Intense Solar Flares Research Articles

Circulation changes in the free atmosphere during proton events associated with type IV radio bursts

New evidence of statistically significant circulation changes in the lower stratosphere and in the middle and upper troposphere following Type IV Proton and Ground Level Events confirms some earlier findings of a relationship between solar activity and weather. The maximum 24-hr circulation changes appear to occur in the North Pacific-Alaskan area. A comparison between the effects that followed the flare sample used in this study with earlier results reported for less intense solar particle emission flare samples, implies that if these particles are responsible for triggering the atmospheric circulation in times of enhanced solar activity, their atmospheric effect is enhanced as we move to the more energetic solar proton events. The physical explanation of the results may possibly be found in numerical-experimental models. Some possible causes of the results are discussed.

Shock waves generated by the intense solar flare of 1972, August 7, 15:00 UT

The dynamic radio spectrum of the class 3B solar flare of 1972, August 7, 15: 00 UT, over the band 10 to 2000 MHz is examined. Type II and type IV bursts in the spectrum are interpreted in terms of a piston-driven shock, which appeared to be travelling at a velocity of about 1500 km s−1 and which generated pulsations in the band 100 to 200 MHz as it passed through the corona. The progress of the shock through the interplanetary plasma was subsequently monitored by Malitson et al. with radio equipment covering the band 0.03 to 2.6 MHz on the IMP-6 satellite.

K? line emission during solar X-ray bursts

Kα X-ray line emission from S, Ar, Ca and Fe is calculated for conditions likely to exist in solar flares. We consider both the non-thermal and thermal phases of flares as indicated by X-ray observations. Impulsive non-thermal events seen at the onset of a flare at photon energies > 20 keV generally give rise to small Kα line fluxes (<250 photons cm-2 s-1) on the basis of data presented by Kane and Anderson. The amount of S Kα radiation in particular depends sensitively on the lower-energy bound of the non-thermal electron distribution giving rise to the impulsive burst, offering a possible means of determining this. Thermal Kα emission is significant for only Fe ions. For S, Ar and Ca, the temperatures required for a sizeable number of electrons with energies greater than the K-ionization potential will also strip these elements to ionization stages too high for Kα transitions to be possible. Comparison of thermal Kα emission from iron during an intense solar flare leads to a very high emission measure on the basis of these calculations, but such a value seems to be compatible with an analysis of the 1–3 A continuum during the same event.

Iron-Line Emission during Solar Flares

view Abstract Citations (41) References (17) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Iron-Line Emission during Solar Flares Doschek, G. A. ; Meekins, J. F. ; Kreplin, R. W. ; Chubb, T. A. ; Friedman, H. Abstract Iron-line emission 1.9 A recorded by NRL Bragg crystal spectrometers on 080-6 during intense solar soft X-ray flares is discussed. Individual emission features are resolved in second order, and variability in emission from Fe xxv relative to inner-shell emission from lower ionization stages is considered. A feature at 1.932 A is attributed to radiation from Fe ii in the photosphere. In the region of the secondorder iron spectra, the two fine-structure components of the first excited P state of hydrogenic argon are resolved. Publication: The Astrophysical Journal Pub Date: December 1971 DOI: 10.1086/151243 Bibcode: 1971ApJ...170..573D full text sources ADS |

The structure of the solar plasma flow generated by solar flares

Characteristics of geomagnetic storms caused by solar flares at different central meridian distances are statistically examined to obtain a two dimensional configuration of the solar plasma flow generated by solar flares. It is shown that the front of the plasma flow is nearly hemispherical, but its energy flux is greatly concentrated in a narrow cone from intense solar flares; therefore, the energy flux has a jet structure. It is shown that these results can be reasonably combined to give a consistent picture by assuming the generation of an interplanetary shock wave by the jet of the solar plasma ejected by a solar flare.

