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1.
In this investigation, we have studied the latitudinal, longitudinal (northern and southern hemispheric) distributions based on 1737 major flares observed during solar cycles 19 and 20 (see subsequent paragraphs) and have arrrived at some interesting results which go to show that as far major flares are concerned latitudewise 11–20° belts, and longitudewise 5–8 places are most prolific in producing major flares in each hemisphere. During the above cycles at least 5 flare zones are present in each hemisphere. In fact these zones seem to produce more than 50% of the total number of energetic flares investigated by us and occupy only <4% area of the Sun. 相似文献
2.
Daily calcium plage areas for the period 1951–1981 (which include the solar cycle 19 and 20) have been used to derive the rotation period of the Sun at latitude belts 10–15 ° N, 15–20 ° N, 10–15 ° S, and 15–20 ° S and also for the entire visible solar disk. The mean rotation periods derived from 10–20 ° S and N, total active area and sunspot numbers were 27.5, 27.9, and 27.8 days (synodic), respectively. A power spectral analysis of the derived rotation rate as a function of time indicates that the rotation rate in each latitude belt varies over time scales ranging from the solar activity cycle, down to about 2 years. Variations in adjacent latitude belts are in phase, whereas those in different hemispheres are not correlated. The rotation rates derived from sunspot numbers also behave similarly though the dependence over the solar cycle are not very apparent. The total plage areas, integrated over the entire visible hemisphere of the Sun shows a dominant periodicity of 7 years in rotation rate, while the other time scales are also discernible. 相似文献
3.
Sunspot data from the Catania Astrophysical Observatory, covering cycles 18, 19, and 20 (1943–1977) have been analyzed, taking into account, besides the usual parameters, the number n of zones, namely latitude belts 5° wide, showing sunspot activity and the area covered by spots for each of these zones. A comparison between our conclusions and those drawn from other authors on the same subject is made. 相似文献
4.
The distribution of the sunspots for the period 1967–1987 (solar cycles 20 and 21) is presented here. We find that the ±11–20° latitude belt is most prolific for the occurrence of various spot types irrespective of magnetic-field ranges. Furthermore, longitudinally sunspots occur most prolifically at six or more places on the Sun. Spatially 7–9 zones are present in each hemisphere (north or south) of the Sun where about 50% sunspots occur and occupy only about 4% area of the Sun. During the above cycles at least 5 flare zones were regularly present in each hemisphere. The existing models cannot explain these active zones on the Sun. Thus, the present analysis emphasizes the need for a new magnetic models of the Sun. 相似文献
5.
The correlation between the long-term intensity variations of cosmic rays at neutron monitor energies and the LDE index measure of solar flares with long-lasting soft X-ray emissions is reported. Three subsequent solar cycles, 20–22, are taken into account and half-monthly data are analyzed. Possible explanation of this correlation is discussed in terms of the recent concepts of cosmic-ray modulation, in particular with merged interaction regions affecting the cosmic-ray intensity. 相似文献
6.
The temporal variations of the occurrence of the (M–X) LDE flares (with the SXR duration exceeding 2 hours) throughout the 20th and the 21st cycles are considered. The characteristics of the 20th cycle: the maximum value of the observed yearly number of LDE flares was in the 1970 (with the total 225 LDE flares observed). The increased LDE flare activities were observed in the years 1972 and 1974 (see Tab. 1). The characteristics of the 21st cycle: the large occurrence of the (M–X) LDE flares was observed form 1979 to 1982. The yearly numbers of the (M–X) LDE flares in 1980–168, 1981–151 and 1982–135 are comparable. The fast decrease of the whole flare activity begun at 1983. The percentual representation of the (M–X) LDE flares in the occurrence rate of all Hα flares fluctuated between 1–3%. 相似文献
7.
