Flare Area Research Articles

Investigation of five white light flares

On the basis of original observations, five white-light flares (WLF) are investigated. Evidence is given that their emission is located in two points brightening on either side of the lineH∥ = 0 and lying at the foot points of chromospheric loops. The area of WLF is ≈ 5 × 10−6 hemisphere, i.e. ≈ 0.007 of Hα flare area; the intensity of WLF is sometimes twice that of the background at the center of the disk. WLF are resolved into more bright and fine knots of ≈ 2′ in diameter. The position of WLF coincides with the brightest knots of Hα flares which are characterized by wide wings with rapid increase and decrease.

Studies of the Dynamic Structure and Spectra of Solar X-Ray Flares

SummaryData from the AS & E X-ray spectrographic telescope on Skylab were used for a preliminary study of two solar flares on 1973, August 9 and September 5. Photographic images taken through broad band filters during the early flare onsets and subsequent evolution of the flares were analyzed by microdensitometry and subsequent conversion to energy maps of the flare areas.

Some notes on flare patrol

Using data from ESSA Research Laboratory bulletins an estimate of the uncertainty for the times of beginning, maximum and ending, and maximum areas of Hα flares reported during 1967 is deduced and discussed. The need for an improvement of the reliability of the solar patrol service is also indicated.

Properties of white light flares

All four large EUV bursts (peak 10–1030 A flux enhancements ⩾ 2 ergs cm−2 s−1 at 1 AU as deduced from sudden frequency deviations), for which there were available concurrent white light observations of at least fair quality, were detected as white light flares. The rise times and maxima of the white light emissions coincided with rise times and maxima of the EUV bursts. The frequency of strong EUV bursts suggests that white light flares may occur at the rate of five or six per year near sunspot maximum. All of the white light flare areas coincided with intense bright areas of the Hα flares. These small areas appeared to be sources of high velocity ejecta in Hα. The white light flares occurred as several knots or patches of 2 to 15 arc-sec diameter, with bright cores perhaps less than 2 arc-sec diameter (1500 km). They preferred the outer penumbral borders of strong sunspots within 10 arc-sec of a longitudinal neutral line in the magnetic field. The peak continuum flux enhancement over the 3500–6500 A wavelength range is about the same order of magnitude as the peak 10–1030 A flux enhancement.

Solar flares in the extreme ultraviolet

Measurements of flare-related impulsive enhancements in solar emission lines in the extreme ultraviolet, observed from the satellite OSO-III, are reported. The enhancement of a line, expressed in percent of the total disk intensity in the line, is of the same order of magnitude as the flare area, expressed in heliocentric square degrees. Rise-times and decay-times of impulsive enhancements average about 2 min and 5 min, respectively. The maximum enhancements of radiation from ions in the chromosphere-corona transition region precede the Hα maximum by an average of 2 min, and occur in the same period of time as the hard component of solar X-rays and the impulsive microwave bursts. Coronal lines in the extreme ultraviolet are less impulsive than the transition region lines in flare-related enhancements and their maxima follow the Hα maximum.

Skin Reaction Specificity of Guinea Pig Immediate Hypersensitivity to Bites of Four Mosquito Species

A group of 70 guinea pigs was randomly assigned to 5 lots. One lot was sensitized by a series of Aedes aegypti bites. The second lot received only Aedes atropalpus bites; the third, Anopheles stephensi; the fourth, Anopheles quadrimaculatus; and the fifth lot, no mosquito bites. After the sensitization period each guinea pig was given a test bite from each of the following: A. aegypti, A. atropalpus, A. quadrimaculatus, and A. stephensi. Immediate skin reactions were evaluated by measuring: (1) area of increased vascular permeability as indicated by diffusion of a serum protein coupling dye, Coomassie Blue, 20 min after initiation of bites; (2) area of wheal and flare at 1 hr after initiation of bites. Skin reactions to bites of the species used to sensitize the guinea pigs were significantly greater than reactions to bites of the other 3 species (heterologous or cross-reactions). Some heterologous reactions were significantly greater than other heterologous reactions and skin trauma reactions of control guinea pigs. Thus, bites of a single species can produce immediate hypersensitivity to more than one species of mosquito. The heterologous reactions indicate that oral secretion of some mosquito species share at least one common antigen with one or more species. The purpose was to sensitize guinea pigs by bites of a single mosquito species and then determine whether or not bites of other species induced immediate hypersensitive skin re-

A solar flare videometer

A new instrument, called a videometer, has been developed to measure solar flare area, peak intensity and integrated intensity in real time. The videometer uses a closed circuit television system to convert an optical Hα image into electrical signals for measurement. Observations of two Class I flares with the videometer are discussed.

