共查询到20条相似文献,搜索用时 31 毫秒
1.
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
2.
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
3.
M. Neugebauer 《Space Science Reviews》1994,70(1-2):319-330
The solar wind emanating from coronal holes (CH) constitutes a quasi-stationary flow whose properties change only slowly with the evolution of the hole itself. Some of the properties of the wind from coronal holes depend on whether the source is a large polar coronal hole or a small near-equatorial hole. The speed of polar CH flows is usually between 700 and 800 km/s, whereas the speed from the small equatorial CH flows is generally lower and can be <400 km/s. At 1 AU, the average particle and energy fluxes from polar CH are 2.5×108 cm–2 sec–1 and 2.0 erg cm–2 s–1. This particle flux is significantly less than the 4×108 cm–2 sec–1 observed in the slow, interstream wind, but the energy fluxes are approximately the same. Both the particle and energy fluxes from small equatorial holes are somewhat smaller than the fluxes from the large polar coronal holes.Many of the properties of the wind from coronal holes can be explained, at least qualitatively, as being the result of the effect of the large flux of outward-propagating Alfvén waves observed in CH flows. The different ion species have roughly equal thermal speeds which are also close to the Alfvén speed. The velocity of heavy ions exceeds the proton velocity by the Alfvén speed, as if the heavy ions were surfing on the waves carried by the proton fluid.The elemental composition of the CH wind is less fractionated, having a smaller enhancement of elements with low first-ionization potentials than the interstream wind, the wind from coronal mass ejections, or solar energetic particles. There is also evidence of fine-structure in the ratio of the gas and magnetic pressures which maps back to a scale size of roughly 1° at the Sun, similar to some of the fine structures in coronal holes such as plumes, macrospicules, and the supergranulation. 相似文献
4.
Y. -M. Wang 《Space Science Reviews》1994,70(1-2):387-390
Empirical studies have shown that the solar wind speed at Earth is inversely correlated with the areal expansion rate of magnetic flux tubes near the Sun. Recent model calculations that include a self-consistent determination of the coronal temperature allow one to understand the physical basis of this relationship; they also suggest why the solar wind mass flux is relatively constant. 相似文献
5.
Recent papers have suggested that the slow solar wind is a super-position of material which is released by reconnection from
large coronal loops. This reconnection process is driven by large-scale motions of solar magnetic flux driven by the non-radial
expansion of the solar wind from the differentially rotating photosphere into more rigidly rotating coronal holes.
The elemental composition of the slow solar wind material is observed to be fractionated and more variable than the fast solar
wind from coronal holes. Recently, it has also been reported that fractionation also occurs in 3He/4He. This may be interpreted
in the frame-work of an existing model for fractionation on large coronal loops in which wave-particle interactions preferentially
heat ions thereby modifying their scale-heights.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
6.
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
7.
Coronal plumes are believed to be essentially magnetic features: they are rooted in magnetic flux concentrations at the photosphere
and are observed to extend nearly radially above coronal holes out to at least 15 solar radii, probably tracing the open field
lines. The formation of plumes itself seems to be due to the presence of reconnecting magnetic field lines and this is probably
the cause of the observed extremely low values of the Ne/Mg abundance ratio.
In the inner corona, where the magnetic force is dominant, steady MHD models of coronal plumes deal essentially with quasi-potential
magnetic fields but further out, where the gas pressure starts to be important, total pressure balance across the boundary
of these dense structures must be considered.
In this paper, the expansion of plumes into the fast polar wind is studied by using a thin flux tube model with two interacting
components, plume and interplume. Preliminary results are compared with both remote sensing and solar wind in situ observations
and the possible connection between coronal plumes with pressure-balance structures (PBS) and microstreams is discussed.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
8.
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
9.
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
10.
