共查询到20条相似文献,搜索用时 15 毫秒
1.
R. Von Steiger 《Space Science Reviews》1998,85(1-2):407-418
This rapporteur paper discusses the solar corona and the solar wind in the context of their chemical composition. The abundances of elements, both obtained by optical and by in situ observations, are used to infer the sources of the slow solar wind and of the fast streams. The first ionisation potential (FIP) fractionation effect is also discussed, in particular the agreed basics and the open questions. This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
2.
Douglas Gough 《Space Science Reviews》1998,85(1-2):141-158
Standard solar models, although they are free from the influence of much of the fluid motion that is bound to be present in the Sun, have been shown by helioseismology to represent the spherically averaged structure of the Sun amazingly well. This state of affairs has come about after painstaking refinements by a great many people of the pertinent microphysics, including that which controls the equation of state, the opacity, the nuclear reaction rates and the diffusion that inhibits gravitational segregation of chemical elements. It has instilled confidence in the modellers in being able to predict the composition of the solar interior. But there are consequences of the flow, related particularly to redistribution of chemical species, that can be difficult to identify observationally, yet which may degrade any inferences we might make. Their potential presence must at least be acknowledged by anyone who tries to asses the reliability of the models. This report summarizes the discussions in the preceding pages of this volume of the current theoretical and observational status of the subject, pointing to many of the caveats that have been raised, and attempting at the same time to put them into a seemingly coherent discourse in the context of our present understanding of the workings of the solar interior. This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
3.
This paper studies the response of the middle atmosphere to the 11-year solar cycle. The study is based on numerical simulations
with the Hamburg Model of the Neutral and Ionized Atmosphere (HAMMONIA), a chemistry climate model that resolves the atmosphere
from the Earth’s surface up to about 250 km. Results presented here are obtained in two multi-year time-slice runs for solar
maximum and minimum conditions, respectively. The magnitude of the simulated annual and zonal mean stratospheric response
in temperature and ozone corresponds well to observations. The dynamical model response is studied for northern hemisphere
winter. Here, the zonal mean wind change differs substantially from observations. The statistical significance of the model’s
dynamical response is, however, poor for most regions of the atmosphere. Finally, we discuss several issues that render the
evaluation of model results with available analyses of observational data of the stratosphere and mesosphere difficult. This
includes the possibility that the atmospheric response to solar variability may depend strongly on longitude. 相似文献
4.
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
5.
L. J. Gray S. A. Crooks M. A. Palmer C. L. Pascoe S. Sparrow 《Space Science Reviews》2006,125(1-4):357-370
Observational evidence of the 11-year solar cycle (SC) modulation of stratosphere temperatures and winds from the ERA-40 dataset
is reviewed, with emphasis on the Northern winter hemisphere. A frequency modulation of sudden warming events is noted, with
warmings occurring earlier in solar minimum periods than in solar maximum periods. The observed interaction between the influence
of the SC and the quasi biennial oscillation (QBO) on the frequency of sudden warmings is noted as a possible clue for understanding
their mechanism of influence. A possible transfer route for the 11-year solar cycle from the equatorial stratopause region
to the lowest part of the stratosphere is proposed, via an influence on sudden warming events and the associated induced meridional
circulation. SC and QBO composites of zonal wind anomalies show anomalous wind distributions in the subtropical upper stratosphere
in early winter. Mechanistic model experiments are reviewed that demonstrate a sensitivity of sudden warmings to small wind
anomalies in this region. Various diagnostics from these experiments are shown, including EP fluxes and their divergence and
also the synoptic evolution of the polar vortex, in order to understand the mechanism of the influence. Some recent GCM experiments
to investigate the SC/QBO interaction are also described. They simulate reasonably well the observed SC/QBO interaction of
sudden warming events and appear to support the hypothesis that tropical/subtropical upper stratospheric wind anomalies are
an important influence on the timing of sudden warmings. 相似文献
6.
J. C. Raymond 《Space Science Reviews》1999,87(1-2):55-66
Order of magnitude variations in relative elemental abundances are observed in the solar corona and solar wind. The instruments
aboard SOHO make it possible to explore these variations in detail to determine whether they arise near the solar surface
or higher in the corona. A substantial enhancement of low First Ionization Potential (FIP) elements relative to high FIP elements
is often seen in both the corona and the solar wind, and that must arise in the chromosphere. Several theoretical models have
been put forward to account for the FIP effect, but as yet even the basic physical mechanism responsible remains an open question.
