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1.
We have produced synoptic maps from daily images of the solar corona on the disk obtained with the Nançay Radioheliograph at 169 MHz during June–August 1984. We discuss briefly the structures seen on the synoptic maps and we compare the location of radio sources with photospheric neutral lines and Ha filaments derived from synoptic charts from Meudon, Boulder, and Stanford. We measured the distance of radio sources from these optical features and compared their distribution with computed random distributions. A criterion of confidence is proposed which, when applied to our data, shows that the metric radio sources of thermal origin are best associated with the large-scale neutral lines shown on the low resolution Stanford magnetograms. This association indicates that the emission comes from arcades of moderately dense loops spanning the neutral line. However, the radio sources are not usually located directly above or very close to neutral lines, but their distribution peaks at distances between 4 and 6°. Our results show no statistically significant association with Meudon filaments. 相似文献
2.
We present new results of heliographic observations of quiet‐Sun radio emission fulfilled by the UTR‐2 radio telescope. The solar corona investigations have been made close to the last solar minimum (Cycle 23) in the late August and early September of 2010 by means of the two‐dimensional heliograph within 16.5–33 MHz. Moreover, the UTR‐2 radio telescope was used also as an 1‐D heliograph for one‐dimensional scanning of the Sun at the beginning of September 2010 as well as in short‐time observational campaigns in April and August of 2012. The average values of integral flux density of the undisturbed Sun continuum emission at different frequencies have been found. Using the data, we have determined the spectral index of quiet‐Sun radio emission in the range 16.5–200 MHz. It is equal to –2.1±0.1. The brightness distribution maps of outer solar corona at frequencies 20.0 MHz and 26.0 MHz have been obtained. The angular sizes of radio Sun were estimated. It is found that the solar corona at these frequencies is stretched‐out along equatorial direction. The coefficient of corona ellipticity varies slightly during above period. Its mean magnitudes are equal to ≈ 0.75 and ≈ 0.73 at 20.0 MHz and 26.0 MHz, respectively. The presented results for continuum emission of solar corona conform with being ones at higher frequencies. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
3.
We present meterwave maps showing a coronal hole at 30.9, 50.0, and 73.8 MHz using the Clark Lake Radioheliograph in October 1984. The coronal hole seen against the disk at all three frequencies shows interesting similarities to, and significant differences from its optical signatures in He i
l10830 spectroheliograms.Using the model of coronal holes by Dulk et al. (1977) we derive the electron density from the radio observations of the brightness temperature. The discrepancy between the density value derived from the Skylab EUV data and that computed from our radio data is even larger than in Dulk et al. 's comparison at similar and higher frequencies. 相似文献
4.
We analysed multifrequency 2-dimensional maps of the solar corona obtained with the Nançay radioheliograph during two solar rotations in 1986. We discuss the emission of the quiet Sun, coronal holes and local sources and its association with chromospheric and coronal features as well as with large-scale magnetic fields. The brightness temperature of the quiet Sun was 5 to 5.5 × 105 K at 164 MHz and 4.5 to 5 × 105 K at 408 MHz. A coronal hole, also detected in the 10830 Å He i line, had a brightness temperature of 4.5 × 105 at 164 and 2.5 × 105 at 408 MHz. We give statistics of source brightness temperatures (on the average 8% above the background at 164 MHz and 14% at 408 MHz), as well as distributions in longitude and latitude. Although we found no significant center-to-limb effect in the brightness temperature, the sources were not visible far from the central meridian (apparently a refraction effect). The brightest sources at 164 MHz were near, but not directly above active regions and had characteristics of faint type I continua. At 408 MHz some sources were observed directly above active regions and one was unambiguously a type I continuum. The majority of the fainter sources showed no association with chromospheric features seen on H synoptic charts, including filaments. Most of them were detected at one frequency only. Sources identified at three frequencies (164, 327, and 408 MHz) were located in regions of enhanced large-scale magnetic field, some of them at the same location as decayed active regions visible one rotation before on synoptic H charts. Multifrequency sources are associated with maxima of the green line corona. The comparison with K-corona synoptic charts shows a striking association of the radio sources with dense coronal regions, associated with the coronal neutral sheet. Furthermore, we detected an enhanced brightness region which surrounds the local sources and is stable over at least one solar rotation. We call this feature a coronal plateau and we identify it with the radio counterpart of the coronal neutral sheet. 相似文献
5.
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
6.
