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1.
On 6 September, 1982 very regular, narrow-band radio pulsations of solar origin were observed on the 410 MHz solar radiometer at the Learmonth Solar Observatory. Initial low-amplitude pulsations with a period of about 3 min gave way to large-amplitude pulsations with a period of about 5 min following a 1B solar flare. Position measurements at 327 MHz with the Culgoora Radioheliograph indicated two sources: a strong, extended source located above a unipolar magnetic region near the centre of the disk and a much weaker source near the west limb. Polarisation measurements indicate the burst to be plasma emission.The radio pulsations were unique in their association with both sympathetic radio emission and optical flares at widely different locations. Interpretation of the observations in terms of sausage mode standing oscillations in a coronal flux tube leads to an estimate of the magnetic flux density B = 45 G at the 400 MHz plasma level. Also a 2.8-fold density increase in the loop after the 1B flare is inferred. 相似文献
2.
The new 100–4200 MHz Ondejov radiospectrograph and the high-time resolution 3 GHz radiometer are described and the observations of fast drift bursts during the increased solar activity of September 5–7, 1992 are presented and analyzed. 相似文献
3.
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
4.
The Very Large Array and the Soft X-ray Telescope (SXT) aboard the Yohkoh satellite jointly observed the rapid growth and decay of a so-called anemone active region on 3–6 April, 1992 (AR 7124). The VLA obtained maps of the AR 7124 at 1.5, 4.7, and 8.4 GHz. In general, discrete coronal loop systems are rarely resolved at 1.5 GHz wavelengths because of limited brightness contrast due to optical depth effects and wave scattering. Due to its unusual anemone-like morphology, however, several discrete loops or loop systems are resolved by both the VLA at 1.5 GHz and the SXT in AR 7124.Using extrapolations of the photospheric field and the radio observations at 4.7 and 8.4 GHz, we find that the microwave emission is the result of gyroresonance emission from a hot, rarefied plasma, at the second and/or third harmonic. The decimetric source is complex -1.5 GHz emission from the leading part of AR 7124 is due to free-free emission, while that in the trailing part of the active region is dominated by gyroresonance emission. We also examine an interesting case of a discrete radio loop with no soft X-ray (SXR) emission adjacent to a hot SXR loop. This observation clearly shows the multithermal nature of the solar corona. 相似文献
5.
This paper determines what should be the difference between the colour of the solar disc centre and the integrated light of the corona at different heights. We define the colour as the ratio of the spectral intensity at = 640 nm and = 490 nm. The optical radiation of the corona is assumed to be caused by a contribution of photospheric light scattered on free electrons in K-corona and by a contribution of the photospheric light scattered on solid dust particles in F-corona. The limb-darkening law was taken from Pierce and Slaughter (1977). The distribution of electron density and brightness of the F-corona was taken from van de Hulst (1950). We indicate that the solar corona should be already close to the limb, more reddish than the centre of the solar disc, where reddening increases with the height due to the increase of the contribution of the F-corona. 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.
B. J. Robinson 《Astrophysics and Space Science》1986,118(1-2):57-61
A large synthesis radio telescope is under construction in Australia at a cost of $A 30.7million. In comprises a 6 km-long compact array of 22 m antenna at Culgoora and a long baseline array of 319 km, achieved by adding another 22 m antenna near Coonabarabran and the existing 64 m antennae at Parkes. On occasion it will be possible to use this arry with one of the deep space network antennas at Tidbinbilla to achieve a baseline of 580 km.The arrays have been designed to provide high-resolution radio images over a wide field with high-dynamic range plus good polarization and spectral line performance. The operating frequency range is from about 327 MHz to over 50 GHz.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984. 相似文献
8.
C. F. Keller 《Solar physics》1971,21(2):425-429
White-light photographs of the solar corona were taken during the March 1970 eclipse from an Air Force NC-135 jet aircraft at an altitude of 36 380 ft. Four photographs each were made for several exposure times varying from 0.1 to 10.0 s. Three each were made with plane polaroid filters whose orientation was varied at 60° intervals. Stabilization of the camera was approximately 10 even during the longest exposures. The corona was recorded to distances beyond 12 R
.A preliminary study of per cent polarization as a function of position with respect to the solar disk for a set of 1.0 s exposures shows an inversion in per cent polarization in the region 6 to 8 R
-polarization decreasing outward to the region and increasing again beyond it. This inversion is most apparent along the major streamers.Intensities traced outward from the Sun in both polar and equatorial directions are compared with previous observations.Work done under the auspices of the U.S. Atomic Energy Commission. 相似文献
9.
