The Australian regional atmospheric reanalysis system, version 2 – BARRA2

Bureau of Meteorology high-resolution Atmospheric Regional Reanalysis for Australia version 2 (BARRA2) is a new regional reanalysis, nested in ERA5 (ECMWF (European Centre for Medium-Range Weather Forecasts) Reanalysis ver. 5), extending from 1979 to near present. It is developed for the Australasia domain, including Australia, New Zealand and parts of the Maritime Continent, at a horizontal grid resolution of 12 km, with a finer 4.4-km grid over Australia. Building on its predecessor (BARRA1), BARRA2 introduces significant improvements by incorporating a broader range of observations and previously unavailable pre-processed data sets. BARRA2 employs a four-dimension-variational assimilation method for the atmosphere and an extended Kalman filter for the land surface, integrating conventional observations and satellite-based radiances, atmospheric motion vector winds, satellite and ground-based Global Navigation Satellite System measurements, and satellite soil moisture data. The modelling system is based on the UK Met Office Unified Model (UM) and the Joint UK Land Simulator (JULES), with updated physics configurations that address limitations of BARRA1. This also includes a convection-permitting configuration for the 4.4-km model. This paper describes the BARRA2 system and assesses the quality of its deterministic outputs for key near-surface meteorological parameters, including temperature, wind and precipitation. The added value of BARRA2 over global reanalyses is evident in coastal and high-terrain regions and within the convection-permitting system. BARRA2 shows quality changes from approximately the year 2000, although these do not appear to negatively affect long-term temperature or rainfall trends at studied sites and regions. Remaining challenges, including modelling biases and data assimilation limitations, are discussed to inform future development.