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1.
We have studied the latitude and longitude (northern and southern hemispheric) distributions based on 2277 LDE flares observed during the period from 1966 to 1986. We have found that there exist active zones, in which the LDE flare occurrence rate is much higher. Latitudinal belts between 11–20° and longitudinal belts around 80–100° are the most prolific places to produce LDE flares. During cycles 20 and 21 these active zones produced 36% of the total number of LDE flares by occupying only 6% area of the Sun.  相似文献   

2.
Using data from the Geostationary Operational Environmental Satellites (GOES) spacecraft in the 1?–?8 Å wavelength range for Solar Cycles 23, 24, and part of Cycles 21 and 22, we compare mean temporal parameters (rise and decay times, and duration) and the proportion of impulsive short-duration events (SDE) and gradual long-duration events (LDE) among C- and ≥?M1.0-class flares. It is found that the fraction of the SDE ≥?M1.0-class flares (including spikes) in Cycle 24 exceeds that in Cycle 23 in all three temporal parameters at the maximum phase and in the decay time during the ascending cycle phase. However, Cycles 23 and 24 barely differ in the fraction of the SDE C-class flares. The temporal parameters of SDEs, their fraction, and consequently the relationship between the SDE and LDE flares do not remain constant, but reveal regular changes within individual cycles and during the transition from one cycle to another. In all phases of all four cycles, these changes have the character of pronounced, large-amplitude “quasi-biennial” oscillations (QBOs). In different cycles and at the separate phases of individual cycles, such QBOs are superimposed on various systematic trends displayed by the analyzed temporal flare parameters. In Cycle 24, the fraction of the SDE ≥?M1.0-class flares from the N- and S-hemispheres displays the most pronounced synchronous QBOs. The QBO amplitude and general variability of the intense ≥?M1.0-class flares almost always markedly exceeds those of the moderate C-class flares. The ordered quantitative and qualitative variations of the flare type revealed in the course of the solar cycles are discussed within the framework of the concept that the SDE flares are associated mainly with small sunspots (including those in developed active regions) and that small and large sunspots behave differently during cycles and form two distinct populations.  相似文献   

3.
A statistical analysis of the surface distribution of the larger solar flares of the 21st cycle is carried out in this paper. The results are as follows: (1) There exist two active longitude belts, 220°–140° and 340°–320°. (2) The distribution of flares is assymetric about the solar equator. (3) Active regions located in 50°–60° E and 10°–20° W are good producers of flares; those in 80°–90° E (i.e., near the East limb) and 60°–70° W are poor producers. (4) The autocorrelation function of the flare series shows that a flare active region has a large probability of producing another flare after one rotation and a small probability of so doing after more than one rotation, and that there is a high probability of a flare occurring in the region next to the one in which a flare has already occurred.  相似文献   

4.
1　ＩｎｔｒｏｄｕｃｔｉｏｎＳｏｌａｒｆｌａｒｅｓｒｅｆｌｅｃｔｔｈｅｅｎｅｒｇｅｔｉｃｓｏｆｃｏｒｒｅｓｐｏｎｄｉｎｇｍａｇｎｅｔｉｃｆｉｅｌｄｓ.Ｒｅｓｅａｒｃｈｉｎｇｔｈｅｓｏｌａｒｆｌａｒｅｐａｒａｍｅｔｅｒｓｉｎ 1 1 - ｙｅａｒｓｏｌａｒｃｙｃｌｅｓｃｏｕｌｄｔｈｒｏｗｌｉｇｈｔｏｎｔｈｅｅｎｅｒｇｅｔｉｃｓｏｆｍａｇｎｅｔｉｃｓｔｒｕｃｔｕｒｅｓｆｏｒｍｉｎｇｔｈｅｂａｓｉｓｏｆｔｈｅｃｈｒｏｍｏｓｐｈｅｒｉｃａｎｄｃｏｒｏｎａｌａｃｔｉｖｉｔｙ .Ｔｈｅｖａｒｉａｂｉｌｉｔｙｏｆｔｈｅ…  相似文献   

