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1.
A synoptic study of the occurrence and polarization of 160 MHz noise storms recorded at Culgoora during the current solar cycle shows that the storm sources occur in large unipolar cells extending >90° in solar longitude and 60° in latitude, with lifetimes of 1 yr. From solar maximum onwards these large cells stretch across the solar equator to form a longitudinal sector pattern reminiscent of that observed in the interplanetary magnetic field. Comparisons with published heliospheric current sheet simulations support this conclusion. The noise storms occur in the strong magnetic fields above large, complex, flare-active sunspots. Unlike most active regions, those associated with noise storms do not always have dominant sunspots as leaders. Rather, about one-third have the dominant sunspot as a follower. The dominant sunspot polarities tend to agree with the long-lived sector structure, implying that emerging magnetic flux occurs at preferred longtitudes on the solar surface.  相似文献   

2.
We present multifrequency radioheliograph observations of solar radio noise storms. The data base consists of observations carried out over 7 different days in the spring months of 1992 and 1993. In all, we present about 82 hours of data with 1 s time resolution at 4 different frequencies between 164 and 410 MHz. The spatial resolutions in the EW and NS directions vary with frequency from 1.2 to 0.8 and 3.7 to 1.5 arc min, respectively. In order to study the characteristics of bursts and continuum, we have developed a method for separating them in the time domain at each frequency. Our main results are: (i) there are no systematic large-scale motions of the continuum, the position is usually stable to within 2 of arc over durations of 3–4 hours and more; (ii) the positions of the continuum at different frequencies are often closer to each other than 1 of arc and have strongly correlated small-scale motions; (iii) the bursts have their positions scattered over the continuum extent and are slightly smaller in size than the underlying continuum; and (iv) there is no evidence for bipolar structures. We discuss the implications of these results for the current models of noise storm emission and for the trapping of suprathermal electrons.Presented at the CESRA Workshop in Potsdam, Germany, 16–20 May, 1994.  相似文献   

3.
Solar radio and microwave sources were observed with the Very Large Array (VLA) and the RATAN-600, providing high spatial resolution at 91 cm (VLA) and detailed spectral and polarization data at microwave wavelengths (1.7 to 20 cm - RATAN). The radio observations have been compared with images from the Soft X-ray Telescope (SXT) aboard theYohkoh satellite and with full-disk phoptospheric magnetic field data from the Kislovodsk Station of the Pulkovo Observatory. The VLA observations at 91 cm show fluctuating nonthermal noise storm sources in the middle corona. The active regions that were responsible for the noise storms generally had weaker microwave emission, fainter thermal soft X-ray emission, as well as less intense coronal magnetic fields than those associated with other active regions on the solar disk. The noise storms did, however, originate in active regions whose magnetic fields and radiation properties were evolving on timescales of days or less. We interpret these noise storms in terms of accelerated particles trapped in radiation belts above or near active regions, forming a decimetric coronal halo. The particles trapped in the radiation belts may be the source of other forms of nonthermal radio emission, while also providing a reservoir from which energetic particles may drain down into lower-lying magnetic structures.Presented at the CESRA-Workshop on Coronal Magnetic Energy Release at Caputh near Potsdam in May 1994.  相似文献   

4.
G. Thejappa 《Solar physics》1991,132(1):173-193
A self-consistent theoretical model for storm continuum and bursts is presented. We propose that the Langmuir waves are emitted spontaneously by an anisotropic loss-cone distribution of electrons trapped in the magnetic field above active regions. These high-frequency electrostatic waves are assumed to coalesce with lower-hybrid waves excited either by the trapped protons or by weak shocks, making the observed brightness temperature equal to the effective temperature of the Langmuir waves.It is shown that whenever the collisional damping ( c ) is more than the negative damping (- A ) due to the anisotropic distribution, there is a steady emission of Langmuir waves responsible for the storm continuum. The type I bursts are generated randomly whenever the collisional damping ( c ) is balanced by the negative damping (- A ) at the threshold density of the trapped particles, since it causes the effective temperature of Langmuir waves to rise steeply. The number density of the particles responsible for the storm radiation is estimated. The randomness of type I bursts, brightness temperature, bandwidth and transition from type I to type III storm are self-consistently explained.On leave from Indian Institute of Astrophysics, Bangalore 560034, India.  相似文献   

