The Unified Model is a

numerical weather prediction Numerical weather prediction (NWP) uses mathematical models of the atmosphere and oceans to predict the weather based on current weather conditions. Though first attempted in the 1920s, it was not until the advent of computer simulation in th ...

and climate modeling software suite originally developed by the

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the European mainland, continental mainland. It comprises England, Scotlan ...

Met Office, and now both used and further developed by many weather-forecasting agencies around the world. 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). The models are grid-point based, rather than wave based, and are run on a variety of

supercomputers A supercomputer is a computer with a high level of performance as compared to a general-purpose computer. The performance of a supercomputer is commonly measured in floating-point operations per second (FLOPS) instead of million instructions p ...

around the world. The Unified Model atmosphere can be coupled to a number of ocean models. 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 profiler A wind profiler is a type of weather observing equipment that uses radar or sound waves ( SODAR) to detect the wind speed and direction at various elevations above the ground. Readings are made at each kilometer above sea level, up to the extent o ...

s, 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). The Unified Model software suite is written in Fortran (originally 77 but now predominantly 90) and uses height as the vertical variable. Because most developments of interest are near to the ground the vertical layers are closer together near the surface.

Principal UM suites at the Met Office

The Met Office runs a range of

Numerical Weather Prediction Numerical weather prediction (NWP) uses mathematical models of the atmosphere and oceans to predict the weather based on current weather conditions. Though first attempted in the 1920s, it was not until the advent of computer simulation in th ...

suites using the UM. All of the models use varying resolutions of

topography Topography is the study of the forms and features of land surfaces. The topography of an area may refer to the land forms and features themselves, or a description or depiction in maps. Topography is a field of geoscience and planetary sc ...

with greater accuracy at higher resolutions. The limiting factor with all models is that for a weather event to be recorded by the model it must be at least three grid points in size. Thus for the global model at 40 km, a weather system must be at least 120 km to be modelled. This means smaller phenomena such as small depressions, smaller hurricanes and large thunderstorms are too small for the model to catch them. As the resolution increases smaller events can be caught, the 1.5 km model for example, is reputedly capable of modelling individual showers.

Global Model

Approximately 16 km resolution with 70 vertical levels.Atmospheric numerical model configurations as of early 2010
Met Office 2010. Covers the entire globe and 168 hours in the future twice a day, the shortest outlook of the synoptic scale models currently in use (most others run out at least 10 days; furthermore, the Unified Model forecasts are only available out 72 hours for non-paying users). The Global model provides boundary information for the now retired North Atlantic European (NAE) model, for which additional shorter runs (48 hours) are produced twice a day. The model is kept close to the real atmosphere using hybrid 4D-Var data assimilationHybrid variational/ensemble data assimilation
. Met Office 2011. of observations.

North Atlantic and European model - Retired

The Met Office's North Atlantic and European model (NAE) model had 70 levels with a 12 km resolution. It is run out to 48 hours from start. Because the UK is at a northern latitude the computer transposes the model area to an equatorial location so the grid points give an area that is more square. This reduces the load on the model, allowing it to run more quickly. The model is kept close to the real atmosphere using 4D-Var data assimilation of observations.

Euro 4km model

70 Vertical levels, 4.4 km horizontal resolution. Run out to 120 hours. Now being superseded by the UKV in many applications.

UKV model

70 Vertical levels, 1.5 km horizontal resolution. Run out to 36 hours (this replaced the UK 4 km model in 2011). The forecast is run every 3 hours using boundary conditions from the 25-km global model.The UKV Model
Met Office, January 2012 The resolution is 1.5 km over the UK, and 4 km over surrounding areas.Issues with high-resolution NWP
discussing the UKV model, Met Office 2010.
discussing the UKV model, Met Office 2011. The UKV model is kept close to observations using 3D-Var data assimilation every 3 hours.

CAM

The Crisis Area Model is a 12 km model that can be run for any area of the world should the need arise. This can include military use (the MMU use this on deployed operations) or environmental catastrophes.

