Prefrontal Troughs over Southern Australia. Part II: A Case Study of Frontogenesis

Abstract

A case study of frontogenesis within a surface prefrontal trough over southern Australia is presented. The trough developed ahead of a surface cold front and, over a period of approximately 24 h, intensified into a mature summertime frontal system while the original front underwent total frontolysis. Two-hourly rawinsonde ascents at three locations were used to examine the structure of the trough both before and after frontogenesis. Diagnosis of the frontogenetic tendencies showed that horizontal deformation of the potential temperature field was the main forcing mechanism. The process studied occurs frequently in the warmer months of the year, and a conceptual model is proposed for the process of frontogenesis within the trough and frontolysis of the preexisting midlatitude front. Important components include differential thermal advection, the action of Coriolis turning in association with ageostrophic vertical circulations, and horizontal deformation of the thermal field.