5.
We derive an occurrence frequency for white-light flares (WLF) of 15.5 ± 4.5 yr?1 during a 2.6 year period following the maximum of solar cycle 21. This compares with a frequency 5–6 yr?1 derived by McIntosh and Donnelly (1972) during solar cycle 20. We find that the higher frequency of the more recently observed WLFs is due to the availability of patrol data at shorter wavelengths (λ ? 4000 Å), where the contrast of the flare emission is increased; the improved contrast has allowed less energetic (and hence more frequently occurring) events to be classified as WLFs. We find that sufficient conditions for the occurrence of a WLF are: active region magnetic class = delta; sunspot penumbra class = K, with spot group area ≥ 500 millionths of the solar hemisphere; 1–8 Å X-ray burst class ≥ X2.  相似文献   

6.
Bai  Taeil 《Solar physics》2003,215(2):327-334
The 160.01-min periodicity was originally found from line-of-sight velocities of the photosphere, and Kotov and Tsap reported a detection of the same periodicity in flare occurrence times. Intrigued by this, I analyze occurrence times of flares of cycles 19–23 to investigate periodicities in the neighborhood of 160 min, cycle by cycle. The 160.01-min periodicity is not detected from any cycle. However, a 160.69 min periodicity is detected in the spectrum for cycle 19, and a 160.32-min periodicity is detected in the power spectrum for major flares of cycle 21. The 160.32-min periodicity did not influence the occurrence rate of flares with X-ray classes below M3.0. Among major flares, the amplitude of modulation increases with increasing X-ray class.  相似文献   

7.
Thirty active regions were observed on the Sun during the period from October 19 to November 20, 2003. Hard X-ray and gamma-ray radiation was detected from four active regions (10484, 10486, 10488, and 10490): 14 solar flares stronger than M5.0 according to the GOES classification were recorded during this period by detectors onboard the Geostationary Operational Environmental Satellite (GOES), Ramaty High Energy Solar Spectroscopic Imager (RHESSI), and other satellites. Five of these flares (and also the M2.7 flare of October 27, 2003) were also observed by the AVS-F apparatus onboard the CORONAS-F satellite. This paper discusses the time profiles and energy spectra of the solar flares of October 26, 2003 (M7.6), and October 29, 2003 (X10), and of the initial phase of the flare of November 4, 2003 (X18), obtained by the AVS-F instrument during the passage of the satellite over the regions near the geomagnetic equator. The spectra of the M7.6 flare of October 26, 2003, and of the initial phase of the X18 flare of November 4, 2003, in the energy band from 0.1 to 17 MeV contain no lines, whereas the spectrum of the flare of October 29, 2003, exhibits nuclear lines and the 2.2-MeV line during the entire flare gamma-ray emission registration. We also report the time profiles of the flare of October 29, 2003, in the energy bands corresponding to the continuum in the energy band 0.3–0.6 MeV, the nuclear lines of 56Fe, 24Mg, 20Ne, 28Si, 12C, and 16O, and the 2.2-MeV neutron-capture line. The analysis of these temporal profile periodograms shows the presence of a thin structure with characteristic scales from 34 to 158 s at the 99% confidence level. The AVS-F apparatus analyzes temporal profiles of low-energy gamma-ray emission with a temporal resolution of 1 ms within the first 4.096 seconds of solar flares. The analysis of the data reveals no regularities in the time series on time scales ranging from 2 to 100 ms at a confidence level of 99% for these three solar flares.  相似文献   

8.
Six solar flares were detected by the AVS-F apparatus onboard the CORONAS-F satellite in January 2005. We discuss the temporal profiles and energy spectra of the solar flares of January 20, 17, and 15, 2005 (class X7.1, X3.8, and X2.6, respectively) on the AVS-F data. The active region NOAA 10720 was the source of these flares. The spectra of the flares of January 17 and 20, 2005 contain nuclear lines, a positron line, and a line due to neutron capture line, while only the positron and neutron capture lines can be identified in the spectrum of the flare of January 15, 2005. The spectral features corresponding to these lines were observed during the whole duration of the flares. Analysis of the temporal profile of the flare of January 20, 2005 with a 1-ms temporal resolution in the energy range 0.1–20 MeV reveals the presence of a thin structure (at the 99% confidence level) with typical timescales of 7 to 35 ms.  相似文献   

