Blocking Action in the Middle Troposphere and its Effect upon Regional Climate: I. An Aerological Study of Blocking Action

A comparative study of five cases of blocking action in the upper westerlies is presented with the two-fold objective of obtaining a more complete description of this phenomenon and of attempting an explanation of its initiation, development and dissipation in terms of parameters derived from an hydraulic analogue. The effect of European blocking upon the zonal and meridional circulation indices and the rôle of blocking in the evolution of hemispheric circulation patterns are discussed. In Part II, to be published later, the results of a preliminary semi-statistical analysis of blocking action, together with a description of the regional precipitation and mean surface-temperature anomalies produced by blocking, are presented. The statistical results obtained are discussed in relation to recent climatic fluktuations.