Our climate model for seasonal prediction
ACCESS-S stands for the Australian Community Climate and Earth-System Simulator – Seasonal. It's our climate forecast system for weekly to seasonal outlooks.
We develop ACCESS-S in collaboration with the United Kingdom Meteorological Office (UKMO). It's based on their global 'coupled model' seasonal forecast system.
A model is a computer simulation of the real world, based on the laws of physics. A coupled model is when different models are linked. ACCESS-S brings together atmosphere, ocean, land and ice models.
For more about how ACCESS-S is used for longer term outlooks, view our Forecasting climate page.
How we use ACCESS-S
ACCESS-S supports several seasonal prediction projects. For example, agricultural sector projects such as the:
- Northern Australia Climate Program
- Forewarned is forearmed project – read the Forewarned is forearmed final report on the Meat & Livestock Australia website.
These projects include research to understand and improve the forecast system. They also seek to understand climate variability and predictability.
Our research helps guide the use of forecasts in applications and other models. For example, models tailored to support the agriculture, fisheries and water sectors.
We work with stakeholders and users to develop new types of forecast products and have a large set of experimental forecast outputs.
Technical details for ACCESS-S
ACCESS-S is a state-of-the-art dynamical (physics-based) modelling system. It comprises:
- a coupled atmosphere–ocean–land–ice model
- a data assimilation system (combining the output from the model with data gathered through observations)
- a strategy for generating forecast ensembles (this is when we run more than one forecast)
- data post-processing to generate forecast products.
The ACCESS-S model is based on the UKMO's global seasonal forecast system, version 5, using the global coupled model configuration 2 (GloSea5-GC2). ACCESS-S has an enhanced ensemble generation strategy to adapt it for multi-week forecasting.
Technical details for the first version of the model are available in 'ACCESS-S1: The new Bureau of Meteorology multi-week to seasonal prediction system', in the Journal of Southern Hemisphere Earth Systems Science (Volume 67 Number 3 2017), on the CSIRO Publishing website.
Latest version – ACCESS-S2
ACCESS-S2 has been producing the forecasts for our seasonal climate outlook since October 2021. This version:
- has a locally developed data assimilation system for the ocean
- improves on the land surface initialisation for soil moisture.
ACCESS-S2 has a longer hindcast period – more than 30 years. Hindcasts are a set of forecasts that are run retrospectively. They are used to check the skill and performance of the system and to calibrate the forecasts.
Real-time and retrospective forecast data available
ACCESS-S2 outlooks are based on running the model several times with slightly different initial conditions. This is called an 'ensemble' and captures a range of likely future scenarios. For our real-time outlooks we run an ensemble with 99 different sets of initial conditions (a 99-member ensemble) to generate our forecasts.
To request data for the real-time outlooks, contact us.
ACCESS-S2 hindcast data (retrospective forecasts) for 1981–2018 are available for research purposes at the National Computational Infrastructure (NCI).