共查询到20条相似文献，搜索用时 875 毫秒
1.
Werner M. Neupert 《Solar physics》1998,177(1-2):181-190
Using extreme ultraviolet (EUV) images of the solar corona, we have carried out a region-by-region study of the association of coronal emission of Feix–Fexvi with Caii K plage areas and intensities reported in Solar-Geophysical Data. We find that emission is dependent on the area and brightness of the plage, with specific correlations varying with the temperature of formation of the emitting coronal ion. If confirmed and extended, this approach may provide a means of estimating coronal EUV levels associated with solar activity and ultimately a proxy method that is more accurate than the sole use of the centimetric radio flux for estimating the coronal component of solar EUV emission. 相似文献
2.
A new solar radio spectrograph to observe solar radio bursts has been installed at the Ichon branch of the Radio Research
Laboratory, Ministry of Information and Communication, Korea. The spectrograph consists of three different antennas to sweep
a wide band of frequencies in the range of 30 MHz ∼ 2500 MHz. Its daily operation is fully automated and typical examples
of solar radio bursts have been successfully observed. In this paper we describe briefly its hardware and data processing
methods. Then we present coronal shock speeds estimated for 34 type II bursts from May 1998 to November 2000 and compare them
with those from other observatories. We also present the close relationship between onset time of type II bursts and X-ray
flares as well as their associations with coronal mass ejections. 相似文献
3.
The comparison of solar radio type III bursts measured at 169 MHz with K corona observations leads to the conclusion that about 75% of the active regions over which type III bursts occur are associated with low density coronal structures. The comparison with X-ray maps of the solar disk shows that all these regions are located in low intensity regions.It is concluded that the idea generally accepted that the type III bursts are associated with dense coronal structures and travel in these structures is not at all proven for a large number of cases. 相似文献
4.
M. R. Kundu 《Solar physics》1996,169(2):389-402
We present a review of selected studies based upon simultaneous radio and X-ray observations of solar flares and coronal transients. We use primarily the observations made with large radio imaging instruments (VLA, BIMA, Nobeyama, and Nançay) along with Yohkoh/SXT and HXT and CGRO experiments. We review the recent work on millimeter imaging of solar flares, microwave and hard X-ray observations of footpoint emission from flaring loops, metric type IV continuum bursts, and coronal X-ray structures. We discuss the recent studies on thermal and nonthermal processes in coronal transients such as XBP flares, coronal X-ray jets, and active region transient brightenings.Dedicated to Cornelis de Jager 相似文献
5.
The association of solar radio bursts of spectral type II and coronal shocks with solar flare ejecta observed in H, the green coronal line, and white-light coronagraphs is examined. Rather than identifying fast-moving optical coronal transients with outward-travelling shock waves that generate type II radio bursts, as has been suggested in some earlier papers, we suggest that, for the most part, such transients should probably be identified with piston-type phenomena well behind the shock. We then discuss a general model, consisting of three main velocity regimes, in which we relate type II radio bursts and coronal shocks to optically-observed ejecta. 相似文献
6.
We present observations of the corona at 169 MHz with the Nançay Radioheliograph during the summer of 1984. We compare synoptic maps of the metric radio emission on the solar disk with synoptic charts of the K-corona as well as of the green and the red lines. Local sources of radio emission are not located near regions of enhanced green or red line emission which, in turn, are in general above chromospheric faculae. Thus the radio emissions located in the surroundings of faculae are apparently related to different loop systems, with lower density. The comparison of the radio data with the K-corona showed one radio source associated with enhanced emission both at 1.3 and at 1.7 R
, apparently a streamer. Other radio sources did not show any clear associations, but were nevertheless located within the coronal plasma sheet, delineated by the large-scale K-corona emission. Moreover the large-scale structure of the corona at 169 MHz was quite similar to the coronal plasma sheet observed at 1.3 R
above the limb. The extent of the radio emission in latitude is very similar to that of the K-corona, while the coronal line emission is more concentrated near the solar equator. 相似文献
7.
