Аннотация:Daily cycling in development of breeze circulation plays an important role in distribution of pollutants coming to the lower atmosphere in coastal regions. Air recirculation in the breeze cell may lead to additional accumulation of pollutants over the coast in day time.
Relationship of wind vector sum L (transport distance) and wind scalar sum S (stagnation) is used to define parameter of recirculation R (R=1–L/S). It changes between 0 and 1. High R values correspond to intensification of breeze cell. Thus in day time under sea breeze influence pollutants are accumulated over the coast, and night land breeze transports them to the sea until next stage of the sea breeze which takes them back to the shore. Low values of R show that air is transported from the coast by the large-scale atmospheric flow, and ventilation is more effective.
The data used in this study is from wind observations during 1960-1990 on 36 hydrometeorological stations of the former Soviet Union situated no far then 10 km from the coast.
Results of the study show that there are two types of year course of recirculation parameter: unimodal (prevails), and bimodal. Time and space features of monthly and yearly mean values of R are analyzed. It is revealed that regime shift of R twice occurred during this period – in the early sixties and middle seventies (fig.1a). This is in a good agreement with noticeable changes at the same time in large-scale atmosphere circulation, precipitation and evaporation over the Black Sea, and it’s surface salinity. Our results show that with increasing of the zonal wind on the 850 hPa from the west (u>0), recirculation is increased, too (fig.1b), so decreasing air ventilation on the coast. When u<0 (east wind) it does not influence to recirculation. Correspondence of recirculation and meridional wind component is not significant.