Variability of atmospheric circulation in Central Europe in the summer season 1881-1998 (on the basis of the Hess-Brezowski classification)

Abstract

This paper analyses the trends and fluctuations of three different indices of circulation above Central Europe in the summer seasons of the period 1881-1998. The daily atmospheric circulation subtypes according to the Hess-Brezowski classification were used as research material. The method applied in the process was prepared by MURRAY and LEWIS (1966) and modified by NIEDZWIEDZ (2000). Appropriate values of the westerly zonal circulation index (W index), the southerly meridional circulation index (S index) and the cyclonicity index (C index) were assigned to each circulation subtype. It was found that in the summer seasons of 1881-1998 the westerly zonal circulation index underwent a reduction while the southerly meridional circulation index was augmented. The observed reduction of the westerly zonal circulation index is mainly the result of a decrease in the number of days characterised by a circulation with a westerly component NW and an increase in the number of days with a circulation containing an easterly component E. At the same time, there was a clear rise of the SW circulation within the westerly zonal circulation.