Solar Wind Outflow Research Articles

HEATING AND ACCELERATION OF THE FAST SOLAR WIND BY ALFVÉN WAVE TURBULENCE

ABSTRACT We present numerical simulations of reduced magnetohydrodynamic (RMHD) turbulence in a magnetic flux tube at the center of a polar coronal hole. The model for the background atmosphere is a solution of the momentum equation and includes the effects of wave pressure on the solar wind outflow. Alfvén waves are launched at the coronal base and reflect at various heights owing to variations in Alfvén speed and outflow velocity. The turbulence is driven by nonlinear interactions between the counterpropagating Alfvén waves. Results are presented for two models of the background atmosphere. In the first model the plasma density and Alfvén speed vary smoothly with height, resulting in minimal wave reflections and low-energy dissipation rates. We find that the dissipation rate is insufficient to maintain the temperature of the background atmosphere. The standard phenomenological formula for the dissipation rate significantly overestimates the rate derived from our RMHD simulations, and a revised formula is proposed. In the second model we introduce additional density variations along the flux tube with a correlation length of 0.04 R ⊙ and with relative amplitude of 10%. These density variations simulate the effects of compressive MHD waves on the Alfvén waves. We find that such variations significantly enhance the wave reflection and thereby the turbulent dissipation rates, producing enough heat to maintain the background atmosphere. We conclude that interactions between Alfvén and compressive waves may play an important role in the turbulent heating of the fast solar wind.

Relative drifts and temperature anisotropies of protons andαparticles in the expanding solar wind: 2.5D hybrid simulations

We perform 2.5D hybrid simulations to investigate the origin and evolution of relative drift speeds between protons and $\alpha$ particles in the collisionless turbulent low-$\beta$ solar wind plasma. We study the generation of differential streaming by wave-particle interactions and absorption of turbulent wave spectra. Next we focus on the role of the relative drifts for the turbulent heating and acceleration of ions in the collisionless fast solar wind streams. The energy source is given by an initial broad-band spectrum of parallel propagating Alfv\'en-cyclotron waves, which co-exists with the plasma and is self-consistently coupled to the perpendicular ion bulk velocities. We include the effect of a gradual solar wind expansion, which cools and decelerates the minor ions. This paper for the first time considers the combined effect of self-consistently initialized dispersive turbulent Alfv\'enic spectra with differentially streaming protons and $\alpha$ particles in the expanding solar wind outflows within a 2.5D hybrid simulation study. In the non-expanding wind, we find a threshold value of the differential streaming $V_{\alpha p} = 0.5 V_\mathrm{A}$, for which the relative drift speed remains nearly steady. For ions, streaming below the threshold value, the waves act to increase the magnitude of the relative drift speed. Ions, which stream faster than the threshold value become subject to nonlinear streaming instability and as the system evolves their bulk velocities decrease. We find that the solar wind expansion strongly affects the relative drift speeds and significantly slows down both ion species for all values of the relative drift speeds considered in this study.

Visible light and ultraviolet observations of coronal structures: physical properties of an equatorial streamer and modelling of the F corona

The present work studies the characteristics of an equatorial streamer visible above the east limb of the Sun on March 2008, during the most recent minimum of solar activity. We analysed the visible light coronagraphic images of SOHO/LASCO and the ultraviolet observations in the H I Lyα spectral line obtained by SOHO/UVCS, and exploited the Doppler dimming effect of the coronal Lyα line to derive the outflow velocity profile of the scattering neutral hydrogen atoms in the streamer region. Taking advantage of the synergy between visible light and ultraviolet observations, we were able to determine all the properties of the coronal structure. In particular, the actual extent of the streamer along the line of sight has been evaluated for the first time. In so doing, the solar wind outflow velocity turned out to be the only free parameter in the theoretical modelling of the Lyα intensity. We found nearly static conditions below