5.
The trajectories of 38 type III storms in the interplanetary medium have been deduced from ISEE-3 radio observations and extrapolated back to the Sun to determine the Carrington coordinates of their footpoints. The analysis assumes radial motion of the solar wind, and the trajectories are projected radially back toward the surface for the last few solar radii. To identify the storm sources, the footpoints were compared to a variety of solar features: to the large-scale neutral line at the base of the current sheet, to active regions, to the small-scale neutral lines and H filaments which trace out active regions, and to coronal holes. Most of the footpoints were found to lie near active regions, in agreement with metric storm locations. There is a weak correlation with H filaments, no apparent association with the current sheet, and an anticorrelation with coronal holes. There is a small excess of storms in the leading half of magnetic sectors.  相似文献   

6.
Radio noise storms show that suprathermal electrons (a few tens of keV) are present in the vicinity of active regions during several hours or even a few days. Where and how these electrons are energized is not yet well known. A flare-like sudden energy release in the active region is in general observed at the onset of noise storms, either as a fully developed flare or, more often, as a soft X-ray brightening without conspicuous H signature. In order to investigate to what extent electrons energized in the active region contribute to the noise-storm emission in the overlying coronal structures, we combine radio imaging (Nançay radioheliograph) with X-ray spectral observations at photon energies of a few keV (GOES) and - for the first time - around 10 keV (WATCH/GRANAT). In two of four studied events the WATCH data show a significant excess of the deka-keV count rate above the expectation from an isothermal fit to the GOES fluxes. Although the electron population producing the deka-keV X-ray emission would be energetic enough to power the simultaneous radio noise storm, the much longer duration of the radio emission requires time-extended particle acceleration. The acceleration probably occurs in the corona overlying the X-ray emitting region, triggered by the processes which give rise to the X-ray brightenings.  相似文献   

7.
A solar type I noise storm was observed on 30 July, 1992 with the radio spectrometer Phoenix of ETH Zürich, the Very Large Array (VLA) and the soft X-ray (SXR) telescope on board theYohkoh satellite. The spectrogram was used to identify the type I noise storm. In the VLA images at 333 MHz a fully left circular polarized (100% LCP) continuum source and several highly polarized (70% to 100% LCP) burst sources have been located. The continuum and the bursts are spatially separated by about 100 and apparently lie on different loops as outlined by the SXR. Continuum and bursts are separated in the perpendicular direction to the magnetic field configuration. Between the periods of strong burst activities, burst-like emissions are also superimposed on the continuum source. There is no obvious correlation between the flux density of the continuum and the bursts. The burst sources have no systematic motion, whereas the the continuum source shows a small drift of 0.2 min–1 along the X-ray loop in the long-time evolution. The VLA maps at higher frequency (1446 MHz) show no source corresponding to the type I event. The soft X-ray emission measure and temperature were calculated. The type I continuum source is located (in projection) in a region with enhanced SXR emission, a loop having a mean density of n e = (1.5 ± 0.4) × 109 cm–3 and a temperature ofT = (2.1 ± 0.1) × 106 K. The centroid positions of the left and right circularly polarized components of the burst sources are separated by 15–50 and seem to be on different loops. These observations contradict the predictions of existing type I theories.Presented at the CESRA-Workshop on Coronal Magnetic Energy Release at Caputh near Potsdam in May 1994.  相似文献   

