π periodicity). We present a method based on surrogate data allowing one to systematically detect coherent structures in turbulent signals. After validating the method on synthetic data, we present recent results based on Cluster observations. We show in particular a direct relationship between the identified phase coherence and intermittency (classically identified as non Gaussian tails of the probability distribution functions) as well as the turbulent energy cascade. We show also how one can: (i) prove the presence of a cascade of turbulent energy when power law spectra are observed; and (ii) test the validity of the Random Phase Approximation usually used in theoretical modeling of turbulence, particularly in quasilinear and weak turbulence theories.
SH43A-1636
Bipolar electrostatic structures observed in the solar wind : comparative study between WIND/WAVES and STEREO/WAVES
Bipolar electrostatic structures are commonly observed in planetary magnetospheric environments but also in the solar wind. They may play a crucial role in transporting energy over long distances. In an earlier work, Mangeney et al. (1998) and Lacombe et al. (2002) have shown, in the solar wind, the presence of a small potential drop across the structures. This work was based on in-situ measurements obtained by the WAVES radio instrument of the WIND mission. The STEREO/WAVES instruments provide us with new in-situ measurements of bipolar electrostatic structures. We will present a comparative study of the observations from the three instruments. A model based on Vlasov-Ampere simulations will be proposed to explain the differences between the measurements of the two instruments.
SH43A-1637
Turbulence and reconnection in coronal heating field line tangling models.
In previous work, we studied the Parker field line tangling problem for coronal heating comprehensively via longtime high-resolution simulations of the dynamics of a coronal loop in cartesian geometry within the framework of reduced magnetohydrodynamics (RMHD). Although the efficient turbulent cascade prevents the magnetic field lines from becoming strongly entangled, current sheets are continuously formed and dissipated. Current sheets are the result of the nonlinear cascade that transfer energy from the scale of convective motions down to the dissipative scales, where it is finally converted to heat and/or particle acceleration. A picture is then realized, where both slightly entangled magnetic field lines and current sheets are present. Here we consider simpler forcing models and higher resolution simulations and substantiate previous scalings for coronal heating, while also discussing critical angles, secondary instabilities and double inertial ranges.
SH43A-1638
Shock front non-stationarity and ion acceleration in supercritical perpendicular shocks
Recently, particle-in-cell simulations demonstrated that quasi-perpendicular shocks are non-stationary and reform on gyro scale of the incoming ions. In this paper, by separating the incoming ions into the reflected and directly transmitted parts, we investigate the mechanisms of ion acceleration in non-stationary perpendicular shock. The energetic particles come from the reflected ions, and the acceleration mechanisms include shock drift acceleration (SDA) and shock surfing acceleration (SSA). In general, the final energy of SDA particles increases with the increase of their initial energy, while the final energy of SSA particles is almost independent on their initial energy. If we fix the shock profile during the different stage of the non- stationary perpendicular shock, the mechanisms of the particle acceleration will change in different profile. SDA is dominant mechanism for particle acceleration when the ramp of the shock is broad, while SSA dominates in shock with narrow shock ramp. When the shock evolves with time, the ions with lower initial energy are accelerated primary by SSA mechanism, while the ions with higher initial energy primary undergo SDA acceleration. The number of the reflected ions changes with time as the shock evolves with time, and the dynamics of particles is more complicated than in fixed shock profile.
SH43A-1639
Evolutive Studies of Heliospheric Turbulent Spectra via Parametric Beating
In this study, the role of a nearly-resonant three-wave parametric beating mechanism involving Alfvén and magnetoacoustic waves is examined in evolving turbulent spectra from the base of the solar corona to the outer heliophere. The mechanism is based upon a simple MHD treatment which yields a dissipation rate that is dependent only upon the wave frequency of the daughter wave, ωhjmn, the kinetic dissipation rate and a coupling efficiency, which in turn depends only upon the ratio of the fluctuating amplitude, uA, to the background Alfvén speed, vA , the plasma beta, β, and the angle of propagation of the daughter wave, θhjmn. It is shown that this mechanism may play an important role in shaping the energy spectrum via the production of fast magnetoacoustic daughter waves, particularly when β is of order unity. This is known to be the case in the sunspot region in the photosphere and lower chromosphere, in the plage region in the lower and middle corona (1.2 solar radii) and in significant portions of the upper corona and the slow solar wind. In these scenarios, this mechanism serves to heat plasma just enough to keep β above unity and drive down the damping rate. At peak efficiencies within the upper corona and near solar wind, the damping time of the driven waves is a few hours. This supports the observation that the total energy carried by Alfvén waves is observed to decrease as heliospheric distance increases, thereby diminishing the overall effectiveness of the mechanism. This feedback process may also control the temperature of plasmas that are attempting to cool by expansion or radiative processes.
