| Popis: |
Circulation modes are highly correlated, yet often distant areas detected in a field of a circulation variable, such as sea level pressure, geopotential heights, wind speed, and wind components. They consist typically of two or more action centres, which simultaneously weaken or strengthen, hence affecting the intensity and direction of atmospheric circulation and consequently surface climatic elements, such as temperature and precipitation. Temporal variability of action centres affects spatiotemporal distribution of impact on surface climatic variables. The availability of gridded datasets allows investigation of temporal behaviour of action centres and its impact on surface climatic variables on long time scales over large regions, which is, therefore, the main scientific topic of this work. Due to a large amount of reanalyses differing in e.g. assimilated type of data and model used for their calculation, the comparison of representation of circulation modes and their temporal evolution of relationships with surface climatic elements is conducted between reanalyses. Circulation modes in reanalyses assimilating both surface and upper troposphere/satellite data (ERA40, JRA-55, NCEP-1) are mostly similar whereas the 20CRv2c reanalysis, which utilizes surface data only, contains biases. Although... |
