GUIDE WAVE ANALYSIS AND FORECASTING - WMO

More documents

Recommendations

Info

68 Figure 6.2 — A simplified output from the AES CSOWM in the form of a four-panel chart of significant wave height contours. The wave parameters are usually plotted according to a wave plot model shown below. Only the wind parameters and swell directions are displayed here. The panels show: the diagnostic (0-hour) wave height chart for 14 March 1993, 12 UTC (top left), the 12-hour forecast valid for 15 March, 00 UTC (bottom left), the 24hour forecast valid for 15 March, 12 UTC (top right), and the 36-hour forecast valid for 16 March, 00 UTC (bottom right) (courtesy CMC, Canada; after Khandekar and Swail, 1995) GUIDE TO WAVE ANALYSIS AND FORECASTING Full plotting scheme Wind Wave Period(s) Wind Speed Swell Wave 10 13 and Direction Period(s) Wind wave Swell Wave Height (m) 8 2 Height (m) Swell Direction Ice valid 14 March 1993, 00 UTC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
in some applications, the zero up/downcrossing period) and the direction in which waves are moving. It should be noted that the convention of wave direction from wave models varies (i.e. “from which” direction or “to which” direction), whereas measured data are invariably presented as the direction “from which” waves travel, consistent with the meteorological convention for wind direction. The parameters for significant height, peak period and direction can be further separated into their wind-sea and swell components giving a total of six additional wave parameters of operational interest. For the sake of completeness, these six wave parameters are often accompanied by three related atmospheric parameters, namely surface pressure, wind speed and wind direction. Either all, or a selected few of these nine parameters can be suitably plotted on a map and disseminated to users. The algorithms for separating wave trains may be quite simple (see Section 3.6) or they may fully partition the spectrum into the wind sea and primary and secondary swell features (Gerling, 1992). In this case for each feature integral parameters for the significant wave height, mean period and mean direction are computed. 6.2 Wave charts A map (or chart) showing spatial distribution of a selected number of wind and wave parameters is called a wave chart. For efficient transmission, a wave chart should be simple and uncluttered. Almost all wave charts show isopleths of significant wave height suitably labelled and a few additional parameters like peak period, wave direction, etc. The chart may provide seastate information in a diagnostic (analysed) or in a prognostic (forecast) form. Examples of typical output from operational centres The AES operational wave model CSOWM is run twice daily at the Canadian Meteorological Center (CMC) in Montreal and is driven by 10 m level winds generated by the CMC regional weather prediction model. Figure 6.2 provides an example of a four-panel wave chart showing wave fields at analysis time (zero-hour forecast) plus forecast fields out to 12, 24 and 36 hours, respectively. The wave height contours refer to the total wave height, H, which is defined as: H2 2 2 = Hwi + Hsw (6.1) In Equation 6.1, H wi and H sw are wind-wave and swellwave heights, respectively. The wave charts cover the north-west Atlantic region extending from the Canadian Atlantic provinces to about 20°W and refer to the “storm of the century” in mid-March 1993 when significant wave heights of 15 m and higher were recorded in the Scotian Shelf region. A similar four-panel chart covering the Canadian Pacific extending from the west coast of Canada out to about the International Date Line is generated by the Pacific version of the CSOWM, which is also run twice a day at the CMC. OPERATIONAL WAVE MODELS 69 Wave charts prepared and disseminated by other national Services typically include wave height contours and a few other selected parameters. For example: • The GSOWM (Global Spectral Ocean Wave Model of the US Navy), which was run operationally at the Fleet Numerical Meteorology and Oceanography Center in Monterey, California, until May 1994 (when it was replaced by an implementation of the WAM model, see Section 5.5.4), produced wave charts depicting contours of significant wave height and primary wave direction by arrows (see Clancy et al., 1986); • The National Oceanographic and Atmospheric Administration (NOAA) in Washington, D.C. (USA) has been running a second generation deepwater global spectral wave model since 1985; the main output from the NOAA Ocean Wave (NOW) model is a wave chart depicting contours of significant wave height and arrows showing primary wave direction. In addition to the global wave model, NOAA also operates a regional wave model for the Gulf of Mexico, which is also a second generation spectral wave model but with shallowwater physics included. A typical output from the regional model is given in Figure 6.3; • The Japan Meteorological Agency (JMA) in Tokyo has been operating a second generation coupled discrete spectral wave model (Uji, 1984) for the north-west Pacific and a hybrid model for the coastal regions of Japan. A typical output from the coupled discrete model is the wave chart in Figure 6.4. In addition, directional wave spectrum output charts for selected locations in the north-west Pacific and in the seas adjacent to Japan are prepared and disseminated — see Figure 6.5 which shows two-dimensional spectra at 12 selected locations near Japan. The wave spectra are displayed in polar diagrams. Such detailed spectral information at selected locations can be very useful for offshore exploration and related activities. For a general discussion on the various types (classes) of wave models see Section 5.5. 