Ridge belts, composed of closely spaced individual ridges 5–20 km wide, form sinuous patterns 30–400 km wide and 200–2000 km long in the plains of northern Venus. They are not homogeneously distributed, but occur primarily in two regions: between 0 ° E and 90 ° E ridge belts are associated with large blocks of tessera, and have a cumulative length of about 13,200 km; and between 150 ° E and 250 ° E, the ridge belts form a fan-shaped pattern and have a total cumulative length of about 25,800 km. Most ridge belts trend within 10 ° of N-S. Five morphologic components exist within the ridge belts: (1) broad ridges, which have no sharp crest and usually occur individually in the plains: (2) discontinuous ridges, with short ridge segments less than 20 km long; (3) paired ridges, with closely spaced ridges (less than 10 km apart) that never merge; (4) parallel ridges, with widely spaced (10–50 km), less prominent ridges; and (5) anastomosing ridges, in which ridges splay at angles up to 30 °. Subtle cross-strike lineaments cut the ridge belts at angles of 30–90 ° to the ridge belt, and augen-shaped plains are often present in anastomosing ridges. We examine the relationships between the components, plains, cross-strike lineaments, and augen-shaped plains in five ridge belts. Broad arches similar to the arches associated with wrinkle ridges on the Moon, Mars and Mercury appear in all of the ridge belts examined. Through studying each of these components individually and in the context of five specific ridge belts, we conclude that these ridge belts formed by compressional forces. The ridge belts form a continuum of deformation, from the simple broad arches (Nephele Dorsa), representing small amounts of shortening, through asymmetric ridge belts in the plains (Pandrosa Dorsa) and adjacent to tessera (Kamari Dorsa), to ridge belts in troughs representing underthrusting (Ausra and Lukelong Dorsa). Underthrusting is also observed along the borders of Lakshmi Planum, associated with Freyja and Danu Montes.The interpreted compressional origins for the ridge belt components suggests that many of the other ridge belts are of compressional origin, although complex origins (involving a combination of extension, shear, and/or compression) for some ridge belts cannot be ruled out. Global high resolution data from the Magellan mission will permit global mapping of the characteristics and distribution of ridge belts and allow further tests for their origin and evolution.'Geology and Tectonics of Venus', special issue edited by Alexander T. Basilevsky (USSR Acad. of Sci., Moscow), James W. Head (Brown University, Providence). Gordon H. Pettengill (MIT. Cambridge, Massachusetts) and R. S. Saunders (J.P.L., Pasadena). 相似文献
8.
During the year 1969 two long-lived centres were active on the Sun at Carrington longitudes 50° < L < 100° and 250° < L < 300°. About 80% of the flares of importance 1B, produced during this period, originated in these zones.The solar modulation of galactic cosmic ray intensity during 1969 was dominated by effects resulting from the activity in the two zones. In fact all the decreases can be related to the passage at the central meridian of the active centres. Persistence of the effects connected to solar regions is found also during rotations in which they do not produce flares in front of the Earth.Seventeen among the twenty-six intensity decreases, observed during this period, can also be correlated to individual flares belonging to the region at central meridian (longitudes ± 40° with respect to the CM).The data suggest that two phenomena are operative to produce decreases of the cosmic ray flux: the passage of the interplanetary corotating stream associated with the active region near the central meridian and the blast wave produced by the flares in front of the Earth. 相似文献
9.
The vast majority of solar flares are not associated with metric Type II radio bursts. For example, for the period February 1980–July 1982, corresponding to the first two and one-half years of the Solar Maximum Mission, 95% of the 2500 flares with peak >25 keV count rates >100 c s–1lacked associated Type II emission. Even the 360 largest flares, i.e., those having >25 keV peak count rates >1000 c s–1, had a Type II association rate of only 24%. The lack of a close correlation between flare size and Type II occurrence implies the need for a 'special condition' that distinguishes flares that are accompanied by metric Type II radio bursts from those of comparable size that are not. The leading candidates for this special condition are: (1) an unusually low Alfvén speed in the flaring region; and (2) fast material motion. We present evidence based on SMM and GOES X-ray data and Solwind coronagraph data that argues against the first of these hypotheses and supports the second. Type II bursts linked to flares within 30° of the solar limb are well associated (64%; 49/76) with fast (>400 km s–1) coronal mass ejections (CMEs); for Type II flares within 15° of the limb, the association rate is 79% (30/38). An examination of the characteristics of 'non-CME' flares associated with Type IIs does not support the flare-initiated blast wave picture that has been proposed for these events and suggests instead that CMEs may have escaped detection. While the degree of Type II–CME association increases with flare size, there are notable cases of small Type II flares whose outstanding attribute is a fast CME. Thus we argue that metric Type II bursts (as well as the Moreton waves and kilometric Type II bursts that may accompany them) have their root cause in fast coronal mass ejections. 相似文献
10.
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
11.
