Case studies of wintertime orographic precipitation over the Brindabella catchment in South-Eastern Australia

Extended periods of orographically enhanced post-frontal precipitation are an important feature of the wintertime climate in the mountainous regions of South-Eastern Australia. Such storms may last for several days, and contribute significantly to alpine catchment inflows, which ultimately feed into the hydrology of the agriculturally dependent Murray-Darling Basin.

Quantitative precipitation forecasting for these events has improved dramatically over the past decades, but as increases in computational capabilities have led to increased model resolution, deficiencies in microphysical parameterisation have become apparent (Stoelinga et. al. 2003). For example, it is unclear whether cloud microphysical features such as liquid water path or cloud top thermodynamic phase are well represented in models such as the Weather Research and Forecasting (WRF) model, and observational comparisons are required to verify this.

Two case studies of wintertime storms in the Brindabella ranges near Canberra are presented where cloud liquid water path measurements are provided by a dual-channel microwave radiometer, and several overpasses of the Moderate-resolution Imaging Spectroradiometer (MODIS) instrument. High resolution WRF model simulations show good agreement in the timing and total accumulation of precipitation amounts, and cloud top characteristics from MODIS compare well with simulated conditions. Liquid water path observations from both MODIS and the ground-based microwave radiometer are consolidated with the simulated values, providing unique insight into the performance of the WRF model's representation of cloud populations in alpine regions in South-Eastern Australia.