Regions of strong land-atmosphere coupling identified in the Global Land Atmosphere Coupling Experiment (GLACE) were coincident with transitional zones between arid and humid regions. GLACE performed simulations over a single Boreal summer, when the soil moisture limitation on evapotranspiration was greatest. This limited the relevance of the results for Australia.
To examine coupling strength over Australia we used a GLACE-like methodology with the Weather and Research Forecasting (WRF) model. The computational efficiency of WRF allowed multiple iterations of the experimental design to establish the sensitivity of the simulated coupling strength for this region. Within WRF we implemented two planetary boundary layer and two cumulus schemes, and three different soil moisture conditions representative of dry, neutral and wet conditions.
The results show that obtaining a robust estimate for the land atmosphere coupling strength is challenging. We could replicate the multiple-model range of GLACE coupling strengths in one model by perturbing the model physics. We could also strongly vary coupling strength by changing the soil moisture state. These two interact such that the sensitivity of coupling strength to model physics is dependent upon the soil moisture state. Drier soils show greater coupling sensitivity to model physics and wetter soils show less coupling sensitivity.
Annette Hirsch is a PhD student at the Australian Research Council (ARC) Centre of Excellence for Climate System Science and the Climate Change Research Centre at the University of New South Wales, in Sydney, Australia. She has published on the impact of land surface initialization approach on sub-seasonal forecast skill in the southern hemisphere, on the representation of climate extreme indices in coupled atmosphere-land surface models, and on modeling low-level boundary layer structure in complex terrain. She has previous worked as a Research Projects Officer in the Commonwealth Scientific and Industrial Research Organisation, and as a Demonstrator at the Fenner School of Environment and Society, Australian National University.