共查询到20条相似文献,搜索用时 812 毫秒
1.
This paper reviews solar flows and magnetic fields observed at the photospheric level. We first present the context in which these observations are performed. We describe the various temporal and spatial scales involved, and the coupling between them. Then we present small-scale flows, mainly supergranulation and flows around active regions. Flows at the global scale are then reviewed, again with emphasis on the flows, i.e. differential rotation, torsional oscillation and meridional circulation. In both small- and global-scale we discuss the coupling between flow fields and magnetic field and give an overview of observational techniques. Finally, the possible connection between studies of solar activity and stellar activity is briefly discussed. 相似文献
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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
4.
We discuss the important parameters of solar neutron and proton emissions that can be determined by measurements with neutron
monitors at the Earth. First, the methods of analysis for solar neutron events detected by neutron monitors are presented.
Illustrations are given to show how these measurements can be used to understand the physics of the neutron production at
the Sun. Second, the analytical methods for high-energy interplanetary solar proton events are presented. We then indicate
how these observations of interplanetary solar protons can be used to infer the proton acceleration mechanisms at or near
the Sun.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
5.
L. F. Burlaga 《Space Science Reviews》1984,39(3-4):255-316
Conclusion Much has been learned about the structure and dynamics of the outer heliosphere during the last decade as a result observations from the Voyager and Pioneer spacecraft. The large scale of the observations forces one to consider the heliosphere from a new perspective, to think of new dynamical processes, and to introduce new concepts. The early studies of isolated gas dynamic flows must be replaced by MHD dynamics of interacting flows and flow systems. The simple deterministic models that have been dominant in early studies of the solar wind are now seen to have limited applicability, and statistical approaches are being developed. New concepts that have been introduced, such as inverse cascades, filtering, entrainment, etc., must be further explored and clarified, to make them more precise and quantitative. MHD turbulence is probably very important in solar wind dynamics, but the subject is poorly developed from a theoretical point of view. The statistical analysis of solar wind parameters has scarcely begun, but it is clearly necessary for an understanding of complex, large-scale flows. The multitude of possible interactions among shocks and flows of various types needs to be explored systematically with observations, models and analytical theory. Voyagers 1 and 2 and Pioneers 10 and 11 are continuing to move through the outer heliosphere and gather data. The lengthy data reduction procedures require even more care in dealing with the low field strengths, densities and temperatures at large heliocentric distances, and the analysis of the complex flows and fields in the outer heliosphere becomes increasingly difficult. Thus one can expect continued growth of our knowledge of the heliosphere, but comprehensive understanding of the data will take some time. If this review stimulates the specialists in solar wind physics to think critically about the results presented and to remedy the deficiencies of current knowledge of the heliosphere, then it will have served its purpose. It is also hoped that this review will serve to encourage specialists in other fields to bring their talents to bear on heliospheric problems and to transfer results of heliospheric physics to their fields. 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.
D. Ryu D. R. G. Schleicher R. A. Treumann C. G. Tsagas L. M. Widrow 《Space Science Reviews》2012,166(1-4):1-35
Magnetic fields appear to be ubiquitous in astrophysical environments. Their existence in the intracluster medium is established through observations of synchrotron emission and Faraday rotation. On the other hand, the nature of magnetic fields outside of clusters, where observations are scarce and controversial, remains largely unknown. In this chapter, we review recent developments in our understanding of the nature and origin of intergalactic magnetic fields, and in particular, intercluster fields. A plausible scenario for the origin of galactic and intergalactic magnetic fields is for seed fields, created in the early universe, to be amplified by turbulent flows induced during the formation of the large scale structure. We present several mechanisms for the generation of seed fields both before and after recombination. We then discuss the evolution and role of magnetic fields during the formation of the first starts. We describe the turbulent amplification of seed fields during the formation of large scale structure and the nature of the magnetic fields that arise. Finally, we discuss implications of intergalactic magnetic fields. 相似文献
8.
The importance of spectroscopy in the 80–800 å region for plasma diagnostics in the solar atmosphere
We discuss the importance of the spectral range from about 80 to 800 Å for determining physical conditions in different regions of the solar atmosphere. We give examples of line ratios that may be used to determine electron densities in quiet Sun regions, active regions, and flares. We discuss the possibility of determining electron temperatures from line ratios in the EUV.We show that profiles as well as intensities of spectral lines must be obtained for a proper interpretation of the spectra. We give approximate parameters for a solar grazing incidence spectrograph suitable for the study of the 80–800 Å wavelength region.Given as an invited review paper at the EGAS Meeting in Munich, Germany, 11–14 July 1978. 相似文献
9.
