共查询到20条相似文献，搜索用时 15 毫秒
1.
R. Grant Athay 《Solar physics》1973,29(2):357-364
Mean density models of the solar corona show evidence for two distinctive density regimes characterized by different density gradients. High density gradients are identified with regions of predominantly open magnetic lines of force and low density gradients are identified with regions of predominantly closed magnetic lines of force. Spectroscopic data yielding equivalent widths of forbidden lines of Fe x and Fe xiv strongly suggest that the coronal temperature for r > 2.5 R
decreases considerably less rapidly in equatorial regions than r
–2/7, which is the decrease predicted by conduction models with open field lines.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
2.
Energetic charged particles, which are often observed in solar active regions, may be also produced in interplanetary space due to the decoupling of ions and electrons in plasma. The Hall term in general Ohm's law is generally thought to be responsible for the decoupling of electrons and ions in plasma during magnetic reconnection. In this paper, a Hall MHD model is developed to study energetic charged particle events produced during fluctuations in the interplanetary magnetic field intensity. Two energetic charged particle events are used to test this model. It is concluded that the Hall effect does not only play the important role in the process of magnetic reconnection, but also in energetic charged particle events produced during fluctuations in the interplanetary magnetic field intensity. 相似文献
3.
W. Köhnlein 《Astrophysics and Space Science》1996,245(1):81-88
Long-term variations of solar wind parameters at 1 AU are correlated with sunspots for the time interval 1973 to 1993 (solar cycles 21, 22). Using theNear-Earth Heliosphere Data OMNI the plasma density, the magnitude of the interplanetary magnetic field, the solar wind velocity and the solar wind temperature show consistent long-term variations in each cycle (21 and 22) — pointing to specifictime-lags in the coupling between sunspots (and the underlying convection zone), the solar corona and the solar wind parameters at 1 AU (ecliptic). 相似文献
4.
S. Serio G. S. Vaiana G. Godoli S. Motta V. Pirronello R. A. Zappala' 《Solar physics》1978,59(1):65-86
We have analyzed X-ray images of the solar corona obtained by the S-054 telescope on Skylab, together with H filtergrams from the Catania Astrophysical Observatory and EUV and magnetic data, to study the morphology and the evolution of the coronal structures associated with prominences (coronal cavities).X-ray cavities are associated with prominences and are enclosed by series of loops of hot plasma typically higher than 5 × 109 cm. Helmet streamers can be observed only at very large heights (> 1 solar radius). The cavities show a higher luminosity when prominences have temporarily disappeared. The density in one of these X-ray cavities ( 3 × 108cm–3) is insufficient to allow formation of dense ( 1011 cm–3) prominences by local condensation from the corona.Prominences associated with young (up to three solar rotations) and old (greater than eight) magnetic neutral lines are significantly less stable than those associated with middle-aged neutral lines. Downward bending of the top of the inner magnetic loop, necessary in some models of prominences, is not detected in these X-ray observations. The relevance of these results to models of prominence formation is discussed.Presently at Osservatorio Astrofisico di Arcetri, Firenze, Italy. 相似文献
5.
C. T. Stelzried G. S. Levy T. Sato W. V. T. Rusch J. E. Ohlson K. H. Schatten J. M. Wilcox 《Solar physics》1970,14(2):440-456
Pioneer VI was launched into a circumsolar orbit on December 16, 1965, and was occulted by the sun in the latter half of November, 1968. During the occultation period, the 2292-MHz S-band telemetry carrier underwent Faraday rotation due to the interaction of this signal with the plasma and magnetic field in the solar corona. The NASA/JPL 210-ft diameter antenna of the Deep Space Network near Barstow, California, was used for the measurement. The antenna feed was modified for automatic polarization tracking for this experiment. The measurement results are interpreted with a theoretical model of the solar corona. This model consists of a modified Allen-Baumbach electron density and a coronal magnetic field calculated both from Mount Wilson magnetograph observations using a source surface model and field extrapolations from the Explorer 33 satellite magnetometer. The observations and the calculated rotation show general agreement with respect to magnitude, sense, and timing, suggesting the source-surface model and field extrapolations from 1 AU are a valid technique to obtain the magnetic field in the corona from 4 to 12 solar radii. Variations present can easily be ascribed to density enhancements known to be present in the corona. Longitudinal variations of the density in the corona cannot be obtained from coronagraph observations, and thus a purely radial variation was assumed. An improved fit to the Faraday rotation data is obtained with an equatorial electron density $$N = 10^8 \left( {\frac{{6000}}{{R^{10} }} + \frac{{0.002}}{{R^2 }}} \right)...{\text{ cm}}^{{\text{ - 3}}} {\text{ (4 < }}R < 12){\text{ }}...$$ where R is in solar radii. The work of W. V. T. Rusch and J. E. Ohlson was supported in part by research sponsored by the Joint Services Electronics Program through the Air Force Office of Scientific Research under Grant AF-AFOSR 69-1622A at the University of Southern California. The work done by K. H. Schatten was in part supported by the National Academy of Science on a National Research Council postdoctoral fellowship. The work of J. M. Wilcox was supported in part by the Office of Naval Research under Contract Nonr 3656(26), by the National Aeronautics and Space Administration under Grant NGR 05-003-230, and by the National Science Foundation under Grant GA-1319 at the University of California at Berkeley. 相似文献
6.
