Unified Model

The Unified Model is a numerical weather prediction and climate modeling software suite originally developed by the United Kingdom Met Office,^[1][2] and now both used and further developed by many weather-forecasting agencies around the world.^[3] The Unified Model gets its name because a single model is used across a range of both timescales (nowcasting to centennial) and spatial scales (convective scale to climate system earth modelling).^[4] The models are grid-point based, rather than wave based, and are run on a variety of supercomputers around the world. The Unified Model atmosphere can be coupled to a number of ocean models.^[5] At the Met Office it is used for the main suite of Global Model, North Atlantic and Europe model (NAE) and a high-resolution UK model (UKV), in addition to a variety of Crisis Area Models and other models that can be run on demand. Similar Unified Model suites with global and regional domains are used by many other national or military weather agencies around the world for operational forecasting.

Data for numerical weather prediction is provided by observations from satellites, from the ground (both human and from automatic weather stations), from buoys at sea, radar, radiosonde weather balloons, wind profilers, commercial aircraft and a background field from previous model runs. The computer model is only adjusted towards the observations using assimilation, rather than forcing the model to accept an observed value that might make the system unstable (and could be an inaccurate observation).^[6] The Unified Model software suite is written in Fortran (originally 77 but now predominantly 90)^[7] and uses height as the vertical variable.^[8] Because most developments of interest are near to the ground the vertical layers are closer together near the surface.^[9]