9.
We investigate the solar flare occurrence rate and daily flare probability in terms of the sunspot classification supplemented with sunspot area and its changes. For this we use the NOAA active region data and GOES solar flare data for 15 years (from January 1996 to December 2010). We consider the most flare-productive 11 sunspot classes in the McIntosh sunspot group classification. Sunspot area and its changes can be a proxy of magnetic flux and its emergence/cancellation, respectively. We classify each sunspot group into two sub-groups by its area: ??Large?? and ??Small??. In addition, for each group, we classify it into three sub-groups according to sunspot area changes: ??Decrease??, ??Steady??, and ??Increase??. As a result, in the case of compact groups, their flare occurrence rates and daily flare probabilities noticeably increase with sunspot group area. We also find that the flare occurrence rates and daily flare probabilities for the ??Increase?? sub-groups are noticeably higher than those for the other sub-groups. In case of the (M+X)-class flares in the ??Dkc?? group, the flare occurrence rate of the ??Increase?? sub-group is three times higher than that of the ??Steady?? sub-group. The mean flare occurrence rates and flare probabilities for all sunspot groups increase with the following order: ??Decrease??, ??Steady??, and ??Increase??. Our results statistically demonstrate that magnetic flux and its emergence enhance the occurrence of major solar flares.  相似文献   

10.
We investigate the statistical distribution of X-class flares and their relationship with super active regions (SARs) during solar cycles 21–23. Analysis results show that X1.0–X1.9 flares accounted for 52.71 % of all X-class flares, with X2.0–X2.9 flares at 20.59 %, X3.0–X4.9 at 13.57 %, X5–X9.9 at 8.37 % and ≥X10 at 4.75 %. All X-class flares occurred around the solar maximum during solar cycle 22, while in solar cycle 23, X-class flares were scattered in distribution. In solar cycle 21, X-class flares were distributed neither in a concentrated manner like cycle 22 nor in a scattered manner as cycle 23. During solar cycles 21–23, 32.2 % of the X1.0–X1.9 flares, 31.9 % of the X2.0–X2.9 flares, 43.3 % of the X3.0–X4.9 flares, 81.08 % of the X5.0–X9.9 flares, and 95.2 % of the ≥X10 flares were produced by SARs.  相似文献   

11.
We studied 24 spotless flares of Ha importance 1 which occurred during the 21st cycle of solar activity. The spotless flares could be grouped in three categories according to their location and time history of the associated active region. Our association of the flares with radio events was based on relative timing and on the flare importances. Weak microwave gradual rise and fall events were frequently recorded during the occurrence of the spotless flares. A few flares from our sample could be associated with impulsive and complex microwave bursts. Only in one case an association of a spotless flare with a significant metric type II/IV event seems to be justified.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   

12.
The NOAA listings of solar flares in cycles 21?–?24, including the GOES soft X-ray magnitudes, enable a simple determination of the number of flares each flaring active region produces over its lifetime. We have studied this measure of flare productivity over the interval 1975?–?2012. The annual averages of flare productivity remained approximately constant during cycles 21 and 22, at about two reported M- or X-flares per region, but then increased significantly in the declining phase of cycle 23 (the years 2004?–?2005). We have confirmed this by using the independent RHESSI flare catalog to check the NOAA events listings where possible. We note that this measure of solar activity does not correlate with the solar cycle. The anomalous peak in flare productivity immediately preceded the long solar minimum between cycles 23 and 24.  相似文献   