THE DYNAMIC CHARACTER OF THE POLAR SOLAR WIND

The Solar and Heliospheric Observatory (SOHO) Large Angle and Spectrometric Coronagraph C2 and Solar Terrestrial Relations Observatory (STEREO) COR2A coronagraph images, when analyzed using correlation tracking techniques, show a surprising result in places ordinarily thought of as quiet solar wind above the poles in coronal hole regions. Instead of the static well-ordered flow and gradual acceleration normally expected, coronagraph images show outflow in polar coronal holes consisting of a mixture of intermittent slow and fast patches of material. We compare measurements of this highly variable solar wind from C2 and COR2A images and show that both coronagraphs measure essentially the same structures. Measurements of the mean velocity as a function of height of these structures are compared with mass flux determinations of the solar wind outflow in the large polar coronal hole regions and give similar results.

ERRATUM: “DIRECT NUMERICAL SIMULATIONS OF REFLECTION-DRIVEN, REDUCED MAGNETOHYDRODYNAMIC TURBULENCE FROM THE SUN TO THE ALFVÉN CRITICAL POINT” (2013, ApJ, 776, 124)

We present direct numerical simulations of inhomogeneous reduced magnetohydrodynamic (RMHD) turbulence between the Sun and the Alfv\'en critical point. These are the first such simulations that take into account the solar-wind outflow velocity and the radial inhomogeneity of the background solar wind without approximating the nonlinear terms in the governing equations. RMHD turbulence is driven by outward-propagating Alfv\'en waves ($z^+$ fluctuations) launched from the Sun, which undergo partial non-WKB reflection to produce sunward-propagating Alfv\'en waves ($z^-$ fluctuations). We present ten simulations with different values of the correlation time $\tau_{\rm c\,\sun}^+$ and perpendicular correlation length $L_{\perp \sun}$ of outward-propagating Alfv\'en waves (AWs) at the coronal base. We find that between 15% and 33% of the $z^+$ energy launched into the corona dissipates between the coronal base and Alfv\'en critical point. Between 33% and 40% of this input energy goes into work on the solar-wind outflow, and between 22% and 36% escapes as $z^+$ fluctuations through the simulation boundary at $r=r_{\rm A}$. The $z^\pm$ power spectra scale like $k_\perp^{-\alpha^\pm}$, where $k_\perp$ is the wavenumber in the plane perpendicular to $\vec{B}_0$. In our simulation with the smallest value of $\tau_{\rm c\,\sun}^+$ ($\sim 2 \mbox{min}$) and largest value of $L_{\perp \sun}$ ($2\times 10^4 \mbox{km}$), we find that $\alpha^+$ decreases approximately linearly with increasing $\ln(r)$, reaching a value of 1.3 at $r=11.1 R_{\sun}$. Our simulations with larger values of $\tau_{\rm c\,\sun}^+$ exhibit alignment between the contours of constant $\phi^+$, $\phi^-$, $\Omega_0^+$, and $\Omega_0^-$, where $\phi^\pm$ are the Els\"asser potentials and $\Omega_0^\pm$ are the outer-scale parallel Els\"asser vorticities.

DIRECT NUMERICAL SIMULATIONS OF REFLECTION-DRIVEN, REDUCED MAGNETOHYDRODYNAMIC TURBULENCE FROM THE SUN TO THE ALFVÉN CRITICAL POINT

We present direct numerical simulations of inhomogeneous reduced magnetohydrodynamic (RMHD) turbulence between the Sun and the Alfven critical point. These are the first such simulations that take into account the solar-wind outflow velocity and the radial inhomogeneity of the background solar wind without approximating the nonlinear terms in the governing equations. RMHD turbulence is driven by outward-propagating Alfven waves (z + fluctuations) launched from the Sun, which undergo partial non-WKB reflection to produce sunward-propagating Alfven waves (z – fluctuations). We present 10 simulations with different values of the correlation time and perpendicular correlation length L ⊥☉ of outward-propagating Alfven waves at the coronal base. We find that between 15% and 33% of the z + energy launched into the corona dissipates between the coronal base and Alfven critical point. Between 33% and 40% of this input energy goes into work on the solar-wind outflow, and between 22% and 36% escapes as z + fluctuations through the simulation boundary at r = r A. The z ± power spectra scale like , where k ⊥ is the wavenumber in the plane perpendicular to B 0. In our simulation with the smallest value of (~2 minutes) and largest value of L ⊥☉ (2 × 104 km), we find that α+ decreases approximately linearly with increasing ln (r), reaching a value of 1.3 at r = 11.1 R ☉. Our simulations with larger values of exhibit alignment between the contours of constant +, –, , and , where ± are the Elsasser potentials and are the outer-scale parallel Elsasser vorticities.