The streaming of solar flare particles and plasma in interplanetary space

A review is given of the features of solar particle emissions which cause various terrestrial disturbances. Three types of corpuscular emissions, namely, solar cosmic rays, energetic storm protons and plasma clouds, are associated with intense solar flares. Outward streaming of the solar wind and of beams of enhanced activity originate from the quiescent solar corona. It is shown that these solar particles propagate through interplanetary space, being modulated in a systematic way by existing magnetic fields. Time variations of solar flare particle flux, and their energy spectrum, are discussed.

Regularities in the Occurrence of Solar Flares

Abstract : Striking regularities in the occurrence of intense solar flares have been identified, and an investigation of these regularities is beginning to provide new information about solar disturbance events. On the basis of earlier work the work recorded here began with the assumption that regular variations, with periodicities of the order of several days, occur on the Sun. The physical nature of these variations is unknown, but it was assumed that one manifestation of their existence is the occurrence of discrete solar disturbances. The general concept was that the probability of occurrences of an event, such as an intense flare, is determined by the phase of the assumed solar periodic variations. (Author)

Streaming of solar particles between Sun and Earth

It has long been known that the physical state of the Earth’s upper atmosphere is closely related to solar activity-the growth and decay of sunspots, the corona, uprushing prominences and bright chromospheric flares. In particular, transient radiative and corpuscular emissions associated with solar flares produce the most outstanding electromagnetic disturbances in the environment of the Earth. It is generally believed that geomagnetic storms are caused by the impact of solar plasma clouds with the geomagnetic field(l). Associated aurora1 and ionospheric effects are the direct consequence of disturbances induced in the upper atmosphere. The evidence of continual agitation of the geomagnetic field in the polar regions suggests a constant stream of incoming particles even during geomagnetically quiet periods. This accords with certain observations of the motion of comet tailP, for which the name solar wind or streaming plasma has been proposed in contrast to the storm-producing plasma cloud(3). The accumulated evidence of recent years indicates that the Sun emits not only lowenergy plasmas but also, on occasions, very-high-energy particles, known as solar cosmic raysc4). Since 1942, eight events showing an unusual increase in cosmic ray intensity have been found in ground-based observations. They were associated with intense solar flares, and the particles arrived at the Earth within very short time-delay, indicating that the energy exceeded the relativistic range. Several small but distinct solar cosmic ray events have also been identified since the International Geophysical Year (1957-8) strengthened considerably the precise world network of neutron monitors. An arrival of sub-relativistic-energy particles is not detectable at ground level, but this information is now available from recently developed rocket and balloon measurements and indirectly by ionospheric observations. These particles emitted from a solar flare impinge onto the ionosphere in the polar-cap regions, thereby producing enhanced ionization and a particular type of aurora1 glow. Thus, the events are known as polar-cap blackouts(5-7), polar-cap absorptionPlO) and polar-glow auroraeol). Direct measurements by balloon(12) and by satellites (13) .have revealed that the energy spectrum of these solar particles is considerably broad, ranging from 1 to 1000 MeV. Statistical studies have shown that such events are much more numerous than was ever suspectedo4), and also that they are closely related to the particular type of solar flares associated with strong radio outbursts of continuum radiationul in particular, comprehensive measurements by recent space probes and satellites. Thus, it is now evident that an enormous number of particles with a considerable wide-energy spectrum is streaming out from the Sun. Since solar particles detected in the environment of

Possible Implications of the Damage by Radiation in the Storage of Propellants in Outer Space and Tentative Methods for Its Measurement

The damage by radiation that can be expected during the storage of hydrogen-bonded propellants in outer space is analized in terms of the available data on radiation levels. On this basis, the alternatives of storing the propellants as liquids or as solids, at low temperature, are discussed, and account is taken of recent results on their thermal behaviour obtained at this Laboratory. Vitreous states of aggregation that could crystallize spontaneously after long periods of irradiation are shown to present some hazards that can be prevented. General considerations of radiation-damage detection in outer space are also made. Paramagnetic resonance is found to be of limited use although it could be used for studying the damage produced by intense solar flares. Solid-state devices are finally recommended.