Cape Lyot H?-heliograph results

The Lyot Hα-heliograph at the Royal Observatory, Cape of Good Hope was in almost daily operation from March 12, 1958 to December 31, 1965. From the records obtained, a definitive list of 2907 flares was compiled, their properties analyzed, and the results presented herein. The data on East-West distribution of activity, although inconclusive, shows an asymmetry of flare activity with 56.5% of the flares West of the central meridian; this is partially due, however, to an inhomogeneous density distribution in the filtergrams. Flare distribution with respect to heliographic longitude, association with spot types and number of spots in the group are also discussed. The frequency of flare areas, rise times, and durations are examined as is their relationship to distance from the disk centre.

Analysis of some solar flares from optical, X-ray, and radio observations

Using an improved isodensitometric technique it has been possible to study in great detail the photometric structure and the evolution of eight flares. A comparison has been made between the evolutive curves and the ones obtained from measurements of solar X-rays and radio fluxes at λλ 3·2 and 21 cm.A reduction of the flare areas (and of the emitted energies) before the flash phase and a continuous pulsation of the flare have been observed. Further it seems that the flares associated with radio bursts or X-ray events are those which show regions of a sufficiently high intensity, the emitting areas not being a very important parameter.The correlation in time between the various examined aspects of the AR seems to indicate that the sequence for the beginning of the different phenomena is, in general: optical flare, X-ray events, radio events.

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.

The Effect of a Solar Wind Blast Wave on the Chromosphere.

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Effect of a Solar Wind Blast Wave on the Chromosphere. Wentzel, Donat G. ; Solinger, Alan B. Abstract The enhanced solar wind following some solar flares is probably caused by coronal heating. The energy involved in the enhanced wind suggests that flare-induced coronal heating occurs over an area extending far beyond the flare area. The resulting disturbance of the underlying nonflaring chromosphere is computed on the assumption that the corona is heated suddenly. In this case, a shock moves downward from the heated region. The increase in the undisturbed chromospheric density ahead of the shock (p) tends to weaken the shock. In addition, magnetic fields may act as a guide for the shock. An increase in field strength along the shock's path constricts the area of the shock front (A) and tends to strengthen the shock. Both effects can be evaluated analytically, using Whitham's theory for shock propagation in inhomogeneous media (J. Fluid Mech. 4, 337, 1958), if both the shock and the chromosphere are considered to be isothermal. The change in Mach number (M) with p and A is given by 1 1 2 dp dA 1+ +-+ dM+-+-= 0. M2 M M-1 p A For plane stratification or vertical magnetic fields (dA =0), the shock penetrates gas increasing in density by one to two orders of magnitude before attenuation becomes significant. Its effect may relate to the flare nimbus and to the disappearance of stria- tion patterns. The strength of a shock entering the field of a sunspot (dA/dp<0) is attenuated much less. Flaring over sunspot umbrae may be initiated by such a shock. Publication: The Astronomical Journal Pub Date: February 1966 DOI: 10.1086/110121 Bibcode: 1966AJ.....71R.402W full text sources ADS |

VLF observations at college, Alaska, of various D-region disturbance phenomena

Between late 1961 and mid-1964 several stabilized VLF transmitters have been monitored at College, Alaska. During that period 1846 optically detected solar flares were observed when our NBA recorder was operating and the path was completely sunlit. Of these, 66 produced phase anomalies on our NBA records. The probability of occurrence increased approximately linearly with flare area, but was less than probabilities for SID's determined by other methods. This indicates the VLF phase is not as sensitive as other SID indicators. The SPA decay was very nearly exponential on the College signals. The decay was significantly faster at 10.2 kc/s than at 20 kc/s frequencies. Polar cap precipitation events disrupt polar VLF propagation. The polar D-region was depressed significantly for periods of up to four or five days after relatively minor PCA events. Immediately after three events the phase from GBR was advanced 180 to 270 degrees beyond normal daytime values. VLF phase anomalies produced by (1) the U.S. and U.S.S.R. high altitude nuclear explosions in 1962, (2) the 20 July 1963 solar eclipse, and (3) the 1 October 1961, sub-auroral-latitude particle precipitation event are shown and discussed.