13.
In this study, the statistical relationship between sunspots and major flares observed in the descending branch of the 20th and in the ascending branch of the 21st solar cycle is evaluated. It is found that the sunspots which produced these major flares are of the type Dki or Eki with magnetic class D and the largest magnetic field strength between 1600 and 2500 G.  相似文献   

14.
Taeil Bai 《Solar physics》2006,234(2):409-419
In the declining phase of the current solar cycle (23), a large number of major flares were produced. In this cycle, the monthly sunspot number continuously remained below 100 since October 2002. However, during four epochs since then, flare activity became very high. Compared to this, each of cycles 21 and 22 produced only one epoch of high activity in the declining phase. In the declining phase of cycle 20, similarly to this cycle, there were four epochs of high flare activity. During 2003 and 2004, the distribution of flare sizes measured in GOES classes was much harder (i.e., proportionately more energetic flares) than during the maximum years. Such pronounced hardening of the size distribution was not observed in the previous cycles. It is of theoretical interest to understand why some cycles are very active in the declining phase, and the high level of activity in the declining phase has practical implications for planning solar observations and forecasting space weather.  相似文献   

15.
The solar soft X-ray (XUV) radiation is important for upper atmosphere studies as it is one of the primary energy inputs and is highly variable. The XUV Photometer System (XPS) aboard the Solar Radiation and Climate Experiment (SORCE) has been measuring the solar XUV irradiance since March 2003 with a time cadence of 10 s and with about 70% duty cycle. The XPS measurements are between 0.1 and 34 nm and additionally the bright hydrogen emission at 121.6 nm. The XUV radiation varies by a factor of ∼2 with a period of ∼27 days that is due to the modulation of the active regions on the rotating Sun. The SORCE mission has observed over 20 solar rotations during the declining phase of solar cycle 23. The solar XUV irradiance also varies by more than a factor of 10 during the large X-class flares observed during the May–June 2003, October–November 2003, and July 2004 solar storm periods. There were 7 large X-class flares during the May–June 2003 storm period, 11 X-class flares during the October–November 2003 storm period, and 6 X-class flares during the July 2004 storm period. The X28 flare on 4 November 2003 is the largest flare since GOES began its solar X-ray measurements in 1976. The XUV variations during the X-class flares are as large as the expected solar cycle variations.  相似文献   

16.
We investigate the connections between the occurrence of major solar flares and subsurface dynamic properties of active regions. For this analysis, we select five active regions that produced a total of 11 flares with peak X-ray flux intensity higher than M5.0. The subsurface velocity fields are obtained from time–distance helioseismology analysis using SDO/HMI (Solar Dynamics Observatory/Helioseismic and Magnetic Imager) Doppler observations, and the X-ray flux intensity is taken from GOES (Geostationary Operational Environmental Satellites). It is found that among the eight amplitude bumps in the evolutionary curves of subsurface kinetic helicity, five (62.5%) of them had a flare stronger than M5.0 occurring within 8 hours, either before or after the bumps. Another subsurface parameter is the Normalized Helicity Gradient Variance (NHGV), reflecting kinetic helicity spread in different depth layers; it also shows bumps near the occurrence of these solar flares. Although there is no one-to-one correspondence between the flare and the subsurface properties, these observational phenomena are worth further studies to better understand the flares’ subsurface roots, and to investigate whether the subsurface properties can be used for major flare forecasts.  相似文献   

17.
The record of flare incidence from January 1969 to October 1988 indicates that the north-south (N-S) distribution of large flares is periodic and approximately in phase with the 11-year sunspot cycle. These data are based on observations of the whole-disk Sun in continuum soft X-rays which commenced in early 1969 and have proceeded without interruption to the present time. The pattern of occurrence, observed for slightly less than two sunspot cycles, is that large flares concentrate in north heliographic latitudes soon after solar minimum and then migrate gradually southward as the cycle progresses. By the end of the cycle, most large flares occur in the south. The degree of N-S asymmetry apparently is a function of the intensity of the flare; the most intense flares show the largest amount of N-S asymmetry. The data suggest that sunspots and flares may be driven by distinctly different excitation mechanisms arising at different levels in the convection zone. This conjecture is supported by recent work of Bai (1987, 1988), who has discovered that the superactive regions producing the majority of flares rotate at a speed substantially different from the Carrington rate, which is based primarily on the observed motion of sunspots.  相似文献   

