The Met Office Unified Model GA7.2GL8.1 and GA7.2.1GL8.1.1 configurations: Developments from GA7GL7: Met Office Forecasting Research Technical Report No: 654

The Unified Model and JULES are used in defined Global Atmosphere and Global Land config-urations to simulate the global atmosphere-land system at the Met Office and at other UM partners.GA7.0GL7.0 was frozen in 2016. However, the NWP performance of this trunk configuration was con-sidered to be unacceptable. The NWP specific branches, GA7.2GL8.1 and GA7.2.1GL8.1.1, were sub-sequently developed by bringing forward a limited number of changes from the next trunk configuration,GA8GL9. These changes included modifications to the land surface, boundary layer and convectionparameterizations and are detailed in this report. The performance of GA7.2GL8.1/GA7.2.1GL8.1.1was substantially better than GA7GL7 across almost all NWP verification scores and data assimilationmetrics. GA7.2GL8.1 was consequently implemented in Parallel Suite 43 (PS43) in December 2019and followed by GA7.2.1GL8.1.1 in PS44 in December 2020. This remained operational until PS45 inMay 2022 when it was replaced by GC4 (GA8GL9 coupled to the GO6 ocean configuration).1