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1.
In this paper we investigate the contribution of gyro-resonance to the SVC of the solar radio emission. We calculated the spatial distributions of the gyroresonance radiation over uinpolar and bipolar active regions at a number of wavelengths and we found some interesting features. We also calculated the spectra of flux and polarization and our results were in general agreement with observations. This suggests that the gyro-resonance radiation is indeed an Important mechanism for the solar SVC.  相似文献   

2.
Active regions on the Sun in the 20th solar cycle are studied with special reference to their association with proton flares based on microwave interferometric observations at Toyokawa Observatory. It has been reconfirmed that the active regions associated with intense S-component emission with a high 3-cm to 8-cm flux ratio are likely to produce proton flares. About one fourth of 259 active regions during the period investigated are found to have definite features in the spatial distribution of polarization at a wavelength of 3 cm. Active regions with one particular type of polarization pattern have a good correlation with the occurrence of proton flares.  相似文献   

3.
Zhang  J.  Gopalswamy  N.  Kundu  M. R.  Schmahl  E. J.  Lemen  J. R. 《Solar physics》1998,180(1-2):285-298
We present the measurement of magnetic field gradient in magnetic loops in the solar corona, based on the multi-wavelength Very Large Array observations of two transient microwave brightenings (TMBs) in the solar active region 7135. The events were observed at 2 cm (spatial resolution 2=) and 3.6 cm (spatial resolution 3=) with a temporal resolution of 3.3 s in a time-sharing mode. Soft X-ray data (spatial resolution 2.5=) were available from the Soft X-ray Telescope on board the Yohkoh satellite. The three-dimensional structure of simple magnetic loops, where the transient brightenings occurred, were traced out by these observations. The 2-cm and 3.6-cm sources were very compact, located near the footpoint of the magnetic loops seen in the X-ray images. For the two events reported in this paper, the projected angular separation between the centroids of 2 and 3.6-cm sources is about 2.3= and 3.1=, respectively. We interpret that the 2 and 3.6-cm sources come from thermal gyro-resonance emission. The 2-cm emission is at the 3rd harmonic originating from the gyro-resonance layer where the magnetic field is 1800 G. The 3.6-cm emission is at the 2nd harmonic, originating from the gyro-resonance layer with a magnetic field of 1500 G. The estimated magnetic field gradient near the footpoint of the magnetic loop is about 0.09 G km=1 and 0.12 G km=1 for the two events. These values are smaller than those observed in the photosphere and chromosphere by at least a factor of 2.  相似文献   

4.
An analysis of the bandlike Jovian decametric emission is presented. A model for the active region that accounts for the observed radiation characteristics is described using the measured parameters of the bandlike emission and a model of the Jovian magnetic field. The active region is characterized not only by the fact that an upward-flowing electron stream is caused to radiate in this region, but the stream itself is broken into radiating electron bunches within the active region. Observed undulations of the emission band on the time-frequency plane are interpreted as motions of the active region along a flux tube. The instantaneous location of the active region along the flux tube shows a dependence on the density of the stream entering the active region. The mechanism responsible for density modulation of the stream appears to be common to both the bandlike and simple-S-burst emission types.  相似文献   

5.
We survey 14 super-active regions (SARs) in the 22nd cycle and 15 SARs in the 23rd cycle. Each produced major flares and major solar storms. Among them, the 25 most violent super active regions (VSARs) are selected based on five parameters: the largest area of sunspots, X-ray flare index (XRI), 10.7 cm radio flux, proton flux and geomagnetic A p index. In order to understand the VSARs, we have investigated a few key magnetic properties of those regions, i.e., net magnetic flux, tilt angle and force-free parameter best. The following results are found: (1) Most VSARs (84%) in our samples have net magnetic flux greater than 1021 Mx, implying that those are seriously unbalanced flux regions. Unbalanced flux active regions probably provide a nest to relate the small-scale to the large-scale magnetic field. (2) Most of the VSARs (68%) are of abnormal magnetic structure, violating the Hale–Nicholson Law. For most of the normal VSARs, the tilt angles are larger than 40°. 84% of the VSARs follow the hemispheric helicity rule. Generally, they have large magnetic twist and writhe helicity. (3) We also enlarge our samples to study the locations of VSARs by adding the top 10 of the major flares, proton events and severe magnetic storms from 1976 to 2001. It is found that 77% in our 30 samples of VSARs were preferentially located in 4 longitude bands, i.e., l c=80°±15° l c=170°±15° l c=260°±15° and l c=350°±15°. The interval of those longitude bands is roughly 90°. From the above results, we suggest that there probably is a special magnetic environment in the sub-photosphere of the four longitude bands where it is preferred to produce abnormal and complex active regions which easily produce major flares and major solar storms. Area, magnetic class, net magnetic flux, Carrington longitude and tilt angle of an active region may serve to predict likelihood of the active region producing hazarded space weather.  相似文献   

