Solar Noise Storms

Book Reviews There is unusual reliance on automata theory examples (not misplaced) for illustration of notions of state, realizability, and the like. Then there is some insistence on stating a number of results in a Banach or Hilbert space setting rather than just a finite-dimensional vector space setting. Finally, there is the module theoretic realization theory taking ofI into the wild blue yonder of category theoretic realization. If students can handle Banach and Hilbert space material, they can be taught their systems theory a little more generally. On the other hand, if they do not know it, a system theory course has to be interrupted to teach them, and to what practical gain? Such refinements do seem more reasonably located in a second course, or a course aimed exclusively at mathematics majors. The same comment applies to the module theoretic approach. As for the category theory, this simply has no place in a book aimed at first-year graduate students. Any author is naturally enthusiastic about his research, and anxious to communicate it to others, but restraint is required on occasion. This reviewer feels that the authors’ judgement failed them when they included in their text material depending on abstract and advanced pure mathematics, and which is at the same time material whose relevance to systems theory is far from generally acknowledged. The fifth point is that the book attempts to cater to students with vastly differing mathematical backgrounds. As a result, the presentation of the systems theory is punctuated by bits of pure mathematics which total perhaps 150 pages. Vector spaces, matrices, Jordan forms, Hilbert spaces, contraction-mapping principle, existence and uniqueness of differential equation solutions are all dealt with, in some cases with proofs. In books applying mathematics, pure mathematics should be relegated to appendices. A second consequence is that the level of mathematical sophistication required of the reader varies greatly within the book.

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Those readers with no knowledge of matrices will not study the category theory material; those with knowledge of category theory will doubtless need little reminding of what a vector space is: but there are parts of the book which will be read by both types. There is a risk that one group will be overpowered, the other bored. The average level of sophistication demanded of the reader is that to be expected of the first-year engineering graduate student, but that at the same time, the variance in level is uncomfortably high. Examples and problems abound. Many are of a pure mathematical nature. This review commenced with the examination of a claim of the preface. It also ends this way. The preface suggests at least four possible course structures for which the book can be used, with clientele drawn from mathematics, computer science and different branches of engineering. If the book was written with the explicit aim of simultaneously meeting four course-determined goals, herein lies the explanation for several of the difficulties of the book alluded to earlier, together with one more. The book, at almost 800 pages, is too long.

Reference (1) R. E. Kalman, Arbib, “Topics tem Theory”, York, 1968.

P. Falb and M. A. in Mathematical SysMcGraw-Hill, New

BRIAND.O.ANDERSON Department of Electrical Engineering, University of Newcastle, New South Wales, Australia

SOLAR NOISE STORMS by 0.

Elgaroy. 375 pp 140 illus, 7 X 10 in. International Series in Natural Philosophy, Vol 90, Pergamon Press, 1977, US $18.00, f9.75.

Radio emissions from solar active regions present striking phenomena which

Journal of The Franklin

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Book can increase the total radio output from the Sun by several orders of magnitude as compared with the changes of less than 1 per cent in the optically radiated power. Following the initial observations over thirty years ago of strong radio frequency radiation from regions of solar disturbance, particularly sunspots and flares, various principal types of radio emission could be discerned. The determination of the characteristic features at first appeared to offer an attractive subject for radio astronomical research, but the subsequent realisation of the many complexities proved a deterrent to some workers from further pursuit of the problems and elucidation of solar radio phenomena. Those researchers who have devotedly continued with improving techniques to investigate and interpret solar radio observations are being rewarded with the emergence of much valuable knowledge of the possible processes of radio emission, the factors governing propagation, and of the nature of solar activity and conditions in the solar atmosphere. Two notable books have previously been published on radiation from the Sun at radio wavelengths, namely Kundu’s Solar Radio Astronomy (Interscience, 1965) and Zheleznyakov’s Radio Emission of the Sun and Planets (Pergamon, 1970). More recent research has added much new information, and the present book by Elgaroy is directed to one major aspect of solar radio emission, the noise storm with its associated Type I bursts, which constitute the commonest form of enhanced radiation at metric wavelengths. Elgaroy has specialised in studies of noise storms during the last 20 years and is especially well qualified to prepare this authoritative up-to-date treatise. The book provides an excellent comprehensive survey of the most significant

Vol. 305, No. 4, April 1978

Reviews

advances in the observation and interpretation of solar radio storms. It describes admirably the various factors that have to be taken into account in understanding the physical processes, for example, the influence of coronal scattering, periodic and ordered characteristics of behaviour, polarisation and the effects of magnetoionic interactions on radio propagation in the solar plasma. Proposed theories on the origin of the radiation are well covered. The book is a valuable guide for astronomers and radio physicists seriously interested in the impact of radio methods on our understanding of solar activity surrounding sunspots. The concentration on solar noise storms and Type I bursts means that one must look to books and review articles elsewhere for surveys of other types of solar radio emission but Elgaroy does consider relationships with Type III and stationary Type IV bursts. Nor does the book include an exposition on the techniques of radio observation. Optically derived solar information is discussed in the context of interpretation, and considerable attention is given to possible magnetic field structures in the source region. Basically, solar radio noise storms offer much scope for further research, and the book well demonstrates the results achieved so far and indicates the opportunities for future study of this readily observed but still incompletely understood aspect of solar activity. The book has been printed by reproducing the author’s typescript. This procedure proves entirely successful in providing at an economical price a well bound and finely presented publication. J. S. HEY. formerly of the Royal Radar Establishment, Maluern, England

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