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1.
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
2.
C. Göran Schultz 《Space Science Reviews》1994,70(1-2):233-239
Some theoretical aspects of solar coronal streamers are discussed with emphasis on the current sheet and reconnection processes going on along the axis of the streamer. The dynamics of the streamer is a combination of MHD and transport, with acceleration of particles due to reconnection and leakage of plasma outwards as a slow solar wind as the observable results. The presence of the almost-closed magnetic bottles of streamers that can store high-energy particles for significant times provides the birdcage for solar cosmic rays, the reconnection in the sheet feeds medium-energy protons into the corona for the large-scale storage needed for certain flare models, and the build-up of excess density sets the stage for coronal mass ejections. 相似文献
3.
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
4.
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
5.
Streamer evaporation is the consequence of heating in ideal MHD models because plasma is weakly contained by the magnetic
field. Heating causes inflation, opening of field lines, and release of solar wind. It was discovered in simulations and,
due to the absence of loss mechanisms, the ultimate end point is the complete evaporation of the streamer. Of course streamers
do not behave in this way because of losses by thermal conduction and radiation. Heating is also expected to depend on ambient
conditions. We use a global MHD model with thermal conduction to examine the effect of changing the heating scale height.
We also extend an analytic model of streamers developed by Pneuman (1968) to show that steady streamers are unable to contain
plasma for temperatures near the cusp greater than ∼ 2 × 106 K.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
6.
R. A. Frazin A. Ciaravella E. Dennis S. Fineschi L. D. Gardner J. Michels R. O'Neal J. C. Raymond C.-R. Wu J. L. Kohl A. Modigliani G. Noci 《Space Science Reviews》1999,87(1-2):189-192
We made streamer observations with the Ultraviolet Coronagraph Spectrometer (UVCS) on the Solar and Heliospheric Observatory (SOHO) during the early part of 1998, which was a time of moderate solar activity. We present an empirical study of coronal ion kinetics using the line profiles from these observations. Our first and most striking result is that the mid-latitude (ML) streamers have much narrower O VI 1032 Å line profiles than the solar minimum equatorial (SME) streamers. Our second result is that the line profiles from a small collection of ions in ML streamers do not seem to be consistent with the ions having a single temperature and turbulent velocity. We discuss several interpretations, including line of sight (LOS) effects. This work is supported by the National Aeronautics and Space Administration under grant NAG-3192 to the Smithsonian Astrophysical Observatory. 相似文献
7.
Roger A. Kopp 《Space Science Reviews》1994,70(1-2):309-316
The working group on coronal streamers convened on the first day of the 2nd SOHO Workshop, which took place in Marciana Marina, Isola d'Elba, 27 September –1 October 1993. Recent progress in streamer observational techniques and theoretical modeling was reported. The contribution of streamers to the mass and energy supply for the solar wind was discussed. Moreover, the importance of thin electric current sheets for determining both the gross dynamical properties of streamers and the fine-scale filamentary structure within streamers, was strongly emphasized. Potential advances to our understanding of these areas of coronal physics that could be made by the contingent of instruments aboard SOHO were pointed out. 相似文献
8.
M. P. Miralles L. Strachan L. D. Gardner P. L. Smith J. L. Kohl M. Guhathakurta R. R. Fisher 《Space Science Reviews》1999,87(1-2):277-281
The Spartan 201 flights from 1993 to 1995 provided us with observations in H I Lyman-α of several coronal hole/streamer boundaries
and adjacent streamers during the declining phase of the current solar cycle: Analysis of the latitudinal dependence of the
line intensities clearly shows that there is a boundary region at the coronal hole/streamer interface where the H I Lyman-α
intensity reaches a minimum value. Similar results are also found in UVCS/SOHO observations. We also discuss differences in
the coronal hole/streamer boundaries for different types of streamers and their changes over the three year period of Spartan
201 observations.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
9.
