Diagnosis of a Cyclogenetic Event in the Western Mediterranean Using an Objective Technique for Scale Separation

Abstract

A cyclogenetic event in the western Mediterranean (4?5 March 1982, during ALPEX-SOP) is diagnosed using an objective analysis technique for quantitative scale separation. The spatial scale separation is applied to investigate the interaction of scales in Mediterranean cyclogenesis, and to isolate the orographically induced features. The technique operates as a low-pass and band-pass filter to extract the large scale and mesoscale signals, respectively. By adding both contributions, an objective analysis of the actual meteorological field is obtained. Geopotential height, temperature and wind fields have been analyzed, and derived quantities as divergence and vorticity have been computed. The synoptic scale contribution is found to exhibit the main characteristics of a developing baroclinic wave driving both the initial Catalonian-Balearic Sea cyclogenesis and the subsequent Alpine cyclogenesis. Several mesoscale features which are difficult to be detected in usual objective analyses (such as the development of the initial low pressure center over the Cataloian?Balearic Sea) are observed. The capability of the technique to isolate the orographically induced features is itself a major concern of this work. The mesoscale fields associated with the lee cyclogenesis indicate that the perturbation induced by the orography has a dipolar structure.