Long-term characterisation of directional wave spectra in the Black Sea and the Sea of Azov

Abstract

Directional wave spectra describe complex sea-states in frequency and directional domains and provide more detailed information than the bulk wave parameters. Using hourly directional wave spectra hindcasted for 42 years (1979–2020), this study aims to assess long-term spectral wave climate in the Black and Azov Seas. Variance densities are averaged over the frequencies and directions for annual, seasonal, and monthly scales to determine spectral wave climate. Furthermore, The individual wave systems observed in each directional wave spectra are determined by referring to the independent spectral peak at each observation. The different sea state 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 the function 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, 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 on the number of wave systems in the wave spectrum and geographic location. The first peaks in the wave spectra are primarily derived from two dominant directions, and ∼54 % of the peaks had a density greater than 2 m2/Hz. In contrast, second and third peaks in the wave spectra are typically derived from three or more dominant directions and rarely exceed 2 m2/Hz density.