Review of Freak Wave Research at ECMWF

Title
Review of Freak Wave Research at ECMWF
Technical memorandum
Date Published
08/2025
Secondary Title
Technical Memoranda
Number
930
Author
Peter Janssen
Publisher
ECMWF
Abstract The ECMWF freak wave warning system is based on a random time series analysis using the envelope wave height. The key quantity of interest is the maximum envelope wave height distribution which for (weakly) nonlinear systems depends on envelope skewness and kurtosis. Expressions for skewness and kurtosis for general spectra are presented, but they are very cumbersome. Therefore, a simple parametrization of skewness and kurtosis of the bound waves and the contribution of the free waves to kurtosis is presented. These parametrisations are validated against computations using the theoretical expressions of the statistical parameters. By adjusting a few parameters in the parametrizations a good agreement with the ’exact’ computations is found. These parametrizations have been introduced in the operational version of ECMWF’s freak wave warning system.
URL https://www.ecmwf.int/en/elibrary/81677-review-freak-wave-research-ecmwf
DOI 10.21957/af89ffdc01
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