SH43A-1640
Propagation of Solar Energetic Particles Associated with Impulsive Solar Flares in Turbulent Interplanetary Magnetic Fields
We discuss the physics of the propagation of an impulsive release of charged particles in a turbulent magnetic field. Test-particle numerical simulations are used to study the propagation of solar energetic particles (SEPs) in interplanetary magnetic turbulence created by the random transverse motions of magnetic footpoints embedded in the solar atmosphere (Giacalone et al. 2006). The turbulence model includes a Kolmogorov-like magnetic field power spectrum containing a broad range of scales from those that lead to large-scale field-line random walk to small scales leading to resonant pitch-angle scattering of energetic particles. We relate our numerical simulations to spacecraft observations and show that a number of features of SEP events observed by ACE and Wind can be reproduced in these simulations. For instance, we find that,the path lengths traveled by particles are different from that expected for a simple Parker spiral; and thus. The resulting velocity dispersion is energy dependent. We also find flux dropouts associated with steep localized gradients. Moreover, since particles sample different field lines which have different path length, their arriving times are non-uniform.
SH43A-1641
Cosmic Ray Diffusion Tensor Throughout the Heliosphere
We calculate the cosmic ray diffusion tensor based on a recently developed model of magnetohydrodynamic (MHD) turbulence in the expanding solar wind [Breech et al., 2008.]. Parameters of this MHD model are tuned by using published observations from Helios, Voyager 2, and Ulysses. We present solutions of two turbulence parameter sets and derive the characteristics of the cosmic ray diffusion tensor for each. We determine the parallel diffusion coefficient of the cosmic ray following the method presented in Bieber et al. [1995]. We use the nonlinear guiding center (NLGC) theory to obtain the perpendicular diffusion coefficient of the cosmic ray [Matthaeus et al. 2003]. We find that (1) the radial mean free path decreases from 1 AU to 20 AU for both turbulence scenarios; (2) after 40 AU the radial mean free path is nearly constant; (3) the radial mean free path is dominated by the parallel component before 20 AU, after which the perpendicular component becomes important; (4) the rigidity P dependence of the parallel component of the diffusion tensor is proportional to P.404 for one turbulence scenario and P.374 for the other at 1 AU from 0.1 GVto 10 GV, but in the outer heliosphere its dependence becomes stronger above 4 GV; (5) the rigidity P dependence of the perpendicular component of the diffusion tensor is very weak. Supported by NASA Heliophysics Guest Investigator grant NNX07AH73G and by NASA Heliophysics Theory grant NNX08AI47G.
SH43A-1642
Kinetic Turbulence Theory for Solar Wind Plasma
Solar wind turbulence is an important ingredient in understanding the Sun-Earth connection. It is generally believed that large-amplitude Alfven waves that are pervasively generated at the solar surface transfer their energy to smaller scale fluctuations until the energy is absorbed by the particles, thereby heating and accelerating the solar wind. However, the actual physics of the wave-particle energy exchange process is not very well understood. The controversy lies with the fact that, on the one hand, the observed preferential heating of the ions in the perpendicular direction points to the cyclotron resonant interaction (the parallel cascade paradigm), while on the other, the MHD turbulence theory predicts that the turbulent cascade should involve low-frequency kinetic Alfven waves propagating predominantly across the ambient magnetic field (perpendicular cascade paradigm). This is a long-standing issue and a topic of ongoing research by many scientists. To resolve this issue, one must develop and solve a fully kinetic turbulence theory based upon Vlasov analysis. This presentation will be a progress report on a research program initiated by the present authors about a year ago. We shall present the formal derivation of the foundational theoretical equations of kinetic plasma turbulence theory that includes self-consistent particle kinetic equation and nonlinear wave kinetic equation that describes quasilinear as well as nonlinear wave-wave coupling among ion-sound wave, kinetic Alfven wave, and Alfven-magnetosonic wave. Some preliminary numerical results shall also be presented.
