共查询到20条相似文献,搜索用时 15 毫秒
1.
D. B. Reisenfeld D. S. Burnett R. H. Becker A. G. Grimberg V. S. Heber C. M. Hohenberg A. J. G. Jurewicz A. Meshik R. O. Pepin J. M. Raines D. J. Schlutter R. Wieler R. C. Wiens T. H. Zurbuchen 《Space Science Reviews》2007,130(1-4):79-86
Analysis of the Genesis samples is underway. Preliminary elemental abundances based on Genesis sample analyses are in good
agreement with in situ-measured elemental abundances made by ACE/SWICS during the Genesis collection period. Comparison of
these abundances with those of earlier solar cycles indicates that the solar wind composition is relatively stable between
cycles for a given type of flow. ACE/SWICS measurements for the Genesis collection period also show a continuum in compositional
variation as a function of velocity for the quasi-stationary flow that defies the simple binning of samples into their sources
of coronal hole (CH) and interstream (IS). 相似文献
2.
Although the elemental composition in all parts of the solar photosphere appears to be the same this is clearly not the case
with the solar upper atmosphere (SUA). Spectroscopic studies show that in the corona elemental composition along solar equatorial
regions is usually different from polar regions; composition in quiet Sun regions is often different from coronal hole and
active region compositions and the transition region composition is frequently different from the coronal composition along
the same line of sight. In the following two issues are discussed. The first involves abundance ratios between the high-FIP
O and Ne and the low-FIP Mg and Fe that are important for meaningful comparisons between photospheric and SUA compositions
and the second involves a review of composition and time variability of SUA plasmas at heights of 1.0≤h≤1.5R
⊙. 相似文献
3.
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
4.
R. A. Leske R. A. Mewaldt C. M. S. Cohen A. C. Cummings E. C. Stone M. E. Wiedenbeck T. T. von Rosenvinge 《Space Science Reviews》2007,130(1-4):195-205
Solar energetic particles (SEPs) provide a sample of the Sun from which solar composition may be determined. Using high-resolution
measurements from the Solar Isotope Spectrometer (SIS) onboard NASA’s Advanced Composition Explorer (ACE) spacecraft, we have
studied the isotopic composition of SEPs at energies ≥20 MeV/nucleon in large SEP events. We present SEP isotope measurements
of C, O, Ne, Mg, Si, S, Ar, Ca, Fe, and Ni made in 49 large events from late 1997 to the present. The isotopic composition
is highly variable from one SEP event to another due to variations in seed particle composition or due to mass fractionation
that occurs during the acceleration and/or transport of these particles. We show that various isotopic and elemental enhancements
are correlated with each other, discuss the empirical corrections used to account for the compositional variability, and obtain
estimated solar isotopic abundances. We compare the solar values and their uncertainties inferred from SEPs with solar wind
and other solar system abundances and find generally good agreement. 相似文献
5.
R. Bodmer P. Bochsler J. Geiss R. von Steiger G. Gloeckler 《Space Science Reviews》1995,72(1-2):61-64
This is the first study of the isotopic composition of solar wind helium with the SWICS time-of flight mass spectrometer. Although the design of SWICS is not optimized to measure3He abundances precisely,4He/3He flux ratios can be deduced from the data. The long term ratio is 2290±200, which agrees with the results obtained with the ICI magnetic mass spectrometer on ISEE-3 and with the Apollo SWC foil experiments.The ULYSSES spacecraft follows a trajectory which is ideal for the study of different solar wind types. During one year, from mid-1992 to mid-1993, it was in a range of heliographic latitudes where a recurrent fast stream from the southern polar coronal hole was observed every solar rotation. Solar wind bulk velocities ranged from 350 km/s to 950 km/s which would, in principle allow us to identify velocity-correlated compositional variations. Our investigation of solar wind helium, however, shows an isotopic ratio which does not depend on the solar wind speed. 相似文献
6.
C. Giammanco P. Bochsler R. Karrer F. M. Ipavich J. A. Paquette P. Wurz 《Space Science Reviews》2007,130(1-4):329-333
Solar chemical abundances are determined by comparing solar photospheric spectra with synthetic ones obtained for different
sets of abundances and physical conditions. Although such inferred results are reliable, they are model dependent. Therefore,
one compares them with the values for the local interstellar medium (LISM). The argument is that they must be similar, but
even for LISM abundance determinations models play a fundamental role (i.e., temperature fluctuations, clumpiness, photon
leaks). There are still two possible comparisons—one with the meteoritic values and the second with solar wind abundances.
In this work we derive a first estimation of the solar wind element ratios of sulfur relative to calcium and magnesium, two
neighboring low-FIP elements, using 10 years of CELIAS/MTOF data. We compare the sulfur abundance with the abundance determined
from spectroscopic observations and from solar energetic particles. Sulfur is a moderately volatile element, hence, meteoritic
sulfur may be depleted relative to non-volatile elements, if compared to its original solar system value. 相似文献
7.
