A comparison between planetary-wave flow regimes and blocking

Abstract

An investigation of the relative similarities in regime classification of an index designed to isolate cases of blocking based upon the kinematic properties of the regional flow, and one which describes the amplitude of the planetary-scale eddy field, is undertaken with observations from 28 Northern Hemisphere winters. The occurrence of blocking patterns persisting 5 days or more over the eastern Pacific is found to coincide in 94% of all cases with the hemispheric flow being characterized by an amplified planetary-scale wave flow regime. However, the occurrence of such an amplitude regime does not necessarily imply the existence of a blocking pattern in the classical sense. In the eastern Pacific, the split flow blocking developed simultaneously with or during an amplified wave regime episode in 30 of 33 cases. Retrogression of blocking patterns to west of the dateline is a frequent occurrence accompanying the decay of amplified planetary-wave episodes. 3/4 of the blocking episodes occurring west of the dateline formed as a part of amplified wave regime events and persisted into their aftermath. Most European blocking episodes (78%) are a part of an amplified-wave flow regime during some part of their life cycle. Blocking in this sector developed along with or during an amplified wave regime in 30 of 51 cases.