Solar Wind Models from the Chromosphere to 1 AU

Recent models of the fast solar wind are characterized by low coronal electron temperatures while proton, α-particle, and minor ion temperatures are expected to be quite high and generally anisotropic, including large temperatures perpendicular to the magnetic field and parallel beams. This entails that the electric field should be relatively unimportant and that solar wind outflows with both high asymptotic flow speeds but maintaining a low mass flux should be a natural outcome of plasma expansion along open polar magnetic field lines. In this chapter we will explain why such changes with respect to the classical, electron thermally driven solar wind have come about and outline the most important remaining concerning the astrophysics of coronal winds.

Magnetohydrostatic model for a coronal hole

A model treating a solar coronal hole as an axially symmetrical magnetic formation that is in equilibrium with the surrounding medium is proposed. The model is applicable in the lower corona (to heights of the order of several hundreds of Mm), where the influence of the solar-wind outflow on the state of the system can still be neglected. The magnetic field of the coronal hole is comprised of a relatively weak open flux that varies with height, which extends into interplanetary space, and a closed field, whose flux closes at the chromosphere near the coronal hole. Simple analytical formulas are obtained, which demonstrate for a given equilibrium configuration of the plasma and field the main effect of interest—the lowering of the temperature and density of the gas in the coronal hole compared to their values in the corona at the same geometric height. In particular, it is shown that, at heights of several tens of Mm, the temperature and density of the plasma in the coronal hole are roughly half the corresponding values at the same height in the corona, if the cross-sectional radius of the hole exceeds the scale height in the corona by roughly a factor of 1.5: R h ≈ 1.5H(T 0). In the special case when R h ≈ H(T 0), the plasma temperature in the hole is equal to the coronal temperature, and the darkening of the coronal hole is due only to an appreciable reduction of the plasma density in the hole, compared to the coronal density. An analogy of the properties of coronal holes and sunspots is discussed, based on the similarity of the magnetic structures of these formations. In spite of the fundamental difference in the mechanisms for energy transport in coronal holes and sunspots, the equilibrium distributions of the plasma parameters in these formations are determined only by the magnetic and gravitational forces, giving rise to a number of common properties, due to their similar magnetic structures.

