From two different models of axisymmetric analytical solutions of the MHD equations that govern the outflow emanating from a magnetized and rotating object, a new hybrid model is presented. The hybrid model input parameters are set from ULYSSES data of the solar wind for solar minimum. Using spacecraft data, the latitudinal dependences of the density, velocity and magnetic field are constrained. This hybrid model is built having in mind the high flexibility of the two original models when applied in their proper domains. Close to the Sun, a three component solution for velocity and magnetic field is used, providing a wind geometry with non-radial streamlines and enabling the description of usual flaring of the field lines observed in coronal holes, specially during solar minimum (Tsinganos & Sauty 1992, Sauty & Tsinganos 1994). From the Alfvén radius to 1 a.u. and further, the hybrid model keeps the latitudinal dependences as flexible as possible at the cost of giving up one of the components of the velocity and magnetic fields and working with the remaining two, turning the streamlines into radial ones (Lima, Priest & Tsinganos, 2001). This two-component model provides the latitudinal versatility needed to deal with sharp variations of certain quantities near the equator, which are observed in ULYSSES data, and thus allowing the description of the way all physical quantities vary with distance to the Sun and with latitude, in some agreement with ULYSSES data.

In modeling of the resonantly scattered coronal Lyα line of HI, the intensity of the chromospheric source is often assumed to be uniform. We investigate here the validity of this assumption. After having established a correlation between the HI 121.6 nm and the HeII 30.4 nm intensitiesCarrington maps of the Lyα chromosphere are built from SOHO/Extreme Ultraviolet Imaging Telescope data. These maps are used to compute the Lyα irradiance at any location in the corona and heliosphere. A 15% latitudinal anisotropy was found at 1 AU. at solar minimum, and this value becomes larger closer to the Sun. The effect of the flux anisotropy on the total intensity of the Lyα resonantly scattered coronal radiation is quantified. We found that at solar minimum, the uniform disk assumption leads to systematically overestimating the total intensity of the polar regions by 15% on average. The evolution of this effect with solar activity and the case of other resonantly scattered coronal lines are discussed.

The three-dimensional structure of the solar wind is strongly dependent upon the Sun`s activity cycle. At low solar activity a bimodal structure is dominant, with a fast and uniform flow at the high latitudes and slow and variable flows at low latitudes. Around solar maximum, in sharp contrast, variable flows are observed at all latitudes. This last kind of pattern, however, is a relatively short-living feature, and quite soon after solar maximum the polar wind tends to regain its role. The plasma parameter distributions for these newborn polar flows appear very similar to those typically observed in polar wind at low solar activity. The point addressed here is about turbulence, known to be able of playing a key role in space plasma heating. A ubiquitous presence of a turbulence of Alfvénic type is a well established feature for low-solar-activity polar wind. Does this hold for the new polar flows seen near solar maximum? An answer is given here through a comparative statistical analysis on parameters as total energy, cross helicity, and residual energy, that well describe the Alfvénic character of fluctuations. Our results indicate that the main features of the Alfvénic turbulence observed in low-solar-activity polar wind are quickly recovered in the new polar flows developed shortly after solar maximum.

Using a 3D forward model of the corona we investigate the structure of the base of the corona. Spectral profiles of various emission lines synthesized from a 3D MHD coronal model allow us to compare the source regions of transition region and coronal line to the magnetic field. By this we can study the connections and interaction of the atmospheric regions as well as transient phenomena. Results of this analysis show that the transition region is mostly originating from the footpoint regions of larger coronal loops, and that small cool loops probably play only a minor role. Furthermore we find spicule-like structures, which are the result of an upward-moving cooling front in a downflow region, which is quite contrary to the traditional scenarios for spicules. This study shows the great potential of forward 3D models of the solar corona for our understanding of the base of the solar corona and thus the source region of the solar wind.

Magnetic Field Directional Turnings (MFDTs) have firstly been identified by Tu and Marsch (1991) in the solar wind during a single case study. These structures, are characterized by a nearly zero cross-helicity, a clear excess of magnetic energy, which brings the normalized residual energy close to -1 and, a rather incompressible character of magnetic field and density fluctuations. MFDTs can be thought of as a special kind of static magnetic structures characterized by directional changes of magnetic field vector. In this paper, it will be shown that MFDTs represent a well distinct and remarkable family of MHD fluctuations which coexist and appear to evolve radially together with Alfvénic fluctuations. Statistical features of these convected structures and their possible origin will be reported and discussed.

With different spectral lines, distinct streamer morphologies are revealed by the Ultraviolet Coronagraph Spectrometer on board the SOHO spacecraft (UVCS/SOHO): a simple streamer morphology with a single peak is found with the HI Lyα line while a more complex bifurcated structure is yielded with the OVI doublets. To use this feature constraining theoretical models for the corona and solar wind, we calculate the two-dimensional density distribution taking the O(+5) ions as test particles flowing in an electron-proton background solar wind. The OVI and HI line emissivities and synthesized images in general agreement with the UVCS observations are obtained. It is shown that the O(+5) ions inside the streamer core are quasi-static and strongly depleted as a result of the gravitational settling. The factors accounting for the observed bifurcated streamer morphology will be analyzed, taking into account the diffusion of O(+5) ions across the magnetic field lines near the cusp. The dynamic behaviour of O(+5) ions both in the outflowing and trapped coronal plasmas will be presented. Especially we compare the new result with that obtained previously using the one-dimensional flow tube solar wind models, which predict the stagnated outflow of O(+5) ions near the cusp (Chen et al., ApJ, 2004 and Chen and Li, ApJL, 2004).

Radio scattering measurements can be used to estimate the solar wind velocity, and these are particularly important near the Sun where direct space-craft measurements have not yet been made. A radio wave passing near the Sun is modulated by fluctuations in electron density, and all radio scattering measurements measure the velocity of this modulation pattern past the observer. Measurements of the spatial characteristics of the density fluctuations, i.e. field aligned anisotropy and a flatter spatial spectrum than that of the magnetic field, suggest that the small scale density fluctuations in the fast polar wind near the Sun are outwards propagating waves. Thus velocity measurements in this region are biased above the flow speed by the wave speed. Modeling velocity measurements in this region, under the assumption that the density fluctuations are static structures convected with the flow, has always required the inclusion of a "random parallel velocity" of unknown origin. Including outwards propagating density waves in the model eliminates the need for this random component and fits the observations very well. Accordingly we believe that the "wave" model is more likely to be correct than the original model. This has two important consequences. First, the estimated flow speeds are reduced by the mean wave speed transverse to the line of sight. This suggests that the acceleration of the fast wind is extended well outwards of 10 Rs. Second, the waves will damp and heat both the electrons and the ions. This heating will also be extended outwards of 10 Rs. The electrons will be heated by electron Landau damping and the ions by cyclotron damping. The energy thus supplied to the wind is comparable with that required to accelerate the fast wind. The waves which best match the observations are obliquely propagating Alfven waves, which could be scattered out of the known population of radially propagating Alfven waves by radially elongated fine structure in the corona.

We report new observational results and insights in the energy release during transient events on sub-flare level in active region coronal loops. Such events seem to be a common feature of active region loops. Our work is based on multi-temperature observations obtained high above the limb by SOHO/SUMER. We conclude that the energy input into the loop system is initiated at one and only one foot point by an asymmetric impulsive mechanism. This trigger does not seem to be connected with any bulk flow and there is no indication that the plasma in the loop is replenished or replaced. These observational facts rule out some of the heating models under discussion. The electron density, N_e however, increases significantly during such events. If no new material is added to the local plasma, then the N_e increase can only be explained by a rapid volume decrease, i.e., by a in-situ pinch effect, compressing and heating the affected plasma.

