EGUsphere EGUsphere EGUsphere EGUsphere Copernicus Publications Göttingen, Germany 10.5194/egusphere-2026-2425 The Met Office Unified Model and JULES Global Atmosphere and Land 9.0 configuration Willett Martin R. https://orcid.org/0000-0003-3833-1414 1 Brooks Melissa E. https://orcid.org/0000-0002-4773-8630 1 Bushell Andrew https://orcid.org/0000-0001-5683-4387 1 Earnshaw Paul https://orcid.org/0000-0002-5447-504X 1 Marzin Charline 1 Smith Samantha 1 Tomassini Lorenzo 1 2 Abraham Nathan Luke https://orcid.org/0000-0003-3750-3544 3 4 Best Martin 1 Edwards John M. https://orcid.org/0000-0001-5784-3218 1 Furtado Kalli 1 6 Hardacre Catherine 1 7 Hewitt Alan J. https://orcid.org/0000-0003-1919-1751 1 Johnson Ben https://orcid.org/0000-0003-3334-9295 1 Lock Adrian 1 Mulcahy Jane P. https://orcid.org/0000-0002-0870-7380 1 Manners James 1 Sellar Alistair https://orcid.org/0000-0002-2955-7254 1 Sheridan Peter 1 Tennant Warren 1 Van Weverberg Kwinten https://orcid.org/0000-0002-5397-7320 1 8 Varma Vidya 5 9 Whitall Michael 1 Met Office, FitzRoy Road, Exeter, Devon, EX1 3PB, United Kingdom School of Mathematics, University of Leeds, Leeds, LS2 9JT, United Kingdom National Centre for Atmospheric Science, University of Cambridge, Cambridge CB2 1EW, United Kingdom Yusuf Hamied Department of Chemistry, University of Cambridge, Cambridge, CB2 1EW, United Kingdom National Institute of Water and Atmospheric Research Ltd (NIWA), Wellington, 6021, New Zealand now at: National Oceanography Center, European Way, Southampton, SO14 3ZH, United Kingdom now at: School of Physical and Chemical Sciences, University of Canterbury, New Zealand now at: Department of Geography, Ghent University, Belgium and Royal Meteorological Institute of Belgium, Ringlaan 3, 1180 Brussels, Belgium now at: The Institute of Climate and Energy Systems – Troposphere (ICE-3), Forschungszentrum Jülich, Wilhelm-Johnen-Straße, 52428 Jülich, Germany 26 05 2026 2026 1 68 Copyright: © 2026 Martin R. Willett et al. 2026 This work is licensed under the Creative Commons Attribution 4.0 International License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/4.0/ This article is available from https://egusphere.copernicus.org/preprints/2026/egusphere-2026-2425/ The full text article is available as a PDF file from https://egusphere.copernicus.org/preprints/2026/egusphere-2026-2425/egusphere-2026-2425.pdf

We describe Global Atmosphere and Land 9.0 (GAL9) and GAL9.1: the latest science configurations of the Met Office Unified Model and JULES land surface model developed for seamless use across weather and climate timescales. GAL9 builds upon GA8GL9. GAL9 includes developments to most areas of the science. Some of the key changes include: moving to a single "mid-level" scheme to represent surface driven deep convection and elevated convection that improves the diurnal cycle of convection, an enhancement to the semi-Lagrangian advection that improves local conservation, improved physical realism in the gravity wave drag scheme by accounting for the effects of humidity and latent heating, and a package of enhancements to the land surface which improve soil moisture profiles and remove the need to apply an observation based albedo scaling. The NWP and climate performance of GAL9 is evaluated against the previous configuration, GA8GL9. In NWP tests GAL9 is shown have reduced errors relative to GA8GL9. The mean climate in GAL9 is shown to be improved relative to GA8GL9 with notable improvements in the top of atmosphere outgoing shortwave radiation. NWP tests of GAL9.0 at 10 km showed a degradation relative to GA8GL9. This issue is resolved in the branch configuration GAL9.1 that includes an improved orography. GAL9/GAL9.1 is the atmosphere and land component of GC5/GC5.1. From early 2026, GC5.1 is being be used as the operational global NWP model at the Met Office and GC5 will be a key component of the UK's contribution to CMIP7.