We study some peculiarities of the time variation of dipole components in the longitudinal field distribution in individual low-latitude belts of the Sun. For analyzing the horizontal dipole rotation and variations of amplitudes we used magnetic and H data.From 1979 to 1981 the rotation of the dipoles of the northern and southern low-latitude belts (0°–30° N and 10°–40° S) occurs with periods of about 26.8 days (N) and 28.2 days (S), in agreement with the results reported by Antonucci, Hoeksema, and Scherrer (1990) and Hoeksema and Scherrer (1987). A uniform rotation of the low-latitude dipoles of these belts continued until the end of 1981. Following the next coincidence of the magnetic poles in longitude the dipoles change in their rotation character. During about 15–20 rotations the low-latitude dipoles co-rotate with a new period close to the Carrington period. This is followed by a rapid (in 3–5 rotations) transition of the poles to a new stable state, also with the Carrington rotation period. The change in rotation and dynamics of the low-latitude dipoles at the end of 1981-beginning of 1982 can be explained either by a mutual penetration of the fields of different hemispheres to the opposite hemisphere or by the onset of the formation of relatively shortlived (15–20 rotations) structures which cover the entire low-latitude belt.Unlike the trajectories of the poles, the dipole amplitudes of the low-latitude belts showed a significant variability. However, simultaneous increases of the amplitudes in both hemispheres correlated with times at which the dipole poles coincide in longitude, and the greatest increase corresponded to the moment of merging of the dipole poles early in 1982. This suggests that sources of large-scale structures of the background field in the low-latitude belts of the Sun or the related fields interacted when the dipole poles coincided. 相似文献
12.
Using KPNO helium 10830 Å synoptic charts of Carrington rotations 1716 through 1739, and by assembling a time sequence representing single latitude zone, rotational properties of coronal holes for five zones of latitudes (±10°, ±20° – ±40°, and ±40° – ±60°) have been examined. It seems that the rotation period of coronal holes is a function of latitude, thus reflecting differential rotation of coronal holes. 相似文献
13.
Atila Özgüç 《Astrophysics and Space Science》1992,187(2):197-207
We have analysed intermediate-term periodicities in the green corona by dividing 10° latitudinal belts for the solar cycles 18, 19, and 20 (1947–1976). Discrete Fourier transform technique was used and three noticeable periodicities (3.48, 2.57, and 2.27 years) were found. The physical origin of these periods is not known, but evidence in our results exclude the possibility that the observed periods are a harmonic due to the method of analyse. The period of 3.48-year is the strongest one. 17.6-month periodicity was found only on around +40° belt while 155-day periodicity was not found in our analysis. 相似文献
14.
E. N. Parker 《Solar physics》1996,163(2):327-333
For solar cycles 20 and 21, the longitudinal distribution of the D, G, and H-type solar flares which are related to the final phases of active region evolution, have been analysed for the northern and the southern hemispheres separately. One active zone has been found for D, G, and H-type flares, and one more active zone has been found for the H-type flares of the northern hemisphere for cycle 20. Two active zones have been found for the D and H-type flares of the northern hemisphere for cycle 21. Southern-hemisphere flares are concentrated in two active zones for cycle 20. The active zone in the northern hemisphere, which rotates with a synodic period of about 26.73 days, produced 30% of the examined D-type flares during cycle 20 and persisted in the same position during the two solar cycles, 20 and 21. The active zone in the southern hemisphere rotated with a synodic period of about 27.99 days. Only the active zone producing D-type flares persisted in the same position during the two solar cycles. 相似文献
15.
Regularities in the longitudinal distribution of high-flare-activity active regions during 1964–1979 have been examined. The Fourier spectrum for each 30°-wide longitude strip in northern and southern hemispheres has been obtained. It is seen that there exist two giant longitude zones in each hemisphere and solar activity remains concentrated in one of the giant zones. It also appears that the leading edge of a giant zone is more active as compared to its following edge. 相似文献
16.
On December 15, 1978, an omnidirectional gamma-ray detector for the energy range 0.3 to 10 MeV was flown from São José dos Campos, Brazil at a latitude of about -23°. Around noon time, when the Sun was in the field of view of the detector, various solar flares of importance SN and SF occurred. The 2.2 MeV line flux was monitored during this time. A statistically significant line flux of (1.55 ± 0.50) × 10–2 photons cm–2 s–1 and (9.97 ± 4.85) × 10–3 photons cm–2 s–1 was observed within a few minutes of t maxima of the two long-duration SN flares respectively, whereas during SF flares only upper limits were obtained. 相似文献
17.