It is known that mode coupling may occur in quasi-transverse magnetic field regions of the solar corona, which produces linear polarization at microwave frequencies. A microwave polarimeter measuring all 4 Stokes parameters at 8.918 GHz simultaneously at three different highfrequency bandwidths (40 kHz, 400 kHz and 5 MHz) has been developed in order to observe the linear component and its Faraday rotation. The respective minimum detectable changes of the Stokes parameters I, Q, U and V are 9, 3 and 1 solar flux unit at an integration time of 1 s. For burst intensities greater than 300 solar flux units, the minimum detectable degree of linear and circular polarization is 1 %–3 %, depending on the bandwidth. Observations of 68 bursts showed that most of the bursts were circularly polarized. No linear polarization could be found within the limits of accuracy of our polarimeter. Two possible explanations for this result are discussed. The possibility of mode coupling however cannot be excluded from these first observations. 相似文献
10.
The dynamic spectrum, a three dimensional record of the radio intensity as a function both of time and frequency, has long been used as a probe of plasma processes in the solar corona. Beginning with the work of Wild and McCready (1950) dynamic spectroscopy has been used to distinguish between the multitude of radio wave emitting phenomena which occur in the solar corona and to infer the physical mechanisms responsible.Stellar dynamic spectroscopy has always been a tantalizing prospect. The vast body of experience with solar dynamic spectroscopy would prove invaluable in interpreting stellar dynamic spectra. Further, the new parameter regimes presented by stellar coronas would allow further insight to be gained in the physical processes at work in stellar coronas.Recently, Bastian and Bookbinder (1987) used the Very Large Array in spectral line mode at 1.4 GHz with a bandwidth of 50 MHz to obtain the first dynamic spectra of nearby flare stars. The spectral resolution was 3.125 MHz and the temporal resolution was 5 s. While the relative bandwidth was less than ideal (/ 5%), the spectra so obtained were sufficient to show the presence of narrowband structure in a radio outburst from the well-known dMe flare star UV Ceti.Several efforts are now underway to obtain stellar dynamic spectra, of both RS CVn binaries and dMe flare stars, with higher degrees of spectral and temporal resolution. Among these are use of a 1024 channel correlator with the 1000' telescope at Arecibo and use of the Berkeley Fast Pulsar Search Machine (Kulkarni et al. 1984) with the Green Bank 140' telescope.
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11.
K. Kai 《Solar physics》1969,10(2):460-464
Radioheliograph observations at 80 MHz are reported of a flare-associated event in which two type II bursts occur in four different sources. The projected centres of the sources lie along an arc subtending an angle of about 150° at the optical flare centre. If the arc represents the projection on the Sun's disk of a shock front passing through the 80 MHz plasma level, the source configuration suggests that the shock wave has originated from the optical flare region and propagated into the corona within a limited cone. On the opposite side of the flare centre, outside the shock cone, there was a stable bipolar source. Strong magnetic fields in this source may have acted as a magnetic wall to the shock wave and inhibited its propagation in this direction. 相似文献
12.
We report here on high angular resolution observations of solar noise storm sources at a frequency of 75 MHz. The data for the study were obtained at the Gauribidanur Radio Observatory (long.: 77°2612 E, lat.: 13°3612 N) about 100 km north of Bangalore, India, during the solar eclipse of 24 October 1995. Our main conclusion is that there are structures of angular size 2.5 arc min in the outer solar corona. 相似文献
13.
The data on optical, X-ray and gamma emission from proton flares, as well as direct observations of flare-associated phenomena, show energetic proton acceleration in the corona rather than in the flare region. In the present paper, the acceleration of protons and accompanying relativistic electrons is accounted for by a shock wave arising during the development of a large flare. We deal with a regular acceleration mechanism due to multiple reflection of resonance protons and fast electrons from a collisionless shock wave front which serves as a moving mirror. The height of the most effective acceleration in the solar corona is determined. The accelerated particle energy and density are estimated. It is shown in particular that a transverse collisionless shock wave may produce the required flux of protons with energy of 10 MeV and of relativistic electrons of 1–10 MeV.The proposed scheme may also serve as an injection mechanism when the protons are accelerated up to relativistic energies by other methods. 相似文献
14.