Statistics associated with Fluctuations of solar wind parameters shows a remarkable dependence on the particular phase of the solar activity. In this work we focused our attention on the waiting time statistics governing the MHD fluctuations of the interplanetary magnetic field. Data from several spacecraft, covering different phases of solar cycle, were used. We found that propagating Alfvénic fluctuations and convected coherent structures strongly influence the statistics which varies from quasi Poissonian to power law. In this work we report about preliminary results and possible implications within the framework of sun-earth connection.

The CMEs with small angular sizes (< 10 degrees) have most simple view in contrast to large CMEs. It is make easier the investigation of theirs nature. In the work is employed a new method for study of small-size CMEs with the use of calibrated data of LASCO C2. The basis for this method is the following experimental result (Solar Phys., 188, 299, 1999): the coronal streamer belt represents sequence of radial rays of increased density (or magnetic tubes) with angular size ~2-3 degrees in which “slow” solar wind (SW) is flowing. Presumably they have origin at the boundaries of the supergranules. It was shown that a movement of the small-size CME occurs inside of such magnetic tube . The appearance of the CME in this place may result in increasing of angular size of the tube about two or three times. Data analysis let us assume that the small-size CME is a “plasmoid” (a restricted blob of plasma with an own magnetic field) that have been thrown in the base of the magnetic tube and is moving along it from the Sun. The estimations for the specific event (October 19, 1999, ~21:00UT, Å-limb) shows that an initial density of the plasmoid (if it is consider that its initial angular size before expansion was d₀ ~ 2-3 degrees) is about 3-4 times the density of the slow SW by which plasmoid propagate in the tube, and an own magnetic field of the plasmoid is 3-5 times greater than undisturbed magnetic field of the tube.

is shown that in brightness rays of the streamer belt there exist additional plasma streams of enhanced density. The streams travel with a steep front whose width δ~ 0.1 Ro, on the order of the spatial resolution of the LASCO-C3 instrument. The additional streams are akin to quasi-stationary slow SW streams in the streamer belts in the following quantities: plasma density, directed velocity, and duration of streams.

One of the parameters characterising the performance of an imaging telescope or spectrometer is a Point Spread Function (PSF). The transit of Mercury across the Sun in 2003 presented an opportunity to determine the PSF of the SOHO/CDS Normal Incidence Spectrometer. A sit & stare observation using a 2’’x240’’ slit was taken in several spectral lines and repeated at six locations on the solar disk, giving six time series of Mercury moving across the slit. We present a novel mathematical method of dealing with the convolution equation and the time series data, by converting it to a matrix equation and using an iterative multiplicative method to solve it. The method is applied to the He I 584 A line data, and the derived PSF is shown.

Various speed of solar wind originates from open magnetic field region such as coronal holes. We investigated the relation between solar wind velocity and magnetic properties of its photospheric sources during the solar minimum (1995-1998). Solar wind velocity observed with interplanetary scintillation at 327 MHz, Solar-Terrestrial Environment Laboratory, Japan, are mapped back to source surface (2.5 solar radii) by using ballistic model and then the photospheric solar wind sources are determined by using potential field calculation of coronal magnetic field from synoptic maps observed at Kitt Peak National Solar Observatory. The photospheric sources are divided into small areas and magnetic flux tube from each small area is calculated. The relation between solar wind velocity (V), magnetic flux expansion rate (f) and photospheric magnetic field (B) are examined by cross-correlation analysis. As results, we found the highest correlation between V and B/f.

The role of Alfven waves in producing siphon flows and oscillations in large coronal loops, extending from one third to two solar radii above the limb, is investigated using an isothermal axisymmetric MHD model of the solar corona with transparent boundary conditions. Alfven waves are introduced as a time-dependent driver for pressure variations at the footpoints of the loops. It is shown how they produce an ever-growing siphon flow when both footpoints are excited. Density enhancements and oscillations are also observed along the apex of the longest loops along which the waves are substantially damped. The periods of oscillations thus found are shown to be comparable to the observed values derived from ultraviolet observations of the corona with UVCS/SOHO.

A major goal in solar physics has during the last five decades been to find how energy flux generated in the solar convection zone is transported and dissipated in the outer solar layers. Progress in this field has been slow and painstaking. However, advances in computer hardware and numerical methods, vastly increased observational capababilities and growing physical insight seem finally to be leading towards understanding. We present numerical simulations of quiet sun heating that span the entire solar atmosphere from the upper convection zone to the lower corona. These models include non-grey, non-lte radiative transport in the photosphere and chromosphere, optically thin radiative losses as well as magnetic field-aligned heat conduction in the transition region and corona. The relation between the mean magnetic field strength and structure and the heating of the corona is discussed.

We present hybrid expanding box simulations of the interaction of left-handed Alfven waves with minor ions and protons. We investigate properties and saturation of the frequency sweeping mechanism in case of minor ions. The numerical simulations show that minor ions is efficiently heated in perpendicular direction but are only slightly accelerated. The saturation is mainly due to the temparature anisotropy when the ion thermal velocity is much smaller than the local Alfven velocity. When the ion thermal velocity becomes comparable with the local Alfven velocity the acceleration becomes stronger and the saturation is influenced by the differential velocity. The simulations are discussed within the context of observations and theoretical models of the evolution of MHD turbulence in the outer corona and accelerating solar wind.

Ulysses spacecraft gives a unique opportunity to study the fast solar wind out of the ecliptic plane. Measurements are performed by the URAP radio receiver instrument on board, using the quasi-thermal noise spectroscopy method. This technique is well-proven and gives accurate meassurements of the electron density and core temperature in various space media. In particular, we used this method to study the large-scale variations of the fast solar wind, during solar cycle 23. The large sample of data (around 170000 points) obtained during the first Ulysses fast latitude scan in 1994-1995 enables us to determine the electron density fluctuation spectrum near solar minimum. We will present this new result and compare to previous work.

We have developed a new set of general transport equations for magnetized, fully ionized gases designed to cover the entire regime from collision-dominated to collisionless flow. In the collision-dominated limit we find transport coefficients (heat flux and thermal force) that are in very good agreement with results from classical transport theory. The equations also describe, reasonably well, the flow of collisionless, ionized gases, and should therefore be well suited to describe the transition region - corona - solar wind system and other fully ionized, expanding stellar atmospheres. The equation set can easily be implemented into existing codes and describes density, drift velocity, parallel and perpendicular temperature and heat flow. In a rapidly expanding coronal geometry the new equations lead to very different solutions, with a much higher coronal density and solar wind mass flux, than gyrotropic equations that are in common use today.

Both adiabatic and non-adiabatic heating occur when solar wind streams collide. Between the streams a ridge of pressure arises that compressionally heats the plasma. Eventually the pressure ridge develops a forward-reverse shock pair that leads to further heating. In order to characterize the strength of the interaction between streams and identify the presence or absence of shocks, we use the total perpendicular pressure (thermal plus magnetic). Shocks or shock-like jumps in pressure are surprisingly frequent, appearing in about 30% of the stream interactions from 1997 to 2002. The height of the pressure maximum indicates the strength of the interaction. This strength often remains in a narrow range over many solar rotations. Comparing the heating in the pressure ridge with and without shocks, we find that the heating associated with the presence of the shock far outweighs the heating due to compression.

The ions of the solar wind have nearly isotropic velocity distributions in spite of conservation of magnetic moment, which ought to be valid in such a collisionless plasma. It must be that some kind of fluctuating field replaces collisions to keep the distribution isotropic, and to make the MHD equations valid. The EFW experiments on the Cluster satellites are furnished with carefully designed antennas which have allowed the observations of low frequency electric fields which are presented here. The magnitudes of the measured fields are estimated to be more than sufficient to maintain the isotropic ion distributions which are observed, and presumably, also to make the solar wind behave as the collisional plasma which is required for the validity of MHD.

