共查询到20条相似文献,搜索用时 812 毫秒
1.
Steven R. Cranmer 《Space Science Reviews》2002,101(3-4):229-294
Coronal holes are the lowest density plasma components of the Sun's outer atmosphere, and are associated with rapidly expanding magnetic fields and the acceleration of the high-speed solar wind. Spectroscopic and polarimetric observations of the extended corona, coupled with interplanetary particle and radio sounding measurements going back several decades, have put strong constraints on possible explanations for how the plasma in coronal holes receives its extreme kinetic properties. The Ultraviolet Coronagraph Spectrometer (UVCS) aboard the Solar and Heliospheric Observatory (SOHO) spacecraft has revealed surprisingly large temperatures, outflow speeds, and velocity distribution anisotropies for positive ions in coronal holes. We review recent observations, modeling techniques, and proposed heating and acceleration processes for protons, electrons, and heavy ions. We emphasize that an understanding of the acceleration region of the wind (in the nearly collisionless extended corona) is indispensable for building a complete picture of the physics of coronal holes. 相似文献
2.
3.
M. K. Bird 《Space Science Reviews》1982,33(1-2):99-126
The radio telemetry links between Earth and a spacecraft near superior conjunction penetrate the corona at ranges well within the acceleration regime of the solar wind. Occultation experiments in the solar corona have been performed on many interplanetary missions beginning with the Mariner and Pioneer series and extending up to the more recent data on Helios, Viking, and Voyager. The changes in group and phase velocity of the radio signal are measured to determine the total electron content of the corona and its fluctuations. The broadening of the carrier signal may be used in combination with the electron content data to derive a solar wind velocity profile. The wave number spectrum of electron density fluctuations in the corona may be inferred from amplitude and phase scintillations of the received signal. Linearly polarized signals, which are rotated along the propagation path by the Faraday effect, can provide information on the coronal magnetic field and its variations.Paper presented at the IX-th Lindau Workshop The Source Region of the Solar Wind. 相似文献
4.
Gloeckler G. Cain J. Ipavich F.M. Tums E.O. Bedini P. Fisk L.A. Zurbuchen T.H. Bochsler P. Fischer J. Wimmer-Schweingruber R.F. Geiss J. Kallenbach R. 《Space Science Reviews》1998,86(1-4):497-539
The Solar Wind Ion Composition Spectrometer (SWICS) and the Solar Wind Ions Mass Spectrometer (SWIMS) on ACE are instruments
optimized for measurements of the chemical and isotopic composition of solar and interstellar matter. SWICS determines uniquely
the chemical and ionic-charge composition of the solar wind, the thermal and mean speeds of all major solar wind ions from
H through Fe at all solar wind speeds above 300 km s−1 (protons) and 170 km s−1 (Fe+16), and resolves H and He isotopes of
both solar and interstellar sources. SWICS will measure the distribution functions of both the interstellar cloud and dust
cloud pickup ions up to energies of 100 keV e−1. SWIMS will measure the chemical, isotopic and charge state composition of
the solar wind for every element between He and Ni. Each of the two instruments uses electrostatic analysis followed by a
time-of-flight and, as required, an energy measurement. The observations made with SWICS and SWIMS will make valuable contributions
to the ISTP objectives by providing information regarding the composition and energy distribution of matter entering the magnetosphere.
In addition, SWICS and SWIMS 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; (vii) the physics of the pickup process of interstellar He in the solar wind; and (viii) the
spatial distribution and characteristics of sources of neutral matter in the inner heliosphere.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
5.
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
6.
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
7.
Steven R. Cranmer 《Space Science Reviews》2012,172(1-4):145-156
The origins of the hot solar corona and the supersonically expanding solar wind are still the subject of much debate. This paper summarizes some of the essential ingredients of realistic and self-consistent models of solar wind acceleration. It also outlines the major issues in the recent debate over what physical processes dominate the mass, momentum, and energy balance in the accelerating wind. A key obstacle in the way of producing realistic simulations of the Sun-heliosphere system is the lack of a physically motivated way of specifying the coronal heating rate. Recent models that assume the energy comes from Alfvén waves that are partially reflected, and then dissipated by magnetohydrodynamic turbulence, have been found to reproduce many of the observed features of the solar wind. This paper discusses results from these models, including detailed comparisons with measured plasma properties as a function of solar wind speed. Some suggestions are also given for future work that could answer the many remaining questions about coronal heating and solar wind acceleration. 相似文献
8.
