The coastal convective interactions experiment

Abstract

Prediction of convective storm environments relies principally upon the broad-scale meteorology (e.g., synoptic boundaries and air masses) in contrast to local-scale (2 -20 km) processes within the planetary boundary layer (PBL). Diurnal heating of the Earth's heterogeneous surface at these finer scales forces circulations (e.g., sea breezes, valley winds, urban heat island circulations) which have been related to trends in the meteorological and climatological activity of storms; however, a quantitative understanding of their interactions with deep convection is limited. This is especially true for physical settings which support a variety of PBL circulations that challenge our understanding of ii Detailed analysis of the CCIE climatology datasets provided an understanding of SEQ hailstorms across a range of spatiotemporal scales. At the inter-annual time scale, the ElNiño Southern Oscillation (ENSO) was shown to have a statistically significant relationship with both hailstorm and sea breeze frequency in SEQ. Synoptic scale southeasterly changes that were found to couple with sea breezes provide the most favourable environment for hailstorms, particularly for southwest SEQ. At the mesoscale, hail development within convective cells was found to be most frequent within the inland limb of maritime air masses on sea breeze days. It was concluded, that the maritime sea breeze air is potentially favourable for convection after modification through inland propagation and the associated entrainment of sensible heat.Investigation of the CCIE field campaign datasets show that diurnal modification of the coastal PBL by near-surface and boundary layer processes provide favourable preconditioning for convective storms. This includes: (1) early sea breeze onset for the city of Brisbane due an urban heat island enhanced land-sea thermal contrast, (2) significant afternoon warming and moistening above the sea breeze attributed to the advection of the inland convective boundary layer coastward under prevailing westerly flow, and (3) substantial variations in near-surface moisture likely associated with topography and landuse. For the 27 November 2014 Brisbane case study hailstorm event, which caused damages exceeding $1.5 billion AUD, these diurnal preconditioning processes are shown to be favourable for the development of a mesoscale convective environment capable of supporting large hailstone growth. The multicell-HP supercell storm mode identified for this event and previous similar events in SEQ is hypothesised to be more sensitive to variations in near-surface and boundary layer instability. This is in contrast to contemporary supercell storms, highlighting the importance of PBL observations for developing an understanding of convective storms in subtropical coastal environments.In summary, this thesis provides a substantial and original contribution towards understanding of subtropical coastal storm environments. The integration of meteorological and climatological datasets from the CCIE provided a wealth of evi...