Long-term variability of surface temperature in the Black Sea, and its connection with the large-scale atmospheric forcing

Satellite, in situ and reanalysis data for the period of 1950–2005 were used to study the long-term variability of sea surface temperature (SST) in the Black Sea and its connection with the major large-scale atmospheric forcing (air temperature, surface wind and North Atlantic Oscillation — NAO). In contrast to the quasi-regular decadal oscillations of the SST typical for the Northern Atlantic, the pattern of long-term SST variability in the Black Sea is better described as an intermittent periods of SST increase/decrees with the duration of approximately 6–10 years and short (1–2 years) and quite abrupt transitions between them. Confirmed is a known fact of existence of the two major surface wind regimes over the Black Sea i.e., Southern–Western (SW) and Northern–Eastern (NE) and new details on the correlations between the zonal and meridional wind components in each regime are added. A new important finding is that the switch between two regimes occurs quite abruptly at values of NAO index slightly less then zero. It was shown that in weak to moderate positive NAO situation the SW wind regime prevail and wind components are well correlated with the NAO index. The long-term variability of winter-mean SST in the Black Sea is reasonably well correlated with the variability of surface air temperature (SAT), which in turn is highly correlated with the meridional component of surface wind. It is shown that strengthening/weakening of the Southern wind or weakening/strengthening of the Northern wind cause SAT and SST increase/decrease. Finally, a conceptual diagram of NAO impact on the meridional component of the surface wind, SAT and SST is presented.