We describe a general method for inferring, from the line emission of an optically thin medium, the physical state of the gas along the column in the line of sight which is sampled by the observations. Since it is not possible to infer the distribution of the physical state parameters with position in the line of sight - any arbitrary rearrangement of material giving equivalent line emission - we seek instead to specify the state in another way. A unique specification is found in terms of the bivariate distribution function (n, T), describing the partitioning of the matter in the gas over the density and temperature. We show that, given sufficient observational data, it is in principle possible to determine both (n, T), and the chemical composition. With less complete data the acuity of the analysis is correspondingly reduced.The method is devised for application to the astronomical case, especially for studies of the solar corona, the chromosphere-corona transition region, planetary nebulae and other optically thin sources. We illustrate the formulation for the situation encountered in the solar corona.Presently on leave of absence from the Institute for Astronomy, University of Hawaii.The National Center for Atmospheric Research is sponsored by the National Science Foundation.John Simon Guggenheim Memorial Fellow, 1970.Of the National Bureau of Standards and the University of Colorado. 相似文献
7.
Spectroheliograms obtained in extreme ultraviolet (EUV) lines and the Lyman continuum are used to determine the rotation rate of the solar chromosphere, transition region, and corona. A cross-correlation analysis of the observations indicates the presence of differential rotation through the chromosphere and transition region. The rotation rate does not vary with height. The average sidereal rotation rate is given by (deg day–1) = 13.46 - 2.99 sin2
B where B is the solar latitude. This rate agrees with spectroscopic determinations of the photospheric rotation rate, but is slower by 1 deg day–1) = 13.46 - 2.99 sin2 than rates determined from the apparent motion of photospheric magnetic fields and from the brightest points of active regions observed in the EUV. The corona does not clearly show differential rotation as do the chromosphere and transition region. 相似文献
8.
Elena Dzifčáková 《Solar physics》1992,140(2):247-267
The ionization equilibrium of the Fe in the solar corona for a non-Maxwellian electron distribution with an enhanced number of particles in the high-energy tail is presented. A parametric form of the distribution function is used to demonstrate the changes in the ionization equilibrium with changes in the shape of the distribution. The results over the range of temperature 105 K T 108 K for different deviations of the distribution from a Maxwellian are given in tabular form. The results can be used for specific applications in the solar corona, especially in the active corona, where deviations from the Maxwellian distribution can be significant. 相似文献
9.
The large-scale density structure of the white-light solar corona has been compared to the organization of the solar magnetic field as identified by the appearance of neutral lines in the photosphere in order to examine whether any consistent relationship exists between the two. Data from the High Altitude Observatory's Mk-III K-coronameter have been used to describe the coronal density structure, and observations from several sources, beginning with observations from the University of Hawaii Stokes Polarimeter have been used to establish the magnetic field distribution. Stanford magnetograms as well as the neutral line inferred from potential field models have also been examined. During the period covering Carrington rotations 1717 to 1736 brightness enhancements in the low corona tend to lie over the global neutral sheet identified in the photospheric magnetic field. The brightest of these enhancements, however, are associated with neutral lines through active regions. These associations are not 1-1, but do hold both in stable and evolving conditions of the corona. We find a significant number of long-lived neutral lines, including filaments seen in H, for which there are not coronal enhancements.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
10.