Wang‐Sheeley‐Arge–Enlil Cone Model Transitions to Operations

http://www.agu.org/journals/sw/swa/news/article/?id=2011SW000669 The National Weather Service's (NWS) Space Weather Prediction Center (SWPC) is transitioning the first large-scale, physics-based space weather prediction model into operations on the NWS National Centers for Environmental Prediction (NCEP) supercomputing system (see also C. Schultz, Space weather model moves into prime time, Space Weather, 9, S03005, doi:10.1029/2011SW000669, 2011). The model is intended to provide 1- to 4-day advance warning of geomagnetic storms from quasi-recurrent solar wind structures and Earth-directed coronal mass ejections (CMEs). A team has been put together at SWPC to bring an advanced numerical model—developed with broad participation of the research community—into operational status. The modeling system consists of two main parts: (1) a semiempirical near-Sun module (Wang-Sheeley-Arge (WSA)) that approximates the outflow at the base of the solar wind; and (2) a sophisticated three-dimensional magnetohydrodynamic numerical model (Enlil) that simulates the resulting flow evolution out to Earth. The former module is driven by observations of the solar surface magnetic field accumulated over a solar rotation and composited into a synoptic map; this input is used to drive a parameterized model of the near-Sun expansion of the solar corona, which provides input for the interplanetary module to compute the quasi-steady (ambient) solar wind outflow. Finally, when an Earth-directed CME is detected in coronagraph images from NASA spacecraft, these images are used to characterize the basic properties of the CME, including speed, direction, and size. This input “cone” representation is injected into the preexisting ambient flow, and the subsequent transient evolution forms the basis for the prediction of the CME's arrival time at Earth, its intensity, and its duration (Figure 1). The system will be delivered to NCEP in fall 2011, to undergo a year of trial operation. During that time, potential improvements to the modeling system will be evaluated, and early assessments of its performance will be undertaken. This transition draws upon contributions from many agencies and institutions, including the Center for Integrated Space Weather Modeling, Community Coordinated Modeling Center, Naval Research Laboratory, National Center for Atmospheric Research, Laboratory for Atmospheric and Space Physics, Office of Naval Research, Air Force Weather Agency (AFWA), and the Air Force Research Laboratory (AFRL). The long-term success of the system will hinge on training (collective experience), the quality of inputs (better interpretation, new observations), customer interactions, and the establishment of an effective operations-to-research (and the reverse) chain, which is critical to the continued improvement of the system. We thank C. Nick Arge for his essential contribution in the development and implementation of the WSA model. Annette Parsons is the AFWA project administrator at SWPC. Douglas Biesecker is the project verification and validation lead at SWPC. Dusan Odstrcil is the Enlil originator and a researcher at George Mason University, Fairfax, Va. George Millward is the project technical lead at SWPC. Steve Hill is the development and transition section lead at SWPC. Vic Pizzo is project scientist at NOAA SWPC, Boulder, Colo.; E-mail: vic.pizzo@noaa.gov

High-Latitude Inner Solar Wind from Pulsar Radio Sounding Observations

Radio sounding experiments probing the inner solar wind by polarized pulses of pulsars PSR B0525+21 (J0528+22) and PSR B531+21 (J0534+22) were carried out in June 2005 and June 2007 on the large phased array of the Lebedev Physical Institute at 111 MHz in the period near the minimum of the solar-activity cycle. The lines of sight toward these pulsars were close to the Sun during the observation sessions. The arrival-time delays for pulses from PSR J0534+22 are used to derive the radial dependence of the mean density of the circumsolar plasma. Comparison with Stanford coronal magnetic-field data, STEREO SECCHI, and SOHO EIT synoptic maps shows that the results are related to the polar coronal holes. The ambient density radial distribution derived from the arrival-time delays for pulses from PSR J0534+22 is stronger than inverse-square law indicating that the acceleration of fast, high-latitude solar-wind outflows, continues to heliocentric distances of (5–10)R S, where R S is the solar radius. The mean plasma density near a solar-activity minimum in the investigated range of heliocentric distances is substantially lower than at the solar-activity maximum.

Intermittent outflows at the edge of an active region – a possible source of the solar wind?

Context. It has already been established that the solar wind may originate at the edges of active regions (ARs), but the key questions of how frequently these outflows occur, and at which height the nascent solar wind originates have not yet been addressed. Aims. We study the occurrence rate of these intermittent outflows, the related plasma activities beneath in the low solar atmosphere, and the interplanetary counterparts of the nascent solar wind outflow. Methods. We use the observations from XRT/Hinode and TRACE to study the outflow patterns. The occurrence frequency of the intermittent outflow is estimated by counting the occurrences of propagating intensity enhancements in height-time diagrams. We adopt observations of SOT/Hinode and EIS/Hinode to investigate the phenomena in the chromosphere associated with the coronal outflows. The ACE plasma and field in-situ measurements near Earth are used to study the interplanetary manifestations. Results. We find that in one elongated coronal emission structure, referred to as strand, the plasma flows outward intermittently, about every 20 min. The flow speed sometimes exceeds 200 km s −1 , which is indicative of rapid acceleration, and thus exceeds the coronal sound speed at low altitudes. The inferred flow speed of the soft-X-ray-emitting plasma component seems a little higher than that of the Fe ix/x-emitting plasma component. Chromospheric jets are found to occur at the root of the strand. Upflows in the chromosphere are also confirmed by blue-shifts of the He ii line. The heliospheric plasma counterpart close to the Earth is found to be an intermediate-speed solar wind stream. The AR edge may also deliver some plasmas to a fraction of the fast solar wind stream, most of which emanate from the neighboring CH. Conclusions. The possible origin of the nascent solar wind in the chromosphere, the observed excessive outflow speed of over 200 km s −1 in the lower corona, and the corresponding intermediate-speed solar wind stream in interplanetary space are all linked in our case study. These phenomena from the low solar atmosphere to the heliosphere near Earth in combination shed new light on the solar wind formation process. These observational results will constrain future modeling of the solar winds originating close to an AR.