8.
A. Böhme 《Solar physics》1990,128(2):399-414
Intense noise storm continua at low frequencies are mostly observed in the later phase of solar cycles (Böhme, 1989). Radioheliographs may be needed to determine whether this effect is mainly caused by type I or type III continua. However, based on single-frequency records from the Tremsdorf Observatory a method to discriminate type I and type III continua even from polarization measurements was derived. Intense 40 MHz continua identified by spectral criteria as a type III continuum are more weakly polarized than type I continua. The increase in the number of intense continua at frequencies 64 MHz during the second, compared to the first, activity maximum of cycle No. 20 was due to an enhanced number of continua with a significant contribution of type I continuum. Relations between the parameters of the continua and the concurrent storm bursts confirm the validity of the above-mentioned ideas and may be useful to test models which try to explain the generation of type I and type III storms under common aspects.  相似文献   

9.
We review high-spatial-resolution observations of the Sun which reflect on the role of mode coupling in the solar corona, and present a number of new observations. We show that typically polarization inversion is seen at 5 GHz in active region sources near the solar limb, but not at 1.5 GHz. Although this is apparently in contradiction to the simplest form of mode coupling theory, in fact it remains consistent with current models for the active region emission. Microwave bursts show no strong evidence for polarization inversion. We discuss bipolar noise storm continuum emission in some detail, utilizing recent VLA observations at 327 MHz. We show that bipolar sources are common at 327 MHz. Further, the trailing component of the bipole is frequently stronger than the leading component, in apparent conflict with the leading-spot hypothesis. The observations indicate that at 327 MHz mode coupling is apparently strong at all mode-coupling layers in the solar corona. The 327 MHz observations require a much weaker magnetic field strength in the solar corona to explain this result than did earlier lower-frequency observations: maximum fields are 0.2 G. This is a much weaker field than is consistent with current coronal models.On leave from the Indian Institute for Astrophysics, Bangalore, India.  相似文献   

10.
Detailed comparisons of Culgoora 160 MHz radioheliograms of solar noise storms and Skylab EUV spectroheliograms of coronal loop structures are presented. It is concluded that: (1) there is a close association between changes in large-scale magnetic fields in the corona and the onset or cessation of noise storms; (2) these coronal changes result from the emergence of new magnetic flux at the photospheric level; (3) although new magnetic flux at the photospheric level is often accompanied by an increase in flare activity the latter is not directly responsible for noise storm activity; rather the new magnetic flux diffuses slowly outwards through the corona at rates 1–2 km s–1 and produces noise storms at 160 MHz 1–2 days later; (4) the coronal density above or in large-scale EUV loop systems is sufficiently dense to account for noise storm emission at the fundamental plasma frequency; (5) the scatter in noise storm positions can be accounted for by the appearance and disappearance of individual loops in a system.  相似文献   

11.
A highly anisotropic packet of solar electron intensities was observed on 6 April 1971 with a sensitive electrostatic analyzer array on the Earth-orbiting satellite IMP-6. The anisotropies of intensities at electron energies of several keV were factors 10 favoring the expected direction of the interplanetary magnetic lines of force from the Sun. The directional, differential intensities of solar electrons were determined over the energy range 1–40 keV and peak intensities were 102 cm–2 s–1 sr–1 eV–1 at 2–6 keV. This anisotropic packet of solar electrons was detected at the sattelite for a period of 4200 s and was soon followed by isotropic intensities for a relatively prolonged period. This impulsive emission was associated with the onsets of an optical flare, soft X-ray emission and a radio noise storm at centimeter wavelengths on the western limb of the Sun. Simultaneous measurements of a type III radio noise burst at kilometric wavelengths with a plasma wave instrument on the same satellite showed that the onsets for detectable noise levels ranged from 500 s at 178 kHz to 2700 s at 31.1 kHz. The corresponding drift rate requires a speed of 0.15c for the exciting particles if the emission is at the electron plasma frequency. The corresponding electron energy of 6 keV is in excellent agreement with the above direct observations of the anisotropic electron packet. Further supporting evidence that several-keV solar electrons in the anisotropic packet are associated with the emission of type III radio noise beyond 50R is provided by their time-of-arrival at Earth and the relative durations of the radio noise and the solar electron packet. Electron intensities at E 45 keV and the isotropic intensities of lower-energy solar electrons are relatively uncorrelated with the measurements of type III radio noise at these low frequencies. The implications of these observations relative to those at higher frequencies, and heliocentric radial distances 50R , include apparent deceleration of the exciting electron beam with increasing heliocentric radial distance.Research supported in part by the National Aeronautics and Space Administration under contracts NAS5-11039 and NAS5-11074 and grant NGL16-001-002 and by the Office of Naval Research under contract N000-14-68-A-0196-0003.  相似文献   

