50th Anniversary of Numerical Weather Prediction Commemorative Symposium. Potsdam, 9–10 March 2000, book oflectures. Edited by Arne Spekat. German Meteorological Society, Berlin. 2001. 255 pp. Price �25.00 (hardback). ISBN3 928903 22 5.

This book contains 12 full-length lectures, one abstract, and an introduction to the talks presented at a specialsymposium held to mark the 50th anniversary of the first serious paper on numerical weather prediction (NWP)—thatpublished by Charney, Fjortoft and Von Neumann in 1950. The first three talks describe the early days of numericalprediction, the next four describe developments, mainly in global modelling, leading to present-day models. The nextthree talks are about developments in the immediate future, and the last three discuss applications and longer-termdevelopments. The contributors are chosen so that most of the main European and North American modelling groupsare represented (though there is little mention of Japanese meteorologists, who perhaps contributed more to climatemodelling at this stage). All of them have made major contributions to the field.

I found the first part of the book the most interesting, as I was less familiar with what was done in the early days. Ijoined the Met Office just in time to be taught graphical methods of forecasting on a training course. It now seemsremarkable that methods of dynamical forecasting had to be designed so that they could be implemented without acomputer (e.g. the solutions of the barotropic vorticity equations described on pp. 34–35). It is also remarkable howmany developments which were thought to have been made much later, such as multigrid methods for the solution ofelliptic equations, had been anticipated in these early calculations (see p. 57).

The first of these three historical chapters is by Norman Phillips, and describes the pioneering efforts of Charney,Rossby, Von Neumann and others in the USA. In particular, he describes the pioneering integrations of 1950 whenCharney, Freeman, Platzman and Smagorinsky worked for 33 24-hour days to complete four 24-hour and two 12-hourforecasts. It was interesting that L. F. Richardson was still around to review the results, but he delegated it to his wife.This was when the basic quasi-geostrophic theory of large-scale flows was developed, and it became clear thatRichardson’s failure of 30 years before could be avoided. However, a number of problems with the quasi-geostrophicformulations then used were not understood in time to allow the models to be improved to give useful forecasts. Instead,even by 1959, the subject was moving towards the primitive equations used today. It was not, however, till 1958 thatoperationally useful results were obtained. This was when the routine collection of data from the World MeteorologicalOrganization network and an automatic analysis procedure came into use.

The second historical chapter is by Aksel Wiin-Nielsen. He describes early graphical forecasting in some detail ina section entitled ‘Waiting for the computer’. He covers the pioneering work of Kibel in Russia. This work was in manyways more advanced than that going on in the West at the time, but there was little communication between Russia andthe West in those days. Early attempts at running operational forecasts in Sweden demonstrated the importance of ahigh-quality initial analysis and of planning operational schedules. Even in 1954, results were obtained with correlationsof 0.61 between observed and forecast 500 hPa forecast changes for 72 hours ahead. The chapter discusses some of thedifficulties in formulating consistent quasi-geostrophic models that were also referred to in the previous chapter. Theseled to the early adoption of the primitive equations. Nowadays there have been large advances in the theory of filteredmodels. If these had been available in the 1950s, such models might have been much more useful and lasted a great deallonger.

The third historical chapter focuses on the work in Deutscher Wetterdienst. This starts with the manual method ofsolving elliptic equations by relaxation used in 1953. This was the context in which a multigrid approach wasdeveloped. It took two weeks to carry out the relaxation for one 12-hour forecast. Computational efficiency has astronger meaning when it applies to people working out calculations with pencil and paper. In 1957, some of the earliestexperiments with the primitive equations were carried out. These were quite successful, and had a big influence inencouraging other groups to adopt the primitive equations. One of the earliest model intercomparison exercises is shownon p. 66, showing that a primitive equation barotropic model was similar in performance to a filtered model. Somecompromises were still necessary, for instance setting the orography to 20% of its actual value. This chapter comesnearer modern times than the previous two, for instance by the early 1960s ‘availability of machine time was no longerthe main bottleneck’. It describes the performance of a 5-level primitive equation model with very simple physics thatwas used up to the 1970s.

The next chapter, by Guri Marchuk, also has a strong historical emphasis. He describes the early developments inRussia, which are not so well known. He then describes the splitting method with which his name is always linked,followed by the adjoint method which he first described in 1974. It is interesting that this method of studying thesensitivity of models to changes in input data was well known at that time; it is only in the last 10 years that it hasbecome a standard method in operational meteorological analysis schemes.

The next five chapters cover developments leading up to modern state-of-the-art modelling. Given the hugeexpansion in work in the area, the contributions cannot be comprehensive. However, they give a good sample of thedevelopments that have occurred. Fedor Mesinger describes limited-area modelling, focusing on the ‘eta’ model that hedesigned and that is used operationally at the National Centers for Environmental Prediction. He also discusses thecurrent debate about lateral boundary conditions and the choice between limited-area and global variable-resolutionmodels, pointing out the benefits obtained by uniformly high resolution over a large area. Now that operational globalspectral models have reached T511 resolution, however, it is not clear that large-area limited-area models have muchfuture. However, Mesinger highlights a number of reasons why at least small-area limited-area models will be aroundfor a long time.

