Composite analyses of individual strong Alaskan and Siberian anticyclones using the ERA-40 dataset for the winter 1978/792001/02 are performed to diagnose key dynamical and thermodynamical features relevant to the development of these systems. The anticyclones are identified using regionally-defined SLP thresholds of 1050 hPa and 1060 hPa, respectively.
The results indicate that atmospheric blocking is an important component in the development of these surface anticyclones as their formation occurs downstream of anomalous upper-tropospheric ridges. The dynamical impact of the ridge associated with the strong Alaskan anticyclone is found to be more impressive than that of the strong Siberian anticyclone. Another key aspect of the development of these strong anticyclones is the role of radiational cooling. The cooling of the near-surface air mass is shown to be important to both anticyclones, but cooling due to radiative effects dominates in the Siberian anticyclone. We also demonstrate that elevated terrain plays a significant role in the local maintenance of cold air mass.