This book presents the first comprehensive account of the properties of plasma loops, the fundamental structural elements of the solar corona. Plasma loops cover a wide range of sizes, and range in temperature from tens of thousands to millions of degrees. They not only define the structure of individual active regions but connect different active regions - even across the solar equator. Loops also play an integral and decisive role in the enormous solar explosions called flares. Over recent years a wealth of space and ground-based observations of loops has been obtained in various widely-spaced regions of the electromagnetic spectrum. In this book the authors have selected the best observational material from the literature on which to base a detailed account of the properties of flare and non-flare loops. The book also explores the larger implications of the loop structures in our understanding of solar and stellar coronae. The text is enhanced by a large number of illustrations and unique and beautiful photographs obtained from the ground and from space.

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SummaryThe formation of loops in the lines of force of a twisted magnetic field confined within a cylinder of radius R, first suggested by AIrven (1950a), is discussed by the method of normal modes. The model first becomes unstable with respect to modes which do not lead to the formation of loops. Ignoring this, the condition obtained for loop formation is that the pitch of the twisted field be less than 'TtR.The velocity of Alfven waves in this model is also discussed.

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SummaryThe relationship of radio bursts of spectral type III to solar flares is investigated by comparing simultaneous optical and radio observations. Over 300 flares are examined, 85 per cent. of which are microflares (class 1-). About 20 per cent. of the flares are associated with type III events, while more than 60 per cent. of the bursts recorded occur during the lifetime of a flare. These bursts tend to occur near the beginning of the flare or even to precede it slightly.The degree of association varies markedly over a period of days. Flares occurring in certain activity regions show a high degree of correlation with bursts, while those occurring in other regions show little or no correlation. The probability of a burst accompanying a flare is greater for larger flares. It is essentially the same for flares on the easteru limb as for flares in the centre of the disk, implying a wide cone of escape for type III radiation. There is an apparent deficit for flares on the westeru hemisphere. The occurrence of a surge with a flare appears to increase somewhat the likelihood of an associated radio event.