Predictability and its relationship to scale interaction processes in blocking

Abstract

This paper addresses that aspect of predictability which appears related to scale interaction processes in blocking. The basic approach consists of synoptic analysis and quasi-geostrophic diagnosis of the dynamical processes in the real versus forecast model atmosphere. Time-longitude plots of a blocking index, together with sequences of 500 mb height charts, are used to show the temporal and spatial relationships of circulation systems of three distinct wavebands; planetary, medium and short scale, defined as total wavenumbers 0-6, 7-12, and 13-30, respectively. The relevant quasi-geostrophic concepts and equations are formulated to permit explicit evaluation of the relative importance of barotropic versus baroclinic mechanisms and the contributions to each of scale interactive and non- (or self-) interactive processes. The case discussed here is the Atlantic/European blocking of January 1987, particularly the initial stage of development (3-12 January). -from Author