Atmospheric models

The Unified Model (UM) is a numerical model of the atmosphere used for both weather and climate applications. It is in continuous development by the Met Office and its partners, adding state of the art understanding of atmospheric processes to new releases.


A seamless modelling approach

Seamless modelling, whereby a single model family can be used for prediction across a range of timescales, has been at the heart of the Met Office strategy for weather and climate prediction since 1990.
The Unified Model applies this seamless modelling approach, which means that the same dynamical core and, where possible, the same parameterization schemes are used across a broad range of spatial and temporal scales on a traceable frame work.
The model is suitable for numerical weather prediction (NWP), seasonal forecasting and climate modelling with forecast times ranging from a few days to hundreds of years. Furthermore, the Unified Model can be used both as a global and a regional model.


Benefits of the seamless approach


Developing one system for multiple uses reduces development effort and allows improvements made for climate science to be applied in our weather forecasting systems, and vice-versa.


Short-range forecasts can be used for learning about error growth and help study the performance of long term climate simulations. Likewise, studying the long-range climatology of the model helps constrain and understand the physical processes used in short-range NWP forecasts.


Using the same model for regional and global modelling gives confidence that the driving mechanisms are consistent.

The dynamical core

The model's dynamical core solves the compressible non-hydrostatic equations of motion with semi-lagrangian advection and semi-implicit time stepping. Sub-grid scale processes such as convection, boundary layer turbulence, radiation, cloud, microphysics and orographic drag are represented by parameterizations. The model uses a grid point discretization on a latitude-longitude grid system with a rotated pole.