A Persistent Cold-Outbreak in the Far East Related to the Blocking Situation

摘要

A case study is made on the so-called Northeasterly pressure pattern accompanied by persistent cold-outbreak over the Far East. The period of investigation covers late September and early October 1954, when this peculiar pattern appeared with unusual distinctness. It is found that an intense cold vortex of Arctic origin, which is displaced southward to northeast Siberia in the course of world-wide decline of zonal index, gives rise to a strong cold air advection eastward along its southern margin. This cold advection is responsible to the establishment of the Northeasterly pattern and continues until the great store of cold air trapped by a blocking high is exhausted. The nature of cold vortex as to its vertical extent and its successive formation in lower latitudes is described. Also, the role of the strong westerlies as the generator of the cold air advection is discussed.