Syun-Ichi Akasofu 《Space Science Reviews》2011,164(1-4):85-132
The concept of geomagnetic storm-producing solar plasma flows has evolved and advanced considerably over the last 100 years or so. This particular field of study began in an effort to understand geomagnetic disturbances and the aurora. The purpose of this paper is try to follow the ways in which early concepts evolved to later ones, not to review each concept in detail. It is fascinating to see a step-by-step buildup of these concepts, from the earliest idea of flow of solar electrons to coronal mass ejections (CMEs). The time line, though tentative, of the studies of geomagnetic storm-producing plasma flows is presented. The author hopes that this paper will serve young researchers in particular to consider how they plan to advance further this scientific field. There is still much uncertainty about geomagnetic storm-producing solar plasma flows. Some of the major questions are listed from the point of view of a geophysicist in the summary sections by grouping them in terms of the quiet-time solar wind, solar streams from corona holes and CMEs associated with solar flares. 相似文献
10.
Rumi Nakamura 《Space Science Reviews》2006,124(1-4):91-101
Consequences of the solar wind input observed as large scale magnetotail dynamics during substorms are reviewed, highlighting
results from statistical studies as well as global magnetosphere/ionosphere observations. Among the different solar wind input
parameters, the most essential one to initiate reconnection relatively close to the Earth is a southward IMF or a solar wind
dawn-to-dusk electric field. Larger substorms are associated with such reconnection events closer to the Earth and the magnetotail
can accumulate larger amounts of energy before its onset. Yet, how and to what extent the magnetotail configuration before
substorm onset differs for different solar wind driver is still to be understood. A strong solar wind dawn-to-dusk electric
field is, however, only a necessary condition for a strong substorm, but not a sufficient one. That is, there are intervals
when the solar wind input is processed in the magnetotail without the usual substorm cycle, suggesting different modes of
flux transport. Furthermore, recent global observations suggest that the magnetotail response during the substorm expansion
phase can be also controlled by plasma sheet density, which is coupled to the solar wind on larger time-scales than the substorm
cycle. To explain the substorm dynamics it is therefore important to understand the different modes of energy, momentum, and
mass transport within the magnetosphere as a consequence of different types of solar wind-magnetosphere interaction with different
time-scales that control the overall magnetotail configuration, in addition to the internal current sheet instabilities leading
to large scale tail current sheet dissipation. 相似文献
11.
We present preliminary results from high resolution observations obtained with the Michelson Doppler Imager (MDI) instrument
on the SOHO of two large solar flares of 14 July 2000 and 24 November 2000. We show that rapid variations of the line-of-sight
magnetic field occured on a time scale of a few minutes during the flare explosions. The reversibility/irreversibility of
the magnetic field of both active regions is a very good tool for understanding how the magnetic energy is released in these
flares. The observed sharp increase of the magnetic energy density at the time of maximum of the solar flare could involve
an unknown component which deposited supplementary energy into the system.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
12.
Semenov Vladimir S. Kubyshkin Igor V. Kiendl Michael T. Biernat Helfried K. Rijnbeek Richard P. Besser Bruno P. 《Space Science Reviews》1997,82(3-4):451-461
In this article we address several criticisms of Petschek-type reconnection models which have recently been raised by Heikkila. We discuss features of the time-dependent Petschek-type models in the context of the solar wind-magnetosphere interaction, and point out that such models can incorporate and reproduce observed features at the magnetopause, such as plasma jets and erosion of the current sheet. We argue that some of Heikkila's criticisms can be attributed to weaknesses in the analysis due to incomplete experimental information, rather than to flaws in the concept of reconnection per se; in this category we include the question of which instability leads to the localised breakup of the magnetopause current sheet. Other criticisms are based on an adherence to steady-state models, and cannot be sustained within the extended time-dependent theory. We discuss, for example, how the time-dependent model can provide a consistent picture of how energy from the incoming solar wind is transferred and converted as it enters the magnetosphere. 相似文献
13.
D. J. McComas J. L. Phillips S. J. Bame J. T. Gosling B. E. Goldstein M. Neugebauer 《Space Science Reviews》1995,72(1-2):93-98
In the 25 months since Jupiter flyby, the Ulysses spacecraft has climbed southward to a heliolatitude of 56°. This transit has been marked by an evolution from slow, dense coronal streamer belt solar wind through two regions where the rotation of the Sun carried Ulysses back and forth between streamer belt and polar coronal hole flows, and finally into a region of essentially continuous fast, low density solar wind from the southern polar coronal hole. Throughout these large changes, the momentum flux normalized to 1 AU displays very little systematic variation. In addition, the bulk properties of the polar coronal hole solar wind are quite similar to those observed in high speed streams in the ecliptic plane at 1 AU. Coronal mass ejections and forward and reverse shocks associated with corotating interaction regions have also been observed at higher heliolatitudes, however they are seen less frequently with increasing southern heliolatitude. Ulysses has thus far collected data from 20° of nearly contiguous solar wind flows from the polar coronal hole. We examine these data for characteristic variations with heliolatitude and find that the bulk properties in general show very little systematic variation across the southern polar coronal hole so far. 相似文献
14.
