Occurrence Of Solar Flares Research Articles

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.

On the altitude at which some solar-flare-induced lonization is released

During the occurrence of certain solar flares and subflares (about 20 to 25% of those optically observed), the instantaneous frequency of a highly stable, CW, HF signal transmitted obliquely through the ionosphere, over distances of the order of 5000 km, is momentarily changed by a few cycles, The change consists of an increase in the frequency, followed by a decrease and, subsequently, a gradual return toward the original received frequency. The rapidly changing portion of the frequency variation lasts only a few minutes (usually less than 5). In addition, the frequency change varies inversely with the operating frequency and proportionally with the path length. Paths separated by many hundreds of kilometers are simultaneously affected. lt is of interest that these pronounced frequency shifts invariably occur prior to the loss of signal characteristic of a short-wave fadeout, and hence could conceivably be used to warn of impending signal loss in modern HF communication systems affording continuous feedback of propagation conditions over the path. In certain cases, however, the flare- induced frequency shift is not followed by a fadeout. The azimuthal angle of arrival of the same signals that have frequency changes during solar flares and subflares also deviates in about one-thirdmore » of the cases. The fact that a HF wave exhibits bearing deviations signifies that a horizontal gradient of ionization, capable of bending the wave, exists. Electron-density gradients are probably produced as a result of solar-flare-induced ionization, especially at times when the sun's energy falls at a grazing angle on the path. The angle usually deviated to the south (toward the subsolar point) of the great-circle path for the Puerto Rico-Palo Alto (PR-SU) path during the season at which these measurements were made. These observations of instantaneous frequency and angle- of-arrival changes during solar flares suggest that new ionization is introduced initially somewhere just above the E region, very probably in the height region 120 to 200 km, although even greater heights are possible. This initial ionization may or may not be followed by the generation of ionization in the absorbing D region. The time variation of height at which solar-flare-induced ionization is released suggests that the ionization-producing radiant energy is initially soft, and then hardens as the flare progresses. (auth)« less

Effect of Intermittent Operation of Flare Patrols on Observed Flare Frequency.

view Abstract Citations (1) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Effect of Intermittent Operation of Flare Patrols on Observed Flare Frequency. Acton, Loren Abstract It is not required that an observing station observe a solar flare throughout its entire lifetime in order to report the flare. For this reason it is necessary to consider the breaks in observing time as well as the actual observing time when calculating flare frequency. This consideration has been neglected in most earlier studies involving the occurrence frequency of solar flares. We used the following method, similar to that of Svestka (Bull. Astron. Inst. Czech. 7, 9-18, 1954), in calculating the "effective observing time" (E.O.T.) for flares of each importance for each observing station. E O T =A O T $Zt tB + t0N, where A.O.T. actual observing time; Bj number of breaks in observing of duration tj t0 N total number of breaks with duration t#t0 t0 mean lifetime of flares of a given importance. After analyzing some 300 flares, each reported by two or more observing stations, we adopted the mean flare lifetimes given in Table I. The percentage changes in observing times range from a low of 4% for 1-flares observed at Capetown to a high of 243 % for 3+ flares observed at the Dunsink Observatory. The mean value for importance 2 flares is about 60%. The application of these corrections yields significant changes in calculations involving the fre- TABLE I. Mean flare lifetime as a function of importance. Imp 1- 1 1+ 2- 2 2+ 3- 3 3+ to (min) to 20 35 50 60 65 70 75 80 quency of occurrence of solar flares. Two examples of such changes are: (1) The shape of the curve of flare frequency vs flare importance is changed, the percentage decrease in flares per hour being larger for the larger flares. (2) The disparity of reported flares per hour between different observing stations (Dodson and Hedeman, J. Ceophys. Research 65, 123, 1960) is considerably lessened when one considers the number of flares per "effective" observing hour rather than the number of flares per actual observing hour. % for 1-flares observed at Capetown to a high of 243 % for 3+ flares observed at the Dunsink Observatory. The mean value for importance 2 flares is about 60%. The application of these corrections yields significant changes in calculations involving the fre- TABLE I. Mean flare lifetime as a function of importance. Imp 1- 1 1+ 2- 2 2+ 3- 3 3+ to (min) to 20 35 50 60 65 70 75 80 quency of occurrence of solar flares. Two examples of such changes are: (1) The shape of the curve of flare frequency vs flare importance is changed, the percentage decrease in flares per hour being larger for the larger flares. (2) The disparity of reported flares per hour between different observing stations (Dodson and Hedeman, J. Ceophys. Research 65, 123, 1960) is considerably lessened when one considers the number of flares per "effective" observing hour rather than the number of flares per actual observing hour. % for 1-flares observed at Capetown to a high of 243 % for 3+ flares observed at the Dunsink Observatory. The mean value for importance 2 flares is about 60%. The application of these corrections yields significant changes in calculations involving the fre- TABLE I. Mean flare lifetime as a function of importance. Imp 1- 1 1+ 2- 2 2+ 3- 3 3+ to (min) to 20 35 50 60 65 70 75 80 quency of occurrence of solar flares. Two examples of such changes are: (1) The shape of the curve of flare frequency vs flare importance is changed, the percentage decrease in flares per hour being larger for the larger flares. (2) The disparity of reported flares per hour between different observing stations (Dodson and Hedeman, J. Ceophys. Research 65, 123, 1960) is considerably lessened when one considers the number of flares per "effective" observing hour rather than the number of flares per actual observing hour. Publication: The Astronomical Journal Pub Date: 1962 DOI: 10.1086/108623 Bibcode: 1962AJ.....67Q.109A full text sources ADS |