S. O. Ifedili 《Solar physics》1974,39(1):233-241
The upper limit on the solar neutron flux from 1–20 MeV has been measured, by a neutron detector on the OGO-6 satellite, to be less than 5 × 10–2 n cm–2 s–1 at the 95% confidence level for several flares including two flares of importance 3B and a solar proton event of importance 3B. The measurements are consistent with the models proposed by Lingenfelter (1969) and by Lingenfelter and Ramaty (1967) for solar neutron production during solar flares. The implied upper limit on the flux of 2.2 MeV solar gamma rays is about the same as the 2.2 MeV flux observed by Chupp et al. (1973). 相似文献
18.
Comparing the records of the radio spectrographs ARTEMIS (100–500 MHz) on the ground and URAP (1–1000 kHz) on the Ulysses spacecraft, we find that most type III bursts extend from the corona to the solar wind. Using the positions of the associated flares, and assuming an average intensity ratio between these two frequency ranges, we derive for the first time the average radiation pattern of interplanetary type III bursts. We find that at 800 kHz it is shifted east of the radial direction by 30° and has a half-width of about 80° at maximum/10; the shift and width increase towards lower frequencies. Ulysses high-latitude observations show that the cross-section perpendicular to the heliospheric equator is about the same. We interpret these properties by refraction effects in local density gradients. 相似文献
19.
S. T. Lindgren 《Solar physics》1968,5(3):382-409
McMath plage region 8818 passed over the visible solar disk on May 17–31, 1967. It was very active from its first appearance on the Eastern limb, several times producing bright optical flares and hard X-ray emission, accompanied by intense type II, type IV and centimeter radio bursts. Nevertheless, no solar particles could be detected near the earth until the evening of May 23, when three bright flares were observed in close succession at 25°–28° E. During the following build-up of the solar particle flux over 36 hours, the galactic cosmic ray flux > 1 GeV decreased gradually by about 5%. The flux of solar particles decreased in two steps on May 25, both accompanied by decreases in the equatorial geomagnetic field. These field depressions are attributed to storm plasma ejected from the parent flare of the May 23 particle event. The propagation of solar particles from May 23 on thus appears to be strongly affected by storm plasma from the parent flare of the May 23 event, without any indications of solar particles being trapped in that plasma.A later particle event early on May 28 was also associated with a bright flare in McMath region 8818, at 33° W. This event displayed a rapid build-up, with electrons arriving first, and an exponential decay. A smooth proton peak, 20 min wide, was detected on May 30 closely associated with an SSC attributed to plasma ejection from the parent flare of the May 28 event.Between the geomagnetic storms beginning on May 25 and May 30 an anomalous daily variation was observed in the cosmic ray flux >1 GeV, the time of maximum falling 7–10 hours earlier than normal. Storm time increases in the flux of galactic cosmic rays were seen on May 26 when the equatorial geomagnetic field was depressed by more than 400 . Low latitude auroras were also observed during that time.On leave from the University of Uppsala, Sweden. 相似文献
20.
We describe our BEARALERT program of predicting solar flares or rapid development of activity in certain sunspot groups. The purpose of the program is to test our understanding of the flare process by making public predictions via electronic mail. Neither the exact timing of the flare nor the possibility of emergence of new active regions can be predicted. But high-resolution observations of the magnetic configuration, Ha brightness and structure and other properties of a region enabled us to announce the onset of 15 of 23 major active regions over a two-year period, and 15 of 32 BEARALERTS were followed by this activity. We used high-resolution real-time data available at the Big Bear Solar Observatory (BBSO). The criteria for prediction are given and discussed, along with those for filament eruption.The success fo the BEARALERT is evaluated by counting the M- and X-class flares in six days following the alert and comparing these results with those of a number of other predictive schemes. We find the single regions chosen had about 30% more flares than the whole disk on random days, or several times more than individual regions chosen at random. There was a gain of 1.5 to 2.0 times in flare frequency compared to regions selected by spot size or complexity. We also find an improvement of 20–40% over large or complex regions that have had some flares already. The ratio of improvement has increased with time as we gained experience. In the 24-hr period following each alert, one or more M-class or greater flares occurred 72% of the time.We also checked the possibility of prediction by the 152-day interval which some workers have claimed, but found those results slightly worse than random and considerably inferior to the BEARALERTS. All of the particularly active regions that were missed either occurred during bad weather at BBSO or were missed because we only issued alerts for one region at a time. 相似文献