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
9.
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
10.
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
11.
M. Pick T. G. Forbes G. Mann H. V. Cane J. Chen A. Ciaravella H. Cremades R. A. Howard H. S. Hudson A. Klassen K. L. Klein M. A. Lee J. A. Linker D. Maia Z. Mikic J. C. Raymond M. J. Reiner G. M. Simnett N. Srivastava D. Tripathi R. Vainio A. Vourlidas J. Zhang T. H. Zurbuchen N. R. Sheeley C. Marqué 《Space Science Reviews》2006,123(1-3):341-382
This chapter reviews how our knowledge of CMEs and CME-associated phenomena has been improved, since the launch of the SOHO mission, thanks to multi-wavelength analysis. The combination of data obtained from space-based experiments and ground based instruments allows us to follow the space-time development of an event from the bottom of the corona to large distances in the interplanetary medium. Since CMEs originate in the low solar corona, understanding the physical processes that generate them is strongly dependant on coordinated multi-wavelength observations. CMEs display a large diversity in morphology and kinematic properties, but there is presently no statistical evidence that those properties may serve to group them into different classes. When a CME takes place, the coronal magnetic field undergoes restructuring. Much of the current research is focused on understanding how the corona sustains the stresses that allow the magnetic energy to build up and how, later on, this magnetic energy is released during eruptive flares and CMEs. Multi-wavelength observations have confirmed that reconnection plays a key role during the development of CMEs. Frequently, CMEs display a rather simple shape, exhibiting a well known three-part structure (bright leading edge, dark cavity and bright knot). These types of events have led to the proposal of the ‘`standard model’' of the development of a CME, a model which predicts the formation of current sheets. A few recent coronal observations provide some evidence for such sheets. Other more complex events correspond to multiple eruptions taking place on a time scale much shorter than the cadence of coronagraph instruments. They are often associated with large-scale dimming and coronal waves. The exact nature of these waves and the physical link between these different manifestations are not yet elucidated. We also discuss what kind of shocks are produced during a flare or a CME. Several questions remain unanswered. What is the nature of the shocks in the corona (blast-wave or piston-driven?) How they are related to Moreton waves seen in Hα? How they are related to interplanetary shocks? The last section discusses the origin of energetic electrons detected in the corona and in the interplanetary medium. “Complex type III-like events,”which are detected at hectometric wavelengths, high in the corona, and are associated with CMEs, appear to originate from electrons that have been accelerated lower in the corona and not at the bow shock of CMEs. Similarly, impulsive energetic electrons observed in the interplanetary medium are not the exclusive result of electron acceleration at the bow shocks of CMEs; rather they have a coronal origin. 相似文献
12.
J. L. Kohl G. L. Withbroe H. Weiser R. M. Macqueen R. H. Munro 《Space Science Reviews》1981,29(4):419-424
The Harvard-Smithsonian Center for Astrophysics and the High Altitude Observatory have defined a joint coronagraphs experiment for a future Spacelab mission. The instrumentation package would include an ultraviolet light coronagraph to measure the intensity and profiles of spectral lines formed between 1.2 and 8 solar radii from Sun center and a white light coronagraph to measure the intensity and polarization of visible light. The overall goals of the joint program are to use new coronal plasma diagnostic techniques to understand the physical processes and mechanisms operating in the solar corona, to understand the acceleration of high-speed and low-speed solar wind streams and to extrapolate this knowledge to other stars in order to help understand the physics of stellar coronae and stellar mass loss.Proceedings of the Conference Solar Physics from Space, held at the Swiss Federal Institute of Technology Zurich (ETHZ), 11–14 November 1980. 相似文献
13.
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
14.
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
15.
