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1.
The goal of Working Group 1 was to discuss constraints on solar wind models. The topics for discussion, outlined by Eckart
Marsch in his introduction, were: (1) what heats the corona, (2) what is the role of waves, (3) what determines the solar
wind mass flux, (4) can stationary, multi-fluid models describe the fast and slow solar wind, or (5) do we need time dependent
fluid models, kinetic models, and/or MHD models to describe solar wind acceleration.
The discussion in the working group focused on observations of "temperatures" in the corona, mainly in coronal holes, and
whether the observations of line broadening should be interpreted as thermal broadening or wave broadening. Observations of
the coronal electron density and the flow speed in coronal holes were also discussed. There was only one contribution on observations
of the distant solar wind, but we can place firm constraints on the solar wind particle fluxes and asymptotic flow speeds
from observations with Ulysses and other spacecraft. Theoretical work on multi-fluid models, higher-order moment fluid models,
and MHD models of the solar wind were also presented.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
2.
The spectroscopic observations of the Ultraviolet Coronagraph Spectrometer (UVCS), on board the SOHO observatory, allow the study and the full characterization of the expansion of the solar atmosphere by means of measurements of the outflow speeds and the physical properties of the wind, directly in the region where the solar plasma is heated and accelerated: the extended corona. During solar minimum, when the magnetic configuration of the corona is rather simple, the open magnetic fields emerging from the wide polar coronal holes channel toward the heliosphere both the fast and the slow wind. The fast wind flows along flux tubes with lower areal divergence than the slow wind which is guided by flux tubes characterized by non-monotonic areal expansion functions. Differences in the physical properties, such as kinetic temperature, electron density, composition and density fluctuations, of the fast and slow wind in the corona are discussed. 相似文献
3.
L. Abbo L. Ofman S. K. Antiochos V. H. Hansteen L. Harra Y.-K. Ko G. Lapenta B. Li P. Riley L. Strachan R. von Steiger Y.-M. Wang 《Space Science Reviews》2016,201(1-4):55-108
While it is certain that the fast solar wind originates from coronal holes, where and how the slow solar wind (SSW) is formed remains an outstanding question in solar physics even in the post-SOHO era. The quest for the SSW origin forms a major objective for the planned future missions such as the Solar Orbiter and Solar Probe Plus. Nonetheless, results from spacecraft data, combined with theoretical modeling, have helped to investigate many aspects of the SSW. Fundamental physical properties of the coronal plasma have been derived from spectroscopic and imaging remote-sensing data and in situ data, and these results have provided crucial insights for a deeper understanding of the origin and acceleration of the SSW. Advanced models of the SSW in coronal streamers and other structures have been developed using 3D MHD and multi-fluid equations.However, the following questions remain open: What are the source regions and their contributions to the SSW? What is the role of the magnetic topology in the corona for the origin, acceleration and energy deposition of the SSW? What are the possible acceleration and heating mechanisms for the SSW? The aim of this review is to present insights on the SSW origin and formation gathered from the discussions at the International Space Science Institute (ISSI) by the Team entitled “Slow solar wind sources and acceleration mechanisms in the corona” held in Bern (Switzerland) in March 2014 and 2015. 相似文献
4.
R. Kallenbach F.M. Ipavich H. Kucharek P. Bochsler A.B. Galvin J. Geiss F. Gliem G. Gloeckler H. Grünwaldt S. Hefti M. Hilchenbach D. Hovestadt 《Space Science Reviews》1998,85(1-2):357-370
Using the high-resolution mass spectrometer CELIAS/MTOF on board SOHO we have measured the solar wind isotope abundance ratios
of Si, Ne, and Mg and their variations in different solar wind regimes with bulk velocities ranging from 330 km/s to 650 km/s.
Data indicate a small systematic depletion of the heavier isotopes in the slow solar wind on the order of (1.4±1.3)% per amu
(2σ-error) compared to their abundances in the fast solar wind from coronal holes. These variations in the solar wind isotopic
composition represent a pure mass-dependent effect because the different isotopes of an element pass the inner corona with
the same charge state distribution. The influence of particle mass on the acceleration of minor solar wind ions is discussed
in the context of theoretical models and recent optical observations with other SOHO instruments.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
5.