12.
On the basis of continuum energy distributions in the wavelength region 3200–11 000 Å, effective temperature for 14 Wolf-Rayet stars are estimated by comparing with Kurucz (1979) model atmospheres. The continuum energy distribution curve shows strong infrared excess emissions above of 5000 Å in every star.  相似文献   

13.
It is well known that sunspots are dark. This statement is not correct in the sunspot atmosphere between the chromosphere and the corona, where sunspots often are brighter than their surroundings. The brightest feature in the sunspot transition region is called a sunspot plume. Not all sunspots contain a plume. We find that 20 out of 21 sunspots show a plume when one magnetic polarity dominates the sunspot region out to a distance of 50 from the sunspot. Most sunspots show downflows that exceed 25 km s–1 in the sunspot plumes at temperatures close to 250000 K. This downflow is not maintained by inflow from the corona, but by gas at transition region temperatures, streaming in flow channels from locations well outside the sunspot. We suggest that this inflow is a necessary requirement for the sunspot plume to occur and present a working hypothesis for the origin of sunspot plumes. This paper is the first thorough spectral analysis of sunspot plumes. It is based on simultaneous observations of ten or six EUV emission lines in 42 sunspot regions with the Coronal Diagnostic Spectrometer – CDS on the Solar and Heliospheric Observatory – SOHO. The line profiles are studied in detail with another SOHO instrument, the Solar Ultraviolet Measurements of Emitted Radiation – SUMER.  相似文献   

14.
Vršnak  B.  Ruždjak  V.  Brajša  R.  Zlobec  P.  Altaş  L.  Özgüç  A.  Aurass  H.  Schroll  A. 《Solar physics》2000,194(2):285-303
A sample of 47 importance 1 flares whose H emission occurred or protruded over umbrae of major sunspots (so called Z-flares) was studied to investigate characteristics of the associated dm–m radio, microwave and soft X-ray emission as the energy release site permeats into regions of strong magnetic fields. A close time association was found between the microwave burst peak and the `contact' of the H emission with the sunspot umbra. The H emission attained maximum close to or a few minutes after the contact. The soft X-ray bursts were delayed more, attaining maximum 0–10 min after the contact. The onset of bursts in the dm–m wavelength range was associated with the period of growth or the peak of the microwave burst. Two categories of type III and IV bursts could be recognized: the ones starting some ten minutes before the microwave peak, and those that begin close to the microwave burst peak. Type III bursts occur preferably when the microwave burst peaks simultaneously with or after the contact. The results are explained presuming that the contact reveals a permeation of the energy release process into a region of strong magnetic fields, where the process intensifies, and where the accelerated particles have access to magnetic field lines extending to large coronal heights. Different manifestations of the energy release process in various magnetic field topologies are considered to account for the various time sequences observed.  相似文献   

15.
We consider potential sources of infrared (1 to 1 mm) continuum in solar flares. Several mechanisms should produce detectable fluxes: in the 350 window for ground-based observations, impulsive emission will arise in synchrotron radiation from 1–10 MeV electrons, and possibly thermal (free-free) continuum from the source of the white-light flare; the hot flare plasma responsible for soft X-ray emission will also emit detectable fluxes of free-free continuum in the largest flares. At shorter wavelengths the dominant infrared emission will come from the H flare itself. Observations in the infrared wavelengths will help to complete our picture of flare structure in both the impulsive and gradual phases.  相似文献   

