Abstract
Abstract. The Met Office Unified Model (UM) is a world-leading atmospheric weather and climate model. In addition to comprehensive simulations of the atmosphere, the UM is capable of running idealised simulations, such as the dry physics Held–Suarez test case, radiative convective equilibrium and simulating planetary atmospheres other than Earth. However, there is a disconnect between the simplicity of the idealised UM model configurations and the full complexity of the UM. This gap inhibits the broad use of climate model hierarchy approaches within the UM. To fill this gap, we have developed the Flexible Modelling Framework for the UM – Flex-UM – which broadens the climate model hierarchy capabilities within the UM. Flex-UM was designed to replicate the atmospheric physics of the Geophysical Fluid Dynamics Laboratory (GFDL) idealised moist physics aqua-planet model. New parameterisations have been implemented in Flex-UM, including simplified schemes for convection, large-scale precipitation, radiation, boundary layer and sea surface temperature (SST) boundary conditions. These idealised parameterisations have been implemented in a modular way, so that each scheme is available for use in any model configuration. This has the advantage that we can incrementally add or remove complexity within the model hierarchy. We compare Flex-UM to ERA5 and aqua-planet simulations using the Isca climate modelling framework (based on the GFDL moist physics aqua-planet model) and comprehensive simulations of the UM (using the GA7.0 configuration). We also use two SST boundary conditions to compare the models (fixed SST and a slab ocean). We find the Flex-UM climatologies are similar to both Isca and GA7.0 (though Flex-UM is generally a little cooler, with higher relative humidity and a less pronounced storm track). Flex-UM has a single Intertropical Convergence Zone (ITCZ) in the slab-ocean simulation but a double-ITCZ in the fixed-SST simulation. Further work is needed to ensure that the atmospheric energy budget closes to within 1–2 W m−2, as the current configuration of Flex-UM gains 9–11 W m−2 (the range covers the two SST boundary conditions). Flex-UM greatly extends the modelling hierarchy capabilities of the UM and offers a simplified framework for developing, testing and evaluating parameterisations within the UM.
Highlights
Earth system models are invaluable tools for predicting future climates and for informing mitigation strategies in response to climate change
Flex-Unified Model (UM) can be configured as a slab-ocean aqua-planet, with a grey radiation scheme, simplified Betts–Miller convection scheme and simple boundary layer scheme; we describe these in detail in Sect
A climate model hierarchy is a sequence of models connecting idealised to comprehensive models, via a series of intermediate-complexity models
Summary
Earth system models are invaluable tools for predicting future climates and for informing mitigation strategies in response to climate change. It is easy to criticise the fidelity of an idealised model; their usefulness is not in their accuracy, it is in their simplicity They offer a simplified test bed for understanding processes, developing new theories, testing hypotheses, bug-fixing model code and developing new parameterisations. When the UM is coupled to an interactive ocean and sea-ice models (Hewitt et al, 2011), it forms the Hadley Centre Global Environmental Model (HadGEM3-GC3.0, Williams et al, 2018, in its third version (HadGEM3) and third Global Configuration (GC3.0) This configuration describes the Met Office global climate model (GCM) used to contribute simulations for the sixth phase of the Climate Model Intercomparison Project (CMIP6). The first SST boundary condition we consider is the slab-ocean aqua-planet configuration, where we validate Flex-UM against the configured Isca climate model. We summarise the new features of Flex-UM in Sect. 5 and motivate possible use cases for the new capabilities within the UM model hierarchy
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