A. Balogh J. A. Gonzalez-Esparza R. J. Forsyth M. E. Burton B. E. Goldstein E. J. Smith S. J. Bame 《Space Science Reviews》1995,72(1-2):171-180
Between its launch in October 1990 and the end of 1993, approximately 160 fast collisionless shock waves were observed in the solar wind by the Ulysses space probe. During the in-ecliptic part of the mission, to February 1992, the observed shock waves were first caused mainly by solar transient events following the solar maximum and the reorganisation of the large scale coronal fields. With the decay in solar activity, relatively stable Corotating Interaction Regions (CIRs) were observed betwen 3 and 5.4 AU, each associated with at least one forwardreverse shock pair. During the out-of-ecliptic phase of the orbit, from February 1992 onwards, CIRs and shock pairs associated with them continued to dominate the observations. From July 1992, Ulysses encountered the fast solar wind flow from the newly developed southern polar coronal hole, and from May 1993 remained in the unipolar magnetic region associated with this coronal hole. At latitudes beyond 30°, CIRs were associated almost exclusively with reverse shocks only. A comprehensive list of shock waves identified in the magnetic field and solar wind plasma data from Ulysses is given in Table 1. The principal characteristics were determined mainly from the magnetic field data. General considerations concerning the determination of shock characteristics are outlined in the Introduction. 相似文献
11.
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
12.
Models of the transition region — corona — solar wind system are investigated in order to find the coronal helium abundance and to study the role played by coronal helium in controlling the the solar wind proton flux. The thermal force on -particles in the transition region sets the flow of helium into the corona. The frictional coupling between -particles and protons and/or the electric polarization field determines the proton flux in the solar wind as well as the fate of the coronal helium content. 相似文献
13.
On the Slow Solar Wind 总被引:1,自引:0,他引:1
A theory for the origin of the slow solar wind is described. Recent papers have demonstrated that magnetic flux moves across
coronal holes as a result of the interplay between the differential rotation of the photosphere and the non-radial expansion
of the solar wind in more rigidly rotating coronal holes. This flux will be deposited at low latitudes and should reconnect
with closed magnetic loops, thereby releasing material from the loops to form the slow solar wind. It is pointed out that
this mechanism provides a natural explanation for the charge states of elements observed in the slow solar wind, and for the
presence of the First-Ionization Potential, or FIP, effect in the slow wind and its absence in fast wind. Comments are also
provided on the role that the ACE mission should have in understanding the slow solar wind.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
14.
At solar maximum, the large-scale structure of the heliospheric magnetic field (HMF) reflects the complexity of the Sun's
coronal magnetic fields. The corona is characterised by mostly closed magnetic structures and short-lived, small coronal holes.
The axis of the Sun's dipole field is close to the solar equator; there are also important contributions from the higher order
terms. This complex and variable coronal magnetic configuration leads to a much increased variability in the HMF on all time
scales, at all latitudes. The transition from solar minimum to solar maximum conditions, as reflected in the HMF, is described,
as observed by Ulysses during its passage to high southern heliolatitudes. The magnetic signatures associated with the interaction regions generated
by short-lived fast solar wind streams are presented, together with the highly disordered period in mid-1999 when there was
a considerable reorganisation in coronal structures. The magnetic sector structure at high heliolatitudes shows, from mid-1999,
a recognisable two-sector structure, corresponding to a highly inclined Heliospheric Current Sheet. A preliminary investigation
of the radial component of the magnetic field indicates that it remains, on average, constant as a function of heliolatitude.
Intervals of highly Alfvénic fluctuations in the rarefaction regions trailing the interaction regions have been, even if intermittently,
identified even close to solar maximum.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
15.
From magnetic fields and coronal heating observed in flares, active regions, quiet regions, and coronal holes, we propose
that exploding sheared core magnetic fields are the drivers of most of the dynamics and heating of the solar atmosphere, ranging
from the largest and most powerful coronal mass ejections and flares, to the vigorous microflaring and coronal heating in
active regions, to a multitude of fine-scale explosive events in the magnetic network, driving microflares, spicules, global
coronal heating, and, consequently, the solar wind.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
16.