E. Marsch 《Space Science Reviews》1999,87(1-2):1-24
There are three major types of solar wind: The steady fast wind originating on open magnetic field lines in coronal holes,
the unsteady slow wind coming probably from the temporarily open streamer belt and the transient wind in the form of large
coronal mass ejections. The majority of the models is concerned with the fast wind, which is, at least during solar minimum,
the normal mode of the wind and most easily modeled by multi-fluid equations involving waves. The in-situ constraints imposed
on the models, mainly by the Helios (in ecliptic) and Ulysses (high-latitude) interplanetary measurements, are extensively
discussed with respect to fluid and kinetic properties of the wind. The recent SOHO observations have brought a wealth of
new information about the boundary conditions for the wind in the inner solar corona and about the plasma conditions prevailing
in the transition region and chromospheric sources of the wind plasma. These results are presented, and then some key questions
and scientific issues are identified.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
6.
Leon Ofman 《Space Science Reviews》2005,120(1-2):67-94
Coronal holes have been identified as source regions of the fast solar wind, and MHD wave activity has been detected in coronal
holes by remote sensing, and in situ in fast solar wind streams. I review some of the most suggestive wave observations, and
discuss the theoretical aspects of MHD wave heating and solar wind acceleration in coronal holes. I review the results of
single fluid 2.5D MHD, as well as multi-fluid 2.5D MHD models of waves in coronal holes, the heating, and the acceleration
of the solar wind be these waves. 相似文献
7.
8.
Many species of pickup ions, both of interstellar origin and from an inner, distributed source have been discovered using
data from the Solar Wind Ion Composition Spectrometer (SWICS) on Ulysses. Velocity distribution functions of these ions were
measured for the first time over heliocentric distances between 1.35 and 5.4 AU, both at high and low latitudes, and in the
disturbed slow solar wind as well as the steady fast wind of the polar coronal holes. This has given us the first glance at
plasma properties of suprathermal ions in various solar wind flows, and is enabling us to study the chemical and, in the case
of He, the isotopic composition of the local interstellar cloud. Among the new findings are (a) the surprisingly weak pitch-angle
scattering of low rigidity, suprathermal ions leading to strongly anisotropic velocity distributions in radial magnetic fields,
(b) the efficient injection and consequent acceleration of pickup ions, especially He+ and H+, in the turbulent solar wind,
and (c) the discovery of a new extended source releasing carbon, oxygen, nitrogen and possibly other atoms and molecules in
the inner solar system. Pickup ion measurements are now used to study the characteristics of the local interstellar cloud
(LIC) and, in particular, to determine accurately the abundance of atomic H, He, N, O, and Ne, the isotopes of He and Ne,
as well as the ionization fractions of H and He in the LIC. Pickup ion observations allow us to infer the location of the
termination shock and, in combination with measurements of anomalous cosmic rays, to investigate termination shock acceleration
mechanisms.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
9.
The SOHO Ultraviolet Coronagraph Spectrometer (UVCS/SOHO) has observed the extended solar corona between 1 and 10 R· for more
than two years. We review spectroscopic and polarimetric measurements made in coronal holes, equatorial streamers, and coronal
mass ejections, as well as selected non-solar targets. UVCS/SOHO has provided a great amount of empirical information about
the physical processes that heat and accelerate the solar wind, and about detailed coronal structure and evolution.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
10.
Radio occultation, ultraviolet, and white-light measurements have expanded our knowledge of the morphology of density and
velocity in polar coronal holes, and made it possible to carry out the first systematic comparisons between the Ulysses solar wind measurements and quantitative white-light observations of the solar corona. This paper summarizes the rationale
and salient features of this new approach which has been used to relate the solar wind observed by Ulysses in 1993–1995 to the inner corona. The statistical characteristics (average, standard deviation, and autocorrelation function)
of the Ulysses density measurements of the fast wind are found to be mirrored in those of polarized brightness measurements of path-integrated
density made by the High Altitude Observatory (HAO) Mauna Loa K-coronagraph at 1.15 R
⊙. These results reinforce the conclusions from comparisons between measurements of the outer and inner corona. They show that
the polar coronal hole extends radially into the solar wind, and that sources of the fast wind are not limited to coronal
holes.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
11.
