Observations of an unusual pair of homologous flares on March 17, 1970

Cliver, E. W.; Wefer, Fred L.

doi:10.1007/bf00153604

Sol Phys

1981

DOI: 10.1007/bf00153604

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Observations of an unusual pair of homologous flares on March 17, 1970

E. W. Cliver

Fred L. Wefer²

Abstract: Correlated optical, radio andX-ray observations are presented for a pair of 'consequently' homologous flares which occurred on March 17, 1970. A rich complexity of behavior in a bright sub-flare with maximum at 14 : 44 UT is repeated in a flare of importance 1B with maximum at 22 : 49 UT. The unusual and interesting aspect of these flares is that the second flare developed at approximately half the rate of the first. A difference in the trigger mechanism of the two flares is suggested as a possible explanation. Show more

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A multiwavelength study of a double impulsive flare

et al. 1984

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Extensive data from the Solar Maximum Mission (SMM) and ground-based observatories are presented for two flares; the first occurred at 12 : 48 UT on 31 August, 1980 and the second just 3 rain later. They were both compact events located in the same part of the active region. The first flare appeared as a typical X-ray flare: the CaxIx X-ray lines were broadened (-= 190 + 40 km s-1) and blue shifted ( -= 60 + 20 km s -1) during the impulsive phase, and there was a delay of about 30 s between the hard and soft X-ray maxima. The relative brightness of the two flares was different depending on the spectral region being used to observe them, the first being the brighter at microwave and hard X-ray wavelengths but fainter in soft X-rays. The second flare showed no significant mass motions, and the impulsive and gradual phases were almost simultaneous. The physical characteristics of the two flares are derived and compared. The main difference between them was in the pre-flare state of the coronal plasma at the flare site: before the first flare it was relatively cool (3 x 106 K) and tenuous (4 x 109 cm-3), but owing to the residual effects of the first flare the coronal plasma was hotter (5 x 106 K) and more dense (3 x 1011 cm -3) at the onset of the second flare. We are led to believe from these data that the plasma filling the flaring loops absorbed most of the energy released during the impulsive phase of the second flare, so that only a fraction of the energy could reach the chromosphere to produce mass motions and turbulence.A simple study of the brightest flares observed by the SMM shows that at least 43 % of them are multiple. Thus, the situation studied here may be quite common, and the difference in initial plasma conditions could explain at least some of the large variations in observed flare parameters. We draw a number of conclusions from this study. First, the evolution of the second flare is substantially affected by the presence of the first flare. Secondly, the primary energy release in the second event is in the corona. Thirdly, the flares occur in a decaying magnetic region, probably as a result of the interaction of existing sheared loops; there is no evidence of emerging magnetic flux. Also, magnetic structures of greatly varying size participate in the flare processes. Lastly, there is some indication that the loops are not symmetrical or stable throughout the flares, i.e. the magnetic field does not act as a uniform passive bottle for the plasma, as is often assumed in flare models.

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A multiwavelength study of a double impulsive flare

et al. 1984

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Pohjolainen

2003

Solar Physics

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Observations of an unusual pair of homologous flares on March 17, 1970

Cited by 2 publications

References 9 publications

A multiwavelength study of a double impulsive flare

A multiwavelength study of a double impulsive flare

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