R. A. Duncan 《Solar physics》1985,97(1):173-182
A comparison of quiescent type I solar radio sources with concurrent intense impulsive type III, V, and type II sources shows that whereas the type I sources are usually small and stable the type III, V, and II sources are usually large and unstable. We conclude that the large size and variability of the type III, V, and II radio sources cannot be attributed to instrumental error or ionospheric refraction but must instead reflect the size and variability of the coronal structures on which they arise. 相似文献
8.
We review recent progress on our understanding of radio emission from solar flares and coronal mass ejections (CMEs) with emphasis on those aspects of the subject that help us address questions about energy release and its properties, the configuration of flare?–?CME source regions, coronal shocks, particle acceleration and transport, and the origin of solar energetic particle (SEP) events. Radio emission from electron beams can provide information about the electron acceleration process, the location of injection of electrons in the corona, and the properties of the ambient coronal structures. Mildly relativistic electrons gyrating in the magnetic fields of flaring loops produce radio emission via the gyrosynchrotron mechanism, which provides constraints on the magnetic field and the properties of energetic electrons. CME detection at radio wavelengths tracks the eruption from its early phase and reveals the participation of a multitude of loops of widely differing scale. Both flares and CMEs can ignite shock waves and radio observations offer the most robust tool to study them. The incorporation of radio data into the study of SEP events reveals that a clear-cut distinction between flare-related and CME-related SEP events is difficult to establish. 相似文献
9.
We examine the problem related to the scattering of a solar radio pulse in a turbulent coronal plasma, taking into account
strong regular refraction. Based on an integral representation of the wave field as an interference integral, we analyze the
distortions of the mean profile of the radio pulse in spike events, for the case of the sources located in high coronal arches.
It is shown that strong regular refraction of radio emission in the coronal arch plays an important role for pulse structuring
during spike events. 相似文献
10.
Synoptic charts for Carrington rotations 1601–1605 (May–August, 1973) were prepared using the central meridian column of the daily 9.1 cm Stanford solar radio maps. These charts were especially contoured to emphasize temperatures near the quiet solar disk level. Synoptic charts of coronal holes from the ATM-Skylab were superimposed on the radio data to investigate the ability of the radio charts to show coronal holes. This brief period is unfortunately the only interval for which both sets of data are available. The conclusion reached is that in spite of certain problems due to active regions, side-lobe effects and a rather large beamwidth, the 9.1 cm synoptic charts can be of substantial value in identifying large coronal holes, especially during periods of low solar activity. Such synoptic charts, therefore, for the years 1962–1973 that Stanford data are available, could enhance significantly the meagre data pool for coronal holes prior to the Skylab mission. 相似文献
11.
Observations of solar radio emission at 3 cm wavelength have been made at Japal-Rangapur Observatory for 1980–1981, the solar maximum year using the 3 m radio telescope. The correlation between microwave solar emissions and the sunspot activity on monthly basis has been found to be high during the maximum phase and in the high cm wavelength band. The basic component has been estimated statistically for successive solar rotations using the data obtained at Japal-Rangapur Observatory. Further, this was compared with the data obtained at other cm wavelengths during 1980–1981 and the solar minimum period 1975–1976 of the 21st cycle. The comparison showed pronounced dips in flux levels at different wavelengths during the summer months of the solar maximum year which may be attributed to the presence of coronal holes in the various levels of the solar atmosphere. The computed basic component values showed pronounced variation at high cm wavelengths for the solar maximum period with dissimilar variations at different wavelengths. During the solar minimum period the variations were negligibly small and showed more or less constant level of activity.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984. 相似文献
12.
