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1.
J. R. Blakey 《Solar physics》1976,46(1):241-245
Observations of McMath region 10433 at 22 GHz using a telescope with a 4 beam during July 1974 revealed the existence events or microbursts with intensities below the sensitivity limit of normal solar patrol instruments. Many of these events were simply the high frequency counterpart of more intense bursts observed at lower frequencies. This note considers the small number of events which suggest that the gyro-synchrotron mechanism alone is incapable of explaining the observations and indicates that a thermal mechanism is needed to explain the high frequency event.On leave of absence from Department of Physics, University of Surrey, Guildford, U.K.  相似文献   

2.
A study has been made of the relation of 19 GHz( = 1.58 cm) solar radio bursts to solar proton emission, with particular reference to the usefulness of relatively long duration bursts with intensities exceeding 50% of the quiet Sun flux (or exceeding 350 × 10–22 W m–2 Hz–1) as indicators of the occurrence of proton events during the four years from 1966–69. 76 to 88% of such bursts are directly associated with solar protons and 60 to 85% of the moderate to large proton events in the four year period could have been predicted from these bursts. The complete microwave spectra of the proton events have also been studied, and have been used to extend the results obtained at 19 GHz to other frequencies, particularly in the 5–20 GHz band. The widely used frequency of 2.8 GHz is not the optimum frequency for this purpose since proton events have a minimum of emission in this region. Most of the radio energy of proton events is at frequencies above 10 GHz. The radio spectra of proton events tend to peak at higher frequencies than most non-proton events, the overall range being 5 to 70 GHz, with a median of 10–12 GHz and a mean of 17 GHz.On leave from the Radio and Space Research Station, Slough, England, as 1969–1970 National Research Council-National Academy of Sciences Senior Post-Doctoral Research Associate at AFCRL.  相似文献   

3.
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   

4.
Repeated raster images of solar active regions taken at the line centers of the Si iv and C iv resonance lines using the University of Colorado (CU) ultraviolet spectrometer aboard OSO-8 reveal dramatic transient brightenings of up to factors of 10. These brightenings last several minutes and frequently show a repetitive character. Inspection of simultaneous H flare patrol records show that these transition zone events are often associated with subflare-like brightenings in the chromosphere. These observations indicate that direct excitation or heating of material already at transition zone temperatures caused by non-thermal particle streams is inadequate to explain the degree of brightening of these lines. The measurements suggest that some process that enhances density of material at 105 K is occurring during these events.  相似文献   

5.
A mm-wave thermal burst has been observed at 73 GHz. The simultaneous observation at 17 GHz revealed that this mm-wave burst was quite a different component from the non-thermal burst co-existing at a cm-wavelength range. Since the source of this burst seemed to be opaque or nearly opaque, the temperature became several tens of thousands degrees. Considering also the similarity between time profiles of the 73 GHz intensity and the H light curve, it is concluded that this mm-wave burst is situated very close to the H flare region.  相似文献   

6.
A millisecond recorder for solar observation at 2.84 GHz was put to work in 1981. From April 1981 to September 1982 it recorded 250spike pulse events, which are here listed together with information on the associated solar flares, hard X-ray bursts and radio bursts. In defining these spike events, particular attention has been paid to ensure the reliability of the recorded data. Statistical analysis of the data has given some interesting results. The spike pulses have shorter duration and higher flux density than were previously known, and the basic units of the spike pulse events are single spike pulses crowded together forming separate clusters. Many spike pulses observed are not yet resolved at 1 ms. Fast spike pulse events are closely correlated with complex magnetic field regions, and are often accompanied by hard X-ray bursts and fast drifting radio bursts. Some such events showed no correspondence with the radio bursts at the same frequency, 2.84 GHz, but corresponded to those occurring at dm and short cm wavelengths. Some theoretical investigations of the spike phonomena have been carried out, the details of which will be discussed elsewhere.  相似文献   

7.
The results of 21/2 yr (July 1967–December 1969) monitoring of solar radio bursts at 19 GHz ( = 1.58 cm) at the Radio and Space Research Station, Slough, are presented. Observations at this frequency are important in helping to define the form of the microwave spectrum of solar bursts since many of the more intense bursts have their spectral peak in the frequency region above 10 GHz. Fifteen bursts with peak flux increases exceeding 1000 × 10–22 Wm–2 Hz–1 were observed during this period.  相似文献   

8.
The discussion of the development curves of several solar flares observed in the H-line leads to some new information about the photometric structure and behaviour of flares of importance from 1 to 2. The main results are as follows. An H-flare appears to be a pulsating phenomenon which, after an initial contraction, rapidly reaches its maximum and then exponentially grows fainter with time.Analytical representations for both the pulsation periods and the exponential decreases are given. Many of the aspects of the flare phenomenon are more violent as the considered intensity level is higher.A discussion on the present day state of solar patrol and some suggestions to improve it to be useful for solar physics is also made in the light of the present analysis.  相似文献   

