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 extending from 1979, developed for the Austral-asia domain, encompassing Australia, New Zealand, and parts of the Maritime Continent, at a horizontal grid resolution of 12 km, with a finer 4.4 km resolution for the Australian domain. Building upon its predecessor, BARRA1, the new system introduces significant improvements, incorporating a broader range of observation types and utilizing pre-processed datasets previously unavailable. BARRA2 employs a 4D-variational assimilation method for the atmosphere and extended Kalman filter for the land surface, integrating conventional observations and satellite-based radiances, atmospheric motion vector winds, radio occultation, soil moisture data, and ground-based zenith total delay measurements. The new systems are based on UK Met Office Unified Model (UM) and the Joint UK Land Simulator (JULES), with updated physics configurations that address known limitations of BARRA1. This includes a convection-permitting configuration for the 4.4 km model. Furthermore, by nesting in ERA5, BARRA2 is currently being updated continuously. This paper provides an overview of the BARRA2 system and evaluates 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 particularly evident in near-coastal and high-terrain regions and within the convection-permitting system. BARRA2 shows quality changes around 2000, although these do not appear to negatively impact long-term temperature or rainfall trends at studied sites and regions. Other identified deficiencies, such as modelling biases and data assimilation challenges, are discussed to inform future development.  Citation: Su C., Torrance J., Rennie S., Howard E., Stassen C., Warren R., Smith A., Dharssi I., Pepler A., Tian S., Lipson M., Steinle P., Franklin C., Le T., Wang C., Masoumi S., & Le Marshall J. 2025 The Australian regional atmospheric reanalysis system, version 2 – BARRA2. Journal of Southern Hemisphere Earth Systems Science 75, ES25032. https://doi.org/10.1071/ES25032