Radio observations of some active regions (ARs) obtained with the Nobeyama radioheliograph at λ=1.76cm are used for estimating the magnetic field strength in the upper chromosphere, based on thermal bremsstrahlung. The results are compared with the magnetic field strength in the photosphere from observations with the Solar Magnetic Field Telescope (SMFT) at Huairou Solar Observing Station of Beijing Astronomical Observatory. The difference in the magnetic field strength between the two layers seems reasonable. The solar radio maps of active regions obtained with the Nobeyama radioheliograph, both in total intensity (I-map) and in circular polarizations (V-map), are compared with the optical magnetograms obtained with the SMFT. The comparison between the radio map in circular polarization and the longitudinal photospheric magnetogram of a plage region suggest that the radio map in circular polarization is a kind of magnetogram of the upper chromosphere. The comparison of the radio map in total intensity with the photospheric vector magnetogram of an AR shows that the radio map in total intensity gives indications of magnetic loops in the corona, thus we have a method of defining the coronal magnetic structure from the radio I-maps at λ=1.76 cm. Analysing the I-maps, we identified three components: (a) a compact bright source; (b) a narrow elongated structure connecting two main magnetic islands of opposite polarities (observed in both the optical and radio magnetograms); (c) a wide, diffuse, weak component that corresponds to a wide structure in the solar active region which shows in most cases an S or a reversed S contour, which is probably due to the differential rotation of the Sun. The last two components suggest coronal loops on different spatial scales above the neutral line of the longitudinal photospheric magnetic field. 相似文献
13.
A set of 21 solar type II radio bursts observed using Hiraiso radio spectrograph have been analysed to study the direction
of propagation of coronal shocks. A simple analysis is carried out to find the approximate angle between the shock normal
and magnetic field by solving the Rankine-Hugoniot MHD relation with assumption of Alfven speed and plasma beta. From this
analysis, it is suggested that both quasi-parallel shocks (favourable) and quasi-perpendicular shocks can generate type II
bursts depending upon the circumstances of the corona. 相似文献
14.
We present the solar wind plasma parameters obtained from the Ulysses spacecraft during its second pole-to-pole fast latitude scan near the 2001 solar maximum. We study the solar wind properties
from the electron density and core temperature measurements made by the radio receiver on Ulysses using the method of quasi-thermal noise spectroscopy. We analyze these parameters as functions of heliographic latitude and
distance. We present their histograms normalized to 1 AU and find a bimodal distribution for the electron core temperature.
The cooler population can be associated with the fast wind flow emanating from coronal holes present at various latitudes.
We discuss a slight north/south asymmetry found for the electron density. Finally, we compare the present results to those
obtained during the 1996 solar minimum and 1991 solar maximum. 相似文献
15.
In this study we continue our investigation of the radio sources located above the neutral line of the radial magnetic field in solar active regions, i.e., the so-called neutral line associated sources (NLS). The nature of NLS is still far from being understood. To study it, we use the spectroscopic capabilities of the new broadband polarimetric facility of the RATAN-600 radio telescope. We study the radio spectra of NLS sources in several solar active regions over a wide range of variations of their sizes. We find the NLS radio emission fluxes to be related to the gradient of the quasi-longitudinal magnetic field in the photosphere. We estimate the vertical positions of NLS relative to the cyclotron radio sources. We find fine spectral features in the NLS emission, which confirm the presence of a current sheet in their sources. We associate the appreciable lack of polarization in such sources with their location near the tops of the coronal arches. 相似文献
16.
Solar radio maps obtained by our group and others over a wide wavelength range (millimeter to meter) and over a considerable time span (1973–1978) have allowed us to compute the radio spectrum of an average coronal hole, i.e., the brightness temperature inside a coronal hole normalized by the brightness temperature of the quiet Sun outside the coronal hole measured at several different radio wavelengths. This radio spectrum can be used to obtain the changes of the quiet Sun atmosphere inside coronal holes and also as an additional check for coronal hole profiles obtained by other methods. Using a standard solar atmosphere and a computer program which included ray tracing, we have tried to reproduce the observed radio spectrum by computing brightness temperatures at many different wavelengths for a long series of modifications in the electron density, neutral particle density and temperature profiles of the standard solar atmosphere. This analysis indicates that inside an average coronal hole the following changes occur: the upper chromosphere expands by about 20% and its electron density and temperature decrease by about 10%. The transition zone experiences the largest change, expanding by a factor of about 6, its electron density decreases by a similar factor, and its temperature decreases by about 50%. Finally in the corona the electron density decreases by about 20% and the temperature by about 15%. 相似文献
17.