G. W. Pneuman 《Solar physics》1973,28(1):247-262
The influence of the solar wind on large-scale temperature and density distributions in the lower corona is studied. This influence is most profoundly felt through its effect upon the geometry of coronal magnetic fields since the presence of expansion divides the corona into magnetically open and closed regions. Each of these regions is governed by entirely different energy transport processes. This results in significant temperature differences since only the open field regions suffer outward conductive heat losses. Because the temperature influences the density in an exponential manner, large density inhomogeneities are to be expected.An approximate method for calculating the temperature and density distribution in a known magnetic field geometry is outlined and numerical estimates are carried out for representative coronal conditions. These estimates show that temperature differences of a factor of about two and density differences of ten can be expected in the lower corona even for uniform base conditions. As a result, we do not regard the so-called coronal holes necessairly as locations of reduced mechanical heating. Alternatively, we suggest that they are regions of open magnetic field lines being continuously drained of energy contert by the solar wind expansion and outward thermal conduction.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
11.
Lewis L. House 《Solar physics》1972,23(1):103-119
A discussion of a program for the computation of coronal emission line polarization is presented. The starting point is a general formulation of the scattering function for magnetic dipole transitions between any two total angular momentum levels, J J, J ± 1. Illustration of the behavior of the scattering function for different transitions is given. The integration of the scattering function over the solar disk and along the line of sight accounting for arbitrary distribution of magnetic fields as well as an inhomogeneous temperature and density structure of the corona is considered next.Sample results are presented for the numerical computation of the angle of maximum polarization and the degree of maximum polarization to be expected from idealized magnetic field configurations such as radial and dipole. A computation is included for a realistic field configuration predicted to exist at the time of the 1966 eclipse. The magnetic field input to the scattering calculation is based upon the potential field extension of photospheric magnetic fields. It is the purpose of the sample calculations to demonstrate how the measurement of emission polarization measurements can be interpreted in terms of the direction of coronal magnetic fields. Factors which lend ambiguity to such interpreations are clearly illustrated from the examples. These include the Hanle-effect depolarization and the depolarization at the Van Vleck angle.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
12.
13.
The radial dependencies of four solar wind parameters (plasma density N, velocity V, temperature T, and magnitude of the interplanetary magnetic field B) are derived from remote sensing data of the solar corona and from in situ measurements in the heliosphere (Helios-1, 2, Pioneer-10, 11, and Voyager-1, 2). Using doubly logarithmic scaling (solar wind parameter vs radial distance from the Sun) one finds two distinct intervals in the ecliptic, i.e., an exponential section within, approximately, the inner heliosphere and a linear section - up to at least 61 AU - in the outer heliosphere. 相似文献
14.
During the total solar eclipse of 11 June, 1983, an imaging dual-channel Fabry-Pérot interferometer was used to obtain line profiles simultaneously in the green 5303 Å [Fe xiv] and the red 6374 Å [Fe x] coronal lines at various positions in the corona. Extensive microdensitometry followed by multi-Gaussian curve-fitting analysis has resulted in the determination of coronal temperatures and velocity separations between different pockets of coronal gas in the line of sight over a large extent of the corona. Fewer high temperature zones are to be found in the corona of 1983 compared with our similar green-line measurements of the solar maximum corona of 1980. The data are consistent with a temperature maximum occurring at 1.2 R
, as found at the 1980 eclipse, but our new data are insufficient to observe farther out than this radius and so determine the position of a maximum. The velocity field in the corona at the 1983 eclipse is less structured compared with that at the 1980 eclipse and is mainly confined to the zone 20–30km s–1. 相似文献
15.
A large equatorial coronal streamer observed in the outer corona (3R
) grew in brightness and size during successive limb passages between October 6, 1973 and January 10, 1974 (solar rotations 1606–1611). Unlike previous studies of streamers and their photospheric associations, no definite surface feature could be identified in the present case. This suggests that the streamer is associated with the large scale photospheric magnetic field. Comparison of the streamer growth with observed underlying photospheric magnetic flux changes indicated that as the streamer increased in brightness, areal extent, and density, the photospheric magnetic flux decreased. Three possible explanations for the streamer's growth are presented; the conceptually simplest being that the decrease in photospheric field results in an opening of the flux tubes under the streamer which permits an increased mass flux through the streamer.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
16.
