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Journal of Southern Hemisphere Earth Systems Science Journal of Southern Hemisphere Earth Systems Science SocietyJournal of Southern Hemisphere Earth Systems Science Society
A journal for meteorology, climate, oceanography, hydrology and space weather focused on the southern hemisphere
RESEARCH ARTICLE (Open Access)

ACCESS-S2: the upgraded Bureau of Meteorology multi-week to seasonal prediction system

Robin Wedd https://orcid.org/0000-0003-0191-6232 A * , Oscar Alves A , Catherine de Burgh-Day https://orcid.org/0000-0002-1975-0042 A , Christopher Down A , Morwenna Griffiths A , Harry H. Hendon A , Debra Hudson A , Shuhua Li A , Eun-Pa Lim https://orcid.org/0000-0001-8273-5358 A , Andrew G. Marshall https://orcid.org/0000-0003-4902-1462 A , Li Shi A , Paul Smith A , Grant Smith A , Claire M. Spillman A , Guomin Wang A , Matthew C. Wheeler A , Hailin Yan A , Yonghong Yin A , Griffith Young A , Mei Zhao A , Yi Xiao A and Xiaobing Zhou A
+ Author Affiliations
- Author Affiliations

A The Bureau of Meteorology, GPO Box 1289, Melbourne, Vic. 3001, Australia.

* Correspondence to: robin.wedd@bom.gov.au

Journal of Southern Hemisphere Earth Systems Science 72(3) 218-242 https://doi.org/10.1071/ES22026
Submitted: 25 July 2022  Accepted: 8 November 2022   Published: 9 December 2022

© 2022 The Author(s) (or their employer(s)). Published by CSIRO Publishing on behalf of BoM. This is an open access article distributed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND)

Abstract

ACCESS-S2 is a major upgrade to the Australian Bureau of Meteorology’s multi-week to seasonal prediction system. It was made operational in October 2021, replacing ACCESS-S1. The focus of the upgrade is the addition of a new weakly coupled data assimilation system to provide initial conditions for atmosphere, ocean, land and ice fields. The model is based on the UK Met Office GloSea5-GC2 seasonal prediction system and is unchanged from ACCESS-S1, aside from minor corrections and enhancements. The performance of the assimilation system and the skill of the seasonal and multi-week forecasts have been assessed and compared to ACCESS-S1. There are improvements in the ACCESS-S2 initial conditions compared to ACCESS-S1, particularly for soil moisture and aspects of the ocean, notably the ocean currents. More realistic soil moisture initialisation has led to increased skill for forecasts over Australia, especially those of maximum temperature. The ACCESS-S2 system is shown to have increased skill of El Nino–Southern Oscillation forecasts over ACCESS-S1 during the challenging autumn forecast period. Analysis suggests that ACCESS-S2 will deliver improved operational forecast accuracy in comparison to ACCESS-S1. Assessments of the operational forecasts are underway. ACCESS-S2 represents another step forward in the development of seasonal forecast systems at the Bureau of Meteorology. However, key rainfall and sea surface temperature biases in ACCESS-S1 remain in ACCESS-S2, indicating where future efforts should be focused.

Keywords: ACCESS-S2, assimilation, Bureau, climate, coupled, data, ENSO, forecast, hindcast, intraseasonal, meteorology, outlook, prediction, reanalysis, seasonal, subseasonal, upgrade.


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