Quantifying the sensitivity of land-atmosphere coupling over Australia

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Copyright: Hirsch, Annette
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Abstract
Land-atmosphere interactions are an important component of the climate system. This thesis examines the role of soil moisture variability on the surface climate of Australia including the role of vegetation on these interactions. First, the sensitivity of the Weather and Research Forecasting Model to land surface initialisation is examined. Simulation skill increases if soil moisture and soil temperature is suitably initialised using values obtained from offline simulations. Secondly, land-atmosphere coupling is evaluated for Australia using four atmospheric physics configurations and two soil moisture scenarios. Australia is demonstrated to be a coupling "hotspot", similar to those previously identified in the Northern Hemisphere. Thirdly, the impact of land use change on land-atmosphere coupling is examined. Regions where vegetation changes from forest to crops are associated with a weakening of the coupling, independent of which model physics are used. This was associated with changes in the surface energy balance that accompany land use change. Finally the resistances to moisture transfer from the land surface to the atmosphere are examined for their influence on land-atmosphere coupling. Perturbations to the aerodynamic resistance change the partitioning of the surface turbulent energy fluxes and subsequently surface temperature. This was associated with the aerodynamic resistance perturbing the terrestrial and atmospheric components of the coupling. The results suggest that land-atmosphere coupling acts mostly through the aerodynamic resistance from the soil surface to the displacement height, which is a function of the boundary layer friction velocity, vegetation cover and vegetation height. Overall this research suggests that the role of vegetation on land-atmosphere coupling is driven by the aerodynamic characteristics of the land surface, which are determined by the parameterisation of the boundary layer and description of the land surface.
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Author(s)
Hirsch, Annette
Supervisor(s)
Pitman, Andrew
Haverd, Vanessa
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Publication Year
2015
Resource Type
Thesis
Degree Type
PhD Doctorate
UNSW Faculty
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