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1.
An impulsive burst of 100–400 keV solar X-rays associated with a small solar flare was observed on October 10, 1970 with a large area scintillator aboard a balloon floating at an altitude of 4.2 g cm-2 above the Earth's surface. The X-ray burst was also observed simultaneously in 10–80 keV range by the OGO-5 satellite and in 8–20 Å range by the SOLRAD-9 satellite. The impulsive X-ray emission reached its maximum at 1643 UT at which time the differential photon spectrum in 20–80 keV range was of the form 2.3 × 104
E
-3.2 photons cm-2 s-1 keV-1 at 1 AU. The event is attributed to a H-subflare located approximately at S13, E88 on the solar disc. The spectral characteristics of this event are examined in the light of the earlier X-ray observations of small solar flares. 相似文献
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A great sunspot group of October 1991 (NOAA 6891 atL = 189,B = –10) was observed, in which an eruptive flare of importance (X2.5/31B) has been reported. A Caii-line 3933 filter was used, and during a time interval of 3 hours more than 90 frames were taken, using a CCD camera. The progress and the distribution in size of the two main flare points have been obtained; they covered an area of about 1800 millionths of the solar disk within a time interval of about 24 min. The average apparent horizontal velocity was 70 km s–1. 相似文献
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On October 24, 1991, a white-light flare was observed both from space and from the ground. A multi-waveband spectral analysis shows that the peak time of the continuum emission coincides well with that of a radio burst at 2840 MHz and with the hard X-ray emission. Three semi-empirical models, corresponding to the pre-flare condition and to the peak time of continuum emission both with and without non-thermal excitation and ionization of hydrogen by an electron beam, have been obtained. The results indicate that there is fast heating both in the chromosphere and the photosphere. Some evidence is given that this WLF is very likely a result of bombardment by an electron beam. By taking into account non-thermal effects, the chromospheric temperature of the semi-empirical model is significantly reduced. 相似文献
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《Astronomy Letters》2000,26(12):821-821
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It was found that in the spectrum of the white-light flare on 11 October, 1974, at the time of continuum maximum, the intensity of K1 in the Caii K line increased very significantly and reached nearly half of the continuum intensity. The duration of this unusual increase is less than 4 min. It seems that existing semi-empirical models can reproduce neither this characteristic nor the chromospheric condensation. 相似文献
9.
Arthur E. Covington 《Solar physics》1972,24(2):405-410
Observations of the flare of October 24, 1969 by Zirin et al. (1971) Solar Phys.
19, 463, are given with accompanying graphs of XUV emissions from satellites and four microwave radio emissions from Sagamore Hill Observatory. This event provides an excellent example of the development of two types of radio spectra within the same center and similar profiles for the hard X-ray burst and the 8800 MHz radio profile. The examination of the 2700 MHz burst from the Dominion Radio Astrophysical Observatory provides a clarification of the radio profile and shows the existence of a long enduring burst not previously considered. This event parallels a similar variation of intensity in the soft X-ray burst. 相似文献
10.
We present SOHO/CDS observations taken during the gradual phase of the X17 flare that occurred on October 28, 2003. The CDS
data are supplemented with TRACE and ground-based observations. The spectral observations allow us to determine velocities
from the Doppler shifts measured in the flare loops and in the two ribbon kernels, one hour and a half after the flare peak.
Strong downflows (>70 km s−1) are observed along the loop legs at transition-region temperatures. The velocities are close to those expected for free
fall. Observations and results from a hydrodynamic simulation are consistent with the heating taking place for a short time
near the top of the arcade. Slight upflows are observed in the outer edges of the ribbons (<60 km s−1) in the EUV lines formed at log T < 6.3. These flows could correspond to the so-called “gentle evaporation.” At “flare” temperatures (Fe xix, log T = 6.9), no appreciable flows are observed. The observations are consistent with the general standard reconnection models
for two-ribbons flares. 相似文献
11.
We present H monochromatic and spectroscopic observations of the sudden disappearance of a dark filament located near the center of the solar disk on October 26, 1989. The event was not associated with the flare activity. The dark filament first disintegrated into two loop-like components, and then each component successively showed ascending motion with a velocity greater than 30 km s–1. Comparison of the H pictures taken before and after the start of this event suggests that the dark filament was originally composed of two magnetic flux loops. 相似文献
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本文介绍了１９９５年１０月２４日亚洲将要发生的日全食概况。提出了届时昆明日食的观测选题。文中对时频、射电和色球观测选题的意义和可能的观测结果作了预测性的讨论。 相似文献
14.
