Przebieg roczny ciśnienia atmosferycznego na Antarktydzie

W artykule przedstawiono zmienność przestrzenną przebiegu rocznego ciśnienia atmosferycznego na Antarktydzie. Stwierdzono dwa typy przebiegów rocznych ciśnienia. Na wybrzeżu występuje przebieg charaktery-zujący się półroczną oscylacją, z maksymalnymi wartościami w sezonie letnim i zimowym oraz najniższymi w przejścio-wych porach roku. We wnętrzu kontynentu najwyższe ciśnienie występuje latem, a najniższe w chłodnej połowie roku. Największe amplitudy roczne ciśnienia występują we wnętrzu kontynentu. W ostatnich dwóch dekadach XX wieku zaznaczyły się istotne zmiany w przebiegu rocznym ciśnienia atmosferycznego.

At the polar latitudes of the Southern Hemisphere a circulation cell functions which is connected with the strong baric wedge feature of the atmosphere occurring between the Antarctic anticyclone and a very deep circumpolar trough by the Antarctic coastline. The circulation system in the Antarctic region shows seasonal variability called Southern Annular Mode (SAM). In the cold season the tropospheric exchange of air masses strengthens due to the increase of the katabatic winds? speed. The relocation of air masses from over Antarctica to its peripheries has an influence on the annual course of the atmospheric pressure. In the elaboration mean monthly air pressure values were taken into account from 106 Antarctic stations from the beginning of measurements to 2000. On the basis of these data the mean annual course of the atmospheric pressure has been counted as well as the yearly pressure range. Annual courses from two periods: 1958-1980 and 1981-2000 were also compared. Over the Antarctic the annual course of the atmospheric pressure is complex. At the costal part of the continent there are two maxima (in summer and in winter) and two minima in the transient seasons. This course is called semi-annual oscillation (SAO) in the literature. However this phenomenon shows certain regional specifics. On the Antarctic Peninsula and South Orkney Islands the winter maximum is more distinct, while minima are shifted to February and November. In the inland the winter maximum decreases with the distance from the coast and at stations situated in the highest parts of the glacial plateau the highest pressure values occur in summer and distinctly lower ones in winter. At some inland stations a slight increase of the pressure can be observed in the middle of winter what refers to the thermal coreless winters occurring frequently in this region. The annual range of the atmospheric pressure decreases from the coast (15-7 hPa) to the interior of the continent, where it reaches values above 20 hPa. During the last two decades of the 20th century significant changes took place in the annual courses of the pressure in comparison to the years 1958-1980. On the South Orkney Islands and the Antarctic Peninsula the pressure increased in summer and in autumn, while in winter distinctly decreased. At the remaining part of the Antarctic coast pressure decrease occurred in every seasons, and in the Weddell Sea region the autumn and spring minimum significantly deepened. At the majority of the stations the annual amplitudes of the atmospheric pressure decreased after 1980. These changes contributed to the disturbances in the functioning of the Antarctic climate system. On the Antarctic Peninsula the air temperature increased, while at many stations in the Eastern Antarctic considerable cooling occurred.