Dr Rob Warren - Honours Project

Does it hail in the tropics?

Supervisor: Rob Warren and Marty Singh
Field of Study: Atmospheric Science

Research into the behaviour of severe local thunderstorms has historically been focused on midlatitude continental regions, particularly the eastern USA, in part because they have the highest density of storm reports. However, analyses of the frequency of occurrence of large-scale environmental conditions conducive to severe storms reveal the potential for substantial severe weather in tropical regions in addition to the midlatitudes. Furthermore, satellite-based observations suggests that the frequency of severe hail (> 2.5 cm diameter) is as high in some tropical continental regions as in known hotspots for severe weather in the midlatitudes.

In this project, we will examine 16 years of radar observations from Darwin, NT, in order to assess the frequency and distribution of surface hail in a well-observed tropical location. Using the dual polarisation capabilities of the Darwin radar, we will apply and evaluate the effectiveness of hail diagnostics originally developed for midlatitude storms in a tropical context. Furthermore, we will use our results to assess the accuracy of satellite-based estimates of tropical hail frequency. Together these analyses will lead to a greater understanding of the prevalence of hail and severe hail in tropical regions, a topic which has so far received little attention in the literature.

For further information contact: Rob Warren

Elevated mixed layers and associated severe thunderstorm environments in Australia

Supervisors: Rob Warren and Michael Reeder
Field of Study: Atmospheric Science

Elevated Mixed Layers (EMLs) are a common feature of severe thunderstorm environments in the Great Plains of the US. They occur when dry boundary-layer air, originating from the elevated deserts of the southwest US and northern Mexico, is advected by southwesterly winds over the top of moister surface air. Combined with high surface dewpoint temperatures, the steep lapse rates which characterise these layers promote large convective available potential energy (CAPE), a key ingredient for intense convection. However, EMLs are by no means unique to the US. For example, they commonly occur over central South America (northern Argentina and Paraguay), which, like the US Great Plains, is a global hotspot for severe weather, particularly large hail. Parts of Australia, including the central east coast and southwest WA, also regularly experience severe thunderstorms during the warm season; however, the prevalence of EMLs in the associated environments remains largely unknown.

In this project we will employ reanalysis data to identify EMLs over Australia and explore their association with severe thunderstorm environments. The frequency and seasonal variation of EML occurrence will be characterised geographically and compared against recent climatological results for North and South America. We will also consider the synoptic-scale weather patterns which promote EML formation. This work will improve our understanding of Australian severe thunderstorm environments and may prove useful in assessing how the frequency of these storms may change in the future.

For further information contact: Rob Warren