Two-dimensional evolutions of two flares of October 18, 1990 have been well observed in the Caii K line with a CCD camera at Norikura station of National Astronomical Observatory in Japan. There are two common characteristics for the flares: 3 - 5 min before the impulsive phase, the heating already begins at the footpoints of the flares, but no asymmetry in line emission has been detected. After the onset of the impulsive phase, Caii K line emission at the footpoints shows strong red asymmetry, with the maximum asymmetry occurring at the same time as the peak of the radio bursts. The maximum downward velocity is about 30 50 km s–1. For flare 1, blue and red asymmetries were observed in two sides of the footpoint area. They developed and attained a maximum nearly at the same time and the inferred Doppler velocities are comparable (30 40 km s–1). This implies that two mass jets started from a small region and ejected along a loop but in opposite directions with roughly equivalent momentum. A possible mechanism has been discussed. 相似文献
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The results of numerical simulation of stochastic acceleration of the heavy ions (3He, 4He, 16O, and 56Fe) are presented for the impulsive solar event of October 5, 2002. The energy spectra of the aforementioned particles have
peculiarities (depressions) in the low-energy region (≤1 MeV nucleon−1). Coulomb losses in the flare plasma and adiabatic losses during interplanetary propagation are considered in the study as
possible causes of such peculiarities. 相似文献
16.
An impulsive flare October 24, 1969 produced two bursts with virtually identical time profiles of 8800 MHz emission and X-rays above 48 keV. The two spikes of hard X-rays correspond in time to the times of sharp brightening and expansion in the H flare. The first burst was not observed at frequencies below 3000 MHz. This cut off is ascribed to plasma cutoff above the low-lying flare.A model of the flare based on H observations at Big Bear shows that the density of electrons with energy above 10 keV is 5 × 107 if the field density is 1011. The observed radio flux would be produced by this electron distribution with the observed field of 200 G. The H emission accompanying the hard electron acceleration is presumed due to excitation of the field atoms by the hard electrons. 相似文献
17.
In this paper we present a further study of the Ml class flare observed on October 22, 2002. We focus on the SOHO Coronal
Diagnostic Spectrometer (CDS) spectral observations performed during a multi-wavelength campaign with TRACE and ground-based
instruments (VTT, THEMIS). Strong blue-shifts are observed in the CDS coronal lines in flare kernels during the impulsive
phase of this flare. From a careful wavelength calibration we deduce upflows of 140 km/s for the Fe XIX flare emission, with
a pattern of progressively smaller flows at lower temperatures. Large line-widths were observed, especially for the Fe XIX
line, which indicate the existence of turbulent velocities. The strong upflows correspond to full shifts of the line profiles.
These flows are observed at the initial phase of the flare, and correspond to the “explosive evaporation”. The regions of
the blueshifted kernels, a few arc seconds away from the flare onset location, could be explained by the chain reaction of
successive magnetic reconnections of growing emerging field line with higher and higher overlying field. This interpretation
is evidenced by the analysis of the magnetic topology of the active region using a linear force-free-field extrapolation of
THEMIS magnetograms. 相似文献
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An X17 class (GOES soft X-ray) two-ribbon solar flare on October 28, 2003 is analyzed in order to determine the relationship
between the timing of the impulsive phase of the flare and the magnetic shear change in the flaring region. EUV observations
made by the Transition Region and Coronal Explorer (TRACE) show a clear decrease in the shear of the flare footpoints during the flare. The shear change stopped in the middle
of the impulsive phase. The observations are interpreted in terms of the splitting of the sheared envelope field of the greatly
sheared core rope during the early phase of the flare. We have also investigated the temporal correlation between the EUV
emission from the brightenings observed by TRACE and the hard X-ray (HXR) emission (E > 150 keV) observed by the anticoincidence system (ACS) of the spectrometer SPI on board the ESA INTEGRAL satellite. The
correlation between these two emissions is very good, and the HXR sources (RHESSI) late in the flare are located within the
two EUV ribbons. These observations are favorable to the explanation that the EUV brightenings mainly result from direct bombardment
of the atmosphere by the energetic particles accelerated at the reconnection site, as does the HXR emission. However, if there
is a high temperature (T > 20 MK) HXR source close to the loop top, a contribution of thermal conduction to the EUV brightenings cannot be ruled out. 相似文献
20.
A new quantitative zebra pattern observation is reported. The mean amplitude ratio of the emission and absorption features of the irregular zebra pattern observed simultaneously with and related to an increased continuum is Q = 3. This is not contradictory to a zebra pattern model in terms of whistler soliton propagation throughout the source of continuum emission. 相似文献