S. Ananthakrishnan 《Journal of Astrophysics and Astronomy》2000,21(3-4):439-444
The ground-based radio astronomy method of interplanetary scintillations (IPS) and spacecraft observations have shown, in
the past 25 years, that while coronal holes give rise to stable, reclining high speed solar wind streams during the minimum
of the solar activity cycle, the slow speed wind seen more during the solar maximum activity is better associated with the
closed field regions, which also give rise to solar flares and coronal mass ejections (CME’s). The latter events
increase significantly, as the cycle maximum takes place. We have recently shown that in the case of energetic flares one
may be able to track the associated disturbances almost on a one to one basis from a distance of 0.2 to 1 AU using IPS methods.
Time dependent 3D MHD models which are constrained by IPS observations are being developed. These models are able to simulate
general features of the solar-generated disturbances. Advances in this direction may lead to prediction of heliospheric propagation
of these disturbances throughout the solar system. 相似文献
18.
Coronal holes as sources of solar wind 总被引：3，自引：0，他引：3
J. T. Nolte A. S. Krieger A. F. Timothy R. E. Gold E. C. Roelof G. Vaiana A. J. Lazarus J. D. Sullivan P. S. McIntosh 《Solar physics》1976,46(2):303-322
We investigate the association of high-speed solar wind with coronal holes during the Skylab mission by: (1) direct comparison of solar wind and coronal X-ray data; (2) comparison of near-equatorial coronal hole area with maximum solar wind velocity in the associated streams; and (3) examination of the correlation between solar and interplanetary magnetic polarities. We find that all large near-equatorial coronal holes seen during the Skylab period were associated with high-velocity solar wind streams observed at 1 AU.Harvard College Observatory-Smithsonian Astrophysical Observatory.A substantial portion of this work was done while a visiting scientist at American Science and Engineering. 相似文献
19.
The formation of solar-wind stream structure is investigated. Characteristic features of the solar and coronal magnetic-field structure, morphological features of the white-light corona, and radio maps of the solar-wind transition (transonic) region are compared. The solar-wind stream structure is detected and studied by using radio maps of the transition region, the raggedness of its boundaries, and their deviation from spherical symmetry. The radio maps have been constructed from radioastronomical observations in 1995–1997. It is shown that the structural changes in the transition region largely follow the changes occurring in regions closer to the Sun, in the circumsolar magnetic-field structure, and in the solar-corona structure. The correlations between the magnetic-field strength in the solar corona and the location of the inner (nearest the Sun) boundary of the transition region are analyzed. The distinct anticorrelation between the coronal magnetic-field strength and the distance of the transition region from the Sun is a crucial argument for the penetration of solar magnetic fields into plasma streams far from the Sun. 相似文献
20.
日冕物质抛射(ChIEs)经常被观测到和其他日面活动相伴生，太阳耀斑、日珥爆发、盔状冕流等许多太阳现象，都与它有直接或间接的关系。射电观测是研究CMEs的一种重要的补充工具。多频率的射电成像观测能很好地研究CMEs的初始阶段，而且可以得到关于CMEs触发机制特征的更多信息。概括了CMEs与低频射电的关系，介绍了低频射电的观测仪器，分析了CMEs低频射电所表现出来的特征，考虑了CMEs的初发机制，总结了尚待解决的问题，表明了CMEs研究是基于多类数据和全电磁辐射波段的。 相似文献