Flare Data Research Articles

Cooling of solar flare plasmas

A simple model for the cooling of solar flare plasmas is considered. This model predicts that an increase in emission measure with decreasing temperature is a general feature of a cooling flare. The results are compared to solar flare data.

A correlation between time-overlapping solar flares and the release of energetic particles

The origin of a large co-rotating solar particle event in August, 1970, is discussed. Proton data from spacecraft at five widely separated heliocentric longitudes are used to identify two distinct release points which are over 100° apart in solar longitude. Optical flare data shows a high incidence of time-overlapping flares between plage regions close to the two release points, indicating a good connection between them. Unusual X-ray and radio emissions are also observed from these regions. The spectrum of the relativistic electrons in the co-rotating particle event is represented by a power law with index γ ≈ −4, considerably steeper than that usually observed from a solar flare. It is concluded that there is a large magnetic loop structure connecting points over 100° apart on the Sun which is able to trap energetic protons and electrons from an earlier solar flare. Subsequent release of these particles establishes an intense, long-lived co-rotating event.

Coupling of microwaves at a selected solar active centre

The presence of an intense S-component associated with the McMath plage 12094 nearly alone in the southern solar hemisphere in October--November 1972, provided a clear example of polarization sense reversal. The measurements were performed with a 7 GHz polarimeter, and the evolution in flux and percent of circular polarization of the S-component contribution is shown, as well as of the radio bursts that occurred in it, identified after flare data (NOAA, 1972). (WDM)

The possible role of energetic electrons in the production of surges

Energetic electrons, which play a major role in the explosive phases of flares, are proposed as the energy source for the production of surges. Flare data from a two-year interval are analyzed to show that the probability of having surges associated with flares is greater when there are accompanying decimeter type III bursts or impulsive 8800 MHz bursts. The model of chromospheric heating by impulsive electrons proposed by Hudson is examined and shown to provide an adequate explanation for the origin of flare surges. The proposed surge model is consistent with the temporal evolution of the flare-surge event and the required surge energy. Surges not accompanied by flares can also probably be explained by the model.

The thermal nature of soft X-ray flares

Soft X-ray flare data in the wavelength range 2.6–10 A are used to examine the time variation of emission measure and electron temperature. The thermal plasma parameters were derived according to a two-temperature model proposed by Herring and Craig (1973). Estimates of electron density and source volume are made by assuming conductive and radiative cooling mechanisms. It is suggested that the present observations imply a multi-thermal interpretation of the soft X-ray flare.

The continuous emission of low energy cosmic rays during solar flares

A new type of diffusion equation is presented in which the shape of the emission curve and the time during which the emission of energetic flare particles from the solar surface occurs can be prescribed. The diffusion equation utilizes a radially dependent diffusion coefficient in the form of D = Mrβand incorporates the convective and decelerative effects of the solar wind as well as external and internal boundary conditions to the interplanetary diffusion medium. The effect of the continuous emission of energetic solar particles on the intensity curves is shown. The logarithmic curve is utilized as a discriminant in testing for continuous emission and it predicts that in high energy events, the particles are released in an impulsive burst within a few minutes after flare onset. The analysis of solar flare data is shown to be independent of either the convective or decelerative effects of the solar wind. The apparent deviation from the radial diffusion coefficient mode of propagation at very low energies is ascribed to continuous emission. The corresponding solar flare data at slightly higher energies or at different tracking satellite stations all indicate adherence to this mode for electrons as well as for protons. It is postulated that even in the very low energy range, the radial mode prevails. On the basis of the accumulated data from twenty six solar flares studied todate, it is asserted that the radial diffusion coefficient model is the basic mode by which solar flare particles propagate through interplanetary space.

Two-component temperature analysis of OSO-5 X-ray flare data

Using data covering the 2.6–10 A wavelength range from the OSO-5 satellite a four-parameter model of the emitting region in a flare process is derived. The thermal emission spectrum of Landini and Fossi is used to calculate the plasma parameters, electron temperature and emission measure. The X-ray flare data is explained by a model which treats the source volume as two time-varying temperature regions.