We investigate the physical properties of the corona above active region loops. The electron temperature, density and elemental abundances at 1.55 solar radii are derived for around 15 active regions using the UVCS data onboard SOHO. These active regions exhibit different temperature characteristics, some with lines emitted from highly ionized ions such as Fe XVIII (formation temperature of 6 million degrees), some with particularly strong emission from lower ionized ions such as SiVIII (formation temperature of 800 thousand degrees). The elemental abundances all show the FIP effect. These physical properties are compared with the magnetic configuration of these active regions. The implication for coronal heating in the active region environment is discussed. This dataset was taken during the SOHO Joint Observing Program 151 in the period of December, 2001 to February, 2002.

In the present work SOHO/CDS observations of a quiescent active region loop are compared to a steady-state, dynamic loop model, with three different heating functions. Predicted temperature and density profiles of the loop are compared to observations from CDS. The space of parameters of the model is investigated. We find that no agreement can be found between model predictions and observations. We also analyze several SUMER intensity maps of active region solar loops in order to compare the observed relative brightnesses of their footpoints and of their coronal section. We determine the observed intensities of coronal lines relative to the transition region and chromospheric emission, and compare them with predictions from loop models having uniform cross section and different heating functions. We find that the loop models overestimate the footpoint emission by orders of magnitude. We speculate that a significant decrease of the cross-section near the footpoints, is the most likely solution to the discrepancy.

We present complete analysis of the spectra obtained during two M-class solar flares (on 1980 August 25 and 1985 July 2) with the Flat Crystal Spectrometer on board the {\it Solar Maximum Mission}. These spectra cover the 7.47-18.97 A spectral range, encompassing the range where the emission from Fe XVII-XXIV configurations with n=3,4,5 provides a wealth of spectral lines suitable for plasma diagnostics. The physical properties of the flaring plasmas (temperature, emission measure, density) are derived as a function of time using strong, unblended lines. Using the diagnostic results, spectra predicted using the latest version of the CHIANTI database (Version 5) have been obtained which were then compared with wavelengths and fluxes of lines in the observed spectra. This comparison has allowed us to 1) identify a host of previously unidentified lines and 2) assess the quality of state-of-the-art atomic physics calculations in the X-ray range. A by-product of this work is the development of a complete spectral atlas for solar flares between 7.47 and 18.97 A.

An important assumption inherent to the usual fluid solar wind models is that the plasma is at equilibrium, dominated by collisions. Therefore the hydrodynamic approach implies that the particles velocity distribution functions are rather close to a Maxwellian. However the observed solar wind electron distributions depart from nearly isotropic Maxwellians, indicating the limited validity of this hypothesis. Indeed the observed electron distribution functions of the solar wind permanently exhibit three different components : a thermal core and a supra-thermal halo, which are always present at all pitch angles, and a sharply magnetic field aligned "strahl" which is usually antisunward-moving. What is the exact origin of such departures from Maxwellian equilibrium ? If the Coulomb collisions could explain the relative isotropy of the core population, the origin of the halo population and more specifically the origin of its sunward-directed part remains unknown. We look for possible observationnal constraints on the processes that could explain the existence of such electron distributions, by examining the radial evolution of its various populations. For this purpose we combine HELIOS (0.3 to 0.7 AU), WIND (1 AU) and ULYSSES (1.3 to 3 AU) observations performed during fast solar wind periods at minimum of activity.

The fire hose instability can take place in a magnetized plasma with temperature anisotropy and in presence of electromagnetic fluctuations; these conditions are naturally developped in the expanding solar wind. We present results from one-dimensional hybrid simulations in the case of propagation along the magnetic field: the behaviour of the fire hose stabilization is investigated and we obtained a threshold condition for this instability. The threshold condition we found is in good agreement with the one derived recently on the base of solar wind observational data. We also performed one-dimensional simulations with the hybrid code implemented with an expanding box model. This kind of simulation shows the consequences of fire hose instability directly on the dynamic of an expanding system: it results that the fire hose instability forces the system to expand along the marginal stability path.

Turbulence transport equations based on a two scale MHD decomposition, non-WKB spatial transport and phenomenological treatment of local homogeneous turbulence, have been able to account well for radial evolution of turbulence energy, correlation scale, cross helicity and temperature. The formalism includes supply of turbulence energy by large scale shear and by pickup ion associated wave particle interactions in the outer heliosphere. This approach has been tested against Voyager and Pioneer datasets at low heliospheric latitudes from 1 AU to beyond 60 AU [1,2]. It also has been compared to Ulysses observations at high latitudes, with similarly good correspondence [3]. We now describe application of this approach to the distribution of turbulence throughout the heliosphere, i.e., at radial distances >0.3 AU and at all latitudes. We incorporate the successful results of previous studies [1,2,3] and devise latitudinal varying boundary conditions using well established constraints at low latitude, and high latitude variations of speed and density extracted from Ulysses data [4]. We discuss and contrast the predictions of the theory for widely varying latitude and radial positions. This approach promises to provide, for the first time, a realistic basis for explaining and/or predicting the MHD turbulence energy and associated parameters that determine charged particle scattering, at all positions in the heliosphere. A few refinements, such as improved pickup ion modeling at all latitudes, are needed to complete the picture [e.g., 5]. This approach will be useful in a variety of applications including ab initio studies of solar cosmic ray modulation. [1] Smith et al, JGR, 106, 8253 (2001) [2] Matthaeus et al, GRL, 31, L12803 (2004) [3] Breech et al, GRL 2004GL022321, in press (2005) [4] McComas et al, JGR 105, 10419 (2000) [5] Isenberg et al, ApJ 592, 564 (2003)

We show that the well known correlation between solar wind speed and temperature can be understood as a consequence of symmetry of the solar wind transport equations, including nonadiabatic turbulence effects. Under a reasonably wide range of circumstances, solutions of the transport equations depend only upon the ratio r/U of distance to solar wind speed. This property is obtained in regions where the Alfv\'en speed is much smaller than the flow speed, where pickup ions are negligible or nearly uniform in space, and where the flow is locally a spherical constant speed expansion. Applied to the temperature equation, the familiar correlation emerges immediately. This property of the transport equations may be able to explain local correlation in which changes of speed are correlated with changes of temperature [1], as well as the overall structure of speed-temperature scatter plots [2]. The analysis can be used to estimate variability of inner temperature boundary conditions close to the sun. It may also clarify why the correlation is reduced in ensembles that include highly nonspherical effects such as CMEs [3]. [1] J. D. Richardson and C. Wang in AIP Conf. Proc. 679: Solar Wind Ten}, 71 (2003) [2] L. F. Burlaga and K. W. Ogilvie, Astrophys. J., 159, 659 (1970) [3] H. Elliott et al. JGR, in press (2005)

The kinetic model of the solar wind is developed in approximation of a stationary flow with spherical symmetry, the quasi-neutral fully ionized hydrogen plasma ejected by the rotating Sun, and the Maxwellian distribution function at the exobase (in the solar corona). We assume also that the Sun´s magnetic field is given as a Parker´s field. The analytical solutions of the kinetic equations for the velocity distribution functions of electrons and protons are derived and used for the calculation of the numerical density, the particle flux of the solar wind, and the plasma polarization potential in the inner heliosphere. The mentioned solutions depend on the non-monotonic total potential formed by the inertial, gravitational, electrical and magnetic fields. The obtained theoretical results are compared to other kinetic models and to the observational data what demonstrates consistency with observed speed and density of the solar wind.