Solar Flares Caused by the Skin Effect in Twisted Magnetic Fields.

view Abstract Citations (12) References (12) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Solar Flares Caused by the Skin Effect in Twisted Magnetic Fields. Wentzel, Donat G. Abstract An optical flare may be caused by the collapse of an unstable chromospheric region, under the action of magnetic forces, toward a surface of minimum but finite magnetic field strength. The compression of the magnetic field during the collapse results in forces which stop the collapse, in a time comparable to the rise time of flare light-curves Turbulence is likely to occur if the velocities of collapse can become comparable to Alfven speeds. The turbulence provides sufficient ohmic dissipation of the magnetic fields to explain the rate of optical emission. The emission is l6calixed in thin surfaces at the eddy boundaries. The total depth of the emitting surfaces crossed by a line of sight is in agreement with inferences from observations. If the same kind of collapse which causes an optical flare in the chromosphere occurs at greater heights, the density is insufficient to radiate away the thermal energy derived from ohmic dissipation. The result is heating, with attendant radio, X-ray, and particle events, instead of an optical flare. The conditions under which turbulence may occur are investigated Some of the consequences of the theory relate to flare light-curves, homologous flares, and rates of expansion of flare areas Publication: The Astrophysical Journal Pub Date: November 1964 DOI: 10.1086/148059 Bibcode: 1964ApJ...140.1563W full text sources ADS |

Formation of Solar Flares without Magnetic Neutral Points.

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Formation of Solar Flares without Magnetic Neutral Points. Wentzel, Donat G. Abstract A flare may be caused by the collapse of an unstable chromospheric region, under the action of magnetic forces, toward a surface of minimum but finite magnetic field strength. The compression of the magnetic field during the collapse results in forces which stop the collapse, in a time comparable to the rise time of flare light curves. Turbulence is likely to occur if the velocities of collapse become comparable to Alfv6n speeds. If turbulence occurs, it can cause sufficient Ohmic dissipation of the magnetic fields to explain the rate of optical emission (Wentzel, Astron. J. 68, 299(A), 1963). The dissipation and emission are localized in thin surfaces at eddy boundaries. The total depth of the emitting surfaces crossed by a line of sight through the flare is of the order of 10 km, in agreement with inferences from observations (Suemoto, Hiei, and Hirayama, J. Phys. Soc. Japan 17, Suppl. A-2, 231). if the same kind of collapse which causes an optical flare in the chromosphere occurs at greater heights, the density is insufficient to radiate away the thermal energy derived from Ohmic dissipation. The result is heating, with attendant favorable conditions for the generation of radio, x-ray, and particle events, instead of an optical flare. Depending on the extent of the collapsing region, optical and heating events may occur alone or together. The conditions under which turbulence may occur and the corresponding gas densities have been investigated numerically. Some of the consequences of the theory relate to flare heights and light curves, increases in density before optical flaring starts, rates of expansion of flare areas, homologous flares, and apparently simultaneous flares. Publication: The Astronomical Journal Pub Date: March 1964 DOI: 10.1086/109250 Bibcode: 1964AJ.....69..151W full text sources ADS |

Pre-Flare Filament Characteristics.