Study of Sudden Cosmic Noise Absorption in Relation to Corresponding X-Ray Flares

In this paper an exhaustive study of X-ray flare which occurred on 13 April 1966 between 0706 and 0716 UT has been made. Raw data for this X-ray flare have been converted to the flux energy in erg cm−2 sec−1 and the corresponding time curves have been plotted. N-h profiles for the D-region for χ values of 30°, 50° and 60° have been worked out at the maximum of the flare. N-h profiles for the χ values of 50° and 60° correspond respectively to Manila and Ondrejov.The SCNA data for Manila on 18 Mc/s and for Ondrejov on 29 Mc/s have been employed to work out a model of effective recombination coefficient (αeff).The height of maixmum electron density comes to about 72 km and the corresponding maximum of absorption is found to occur at about 68 km. This is in agreement with the result of Mitra et al. (1966).

The effect of a bounded interplanetary diffusion medium on the propagation of solar flare cosmic rays

An analysis of solar flare data indicates that the graph of log(nt 3/(2−β)) deviates late in the solar event from the straight line predicted for the infinite, unbounded interplanetary medium. It is shown by mathematical analysis, utilizing a model based on the radial diffusion coefficient D = Mr β, with β ≃ 1, that the deviation can be ascribed to the loss of flare particles through an external boundary at about 5–6 AU from the Sun. An inner region terminating at 5–6 AU, followed by an extensive region of increasingly less resistance to the diffusion of flare particles is also feasible and it is shown that measurements taken at the Earth cannot predict the extent of this outer region. The results are applicable to either the isotropic or highly anisotropic models. The constant diffusion model is shown to be inadequate since it requires a boundary ⩽ 1.5 AU from the Sun. In view of the present and previous studies of solar flare data, it is asserted that the fundamental principle governing the diffusion of solar flare particles through interplanetary space is the radial diffusion coefficient mode of propagation.

A Method of Evaluating Radiation Risks for Manned Space Flights

Problems concerning an evaluation of the hazard from doses of ionizing radiation during manned space flight are discussed. A method is given for statistically combining solar flare data with assessments of the likelihood for biological responses. This approach is aimed at synthesizing radiophysical and radiobiological data so that the interfaces between radiation, crew safety, and mission success can be better related to other hazards during mission planning.

Apparent Area as a Basis for Solar Flare Importance

view Abstract Citations (4) References (1) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Apparent Area as a Basis for Solar Flare Importance Sawyer, Constance B. Abstract If flare importance, based primarily on area, is to be insensitive to the flare's position on the solar disk, we need to know how apparent area depends on position. Earlier studies show that the ratio of corrected to apparent area seems to differ between small and large flares. Calculations based on a simplified model show that this apparent dependence is not real, but is introduced by observational loss of small flares. A relation between corrected area and apparent area that depends on central distance alone provides an adequate description of extensive world-wide flare data. Publication: The Astrophysical Journal Pub Date: January 1967 DOI: 10.1086/148991 Bibcode: 1967ApJ...147..193S full text sources ADS |

A daily index of solar flare activity

We define and compute a daily flare index that is similar to the index of solar flare activity originally published by the High Altitude Observatory. The H.A.O. index measures the integrated intensity of flare radiation, and the new index shares its clear physical interpretation and parallels geophysical effects in a similar way. The Space Disturbances Laboratory Index Iƒ is based on complete worldwide standardized flare data and is defined as a function of the single variable flare area. This simple definition is made possible by the fact that the duration of the observable flare is related to apparent area independently of the flare's position on the solar disk. Characteristics of the index Iƒ are compared to those of other flare indices.

Sudden Increase in Long-wave Field Intensity (SIL) and Its Association with Solar Flares and Other Geophysical Events

ABSTRACTThe paper deals with a radio method developed recently at the Research Department of All India Radio for detecting the occurrence of solar flares. Continuous recording at Delhi of the received field strength of sky-wave from Radio Tashkent (164 kc/s., distance: 1630 km. from Delhi) has indicated that a sudden increase in the amplitude of the received signal (abbreviated SIL) is almost always associated with the occurrence of a solar flare. SIL data presented in this paper cover the period August 1958 to July 1960 during which 567 SIL's have been observed. The observed SIL's have been compared with flare data collected from observatories and nearly 85 per cent of the total number of SIL's are found to agree with optical flares. The timings of SIL have been compared with corresponding flare and very good agreement found to exist between the times of beginning, maximum and total duration of the two events. A quantitative classification of flare has also been attempted from the relative increase in si...

