Wave Buoy Measurements at Short Fetches in the Black Sea Nearshore: Mixed Sea and Energy Fluxes

Wave buoy measurements were carried out near the north-eastern Black Sea coast at the natural reserve Utrish in 2020-2021. Totally about 11 months of data records were collected during two stages of the experiment at 600 and 1500 meters offshore and depths of 18 and 42 meters. The measured waves propagate almost exclusively from the seaward directions. Generally, the waves do not follow the local wind directions, thus, implying a mixed sea state. Nevertheless, dependencies of dimensionless wave heights on periods based on the wind speed scaling appear to be close to previously established empirical laws for the wind-driven seas. The results of the wave turbulence theory are applied for estimates of spectral energy fluxes and their correspondence to the energy flux from the turbulent wind pulsations. These estimates are consistent with today's understanding of wind-wave interaction. It is shown that the main fraction of the wind energy flux goes to the direct Kolmogorov-Zakharov cascade to high wave frequencies and then to dissipation in small scales. Less than 1% of the wind energy flux is directed to low frequency band (the so-called inverse Kolmogorov-Zakharov cascade), thus, providing wave energy growth.

Automated summary

Wave buoy measurements were conducted near the north-eastern Black Sea coast at Utrish natural reserve in 2020-2021. The measured waves primarily propagated from the seaward directions and did not strictly follow the local wind directions, indicating a mixed sea state. The relationship between dimensionless wave heights and periods based on wind speed scaling closely matched previously established empirical laws for wind-driven seas. The results of wave turbulence theory were applied to estimate spectral energy fluxes and their correspondence to turbulent wind pulsations, demonstrating consistency with current understanding of wind-wave interaction. The majority of wind energy flux was found to contribute to the direct Kolmogorov-Zakharov cascade to high wave frequencies and subsequent dissipation in small scales, while less than 1% directed to the low frequency band, facilitating wave energy growth.