16.
K X-ray line emission from S, Ar, Ca and Fe is calculated for conditions likely to exist in solar flares. We consider both the non-thermal and thermal phases of flares as indicated by X-ray observations. Impulsive non-thermal events seen at the onset of a flare at photon energies > 20 keV generally give rise to small K line fluxes (<250 photons cm-2 s-1) on the basis of data presented by Kane and Anderson. The amount of S K radiation in particular depends sensitively on the lower-energy bound of the non-thermal electron distribution giving rise to the impulsive burst, offering a possible means of determining this. Thermal K emission is significant for only Fe ions. For S, Ar and Ca, the temperatures required for a sizeable number of electrons with energies greater than the K-ionization potential will also strip these elements to ionization stages too high for K transitions to be possible. Comparison of thermal K emission from iron during an intense solar flare leads to a very high emission measure on the basis of these calculations, but such a value seems to be compatible with an analysis of the 1–3 Å continuum during the same event.NAS/NRC Resident Research Associate.Visiting Scientist, High Altitude Observatory, NCAR, Boulder, Colo. 80302.  相似文献   

17.
EUV and Magnetic Activities Associated with Type-I Solar Radio Bursts   总被引：1，自引：0，他引：1  
Type-I bursts (i.e. noise storms) are the earliest-known type of solar radio emission at the meter wavelength. They are believed to be excited by non-thermal energetic electrons accelerated in the corona. The underlying dynamic process and exact emission mechanism still remain unresolved. Here, with a combined analysis of extreme ultraviolet (EUV), radio and photospheric magnetic field data of unprecedented quality recorded during a type-I storm on 30 July 2011, we identify a good correlation between the radio bursts and the co-spatial EUV and magnetic activities. The EUV activities manifest themselves as three major brightening stripes above a region adjacent to a compact sunspot, while the magnetic field there presents multiple moving magnetic features (MMFs) with persistent coalescence or cancelation and a morphologically similar three-part distribution. We find that the type-I intensities are correlated with those of the EUV emissions at various wavelengths with a correlation coefficient of 0.7?–?0.8. In addition, in the region between the brightening EUV stripes and the radio sources there appear consistent dynamic motions with a series of bi-directional flows, suggesting ongoing small-scale reconnection there. Mainly based on the induced connection between the magnetic motion at the photosphere and the EUV and radio activities in the corona, we suggest that the observed type-I noise storms and the EUV brightening activities are the consequence of small-scale magnetic reconnection driven by MMFs. This is in support of the original proposal made by Bentley et al. (Solar Phys. 193, 227, 2000).  相似文献   

18.
This paper presents discrete chorus type emissions observed in January/July, 1970 during the routine recording of whistlers and VLF emissions at our low latitude ground station Gulmarg (geomag. lat., 24°26N; geomag. long., 147°09 E). The chorus type emissions are comprised of discrete, sometimes overlapping, tones of one or more spectral shapes (risers, falling tones, hooks, etc.). It is shown that these emissions are generated in the equatorial plane (L1.2) by cyclotron resonance between the propagating wave and gyrating electrons.  相似文献   

19.
This investigation shows that statistically there are significant time delays between H and hard X-ray (HXR) emissions during solar flares; most impulsive flares produce HXR emissions up to 1 min before and up to 2 min after the onset of H emission. HXR emissions are also found to be peaked up to 2 min before the H emissions.  相似文献   

20.
We present two-dimensional solar maps at 5.2 cm computed from one-dimensinal observations with the Siberian Solar Radio Telescope (SSRT), using Earth rotation aperture synthesis techniques. The resolution attained with the E-W branch of the instrument is 15 by 45 for a solar declination of about 23°. Maps during the period of June 8 to 13, 1988 clearly show the quiet-Sun background, sunspot and plage associated emission as well as compact sources above the neutral line in some active regions. We found that the latter disappear as the gradient of the longitudinal magnetic field decreases. We also detected emission associated with active regions behind the limb, apparently from unresolved loops, extending up to 40. The prospects of the SSRT, as a dedicated solar instrument, are discussed.  相似文献   

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