Long-term spectral wave climate in the Black Sea based on directional wave spectra

Abstract

Abstract Directional wave spectra describe complex sea states in frequency and directional domains and provide more detailed information than the bulk wave parameters. Spectral wave informations are important for the design of ships and offshore structures. Using hourly directional wave spectra hindcasted for a period of 42 years between 1979 and 2020, long-term spectral wave climate in the Black and Azov Seas was assessed. To determine the climatic wave spectrum, variance densities are averaged over the frequencies and directions for annual and seasonal, monthy scales. Futhermore, The individual wave system observed in each directional wave spectra are determined referring to the independent spectral peak at each observation. The different sea states conditions, including the uni-modal and multi-modal wave systems are classified and analysed; The energy, frequency, and direction of the three first prominent individual wave system peaks are deeply evaluated as a function of the sea state conditions. Occurrences as foction of spectral peak density and directions of the prominent individual wave system peaks are also computed and discussed. The results reveal that multi-modal spectra are more frequent in most regions, although the highest peak density values and lowest peak frequencies were observed within the wave spectra of uni-modal sea states. The spectral peak densities, frequencies, and directions depend both on the number of wave systems in the wave spectrum and on the geographic location. The first peaks in the wave spectra are mostly derived from two dominant directions and ~ 54% of the peaks had a density greater than 2 m2/Hz. In contrast, the second and third peaks in the wave spectra are typically derived from three or more dominant directions and rarely exceed a density of 2 m2/Hz.