Upgrades to the Australian limited area data assimilation system

This paper describes the changes which have been made to the Australian operational limited area data assimilation system, RASP. The main modifications are improved resolution, with the grid spacing being halved to 75 km, a small increase in vertical resolution, improved representation of topography, and refinements to the filtering, physical parametrisation and lateral boundary specification. Results from three parallel trial periods are described. These trials were conducted in the Bureau of Meteorology Research Centre (BMRC), but exactly duplicated operational practice. Objective verifications, including results from a new objective rainfall forecast verification package, are presented, and these demonstrate superior performance of the new system over the old. A series of case studies are then presented, illustrating the types of differences which can be expected between the forecasts from the two systems.