6.
The lack of open literature publication of the distributional properties of the cm-λ spectra of solar microwave bursts has lead to some erroneous concepts of the typical characteristics of these spectra. To provide more accurate information, this paper sets forth various distributions of the peak flux density spectra of large numbers of bursts, based on observations of the Sagamore Hill Radio Observatory at nine discrete frequencies between 245 and 35000 MHz over the years 1968–1971. As a foundation for the distribution studies, the basic spectral classification system is outlined. The majority of burst spectra were found to contain a cm-λ component having a single spectral maximum in the 1400 to 35000 MHz range; such spectra are designated C type. A study of the correlation of the spectral maximum frequency f max of the cm component and the photospheric magnetic field strength of the associated region shows a tendency for greater correlation at higher f max for stronger magnetic sssfields. A study of the correlation for C type spectra between f max and the quasi-cutoff frequency f qc on the low-frequency side shows that for bursts of moderate peak flux density (50–500 sfu) f qc is well correlated with f max; a good fit to the relation f max=A f qc is found with A =3.4. The possible attenuating mechanisms responsible for the spectral shaping of the cm component are discussed.  相似文献   

7.
We present multi-frequency observations and model computations of the microwave emission of a solar active region. The radio observations were obtained with the RATAN-600 at several wavelengths between 0.8 and 31.6 cm and with the VLA at 6 and 20 cm. The active region was also observed in the EUV O Iv lines by the HRTS instrument aboard the Space Shuttle Spacelab-2 mission. These lines are formed in the chromosphere-corona transition region and their intensity ratio is sensitive to pressure. Photospheric magnetograms provided both the longitudinal and the transverse component of the magnetic field. The microwave observations were checked against model computations taking into account both the free-free and the gyro-resonance emission mechanisms and using the pressure data from the O IV lines. The magnetic field was computed through constant- force-free extrapolations of the longitudinal photospheric field. We computed both the flux from 2 to 20 cm and the spatial structure of the microwave emission at 6 and 20 cm. The comparison of the computed and observed flux spectra allowed us to estimate the magnetic field strength at the base of the transition region and in the low corona, as well as the values of the conductive flux and the height of the base of the transition region. The model maps at 6 cm and 20 cm showed that was not constant above the active region; the same conclusion was reached on the basis of the photospheric observations. The use of pressure measurements allowed us to identify microwave structures which were determined by pressure enhancements. At 6 cm the computations confirmed the fact that the magnetic field is the principal factor that determines the structure of sunspot-associated sources and showed that the effect of pressure variations was small. Pressure variations were more important at 20 cm, where the peak of the emission was associated with the sunspot and a diffuse component was associated with the plage which had an average pressure higher by a factor of 1.54 than the sunspot.  相似文献   