Solar radio emissions and geophysical disturbances during July 1959

This paper briefly summarizes spectral observations of solar radio bursts taken at Fort Davis, Texas, and Sydney, Australia, during July 1959, and relates these observations to the geophysical disturbances at that time. The period is notable because of the occurrence of several great solar flares and their subsequent terrestrial effects. Some of these events have been described elsewhere [Winckler, 1960]. Spectral observations of solar radio emission were made at Fort Davis for 98 per cent of the possible observing time during July 1959. The daily observing period covered the hours 1230 until 0145 UT the following Greenwich day, i.e., from sunrise to sunset. The equipment at Fort Davis comprised five sweep-frequency receivers, which together gave complete coverage of the range 25–580 Mc/s. At 100 Me/s, bursts of intensities 1, 2, and 3 correspond to signal intensities of 5–40, 40–200, and >200 watts m−2 cps−1×10−22 respectively. Similar spectral observations were also made at Sydney, Australia, over the frequency range 25–210 Mc/s. As the Australian results are of interest in the study of the solar-terrestrial events during July 1959, their published observations are included in Table 1. No observations were made at Sydney on July 4, 11, 18, or 25. Their observing periods generally were from about 2300 until about 0600 UT the following Greenwich day. The Australian intensity figures are not the same as those given for Fort Davis, but they are of the same order.

Observations of Radio Noise Storms on Jupiter During the 1960 Apparition.

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Observations of Radio Noise Storms on Jupiter During the 1960 Apparition. Carr, T. D. ; Smith, A. G. ; Chatterton, N. ; Six, F. Abstract The radio noise sporadically emitted by Jupiter was monitored at several frequencies between 10 and 27.6 Mc for approximately six months during the 1960 apparition. Observations were made at the University of Florida Radio Observatory and at the Maipu' Radio-astronomical Observatory of the University of Chile. Activity was found to be considerably greater than during the two previous apparitions. Activity was greatest in the vicinity of 18 Mc, and was slight at 27.6 Mc. The principal source is still centered at approximately the same System III longitude that it has occupied during the six previous years for which data are available. The polarization of the radiation at 22.2 Mc was almost always right- handed elliptical at both observatories. The fact that the same polarization sense was observed from stations above and below the geomagnetic equator apparently rules out the possibility that the polarization originates in the terrestrial ionosphere. A noise storm was usually confined to a frequency band a few megacycles wide, but the active band often drifted slowly up or down the spectrum. The spectrum of each pulse making up a storm was usually a few tenths of a megacycle wide. Simultaneous observations at 10 Mc and 20 Mc revealed that noise occurring at these harmonically related frequencies is not correlated. Striking differences in 18-Mc bursts observed simultaneously from Chile and Florida are attributed to scintillations arising in the terrestrial ionosphere. The theory that the radiation arises from the entry of solar particles into Jupiter's magnetic field is being tested by correlating the noise data obtained in Chile at Jovian opposition with the occurrence of solar flares and geomagnetic disturbances. This work is being sponsored by the National Science Foundation, the Office of Naval Research, and the U.S. Army Office of Ordnance Research. Publication: The Astronomical Journal Pub Date: 1960 DOI: 10.1086/108128 Bibcode: 1960AJ.....65R.485C full text sources ADS |

The Study of Solar Flares by Means of Very Long Radio Waves

The phase of very long radio waves reflected from the ionosphere is very-sensitive to the occurrence of solar flares. The course of the ionospheric disturbance can be followed in detail and a measure of the maximum disturbance given. A method is outlined which may lead to the identification of the radiation which disturbs the ionosphere. Continuous automatic records provide abundant data of great value to the study of solar-terrestrial relations.

OCCURRENCE OF SOLAR FLARES WHERE NO SUNSPOT GROUP WAS OBSERVED

OCCURRENCE OF SOLAR FLARES WHERE NO SUNSPOT GROUP WAS OBSERVED