18.
We present the study of 20 solar flares observed by “Solar X-ray Spectrometer (SOXS)” mission during November 2003 to December 2006 and found associated with coronal mass ejections (CMEs) seen by LASCO/SOHO mission. In this investigation, X-ray emission characteristics of solar flares and their relationship with the dynamics of CMEs have been presented. We found that the fast moving CMEs, i.e., positive acceleration are better associated with short rise time (< 150 s) flares. However, the velocity of CMEs increases as a function of duration of the flares in both 4.1–10 and 10–20 keV bands. This indicates that the possibility of association of CMEs with larger speeds exists with long duration flare events. We observed that CMEs decelerate with increasing rise time, decay time and duration of the associated X-ray flares. A total 10 out of 20 CMEs under current investigation showed positive acceleration, and 5 of them whose speed did not exceed 589 km/s were associated with short rise time (< 150 s) and short duration (< 1300 s) flares. The other 5 CMEs were associated with long duration or large rise time flare events. The unusual feature of all these positive accelerating CMEs was their low linear speed ranging between 176 and 775 km/s. We do not find any significant correlation between X-ray peak intensity of the flares with linear speed as well as acceleration of the associated CMEs. Based on the onset time of flares and associated CMEs within the observing cadence of CMEs by LASCO, we found that in 16 cases CME preceded the flare by 23 to 1786 s, while in 4 cases flare occurred before the CME by 47 to 685 s. We argue that both events are closely associated with each other and are integral parts of one energy release system.  相似文献   

19.
We present the results of studying the impact linear polarization of 32 solar flares of X-ray classes C, M, and X (two flares) observed with the Large Solar Vacuum Telescope. It has turned out that there is evidence for impact polarization only in 13 of them. The newly obtained data have confirmed that the linear Stokes parameters are predominantly 2–7%, while the spatial sizes of flaring points with nonzero Stokes parameters are small (1″-2″). Two features of the manifestation of impact polarization in flares revealed by these studies are of greatest interest: (1) at the two foot points of a single flare loop or an arcade of loops, both the Hα intensity profiles and the Stokes profiles differ in behavior; (2) based on the Hα line, we have found for the first time that the sign of the Stokes parameters changes not only across the flare ribbon but also with depth of the chromosphere.  相似文献   

20.
The solar irradiance in the Extreme Ultraviolet (EUV) spectral bands has been observed with a 15 s cadence by the SOHO Solar EUV Monitor (SEM) since 1995. During remarkably intense solar flares the SEM EUV measurements are saturated in the central (zero) order channel (0.1–50.0 nm) by the flare soft X‐ray and EUV flux. The first order EUV channel (26–34 nm) is not saturated by the flare flux because of its limited bandwidth, but it is sensitive to the arrival of Solar Energetic Particles (SEP). While both channels detect nearly equal SEP fluxes, their contributions to the count rate is sensibly negligible in the zero order channel but must be accounted for and removed from the first channel count rate. SEP contribution to the measured SEM signals usually follows the EUV peak for the gradual solar flare events. Correcting the extreme solar flare SEMEUV measurements may reveal currently unclear relations between the flare magnitude, dynamics observed in different EUV spectral bands, and the measured Earth atmosphere response. A simple and effective correction technique based on analysis of SEM count‐rate profiles, GOES X‐ray, and GOES proton data has been developed and used for correcting EUV measurements for the five extreme solar flare events of July 14, 2000, October 28, November 2, November 4, 2003, and January 20, 2005. Although none of the 2000 and 2003 flare peaks were contaminated by the presence of SEPs, the January 20, 2005 SEPs were unusually prompt and contaminated the peak. The estimated accuracy of the correction is about ±7.5% for large X‐class events. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

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