The temperature structure of the transition region between the chromosphere and corona is discussed in the context of current ideas about magnetic fields in these layers. Magnetic channeling of the downward conductive heat flow from the corona into the regions of enhanced field at the supergranulation boundaries is proposed as a mechanism for explaining the measured intensities of solar ultraviolet emission lines which originate in layers with temperatures below 105 °K. It is shown that nearly all of the observed ultraviolet line emission originates in interspicule regions, and that this emission plays an important part in the energy balance of the cooler layers of the transition region. It is suggested that certain motions observed in the upper chromosphere may represent the earliest visual evidence for conversion of inflowing conduction energy into kinetic motions.On leave from the Observatory Sonnenborgh at Utrecht, The Netherlands. 相似文献
17.
The effect of a background signal on the signal-to-noise ratio is discussed, with particular application to ground-based observations of emission lines in the solar corona with the proposed Advanced Technology Solar Telescope. The concepts of effective coronal aperture and effective coronal integration time are introduced. Specific expressions are developed for the 1 measurement errors for coronal intensity, coronal electron density, coronal velocity, and coronal magnetic field measurements using emission lines and including a background. 相似文献
18.
A study of the background corona near solar minimum 总被引：2，自引：0，他引：2
The white light coronagraph data from Skylab is used to investigate the equatorial and polarK andF coronal components during the declining phase of the solar cycle near solar minimum. Measurements of coronal brightness and polarization brightness product between 2.5 and 5.5R
during the period of observation (May 1973 to February 1974) lead to the conclusions that: (1) the equatorial corona is dominated by either streamers or coronal holes seen in projections on the limb approximately 50% and 30% of the time, respectively; (2) despite the domination by streamers and holes, two periods of time were found which were free from the influences of streamers or holes (neither streamers nor holes were within 30° in longitude of the limb); (3) the derived equatorial background density model is less than 15% below the minimum equatorial models of Newkirk (1967) and Saito (1970); (4) a spherically symmetric density model for equatorial coronal holes yields densities one half those of the background density model; and (5) the inferred brightness of theF-corona is constant to within ±10% and ±5% for the equatorial and polar values, respectively, over the observation period. While theF-corona is symmetric at 2R
it begins to show increasing asymmetry beyond this radius such that at 5R
the equatorialF-coronal brightness is 25% greater than the polar brightness.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
19.
The brightness of the solar corona due to Thomson scattering depends linearly on the electron density, while the brightness due to the Balmer continuum is proportional to its square. As a consequence, information on the distribution of the electron density in the corona can be obtained by comparing the radial profiles of the surface brightness in both continua. This idea was explored for the first time in the solar eclipse of November 03, 1994, in Foz do Iguaçu, PR, Brazil. Pictures of the corona were obtained with interference filters, one centered at 477 nm (Thomson continuum) and another one at 347 nm (Balmer continuum). The second filter also transmits the Thomson continuum through its spectral window, so that the Balmer images contain Thomson contamination. This paper reports on the observational results and presents their preliminary analysis. It was found that in certain radial directions, the normalized profiles of both continua (Thomson and contaminated Balmer) coincide, but in other directions they differ significantly. The non-coincident profiles may only occur if Balmer emission becomes important in relation to the Thomson scattering. A simple calculation shows that in such cases the electron density in the inner corona must exceed the values of standard models by up to 6.1 × 104 times, maintaining however the total number of electrons along the line of sight in agreement with the prediction of standard models. It is concluded that the corona contains high electron concentration in cloudlets of subtelescopic sizes down to 106 cm. The varied behavior of the radial profiles of both continua in different radial directions, suggests that the subtelescopic structures might be related to the spatially variable topology of coronal magnetic flux tubes. 相似文献
20.
Yohkoh observations strongly suggest that electron acceleration in solar flares occurs in magnetic reconnection regions in the corona above the soft X-ray flare loops. Unfortunately, models for particle acceleration in reconnecting current sheets predict electron energy gains in terms of the reconnection electric field and the thickness of the sheet, both of which are extremely difficult to measure. It can be shown, however, that application of Ohm's law in a turbulent current sheet, combined with energy and Maxwell's equations, leads to a formula for the electron energy gain in terms of the flare power output, the magnetic field strength, the plasma density and temperature in the sheet, and its area. Typical flare parameters correspond to electron energies between a few tens of keV and a few MeV. The calculation supports the viewpoint that electrons that generate the continuum gamma-ray and hard X-ray emissions in impulsive solar flares are accelerated in a large-scale turbulent current sheet above the soft X-ray flare loops. 相似文献