Quasi-Periodicity of the Black Sea Wind Spatial-Temporal Variability and Its Relation with the North Atlantic Oscillation phases

Abstract

Quasi-periodic features of the inter-annual and inter-decadal spatial-temporal variability of the wind speed absolute value (W) in the Black Sea area are assessed based on a series of 60–100-year-long direct observations performed at eight coastal stations, and also on the reanalysis data obtained from the NDP-048, WDC, NCDC, NCEP/NCAR (1948–2011) and MERRA (1980–2015) arrays. Three groups of oscillations with the periods T about 60–90, 20–40 and 3–15 years that present in the W direct data are shown by means of the wavelet analysis. As for long-period oscillations (Т ~ 60–90 years), possible relations of such quasi-periodicity with the phases of the North Atlantic Oscillation index characterizing the atmospheric circulation features are investigated. Calculated according to the MERRA array reanalysis, the mean anomalies of January – February average W series separately for groups of years with the values of the NAO index > +1 and ←1 demonstrated in their dynamics the values of different signs for the same Black Sea areas. It is revealed that during the periods when the index positive phase is mainly predominant, the W positive anomaly is formed over the south-western, south-eastern and eastern parts of the sea adjacent to the coast at a distance 20–100 km from it, and the W negative anomaly – over the rest of the sea. During the years when the index phase is mainly negative, the signs of the W anomalies over almost the same regions change to the opposite ones.

Keywords

• the Black Sea
• wind speed module
• inter-annual variability
• quasi-periodicity
• North Atlantic Oscillation