9.
Lara  A.  Gopalswamy  N.  Kundu  M. R.  Pérez-EnrÍquez  R.  Koshiishi  H.  Enome  S. 《Solar physics》1998,178(2):353-378
We have studied the properties and evolution of several active regions observed at multiple wavelengths over a period of about 10 days. We have used simultaneous microwave (1.5 and 17 GHz) and soft X-ray measurements made with the Very Large Array (VLA), the Nobeyama Radio Heliograph (NRH) and the Soft X-ray Telescope (SXT) on board the Yohkoh spacecraft, as well as photospheric magnetograms from KPNO. This is the first detailed comparison between observations at radio wavelengths differing by one order of magnitude. We have performed morphological and quantitative studies of active region properties by making inter-comparison between observations at different wavelengths and tracking the day-to-day variations. We have found good general agreement between the 1.5 and 17 GHz radio maps and the soft X-rays images. The 17 GHz emission is consistent with thermal bremsstrahlung (free-free) emission from electrons at coronal temperatures plus a small component coming from plasma at lower temperatures. We did not find any systematic limb darkening of the microwave emission from active regions. We discuss the difference between the observed microwave brightness temperature and the one expected from X-ray data and in terms of emission of a low temperature plasma at the transition region level. We found a coronal optical thickness of 10-3 and 1 for radiation at 17 and 1.5 GHz, respectively. We have also estimated the typical coronal values of emission measure ( 5 × 1028 cm-5), electron temperature ( 4.5 × 1066 K) and density ( 1.2 × 109 cm3). Assuming that the emission mechanism at 17 GHz is due to thermal free-free emission, we calculated the magnetic field in the source region using the observed degree of polarization. From the degree of polarization, we infer that the 17 GHz radiation is confined to the low-lying inner loop system of the active region. We also extrapolated the photospheric magnetic field distribution to the coronal level and found it to be in good agreement with the coronal magnetic field distribution obtained from microwave observations.  相似文献   

10.
We present here the results of the first systematic study of electrons of energies greater than 10 MeV associated with solar flares. We have made direct measurements of the frequency with which these particles are found in solar flare related events, the spectra of the particles, and the evolution of the spectra during these events. In addition the nature of the propagation of these electrons is studied and the degree of anisotropy in their diffusion is measured for the first time.The observations were made aboard the spacecraft OGO-5 from 1968, March through 1969, August. It is found that electrons in the energy range 12–45 MeV are normally present in major solar particle events. The time-intensity profiles of the fluxes indicate diffusive propagation; and the time-to-maximum intensity is found to vary with solar longitude in a way which can only be the result of anisotropic propagation with the perpendicular diffusion coefficient comparable in magnitude to, but smaller than, the parallel diffusion coefficient. Spectra during the observed events fit the power law AE – with 2.5 3.8. The time evolution of the spectrum throughout the course of the 4 most intense events shows that the spectrum steepens rapidly during the initial phase but retains a constant slope through the decay phase.Events which behave in a manner which is not described by the normal diffusion picture are also discussed. These examples show phenomena other than direct flare injection followed by anisotropic diffusion.This work was supported in part by the National Aeronautics and Space Administration under Contract NAS 5-9096 and Grant NGL 14-001-005.Submitted to the Department of Physics, University of Chicago, Chicago, Illinois in partial fulfillment of the requirements for the Ph. D. degree.NASA Trainee 1967–1969.  相似文献   

11.
In this paper, the observed solar radio pulsations during the bursts at 9.375 GHz are considered to be excited by some plasma instability. Under the condition of the conservation of energy in the wave-particle interaction, the saturation time of plasma instabilities is inversely proportional to the initial radiation intensity, which may explain why the repetition rate of the pulsations is directly proportional to the radio burst flux at 9.375 GHz as well as 15 GHz and 22 GHz. It is also predicted that the energy released in an individual pulse increases with increasing the flux of radio bursts, the modularity of the pulsations decreases with increasing the flux of radio bursts, these predictions are consistent with the statistical results at 9.375 GHz in different events. The energy density of the non-thermal particles in these events is estimated from the properties of pulsation. For the typical values of the ambient plasma density (109 cm–3) and the ratio between the nonthermal and ambient electrons (10–4), the order of magnitude of the energy density and the average energy of the nonthermal electrons is 10–4 erg/cm3 and 10 kev, respectively. It is interesting that there are two branches in a statistical relation between the repetition rate and the radio burst flux in a special event on March 11–17, 1989, which just corresponds to two different orders of magnitude for the quasi-quantized energy released in these five bursts. This result may be explained by the different ratios between the thermal and the nonthermal radiations.  相似文献   