   The known kinetic models of the solar wind are developed on the base of the one- and two-particle distribution functions (e.g. [1], [2]).
   The multiparticle statistical approach based on the Liouville equation is applied in this paper to the solar wind..
   The analytical formulae for the statistic moments (number density and bulk speed of the flow) are derived on the base of the multiparticle distribution functions in the frame of the following assumptions: collisionless steady and spherically symmetrical flow; quasi-neutral fully ionized two-component (hydrogen) plasma; equilibrium plasma state at the exobase (in the low solar corona). These dependences of the solar wind density and the speed on the heliocentric distance coincide with the respective results of the two-particle kinetic model [3] and consist with the observed data [4].
   The fluctuation distribution function is also developed on the base of the considered approach. The character of this function depends on the scale applied for averaging the multiparticle distribution function (i.e. the solution of the Liouville equation). This can result in qualitative differences of observed particle energy specters because of different space resolving power of measurements or scales of data processing.
References.
[1] Issautier K, Meyer-Vernet N, Pierrard V and Lemaire J Astrophys. Space Sci. 2001, 277, pp 189-193.
[2] Y.M.Vasenin, N.R.Minkova. Journal of Physics A: Mathematical and General, 2003, 36, pp 6215-6220.
[3] Y.M. Vasenin, N.R. Minkova, and A.V. Shamin. Proceedings of 11th International Congress on Plasma Physics: ICPP2002. AIP Conference Proceedings 669, 2003, pp 516-519
[4] Koehnlein W. Solar Physics, 1996, 169, pp 209-213.

Solar flares are the manifestation of a sudden, intense and spatially localized energy release in the solar atmosphere which may raise the coronal temperature up to 10⁷ K. It is generally agreed ([Kulsrud, 1998] and [Priest & Forbes, 2000]) that the energy source comes from magnetic reconnection which provides a mechanism for the topological rearrangement of the magnetic field lines that in this way liberate thermal and kinetic energy. In 1988 E.N. Parker suggested a physical mechanism for the coronal heating based on the so-called "nano-eruptions". Parker's idea is that stochastic photospheric fluid motions shuffle the footpoints of magnetic coronal loops. Because of the high electrical conductivity of the plasma which forms the solar corona the magnetic field is 'frozen in' to the plasma so the relaxation of the loops leeds to a complex, tangled magnetic field which is force free everywhere but in numerous small electrical current sheets. When the current in this sheets goes beyond certain threshold magnetic reconnection takes place. Parker's model include all the ingredients necessary to produce a self-organized critical state (SOC state, [Bak, 1996] ): a dissipative system subject to a local instability requiring a triggering condition (magnetic reconnection), a slowly driven open system, and an external forcing mechanism on a long time scale compared to the dynamical time scales. In the last decade many efforts have been made to provide a SOC model for solar flares (see [Charbonneau et al., 2001] and refeences therein). One of the weak points of those SOC models is that it is difficult to identify in the numerical model the main quantities involved in the magnetic reconnection phenomena. We are working towards a new generation of SOC models. We construct a 2D lattice formed of parallel 'field lines' that are randomly deformed leading to the development of discontinuities in the field lines, we applied a redistribution rule obtaining an avalanching system for different sizes of the lattice. We use this simple device as a working scheme that will lead us to a more physically realistic SOC numerical model of solar flares.

During May 1996 and February 2003 two different comets passed through the field-of-view of the LASCO C3 coronagraph. These comets (C/1996 B2 Hyakutake and Comet C/2002 V1 NEAT) passed within 0.26 and 0.1 AU of the Sun, respectively. Ion tail orientations from these comets were used to estimate solar wind speeds during solar minimum and maximum conditions. We have used the Wang-Sheeley (WS) model to estimate the solar wind speed in the vicinity of the comet for comparison with the ion-tail results. Comet Hyakutake’s orbit produced a track along the source surface (2.5 Rsun) for Helioigraphic Latitudes between 0 and 55 degrees and Carrington Longitudes of 150 to 350 degrees. Comet NEAT’s orbit produced a comet track along the source surface at Heliographic Latitudes ranging from 70 degrees North to 40 degrees South and nearly constant Carrington Longitude (120 degrees). Photospheric magnetic field maps from Carrington Rotation 1908 and 1999 measured at three observatories (Wilcox, Kitt Peak, and Mt. Wilson) were used as inputs to the WS model. For the solar minimum case the ion-tail and WS model results were comparable regardless of observatory. For the solar maximum case two of the model results (Wilcox and Kitt Peak) placed the current sheet at similar latitudes (40-45 degrees North) while the third (Mt. Wilson) placed the current sheet at lower latitudes (20 degrees) and appeared to agree with the current sheet placement implied by the ion-tail results. In this presentation we will discuss the methods of solar wind speed determination from ion-tail observations, present the comparison of solar wind speeds derived from the ion tail measurements with values derived from magnetic field observations, and discuss differences in photospheric magnetic field maps that could affect the location of the current sheet.

Photometric, spectroscopic and polarimetric observations in the He 1083 nm line provide important diagnostic information on the structure and dynamics of the chromosphere. We will describe an imaging instrument designed to probe the chromosphere in the He 1083nm line, based on a Helium magneto-optical filter. The instrument has a narrow passband (< 0.005 nm) high throughput and stability, making it ideal for making high cadence observations in support of studies of chromospheric dynamics and wave propagation. We will describe the characteristics of the instrument and present preliminary observations.

A model of MHD turbulence in a coronal loop is presented. The model describe the injection, due to magnetic field footpoint motions, the storage and the dissipation of energy in the system. We assume a homogeneous ambient longitudinal magnetic field, a low beta and an high aspect ratio, which allows us to use the set of reduced MHD equations (RMHD). The model is based on the use of shell technique in the wave vector space orthogonal to the ambient magnetic field, while the dependence on the longitudinal coordinate is preserved. In the numerical simulation we apply a forcing at the base of the system with velocity amplitudes characteristic of the photospheric motions, and we obtain inside of the system velocity fluctuation values in agreement with non thermal mass motions deduced from coronal observations. In this framework the magnetic system work like resonance cavity for the velocity fluctuation, which drive the nonlinear cascade, so the dissipation spikes. Comparisons of the velocities with coronal observations during flaring are presented. Nonlinear interactions give rise to an energy cascade towards smaller scales where energy is dissipated in an intermittent way. Due to the propagation along the strong magnetic field, dissipative structures propagate along the loop with Alfvén speed. The statistical analysis on the intermittent dissipative events compares well with all observed properties of nanoflare emission statistics. These results naturally emerge from the dynamical evolution without need of ad-hoc hypothesis.

We have used a 3-D numerical magnetohydrodynamic (MHD) model to simulate corotating structured ambient solar wind as well as some transient interplanetary disturbances. Although the ideal MHD approximation enables replication of many large-scale solar wind structures and 3-D dynamic interactions, this approach faces inherent limitations in reproducing radial temperature profiles, the positions of interplanetary shocks, and shock jump conditions. Instead of attempting to derive more realistic thermodynamics of the solar wind through inclusion of more more detailed particle transport and wave dissipation physics, we are attempting to reproduce temperature profiles observed by Helios (for the inner heliosphere) and Ulysses (for the mid heliosphere) through the use of empirically derived polytropic index and/or volumetric heating as function of heliocentric distance. Results from parametric studies and comparisons with radially aligned spacecraft observations are presented and discussed.