6.3 Coded wave products Measured wave data (perhaps from a Waverider buoy or a directional wave buoy) can be reported or disseminated using a code called WAVEOB. This code is constructed to allow for wave parameters and one-dimensional or two-dimensional spectral information. For a one-dimensional spectrum (perhaps measured by a heave sensor), the report consists of a maximum spectral density value followed by ratios of individual spectral densities to the maximum value. For a twodimensional spectrum, the report consists of directional wave functions in the form of mean and principal wave directions together with first and second normalized polar Fourier coefficients.
Page 1 and 2:
WORLD METEOROLOGICAL ORGANIZATION G
Page 3 and 4:
© 1998, World Meteorological Organ
Page 5 and 6:
IV Chapter 7 - WAVES IN SHALLOW WAT
Page 7 and 8:
ACKNOWLEDGEMENTS The revision of th
Page 9 and 10:
VIII has been included particularly
Page 11 and 12:
X considerable attention. Annex III
Page 13 and 14:
2 η Crest Zero level a H = 2a a Tr
Page 15 and 16:
4 Figure 1.5 — Paths of the water
Page 17 and 18:
6 When waves propagate into shallow
Page 19 and 20:
8 1.3.2 Wave groups and group veloc
Page 21 and 22:
10 wavelengths in a given sea state
Page 23 and 24:
12 for instance, a frequency of 0.1
Page 25 and 26:
14 in which E(f) is the variance de
Page 27 and 28: 16 2.1.1 Wind and pressure analyses
Page 29 and 30: 18 GUIDE TO WAVE ANALYSIS AND FOREC
Page 31 and 32: 20 Figure 2.2(a) (right) — Usual
Page 33 and 34: 22 As a quick approximation of ocea
Page 35 and 36: 24 GUIDE TO WAVE ANALYSIS AND FOREC
Page 37 and 38: 26 Gr G Gr ∇p C Cnf ∇p C Cnf
Page 39 and 40: 28 POINT C — The effect of warm a
Page 41 and 42: 30 a general sense, and can be appl
Page 43 and 44: 32 Free atmosphere Ekman layer Cons
Page 45 and 46: 3.1 Introduction This chapter gives
Page 47 and 48: ange of directions. Also, waves at
Page 49 and 50: small enough that swell can survive
Page 51 and 52: Figure 3.7 — Structure of spectra
Page 53 and 54: 4.1 Introduction CHAPTER 4 WAVE FOR
Page 55 and 56: necessary to forecast waves for a p
Page 57 and 58: TABLE 4.4 Additional wave informati
Page 59 and 60: TABLE 4.6 Ranges of swell periods a
Page 61 and 62: this situation, the angular spreadi
Page 63 and 64: the energy flux is c gH 2 . This is
Page 65 and 66: α0, degrees Solution: 80° 70° 60
Page 67 and 68: 5.1 Introduction National Meteorolo
Page 69 and 70: only once, since it is usual to sto
Page 71 and 72: Frequency 0.050 0.067 0.083 0.100 0
Page 73 and 74: The models may differ in several re
Page 75 and 76: The CH class may include many semi-
Page 77: 6.1 Introductory remarks Since the
Page 81 and 82: OPERATIONAL WAVE MODELS 71 Figure 6
Page 83 and 84: give large differences in the compa
Page 85 and 86: Wind (m/s) Waves (m) Buoy/GSOWM Wav
Page 87 and 88: TABLE 6.2 Numerical wave models ope
Page 89 and 90: TABLE 6.2 (cont.) Country Name of m
Page 91 and 92: 7.1 Introduction The evolution of w
Page 93 and 94: water boundary into shallow water.
Page 95 and 96: eflected waves, although the latter
Page 97 and 98: Energy (cm 2 /Hz) Energy (cm 2 /Hz)
Page 99 and 100: 8.1 Introduction Wave data are ofte
Page 101 and 102: matter and timing the intervals bet
Page 103 and 104: a Directional Waverider (Barstow et
Page 105 and 106: 80°N 60°N 40°N 20°N 0° -20°S
Page 107 and 108: a combination of sea-surface temper
Page 109 and 110: 8.7.1 Digital analysis of wave reco
Page 111 and 112: 9.1 Introduction Chapter 8 describe
Page 113 and 114: Presentation of data and wave clima
Page 115 and 116: the monsoon season of June to Septe
Page 117 and 118: Probability of non-exceedance case
Page 119 and 120: individual wave height derived usin
Page 121 and 122: emote, data-sparse areas. However,
Page 123 and 124: TABLE 9.2 (cont.) Country Source of
Page 125 and 126: For a storm hindcast, select the mo
Page 127 and 128: TABLE 9.3 (cont.) Country Model use
Page 129 and 130:
ANNEX I ABBREVIATIONS AND KEY TO SY
Page 131 and 132:
Abbreviation/ Definition Symbol MOS
Page 133 and 134:
CODE FORM: D . . . . D or IIiii* SE
Page 135 and 136:
sensors, spectral peak wave period
Page 137 and 138:
cs1cs1 The ratio of the spectral de
Page 139 and 140:
M jM j n mn m n smn sm n bn bn b P
Page 141 and 142:
1744 Im Indicator for method of cal
Page 143 and 144:
The following distributions are bri
Page 145 and 146:
4. Weibull distribution Probability
Page 147 and 148:
8. Fisher-Tippett Type I (FT-I) (or
Page 149 and 150:
ANNEX IV THE PNJ (PIERSON-NEUMANN-J
Page 151 and 152:
ANNEX IV 141 Duration graph. Distor
Page 153 and 154:
REFERENCES Abbott, M. B., H. H. Pet
Page 155 and 156:
REFERENCES 145 Carter, D. J. T., P.
Page 157 and 158:
REFERENCES 147 Gumbel, E. J., 1958:
Page 159 and 160:
REFERENCES 149 Maat, N., C. Kraan a
Page 161 and 162:
Slutz, R. J., S. J. Lubker, J. D. H
Page 163 and 164:
SELECTED BIBLIOGRAPHY CERC, 1984: C
Page 165 and 166:
156 Energy . . . . . . . . . . . .
Page 167 and 168:
158 steepness . . . . . . . . . . .
show all

GUIDE WAVE ANALYSIS AND FORECASTING - WMO

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?