040604_WMO Guide to Wave Analysis and Forecasting - WMO 702_1998.pdf

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Unformatted text preview: WORLD METEOROLOGICAL ORGANIZATION GUIDE TO WAVE ANALYSIS AND FORECASTING 1998 (second edition) WMO-No. 702 WORLD METEOROLOGICAL ORGANIZATION GUIDE TO WAVE ANALYSIS AND FORECASTING 1998 (second edition) WMO-No. 702 Secretariat of the World Meteorological Organization – Geneva – Switzerland 1998 © 1998, World Meteorological Organization ISBN 92-63-12702-6 NOTE The designations employed and the presentation of material in this publication do not imply the expression of any opinion whatsoever on the part of the Secretariat of the World Meteorological Organization concerning the legal status of any country, territory, city or area, or of its authorities or concerning the delimitation of its fontiers or boundaries. CONTENTS Page FOREWORD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V ACKNOWLEDGEMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VI INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VII Chapter 1 – AN INTRODUCTION TO OCEAN WAVES 1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 The simple linear wave . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3 Wave fields on the ocean . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 6 Chapter 2 – OCEAN SURFACE WINDS 2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 Sources of marine data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3 Large-scale meteorological factors affecting ocean surface winds . . . . . . . . . . . . . . . . . 2.4 A marine boundary-layer parameterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5 Statistical methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 16 21 27 32 Chapter 3 – WAVE GENERATION AND DECAY 3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2 Wind-wave growth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3 Wave propagation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4 Dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5 Non-linear interactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.6 General notes on application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 35 36 39 40 41 Chapter 4 – WAVE FORECASTING BY MANUAL METHODS 4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2 Some empirical working procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3 Computation of wind waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4 Computation of swell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5 Manual computation of shallow-water effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 45 45 47 52 Chapter 5 – INTRODUCTION TO NUMERICAL WAVE MODELLING 5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2 Basic concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3 The wave energy-balance equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4 Elements of wave modelling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5 Model classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 57 58 58 62 Chapter 6 – OPERATIONAL WAVE MODELS 6.1 Introductory remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2 Wave charts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3 Coded wave products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4 Verification of wave models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.5 Wave model hindcasts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.6 New developments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 69 69 70 75 80 IV CONTENTS Page Chapter 7 – WAVES IN SHALLOW WATER 7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2 Shoaling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3 Refraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.4 Diffraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.5 Wave growth in shallow waters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.6 Bottom friction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.7 Wave breaking in the surf zone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.8 Currents, set-up and set-down . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 81 82 84 85 86 87 88 Chapter 8 – WAVE DATA, OBSERVED, MEASURED AND HINDCAST 8.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2 Differences between visual and instrumental data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.3 Visual observations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.4 Instruments for wave measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.5 Remote sensing from large distances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.6 Wave data in numerical models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.7 Analysis of wave records . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.8 Sources of wave data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 89 89 91 93 98 98 100 Chapter 9 – WAVE CLIMATE STATISTICS 9.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.2 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.3 Presentation of data and wave climate statistics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.4 Estimating return values of wave height . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.5 Further reading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.6 Wave climatologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 101 103 105 109 109 ANNEXES I ABBREVIATIONS AND KEY TO SYMBOLS .............................. 