The collisional mean free path of a thermal particle in the solar corona is of the order 10^-4 to 10^-2 times the typical scale variation of macroscopic quantities such as the density or the temperature. Under such conditions the heat conduction between the corona and the upper chromosphere may depart substantially from the classical Spitzer -Härm form. We present numerical simulations which suggest that this is indeed the case.

Using the MTOF (Mass Time Of Flight) sensor of the CELIAS (Charge, Element, and Isotope Analysis System) investigation on SOHO we have studied the behavior of the oxygen to proton ratio and the iron to proton ratio in different solar wind flow types. Abundance ratios for iron and oxygen are compared to photospheric and meteoritic values. We have also identified a number of intervals in which there is a dramatic decrease in the density of the heavy ions with no corresponding decrease in the proton density.

In this work we investigate the observational properties of small scales turbulent heating in a coronal loop. We model the heating and cooling phases of a loop following impulsive events generated according to the 3D model of Buchlin at al. (2003). This is simiklar to Cargill '94 approach where energy inputs are provided in very small braids. Then, we simulate the radiative losses, we build synthetic spectra of emitted coronal lines and we investigate their properties.

In this work we determine the electron temperature and density along an equatorial streamer observed in 1997. These quantities are obtained by comparing the H-Lya and H-Lyb emissions in the streamer. For this work we used spectroscopic data from SOHO/UVCS from 1.2 to 5 Rsun.

We synthesized emission line spectra from a 3D coronal model with heating through flux braiding and study the temporal fluctuations of this synthetic corona as well as implications for the interpretation of real observations. While the line emissivity is changing only gradually in the corona, the Doppler shifts directly react to the heating mechanism, and thus we can see a remnant of the photospheric driver in the coronal Doppler shifts. The (rms) fluctuations we see in line intensity compare well with those observed on the Sun. Besides the good match to the average observed Doppler shifts and emission measures, this gives yet another piece of evidence that flux braiding is the dominant heating process in the coronae of cool stars. A side product of these investigations is the possibility to create raster maps as obtained by present EUV spectrometers. This investigation shows the limitations of present instrumentation to investigate the Doppler shifts and sets clear requirements for future instrumentation.

Presented is a modification of the Parker spherically symmetric solar wind model. The energy conservation equation in the form proposed by Chamberlain adds two Parker’s equations of continuity and momentum conservation, but terms describing the thermal bremsstrahlung and the recombination emission are incorporated into the Chamberlain equation. The heat source is assumed in the Parker critical point. The position and the temperature of this point are determined self-consistently from the requirement of finite flow acceleration there. The system was integrated numerically from the temperature minimum region up to the Earth orbit. The model turns out to be able to connect typical conditions in the upper photosphere (N=0,85 10¹¹ cm^-3, T=4170 K) and in the solar wind (N=7,42 cm^-3, T=1,6 10⁵ K, V=512 km/s). The temperature and the position of the critical point were obtained as follows: T=1,8 10⁶ K, r=2,75 solar radii. Possible mechanisms of energy continuous release at the critical point are discussed.

Viewed as a stochastic process, the solar wind is expected to be stationary over time periods much greater than the 22 year solar cycle and much less than the evolution time of the sun (~10⁹ years). For time periods shorter than the 22 year cycle or the 11 year half-cycle, it is known that the solar wind is not statistically stationary. For example, in the ecliptic plane, 200-day averages of the radial solar wind velocity are larger during the declining phase of the solar cycle when high speed streams are generally more intense than during the rest of the cycle. To accurately determine power spectra of solar wind fluctuations from time series covering less than 10 or 20 years it is essential to first verify that the statistical properties of the solar wind are uniform over the entire time interval under study. For this purpose, statistical analyses are performed using solar wind data obtained by NASA’s Advanced Composition Explorer (ACE) during the 7 year period 1998-2004. The results of this analysis are used to evaluate the approximate stationarity of the data over different subintervals of the complete time record.

We compute flares waiting time distribution and waiting distance distribution using Parzen-Rosenblatt method and two years of data from a flare catalog that was built at the Solar Influences Data analysis Center (SIDC) of the Royal Observatory of Belgium based on the SEC/NOAA daily events lists. This catalog includes smaller flares than the ’solarsoft’ one used in a pre-vious study [Lepreti et al. 2001, 2003]. For the solarsoft list, we have found power-law or exponential distributions, depending on the definition of waiting times, in qualita-tive and quantative agreement with Wheatland et al. 1998; Lepreti et al. 2001, 2003, Buchlin et al, 2004. However for SIDC database, the type of distribution is much less sensitive on waiting times definition. PDFs have heavy tails with an approximately power-law decay, but characteristic times are present also. We compare these distribu-tions with the waiting time distributions from a lattice coronal heating model with the different scales of magnetic driving and using different type of current sheet dissipation [Krasnoselskikh et al. 2002, Podladchikova et al. 2003].

The solar wind structure near the Sun is deduced using the O⁵⁺ outflow velocities using the SOHO/LASCO data (Strachan et al, 2000) as well as Interplanetary Scintillation (IPS) observations near the Sun. This has been compared with the flux tube expansion factor (FTE) obtained using the Current Sheet Surce Surface Model (CSSS) of the corona. The CSSS model, developed by Zhao and Hoeksema (1995), has been shown to reproduce the radial variation of non--radial mid--latitude helmet streamers between 2.5 and 30 R_sun. The CSSS model has the advatage of a cusp surface at the cusp point of coronal streamers, which divides the corona into three regions, one bounded by the photosphere and the cusp surface, second, between the cusp surface and the source surface can be placed anywhere between 2.5 and 30 R_sun, and the third one, beyond the source surface. In the model, the magnetic field between the cusp surface and the source surface are all open but not constrained to be radial. Also, the source surface, can be placed closer to the Alfven critical point than the one in traditional Potential Field Source Surface model. The magnetic field computed using the CSSS model has been found to be rather uniform consistent with Ulysses observation. We present the preliminary results of the prediction of solar wind speed near the Earth using the CSSS model and the solar wind profile obtained near the Sun. Results of a comparison of HELIOS data will also be presented.

A new and complete dataset is being developed characterizing heavy ions in the solar wind. These data come from measurements of the Solar Wind Ion Composition Spectrometer (SWICS) and Solar Wind Ion Mass Spectrometer (SWIMS) on the ACE spacecraft. The data are obtained by an inversion method by von Steiger et. al.(2000). The result is a dataset that sets a new standard in mass and charge resolution for these instruments. We discuss the data and their application for science problems relating to the origin of the solar wind, it's expansion in the low corona and in the heliosphere.