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
8.
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
9.
R. J. Murphy 《Space Science Reviews》2007,130(1-4):127-138
Interactions of ions accelerated in solar flares produce gamma-ray lines and continuum and neutrons. These emissions contain
a rich set of observables that provides information about both the accelerated ions and the environment where the ions are
transported and interact. Ion interactions with the various nuclei present in the ambient medium produce gamma-ray lines at
unique energies. How abundance information is extracted from the measurements is discussed and results from analyses of a
number of solar flares are presented. The analyses indicate that the composition of the ambient gas where the ions interact
(typically at chromospheric densities) is different from that of the photosphere and more like the composition of the corona,
exhibiting low-FIP elemental enhancements that may vary from flare to flare. Evidence for increased Ne/O and the photospheric
3He abundance is also discussed. 相似文献
10.
Understanding properties of solar energetic particle (SEP) events associated with coronal mass ejections has been identified
as a key problem in solar-terrestrial physics. Although recent CME shock acceleration models are highly promising, detailed
agreement between theoretical predictions and observations has remained elusive. Recent observations from ACE have shown substantial
enrichments in the abundances of 3He and He+ ions which are extremely rare in the thermal solar wind plasma. Consequently, these ions act as tracers of their source material,
i.e.,
3He ions are flare suprathermals and He+ ions are interstellar pickup ions. The average heavy ion composition also exhibits unsystematic differences when compared
with the solar wind values, but correlates significantly with the ambient suprathermal material abundances. Taken together
these results provide compelling evidence that CME-driven shocks draw their source material from the ubiquitous but largely
unexplored suprathermal tail rather than from the more abundant solar wind peak. However, the suprathermal energy regime has
many more contributors and exhibits much larger variability than the solar wind, and as such needs to be investigated more
thoroughly. Answers to fundamental new questions regarding the preferred injection of the suprathermal ions, the spatial and
temporal dependence of the various sources, and the causes of their variability and their effects on the SEP properties are
needed to improve agreement between the simulations and observations. 相似文献
11.
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
12.
M. I. Desai G. M. Mason R. E. Gold S. M. Krimigis C. M. S. Cohen R. A. Mewaldt J. E. Mazur J. R. Dwyer 《Space Science Reviews》2007,130(1-4):243-253
Using high-resolution mass spectrometers on board the Advanced Composition Explorer (ACE), we surveyed the event-averaged
∼0.1–60 MeV/nuc heavy ion elemental composition in 64 large solar energetic particle (LSEP) events of cycle 23. Our results
show the following: (1) The Fe/O ratio decreases with increasing energy up to ∼10 MeV/nuc in ∼92% of the events and up to
∼60 MeV/nuc in ∼64% of the events. (2) The rare isotope 3He is greatly enhanced over the corona or the solar wind values in 46% of the events. (3) The heavy ion abundances are not
systematically organized by the ion’s M/Q ratio when compared with the solar wind values. (4) Heavy ion abundances from C–Fe exhibit systematic M/Q-dependent enhancements that are remarkably similar to those seen in 3He-rich SEP events and CME-driven interplanetary (IP) shock events. Taken together, these results confirm the role of shocks
in energizing particles up to ∼60 MeV/nuc in the majority of large SEP events of cycle 23, but also show that the seed population
is not dominated by ions originating from the ambient corona or the thermal solar wind, as previously believed. Rather, it
appears that the source material for CME-associated large SEP events originates predominantly from a suprathermal population
with a heavy ion enrichment pattern that is organized according to the ion’s mass-per-charge ratio. These new results indicate
that current LSEP models must include the routine production of this dynamic suprathermal seed population as a critical pre-cursor
to the CME shock acceleration process. 相似文献
13.
We review recent advances in determining the elemental, charge-state, and isotopic composition of 1 to 20 MeV per nucleon ions in solar energetic particle (SEP) events and outline our current understanding of the nature of solar and interplanetary processes which may explain the observations.The composition within individual SEP events may vary both with time and energy, and will in general be different from that in other SEP events. Average values of relative abundances measured in a large number of SEP events, however, are found to be roughly energy independent in the 1 to 20 MeV per nucleon range, and show a systematic deviation from photospheric abundances which seems to be organized in terms of the first ionization potential of the ion.Direct measurements of the charge states of SEPs have revealed the surprisingly common presence of energetic He+ along with heavy ions with typically coronal ionization states. High-resolution measurements of isotopic abundance ratios in a small number of SEP events show these to be consistent with the universal composition except for the puzzling overabundance of the SEP 22Ne/20Ne relative to this isotopes ratio in the solar wind. The broad spectrum of observed elemental abundance variations, which in their extreme result in composition anomalies characteristic of 3He-rich, heavy-ion rich and carbon-poor SEP events, along with direct measurements of the ionization states of SEPs provide essential information on the physical characteristics of, and conditions in the source regions, as well as important constraints to possible models for SEP production.It is concluded that SEP acceleration is a two-step process, beginning with plasma-wave heating of the ambient plasma in the lower corona, which may include pockets of cold material, and followed by acceleration to the observed energies by either flare-generated coronal shocks or Fermi-type processes in the corona. Interplanetary propagation as well as acceleration by interplanetary propagating shock will often further modify the composition of SEP events, especially at lower energies. 相似文献
14.