A radio method of detecting solar flares

The paper deals with a radio method developed recently at the Research Department of All India Radio for detecting the occurrence of solar flares. Continuous recording at Delhi of the received field strength of skywave from Radio Tashkent (164 kc/s; distance 1630 km from Delhi) has indicated that a sudden increase in the amplitude of the received signal (abbreviated SIL) is almost always associated with the occurrence of a solar fiare. SIL data presented in this paper cover the period August, 1958–July, 1960 during which 569 SIL's have been observed. The observed SIL's have been compared with flare data collected from observatories and nearly 85 per cent of the total number of SIL's are found to agree with optical flares. The timings of SIL have then been compared with corresponding flares and very good agreement was found to exist between the times of beginning, maximum and total duration of the two events. A quantitative classification of flare has also been attempted from the relative increase in signal during a SIL. The other radio methods of detecting a solar flare namely, SWF, SCNA, SEA, SNB and magnetic crotchets have also been considered, in order to assess the relative advantage of the SIL method over others. It is observed that, as a single method known at present, the SIL gives the highest number of flares from a single reporting station. The timings of a flare can also be given much more precisely and accurately from the recording of a SIL than from the observation of an “optical” flare. The SIL method of detecting a solar flare thus appears to be a very promising one. A system of reliable short-term forecasting of ionospheric and magnetic storms from the observed SIL can be envisaged in the near future.

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.

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.

Survey of number of solar flares observed during the international geophysical year

According to the McMath-Hulbert Observatory working list of world-wide flares there were more than 6700 solar events during the IGY for which at least one observer estimated the importance to be >¯1. According to reports to World Data Centers the flare patrol was gratifyingly complete and uniform. However, examination of the starting times of the reported flares reveals evidence for a serious lack of homogeneity in the IGY flare data. Approximately twice as many flares, >¯1, were reported per hour from 05h to 16h UT as during the remainder of the Universal Day. This strong dependence on UT exists in the flare data for each month of the IGY. Examination of the patrol hours and flare reports for May and July 1958 for each of the 19 Hα cinematographic patrol stations shows that the principal photographic patrol stations fail to confirm the very high rate of flare occurrence for 05h to 16h UT that appears in the total IGY data. Visual observations between 05h and 16h UT, apparently constitute the principal source of inhomogeneity in the flare data. For the hours 17 to 04 in the Universal Day the IGY flare reports are based primarily on the cinematographic patrol. Comparison of the number of flares and subflares indicates that in the IGY data for the hours 05 to 16 UT many flare events are listed as flares that probably would have been classified as subflares by the principal cinematographic observers.

Studies at the McMath-Hulbert Observatory of Radio Frequency Radiation at the Time of Solar Flares

The complex flare phenomenon is described in terms of its photographic aspect on H? spectroheliograms, associated prominence activity, terrestrial effects, and the general pattern of radio frequency emission. Flare-associated events at 2800 and 200 mc are reviewed, and the association between flares and the onset of 200-mc noise storms is discussed. Records of 2800 and 200-mc radiation at the time of 277 flares are compared. Flare-events at frequencies less than 200 mc are considered, and a study of 496 flares at 80 mc is summarized. An effort is made to compare reports of dynamic spectra at radio frequencies with flare data and single frequency records. The apparently close association between flares with major early bursts at frequencies ?200 mc and geomagnetic disturbances is discussed.

Solar Flares and Magnetic Storms (Second Paper)

Examination of a relationship found between intense (3 +) solar flares within the central zone of the Sun's disk and subsequent geomagnetic activity has been extended to less intense flares (3 and 2). With flares of intensity 3 there is a small statistical rise of geomagnetic activity within a few days of the mean flare; in individual cases the disturbance is generally less intense and is certainly less probable than for flares 3 +. There is no perceptible rise of geomagnetic activity after the mean flare of intensity 2. Some distinctive flares 3 are tabulated for comparison with the most intense flares dealt with in the first paper. Radio fade-out data confirm in a general way a small statistical rise of geomagnetic activity within a few days after the mean fade-out, but the results are less definitive than those from the solar flare data.