The NASA Genesis mission collected solar wind on ultrapure materials between November 30, 2001 and April 1, 2004. The samples were returned to Earth September 8, 2004. Despite the hard landing that resulted from a failure of the avionics box to deploy the parachute, many samples were returned in a condition that will permit analyses. Analyses of these samples should give a far better understanding of the solar elemental and isotopic composition [1]. Further, the photospheric composition is thought to be representative of the solar nebula, so that the Genesis mission will provide a baseline for the average solar nebula composition with which to compare present-day compositions of planets, meteorites, and asteroids. Sample analysis is currently underway.
The Genesis samples must be placed in the context of the solar and solar-wind conditions under which they were collected. Solar wind is elementally fractionated from the photosphere by the forces that accelerate the ions off of the Sun. The elemental fractionations differ for different solar-wind regimes [e.g., 2,3]. To explore this, Genesis collected solar wind samples sorted into three regimes: ‘coronal hole’ (CH), ‘interstream’ (IS), and ‘coronal mass ejection’ (CME). To carry this out, plasma ion and electron spectrometers continuously monitored the solar wind proton density, velocity, temperature, the alpha/proton ratio, and angular distribution of suprathermal electrons, and used these parameters to distinguish between the solar-wind regimes during collection. In addition, other spacecraft, were monitoring the solar-wind conditions from the L1 orbit at the same time.
Here we report on the regime-specific solar wind conditions from in-situ instruments over the course of the collection period. Further, we use composition data from the SWICS (Solar Wind Ion Composition Spectrometer) instrument on ACE to examine the FIP fractionation between solar wind regimes, and compare these to the FIP analysis of Ulysses/SWICS composition data [3]. We find significant differences in ACE- and Ulysses-based fractionations which cannot be explained by differences in analysis techniques. Compared to Ulysses, the ACE composition shows a greater discrimination between IS and CH wind, as well as a substantial shift in the overall fractionation. In the case of the Mg/O abundance ratio, the IS-to-CH ratio is 1.4 for Ulysses vs. 1.9 for ACE; and the mean fractionation relative to the photosphere is 2.3 for Ulysses and nearly averages to one for ACE. We also find that CMEs show a greater FIP fractionation than either the IS or CH wind.
Finally, we examine the ramifications of new photospheric abundance data [4] on solar wind FIP fractionation. The new abundance data indicate a metallicity (Z/X) for the Sun almost a factor of two lower than that reported in the widely used compilation of Anders & Grevesse [5]. The new photospheric abundances tend to reduce the degree of solar wind fractionation.
References: [1] Burnett D.S. et al. (2003) Spa. Sci. Rev. 105, 509-534. [2] Neugebauer M. (1991) Science 252, 404-409. [3] Von Steiger, R. et al. (2000) J. Geophys. Res. 105, 27,217. [4] Asplund M., Grevesse N., and Sauval A.J. (2005) The Solar Chemical Composition, in Cosmic Abundances as Records of Stellar Evolution and Nucleosynthesis, ASP Conference Series, Vol. XXX, F.N. Bash, T.G. Barnes, eds., in press. [5] Anders E. and Grevesse N. (1989) Geochim. Cosmochim. Acta 53, 197-214.

The non equilibrium characteristics of the solar wind electron distribution functions (EDFs) at 1 AU are of great importance in many aspects, for instance in understanding heat conduction, plasma microinstabilities and transport in weakly collisional plasma, as well as in the scenario at the origin of the solar wind. It has been known for a long time that, in the free solar wind, EDFs display both thermal ("core") and suprathermal ("halo" and "strahl") populations; more recently a super-halo population has also been identified. The usual model used to characterize the observed solar wind EDF is a sum of two bi-Maxwellians, the core-halo model, with a core-halo drift velocity oriented along the interplanetary magnetic field. Other recent works have emphasized the Lorentzian nature of EDFs, i.e. the importance of their suprathermal tails, which should play a crucial role in the exospheric expansion of the slow and fast solar wind. Based on either the core-halo or the Lorentzian (or Kappa) models, kinetic instabilities in space plasma have been discussed in the literature and wave growth rates have been calculated. However both models are not appropriate to accurately characterize the solar wind EDFs because they do not account properly for some important features of the observed EDFs. It is therefore important to determine and characterize more precisely the nature of the EDFs, and in particular the nature of their suprathermal tails, in the two typical solar winds.
The 3DP experiment on the WIND spacecraft provides measurements of the full 3D electron distributions from energies of the order of few eV to above 100 keV, with a high-sensitivity, wide dynamic range, good energy and angular resolutions, and high time resolution (~3s). Wind's in-ecliptic orbits cover prolongated periods in the ambient, slow and fast, solar wind near L1, during the last minimum of solar activity. New characteristics of EDF are established and their origins are discussed. Their consequences in different field of space plasma processes are also investigated.

In the Alfvenic regime, i.e. for frequencies below the local proton cyclotron frequency, solar wind MHD turbulence exhibits what appears like an inertial domain, with power-law spectra and scale-invariance, suggesting as in fluid turbulence, a nonlinear energy cascade from the large "energy containing" scales towards the small scales where dissipation by kinetic effects is presumed to act. However, the intermittent character of solar wind fluctuations is much more important than in ordinary fluids. Indeed, the fluctuations consist of a mixture of random fluctuations and small-scale "singular" or coherent structures. This intermittency modifies significantly the scaling exponents of actual power-law spectra, which are directly related to the physical nature of the energy cascade taking place in the solar wind. The identification of the most intermittent structures and their relation to dissipation represents then a crucial problem in the framework of turbulence.
We present here an approach to study the scaling laws and intermittency based on the use of Wavelet transforms on simultaneous WIND 3s resolution particle and magnetic field data from the 3DP and the MFi experiments respectively. Using the Haar wavelet transform, spectra and structure functions are calculated. We show that a small number of coherent singular structures are responsible for the intermittency in the solar wind; outside of these structures the statistical distribution of the fluctuations have standard scaling properties. We finally discuss the various effects which may be important for the formation of these structures in the absence of collisions.

In the solar wind at 1 AU, coherent electrostatic waveforms in the ion acoustic frequency range (fpi < f < fpe) have been recently observed by the WAVES/TDS instrument on WIND. These unique, very high-time resolution observations have shed a new light on the nature of the ion-acoustic-like wave activity, observed in the solar wind by several spacecraft for more than 3 decades using spectral wave receivers. The TDS observations have shown that this electrostatic wave activity is actually coherent with properties similar to those of ion-acoustic waves, and is made of a mixture of quasi-sinusoidal wave trains, with properties similar to those of ion acoustic waves, and solitary-like structures with scales of tens of Debye lengths. The latter structures have been interpretated in terms of Weak Double Layers (WDLs), since they sustain a net potential drop across the structure of roughly 1 mV generally directed towards the Earth and it was suggested that the interplanetary electric field is not continuous but results from a succession of WDLs distributed intermittently betweent the solar corona and the earth orbit.
The properties of these waves, their occurrence and their relation with important plasma parameters have been studied and published in earlier papers. However, a calibration error was recently found in the data reduction procedure, which affects only the phase of the waveforms, not their amplitude. This error has been corrected and the data and the previous results are revisited. We present here a new statistical analysis of the wave properties and their occurrence. We show that the main results that have been affected by the error concern the solitary-like structures or WDLs. They are found to be bipolar (instead of tripolar) like those observed in many regions of the Earth environment under different plasma regimes, but they still sustain a net potential difference across the structure. Finally, earlier conclusions are rediscussed in accordance to these new observations.

We have observed several flares with multiple instruments (ground based instruments: THEMIS and VTT, SOHO/CDS, TRACE, RHESSI). The RHESSI analysis allows us to distangle between thermal and non-thermal effects driven by magnetic reconnections during the flares. We analyse the spatially resolved flows seen in the atmosphere by using spectroscopic diagnostics during the gradual phase of flares. Evaporation and downflows in postflare loops are observed over a large range of temperatures and for the first time flows of hot plasma loops can be quantified. Some flows are nevertheless not well understandable in the frame of reconnection models.

The LASCO-C1 coronagraph on SOHO was designed to perform spectroscopic diagnostics of coronal structures. It uses a tunable Fabry-Pérot interferometer to generate images at different wavelengths around certain emission lines of interest. We present results from spectral scans of the coronal green and red emission lines From the line profiles physical quantities like temperatures (from line widths), and flow velocities (from Doppler shifts) along the line of sight were deduced.