119 II FM 65-IX WAVEOB – REPORT OF SPECTRAL WAVE INFORMATION FROM A SEA STATION OR FROM A REMOTE PLATFORM (AIRCRAFT OR SATELLITE) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 III PROBABILITY DISTRIBUTIONS FOR WAVE HEIGHTS . . . . . . . . . . . . . . . . . . . . . 133 IV THE PNJ (PIERSON-NEUMANN-JAMES, 1955) WAVE GROWTH CURVES. . . . . . 139 REFERENCES AND SELECTED BIBLIOGRAPHY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 INDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155 FOREWORD The national Meteorological Services of a large number of maritime countries have, for many years now, been engaged in the provision of ocean wave forecast and hindcast services in support of the requirements of users in the whole range of maritime activities (shipping, fisheries, offshore mining, commerce, coastal engineering, construction, recreation, and so on). In recognition of this, and of the relative lack of easily accessible guidance material on wave forecasting methodology suitable for use by national Meteorological Services in developing countries, the WMO Guide to wave analysis and forecasting was prepared by a group of experts and published in 1988 as publication WMO-No. 702. This formal WMO Guide updated and replaced the earlier, very popular, WMO Handbook on the same subject, first published in 1976. In further recognition, both of the requirements of national Meteorological Services for the provision of ocean wave-related services and also of the rapid developments which were occurring in wave measurement, analysis and forecast techniques, the WMO Commission for Marine Meteorology (CMM) established in 1984 a WMO wave programme. The various elements of this programme are implemented, reviewed and updated by the CMM Subgroup on Wave Modelling and Forecasting. One of these elements involves the continuous review and revision, as necessary, of the Guide to wave analysis and forecasting. To this end, the sub-group established, in 1991, an ad hoc group of experts, under the chairmanship of Dr A. K. Laing (New Zealand), to undertake a complete revision and updating of the Guide, in the light of new developments and especially of feedback from users of the first edition. The international team of experts, directed by Dr Laing, individually prepared substantially revised versions of the different chapters of the Guide. These individual contributions were subsequently coordinated, assembled and edited by Dr Laing into a draft, which was then submitted to a wide network of wave experts for review and comment. Reviewers’ comments were incorporated to the extent possible and a final editing of a new, second edition of the Guide was made by Dr Laing. No publication such as this can ever be perfect, particularly in such a continuously developing field of science and technology, and further additions and modifications will undoubtedly be required in the future. Nevertheless, it is firmly believed that this second edition of the Guide to wave analysis and forecasting will continue to prove a very valuable publication in support of the marine services provided by WMO’s maritime Members. It is also believed that it continues to meet very well its two-fold objectives: to provide introductory but self-sufficient guidance material for use in the provision of basic wave forecast services, while at the same time acting as a source text and a guide to further reading on the subject. Detailed acknowledgements to authors are given with each section and chapter as appropriate, but I should like here, on behalf of the World Meteorological Organization, to express my sincere appreciation to all the experts (authors, reviewers and particularly Dr Laing) who have contributed so much to this important and valuable publication. (G. O. P. Obasi) Secretary-General ACKNOWLEDGEMENTS The revision of this Guide to wave analysis and forecasting has been very much a team effort, involving a number of experts from several countries in various aspects of ocean waves. Overall direction of the project has been undertaken by Dr Andrew Laing (New Zealand). The chapter editors/authors have had overall responsibility for the revision of each chapter and, in cases where substantial assistance has been given, co-authors are acknowledged. Much of the material is derived from the first edition of the Guide and the present editor would like to once again acknowledge the efforts put into that publication by the editor E. Bouws, and the chapter editors E. Bouws, L. Draper, A. K. Laing, D. J. T. Carter, L. Eide and J .A. Battjes. The present edition has been produced with specific attributions due to: • Overall direction and introduction: A. K. Laing, National Institute of Water and Atmospheric Research (NIWA), Wellington, New Zealand • Chapter 1: A. K. Laing, NIWA, Wellington, New Zealand • Chapter 2: W. Gemmill, National Meteorological Center (NMC), Washington D.C., USA • Chapter 3: A. K. Magnusson, Norwegian Meteorological Institute (DNMI), Bergen, Norway M. Reistad, DNMI, Bergen, Norway • Chapter 4: L. Burroughs, National Meteorological Center (NMC), Washington D.C., USA • Chapter 5: M. Reistad, DNMI, Bergen, Norway A. K. Magnusson, DNMI, Bergen, Norway • Chapter 6: M. Khandekar, Atmospheric Environment Service (AES), Toronto, Canada • Chapter 7: L. Holthuijsen, Delft Technical University, Delft, the Netherlands • Chapter 8: J. A. Ewing, United Kingdom D. J. T. Carter, Satellite Observing Systems, Godalming, Surrey, United Kingdom • Chapter 9: D. J. T. Carter, Satellite Observing Systems, Godalming, Surrey, United Kingdom V. Swail, Atmospheric Environment Service (AES), Toronto, Canada Illustrations have been acknowledged in the captions. Otherwise they have been taken from the previous edition of the Guide or specially prepared