Evidence for gravitational settling is also found at larger heights in quiescent streamers. The question is why the heavier
elements don't settle out completely.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
7.
M.-L Chanin 《Space Science Reviews》2006,125(1-4):261-272
In the last 45 years I have studied the thermal structure of the atmosphere from the thermosphere down to the stratosphere,
and found evidence of its variability in relationship with the change of solar irradiation during the 11-year solar cycle.
I would review, in the light of recent model results, the measurements which I had made since the 1960s and which, for some
of them, did not find any explanation at the time of their publication. The data were obtained by two different techniques,
rockets and lidars and correspond to different regions of the atmosphere from the upper thermosphere to the stratosphere.
The expectation was until recently that the atmosphere should be warmed by an increase of solar flux in the course of the
solar cycle due to the increase of UV flux. It has been shown to be the case in the tropical stratosphere and at all latitudes
in the upper thermosphere. But, at high and mid latitudes and at other altitudes, the reverse situation was found to exist
and, until recently, this cooling observed in parts of the atmosphere with increasing solar flux had never been simulated
by models. In addition to reviewing our own data, the paper will present recent results using other dataset which support
our observations. It is only recently that we succeeded with a model able to tune the forcing by planetary waves at the tropopause
level and thus reproduce such behaviour. 相似文献
8.
The interaction of the solar wind with the Martian exosphere and ionosphere leads to significant loss of atmosphere from the
planet. Spacecraft data confirm that this is the case. However, the issue is how much is actually lost. Given that spacecraft
coverage is sparse, simulation is one of the few ways for these estimates to be made. In this paper the evolution of our attempts
to place bounds on this loss rate will be addressed. Using a hybrid particle code the loss rate with respect to solar EUV
flux is addressed as well as a variety of numerical and chemical issues. The progress made has been of an evolutionary nature,
with one approach tried and tested followed by another as the simulations are improved and better estimates are produced.
The results to be reported suggest that the ion loss rates are high enough to explain the loss of water from Mars during earlier
solar epochs. 相似文献
9.
Jeongwoo Lee 《Space Science Reviews》2007,133(1-4):73-102
Solar active region coronae are known for strong magnetic fields permeating tenuous plasma, which makes them an ideal astronomical
laboratory for magnetohydrodynamics research. It is, however, relatively less known that this physical condition also permits
a very efficient radiation mechanism, gyro-resonant emission, produced by hot electrons gyrating in the coronal magnetic field.
As a resonant mechanism, gyro-emission produces high enough opacity to fully reveal the coronal temperature, and is concentrated
at a few harmonics of the local gyrofrequency to serve as an excellent indicator of the magnetic field. In addition, the polarization
of the ubiquitous free–free emission and a phenomenon of depolarization due to mode coupling extend the magnetic field diagnostic
to a wide range of coronal heights. The ability to measure the coronal temperature and magnetic field without the complications
that arise in other radiative inversion problems is a particular advantage for the active region radio emissions available
only at these wavelengths. This article reviews the efforts to understand these radiative processes, and use them as diagnostic
tools to address a number of critical issues involved with active regions. 相似文献
10.
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
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.
从工程实际出发对工程上常用的聚光器进行性能比较,可以得出适合太阳能火箭发动机(STP)的聚光器及其具有的性能优点。在研究此种聚光器设计方法的过程中,推导出相关公式和其中的关键技术,这对STP聚光器的工程设计具有重要的指导价值。 相似文献
13.
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
14.
SOHO: The Solar and Heliospheric Observatory 总被引:1,自引:0,他引:1
The Solar and Heliospheric Observatory (SOHO), together with the Cluster mission, constitutes ESA's Solar Terrestrial Science Programme (STSP), the first Cornerstone of the Agency's long-term programme Space Science — Horizon 2000. STSP, which is being developed in a strong collaborative effort with NASA, will allow comprehensive studies to be made of the both the Sun's interior and its outer atmosphere, the acceleration and propagation of the solar wind and its interaction with the Earth. This paper gives a brief overview of one part of STSP, the SOHO mission. 相似文献
15.
