REVIEWS 1699

Fluid mechanics of the atmosphere. By R. A. Brown. Academic Press Inc. Pp. 489. Price f69.95 (hardback). This book is designed as an introduction to fluid mechanics, particularly for beginners in atmospheric

science. The bias towards the atmosphere is manifested by the choice of examples and by one or two more specialized chapters near the end of the book, but otherwise the subjects covered are much as one would expect from any such text on fluid mechanics, irrespective of the intended field of application. The first part of the book is an extended introduction to the subject in general and to some necessary technical details, such as vector calculus, dimensional analysis and tensors. The second part is a detailed treatment of the governing equations, moving on to vorticity dynamics, idealized flows, waves and eddies and, finally, boundary layers. This book is therefore aiming to fill a role similar to that of existing and well-regarded books such as those by Acheson and Batchelor, and it is appropriate to measure it against their exacting standards.

The author has clearly thought a good deal about the requirements of a book that is to be an effective aid to students. He is not afraid to repeat key points in different places. The text is interrupted at regular intervals by worked examples. At the end of each chapter there is a summary section (which in some cases might be better relabelled as a discussion), a summary of key points and equations in tabular form and a set of problems, with answers at the very end of the book. All this is very welcome. Where the book is less satisfactory is in its presentation of the technical details. The author has an understandable desire to explain key results as transparently as possible. But the explanations are often long-winded, sometimes imprecise and, occasionally, just plain wrong.

Consider a worked example to establish the identity V.(@) = +V-u + u.V+. First it is stated that the chain rule is used in the proof. But it is not the chain rule, it is the product rule for differentiation. Then it is noted that there would be additional terms in curvilinear coordinates. But the important point is that this identity is coordinate-independent (though of course the extra terms would need to be included in the book- keeping if it was decided to prove the identity in a curvilinear system). The statement concerning curvilinear coordinates is made for completeness, but serves only to confuse the issue. Unfortunately this sort of thing occurs in a number of places in the book, where the issues being explained are not quite so straightforward. There are also a number of typographical errors and cases where the choice of notation is unfortunate and misleading.

In the first four introductory chapters there is certainly some useful material. For instance, the discussion of scaling, dimensional analysis and similarity in Chapter 3 is important. One of the things that students find confusing about fluid mechanics is the widely different forms of the governing equations that are used in different areas of application. It is important to convince them that, although each form appears to be accepted without question in a particular application, it is usually possible, on the basis of scaling, to derive it in a rational, if perhaps not rigorous, way from the full equations. Similarly it will be useful for many students to have the self-contained development of the use of tensors in Chapter 4. Characteristically however, there is some unnecessary confusion and ambiguity here. For instance, when stress is being defined, and the forces on a parcel evaluated, the issue of the deformation of the parcel also somehow gets involved. And when the velocity gradient tensor is being considered, the author chooses to distinguish between the diagonal and off- diagonal parts of the tensor, without apparently realizing that this distinction is not a coordinate-independent one. He also has a tendency throughout the book to refer to tensors as ‘operators’, an unfortunate term in view of the common confusion amongst students (in my experience), that tensors and matrices are one and the same thing. This leads to the somewhat extraordinary statement in a later chapter that the ‘operator u has no physical significance’. ( u i s the stress tensor). Use of a symbolic index-free notation for tensor manipulation is encouraged, e.g. for the tensor product of a tensor and a vector, without ever giving a clear convention for such notation that avoids ambiguity over expressions such as V.(uv).

The second part of the book starts off in Chapter 5 with discussion of mass conservation and continuity. The very first paragraph raises the issue of modelling certain flows using singular point sources and sinks of mass, and one feels that this is an unnecessarily technical motivation for what is to follow, where the mass continuity equation is derived in three, or perhaps four, independent ways. Compressible flows are also considered, though here some details are incorrect. The book then moves on in Chapters 6, 7 and 8 to momentum, energy and vorticity. This is all standard stuff and dealt with thoroughly, but again with a tendency to repetition that is intended to clarify, but might well confuse. There are infelicities in notation and terminology. One that particularly annoyed this reviewer was the use, more than once, of the ‘cross product of u’, meaning ‘curl u’. The following Chapter 9 deals with potential flow. This seems primarily an opportunity to discuss various simple flows, including simple vortex Rows, presented in an ad hoc manner, rather than a systematic treatment of the construction of solutions to boundary-value problems. The final two chapters are the most clearly aimed towards the atmosphere and discuss, respectively, perturbations (meaning waves, instabilities and turbulence) and boundary layers. The first begins with a qualitative discussion and then gets down to the details of Reynolds averaging, and the division of the equations into mean and disturbance parts. This is certainly material that has to be spelled out carefully to beginners in the field, but it seems a pity that here the example chosen leads to equations that densely cover one and a half pages and that once the division has been made there is no real attempt to show that all the work was worthwhile. Perhaps it is intended that the presented equations will be useful for reference purposes. The second discusses boundary layers (one of the author’s own research interests), beginning with a derivation of the boundary-layer equations and moving on to Ekman layers. The latter is dealt with in some detail, including the effects of varying diffusivity and organized eddies, and the shear instability of the basic solution. The physical discussion of the instability is imprecise in its

1700 REVIEWS

statement that displacing vortices leads to ‘forces’ on neighbouring fluid particles. (The response to such a displacement is better characterized as a velocity and not an acceleration.) But on the whole this chapter, which finishes with the surface layer, is a reasonable end to the book, which has brought the reader from fluid- mechanical basics to the beginnings of the complications of real atmospheric Rows.