view Abstract Citations (2) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Pre-Flare Filament Characteristics. Ramsey, H. E. ; Smith, S. F. Abstract A consistent picture of a pre-flare filament action has been drawn from a study of all flares of importance 2 or greater, cinematographically recorded by the Lockheed Observatories, from January 1959 to January 1963. Extensive observations in the wings of Ha (Ha - .5 A and Ha~ .5 A) allow the detection and interpretation of a precursory filament action to the type of flare associated filament disappearance described by Bruzek and others. The entire filament action, both prior and concurrent with a flare, is observed with seven overlapping phases: (1) increased opacity (darkening), (2) arch-like expansion, (3) breakup of the filament, (4) transition from absorption to emission, (5) sudden disappearance, (6) ejection of matter, (7) appearance of absorption matter during a flare. Although the order of the phases is consistent for every observation, not all phases are observable in any one wavelength on any one location on the solar disk. The first phase is uniformly observed in the blue wing of Ha, and has begun as early as 53 min before a flare. The flare appears during or any time after the third phase. The most generally observed phase of the action is the sudden disappearance of the filament within minutes before or during the rise of the flare. Of 71 major flares studied, 32% are associated with one or more phases, always including the sudden disappearance. Twenty-five percent are classed as indeterminate, because of lack of pre-flare obobservations. Six percent are ambiguous. Thirtyseven percent show no association with filaments within or proximate to the flare area. The various phases of the filament action should be useful in interpreting some observations of rare events reported by other observatories. The frequent occurrence of the filament action suggests it is intimately linked with the flare mechanism. Publication: The Astronomical Journal Pub Date: June 1963 DOI: 10.1086/108969 Bibcode: 1963AJ.....68..290R full text sources ADS |

A study of Sacramento Peak flares. II: Flare areas and importance classifications

A study of Sacramento Peak flares. II: Flare areas and importance classifications

Flare-associated magnetic activity in the sun.

Observations of the longitudinal Zeeman effects in a solar active center show the variations of magnetic field streng~h during a period of 144 minutes on 30 April 1958, which included the development and decay of a flare of importance I ~. The measurements show that the flare crossed the neutral line of zero longitudinal field, and, although the extremities lay in regions of steep field gradients, most of the flare area was a region of low gradient. A small but pronounced S pole within the flare area developed and faded away in exact synchronism with the flare intensity. However, the large magnetic changes affected the whole field of the active center. The integrated magnetic energy of the region underwent a sharp decrease of about 16 per cent during the 14 minute rising phase of flare intensity, and an even sharper recoverN to its initial value immediately after flare maximum. This behavior was shared by the large sunspot fields and the area outside the sunspots. On the assumption that the field was 5000 km deep, the energy change of the active center amounted to 4 X I0~' ergs. The Ha radiation of the flare during its life was about 1028 ergs. Thus the changes in magnetic energy prob~bly exceed the total radiation of the flare in the Balmer and Lyman series by a considerable factor. Sacramento Peak Observatory Sunspot, New Mexico

Photometry of Solar Flares.