The Very Large Array (VLA) and the frequency agile interferometer at the Owens Valley Radio Observatory (OVRO) were used to observe the M8.1 flare of 23 June, 1988. The VLA obtained images prior to and during the flare at 333 MHz, and at 1.5 and 4.7 GHz. The frequency agile interferometer at Owens Valley obtained interferometer amplitude and total power spectra of the flare at 45 frequencies between 1 and 18 GHz. The observations were supplemented by radiometer measurements made by the USAF RSTN network site at Palehua, HI, by GOES soft X-ray observations, by USAF SOON H filtergrams, and by a KPNO photospheric magnetogram.The radio data reveal a wide variety of phenomena, including: (i) a multiply impulsive microwave burst that is essentially thermal in character; (ii) stationary discrete components at 1.5 GHz, associated temporally and spatially with distant brightenings in Ha; (iii) a dynamical component at 1.5 GHz associated with hot plasma moving subsonically into the corona; (iv) the appearance of intense, short-lived, decimetric burst activity near the lead sunspot in the active region at 1.5 GHz, indicative of a high degree of inhomogeneity in the source.The unusually complete radio coverage allows us to investigate the transport of energy from the initial site to sites of distant H brightenings. The transport of energy appears to be most consistent with slow, thermal processes, rather than rapid transport by nonthermal electron beams. 相似文献
15.
V. V. Zaitsev 《Solar physics》1971,20(1):95-105
An interpretation is suggested for the rain type radio bursts on the basis of a pulsating regime of the stream instability. This regime may occur in ejected stabilized ion streams trapped in the region in which the magnetic field of the corona has a typical bipolar structure. 相似文献
16.
Meter-wavelength observations are presented for the solar radio storm of August 17–22, 1968. The data comprise dynamic spectra and high-resolution brightness distributions from the 80 MHz radioheliograph.It is found that the storm consisted essentially of type III bursts at the lower frequencies and type I at the higher frequencies; the transition, usually near 60 MHz, was fairly sharp. The type I source was located over an active region associated with a large sunspot group. The type III position was displaced about 0.5 R
transversely from the type I, in a region of low magnetic field.The evident close association between the two types of emission can best be explained by disturbances originating in the type I region, propagating outwards through a region of weak magnetic field, and triggering an electron acceleration process, probably at the cusp of a helmet structure. The observed frequency and spatial relationship between the type I and type III components in events of this kind follow as a natural consequence of this model.A comparison of these results with the hectometer-wavelength satellite observations of the 1968 August event makes possible a qualitative estimate of the outward path of the type III exciters through the corona, and it is apparent that below the solar wind region of the corona this path departs considerably from the radial direction. 相似文献
17.
J. Roosen 《Solar physics》1969,7(3):448-462
The quiet component of the 9.1-cm solar radio emission is studied from the Stanford radioheliograms covering the period April–October 1964. The distribution of the brightness temperature in heliographic coordinates is not entirely uniform, but positive and negative departures from the average value appear at a number of stable locations. The most important negative departure crosses the central meridian 4 days before the maximum of the recurrent geomagnetic activity. Two out of three less important brightness depressions are connected with geomagnetic disturbances in the same manner. It is suggested that the brightness depressions are identical with M-regions.The result is confirmed by the construction of polytrope models for the solar wind, for various values of the parameters (the polytrope index) and T (the temperature in the inner corona). The velocities near the earth's orbit and in the inner corona are computed as functions of the model parameters, the density results from the observed proton flux at 1 AU. For quiet conditions the model with T = 1.26 × 106 K and = 1.10 is appropriate. The corresponding density and temperature in the corona lead to a value of 4000 K for the contribution of the corona to the 9-cm brightness. For disturbed conditions the suitable model has the parameters T 2.0 × 106 K, a 1.04. It being given that the proton flux at 1 AU is relatively constant, the equation of continuity leads to a low coronal density because of the high solar-wind velocity. The corresponding coronal contribution to the 9-cm brightness is of the order of 10 K. This confirms that the brightness temperature is considerably reduced in the regions where the enhanced solar wind originates. We suggest the name coronal depression for such regions.Papers II and III will appear in forthcoming issues of this journal. 相似文献
18.
