GUIDE WAVE ANALYSIS AND FORECASTING - WMO

6.1 Introductory remarks
Since the pioneering development of wave forecasting
relations by Sverdrup and Munk (1947), operational
wave analysis and forecasting has reached quite a
sophisticated level. An introduction to modern numerical
wave models has been provided in Chapter 5.
National Meteorological Services of many maritime
countries now operationally use numerical wave models
which provide detailed sea-state information at given
locations. Often this information is modelled in the form
of two-dimensional (frequency-direction) spectra. The
two-dimensional spectrum, which is the basic output of
all spectral wave models, is not by itself of great operational
interest; however, many wave products which can
be derived from this spectrum are of varying operational
utility depending upon the type of coastal and offshore
activity. An example of a schematic representation of a
two-dimensional spectrum is given in Figure 6.1. The
spectra were generated by the Canadian Spectral Ocean
Wave Model (CSOWM), developed by the Atmospheric
CHAPTER 6
OPERATIONAL WAVE MODELS
M. Khandekar: editor
15 UTC 14 Nov. 1991 15 UTC 20 Nov.
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Environment Service (AES) of Canada. The four spectra
shown refer to four overpass times of the satellite
ERS-1 during the wave spectra validation field experiment
conducted on the Grand Banks of Newfoundland
in the Canadian Atlantic from 10 to 25 November 1991.
The wind-sea regions of the wave field are the elongated
energy maxima located opposite to the wind direction
and around the wind-sea frequency of about 0.15 Hz.
The wave energy maxima outside of the wind-sea region
are the swells generated by the model during the twoweek
period of the field experiment (for additional
details, see Khandekar et al., 1994).
Significant wave height may be regarded as the
most useful sea-state parameter. As defined earlier (in
Section 1.3.3), the significant wave height describes the
sea state in a statistical sense and is therefore of universal
interest to most offshore and coastal activities. The
significant wave height can be easily calculated from the
two-dimensional spectrum, using a simple formula.
Besides significant wave height, two other parameters,
which are of operational interest, are the peak period (or,
Figure 6.1 —
Normalized wave directional spectra
generated by the AES CSOWM at a grid
point location in the Canadian Atlantic.
The spectra are presented in polar plots
with concentric circles representing
frequencies, linearly increasing from
0.075 Hz (inner circle) to 0.30 Hz (outer
circle). The isopleths of wave energy are
in normalized units of m 2 /Hz/rad and are
shown in the direction to which waves
are travelling in relative units from 0.05
to 0.95. Model generated wind speed and
direction are also shown (from
Khandekar et al., 1994)