The second Met Office Unified Model-JULES Regional Atmosphere and Land configuration, RAL2

In this paper we define RAL2 - the second Regional Atmosphere and Land (RAL) science configuration for regionalmodelling. RAL2 uses the Unified Model (UM) as the basis for the atmosphere and the Joint UK Land Environment Simulator(JULES) for the land. RAL2 defines the science configuration of the dynamics and physics schemes of the atmosphere andland and builds on the baseline of RAL1. There are two RAL2 sub-releases, one for mid-latitudes (RAL2-M) and onefor tropical regions (RAL2-T). We document the differences between them and where appropriate discuss how RAL2 relates toRAL1 and the corresponding configuration of the global forecasting model. Our results show an increase in medium and lowcloud amounts in the mid-latitudes leading to improved cloud forecasts. The increase in cloud amount leads to a reduceddiurnal cycle of screen temperature. There is also a reduction in the frequency of heavier precipitation rates. RAL2 isexpected to be the last RAL science configuration with two sub-releases as research effort is focused on producinga single defined configuration of the model that performs effectively in all regions of the world.