V. E. Abramov-Maximov G. B. Gelfreikh N. I. Kobanov K. Shibasaki S. A. Chupin 《Solar physics》2011,270(1):175-189
The nature of the three-minute and five-minute oscillations observed in sunspots is considered to be an effect of propagation
of magnetohydrodynamic (MHD) waves from the photosphere to the solar corona. However, the real modes of these waves and the
nature of the filters that result in rather narrow frequency bands of these modes are still far from being generally accepted,
in spite of a large amount of observational material obtained in a wide range of wave bands. The significance of this field
of research is based on the hope that local seismology can be used to find the structure of the solar atmosphere in magnetic
tubes of sunspots. We expect that substantial progress can be achieved by simultaneous observations of the sunspot oscillations
in different layers of the solar atmosphere in order to gain information on propagating waves. In this study we used a new
method that combines the results of an oscillation study made in optical and radio observations. The optical spectral measurements
in photospheric and chromospheric lines of the line-of-sight velocity were carried out at the Sayan Solar Observatory. The
radio maps of the Sun were obtained with the Nobeyama Radioheliograph at 1.76 cm. Radio sources associated with the sunspots
were analyzed to study the oscillation processes in the chromosphere – corona transition region in the layer with magnetic
field B=2000 G. A high level of instability of the oscillations in the optical and radio data was found. We used a wavelet analysis
for the spectra. The best similarities of the spectra of oscillations obtained by the two methods were detected in the three-minute
oscillations inside the sunspot umbra for the dates when the active regions were situated near the center of the solar disk.
A comparison of the wavelet spectra for optical and radio observations showed a time delay of about 50 seconds of the radio
results with respect to the optical ones. This implies an MHD wave traveling upward inside the umbral magnetic tube of the
sunspot. For the five-minute oscillations the similarity in spectral details could be found only for optical oscillations
at the chromospheric level in the umbral region or very close to it. The time delays seem to be similar. Besides three-minute
and five-minute ones, oscillations with longer periods (8 and 15 minutes) were detected in optical and radio records. Their
nature still requires further observational and theoretical study for even a preliminary discussion. 相似文献
7.
The radio emission from the solar corona is related to the configuration of the inner atmosphere. By studying the Sun at multiple
frequencies, different layers of plasma in solar atmosphere are probed. We use the Mauritius Radio Telescope. The quiet Sun
period, difference maps using synthesized 1D maps reveal a certain regular feature, the origin of which is not thoroughly
understood and which is attributed to the solar differential rotation. For the active Sun period, the coronal emission is
linked to the magnetic field configuration originating from the inner atmosphere. As expected, a strong correlation exists
between the MRT 151 MHz and Nancay 164 MHz radio emission.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
Maps of the brightness distribution of the ‘quiet Sun’ at 80 and 160 MHz reveal the presence of features both brighter and darker than average. The ‘dark’ regions are well correlated with dark regions on UV maps; we deduce that they result from ‘coronal holes’. The ‘bright’ regions are associated with quiescent filaments and not plages or bright regions on microwave or UV maps; we deduce that they result from ‘coronal helmets’.
When coronal holes appear near the centre of the disk we can estimate the density and kinetic temperature in the holes from the radio observations. For a hole observed on 1972 July 20–21, we find T ≈ 0.8 × 106 inside the hole and T ≈ 1.0 × 106 in average regions outside the hole. Inside the hole the density is estimated to be about one-quarter of that in Newkirk's model of the spherically symmetric corona.
Variations in brightness at a fixed height above the limb are generally well correlated with scans at a similar height made with a K-coronameter. Occasional differences may result from streamers protruding beyond the limb from the back of the Sun. These can be seen by the K-coronameter but, because of refraction of the radio rays, not by the radio-heliograph.
相似文献9.
We describe the technique and results of modelling the solar radio emission during the maximum phase of the solar eclipse
of March 29, 2006 on the RATAN-600. The aim of modelling is to refine the brightness temperature of the solar corona at the
distances up to two solar radii from the center of the optical disk of the Sun. We obtained the distribution of brightness
temperature in the vicinity of the coronal hole above the solar North Pole at the wavelength of 13 cm. The results of modelling
showed that brightness temperatures of the coronal hole at the distances greater than 1.02 RC (here RC is the radius of the optical disk of the Sun) is substantially lower than the expected average brightness temperature of
a typical coronal hole, and that of the quiescent Sun (below 30000 K) at the wavelength of 13 cm. The classical Baumbach-Allen
formula for electron density in a spherically symmetric corona agrees with the results of observations starting at distances
of (1.4–1.5) RC. 相似文献
10.