12.
Torsti  J.  Valtonen  E.  Kocharov  L. G.  Vainio  R.  Riihonen  E.  Anttila  A.  Laitinen  T.  Teittinen  M.  Kuusela  J. 《Solar physics》1997,170(1):179-191
The energetic particle instrument ERNE on-board SOHO started its observations on December 15, 1995. The low-energy sensor of ERNE, LED, is capable of measuring particles in the energy range from 1 to 10 MeV nucl-1. From the beginning of the year 1996 until May 22, 1996, LED-observations included four energetic particle events above threshold intensities. An energetic particle event caused by a corotating interaction region that accelerated protons upto 10 MeV, was observed during January 20–25. Another similar particle event occured on May 6–12. The events were separated by four solar rotation periods. They had similar time profiles, but the one in May had a harder spectrum and a lower intensity level. The 4He-to-proton ratios were in accordance with the solar wind value. Energetic particles observed during April 22–23 and May 14–17 were accelerated at the Sun. The first one was apparently an outcome from an active region observed on the west limb by telescopes on-board SOHO. Protons were detected at energies from 1 to 10 MeV. For this event, the4He-to-proton ratio in the range 1.5–5 MeV nucl-1 was 3%. No 3He ions were detected. The period of May 14–15 was, in contrast, extremely 3He-rich: it had a3He-to-proton ratio of 1.5 ± 0.6 and a 3He-to- 4He ratio as high as 8. The period of May 14–17 comprised at least three individual, one-day-long events. The first two events were 3He-rich, while the last one seemed to have a normal composition.  相似文献   

13.
Multiple-beam observations of solar flares at submillimeter wavelengths need detection with at least four beams to derive the flux density $\mbox{$F$} $ of the emitting source, its size, and centroid position. When this condition is not fulfilled, the assumptions on the location and/or size of the emitting source have to be made in order to compute $\mbox{$F$}$ . Otherwise, only a flux density range $\mbox{$\Delta F$}$ can be estimated. We report on simultaneous flare observations at 212 and 210 GHz obtained by the Solar Submillimeter Telescope (SST) and the Bernese Multibeam Radiometer for Kosma (BEMRAK), respectively, during two solar events on 28 October 2003. For both events, BEMRAK utilized four beam information to calculate the source flux density F 210, its size and position. On the other hand, the SST observed the events with only one beam, at low solar elevation angles and during high atmospheric attenuation. Therefore, because of these poor observing conditions at 212 GHz, only a flux density range ΔF 212 could be estimated. The results show that ΔF 212 is within a factor of 2.5 of the flux density F 210. This factor can be significantly reduced (e.g. 1.4 for one of the studied events) by an appropriate choice of the 212 GHz source position using flare observations at other wavelengths. By adopting the position and size of the 210 GHz source measured by BEMRAK, the flux density at 212 GHz, F 212b, is comparable to F 210 within the uncertainties, as expected. Therefore our findings indicate that even during poor observing conditions, the SST can provide an acceptable estimate of the flux density at 212 GHz. This is a remarkable fact since the SST and BEMRAK use quite different procedures for calibration and flux density determination. We also show that the necessary assumptions made on the size of the emitting source at 212 GHz in order to estimate its flux density are not critical, and therefore do not affect the conclusions of previous studies at this frequency.  相似文献   

14.
Using data from ESSA Research Laboratory bulletins an estimate of the uncertainty for the times of beginning, maximum and ending, and maximum areas of H flares reported during 1967 is deduced and discussed. The need for an improvement of the reliability of the solar patrol service is also indicated.  相似文献   

15.
Data are presented from the IMP-4 satellite of 0.3–12 MeV electrons from the Sun between May 24, 1967 and May 2, 1969. Correlations with contemporary proton intensity increases at energies above 1 MeV are studied. Classical solar flare events such as those frequently observed from 30°W–60°W in solar longitude are not discussed. Categories of unusual events are defined and examples of each type are given. Discussion of these events centers around the emission and propagation of energetic particles from the point of origin on the Sun to the Earth. The results of this study are the following: (1) The differential electron energy spectrum (0.3–12 keV) from solar flares appears to be a constant of the flare process, with the spectral index = (-)3.0 ± 0.2. (2) Particle emission from solar flares contains a prompt component, which is injected into the interplanetary medium beyond the Sun and which is responsible for the diffusion characteristics of solar particle events, and a delayed component which is effectively contained in the lower solar atmosphere where it diffuses typically ± 100° in longitude and gradually escapes into interplanetary space. The delayed component gives rise to the corotating features commonly observed after the impulsive and diffusive onset from the prompt component. This is not the same as the two component model discussed by Lin (1970a) in which 40 keV electrons are often observed as a separate phenomenon and frequently precede higher energy particles observed at 1 AU. (3) Storage of electrons > 300 keV and protons > 1 MeV is essential to explain emission and propagation characteristics of solar particle events. In some rare cases the storage mechanism appears to be very efficient, culminating in a catastrophic decay of the trapping region. (4) The events with low proton/electron ratios all occur at least three weeks after the previous relativistic electron producing flare.  相似文献   