A. Balogh V. Bothmer N.U. Crooker R.J. Forsyth G. Gloeckler A. Hewish M. Hilchenbach R. Kallenbach B. Klecker J.A. Linker E. Lucek G. Mann E. Marsch A. Posner I.G. Richardson J.M. Schmidt M. Scholer Y.-M. Wang R.F. Wimmer-Schweingruber M.R. Aellig P. Bochsler S. Hefti Z. Mikić 《Space Science Reviews》1999,89(1-2):141-178
Corotating Interaction Regions (CIRs) form as a consequence of the compression of the solar wind at the interface between
fast speed streams and slow streams. Dynamic interaction of solar wind streams is a general feature of the heliospheric medium;
when the sources of the solar wind streams are relatively stable, the interaction regions form a pattern which corotates with
the Sun. The regions of origin of the high speed solar wind streams have been clearly identified as the coronal holes with
their open magnetic field structures. The origin of the slow speed solar wind is less clear; slow streams may well originate
from a range of coronal configurations adjacent to, or above magnetically closed structures. This article addresses the coronal
origin of the stable pattern of solar wind streams which leads to the formation of CIRs. In particular, coronal models based
on photospheric measurements are reviewed; we also examine the observations of kinematic and compositional solar wind features
at 1 AU, their appearance in the stream interfaces (SIs) of CIRs, and their relationship to the structure of the solar surface
and the inner corona; finally we summarise the Helios observations in the inner heliosphere of CIRs and their precursors to
give a link between the optical observations on their solar origin and the in-situ plasma observations at 1 AU after their
formation. The most important question that remains to be answered concerning the solar origin of CIRs is related to the origin
and morphology of the slow solar wind.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
12.
Thomas H. Zurbuchen Rudolf von Steiger Jacob Gruesbeck Enrico Landi Susan T. Lepri Liang Zhao Viggo Hansteen 《Space Science Reviews》2012,172(1-4):41-55
In this discussion of observational constraints on the source regions and acceleration processes of solar wind, we will focus on the ionic composition of the solar wind and the distribution of charge states of heavy elements such as oxygen and iron. We first focus on the now well-known bi-modal nature of solar wind, which dominates the heliosphere at solar minimum: Compositionally cool solar wind from polar coronal holes over-expands, filling a much larger solid angle than the coronal holes on the Sun. We use a series of remote and in-situ characteristics to derive a global geometric expansion factor of?~5. Slower, streamer-associated wind is located near the heliospheric current sheet with a width of 10–20°, but in a well-defined band with a geometrically small transition width. We then compute charge states under the assumption of thermal electron distributions and temperature, velocity, and density profiles predicted by a recent solar wind model, and conclude that the solar wind originates from a hot source at around 1 million?K, characteristic of the closed corona. 相似文献
13.
L. Ofman M. Romoli G. Noci G. Poletto J. L. Kohl R. A. Howard C. St. Cyr C. E. Deforest 《Space Science Reviews》1999,87(1-2):287-290
In recent UVCS/SOHO White Light Channel (WLC) observations we found quasi-periodic variations in the polarized brightness
(pB) in the polar coronal holes at heliocentric distances of 1.9 to 2.45 solar radii. The motivation for the observation is
the 2.5D MHD model of solar wind acceleration by nonlinear waves, that predicts compressive fluctuations in coronal holes.
In February 1998 we performed new observations using the UVCS/WLC in the coronal hole and obtained additional data. The new
data corroborate our earlier findings with higher statistical significance. The new longer observations show that the power
spectrum peaks in the 10–12 minute range. These timescales agree with EIT observations of brightness fluctuations in polar
plumes. We performed preliminary LASCO/C2 observations in an effort to further establish the coronal origin of the fluctuations.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
14.