for this edition. Contact with contributors can be made through the Ocean Affairs Division of the WMO Secretariat. The Editor would like to thank the Secretariat staff who assisted in the preparation of this publication. INTRODUCTION Overview The subject of this Guide is ocean waves, and specifically those generated by the wind. Such waves affect our coasts and activities of all kinds which we pursue at the coast, near the coast and out to sea. At any given time the waves are a result of the recent history of winds over often quite broad expanses of ocean. Indeed, knowledge of the winds allows us to diagnose the wave conditions. Just as the winds vary considerably in time and space, so do the waves. Hence, because there is some short-term predictability in the winds, there is an associated predictability for wind waves, enabling operational forecasts to be made. On the other hand, longer term estimates of wave conditions must be based on climatological information for which measurements, observations or “synthetic” data are needed. Estimates of likely future conditions or extremes may be required and there are often limited data to work with, making the correct choice of technique critical. The objective of this Guide is to provide basic information and techniques in the analysis and forecasting of ocean waves. The Guide is not intended to be a comprehensive theoretical treatment of waves, nor does it contain details of present research activity, rather it focuses on providing a general overview with more detail on aspects considered useful in the practice of wave analysis and forecasting. The latest research into wave processes and modelling is given a thorough treatment in the recently published book, Dynamics and modelling of ocean waves (Komen et al., 1994), and an extensive treatment of problems related to wave data and their use is provided in Waves in ocean engineering: measurement, analysis, interpretation (Tucker, 1991). For problems specifically related to coastal engineering, a comprehensive reference is the Shore protection manual (CERC 1973, 1984). The primary users of this publication are seen as being professionals and technicians involved in operations which are affected by ocean waves, that is a fairly wide community of marine operators and those providing specialized services to them. Marine weather forecasters form a key group, but the Guide is equally intended for the potential users of wave data analyses, forecasts and climatological products. This edition of the WMO Guide to wave analysis and forecasting replaces the 1988 edition of the same name, which in turn replaced the 1976 WMO Handbook on wave analysis and forecasting. In all editions it has been recognized that the interpretation of wave data and products demands a good understanding of the processes by which these products are derived. An overview of the elementary theory is therefore necessary in this Guide and, wherever a technique or source of data is introduced, sufficient background information has been included to make this publication as self-contained as possible. Whilst many of the basics have remained consistent between editions, there are developments which are creating new opportunities in wave information services. In recent years, an increasing number of wave products incorporate data from satellites or are synthesized from simulations using numerical wave models. Indeed, many forecasting centres are operationally using numerical models. Effective use of these products is only possible if the forecasters and other users have sufficient knowledge about the physical background of wave modelling and satellite observations. Wave modelling was given prominence in the 1988 Guide, an emphasis which has been retained in this edition. The concerted international effort of the 1980s to develop physically realistic wave models has culminated in a generation of wave models which have been thoroughly researched, tested and are now becoming operational tools. Wave modelling has “come of age” with this development. This does not mean that the problem is solved, far from it. For example, dissipation plays a critical role in the energy balance, but is poorly known and is generally formulated to satisfy closure of the energy-balance equation. Further, for computational reasons, operational models must all use parameterizations of the wave-wave interactions which control the distribution of energy within the wave spectrum. The problems of wave evolution in shallow water and interaction with surface currents also require continuing efforts. The present edition also includes a catalogue describing present day operational wave models and it is worth noting that regular updates of such models are given in WMO Marine Meteorology and Related Oceanographic Activities Report No. 12 and its supplements (see WMO, 1994(a)). Further, wave modelling has now been used extensively in synthesizing wave data for climatological purposes. Hence, in the chapter on wave statistics specific treatment of wave climatologies is presented, including the use of wave models in hindcasting. Another exciting development since the last edition has been the increase in wave and wind data available from satellites. Thus, new material on this source of data VIII GUIDE TO WAVE ANALYSIS AND FORECASTING has been included particularly in the chapters on wind fields, wave data, climate and statistics. These data are also now being used in conjunction with wave models to provide improved initializations and to validate hindcast data. Reference is given to some of the...
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