Prominent enhancements in Doppler scintillation lasting a fraction of a day (solar source several degrees wide) and overlying the neutral line represent the signature of the heliospheric current sheet and the apparent interplanetary manifestation of coronal streamers near the Sun. This first detection of coronal streamers in radio scintillation measurements provides the link betweenin situ measurements of the spatial wavenumber spectrum of electron density fluctuations beyond 0.3 AU and earlier measurements deduced from radio scintillation and scattering observations inside 0.3 AU. Significant differences between the density spectra of fast streams and slow solar wind associated with the heliospheric current sheet near the Sun reinforce the emerging picture that high- and low-speed flows are organized by the large-scale solar magnetic field, and that while the contrast between solar wind properties of the two flows is highest near the Sun, it undergoes substantial erosion in the ecliptic plane as the solar wind expands. 相似文献
10.
Yuri I. Yermolaev 《Space Science Reviews》1994,70(1-2):379-386
The properties of different solar wind streams depend on the large scale structure of the coronal magnetic field. We present average values and distributions of bulk parameters (density, velocity, temperature, mass flux, momentum, and kinetic and thermal energy, ratio of thermal and magnetic pressure, as well as the helium abundance) as observed on board the Prognoz 7 satellite in different types of the solar wind streams. Maximum mass flux is recorded in the streams emanating from the coronal streamers while maximum thermal and kinetic energy fluxes are observed in the streams from the coronal holes. The momentum fluxes are equal in both types of streams. The maximum ratio of thermal and magnetic pressure is observed in heliospheric current sheet. The helium abundance in streams from coronal holes is higher than in streams from streamers, and its dependences on density and mass flux are different in different types of the streams. Also, the dynamics of -particle velocity and temperature relative to protons in streams from coronal holes and streamers is discussed. 相似文献
11.
R. S. Steinolfson 《Space Science Reviews》1994,70(1-2):289-294
Numerical solutions of the time-dependent MHD equations are used to generate ambient coronal streamer structures in a corona characteristic of that near solar minimum. The streamers are then disrupted by slow photospheric shear motion at the base of magnetic field lines within the closed field region, which is currently believed to be responsible for producing at least some CMEs. In contrast to several other simulations of this phenomena, the polytropic index is maintained at a value of 5/3 through the addition of coronal heating. Observations are used as a guide in determining the thermodynamic structure and plasma beta in the ambient corona. For a shear speed of 2.5 km/sec, the streamer configuration evolves slowly for about 65 hours before erupting outward with the formation of a CME. The bright CME leading edge travels outward at a speed of about 240 km/sec, and the sheared field lines follow at a somewhat slower speed. A closed magnetic field region is ejected as the magnetic field lines that were opened by the CME reconnect and reform the streamer. 相似文献
12.
This paper contains a summary of the topics treated in the working group on abundance variations in the solar atmosphere and
in the solar wind. The FIP bias (overabundance of particles with low First Ionization Potentials over photospheric abundances)
in coronal holes and coronal hole associated solar wind amounts to values between 1 and 2. The FIP bias in the slow solar
wind is typically a factor 4, consistent with optical observations in streamers. In order to distinguish between different
theoretical models which make an attempt to explain the FIP bias, some observable parameters must be provided. Unfortunately,
many models are deficient in this respect. In addition to FIP fractionation, gravitational settling of heavy elements has
been found in the core of long lived streamers. The so-called electron 'freeze in' temperatures derived from in situ observed
ionization states of minor ions in the fast wind are significantly higher than the electron temperatures derived from diagnostic
line ratios observed in polar coronal holes. The distinction between conditions in plumes and interplume lanes needs to be
further investigated. The 'freeze in' temperatures for the slow solar wind are consistent with the electron temperatures derived
for streamers.
This revised version was published online in June 2006 with corrections to the Cover Date. 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.
Guhathakurta Madhullika Sittler Ed Fisher Richard Kucera Theresa Gibson Sarah McComas Dave Skoug Ruth 《Space Science Reviews》2001,97(1-4):45-50
The large-scale coronal magnetic fields of the Sun are believed to play an important role in organizing the coronal plasma
and channeling the high and low speed solar wind along the open magnetic field lines of the polar coronal holes and the rapidly
diverging field lines close to the current sheet regions, as has been observed by the instruments aboard the Ulysses spacecraft from March 1992 to March 1997. We have performed a study of this phenomena within the framework of a semi-empirical
model of the coronal expansion and solar wind using Spartan, SOHO, and Ulysses observations during the quiescent phase of the solar cycle. Key to this understanding is the demonstration that the white
light coronagraph data can be used to trace out the topology of the coronal magnetic field and then using the Ulysses data to fix the strength of the surface magnetic field of the Sun. As a consequence, it is possible to utilize this semi-empirical
model with remote sensing observation of the shape and density of the solar corona and in situ data of magnetic field and
mass flux to predict values of the solar wind at all latitudes through out the solar system. We have applied this technique
to the observations of Spartan 201-05 on 1–2 November, 1998, SOHO and Ulysses during the rising phase of this solar cycle and speculate on what solar wind velocities Ulysses will observe during its polar passes over the south and the north poles during September of 2000 and 2001. In order to do
this the model has been generalized to include multiple streamer belts and co-located current sheets. The model shows some
interesting new results.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
15.