Solar Flare Helium in Satellite Materials

Samples of Al and Pb from Discoverer 17, which was flown during the intense solar flare of Nov. 12, 1960, are analyzed for He/sup 3/ and He/sup 4/ content. lt is concluded that the Hes/up 3/, and some of the He4, found in the samples represent stopped particles from the solar burst. It is estimated that the flare particles had a He/sup 3//He/sup 4/ ratio of 0.02. (T.F.H.)

Sudden Cosmic Noise Absorption at 29 Mc/s

Cosmic radio noise observations at 29 Mc/s made at Hyderabad, India (17� 26' N., 78� 27' E.), have been compared with solar flare data for the year 1958. For flares of importance 3 or 3�, there is a correlation of 84% with regard to related effects observed in the cosmic noise records. These effects are either enhanced radio emission or SCNA's. Particular study of the 9 SCNA's observed during the year and comparison with results of Bhonsle working at Ahmedabad, India (23� 02' N., 72� 38' E.), reveal that (a) even in the case of intense flares initial conditions in the terrestrial atmosphere govern the production and maintenance of an SCNA, and (b) therefore, at least at frequencies above 25 Mc/s, SCNA's cannot be used for patrolling even intense solar flares.

Velocities of Shock Fronts in Solar Corona Generating Type II Radio Bursts at Metre Wavelengths

At the time of intense solar flares, various types of enhanced radio emission from the Sun have been observed. Using such techniques as the swept frequency technique first developed by Wild and his associates, these enhanced emissions have been classified into five types. Of particular interest to radio astronomy at metre wavelengths is the slow drift type II bursts. A comprehensive study of these bursts has been made by Roberts (1959). It is now supposed that at the start of a flare an explosion occurs in the lower regions of the solar atmosphere ejecting a column of gas which travels radially outward from the region of the flare. This column of gas is bounded by a shock front which moves forward relative to this gas. This shock front is assumed to excite plasma oscillations in the solar corona giving rise to type II radiation. Velocities of these shock fronts have been determined by various workers.

A Method of Estimating Ionospheric Absorption Heights from Recovery Times

IT is generally agreed that the absorption of radio waves in the ionosphere occurs at heights below about 100 km. In a particular instance it is usually possible to deduce the approximate height by indirect reasoning. For example, Hultquist1 has used indirect evidence to place the abnormal absorption which follows intense solar flares at heights as low as 50 km. As yet there are too few direct measurements (using rockets) to provide a complete and consistent picture. This communication suggests a new method of estimating the height of the regions responsible for abnormal absorption of the kind associated with auroral disturbances.

Charged particles in the inner Van Allen radiation belt

A nuclear emulsion stack was flown through the lower part of the inner Van Allen radiation belt a few days after the intense solar flares of July 10 to 16, 1959. The stack looked out through a thin window on the mounting plate at the rear of the nose cone. Protons with incident energies down to 42 Mev were recorded. The total proton flux is about one-third that reported by Freden and White; the difference may be due to the lower peak altitude of the flight reported here. Above 100 Mev the proton spectrum is consistent with the neutron albedo hypothesis. Below 100 Mev, however, there is evidence of structure with a peak or plateau in the region of 80 Mev. This structure may be due to solar protons.

太陽活動とオゾン層について

A statistical investigation of the variation of total ozone amount as measured by the deviation of ten-day running means to find out the influence of intense solar flares or of an intense solar corpuscular bombardment was carried out, each concerning with varying latitudinal belt.The method of calculation was the key day test or the superposed epoch method to see the variation from three-days before through ten-days after the key day. The ozone data used were those of twenty-two stations of the world namely, of Japan (5), America (5), Australia (3), Italy (3), Iceland (1), India (4) and of Switzerland (1), covering the period from January 1958 to March 1959.Key days were defined in two ways, namely the day when geomagnetic Ap index was greater than 45 and the day when the flare index, as defined by this author basing on the world wide flare data, was greater than 1500.According to the results of calculation ozone increased on the third or forth day after the flare key day except in the zone of lowest latitude. The statistical test did not show in general a property so much remarkable as to exceed the 5% confidence limit except the increase of ozone on the third day in the zone of 20∼30° latitude.In the case of geomagnetic key day generally none of the variation exceeded the 5% confidence limit except the case of 8 th day at the highest latitudinal belt. Also at the same zone it showed the tendency to decrease on the third day which is to be noted when compared with the increase of temperature at 100mb in the auroral zone that was reported by Ward.