8.
A statistical analysis of the contemporary (1954-1975) solar flare particle events has been made for the parametersF (integrated, proton fluence in cm-2 in an event with kinetic energy above 10 MeV) andR 0 (the characteristic rigidity). These data are compared with the long-term averaged values determined from stable- and radio-nuclide measurements of lunar samples. The analysis shows that the ancient solar flare proton spectrum was harder (higher R0 values) compared to that observed in contemporary flares. A similar analysis can not be made for the mean long-term averaged flux (ˉJ, cm-2 S-1), since the contemporary averages suffer from an uncertainty due to the statistics of a single event. However, the average flux estimates for time durations 〈T〉 exceeding 103 yr, are free from such uncertainties. The long-term averaged ˉJ values obtained over different time scales (104 - 106 yr) suggest a possible periodic variation in solar flare activity, with enhanced flux level during the last 105 yr. The available data rule out the occurrence of giant flares, with proton fluence exceeding 1015 cm-2 during the last million years.  相似文献   

9.
COPY THE ORIGINAL Analysis of the total eclipse observation of 1997 March 9 at wavelength 8.6 mm, shows that, at this wavelength, the solar radius is 1.012 R⊙, the total flux density is 2540 sfu, the mean brightness temperature of the solar disk is 9632 K, and the brightness temperature distribution shows limb brightening at the inner edge of the solar disk, the average brightness at 0.936−0.992 R⊙ being 9.7% above the central brightness.  相似文献   

10.
Zongjun Ning 《Solar physics》2014,289(4):1239-1256
Quasi-periodic oscillations in soft X-rays (SXR) are not well known due to the instrument limitations, especially the absence of imaging observations of SXR oscillations. We explore the quasi-periodic oscillations of SXR at 3?–?6 keV in a solar flare observed by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) on 26 December 2002. This was a B8.1 class event and showed three X-ray sources (S1, S2, and S3) at 3?–?6 keV and two sources (S1 and S2) at 12?–?25 keV. The light curves of the total fluxes display a two-minute oscillation at 3?–?6 keV, but not in the energy bands above 8 keV. To investigate imaging observations of the oscillations, we prepared CLEAN images at seven energy bands between 3 keV and 20 keV with an eight-second integration. The light curves of three sources were analyzed after integrating the flux of each source region. We used the Fourier method to decompose each source light curve into rapidly varying and slowly varying components. The rapidly varying components show seven individual peaks which are well fitted with a sine function. Then we used the wavelet method to analyze the periods in the rapidly varying component of each source. The results show that three sources display damped quasi-periodic oscillations with a similar two-minute period. The damped oscillations timescale varies between 2.5 to 6 minutes. Source S1 oscillates with the same phase as S3, but is almost in anti-phase with S2. Analyzing the flaring images in more detail, we found that these oscillation peaks are well consistent with the appearance of S3, which seems to split from or merge with S2 with a period of two minutes. The flare images with a high cadence of one second at 3?–?6 keV show that source S3 appears with a rapid period of 25 seconds. The two-minute oscillation shows the highest spectral power. Source S3 seems to shift its position along the flare loop with a mean speed of 130 km?s?1, which is of the same order as the local sound speed. This connection between the oscillation peaks and emission enhancement appears to be an observational constraint on the emission mechanism at 3?–?6 keV.  相似文献   

11.
We propose that when all sources on the solar disc are taken into account, the S component at 10.7 cm wavelength is dominated by thermal free-free (bremsstrahlung) emission. It is not produced only in the vicinity of sunspots; more than 60% of the total flux may be due to a widely-distributed emission associated with the hot complexes of activity. Using a model for the solar atmosphere based upon an assumption of weak (or vertical) magnetic fields, the spectrum of the S-component is calculated and its sensitivity to changes in the model parameters investigated. Variation of the thicknesses of the chromosphere, transition region and mixed zone cause only small changes in the S-component spectrum; there is a much stronger dependence upon the plasma density, particularly at the base of the corona. The behaviour of the S-component at 10.7 cm wavelength is examined in more detail. We find that the largest contribution to the 10.7 cm flux originates in the low corona, that structural changes affect it only slightly, but that it is strongly density-related. This dependence upon few quantities, together with its relative localization in the low corona, contributes to the usefulness of the 10.7 cm flux as an index of solar activity.Summer Student Worker, 1988.  相似文献   