Spacecraft missions to the outer heliosphere have clearly shown that the thermal protons that make up the solar wind are hotter than simple adiabatic expansion would predict. By 30 AU the protons are 10x hotter than adiabatic expansion would predict and by 70 AU they are 100x hotter. We examine a theory that describes this heating by applying it to the observations using time-varying 1 AU measurements as input. Inside 20 AU wind shear and shocks provide the dominant energy source to drive the turbulence. Outside 20 AU little remains to inject energy into the fluctuations except newborn interstellar pickup protons. The theory is built on a combination of 2-D magnetohydrodynamic turbulence concepts and the latest kinetic theory describing the scattering of newborn interstellar pickup protons. We find that application of the theory to the observations produces encouraging agreement at the same time that it illuminates latitudinal effects associated with solar minimum conditions. In the end, further development of the theory is needed to close the factor of 2 gap that is seen between observed and predicted proton temperatures beyond 40 AU.

We have assembled a data base of over 800 intervals of solar wind observations recorded by the ACE spacecraft at 1 AU and examined the computed spectral characteristics of the magnetic fluctuations in the inertial range. We find a strong correlation between the variance anisotropy of the magnetic fluctuations, the proton plasma beta, and the amplitude of the total magnetic fluctuation. At the time of this writing it is not possible to say which is the source of the other, but it seems clear that the variance anisotropy for solar wind magnetic field fluctuations is linked to either the proton beta or the amplitude of the fluctuations or both. This has important implications for the nature of solar wind turbulence and the rate of spectral cascade and may support published explanations for the observed compressive component.

We have created a data base of over 800 interplanetary magnetic field spectra recorded by the ACE spacecraft and we use this data base to study the spectral characteristics of the dissipation range at 1 AU. This data base was constructed to span a wide range of parameter space including magnetic clouds and open field lines with a broad range of bulk plasma parameters (IMF intensity, proton beta, etc.). We contrast the dissipation range observations with the characteristics of the inertial range spectra for the same intervals and corroborate the earlier results of Leamon et al. [1998a,b; 2000]. We also demonstate the the spectral index for dissipation range fluctuations is controlled by the rate of energy cascade through the spectrum. This stands in stark contrast to the results for Navier-Stokes fluids.

This paper describes results on the coronal/solar wind magnetic field in the heliocentric distance range of 5 - 12 solar radii, obtained with the Very Large Array (VLA) radiotelescope of the National Radio Astronomy Observatory. The VLA can measure Faraday rotation of extragalactic radio sources viewed through the corona. A number of empirical models for the coronal plasma density in this part of space exist, allowing retrieval of a model magnetic field. Results from a number of VLA observing projects are consistent with a magnetic field model presented in Mancuso and Spangler (ApJ 539, 480, 2000), which is a modification of a model published by Paetzold et al (Sol. Phys. 109, 91, 1987). The magnitude of departures from this model, and their interpretation in terms of physical properties of the corona, will be discussed. A unique capability of radio galaxy observations is the ability to probe small scale structures in the corona, by measurement of the Faraday rotation measure on closely-spaced lines of sight. Illustrative results will be presented from observations of the radio galaxy 3C228 in August, 2003, which feature simulataneous rotation measure measurements on lines of sight separated in the corona by 0 to 30,000 km. Finally, the proposed LOFAR low frequency radio telescope will have the potential to make similar measurements at much greater heliocentric distances. Estimates of the magnitude of the Faraday rotation at these distances, and discussion of the associated experimental challenges, will be presented.

Coronal streamers are believed to be one of the source regions for the slow speed wind. For this work we investigate the relationship between the physical properties of these coronal streamer source regions and the final state of the slow speed wind at 1 AU. To do this we determine kinetic temperatures and outflow velocities for hydrogen and O5+ ions in the streamer source regions of slow wind using spectroscopic diagnostics from the SOHO Ultraviolet Coronagraph Spectrometer (UVCS) combined with electron density diagnostics from the Large Angle and Spectrometric Coronagraph (LASCO). The properties from these regions are compared with measurements of speeds, densities, and thermal temperatures for protons, and O7+/O6+ ratios determined from SOHO/MTOF, ACE/SWEPAM, and ACE/SWICS. Taken together, these data provide constraints on the heating and acceleration processes for the slow speed wind. This work is supported in part by NASA Grant NAG5-12781 to the Smithsonian Astrophysical Observatory.

Slow solar wind is believed to arise in the legs or near the cusp of streamers, inside the brightness boundary. In an earlier study, we used an analytic model of flow in this layer to analyze the effect of the magnetic field on the geometry of the flow (Suess and Nerney, ApJ, v565, p1275, 2002). That study successfully described those conditions that can lead to a decrease of the flow speed with increasing height near the cusp of the closed magnetic helmet inside the streamer. We have generalized that model to describe outflow in an arbitrarily thin layer inside the brightness boundary. The flow geometry now can also be constrictive or divergent above the cusp and we show solutions of this type. A diverging streamer or ray above 2-3 solar radii is shown to indicate the plasma beta is greater than unity inside the streamer and less than unity outside. The same argument can be used to discover the height above which the plasma beta in plumes, inside coronal holes, is greater than unity.

In many situations observed in space plasmas, large MHD scales are believed to act as reservoir for a nonlinear cascade, bringing fluctuation energy to scales where kinetic processes (Landau or cyclotron resonnances) can transform them into thermal energy. These kinetic processes operate at smaller spatial scales and more rapid time scales, so that a numerical simulation describing both the nonlinear cascade and the kinetic processes were, untill recently, out of reach. The rapid increase of computing efficiency allows now to study the competition between these two processes in more realistic simulations. We study the relaxation of an initially isotropic spectrum of Alfven waves by means of high resolution hybrid simulation. We examine the process and properties of the related heating of the proton population and compare our results with in situ observations.

We have developed a three-dimensional steady-state MHD model of the solar corona and solar wind. The model covers the region from the coronal base to 100 AU and accounts for the effects of pickup protons in the distant heliosphere. To attain these ends, the two-region model of Usmanov and Goldstein [2003] was modified to become fully three-dimensional and to include a region III that extends from 1-100 AU and incorporates a population of interstellar pickup protons and its interaction with the solar wind protons. Following the approach of Isenberg [1986] and Whang [1998], we consider the solar wind outside 1 AU as a combination of three comoving species -- solar wind protons, electrons, and pickup protons -- and solve the MHD equations with source terms due to photoionization and charge exchange. Separate energy equations are included for solar wind and pickup protons. We compute the global structure of the solar wind from the coronal base out to 100 AU, compare the results with Ulysses and Voyager 2 observations, and present a study of the effects of the pickup protons on solar wind properties.

In this presentation we provide the physical properties derived for three streamers observed in 2003 by the Ultraviolet Coronal Spectrometer (UVCS) aboard the Solar and Heliospheric Observatory (SOHO). These properties include outflow velocities, photospheric normalized absolute elemental abundances, kinetic and electron temperatures. The elemental abundances of O, Si, Fe, S, and Ar are examined with regards to the first ionization potential (FIP) effect. These measurements are conducted along varies latitudinal and radial positions within these three streamers. The electron densities found within these streamers, provided from LASCO pB measurements, are also presented here.

We investigate the non-linear evolution of Alfvén waves in a stratified atmosphere with wind, from the photosphere out to the Alfvénic point, where the wind speed equals the velocity of the waves. Photosphere and chromosphere are modeled as isothermal layers while the corona is expanding supra-spherically and its temperature peaks at about 3 solar radii and then falls off. The Transition Region is modeled as a discontinuity through which the net energy flux is conserved. Nonlinear interactions, triggered by wave reflection due to the atmospheric gradients, are assumed to occur mainly in directions perpendicular to the mean magnetic field. The nonlinear coupling between waves propagating in opposite directions is modeled by a phenomenological term, containing an integral turbulent length scale. It involves three waves of different frequencies which form a rough guide to investigate the spectral evolution in such a composite atmosphere. Reflection depends on the frequency while non-linear interaction couples the waves evolution, smoothing the differences in response to the density gradients. All the different characteristic scale heights of the layer considered and the efficiency of the non linear coupling finally determine the global evolution of the spectrum. Low frequency waves, which suffer the strongest reflection, drive dissipation for waves across the whole spectrum; lower coronal temperatures, by increasing density gradients and therefore reflection, also enhance the dissipation rate. We find that for typical coronal gradients, the power-law index of a wave-spectrum does not change significantly from the coronal base to the Alfvénic point.

