Main APS4 differences
APS4 represents a significant upgrade to the Bureau's global NWP capability and results in an overall increase in forecast skill.
There are major changes to the physics of the global model and the ensemble generation compared to ACCESS-G3/GE3.
Key enhancements include:
- An upgrade of the model configuration from GA6/GL6 (global atmosphere/land version 6) to GA8/GL9 (global atmosphere version 8; land version 9). This represents significant physics changes affecting most areas of model science, but especially as related to the convection scheme and the representation of the land surface.
- An improved method of ensemble generation – ensemble of four-dimensional ensemble-variational (En4DEnVar) data assimilation (DA) – which is more closely aligned with the DA system of ACCESSG and produces more reliable probability forecasts.
- Improved land surface DA with the inclusion of analyses of soil-, skin- and snow temperature