This is quite a long book (about 480 pages) and any purchaser would not presumably feel short-changed in terms of quantity. Two particularly positive features are that it is accessible to students who are not well prepared in vector and tensor calculus and that it includes a large number of worked examples. The latter should be a genuine help to students and also to those preparing to teach this subject.But it is difficult, for the reasons outlined above, to see this book as quite in the same league as the well-established texts mentioned earlier.

PETERHAYNES

Principles of environrnentalphysics. By J. L. Monteith & M. H. Unsworth. Edward Arnold, Sevenoaks. 2nd edition, 1990. Pp. xii + 291. Price f15.99 (f32.00 hardback). ISBN 0 7131 2931 X.

The first edition of this text (J. L. Monteith, 1973) was reviewed by J. R. Milford in the April 1974 edition of the Quarterly Journal (Vol. 100, no. 424) where it was predicted to be ‘an outstandingly useful volume for years to come for research workers, and for teachers of biology, of meteorology and also of physics’. My own use of the book, first as a student then as a researcher and teacher, is evident in the battered state of my first edition copy, and bears witness to the truth of Milford’s statement. The faded green book by Monteith has now been replaced by the (still) smart tome, in second edition blue, of Monteith and Unsworth. I am sure that in time it will become as disreputable in appearance as its predecessor!

The book begins with several chapters of basic physics: gas laws, transport laws and radiation laws, which provide the necessary background for the following discussions. Radiation is the means by which the earth receives its energy from the sun, and chapters 4 to 6 take the reader through considerations of the natural radiation environment, interception by bodies, and the fate (absorption, reflection, transmission) of the intercepted radiation. Examples are drawn from both the plant and animal kingdoms with the simplified geometry of cylinders and ellipses representing the human form and plant canopies. Once radiation is absorbed its energy is used for heating, evaporation or photochemical reactions, all of which involve transfer of heat or mass. Following the energy train Monteith and Unsworth cover momentum transfer, heat transfer and mass transfer, illustrating theoretical treatment of these subjects with applications to our Rora and fauna (more cylinders and spheres). All the principles and processes already discussed are then brought together in discussion of the heat budget of vegetation and animals, and given a chapter each for steady-state conditions. Both wet and dry surfaces are considered, and in the animal chapter man is used as one of the case studies: temperature stress is an experience that most people can relate to. Finally, the response of systems to changing conditions (the weather) is covered in the last three chapters, first for soil and then for crops; details are given of techniques for the measurement of fluxes, and interpretation of those measurements.

To those readers conversant with the first edition, much of the subject matter in the second edition will appear familiar, although it has been updated and repackaged. There is a new chapter on particle transfer, a section on remote sensing, and the final three chapters cover advances since 1973 in theory and experimental procedures for systems in a transient environment. The references have been extended and updated to match the text. The reorganizatim of topics, particularly in the more applied later chapters, provides a more logical progression through the subject matter, and a more readable book.

A continuous complaint of students of environmental science, rather than environmental physics, on approaching this subject is ‘too many equations’. While it is not possible to avoid mathematics, Monteith and Unsworth have restricted their numerical coverage to a level which anyone with an understanding of basic calculus should be able to follow.

The general presentation of the book has been improved with large, clear diagrams which are particularly welcome to those of us searching for illustrations for lecture courses. It is therefore a shame that the book suffers from a number of careless editing errors: Table A.3 reverts to a fault in the 1973 edition (corrected in 1975) where data for a temperature of 25°C are attributed to 20°C. On page 38 the table of wavebands identifies 300-400 nm as ultraviolet, the full ultraviolet waveband is 200-400 nm (correctly mentioned in the text). Other examples of minor irritations include spelling mistakes and dimensions wrongly stated (Stefan’s constant is correct on p. xi but incorrect on p. 26). However, these small failings should not detract attention from a book which should be compulsory reading for all physicists, biologists and environmental scientists.

ANN WEBB

Oceanography in the Indian Ocean. Edited by B. N. Desai. A. A. Balkema Uitgevers B.V. Pp. 772. Price f60.00 (hardback). ISBN 90 5410 228 4.

The Indian Ocean differs from its neighbours in a number of important aspects-not least in being until recently the least studied. Unlike the Atlantic and the Pacific it does not stretch from pole to pole and this contributes to a unique Indian Ocean climate. Around its northern perimeter the land masses are comparatively barren. Because the ocean is cut off from the deep-reaching vertical convection areas of the northern hemisphere there is a sluggish circulation and weak renewal in the deep northern part of the ocean.