T. H. Zurbuchen S. Hefti L. A. Fisk G. Gloeckler R. Von Steiger 《Space Science Reviews》1999,87(1-2):353-356
The transition between coronal hole associated fast solar wind and slow solar wind is studied using data from the high resolution
mass spectrometer SWICS on ACE. We discuss the data in the framework of a recent theory about the global heliospheric magnetic
field and conclude that the data are consistent with magnetic connections between field-lines in the fast and in the slow
wind.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
17.
H. Kunow M.A. Lee L.A. Fisk R.J. Forsyth B. Heber T.S. Horbury E. Keppler J. Kóta Y.-Q. Lou R.B. McKibben C. Paizis M.S. Potgieter E.C. Roelof T.R. Sanderson G.M. Simnett R. Von Steiger B.T. Tsurutani R.F. Wimmer-Schweingruber J.R. Jokipii 《Space Science Reviews》1999,89(1-2):221-268
Ulysses observed a stable strong CIR from early 1992 through 1994 during its first journey into the southern hemisphere. After
the rapid latitude scan in early 1995, Ulysses observed a weaker CIR from early 1996 to mid-1997 in the northern hemisphere
as it traveled back to the ecliptic at the orbit of Jupiter. These two CIRs are the observational basis of the investigation
into the latitudinal structure of CIRs. The first CIR was caused by an extension of the northern coronal hole into the southern
hemisphere during declining solar activity, whereas the second CIR near solar minimum activity was caused by small warps in
the streamer belt. The latitudinal structure is described through the presentation of three 26-day periods during the southern
CIR. The first at ∼24°S shows the full plasma interaction region including fast and slow wind streams, the compressed shocked
flows with embedded stream interface and heliospheric current sheet (HCS), and the forward and reverse shocks with associated
accelerated ions and electrons. The second at 40°S exhibits only the reverse shock, accelerated particles, and the 26-day
modulation of cosmic rays. The third at 60°S shows only the accelerated particles and modulated cosmic rays. The possible
mechanisms for the access of the accelerated particles and the CIR-modulated cosmic rays to high latitudes above the plasma
interaction region are presented. They include direct magnetic field connection across latitude due to stochastic field line
weaving or to systematic weaving caused by solar differential rotation combined with non-radial expansion of the fast wind.
Another possible mechanism is particle diffusion across the average magnetic field, which includes stochastic field line weaving.
A constraint on connection to a distant portion of the CIR is energy loss in the solar wind, which is substantial for the
relatively slow-moving accelerated ions. Finally, the weaker northern CIR is compared with the southern CIR. It is weak because
the inclination of the streamer belt and HCS decreased as Ulysses traveled to lower latitudes so that the spacecraft remained
at about the maximum latitudinal extent of the HCS.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
18.
Martin A. Lee 《Space Science Reviews》2007,130(1-4):221-229
Gradual solar energetic particle (SEP) events are evidently accelerated by coronal/interplanetary shocks driven by coronal
mass ejections. This talk addresses the different factors which determine the composition of the accelerated ions. The first
factor is the set of available seed populations including the solar wind core and suprathermal tail, remnant impulsive events
from preceding solar flares, and remnant gradual events. The second factor is the fractionation of the seed ions by the injection
process, that is, what fraction of the ions are extracted by the shock to participate in diffusive shock acceleration. Injection
is a controversial topic since it depends on the detailed electromagnetic structure of the shock transition and the transport
of ions in these structured fields, both of which are not well understood or determined theoretically. The third factor is
fractionation during the acceleration process, due to the dependence of ion transport in the turbulent electromagnetic fields
adjacent to the shock on the mass/charge ratio. Of crucial importance in the last two factors is the magnetic obliquity of
the shock. The form of the proton-excited hydromagnetic wave spectrum is also important. Finally, more subtle effects on ion
composition arise from the superposition of ion contributions over the time history of the shock along the observer’s magnetic
flux tube, and the sequence of flux tubes sampled by the observer. 相似文献
19.
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
20.
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