12.
From the UCSD OSO-7 X-ray experiment data, we have identified 54 X-ray bursts with 5.1–6.6 keV flux greater than 103 photon cm?2 keV?1 which were not accompanied by visible Hα flare on the solar disk. By studying OSO-5 X-ray spectroheliograms, Hα activity at the limb and the emergence and disappearance of sunspot groups at the limb, we found 17 active centers as likely seats of the X-ray bursts beyond the limb. We present the analysis of 37 X-ray bursts and their physical parameters. We compare our results with those published by Datlowe et al. (1974a, b) for disk events. The distributions of maximum temperature, maximum emission measure, and characteristic cooling time of the over-the-limb events do not significantly differ from those of disk events. We show that of conduction and radiation, the former is the dominant cooling mechanism for the hot flare plasma. Since the disk and over-the-limb bursts are similar, we conclude that the scale height for X-ray emission in the 5–10 keV range is large and is consistent with that of Catalano and Van Allen (1973), 11000 km, for primarily 1–3 keV emission. Twenty-five or about 2/3 of the over-the-limb events had a non-thermal component. The distribution of peak 20 keV flux is not significantly different from that of disk events. However, the spectral index at the time of maximum flux is significantly different for events over the limb and for events near the center of the disk; the spectral index for over-the-limb events is larger by about δγ = 3/4. If hard X-ray emission came only from localized sources low in the chromosphere we would expect that hard X-ray emission, would be occulted over the limb; on the contrary, the observation show that the fraction of soft X-ray bursts which have a nonthermal component is the same on and off of the disk. Thus hard X-ray emission over extended regions is indicated.  相似文献   

13.
The correlation between the proton flux intensity I p with the energies E p > 1?100 MeV and radio burst parameters for 107 solar energetic events is considered using the observation data for 1989?C2005 obtained with GOES and Wind satellites, as well as the Radio Solar Telescope Network (RSTN). It has been revealed that 73 and 77% of the events were accompanied by type-II radio bursts in the meter (m II, 25?C299 MHz) and the decameter-hectometer (DH II, 20 kHz?C14 MHz) wavelength ranges, respectively. The correlation coefficient between I p and the frequency drift velocity of the type-II bursts V II did not exceed 0.40. As V II increased, the intensity of I p increased for the m-II bursts and decreased for the DH-II bursts. Coronal shock waves accelerate protons more efficiently than interplanetary waves, and their contribution to acceleration increases with an increase in the particle energy E p . The acceleration of solar energetic particles in the region of the flare energy release is predominant.  相似文献   

14.
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   

15.
The determination of the location of the region of origin of hard X-rays is important in evaluating the importance of 10–100 keV electrons in solar flares and in understanding flare particle acceleration. At present only limb-occulted events are available to give some information on the height of X-ray emission. In fifteen months of OSO-7 operation, nine major soft X-ray events had no reported correlated Hα flare. We examine the hard X-ray spectra of eight of these events with good candidate X-ray flare producing active regions making limb transit at the time of the soft X-ray bursts. All eight bursts had significant X-ray emission in the 30–44 keV range, but only one had flux at the 3σ level above 44 keV. The data are consistent with most X-ray emission occurring in the lower chromosphere, but some electron trapping at high altitudes is necessary to explain the small nonthermal fluxes observed.  相似文献   

16.
Measurements of the solar X-ray spectrum between 3 Å and 15 Å are reported. They were made with two slitless Bragg crystal spectrometers flown on a Sun-pointed Skylark rocket on 8 August, 1967.The use of a beryl crystal has provided higher spectral resolution than hitherto in the spectral range 12 Å and 15 Å leading, in particular, to a revised identification of the strong line at 13.71 Å. Separate components of the stronger emission lines are clearly seen from each of three coronal active regions which may be identified on radio and X-ray spectroheliograms.The absolute line fluxes are used to determine a model for each active region in terms of the differential emission measure as a function of electron temperature. Emission lines due to the transition 1s 2 1 S 0 – 1s2s 3 S 1 in several helium-like ions are identified and values of the local electron density derived from measurement of the line flux in these ions.  相似文献   

