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Guide to Wave Analysis and Forecasting Guide to Wave Analysis and Forecasting 2018 edition WEATHER CLIMATE WATER CLIMATE WEATHER WMO-No. 702 Guide to Wave Analysis and Forecasting 2018 edition WMO-No. 702 EDITORIAL NOTE METEOTERM, the WMO terminology database, may be consulted at https://public.wmo.int/en/ meteoterm. Readers who copy hyperlinks by selecting them in the text should be aware that additional spaces may appear immediately following http://, https://, ftp://, mailto:, and after slashes (/), dashes (-), periods (.) and unbroken sequences of characters (letters and numbers). These spaces should be removed from the pasted URL. The correct URL is displayed when hovering over the link or when clicking on the link and then copying it from the browser. WMO-No. 702 © World Meteorological Organization, 2018 The right of publication in print, electronic and any other form and in any language is reserved by WMO. Short extracts from WMO publications may be reproduced without authorization, provided that the complete source is clearly indicated. Editorial correspondence and requests to publish, reproduce or translate this publication in part or in whole should be addressed to: Chair, Publications Board World Meteorological Organization (WMO) 7 bis, avenue de la Paix Tel.: +41 (0) 22 730 84 03 P.O. Box 2300 Fax: +41 (0) 22 730 81 17 CH-1211 Geneva 2, Switzerland Email: [email protected] ISBN 978-92-63-10702-2 NOTE The designations employed in WMO publications and the presentation of material in this publication do not imply the expression of any opinion whatsoever on the part of WMO concerning the legal status of any country, territory, city or area, or of its authorities, or concerning the delimitation of its frontiers or boundaries. The mention of specific companies or products does not imply that they are endorsed or recommended by WMO in preference to others of a similar nature which are not mentioned or advertised. PUBLICATION REVISION TRACK RECORD Part/ Date chapter/ Purpose of amendment Proposed by Approved by section CONTENTS Page PUBLICATION REVISION TRACK RECORD . iii FOREWORD . ix ACKNOWLEDGEMENTS . x INTRODUCTION . xi Overview .................................................................. xi Terminology ............................................................... xii Climatological issues ........................................................ xiii Structure of this guide ....................................................... xiii CHAPTER 1 . OCEAN‑SURFACE WAVES . 1 1.1 Introduction ............................................................... 1 1.2 Simple linear waves ......................................................... 2 1.2.1 Basic definitions ..................................................... 2 1.2.2 Basic relationships ................................................... 3 1.2.3 Orbital motion of water particles ....................................... 4 1.2.4 Energy in waves ..................................................... 5 1.2.5 Influence of water depth .............................................. 5 1.2.6 Refraction and diffraction ............................................. 7 1.2.7 Breaking waves ...................................................... 8 1.3 Wave fields on the ocean ..................................................... 10 1.3.1 Decomposition of simple waves ........................................ 10 1.3.2 Wave groups and group velocity ....................................... 11 1.3.3 Statistical description of wave records ................................... 12 1.3.4 Duration of wave records ............................................. 13 1.3.5 Use of statistical parameters ........................................... 14 1.3.6 Distribution of wave heights ........................................... 14 1.3.7 Wave spectra ........................................................ 15 1.3.8 Wave parameters derived from a spectrum .............................. 18 1.3.9 Model forms of wave spectra .......................................... 20 1.3.10 Remarks on the directional wave spectrum .............................. 22 CHAPTER 2 . OCEAN‑SURFACE WINDS . 24 2.1 Introduction ............................................................... 24 2.2 Sources of marine data ....................................................... 25 2.2.1 Ship weather reports ................................................. 25 2.2.1.1 Estimated winds. 26 2.2.1.2 Measured winds. 27 2.2.2 Moored and drifting buoy reports ...................................... 27 2.2.3 Land (coastal) stations ................................................ 28 2.2.4 Common height adjustment of in situ data .............................. 28 2.2.5 Satellite data ........................................................ 29 2.3 Marine boundary layers ...................................................... 30 2.3.1 Constant flux layer ................................................... 32 2.3.2 Surface roughness ................................................... 33 2.3.3 Stability effects ...................................................... 33 2.4 Large-scale meteorological factors affecting ocean-surface winds .................. 37 2.4.1 Wind and pressure analyses ........................................... 37 2.4.2 Geostrophic wind .................................................... 39 2.4.3 Gradient wind ....................................................... 42 2.4.4 Surface friction effects ................................................ 45 vi GUIDE TO WAVE ANALYSIS AND FORECASTING Page 2.4.5 Thermal wind ....................................................... 46 2.4.6 Isallobaric wind ...................................................... 47 2.4.7 Diffluence of wind fields .............................................. 47 2.4.8 Wind shear in frontal zones ............................................ 48 2.4.9 Streamline analyses in the tropics ...................................... 50 2.4.10 Tropical cyclone analysis .............................................. 50 2.5 Numerical weather prediction ................................................ 52 2.5.1 Grid-point models ................................................... 53 2.5.2 Spectral models ..................................................... 53 2.5.3 Limited-area models ................................................. 53 2.5.4 Boundary-layer parameterization ...................................... 55 2.5.5 Coupled models ..................................................... 55 2.5.6 Data assimilation .................................................... 55 2.5.7 Reanalyses .......................................................... 56 2.5.8 Ensemble prediction ................................................. 56 CHAPTER 3 . WAVE GENERATION AND DECAY . 59 3.1 Introduction ............................................................... 59 3.2 Wind-wave growth .......................................................... 59 Empirical formulae and wind-wave growth curves ........................ 61 3.3 Wave propagation .......................................................... 63 3.3.1 Angular spreading ................................................... 64 3.3.2 Dispersion .......................................................... 64 3.4 Wave dissipation ............................................................ 66 3.4.1 Deep-water-wave dissipation .......................................... 66 3.4.2 Shallow-water-wave dissipation ........................................ 67 3.4.3 Swell dissipation. 68 3.5 Non-linear wave–wave interactions ............................................ 69 3.6 General notes on source terms ................................................ 71 CHAPTER 4 . MANUAL WAVE FORECASTING . 73 4.1 Introduction ............................................................... 73 4.2 empirical working procedures ................................................ 75 4.2.1 Variable winds ....................................................... 76 4.2.2 Estimating fetch ..................................................... 76 4.2.3 Wave growth ........................................................ 77 4.2.4 Swell decay ......................................................... 78 4.2.5 Speed and motion of wave groups ..................................... 78 4.2.6 Miscellaneous ....................................................... 79 4.3 Computation of wind waves .................................................. 79 4.3.1 Determination of sea-state characteristics for given wind speed and fetch .... 79 4.3.2 Determination of sea state for increasing wind speed. 80 4.3.3 Extrapolation of an existing wave field with further development from a constant wind ..................................................... 81 4.3.4 Extrapolation of an existing wave field with further development from an increasing wind ................................................... 82 4.3.5 Determination of the effects of a dynamic or trapped fetch for a tropical cyclone moving at different speeds .............................. 82 4.4 Computation of swell ........................................................ 84 4.4.1 Distant storms ....................................................... 84 4.4.2 Distant storms with long fetch ......................................... 86 4.4.3 Swell arriving at point of observation from a nearby storm ................. 88 4.4.4 Further examples .................................................... 90 4.5 Computation of shallow-water effects .........................................
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