An analysis of future changes in extreme rainfall over Australian regions based on GCM simulations and Extreme Value Analysis.

Abstract:

An accurate representation of near-surface winds in global forecast models is important in the calculation of surface energy exchange, air pollution dispersion as well as in aviation and wind engineering applications. In a summary paper, Holtslag (2006) points out that a number of model errors can arise from shortcomings in the representation of the stably stratified planetary boundary layer (SBL). A recent intercomparison of Single Column Models (SCMs), which formed part of the second GEWEX Atmospheric Boundary Layer Study (GABLS2, http://www.met.wau.nl/projects/Gabls/index.htm), found a large spread of results for all model forecast parameters (Svensson and Holtslag, 2007). The greatest difference between the model simulations and observations was in the representation of the diurnal cycle of 10-metre wind speed. The amplitude of this diurnal variation was found to be significantly underpredicted with wind speeds generally too high under nighttime stable conditions. In this paper, model sensitivities to changes in the fluxprofile relationships of momentum under stably stratified conditions are investigated using a SCM version of the UK Met Office Unified Model (UM, version 6.3) that forms the atmospheric component of the Australian Community Climate and Earth System Simulator (ACCESS).