SH43A-1643 TI: Nonpropagating mirror-mode structures are commonly observed in many regions of natural plasma such as solar wind, planetary magnetosheaths, in cometary plasma, Io wake, terrestrial ring current and even on the outskirts of solar system. Mirror structures are typically observed in the shape of magnetic holes or peaks. The relatively low time resolution plasma data from the Cluster CIS instrument have been used to show that the magnetic holes are most commonly observed in a mirror stable plasma. However the duration of the magnetic hole is typically much smaller than time resolution of the Cluster plasma measurements. However, the THEMIS spacecraft are able to provide plasma parameters with a time resolution of 3 seconds. This enables the collection of a number of plasma distributions during the observation of a typical magnetic hole. The THEMIS data show that at the moment when the magnetic hole is observed the threshold of linear mirror instability is usually exceeded and the plasma is therefore mirror unstable. These experimental findings are explained by the nonlinear dynamics of mirror waves.
SH43A-1644
Diffusion of energetic particles in dynamical solar wind turbulence
Previous numerical simulations (Qin et al., GRL, 29(4), 1048, 2002; ApJL, 578(2), L117, 2002) found that the transport of energetic particles behaves as sub-diffusive in magnetic turbulence with weak 3D structures, but their diffusive behavior can be recovered with strong 3D turbulence structures. Magnetic turbulence in the solar wind is large and strongly 3d; therefore, energetic particle transport in the heliosphere is most likely to be diffusive. Under certain parameter regions, the perpendicular mean free path of particles could be as large as their parallel one because of nonlinear effects. These simulations led to the so called Nonlinear Guiding Center theory (NLGC, Matthaeus et al. ApJL, 2003) that can describe the perpendicular diffusion of energetic particles very well at least when compared model simulations. However, in all the previous simulations turbulence was usually assumed to be time-independent, thus the NLGC theory has only been tested by simulations in time-independent cases. In this paper we develop numerical models of particle transport in dynamic magnetic turbulence. Conditions for recovery of diffusive behavior of particle transport will be reestablished and the NLGC theory will be retested by new simulation results.
SH43A-1645
Measurement of Phase Coherence in Space Turbulence
In many space plasmas such as Magnetosheath, intense magnetic fluctuations are permanently observed, with power law spectra. Assuming these fluctuations belong to some kind of turbulence, which can legitimately be suspected, spectra are clearly not sufficient to characterize it. Is this turbulence made of non linear "phase-coherent" structures, like in the classical Kolmogorov image, or is it made of incoherent waves as in weak turbulence? Is it homogeneous in space and scales or is it intermittent? … Many methods allow analyzing the statistical properties of turbulence, and the results obtained by tools such as structure functions or wavelets are of course influenced by all these properties, such providing indirect information about them. But few of them are specifically dedicated to the study of phase coherence so that the consequences that can be inferred from them are generally not univocal for this point of view. We will review those few tools existing in the literature that allow measuring more directly the phase coherence and present a new method, called "phase gradient analysis", which we are presently developing for this analysis. Preliminary results of this new tool will be presented.
SH43A-1646
4D Model for MHD Wave Turbulence in the Solar Corona and Solar Wind
The mechanisms of the plasma heating in the solar corona and the solar wind acceleration are still not well understood. Despite this lack of knowledge, a realistic model of the solar corona and inner heliosphere must somehow incorporate these mechanisms -- at least at the phenomenological level -- in order to properly agree with the variety of observational data. Such data ranges from EIT images of the lower corona to the solar wind parameters at 1 AU. Turbulent MHD waves have been suggested as a possible mechanism both to heat the corona and to accelerate the solar wind. Heating is dominated by wave dissipation, which is likely intensified by the wave cascade process, while the main contribution to the solar wind acceleration probably comes from the wave pressure gradient. Hence, a consistent model of the wave turbulence in the inner heliosphere should be based on a wave transport equation which describes the energy and momentum exchange between the turbulent waves and the background plasma through these two effects. As these are dependent on the wave energy spectra, said model becomes effectively four-dimensional (three spatial coordinates plus wave frequency). In the work we present a newly developed computational model in which the coupled system of the wave transport equation and the MHD equations is solved. The model is implemented within the Space Weather Modeling Framework (SWMF) and applied to simulate the solar corona and solar wind. The simulation results are compared with observations. The model may be further extended to include the interaction of MHD waves with solar energetic particles.
