Global Wave Statistics Online Help

Synthesis of Wave Height and Period Statistics

The statistics of wave height and period are modelled in the form of joint probability distributions, commonly known as scatter diagrams. The modelling is based on a so-called 'Bivariate lognormal' distribution, and in the case of the Global Wave Statistics Online output involves five modelling parameters, two depending only on wave height and the others involving dependence on wave period. The two height-dependent parameters can be computed directly from the wave height statistics derived as above. The other three can be computed from these height-dependent parameters by use of empirical formulae, with coefficients derived by regression analysis of measured wave height and period data. The empirical formulae used include some dependence of the coefficients on the level of swell as indicated by the value of the parameter H2. On this basis, all the five parameters needed in association with the enhanced wave height distribution to determine the complete joint-probability distribution can be computed from input of wave height statistics alone. In the case of the original NMIMET output, the distribution is computed in a fully analytical form from input of 6 parameters, 3 of which serve to describe the enhanced wave height distribution as explained in Appendix_A3.

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