Field-based study and parametrisation of quiescent periods in ocean waves

Quiescent periods in ocean wave environments are studied using an extensive range of field data acquired from three different oceans with the aim of determining whether these periods can be predicted using probabilistic methods by parameterising their probability as a function of sea state parameters. To construct the probabilistic model, it is hypothesized that the probability distribution of the number of successive waves below a certain limit can be described by a geometric distribution function, with the key parameter, denoted by p , representing the failure probability of two successive waves falling below a specified wave height threshold. From a physical perspective, p is expected to decay exponentially from 1 to 0 as the wave height threshold increases. Analysis of the field data confirms that the parameter p decays exponentially with increasing wave height, as expected, and can be parameterised as a function of the wave height threshold. Additionally, a secondary dependence of p on the steepness-to-bandwidth ratio, related to wave group properties, was observed and included in the parametrisation. The parameterisation can be used to predict duration of quiescent period in real ocean wave fields for practical purposes. • Quiescent periods in real wave fields of three different oceans are investigated. • The probability distribution of number of successive waves below a certain limit is estimated using a geometric distribution function. • A parameterisation of the probability in terms of the limit is obtained with a secondary dependence on wave-group properties. • The parameterisation can be used to predict duration of quiescent period in real ocean wave fields for practical purposes.