John C. Raymond Raid Suleiman John L. Kohl Giancarlo Noci 《Space Science Reviews》1998,85(1-2):283-289
A great deal of evidence for elemental abundance variations among different structures in the solar corona has accumulated
over the years. Many of the observations show changes in the relative abundances of high- and low-First Ionization Potential
elements, but relatively few show the absolute elemental abundances. Recent observations from the SOHO satellite give absolute
abundances in coronal streamers. Along the streamer edges, and at low heights in the streamer, they show roughly photospheric
abundances for the low-FIP elements, and a factor of 3 depletion of high-FIP elements. In the streamer core at 1.5 R·, both
high- and low-FIP elements are depleted by an additional factor of 3, which appears to result from gravitational settling.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
16.
Alexeev Igor I. Belenkaya Elena S. Bobrovnikov Sergey Yu. Kalegaev Vladimir V. 《Space Science Reviews》2003,107(1-2):7-26
A magnetohydrodynamic model of the solar wind flow is constructed using a kinematic approach. It is shown that a phenomenological
conductivity of the solar wind plasma plays a key role in the forming of the interplanetary magnetic field (IMF) component
normal to the ecliptic plane. This component is mostly important for the magnetospheric dynamics which is controlled by the
solar wind electric field. A simple analytical solution for the problem of the solar wind flow past the magnetosphere is presented.
In this approach the magnetopause and the Earth's bow shock are approximated by the paraboloids of revolution. Superposition
of the effects of the bulk solar wind plasma motion and the magnetic field diffusion results in an incomplete screening of
the IMF by the magnetopause. It is shown that the normal to the magnetopause component of the solar wind magnetic field and
the tangential component of the electric field penetrated into the magnetosphere are determined by the quarter square of the
magnetic Reynolds number. In final, a dynamic model of the magnetospheric magnetic field is constructed. This model can describe
the magnetosphere in the course of the severe magnetic storm. The conditions under which the magnetospheric magnetic flux
structure is unstable and can drive the magnetospheric substorm are discussed. The model calculations are compared with the
observational data for September 24–26, 1998 magnetic storm (Dst
min=−205 nT) and substorm occurred at 02:30 UT on January 10, 1997.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
17.
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
18.
A review is presented of the interaction of the solar wind with the magnetic field of the earth. The material is developed primarily from an observational point of view. The early observations are covered through late 1963, with primary emphasis on the sunward interaction region. The historical review of the early results is discussed in terms of the significant contributions of each satellite observation and in the light of our present concept of the solar wind-geomagnetic field interaction. Subsequent to 1963 the observations tend to overlap such that a strictly historical treatment is not tractable and the material is presented from a phenomenological approach. The daytime and night-time hemispheres are covered separately in terms of the significant and separable phenomena which dominate the structure and dynamics of these two regions. Satellite and deep space probe data are compared with relevant theory. Further observational eflorts needed to improve our understanding of the details of the solar wind-geomagnetic field interaction are also discussed. 相似文献
19.
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
20.
Giannina Poletto 《Space Science Reviews》1994,70(1-2):241-252
Streamers have been observed since far back in time, but our knowledge of their morphology and of their physical characteristics is still very limited. As a consequence, the present streamer picture is largely incomplete: because individual features are poorly known, their role in more general phenomena (like the evolution of the global corona or the solar wind mass and flow pattern) is also poorly known. In this presentation, the more relevant open problems in the understanding of streamers will be illustrated and it will be shown how new data acquired by SOHO may help us to reach a better understanding of these structures. 相似文献