Previous studies of the source regions of solar wind sampled by ACE and Ulysses showed that some solar wind originates from open magnetic flux rooted in active regions. These solar wind sources were labeled active-region sources when the open flux was from a strong field region with no corresponding coronal hole in the NSO He 10830 Å synoptic coronal-hole maps. Here, we present a detailed investigation of several of these active-region sources using ACE and Ulysses solar wind data, potential field models of the corona, and solar imaging data. We find that the solar wind from these active-region sources has distinct signatures, e.g., it generally has a higher oxygen charge state than wind associated with helium-10830 Å coronal-hole sources, indicating a hotter source region, consistent with the active region source interpretation. We compare the magnetic topology of the open field lines of these active-region sources with images of the hot corona to search for corresponding features in EUV and soft X-ray images. In most, but not all, cases, a dark area is seen in the EUV and soft X-ray image as for familiar coronal-hole sources. However, in one case no dark area was evident in the soft X-ray images: the magnetic model showed a double dipole coronal structure consistent with the images, both indicating that the footpoints of the open field lines, rooted deep within the active region, lay near the separatrix between loops connecting to two different opposite polarity regions. 相似文献
11.
Previous studies of the source regions of solar wind sampled by ACE and Ulysses showed that some solar wind originates from open magnetic flux rooted in active regions. These solar wind sources were labeled active-region sources when the open flux was from a strong field region with no corresponding coronal hole in the NSO He 10830 Å synoptic coronal-hole maps. Here, we present a detailed investigation of several of these active-region sources using ACE and Ulysses solar wind data, potential field models of the corona, and solar imaging data. We find that the solar wind from these active-region sources has distinct signatures, e.g., it generally has a higher oxygen charge state than wind associated with helium-10830 Å coronal-hole sources, indicating a hotter source region, consistent with the active region source interpretation. We compare the magnetic topology of the open field lines of these active-region sources with images of the hot corona to search for corresponding features in EUV and soft X-ray images. In most, but not all, cases, a dark area is seen in the EUV and soft X-ray image as for familiar coronal-hole sources. However, in one case no dark area was evident in the soft X-ray images: the magnetic model showed a double dipole coronal structure consistent with the images, both indicating that the footpoints of the open field lines, rooted deep within the active region, lay near the separatrix between loops connecting to two different opposite polarity regions. 相似文献
12.
The LASCO-C2 coronagraph aboard the SOHO solar observatory has been providing a continuous flow of coronal images since 1996.
Synoptic maps for each Carrington rotation have been built from these images, and offer a global view of the temporal evolution
of the solar corona, particularly the occurrence of transient events. Coronal Mass Ejections (CMEs) present distinct signatures
thus offering a novel approach to the problem of their identification and characterization. We present in this article an
automated method of detection based on their morphological appearance on synoptic maps. It is based on adaptive filtering
and segmentation, followed by merging with high-level knowledge. The program builds a catalog which lists the CMEs detected
for each Carrington Rotation, together with their main estimated parameters: time of appearance, position angle, angular extent,
average velocity and intensity. Our final catalog LASCO-ARTEMIS (Automatic Recognition of Transient Events and Marseille Inventory
from Synoptic maps) is compared with existing catalogs, CDAW, CACTUS and SEEDS. We find that, likewise the automated CACTUS
and SEEDS catalogs, we detect many more events than the CDAW catalog which is based on visual detection. The total number
of detected CMEs strongly depends upon the sensitivity to small, faint and numerous events. 相似文献
13.
N. A. Lotova K. V. Vladimirskii V. N. Obridko B. P. Filippov O. A. Korelov 《Astronomy Letters》2005,31(8):546-556
We study the formation of solar-wind streams in the years of maximum solar activity 2000–2002. We use observations of the scattering of radio emission by solar-wind streams at distances of ～4–60RS from the Sun, data on the magnetic field structure and strength in the source region (R ～ 2.5RS), and observations with the LASCO coronagraph onboard the SOHO spacecraft. Analysis of these data allowed us to investigate the changes in the structure of circumsolar plasma streams during the solar maximum. We constructed radio maps of the solar-wind transition, transonic region in which the heliolatitudinal stream structure is compared with the structure of the white-light corona. We show that the heliolatitudinal structure of the white-light corona largely determines the structure of the solar-wind transition region. We analyze the correlation between the location of the inner boundary of the transition region Rin and the magnetic field strength on the source surface |BR|. We discuss the peculiarities of the Rin = F(|BR|) correlation diagrams that distinguish them from similar diagrams at previous phases of the solar cycle. 相似文献
14.