GLOBAL SIMULATION OF AN EXTREME ULTRAVIOLET IMAGING TELESCOPE WAVE

We use the observation of an Extreme Ultraviolet Imaging Telescope (EIT) wave in the lower solar corona, seen with the two Solar Terrestrial Relations Observatory (STEREO) spacecraft in extreme ultraviolet light on 2007 May 19, to model the same event with a three-dimensional (3D) time-depending magnetohydrodynamic (MHD) code that includes solar coronal magnetic fields derived with Wilcox Solar Observatory magnetogram data, and a solar wind outflow accelerated with empirical heating functions. The model includes a coronal mass ejection (CME) of Gibson and Low flux rope type above the reconstructed active region with parameters adapted from observations to excite the EIT wave. We trace the EIT wave running as circular velocity enhancement around the launching site of the CME in the direction tangential to the sphere produced by the wave front, and compute the phase velocities of the wave front. We find that the phase velocities are in good agreement with theoretical values for a fast magnetosonic wave, derived with the physical parameters of the model, and with observed phase speeds of an incident EIT wave reflected by a coronal hole and running at about the same location. We also produce in our 3D MHD model the observed reflection of the EIT wave at the coronal hole boundary, triggered by the magnetic pressure difference between the wave front hitting the hole and the boundary magnetic fields of the coronal hole, and the response of the coronal hole, which leads to the generation of secondary reflected EIT waves radiating away in different directions than the incident EIT wave. This is the first 3D MHD model of an EIT wave triggered by a CME that includes realistic solar magnetic field, with results comparing favorably to STEREO Extreme Ultraviolet Imager observations.

THE NASCENT FAST SOLAR WIND OBSERVED BY THE EUV IMAGING SPECTROMETER ON BOARD HINODE

The origin of the solar wind is one of the most important unresolved prob- lems in space and solar physics. We report here the first spectroscopic signatures of the nascent fast solar wind on the basis of observations made by the EUV Imaging Spectrometer (EIS) on Hinode in a polar coronal hole, in which patches of blueshift are clearly present on dopplergrams of coronal emission lines with a formation temperature of lg(T/K)=6.0. The corresponding upflow is associated with open field lines in the coronal hole, and seems to start in the solar transition region and becomes more prominent with increasing temperature. This temperature-dependent plasma outflow is interpreted as evidence of the nascent fast solar wind in the polar coronal hole. The patches with significant upflows are still isolated in the upper transition region but merge in the corona, in agreement with the scenario of solar wind outflow being guided by expanding magnetic funnels.

Origin of the solar wind: Astrophysical and plasma-physical aspects of the problem

