Small Scale Processes in Geophysical Fluid Flows , Lakshmi H.Kantha and Carol AnneClayson Academic Press, San Diego, Calif., 2000. $115.00 (888 pp.). ISBN 0-12-434070-9

The complexity in the motions of fluids flowing over Earth’s surface (in both atmosphere and ocean) is the result in large part of the great range of physical scales at play. The largest length scales are planetary, and the largest time scales are unknown (but certainly many tens of years). The smallest scales (millimeters-to-cen-timeters, and seconds) are those dominated by three-dimensional turbulence and at which irreversible thermodynamic transfers occur. Although the highly nonlinear equations governing fluid flow (the Navier–Stokes equations) have been well known for over a century, and can be solved numerically, they cannot be solved simultaneously at all geophysical scales. This means that any attempt to model geophysical flows on the scales important for weather patterns or climatic variations requires parameterization of processes occurring at smaller scales. These processes are the focus of Small Scale Processes in Geophysical Fluid Flows , by Lakshmi H. Kantha and Carol Anne Clayson.

The authors discuss a range of phenomena involving small-scale processes in geophysical flows. These include 3D turbulence and the various instability mechanisms leading to turbulence. One example is convective instability, caused by heating the fluid from below (as in the lower atmosphere during the day), or by cooling from above (as in the upper ocean at night). Another example is the breaking of gravity waves either at the surface of the ocean or in the interior of the ocean or atmosphere. While all are governed by the same set of equations, some understanding of the physics of each process can be gained by simplification, leading to a categorization of small scale motions.

The limitations of simplification are evident in our lack of understanding of many of the aspects of small scale processes. As an example, while surface gravity waves have been a subject of scrutiny over the past century and a half, the fundamental processes by which they are generated and break have eluded clear description. Since it is thought that the great bulk of the air–sea transfer of heat, momentum, and moisture occurs when waves break, this lack of a basic understanding limits our ability to quantify transfer rates, a basic requirement for accurate coupled ocean–atmosphere model predictions.

Over the past few decades, considerable effort to develop innovative new means to observe small-scale processes in their detail has led to important discoveries and new insights. Fittingly, the authors begin each chapter with a presentation of the important observational results relating to particular processes, together with a brief history of the field’s development and a discussion of the basic physics involved. However, I found the emphasis of the text to be on how the processes are modeled and/or parameterized in larger scale models. This is presumably a reflection of Kantha’s primary research interests.

The authors clearly state that this book was not intended to be a monograph. It is not. There are texts that better present the fundamentals of internal waves ( Waves in Fluids, by James Lighthill, Cambridge U. Press, 1978), surface gravity waves ( Dynamics and Modeling of Ocean Waves , edited by G. J. Komen et al, Cambridge U. Press, 1994) and the effects of flow over topography (Topographic Effects in Stratified Flows , by Peter G. Baines, Cambridge U. Press, 1995). There is as yet no basic text that unifies the fundamental aspects of turbulence in geophysical flows—stratification, shear, rotation, and natural topography. None of the texts mentioned, however, provides the reader with such a broad and current review as is offered in Small Scale Processes. Its authors have done an exhaustive job of reviewing the important developments in the field, even to the extent of presenting all of the recent estimates of various phenomenological constants. While this makes the book somewhat tedious to read in places, it soon becomes clear where to skim.

Our abilities to observe small-scale processes continue to evolve at a rapid pace. This, of course, means such a review text as this is already somewhat outdated. At the time it was written, for example, there had been few hints of internal gravity wave generation over rough topography in the ocean, as the authors state. Since then, however, several research groups have shown the importance of rough topography on both mixing and the internal wave field, including important examples in the deep ocean.

The authors have done a valuable service to the community. I expect this text to be the starting point for many researchers new to a specific aspect of the field.