Lennart Bengtsson describes the development of medium-range forecasts, primarily at the European Centre forMedium-Range Weather Forecasts (ECMWF). He describes some of the early planning of the ECMWF system,

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particularly the interfaces to the global communications system and the top-level design of the operational softwaresystem. ECMWF had the unique opportunity to design a system from scratch, with a good idea of what componentswere needed. Other centres had gone through a more gradual evolution. This is the first point in the book where we seethe strong synergy with climate modelling. ECMWF was set up because the challenge of combining models of thestandard required for climate simulation with advanced data-assimilation systems was seen from the outset. Thus thischapter has a strong focus on data assimilation, quality control, initialization, and physical parametrizations, while theearlier chapters in the book were almost exclusively concerned with dynamical formulation of the models. Bengtssondescribes the performance of the ECMWF system up to the date of the meeting. I am sure he would have liked to showthe spectacular recent improvements (over the last 18 months) resulting from the higher-resolution model and the newsatellite data. The diagrams on p. 131 would have looked impressively different.

Krishnamurti contributes a chapter on tropical NWP. It was realized very early on that convective systems andtropical cyclones were the main features that had to be predicted. Thus one of the main topics of the chapter is theanalysis and initialization of convective systems using satellite data, in particular ‘physical initialization’, where themodel parametrizations are used to help infer information from the data. His main focus in tropical cyclone prediction isin the benefits of using ensemble forecasts to improve track predictions.

Werner Wergen then describes the development of a modern NWP software suite at Deutscher Wetterdienst, andAndrew Staniforth describes similar developments at Environment Canada and the Met Office. Both chapters discussthe issue of how to create an efficient unified software system for prediction at all scales, and some of the choicesbetween single variable resolution models and a suite of one- or two-way nested models. The operational requirementsplay a key role in the design. Andrew Staniforth’s chapter also discusses the issue of equation sets, in particular pointingout the benefits of adopting the full compressible Navier–Stokes equations rather than the compromised versions of itused by meteorological models in the past.

Jean-Francois Geleyn contributes a challenging chapter mainly looking ahead to what problems will be mostimportant in 10, or even 50, years time. He covers both scientific issues and the institutional issues of how many NWPcentres there will be in the future. He even discusses computer programming issues (p. 213 has an example of actualcode) to illustrate the current debate between parallel vector and parallel scalar processors. He identifies many issues,but in particular that ‘the stochastic side will become paramount in any NWP activity’. At the end he says that hischapter will ‘give a very good laugh to people that would read it in 50 years, perhaps even in 10 years’.

The last part of the book covers ‘Applications and the future’. Tim Palmer contributes an authoritative talk onprobability forecasting and ensemble prediction. He starts with basic theory, showing the different types of error growthfrom different initial data. He shows how an ensemble of forecasts can be generated efficiently, and how itsperformance can be assessed. He then moves on to the important issue of how to use such forecasts, showing how thevalue depends on the type of customer using the forecast.

Unfortunately, Anton Eliassen’s talk on ‘Long range transport of air pollution’ is only represented by an abstract.Using NWP to predict the spread of pollutants has been a major achievement of recent years, for instance the modellingof the Chernobyl plume and the modelling of the spread of volcanic ash from eruptions near Iceland. The lectureemphasized the acid rain problem affecting Scandinavian lakes as the original driver behind research into this problem.

The final chapter, by Mojib Latif, discusses the prediction of seasonal variability, particularly that driven byatmosphere–ocean interaction. He illustrates the El Nino mechanism, and ends (p. 253) with a prediction that ‘theAtlantic thermohaline circulation may strengthen during the next decades’. It will be interesting to see if he is right. It isalso interesting to speculate what the proceedings of the meeting to celebrate the 100th anniversary of NWP will be like.

MIKE CULLEN

Physical principles of remote sensing. By W. G. Rees. Cambridge University Press. 2001. xv + 343 pp. Price £24.95(paperback), £70.00 (hardback). ISBNs 0 521 66948 0, 0 521 66034 3.

This book, written in the style of an undergraduate textbook, in 11 chapters systematically covers all the topics ofremote sensing from theory of electromagnetic wave propagation, its interaction with the surfaces and the atmosphere,its detection and measurement (passive and active systems), the observing platforms and data interpretation. In fact, allaspects and applications of remote sensing are given an airing and the associated physics introduced. Each chapter(except the introductory one) concludes with a set of related numerical problems to be solved.

The author has done an excellent job in bringing together such a range of topics into one comprehensive volumeand it is a good starting point for a critical appraisal of what can and cannot be achieved in remote sensing. However, aconsequence of a broad-brush treatment compressed into some 343 pages is that it will leave some readers a bitfrustrated. For example, for the atmospheric sounding community this book would not be a first choice. The radiativelyactive molecules in the atmosphere, CO2, O3, H2O, etc., behave somewhat differently to the simple diatomic moleculesdiscussed in the text—i.e. they have multiple rotational/vibration bands with and without Q branches. The principle of‘weighting function’ is explained, but the differences between microwave and infrared sounding in the absence of cloudare not brought out (the sharpening effect of the faster temperature dependence). For meteorologists a major problemwith both microwave and infrared temperature sounding is the poor height resolution (about 7 km), which cannotcorrectly resolve temperature inversions. In fact, satellite soundings for the first 30 years have had little impact on

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