An investigation of MHD wave interactions in a linear shear flow using the Lagrangian displacement approach based on the MHD variational principle for waves in a given linear shear flow is carried out. Kelvin's method is used, in which a Fourier solution is sought in the frame of the background shear flow. The equations reduce to three coupled oscillator equations, with time dependent coefficients and with source terms proportional to the entropy perturbation. Normal mode analysis of the oscillator equations reveals that in the absence of entropy perturbations, the system admits a wave action conservation integral consisting of positive and negative energy waves. The implications of these results for the interaction of MHD waves in the shear flow between fast polar coronal hole wind and slow streamer belt solar wind in the helioequatorial region are explored.

The abundance of nitrogen in the heliosphere is an enigma. Laboratory analysis of lunar soils shows that trapped nitrogen is overabundant in them by about one order of magnitude relative to all noble gases, which in turn are efficiently trapped in the lunar regolith. On the other hand, the Solar Wind Ion Mass Spectrometer (SWIMS) on ACE has successfully measured the elemental abundance of nitrogen in the solar wind, N/O ~ 0.121 +/- 0.014, in good agreement with the photospheric value of N/O ~ 0.123 and with the SEP-dervied coronal value. In this work we determine the abundance ratio N/Ne and investigate the variability of N/O and of N/Ne in the solar wind. Nitrogen is not readily measured in the solar wind with spaceborn TOF mass/mass per charge spectrometers such as SWICS because it is not very abundant and is neighbored in mass and in mass per charge by the more abundant heavy ions, oxygen and carbon. For this reason, previous elemental abundance determinations of nitrogen in the solar wind have had large intrinsic uncertainties. However, with SWIMS, nitrogen is cleanly separated from its neighbors and its abundance can be accurately measured. Analyzing data from 1998 to 2004, we have found no unexpected variability of N in the solar wind, the ratios N/O and N/Ne are consistent with a constant value throughout this period of dramatically changing solar activity. We apply this finding to different ideas relating nitrogen in lunar soils to widely different solar input in the distant past and find that our result provides further evidence for a non-solar origin of most of nitrogen in lunar soils.

The solar magnetic field is key to understanding the Sun and its atmosphere, but the lack of detailed measurements everywhere in the solar atmosphere except for the surface of the Sun has made progress challenging. Instead, our notions of the solar atmosphere are based mainly on density structure observed in white-light images and measurements of solar emission, all without the benefit of magnetic field measurements to provide insight into how the field interacts with the surrounding plasma to produce the observed coronal phenomena. This poor state of knowledge serves to remind us that exploring the solar atmosphere still is an observational science, and that our understanding is expected to evolve with the availability of new observations and new insight. Starting with unexpected results from radio occultation measurements of the solar corona a decade ago, advances have been made by systematically synthesizing available solar and solar wind observations into a coherent picture of the solar atmosphere, and reported at the Solar Wind meetings. Radio occultation measurements of density structure showed that the corona is permeated by ubiquitous small-scale filamentary structures whose larger sizes are directly related to those in white-light images (Solar Wind 8). Quantitative profiles of white-light measurements reinforced what radio occultation measurements revealed earlier, that polar coronal holes extend radially into interplanetary space, thus implying that fast wind emerges from the quiet Sun as well as polar coronal holes (Solar Wind 9). Finally, combining in situ Ulysses solar wind measurements, Yohkoh soft X-ray observations, filamentary density structure of white-light and radio occultation measurements, and coronal magnetic field direction deduced from polarization measurements, demonstrated that the coronal magnetic topology is dominated by open and predominantly radial magnetic field lines (Solar Wind 10). This paper adds further to this unified picture, and its purpose is two-fold. The first is to explain why the density structure seen in solar eclipse pictures is not shaped by highly non-radial magnetic fields, as first impressions may suggest, and is, therefore, not in conflict with the preponderance of radial coronal magnetic fields. The second purpose is to explain how the solar magnetic field, comprising closed fields at the base of the corona, ubiquitous and predominantly radial open fields in the corona, and the polarity reversal forming the heliospheric current sheet, gives rise to the observed variations in plasma properties of the corona and interplanetary space. Of particular importance is the new insight into the variations in solar wind acceleration.

Although much advance was lately done in understanding the small-scale transient events seen on the Sun at transition region temperatures, it is still not clear what is the connection between the events seen on the disk and the ones from the limb. In this contribution we will investigate different types of short-lived events such as spicule-like structures, bi-directional jets and blinkers, and the possible link between them. The data selected for this study were obtained as time series in polar coronal holes by SUMER/SoHO. The short exposure time (from 15 sec to 1 min), the almost fixed position of the slit (due to a reduced effect of the solar rotation at the poles) and the coverage of both on-disk and off-limb regions, together with the good spectral information of our data, give us an excellent opportunity to analyse the temporal evolution and other spectral characteristics of these events, as well as allowing a comparison between them.

Coronal holes have open magnetic field and are the source of high-speed solar wind. The network magnetic fields at the edges of supergranules are believed to be the source of coronal heating and solar wind acceleration in quiet regions and coronal holes, through small-scale explosive events such as mini-filament eruptions, microflares, macrospicules, and spicules (e.g., Axford & McKenzie, 1992, 1997; Falconer et al., 2003). From SOHO/SUMER EUV spectrograph observations, Hassler et al (1999) found upflows at the base of coronal holes. The pattern of the upflows matches the chromospheric magnetic network, the strongest upflows being centered on the network magnetic flux. Clarifying the structure and dynamics of the small-scale events in the network and their magnetic topology is important for understanding how network activity might drive coronal heating and solar wind acceleration. In September 2004, we observed coronal holes from Big Bear Solar Observatory (BBSO) in coordination with TRACE. The BBSO observations are magnetograms and high-resolution Hα movies. The TRACE observations are UV/EUV movies having cadence and spatial resolution comparable to those of the Hα movies. From these observations, we report the dynamics, structure, and magnetic setting of small-scale explosive events in coronal holes. Using physical parameters derived from the observations, such as the birthrate of events and the magnetic field strength, plasma density and eruption velocity in the events, we consider whether network activity in coronal holes can provide enough energy flux for coronal heating and solar wind acceleration.

Thermal noise spectroscopy is based on a passive measurement of the plasma wave spectrum with a long electric antenna, and yields directly the density and the kinetic temperature of a stable electron velocity distribution. This method is a powerful tool to measure in situ the electron thermodynamic quantities in natural plasmas, and has been used in the solar wind, planetary ionospheres and plasmaspheres or cometary tails. In this work, we will revisit the electron density and temperature derived from the electrostatic noise measurement made with the URAP dipole electric antenna on Ulysses, as this probe flew by pole-to-pole during the minimum solar activity (1994-95). The electron velocity distribution is modeled by a generalized Lorentzian or ''kappa'' distribution. This model is especially adapted in the solar wind, whose electron velocity distribution has a conspicuous suprathermal tail. The three fitted parameters are the electron density, temperature and kappa index of the distribution, and we will discuss their variations with heliocentric distance and latitude. We will especially focus on the variation of the total temperature with distance during the solar minimum at high latitudes and compare it with the temperature profile predicted by a kinetic collisionless model of the solar wind.