view Abstract Citations (19) References (7) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Photometry of Solar Flares. Dodson, Helen W. ; Hedeman, E. Ruth ; McMath, Robert R. Abstract On the basis of photometric light-curves for 194 flares and subflares, the following data have been derived. 1.Ha intensity often varies differently in different parts of the same flare. 2.The change of Ha intensity with time in a flare can be well represented by the series of curves given by the equation iog =(iog Ii ax) t a(t-trnax), where t is measured in minutes and a is positive for the ascending branch, negative for the descending branch, and takes values between 0.40 and 0.00313. For the descending branch of the light-curve, a is always smaller than for the ascending branch. The most usual value of a for the ascending branch is 0.10; for the descending branch a is -<0.025 for 87 per cent of the cases. 3.Ha flare intensities have been measured in units of both the local and the centra] continuum at x 6590. In the former, average Ha intensity at flare maximum ranged from 0.66 for subflares and 0.88 for flares of importance 1 to intensity 1.17 and 1.28 for flares of importance 2 and 3, respectively. In units of the central continuum the average values are about 0.1 lower. The brightest measured maximum was 1.9 times the local continuum for a flare at CMD 72 . 4.No convincing relationship has been found between rate of increase of intensity and maximum intensity attained by the flare. However, the slowest rate of increase apparently diminishes the chances of attaining a maximum as bright as the contmuous spectrum. 5.There is evidence for center-to4imb variation in numerous characteristics of the Ha flares in this study. The slowest rates of rise and decline were observed only for flares ithin 55 of the central meridian, and the fastest rates of decline only for flares within 40 of the solar limb. Average intensity in units of the local continuum increased with increasing central meridian distance of the flares. In units of the central continuum, the average intensity diminished from center to limb. "Limb-darkening" equations for the flares and subflares are as follows: Flares: lc=O.63+O.34COS 0, Subilares: lc=O.36+O.26CC)S 0. For flares of the same importance, average duration diminished with increasing distance from the center of the disk. Near the center of the disk, the Ha flare usua]ly lasted as long as, or longer than, the associated ionospheric disturbance, but for flares near the limb the reverse was true. 6.For the flares in this study, area and intensity increase together, but the correlation coefficient of these two measures is only 0.58 + 0.03 p.e. 7.Flare duration was associated more closely with flare area than with maximum intensity. The duration of flares as measured by photometric light-curves is much longer than the average duration of flares reported in the Quarterly Bulletin of Solar Activity. 8.The reported starting times of SID's usually fall during the period of increasing intensity in the flare. Except in unusual cases, SID's were not reported unless the flare intensity was at least 0.8 of the local continuum and the area was of the order of 200 millionths of the solar disk. Near the limb the SID often lasts longer than the Ha flare. 9.There is apparently less diminution from center to limb in the ionizing radiation from flares than in Ha. 10. The ionospheric disturbances were unusually small for certain large and relatively bright flares associated with the onsets of 200-Mc/s noise storms. 11. Examination of ionospheric records for the times of the flares and subflares in this study has provided evidence for a new type of flare-associated ionospheric effect, a gradual ionospheric disturbance, in contradistinction to the sudden SID or Dellinger effect. The 45 reported SID's have been augmented by 19 additional, well-confirmed ionospheric disturbances and by 23 less certain events. 12. There is no evidence to indicate that subflares are not just smaller, fainter examples of the flare phenomenon. Flares and subflares in this study have similar disk distributions and rates of increase and decrease of intensity. Ionospheric disturbances accompanied at least four of the brightenings here classified as subflares. Publication: The Astrophysical Journal Supplement Series Pub Date: February 1956 DOI: 10.1086/190027 Bibcode: 1956ApJS....2..241D full text sources ADS |

Heights of Solar Flares.

view Abstract Citations (12) References (1) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Heights of Solar Flares. Warwick, James W. Abstract The observed area of a solar flare is a combination of two areas: the area of the sides of the flare as it would be seen at the limb and the area of the top of the flare as it would be seen at the center of the disk. The change in measured areas of Ha flares observed at the center of the disk and at some distance from the center of the disk is used to derive information on heights of flares. A preliminary analysis of the raw data indicates that flares are neither flat nor needle-shaped. Explicit height distributions, functions of flare area, are derived from the smoothed data. The shape assumed here for a typical flare appears to be more realistic than that proposed by Waldrneier. The height-frequency distribution is well represented by exp [- phi, where P is the reciprocal of 20,300 km. Flares at the limb of the sun should therefore be visible as low, but extremely bright, prominences. Publication: The Astrophysical Journal Pub Date: March 1955 DOI: 10.1086/145996 Bibcode: 1955ApJ...121..376W full text sources ADS |

Flare Height and Association with SID's.

view Abstract Citations (15) References (4) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Flare Height and Association with SID's. Warwick, Constance S. Abstract The measured heights of limb flares yield a height-frequency distribution that agrees, within observational uncertainties, with that derived by J. W. Warwick from areas of disk flares. No certain case is found of an SID (sudden ionospheric disturbance) associated with a flare of height less than 15,000 km above the Ha limb. The existence of a minimum flare height for SID association suggests that SID's are caused by Lyman radiation rather than by soft X-rays. The observed value of 15,000 km for the minimum height above the Ha limb agrees fairly well with the value 11,000 km, the height above the photosphere at which optical depth becomes unity for Lyman-a radiation in Piddington's model. Values of the fraction of SID-associated flares at different distances from the center of the disk are consistent with the idea of a critical flare height for SID association. Publication: The Astrophysical Journal Pub Date: March 1955 DOI: 10.1086/145997 Bibcode: 1955ApJ...121..385W full text sources ADS |