J. Büchner 《Space Science Reviews》2006,124(1-4):345-360
Reconnection is a major commonality of solar and magnetospheric physics. It was conjectured by Giovanelli in 1946 to explain
particle acceleration in solar flares near magnetic neutral points. Since than it has been broadly applied in space physics
including magnetospheric physics. In a special way this is due to Harry Petschek, who in 1994 published his ground breaking
solution for a 2D magnetized plasma flow in regions containing singularities of vanishing magnetic field. Petschek’s reconnection
theory was questioned in endless disputes and arguments, but his work stimulated the further investigation of this phenomenon
like no other. However, there are questions left open. We consider two of them – “anomalous” resistivity in collisionless
space plasma and the nature of reconnection in three dimensions. The CLUSTER and SOHO missions address these two aspects of
reconnection in a complementary way -- the resistivity problem in situ in the magnetosphere and the 3D aspect by remote sensing of the Sun. We demonstrate that the search for answers to both questions
leads beyond the applicability of analytical theories and that appropriate numerical approaches are necessary to investigate
the essentially nonlinear and nonlocal processes involved. Necessary are both micro-physical, kinetic Vlasov-equation based
methods of investigation as well as large scale (MHD) simulations to obtain the geometry and topology of the acting fields
and flows. 相似文献
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Szegö Károly Glassmeier Karl-Heinz Bingham Robert Bogdanov Alexander Fischer Christian Haerendel Gerhard Brinca Armando Cravens Tom Dubinin Eduard Sauer Konrad Fisk Len Gombosi Tamas Schwadron Nathan Isenberg Phil Lee Martin Mazelle Christian Möbius Eberhard Motschmann Uwe Shapiro Vitali D. Tsurutani Bruce Zank Gary 《Space Science Reviews》2000,94(3-4):429-671
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E. Nielsen H. Zou D. A. Gurnett D. L. Kirchner D. D. Morgan R. Huff R. Orosei A. Safaeinili J. J. Plaut G. Picardi 《Space Science Reviews》2006,126(1-4):373-388
The Martian ionosphere has for the first time been probed by a low frequency topside radio wave sounder experiment (MARSIS)
(Gurnett et al., 2005). The density profiles in the Martian ionosphere have for the first time been observed for solar zenith angles less
than 48 degrees. The sounder spectrograms typically have a single trace of echoes, which are controlled by reflections from
the ionosphere in the direction of nadir. With the local density at the spacecraft derived from the sounder measurements and
using the lamination technique the spectrograms are inverted to electron density profiles. The measurements yield electron
density profiles from the sub-solar region to past the terminator. The maximum density varies in time with the solar rotation
period, indicating control of the densities by solar ionizing radiation. Electron density increases associated with solar
flares were observed. The maximum electron density varies with solar zenith angle as predicted by theory. The altitude profile
of electron densities between the maximum density and about 170m altitude is well approximated by a classic Chapman layer.
The neutral scale height is close to 10 to 13 km. At altitudes above 180 km the densities deviate from and are larger than
inferred by the Chapman layer. At altitudes above the exobase the density decrease was approximated by an exponential function
with scale heights between 24 and 65 km. The densities in the top side ionosphere above the exobase tends to be larger than
the densities extrapolated from the Chapman layer fitted to the measurements at lower altitudes, implying more efficient upward
diffusion above the collision dominated photo equilibrium region. 相似文献
19.
We discuss the degree to which radio propagation measurements diagnose conditions in the ionized gas of the interstellar medium (ISM). The “signal generators” of the radio waves of interest are extragalactic radio sources (quasars and radio galaxies), as well as Galactic sources, primarily pulsars. The polarized synchrotron radiation of the Galactic non-thermal radiation also serves to probe the ISM, including space between the emitting regions and the solar system. Radio propagation measurements provide unique information on turbulence in the ISM as well as the mean plasma properties such as density and magnetic field strength. Radio propagation observations can provide input to the major contemporary questions on the nature of ISM turbulence, such as its dissipation mechanisms and the processes responsible for generating the turbulence on large spatial scales. Measurements of the large scale Galactic magnetic field via Faraday rotation provide unique observational input to theories of the generation of the Galactic field. 相似文献
20.
Stefano Ettori Annamaria Donnarumma Etienne Pointecouteau Thomas H. Reiprich Stefania Giodini Lorenzo Lovisari Robert W. Schmidt 《Space Science Reviews》2013,177(1-4):119-154
We review the methods adopted to reconstruct the mass profiles in X-ray luminous galaxy clusters. We discuss the limitations and the biases affecting these measurements and how these mass profiles can be used as cosmological proxies. 相似文献