Energetics and dynamics of subtropical Australian east coast Cyclones: Two contrasting cases

Abstract

The subtropical east coast region of Australia is characterized by the frequent occurrence of low pressure systems, known as east coast lows (ECLs). The more intense ECLs can cause severe damage and disruptions to this region. While the term "east coast low" refers to a broad classification of events, it has been argued that different ECLs can have substantial differences in their nature, being dominated by baroclinic and barotropic processes in different degrees. Here we reexamine two well-known historical ECL case studies under this perspective: the Duck storm of March 2001 and the Pasha Bulker storm of June 2007. Exploiting the cyclone phase space analysis to study the storms' full three-dimensional structure, we show that one storm has features similar to a typical extratropical frontal cyclone, while the other has hybrid tropical-extratropical characteristics. Furthermore, we examine the energetics of the atmosphere in a limited area including both systems for the ECL occurrence times, and show that the two cyclones are associated with different signatures in the energy conversion terms. We argue that the systematic use of the phase space and energetics diagnostics can form the basis for a physically based classification of ECLs, which is important to advance the understanding of ECL risk in a changing climate.