Diagnostic analyses on blocking system of a severe cold case

The quasi-geostrophic process was diagnosed for a case of severe cold air breakout under the blocking situation during 16 - 18 March of 1998. The attention was focused on the relationship between the surface anticyclone and 500 hPa blocking high. The results indicate that the cold outbreak is associated with the adjustment of blocking situation in the Ural Area, i.e. the collapsing and rebuilding of the Ural Mountain blocking high. The temperature advections in the lower troposphere shown that the polar cold air invading from the northwest caused the Ural blocking high collapsed, and a new ridge developed rapidly was due to the warm advection on the southwestern side which led to the Ural blocking high rebuilt. In addition, the distribution of the vertical motion on 700 hPa shown that the surface high splitting was related to the considerable upward motion located on the southeastern part of surface high.EI03340-3473