The production of cosmic radiation by a solar flare on August 31, 1956

It is shown that the neutron counting rates observed by three widely separated recorders increased by approximately two percent about half an hour after the observation of an intense solar flare at 1226 U.T. on August 31, 1956. The event, as observed at all three stations, exhibited the abrupt onset, and gradual recovery typical of solar flare effects. The time delay between the first visual sighting of the flare, and the earliest arrival of cosmic radiation at the earth was about 20 min. It is shown that the quantity of cosmic radiation which arrived at the earth was two to three orders of magnitude less than the quantities which arrived during earlier flare effects. Consideration of the temporal dependence of the small flare effect suggests that only a small quantity of cosmic radiation was produced in the solar flare.

Geomagnetic Pulsation Accompanying with the intense Solar Flare

Geomagnetic Pulsation Accompanying with the intense Solar Flare

Radio Noise-bursts from Solar M-Regions

IN 1932, Bartels put forward the hypothesis that moderate geomagnetic storms with gradual commencements were associated with certain active regions on the sun which he called M-regions. Solar and geomagnetic studies in later years have confirmed the existence of these magnetically effective areas; but their exact nature still remains obscure. Some authors consider them to be regions from which sunspots have just disappeared, leaving behind a certain amount of activity; others regard them as long-lived dark filaments emitting slow corpuscles and closely connected with bright coronal patches. Our knowledge about the origin of the more intense geomagnetic storms, on the other hand, is more certain. These are characterized by sudden commencements and show very close correlation with solar flares, which occur in the neighbourhood of spot-groups. Observational results of recent years have provided satisfactory evidence of the emission of both corpuscular and electromagnetic wave radiations from intense solar flares; the geomagnetic storm associated with a flare is due to the corpuscles and commences about one to two days after the optical observation of the flare, and the ultra-violet component of the wave radiation produces, in favourable circumstances, a ‘crochet’ in the magnetic traces synchronously with the flare, while the longwave component in the radio-frequency region appears as a noise-burst almost synchronously with the flare. But, to our knowledge, no observational evidence has so far been published indicating that M-regions also can produce crochet-like disturbances in geomagnetic records and simultaneously emit radio waves similar to the noise-bursts from flares. The evidence provided by our recent observations in this regard is therefore of interest.

Geomagnetic Effects of Solar Flares

From a study of the geomagnetic effects produced at widely separated stations on three occasions of intense solar flares, McNish1 concluded that “the change in the magnetic field caused by the chromospheric eruption consisted of an augmentation of the diurnal-variation departure, obtaining at that time in each element”. This result, which has had important repercussions on the theory of the solar and lunar daily magnetic variations, was supported by Newton's2 paper concerning the geomagnetic flare effects occurring at Abinger (England) during 1936–46.

Some Geomagnetic Disturbances At Alibag Observatory (India)&amp; Allied Radio And Solar Effects (1937-1946).

The paper presents an account of some magnetic disturbances associated with solar flares and radio fade out during the period 1937-1946. The ionospheric irregularities associated with four great magnetic storms recorded at the magnetic Observatory Alibag (Bombay) are discussed. On some occasions in intense solar flare is followed about a day later by a great magnetic storm, This occurs far more often than by chance. The presence of a , Crochet " in the magnetic records occurring simultaneously with a radio fade out and the appearance of a solar eruption or flare has been interpreted as showing that radiation from the flare traveling with the speed of light causes the " Crochet", while the magnetic storm which appears between 18 and 30 hours later is attributed to corpuscular radiation traveling at a speed of 1,000 to 2,000 miles/sec.&#x0D; A list of sudden ionospheric disturbances or the Dellinger type from observations made in India during the period 1937-1946 has been collected and the principal features of the observations discussed.