The GOES C7.5 flare on 20 February 2002 at 11:07 UT is one of the first solar flares observed by RHESSI at X-ray wavelengths. It was simultaneously observed at metric/decimetric wavelengths by the Nançay radioheliograph (NRH) which provided images of the flare between 450 and 150 MHz. We present a first comparison of the hard X-ray images observed with RHESSI and of the radio emission sites observed by the NRH. This first analysis shows that: (1) there is a close occurrence between the production of the HXR-radiating most energetic electrons and the injection of radio-emitting non-thermal electrons at all heights in the corona, (2) modifications with time in the pattern of the HXR sources above 25 keV and of the decimetric radio sources at 410 MHz are observed occurring on similar time periods, (3) in the late phase of the most energetic HXR peak, a weak radio source is observed at high frequencies, overlying the EUV magnetic loops seen in the vicinity of the X-ray flaring sites above 12 keV. These preliminary results illustrate the potential of combining RHESSI and NRH images for the study of electron acceleration and transport in flares. 相似文献
15.
Time-latitudinal distributions of the solar-surface magnetic fields and the green corona (530.3 nm, Fe XIV) intensities in
the period 1975 – 2004 are analyzed. Meridional migration maps show that time-varying components consist of both the poleward
and equatorward belts over a solar cycle. The green-corona maps are, for the first time, directly compared with magnetic flux
charts, yielding a good association between the green corona and magnetic fields; this is most reliably seen at high latitudes. 相似文献
16.
V. M. Bogod O. A. Golubchina G. N. Zhekanis A. N. Korzhavin V. S. Kotel’nikov N. A. Nizhel’skij P. G. Tsybulev 《Astrophysical Bulletin》2007,62(4):360-368
We report the results of unique observations of the solar eclipse of March 29, 2006 over a wide radio-wavelength range from 1 to 50 cm made with the large RATAN-600 stationary radio telescope during the maximum eclipse phase performed using the method of the source transit across the fixed beam pattern. The multifunctional opportunities of the radio telescope allowed observations to be performed simultaneously in a part of the Northern sector of RATAN-600 and in the Southern-sector plus periscope mode using all the available receiving equipment at the corresponding secondary mirrors. At the time of maximum eclipse phase a narrow 1—3-arcsec wide crescent-shaped band near the North Solar Pole remained visible out of the entire solar disk covered by the Moon. We achieved high flux sensitivity, which allowed us to discover a large polar radio source located above the North Solar Pole and obtain detailed data on its radiation and spatial structure. Moreover, we detected optically thin radiation of the solar corona at the brightness-temperature level of several K or several tens of K. We find this radiation to extend beyond the solar limb out to the heliocentric distances of one solar radius. These data are unique in that they are not contaminated by scattered radiation of the solar radio disk, which usually shows up in ordinary observations. We are the first to obtain a detailed spectrum of the radiation of a high-latitude prominence at many wavelengths with a 1% frequency resolution in the microwave range, which allowed us to estimate its magnetic field at a number of levels in the lower corona. 相似文献
17.
18.
A. Gherardi M. Romoli E. Pace M. Pancrazzi G. Rossi D. Paganini M. Focardi 《Astrophysics and Space Science》2009,320(1-3):239-241
The HERSCHEL/SCORE is a suborbital mission which will observe the solar corona in UV and in visible light for measurements of solar corona. The coronagraph for such observation is an Italian instrument and, in particular, the CCD camera detectors are developed at the XUVLab of the Department of Astronomy and Space Science of Florence University. Such detectors communicate with the onboard computer by means the IEEE1355 Spacewire standard interface (developed in our laboratories) and implement a lot of smart and custom procedures for imaging. The main innovation of SCORE coronagraph is the first use in space of a variable retarder plate based on liquid crystals and the optical design capable of simultaneous observation in UV and Visible light. 相似文献
19.
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
20.
Phillips K.J.H. Read P.D. Gallagher P.T. Keenan F.P. Rudawy P. Rompolt B. Berlicki A. Buczylko A. Diego F. Barnsley R. Smartt R.N. Pasachoff J.M. Babcock B.A. 《Solar physics》2000,193(1-2):259-271
The Solar Eclipse Coronal Imaging System (SECIS) is an instrument designed to search for short-period modulations in the solar corona seen either during a total eclipse or with a coronagraph. The CCD cameras used in SECIS have the capability of imaging the corona at a rate of up to 70 frames a second, with the intensities in each pixel digitised in 12-bit levels. The data are captured and stored on a modified PC. With suitable optics it is thus possible to search for fast changes or short-period wave motions in the corona that will have important implications for the coronal heating mechanism. The equipment has been successfully tested using the Evans Solar Facility coronagraph at National Solar Observatory/Sacramento Peak and during the 11 August 1999 eclipse at a site in north-eastern Bulgaria. The instrument is described and preliminary results are outlined. 相似文献