Characteristics of shocks in the solar corona,as inferred from radio,optical, and theoretical investigations 总被引:1,自引:0,他引:1
Solar radio bursts of spectral type II provide one of the chief diagnostics for the propagation of shocks through the solar corona. Radio data on the shocks are compared with computer models for propagation of fast-mode MHD shocks through the solar corona. Data on coronal shocks and high-velocity ejecta from solar flares are then discussed in terms of a general model consisting of three main velocity regimes.An invited paper presented at STIP Workshop on Shock Waves in the Solar Corona and Interplanetary Space, 15–19 June, 1980, Smolenice, Czechoslovakia. 相似文献
16.
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
17.
C. M. S. Cohen R. A. Mewaldt R. A. Leske A. C. Cummings E. C. Stone M. E. Wiedenbeck T. T. von Rosenvinge G. M. Mason 《Space Science Reviews》2007,130(1-4):183-194
Solar abundances can be derived from the composition of the solar wind and solar energetic particles (SEPs) as well as obtained
through spectroscopic means. Past comparisons have suggested that all three samples agree well, when rigidity-related fractionation
effects on the SEPs were accounted for. It has been known that such effects vary from one event to the next and should be
addressed on an event-by-event basis. This paper examines event variability more closely, particularly in terms of energy-dependent
SEP abundances. This is now possible using detailed SEP measurements spanning several decades in energy from the Ultra Low
Energy Isotope Spectrometer (ULEIS) and the Solar Isotope Spectrometer (SIS) on the ACE spacecraft. We present examples of
the variability of the elemental composition with energy and suggest they can be understood in terms of diffusion from the
acceleration region near the interplanetary shock. By means of a spectral scaling procedure, we obtain energy-independent
abundance ratios for 14 large SEP events and compare them to reported solar wind and coronal abundances as well as to previous
surveys of SEP events. 相似文献
18.
Markus J. Aschwanden 《Space Science Reviews》2012,171(1-4):3-21
Ground Level Enhancement (GLE) events represent the most energetic class of solar energetic particle (SEP) events, requiring acceleration processes to boost ?1?GeV ions in order to produce showers of secondary particles in the Earth’s atmosphere with sufficient intensity to be detected by ground-level neutron monitors, above the background of cosmic rays. Although the association of GLE events with both solar flares and coronal mass ejections (CMEs) is undisputed, the question arises about the location of the responsible acceleration site: coronal flare reconnection sites, coronal CME shocks, or interplanetary shocks? To investigate the first possibility we explore the timing of GLE events with respect to hard X-ray production in solar flares, considering the height and magnetic topology of flares, the role of extended acceleration, and particle trapping. We find that 50% (6 out of 12) of recent (non-occulted) GLE events are accelerated during the impulsive flare phase, while the remaining half are accelerated significantly later. It appears that the prompt GLE component, which is observed in virtually all GLE events according to a recent study by Vashenyuk et al. (Astrophys. Space Sci. Trans. 7(4):459–463, 2011), is consistent with a flare origin in the lower corona, while the delayed gradual GLE component can be produced by both, either by extended acceleration and/or trapping in flare sites, or by particles accelerated in coronal and interplanetary shocks. 相似文献
19.
U. Feldman 《Space Science Reviews》1998,85(1-2):227-240
Recent spectroscopic measurements from instruments on the Solar and Heliospheric Observatory (SOHO) find that the coronal
composition above a polar coronal hole is nearly photospheric. However, similar SOHO observations show that in coronal plasmas
above quiet equatorial regions low-FIP elements are enhanced by a factor of ≈ 4. In addition, the process of elemental settling
in coronal plasmas high above the solar surface was shown to exist. Measurements by the Ulysses spacecraft, which are based
on non-spectroscopic particle counting techniques, show that, with the exception of He, the elemental composition of the fast
speed solar wind is similar to within a factor of 1.5 to the composition of the photosphere. In contrast, similar measurements
in the slow speed wind show that elements with low first ionization potential (FIP < 10 eV) are enhanced, relative to the
photosphere, by a factor of 4-5. By combining the SOHO and Ulysses results, ideas related to the origin of the slow speed
solar wind are presented. Using spectroscopic measurements by the Solar Ultraviolet Measurement of Emitted Radiation (SUMER)
instrument on SOHO the photospheric abundance of He was determined as 8.5 ± 1.3% (Y = 0.248).
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
20.
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