The Australian Regional Atmospheric Reanalysis System, version 2 (BARRA2)

Chun-Hsu Su; Joshua Torrance; Susan Rennie; Emma Howard; Christian Stassen; Rob Warren; Andy Smith; Imtiaz Dharssi; Acacia Pepler; Siyuan Tian; Mathew Lipson; Peter Steinle; Charmaine Franklin; Tan Le; Carl Wang; Salim Masoumi; John Le Marshall

Just Accepted

This article has been peer reviewed and accepted for publication. It is in production and has not been edited, so may differ from the final published form.

The Australian Regional Atmospheric Reanalysis System, version 2 (BARRA2)

Chun-Hsu Su , Joshua Torrance , Susan Rennie , Emma Howard , Christian Stassen , Rob Warren, Andy Smith, Imtiaz Dharssi, Acacia Pepler , Siyuan Tian , Mathew Lipson, Peter Steinle, Charmaine Franklin, Tan Le, Carl Wang, Salim Masoumi, John Le Marshall

Abstract

Bureau of Meteorology high-resolution Atmospheric Regional Reanalysis for Australia version 2 (BARRA2) is a new regional reanalysis, nested in ERA5, 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 upon its predecessor (BARRA1), BARRA2 introduces significant improvements by incorporating a broader range of observations and previously unavailable pre-processed datasets. BARRA2 employs a 4D-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 around the year 2000, although these do not appear to negatively impact 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.

ES25032 Accepted 31 August 2025