We present a solar wind model which takes into account the possible origin of fast solar wind streams in coronal plumes. We treat coronal holes as being made up of essentially 2 plasma species, denser, warmer coronal plumes embedded in a surrounding less dense and cooler medium. Pressure balance at the coronal base implies a smaller magnetic field within coronal plumes than without. Considering the total coronal hole areal expansion as given, we calculate the relative expansion of plumes and the ambient medium subject to transverse pressure balance as the wind accelerates. The magnetic flux is assumed to be conserved independently both within plumes and the surrounding coronal hole. Magnetic field curvature terms are neglected so the model is essentially one dimensional along the coronal plumes, which are treated as thin flux-tubes. We compare the results from this model with white-light photographs of the solar corona and in-situ measurements of the spaghetti-like fine-structure of high-speed winds. 相似文献
15.
J. K. Edmondson 《Space Science Reviews》2012,172(1-4):209-225
The heating of the solar corona and therefore the generation of the solar wind, remain an active area of solar and heliophysics research. Several decades of in situ solar wind plasma observations have revealed a rich bimodal solar wind structure, well correlated with coronal magnetic field activity. Therefore, the reconnection processes associated with the large-scale dynamics of the corona likely play a major role in the generation of the slow solar wind flow regime. In order to elucidate the relationship between reconnection-driven coronal magnetic field structure and dynamics and the generation of the slow solar wind, this paper reviews the observations and phenomenology of the solar wind and coronal magnetic field structure. The geometry and topology of nested flux systems, and the (interchange) reconnection process, in the context of coronal physics is then explained. Once these foundations are laid out, the paper summarizes several fully dynamic, 3D MHD calculations of the global coronal system. Finally, the results of these calculations justify a number of important implications and conclusions on the role of reconnection in the structural dynamics of the coronal magnetic field and the generation of the solar wind. 相似文献
16.
R. Esser 《Space Science Reviews》1999,87(1-2):93-104
Summarized below are the discussions of working group 3 on "Coronal hole boundaries and interactions with adjacent regions"
which took place at the 7th SOHO workshop in Northeast Harbor, Maine, USA, 28 September to 1 October 1998. A number of recent
observational and theoretical results were presented during the discussions to shed light on different aspects of coronal
hole boundaries. The working group also included presentations on streamers and coronal holes to emphasis the difference between
the plasma properties in these regions, and to serve as guidelines for the definition of the boundaries. Observations, particularly
white light observations, show that multiple streamers are present close to the solar limb at all times. At some distance
from the sun, typically below 2 R, these streamers merge into a relatively narrow sheet as seen, for example, in LASCO and
UVCS images. The presence of multiple current sheets in interplanetary space was also briefly addressed. Coronal hole boundaries
were defined as the abrupt transition from the bright appearing plasma sheet to the dark coronal hole regions. Observations
in the inner corona seem to indicate a transition of typically 10 to 20 degrees, whereas observations in interplanetary space,
carried out from Ulysses, show on one hand an even faster transition of less than 2 degrees which is in agreement with earlier
Helios results. On the other hand, these observations also show that the transition happens on different scales, some of which
are significantly larger.
The slow solar wind is connected to the streamer belt/plasma sheet, even though the discussions were still not conclusive
on the point where exactly the slow solar wind originates. Considered the high variability of plasma characteristics in slow
wind streams, it seems most likely that several types of coronal regions produce slow solar wind, such as streamer stalks,
streamer legs and open field regions between active regions, and maybe even regions just inside of the coronal holes. Observational
and theoretical studies presented during the discussions show evidence that each of these regions may indeed contribute to
the solar slow wind.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
17.