16.
Intense geomagnetic storms with DST index -100 nT were recorded on 9 March and 11 March 1993 associated with solar activity on 6 March and 9-10 March, respectively. In this paper, we discuss the characteristic features of the solar origins of the two events that gave rise to coronal and interplanetary disturbances and as a consequence produced strong geomagnetic activity at the Earth. The source of the activity in one case is attributed to a major 3M7.0 flare that occurred on 6 March 1993 and in the other case, to two large filament disruptions on the disk during 9-10 March, 1993. Both these sources were found to be located near changing or varying low-latitude coronal holes. They were also located close to the heliospheric currents sheets. Distinct X-ray activity was observed for both the events as observed by the Yohkoh SXT telescope. The detailed evolution and a comparison of these events on the basis of Yohkoh soft X-ray observations are presented here.  相似文献   

17.
The solar burst of 21 May, 1984, 13 26 UT, showed radio spectral emission with a turnover frequency above 90 GHz, well correlated in time with the hard X-ray emission. It consisted of seven major time structures (1–3 s in duration), of which each was composed of several fast pulses with rise times between 30 and 60 ms. The spectral indices of the millimeter and hard X-ray emission exhibited sudden changes during each major time structure. The subsecond pulses were nearly in phase at 30 and 90 GHz, but their relative amplitude at 90 GHz ( 50%) were considerably larger than at 30 GHz (<5%). It was also found that the 90 GHz and the 100 keV X-rays fluxes were proportional to the repetition rate of the subsecond pulses, and that the hard X-ray power law index hardens with increasing repetition rate.Proceedings of the Second CESRA Workshop on Particle Acceleration and Trapping in Solar Flares, held at Aubigny-sur-Nère (France), 23–26 June, 1986.  相似文献   

18.
Usually the gyrosynchrotron emission of microwave bursts from electron populations with a power-law (PL) energy distribution has been considered under the assumption that the spectral index of the distribution is constant over a wide range of energies. Meanwhile, there is strong evidence, in particular from hard X-ray and -ray, but also from cm/mm wavelength radio observations, that in many solar flare events the spectrum of the emitting electrons is characterized by a significant hardening at energies above 100–500 keV. We present some examples of calculated microwave burst spectra at cm/mm wavelengths taking into account the above evidence. It is shown that a break in the energy spectrum of the PL electrons can indeed result in a spectral hardening sometimes observed in microwave bursts at frequencies above 10–30 GHz.  相似文献   

19.
Solar flares and the cosmic ray intensity   总被引：2，自引：0，他引：2  
C. J. Hatton 《Solar physics》1980,66(1):159-165
The relationship between the cosmic ray intensity and solar activity during solar cycle 20 is discussed. A model is developed whereby it is possible to simulate the observed cosmic ray intensity from the observed number of solar flares of importance 1. This model leads to a radius for the modulation region of 60–70 AU. It is suggested that high speed solar streams also made a small contribution to the modulation of cosmic rays during solar cycle 20.  相似文献   

20.
Solar proton events have been studied for over thirty years and a great deal of lore has grown around them. It is the purpose of this paper to test some of this lore against the actual data. Data on solar proton events now exist for the period from 1956 to 1985 during which time 140 events took place in which the event integrated fluxes for protons of energy > 30 MeV was larger than 105 particles cm-2. We have studied statistical properties of event integrated fluxes for particles with energy > 10 MeV and for particles with energy > 30 MeV. Earlier studies based on a single solar cycle had resulted in a sharp division of events into ordinary and anomalously large events.Two such entirely separate distributions imply two entirely separate acceleration mechanisms, one common and the other very rare. We find that the sharp division is neither required nor justified by this larger sample. Instead the event intensity forms a smooth distribution for intensities up to the largest observed implying that any second acceleration mechanism cannot be rare. We have also studied the relation of event sizes to the sunspot number and the solar cycle phase. We find a clear bimodal variation of annual integrated flux with solar cycle phase but no statistically significant tendency for the large events to avoid sunspot maximum. We show there is almost no relation between the maximum sunspot number in a solar cycle and the solar cycle integrated flux. We also find that for annual sunspot numbers greater than 35 (i.e., non-minimum solar cycle conditions) there is no relation whatsoever between the annual sunspot numbers and annual integrated flux.  相似文献   

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