Magneto-gravity Waves Trapped in the Lower Solar Corona 总被引:1,自引:0,他引:1
Yu-Qing Lou 《Space Science Reviews》1999,87(1-2):261-264
The possibility of trapped magneto-gravity waves in the lower solar corona with an open magnetic field is discussed. Intensity variations and/or Doppler shifts of relevant UV, EUV and x-ray spectral lines in the chromosphere, transition region and lower corona may reveal the existence of such low-frequency modes (with periods longer than ∼ 1.5 hour). The spectrum may be either discrete or continuous depending on the reflection property of the narrow transition region. These modes can be utilized to probe the dynamics of the upper chromosphere, transition region and lower corona; they may also play an important role in coronal heating. This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
16.
The solar wind charge state and elemental compositions have been measured with the Solar Wind Ion Composition Spectrometers
(SWICS) on Ulysses and ACE for a combined period of about 25 years. This most extensive data set includes all varieties of
solar wind flows and extends over more than one solar cycle. With SWICS the abundances of all charge states of He, C, N, O,
Ne, Mg, Si, S, Ar and Fe can be reliably determined (when averaged over sufficiently long time periods) under any solar wind
flow conditions. Here we report on results of our detailed analysis of the elemental composition and ionization states of
the most unbiased solar wind from the polar coronal holes during solar minimum in 1994–1996, which includes new values for
the abundance S, Ca and Ar and a more accurate determination of the 20Ne abundance. We find that in the solar minimum polar coronal hole solar wind the average freezing-in temperature is ∼1.1×106 K, increasing slightly with the mass of the ion. Using an extrapolation method we derive photospheric abundances from solar
wind composition measurements. We suggest that our solar-wind-derived values should be used for the photospheric ratios of
Ne/Fe=1.26±0.28 and Ar/Fe=0.030±0.007. 相似文献
17.
Klaus Wilhelm Eckart Marsch Bhola N. Dwivedi Uri Feldman 《Space Science Reviews》2007,133(1-4):103-179
In Part I of this review, the concepts of solar vacuum-ultraviolet (VUV) observations were outlined together with a discussion
of the space instrumentation used for the investigations. A section on spectroradiometry provided some quantitative results
on the solar VUV radiation without considering any details of the solar phenomena leading to the radiation. Here, in Part
II, we present solar VUV observations over the last decades and their interpretations in terms of the plasma processes and
the parameters of the solar atmosphere, with emphasis on the spatial and thermal structures of the chromosphere, transition
region and corona of the quiet Sun. In addition, observations of active regions, solar flares and prominences are included
as well as of small-scale events. Special sections are devoted to the elemental composition of the solar atmosphere and theoretical
considerations on the heating of the corona and the generation of the solar wind. 相似文献
18.
The space-based Solar and Heliospheric Observatory (SOHO) is a joint venture of ESA and NASA within the frame of the Solar Terrestrial Science Programme (STSP), the first Cornerstone of ESA's long-term programme Space Science — Horizon 2000. The principal scientific objectives of the SOHO mission are: a) a better understanding of the structure and dynamics of the solar interior using techniques of helioseismology, and b) a better insight into the physical processes that form and heat the Sun's corona, maintain it and give rise to its acceleration into the solar wind. To achieve these goals, SOHO carries a payload consisting of 12 sets of complementary instruments which are briefly described here. 相似文献
19.
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
20.
Johannes Geiss is a world leader and foremost expert on measurements and interpretation of the composition of matter that
reveals the history, present state, and future of astronomical objects. With his Swiss team he was first to measure the composition
of the noble gases in the solar wind when in the late 1960s he flew the brilliant solar wind collecting foil experiments on
the five Apollo missions to the moon. Always at the forefront of the art of composition measurements, he with his colleagues
determined the isotopic and elemental composition of the solar wind using instruments characterized by innovative design that
have provided the most comprehensive record of the solar wind composition under all solar wind conditions at all helio-latitudes.
He discovered heavy interstellar pickup ions, from which the composition of the neutral gas of the Local Interstellar Cloud
is determined, and the “Inner Source” of pickup ions. Johannes Geiss played a key role both in the in-situ measurements and
modeling of molecular ions in comets, and the interpretation of these data. He and co-workers measured the composition of
plasmas in the magnetospheres of Earth and Jupiter. Here we highlight Johannes Geiss’ many discoveries and seminal contributions
to our knowledge of the composition of matter of the Sun, solar wind, interstellar gas, early universe, comets and magnetospheres. 相似文献