R. Karrer P. Bochsler C. Giammanco F. M. Ipavich J. A. Paquette P. Wurz 《Space Science Reviews》2007,130(1-4):317-321
Using the Mass Time-of-Flight Spectrometer (MTOF)—part of the Charge, Elements, Isotope Analysis System (CELIAS)—onboard the
Solar Heliospheric Observatory (SOHO) spacecraft, we derive the nickel isotopic composition for the isotopes with mass 58,
60 and 62 in the solar wind. In addition we measure the elemental abundance ratio of nickel to iron. We use data accumulated
during ten years of SOHO operation to get sufficiently high counting statistics and compare periods of different solar wind
velocities. We compare our values with the meteoritic ratios, which are believed to be a reliable reference for the solar
system and also for the solar outer convective zone, since neither element is volatile and no isotopic fractionation is expected
in meteorites. Meteoritic isotopic abundances agree with the terrestrial values and can thus be considered to be a reliable
reference for the solar isotopic composition. The measurements show that the solar wind elemental Ni/Fe-ratio and the isotopic
composition of solar wind nickel are consistent with the meteoritic values. This supports the concept that low-FIP elements
are fed without relative fractionation into the solar wind. Our result also confirms the absence of substantial isotopic fractionation
processes for medium and heavy ions acting in the solar wind. 相似文献
15.
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
16.
Robert F. Wimmer-Schweingruber Rudolf Von Steiger Johannes Geiss George Gloeckler Fred M. Ipavich Berend Wilken 《Space Science Reviews》1998,85(1-2):387-396
Recent observations with UVCS on SOHO of high outflow velocities of O5+ at low coronal heights have spurred much discussion about the dynamics of solar wind acceleration. On the other hand, O6+ is the most abundant oxygen charge state in the solar wind, but is not observed by UVCS or by SUMER because this helium-like
ion has no emission lines falling in the wave lengths observable by these instruments. Therefore, there is considerable interest
in observing O5+ in situ in order to understand the relative importance of O5+ with respect to the much more abundant O6+. High speed streams are the prime candidates for the search for O5+ because all elements exhibit lower freezing-in temperatures in high speed streams than in the slow solar wind. The Ulysses
spacecraft was exposed to long time periods of high speed streams during its passage over the polar regions of the Sun. The
Solar Wind Ion Composition Spectrometer (SWICS) on Ulysses is capable of resolving this rare oxygen charge state. We present
the first measurement of O5+ in the solar wind and compare these data with those of the more abundant oxygen species O6+ and O7+. We find that our observations of the oxygen charge states can be fitted with a single coronal electron temperature in the
range of 1.0 to 1.2 MK assuming collisional ionization/recombination equilibrium with an ambient Maxwellian electron gas.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
17.
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
18.
19.
The kinetic properties of heavy ions in the solar wind are known to behave in a well organized way under most solar wind flow conditions: Their speeds are all equal and faster than that of hydrogen by about the local Alfvén speed, and their kinetic temperatures are proportional to their mass. The simplicity of these properties points to a straightforward physical interpretation; wave-particle interactions with Alfvén waves are the probable cause. With the SWICS sensor on board Ulysses, it is now possible to investigate the kinetic properties of many more ion species than before. Furthermore, the transition of Ulysses into the fast stream emanating from the south polar coronal hole since 1992 allows us to study these properties both in the slow, interstream solar wind, as well as in an unambiguously identified fast stream. We present data from SWICS/Ulysses on the dominant ions of He, C, O, Ne, and Mg. As a result we find that, both in the slow wind and in fast streams, the isotachic property is obeyed even better than it could be determined by the ICI instrument on ISEE-3. The mass proportionality ofT
kin is also shown to hold for these ions, including the newly identified C and Mg. 相似文献
20.
The Sun is the largest reservoir of matter in the solar system, which formed 4.6 Gyr ago from the protosolar nebula. Data
from space missions and theoretical models indicate that the solar wind carries a nearly unfractionated sample of heavy isotopes
at energies of about 1 keV/amu from the Sun into interplanetary space. In anticipation of results from the Genesis mission’s
solar-wind implanted samples, we revisit solar wind isotopic abundance data from the high-resolution CELIAS/MTOF spectrometer
on board SOHO. In particular, we evaluate the isotopic abundance ratios 15N/14N, 17O/16O, and 18O/16O in the solar wind, which are reference values for isotopic fractionation processes during the formation of terrestrial planets
as well as for the Galactic chemical evolution. We also give isotopic abundance ratios for He, Ne, Ar, Mg, Si, Ca, and Fe
measured in situ in the solar wind. 相似文献