Mountain Wave Models

This high resolution model provides information on

mountain waves In meteorology, lee waves are atmospheric stationary waves. The most common form is mountain waves, which are atmospheric internal gravity waves. These were discovered in 1933 by two German glider pilots, Hans Deutschmann and Wolf Hirth, above ...

for a variety of locations around the UK and other areas of interest to the Met Office.

Met Office's Global Wave Model

This models sea waves around the world.

UM suites outside the Met Office

Unified Model suites which are similar to those from the Met Office are run by the Australian

Bureau of Meteorology The Bureau of Meteorology (BOM or BoM) is an executive agency of the Australian Government responsible for providing weather services to Australia and surrounding areas. It was established in 1906 under the Meteorology Act, and brought together ...

, the Australian

Commonwealth Scientific and Industrial Research Organisation The Commonwealth Scientific and Industrial Research Organisation (CSIRO) is an Australian Government agency responsible for scientific research. CSIRO works with leading organisations around the world. From its headquarters in Canberra, CSIRO ...

, the

South African Weather Service The South African Weather Service (SAWS) is the meteorological service under the South African government's Department of Environmental Affairs and Tourism. SAWS is a member of the World Meteorological Organization. Under the South African Wea ...

, the

Norwegian Meteorological Institute The Norwegian Meteorological Institute ( no, Meteorologisk institutt), also known internationally as MET Norway, is Norway's national meteorological institute. It provides weather forecasts for civilian and military uses and conducts research in m ...

, the New Zealand

National Institute of Water and Atmospheric Research The National Institute of Water and Atmospheric Research or NIWA ( mi, Taihoro Nukurangi), is a Crown Research Institute of New Zealand. Established in 1992, NIWA conducts research across a broad range of disciplines in the environmental scien ...

, the outh Korea Meteorological Administration and the National Centre for Medium Range Weather Forecasting, a subordinate office of the Indian

Ministry of Earth Sciences The Ministry of Earth Sciences was formed on 29 January 2006 from a merger of the India Meteorological Department (IMD), the National Centre for Medium Range Weather Forecasting (NCMRWF), the Indian Institute of Tropical Meteorology (IITM), Pune ...

Australian Bureau of Meteorology

The Australian

, have an operational 12 km resolution global forecasting system utilizing the Unified Model. This global system provides boundary conditions for a number of higher resolution regional systems also using the Unified Model.

outhKorea Meteorological Administration

The outh Korea Meteorological Administration have an operational 10 km resolution global forecasting system utilizing the Unified Model. This global system provides boundary conditions for a 1.5 km resolution local Unified Model NWP system covering the Korean Peninsula Region.

UKCA

United Kingdom Chemistry & Aerosols ( UKCA) is a sub-model of the UM that deals with trace gas and aerosol chemistry within the model. This includes calculating the concentrations of climatically relevant gases such as

methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Ea ...

and

ozone Ozone (), or trioxygen, is an inorganic molecule with the chemical formula . It is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen that is much less stable than the diatomic allotrope , breaking down in the lo ...

, as well as the composition and evolution of aerosols. As with most of the UM, the UKCA was written in a collaboration between the

UK Met Office The Meteorological Office, abbreviated as the Met Office, is the United Kingdom's national weather service. It is an executive agency and trading fund of the Department for Business, Energy and Industrial Strategy and is led by CEO Penelope ...

and UK Academia.

JULES

Joint UK Land Environment System is a land surface model that has been developed in a collaboration between the Met Office and other research institutes.JULES collaboration
The Met Office 2011. Accessed 10 November 2011 JULES models the exchange of heat and moisture between the Unified Model atmosphere and the land surface and vegetation. JULES can also be used offline to estimate the impacts of different climate models on the land surface and hydrology.

References

External links

Unified Model Collaboration webpage
at the Met Office.
Unified Model Papers

Introduction to the UM by NCAS
{{Atmospheric, Oceanographic and Climate Models Numerical climate and weather models Met Office Scientific simulation software