SH43A-1647
Composition and Spectral Properties of the 1 AU Quiet-Time Suprathermal Ion Population During Solar Cycle 23
We have surveyed the spectral and compositional properties of suprathermal heavy ions during quiet times from 1995 January 1 to 2007 December 31 using Wind/STEP and ACE/ULEIS at energies between 0.04 and 2.56 MeV/nucleon. We find that: (1) Quiet-time Fe/O and C/O abundances are correlated with solar cycle activity, reflecting corresponding values measured in solar energetic particle (SEP) and interplanetary (IP) shock events during solar maximum, and those measured in the solar wind (SW) and corotating interaction regions (CIRs) during solar minimum conditions. (2) The 3He/4He ratio lies in the 3% - 8% range during the quiet times of 1998 - 2004 with an average 3He abundance of ~27.4%. This ratio drops to 0.3% - 1.2% during 2005 - 2007 and the 3He quiet-time abundance drops to ~5%. (3) All heavy ion species exhibit suprathermal tails between 0.04 - 0.32 MeV/nucleon with spectral indices ranging from ~1.27 to 2.29. These tails sometimes extend above ~2 MeV/nucleon with Fe spectra rolling over at lower energies than those of CNO. (4) The suprathermal tail spectral indices of heavier species (i.e., Fe) are harder than those of the lighter ones (i.e., CNO). These indices do not exhibit a clear solar cycle dependence and for ~50% of the time, they deviate significantly from the 1.5 value. These compositional observations provide evidence that even during the quietest times in interplanetary space, the suprathermal population (3He and C-through-Fe) consists of ions from different sources whose relative contributions vary with solar activity. The heavy ion energy spectra exhibit suprathermal tails with variable spectral indices that do not exhibit the spectral index of 1.5 predicted by some recent models.
SH43A-1648
Acceleration and heating of solar wind ions by turbulent wave spectrum
We model the heating and the acceleration of multi-ion plasma of the solar wind by turbulent spectrum of Alfvénic fluctuations in the resonant and nonresonant frequency range. The modeling effort is guided by the observed properties of the spectrum and the measured physical parameters of the solar wind plasma in the heliosphere in-situ, as well as close to the sun from remote sensing observations. We start with 2.5D multifluid model that includes ion-cyclotron terms to study the nonresonant wave heating and acceleration, and proceed with 2D hybrid model that extends into the resonant frequency range. In addition to protons the model includes helium ions, and other heavy ions, and the results of the turbulent Alfvénic wave spectrum is compared to observation. In the hybrid model the protons and heavy ions are treated kinetically, while the electrons are included as neutralizing background fluid. This model allows to extend the study to resonant frequency range, and explore the nonlinear saturation of the heating for resonant and nonresonant waves. The models are used to explore the effect of non-homogeneous background density across the magnetic field, and of ion beams on the heating by turbulent wave spectrum.
SH43A-1649
Proton Cyclotron Heating and Beam Generation in the Solar Wind
We present results from hybrid expanding simulations of the solar wind plasma. We investigate the role of kinetic processes in shaping the proton distribution function along the wind expansion in the prensence of an initial spectrum of Alfvén waves. We find that both wave-particle and wave-wave interactions play a role in the ion evolution, in particular waves interact with protons through ion-cyclotron resonace and non-linear trapping due to the growth of parametric instabilities. Cyclotron interactions control the evolution of the temperature anisotropy providing a perpendicular heating which contrasts the adiabatic cooling caused by the expansion. Ion-acoustic modes driven by parametric effects produce a velocity beam in the particle distribution function. We discuss and compare our results with direct solar wind observations between 0.3 and 1 AU, and we find that the resulting proton distribution functions are in reasonable agreement with Helios data.