17.
We demonstrate that even in the absence of flares there are very often volumes of hot plasma in the corona above active regions with temperatures in excess of 10 million degrees. Characteristics of this hot plasma and its time variations seem to be different in active regions of different phase of development. These hot plasma regions are sources of very weak, but clearly recognizable, X-ray emission above 3.5 keV. Long-lived X-ray brightenings, 104 times weaker than a flare, but lasting up to 10 hr occur predominantly along the H ∥ = 0 line, apparently low in the corona. After major flares, long-lived X-ray emission is also radiated from tops of arches extending high into the corona. Some other long-lived sources, far from the H∥ = 0 line, may be associated with newly emerging flux. Short-lived X-ray sources, with fluxes ranging from subflare levels to 10?3 times the flare flux, last for 2 to more than 30 min and are probably microflares. They seem to be most frequent in growing young active regions and appear often in areas with newly emerging flux.  相似文献   

18.
R. M. Straka 《Solar physics》1971,21(2):469-480
Measurements were made of the 7 March, 1970 solar eclipse by the AFCRL Sagamore Hill Radio Observatory in Hamilton, Massachusetts, on the wavelengths of 0.86, 1.95, 3.4, 6.0, 11.1, 21.2, 49.5, and 122.5 cm. Near-total obscuration (m=0.96) occurred at eclipse maximum. Source flux spectra for the intense sources located in McMath plages 10 618(SE), 10617(NE), and 10 607(NW) show gyro-resonance spectral peaking, whereas the less intense bremsstrahlung emission is observed for the weaker sources in plages 10 614 and 10 619. Associated one-dimensional source sizes for these regions vary from 0.8 arc min (at 3.4 cm) to 5.4 arc min (at 49.5 cm); with sizes at a particular wavelength increasing with intensity of the source. An estimated flux spectrum of the undisturbed radio Sun for 7 March, 1970 is given and compared to the spectrum for the solar minimum of 1964. In plage 10 607 a weak halo emission was isolated from the intense emission from the central source over the spot. The measure of emission from the halo above plage 10 607 was calculated to be 7 × 1027 electron2/cm5.  相似文献   

19.
1–8 Å, 2–12 Å and 8–20 Å non-flare X-ray flux data and 9.1 cm spectroheliograms for 1237 days during the period July 1966 to June 1970 have been studied to derive physical models of λ < 20 Å X-ray emitting regions on the Sun under quiescent (non-flare) conditions. The preferred regions of emission below 20 Å which coincide with the coronal active regions characterised by enhanced 9.1 cm microwave emission are found to have temperature lying between 1.8 and 3 × 106 K, emission measure 1049–1050 and electron density 109-1010 per cc. The average area of an active region is 1020 cm2. A slow gradient of temperature and electron density is seen to exist around a region of peak activity, both temperature and electron density decreasing outwards. Based on the derived physical model of the emitting regions a new method is presented for calculating X-ray flux and spectral energy distribution in this wave length region using daily 9.1 cm solar spectroheliograms. The calculated values are in good agreement with the observed values.  相似文献   

20.
《New Astronomy Reviews》1999,43(8-10):629-632
We present preliminary results from a VLBI survey at λ=6 cm of a sample of 35 sources with flux densities of 2–100 mJy. These sources were selected from the VLA FIRST survey at λ=20 cm, in a 3 degree field around the bright calibrator 1156+295, simply by imposing S20>10 mJy and θ<5 arcsec. MERLIN observations at λ6 cm detected 70/127 of these sources with a threshold of 2 mJy at 50 mas resolution and the closest 35 of these to the calibrator were observed with the VLBA+EVN in snapshot mode at λ6 cm. These sources are a mixture of flat and steep-spectrum sources and include: weak flat-spectrum nuclei of large radio galaxies, low power AGN in nearby galaxies and radio quiet quasars. With these short observations, the sensitivity is limited and most appear as either core-jets or simple point sources on the milliarcsec scale. Nonetheless, it is encouraging that with only 10 minutes observation per source, at least 35% of all sources with S20>10 mJy can be detected and imaged with global 6 cm VLBI.  相似文献   

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