Ester Antonucci 《Space Science Reviews》2006,124(1-4):35-50
The dynamics of the solar corona as observed during solar minimum with the Ultraviolet Coronagraph Spectrometer, UVCS, on
SOHO is discussed. The large quiescent coronal streamers existing during this phase of the solar cycle are very likely composed
by sub-streamers, formed by closed loops and separated by open field lines that are channelling a slow plasma that flows close
to the heliospheric current sheet. The polar coronal holes, with magnetic topology significantly varying from their core to
their edges, emit fast wind in their central region and slow wind close to the streamer boundary. The transition from fast
to slow wind then appears to be gradual in the corona, in contrast with the sharp transition between the two wind regimes
observed in the heliosphere. It is suggested that speed, abundance and kinetic energy of the wind are modulated by the topology
of the coronal magnetic field. Energy deposition occurs both in the slow and fast wind but its effect on the kinetic temperature
and expansion rate is different for the slow and fast wind. 相似文献
18.
Nandita Srivastava Rainer Schwenn Bernd Inhester Guillermo Stenborg Borut Podlipnik 《Space Science Reviews》1999,87(1-2):303-306
The slow solar wind (< 400 km s-1) appears to initiate from the regions in the corona where magnetic fields are closed, or from the interface between streamers
and other coronal regions. The nature of the acceleration of slow solar wind is not yet well known. LASCO observations of
gradually evolving mass ejections offer us a good opportunity to study the speed and acceleration profiles of the slow solar
wind from a distance of 1.1 up to 30 R⊙. We present speed and acceleration profiles of slow solar wind, derived on the basis of measurements of mass flows in several
cases of gradual mass ejections and present them in perspective of earlier work.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
19.
Margarita Karovska Brian E. Wood John W. Cook Russell A. Howard Guenter E. Brueckner 《Space Science Reviews》1999,87(1-2):219-222
We present the results from a study of the dynamical properties of polar jets in the Sun's polar regions using LASCO C2 coronagraph
and EIT observations. In the simplest impulsive acceleration scenarios for jets, gravity is expected to be the dominant force
on the jet following the initial acceleration, especially in the Sun's polar regions where the open magnetic fields should
not significantly impede the jet's motion. Our analysis shows that although at low heights the kinematics of the jets could
be consistent with a gravitational deceleration of the ejected plasma, at higher heights their motions may simply follow the
ambient solar wind outflow. If so, the polar jets can be used as tracers of the solar wind in coronal holes.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
20.
G. Gloeckler H. Balsiger A. Bürgi P. Bochsler L. A. Fisk A. B. Galvin J. Geiss F. Gliem D. C. Hamilton T. E. Holzer D. Hovestadt F. M. Ipavich E. Kirsch R. A. Lundgren K. W. Ogilvie R. B. Sheldon B. Wilken 《Space Science Reviews》1995,71(1-4):79-124
The Solar Wind and Suprathermal Ion Composition Experiment (SMS) on WIND is designed to determine uniquely the elemental, isotopic, and ionic-charge composition of the solar wind, the temperatures and mean speeds of all major solar-wind ions, from H through Fe, at solar wind speeds ranging from 175 kms–1 (protons) to 1280 kms–1 (Fe+8), and the composition, charge states as well as the 3-dimensional distribution functions of suprathermal ions, including interstellar pick-up He+, of energies up to 230 keV/e. The experiment consists of three instruments with a common Data Processing Unit. Each of the three instruments uses electrostatic analysis followed by a time-of-flight and, as required, an energy measurement. The observations made by SMS will make valuable contributions to the ISTP objectives by providing information regarding the composition and energy distribution of matter entering the magnetosphere. In addition SMS results will have an impact on many areas of solar and heliospheric physics, in particular providing important and unique information on: (i) conditions and processes in the region of the corona where the solar wind is accelerated; (ii) the location of the source regions of the solar wind in the corona; (iii) coronal heating processes; (iv) the extent and causes of variations in the composition of the solar atmosphere; (v) plasma processes in the solar wind; (vi) the acceleration of particles in the solar wind; and (vii) the physics of the pick-up process of interstellar He as well as lunar particles in the solar wind, and the isotopic composition of interstellar helium. 相似文献