At what evolutionary stage of the Sun as a star the accumulation of its matter from the interstellar medium ended and the dominant outflow of solar wind (SW) streams started is one of the main outstanding questions in the astrophysical aspect of the problem of SW origin. It is unknown when and how this happened in detail, although the onset of thermonuclear reactions in the solar interior undoubtedly played a crucial role in the energetics and dynamics of the star, which could lead to such a change of the regimes. Therefore, it is hypothesized that the accretion or plasma outflow from the star was determined by the preceding evolution, i.e., by the “memory“ and not just by the distribution of instantaneous density, temperature, magnetic field, and other macroscopic parameters of the system that consists of this star, its nearest stellar environment, and interstellar gas. Depending on this, neighboring stars can serve as donors or acceptors of interstellar gas. Some of them can simultaneously or alternately play both roles. The polytropic solution for centrally symmetric flows obtained by Bondi is degenerate in the sign of the radial velocity. It is suitable for describing the quasi-stationary regimes of both types. However, the theory of transient processes has not been developed. Hence, the question of whether there exist stars similar in their internal structure and parameters to the present-day Sun but without stellar wind emission or even with interstellar gas accretion can be answered only observationally. The possibility that such stars exist is not ruled out; it does not contradict any laws of nature. The plasma-physical aspect of the problem of SW origin concerns much shorter time intervals than the main evolutionary time scale measured in billions of years. Hence, this aspect of the problem has been studied much better, although it is also fairly complex and has not yet been solved in much detail due to the multi-scale character of the flow formation processes. The SW as a permanent supermagnetosonic plasma outflow in the radial direction appears against the background of much more powerful nonequilibrium and unsteady motions, which are ordered only partially in the upper solar atmosphere and corona (turbosphere). The instantaneous SW state is controlled by the fluxes of free energy, matter, and momentum that enter the corona from the convection zone and underlying solar atmospheric layers. Although the main physical mechanisms of the transport of free energy of the electromagnetic field and plasma are generally well known, they need a quantitative analysis as applied to specific realizations in frequent and rare particle collisions in the solar corona to ascertain the nonlocal processes of the formation of fields and plasma flows, including the SW.

Radio sounding of the circumsolar plasma using polarized pulsar pulses

We present the results of radio sounding observations probing the inner solar wind near the minimum of the solar-activity cycle, using polarized pulses from PSR B0525+21 and PSR B0531+21 received when the lines of sight toward these pulsars were close to the Sun. The observations were obtained in June 2005 and June 2007 on the Large Phased Array of the Lebedev Physical Institute at 111 MHz. An upper limit for the scattering of giant pulses from PSR B0531+21 due to their passage through the turbulent solar-wind plasma is determined. The arrival-time delays for pulses from PSR B0531+21 are used to derive the radial dependence of the mean density of the circumsolar plasma. The resulting density distribution indicates that the acceleration of fast, high-latitude solar-wind outflows continues to heliocentric distances of 5–10R ⊙, where R ⊙ is the solar radius. The mean plasma density at heliocentric distances of about 5R ⊙ is 1.4 × 104 cm−3, substantially lower than at the solar-activity maximum. This is associated with the presence of polar coronal holes. The Faraday rotation measure at heliocentric distances of 6–7R ⊙ is estimated. Deviations of the spatial distribution of the magnetic field from spherical symmetry are comparatively modest in the studied range of heliocentric distances.

Supernova Collisions with the Heliosphere

Nearby supernova explosions—within a few tens of pc of the solar system—have become a subject of intense scrutiny, due to the discovery of live undersea 60 Fe from an event 2.8 Myr ago. A key open question concerns the delivery of supernova ejecta to the Earth, in particular penetration of the heliosphere bythe supernova remnant (SNR). We present the first systematic numerical hydrodynamical study of the interaction between a supernova blast and the solar wind. Our simulations explore dynamic pressure regimes that are factors � 10 above those in other studies of the heliosphere under exotic conditions, for supernovae exploding at a range of distances through different interstellar environments, and interacting with solar winds of varying strengths. Our results are qualitatively consistent with the structure of the contemporary heliosphere modeled byprevious work,but compressedto within the inner solar system. We demonstrate that key characteristics of the resulting heliospheric structure follow simple scaling laws that can be understoodinterms of pressure-balancearguments,and which are inagreement withprevious work.Our modelsshow that a 10 pc supernova event, incident on a solar-wind outflow with the mean observed properties, compresses the heliopause to just beyond 1 AU. We also demonstrate scenarios where the supernova remnant compresses the heliopause to within 1 AU, in which cases supernova material will be directly deposited on Earth. Since 8 pc marks the nominal ‘‘kill radius’’ for severe biosphere damage, any extinction-level events should have left terrestrial deposits of supernova debris. We conclude with a brief discussion of the effect of our approximations and the impact of additional physics. Subject headingg astrobiology — interplanetary medium — solar wind — supernovae: general Online material: color figures

