Analysis of Variance of the Black Sea Level Oscillations in a Wide Range of Frequencies

Abstract

Based on the long-term observations in the Black Sea, the features of spatial distribution of the sea level oscillations’ variance in five different frequency ranges were studied. The series of the hourly sea level observations carried out at 23 coastal tide gauges were used to analyze mesoscale and synoptic variability. To assess seasonal and inter-annual sea level variability, long-term monthly average level values obtained at the stations of Varna, Ust-Dunaisk, Odessa, Sevastopol, Tuapse, Poti, and Batumi were used. The hourly observations permitted to calculate the sea level spectra for the periods 2 hours – 70 days, and the monthly average sea level values – the spectra for the periods 70 days – 10 years. Formation of the Black Sea level oscillations’ spectrum was analyzed in a wide frequency range. For each of five chosen ranges of frequency variability, its contribution to the total energy of non-tidal sea level variations was quantitatively assessed. Variance of inter-annual sea level oscillations in the Black Sea is relatively homogenous and is within 28 to 37 cm 2 . The range of seasonal sea level oscillations is wider: 16–37 cm 2 . The intra-annual sea level oscillations differ significantly depending on the region: the smallest values are recorded in Sevastopol – 20 cm 2 , the largest ones – in Poti and Kasperovka – up to 35 cm 2 . In general, synoptic and mesoscale sea level oscillations testify to substantial inhomogeneity in the variance distribution over the water area. The highest values resulting from the surface wind effect are observed in the shallow northwestern part of the Black Sea. At the stations of the Caucasian coast of the Black Sea (Tuapse, Poti, Batumi) and near the Crimean coast (Sevastopol), variance of the seasonal and intra-annual sea level oscillations exceeds that of the synoptic ones by about 1.5–2 times, whereas in the Black Sea northwestern part, the greatest contribution to the total sea level variance is made by the synoptic component. Acknowledgements: the study is carried out within the framework of the state task of FASO, Russia on the theme No. 0149-2018-0015 “Tectonics of the deformed lithosphere plates and geodynamic evolution of the ocean lithosphere: geodynamic evolution of the Arctic and the transition zone from the Pacific Ocean to Eurasia; development of catastrophic and potentially dangerous processes in the subduction zones, marginal and internal seas, and coastal zone, analysis of their geo-ecological consequences; assessment and genesis of minerals of the continental remote areas and intra-oceanic regions, marginal and internal seas” and at financial support of the RFBR grant No. 16-35-60071 “Study of the mechanism of the level oscillation formation in the Baltic, Black and Caspian seas in the period ranges from hours to years based on the data of coastal and satellite observations, as well as numerical modeling”.