Purpose. The work is aimed at studying the response of the Black Sea upper layer to the intrusion of cold air in January 23–25, 2010.

Methods and Results. The NOW coupled mesoscale sea – atmosphere model with the 1 km resolution was used to study the sea fields numerically. The change in sea surface temperature in January 23–25, 2010 resulted from the cold intrusion was reproduced. The basic factors which had influenced the change in the upper layer temperature, namely horizontal advection, cooling of the sea surface due to the sensible and latent heat fluxes and the impact of vertical turbulent mixing were considered and quantitatively assessed. The main changes that took place in the cold intermediate layer were investigated.

Conclusions. The change in vertical distribution of the monthly average temperature, salinity and density is considered based on the Copernicus reanalysis data for 2009–2010. The presence of a cold intermediate layer at the average depth 60 m in all the months except for the transitional winter-spring period is shown. The results of NOW modeling reveal the fact that decrease in the surface temperature over the most sea area occurred as a result of heat and mass exchange with the atmosphere. The influence of horizontal advection and mixing through the lower boundary of the cold intermediate layer was manifested only in certain small areas, in other words, it produced a local effect. Convective cooling spanned the upper mixed layer up to the depths about 40–45 m and amounted to ~ 1°С. Besides, it is shown that during the cold air intrusion, the depth of cold intermediate layer increased. The notion that the local cold waters in the shallow northwestern part of the sea are secondary as a source of formation of the cold intermediate layer has been confirmed. The density of colder, but less saline coastal water prevents its sinking to the upper boundary of cold intermediate layer.