James W. Warwick 《Solar physics》1968,5(1):111-117
A major radio burst at decametric frequencies at 1638 UT on June 9, 1959 is apparently a Type-IV continuum burst of the kind that drifts from high to low frequencies. We present observations of flux variations and East-West positions of the emission at both 18 and 38 MHz. The burst moves outward at a speed of about 4700 km·sec?1 at each frequency to a height of about 3 R ⊙ from the sun's center and then returns to the sun. This behavior is not simultaneous at 18 MHz and 38 MHz; the outward moving phase of 18 MHz emission occurs during the return phase of 38 MHz. We suspect that a solitary Alfvén wave or shock traverses the outer corona at the time of this burst. Relativistic electrons created low in the solar atmosphere travel freely along radial lines of force up to the coronal-streamer heights of the Type-IV burst. Upon encountering the shock, the electrons emit locally intense synchrotron emission, and pass through the shock on out into interplanetary space. This model appears to be consistent with other shock front phenomena in interplanetary space and the corona. Finally, the Razin effect (Boischot and Clavelier, 1967) suggests that low-frequency cut-offs in Type-IV bursts ought to be quite constant in frequency, and not higher than between 0.4 to 4 MHz. 相似文献
19.
We derive the electron density distribution in the ecliptic plane, from the corona to 1 AU, using observations from 13.8 MHz to a few kHz by the radio experiment WAVES aboard the spacecraft Wind. We concentrate on type III bursts whose trajectories intersect the spacecraft, as determined by the presence of burst-associated Langmuir waves, or by energetic electrons observed by the 3-D Plasma experiment. For these bursts we are able to determine the mode of emission, fundamental or harmonic, the electron density at 1 AU, the distance of emission regions along the spiral, and the time spent by the beams as they proceed from the low corona to 1 AU. For all of the bursts considered, the emission mode at burst onset was the fundamental; by contrast, in deriving many previous models, harmonic emission was assumed.By measuring the onset time of the burst at each frequency we are able to derive an electron density model all along the trajectory of the burst. Our density model, after normalizing the density at 1 AU to be ne(215 R0)=7.2 cm–3 (the average value at the minimum of solar activity when our measurements were made), is ne=3.3×105 r–2+4.1×106 r–4+8.0×107 r–6 cm–3, with r in units of R0. For other densities at 1 AU our result implies that the coefficients in the equation need to be multiplied by n
e
(1 AU)/7.2.We compare this with existing models and those derived from direct, in-situ measurements (normalized to the same density at 1 AU) and find that it agrees very well with in-situ measurements and poorly with radio models based on apparent source positions or assumptions of the emission mode. One implication of our results is that isolated type III bursts do not usually propagate in dense regions of the corona and solar wind, as it is still sometimes assumed. 相似文献
20.
On April 3, 4, 6, and 8, 1978, solar observations were made using the Haystack 120 ft telescope at 8, 15, 22, and 43 GHz. H filtergrams obtained at the Sacramento Peak Observatory on the same days showed an average of more than 30 filaments or filament fragments (per day) on the disk. Most of these appeared as depressions in brightness temperature at 15 and 22 GHz. Because of the relatively low spatial resolution at 8 GHz, only a few appeared at that frequency, and presumably because of lower opacity in filaments at higher frequencies, few depressions were visible at 43 GHz. At 15 and 22 GHz, more depressions appeared than H filaments, but virtually all the radio depressions overlay magnetic neutral lines. Taking the data sets for each day as independent samples, we found that at 22 GHz, 46 of the 77 radio depressions were associated with H filaments; at 15 GHz the correlation was smaller; only 27 out of 48 being associated with the H filaments. The data imply that the microwave depression features are the result of absorption by filaments and perhaps also the result of other effects of the associated filament channel, but not necessarily coronal depletion. The effects of filament absorption are, statistically, about twice as effective as other phenomena (such as absorption by material invisible in H, for example) in creating the radio depression. A center-to-limb study of a single large filament clearly showed that at 15 and 22 GHz the absorption by cool hydrogen supported above the neutral line was the predominant factor in producing the observed depression at radio frequencies. 相似文献