Source regions of solar wind disappearance events

During the period 1999–2002 there have been three instances, in May 1999, March 2002, and May 2002, respectively, when the solar wind densities at 1 AU dropped to abnormally low values (<0.1 cm−3) for extended periods of time (12–24 h). These long‐lasting low‐density anomalies observed at 1 AU are referred to as “solar wind disappearance events” and in this paper, we locate the solar sources of the two disappearance events in March and May 2002 and show that like the well‐studied disappearance event of 11 May 1999, these events too originate in active region complexes located at central meridian and are characterized by highly nonradial solar wind outflows. We also show that during disappearance events, the interplanetary magnetic field is stable and unipolar and the associated solar wind outflows have extended Alfvén radii. Using the fact that solar wind flows from active regions have higher ratios of O7+/O6+ than wind from coronal holes, we try to pinpoint the solar sources of these very unusual and rare events and show that they represent the dynamic evolution of either active region open fields or small coronal hole boundaries embedded in or near large active region complexes located at or close to central meridian.

On the Propagation and Dissipation of Alfvén Waves in Coronal Holes

We underline the importance of Alfven wave dissipation in the magnetic funnels through the viscous and resistive plasma. Our results show that Alfven waves are one of the primary energy sources in the innermost part of coronal holes where the solar wind outflow starts.

Investigating SUMER Coronal Hole Observations: A Robust Method of Raster Reduction

We present a physically constrained, comprehensive, and robust means of reducing long-duration spectroscopic raster observations made in the important 1530-1555 A wavelength range by the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) instrument on the Solar and Heliospheric Observatory (SOHO). Our method performs corrections in spatial, spectral, and temporal domains following application of the standard SUMER data reduction package to minimize the net Doppler shift of neutral and singly ionized silicon emission lines in the chromosphere. We have applied this method to seven raster observations of the same equatorial coronal hole acquired over a 5 day period, 1999 November 3-8, and to the well-studied observations of 1996 September 21-22. This technique allows us to make physically consistent analyses of multiple SUMER rasters and will aid in future investigations of the solar rest wavelength of the important Ne VIII 770 A emission line and, as a result, of the properties of transition region blueshifts—specifically, their correlation to multithermal radiance structure, supergranular network patterns, and the coronal magnetic environment at the perceived lower boundary of solar wind outflow.

Wave acceleration of the fast solar wind

Observations show that the solar wind exhibits two modes of outflow: the slow (∼400 km s −1), high density, highly variable wind that emerges from equatorial solar regions, and the high latitude, fast (∼800 km s −1), low density, steady solar wind. The bi-modal solar wind outflow is most evident near minima of solar activity. Theoretical studies of the fast solar wind in open magnetic structures motivated by SOHO, Ulysses, and Helios observations indicate that both, high frequency kinetic waves, and low frequency MHD waves play a role in its acceleration and heating. Ion-cyclotron waves have been suggested as the main energy source of the solar wind. However, there are theoretical difficulties with the ion-cyclotron wave heating of the protons, and these waves do not heat electrons. Low frequency MHD waves are still the best candidates to transport momentum and energy far from the Sun, to accelerate the solar wind on large spatial scales. I will present recently developed two-dimensional three-fluid model that includes explicit wave acceleration, and visco-resistive dissipation. The model describes electrons, protons, and minor ions as three coupled fluids that are heated by different heating processes with the parameters constrained by observations. I will present the results of 2.5D three-fluid simulations of the fast solar wind plasma that combine the effects of MHD waves self-consistently, and ion-cyclotron waves parametrically on the acceleration and heating processes. I will present the results of hybrid kinetic models of ion-cyclotron wave heating of the heavy ions in the solar wind plasma.